Occupational Exposure to Respirable Crystalline Silica

SUMMARY

The Occupational Safety and Health Administration (OSHA) is amending its existing standards for occupational exposure to respirable crystalline silica. OSHA has determined that employees exposed to respirable crystalline silica at the previous permissible exposure limits face a significant risk of material impairment to their health. The evidence in the record for this rulemaking indicates that workers exposed to respirable crystalline silica are at increased risk of developing silicosis and other non-malignant respiratory diseases, lung cancer, and kidney disease. This final rule establishes a new permissible exposure limit of 50 micrograms of respirable crystalline silica per cubic meter of air (50 [mu]g/m\3\) as an 8-hour time- weighted average in all industries covered by the rule. It also includes other provisions to protect employees, such as requirements for exposure assessment, methods for controlling exposure, respiratory protection, medical surveillance, hazard communication, and recordkeeping. OSHA is issuing two separate standards--one for general industry and maritime, and the other for construction--in order to tailor requirements to the circumstances found in these sectors.

 
CONTENT

Federal Register, Volume 81 Issue 58 (Friday, March 25, 2016)

Federal Register Volume 81, Number 58 (Friday, March 25, 2016)

Rules and Regulations

Pages 16285-16890

From the Federal Register Online via the Government Publishing Office www.gpo.gov

FR Doc No: 2016-04800

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Vol. 81

Friday,

No. 58

March 25, 2016

Part II

Book 2 of 3 Books

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Department of Labor

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Occupational Safety and Health Administration

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29 CFR Parts 1910, 1915, and 1926

Occupational Exposure to Respirable Crystalline Silica; Final Rule

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DEPARTMENT OF LABOR

Occupational Safety and Health Administration

29 CFR Parts 1910, 1915, and 1926

Docket No. OSHA-2010-0034

RIN 1218-AB70

Occupational Exposure to Respirable Crystalline Silica

AGENCY: Occupational Safety and Health Administration (OSHA), Department of Labor.

ACTION: Final rule.

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SUMMARY: The Occupational Safety and Health Administration (OSHA) is amending its existing standards for occupational exposure to respirable crystalline silica. OSHA has determined that employees exposed to respirable crystalline silica at the previous permissible exposure limits face a significant risk of material impairment to their health. The evidence in the record for this rulemaking indicates that workers exposed to respirable crystalline silica are at increased risk of developing silicosis and other non-malignant respiratory diseases, lung cancer, and kidney disease. This final rule establishes a new permissible exposure limit of 50 micrograms of respirable crystalline silica per cubic meter of air (50 mug/m\3\) as an 8-hour time-

weighted average in all industries covered by the rule. It also includes other provisions to protect employees, such as requirements for exposure assessment, methods for controlling exposure, respiratory protection, medical surveillance, hazard communication, and recordkeeping.

OSHA is issuing two separate standards--one for general industry and maritime, and the other for construction--in order to tailor requirements to the circumstances found in these sectors.

DATES: The final rule is effective on June 23, 2016. Start-up dates for specific provisions are set in Sec. 1910.1053(l) for general industry and maritime and in Sec. 1926.1153(k) for construction.

Collections of Information

There are a number of collections of information contained in this final rule (see Section VIII, Paperwork Reduction Act). Notwithstanding the general date of applicability that applies to all other requirements contained in the final rule, affected parties do not have to comply with the collections of information until the Department of Labor publishes a separate notice in the Federal Register announcing the Office of Management and Budget has approved them under the Paperwork Reduction Act.

ADDRESSES: In accordance with 28 U.S.C. 2112(a), the Agency designates Ann Rosenthal, Associate Solicitor of Labor for Occupational Safety and Health, Office of the Solicitor of Labor, Room S-4004, U.S. Department of Labor, 200 Constitution Avenue NW., Washington, DC 20210, to receive petitions for review of the final rule.

FOR FURTHER INFORMATION CONTACT: For general information and press inquiries, contact Frank Meilinger, Director, Office of Communications, Room N-3647, OSHA, U.S. Department of Labor, 200 Constitution Avenue NW., Washington, DC 20210; telephone (202) 693-1999; email meilinger.francis2@dol.gov.

For technical inquiries, contact William Perry or David O'Connor, Directorate of Standards and Guidance, Room N-3718, OSHA, U.S. Department of Labor, 200 Constitution Avenue NW., Washington, DC 20210; telephone (202) 693-1950.

SUPPLEMENTARY INFORMATION: The preamble to the rule on occupational exposure to respirable crystalline silica follows this outline:

I. Executive Summary

II. Pertinent Legal Authority

III. Events Leading to the Final Standards

IV. Chemical Properties and Industrial Uses

V. Health Effects

VI. Final Quantitative Risk Assessment and Significance of Risk

VII. Summary of the Final Economic Analysis and Final Regulatory Flexibility Analysis

VIII. Paperwork Reduction Act

IX. Federalism

X. State-Plan States

XI. Unfunded Mandates

XII. Protecting Children From Environmental Health and Safety Risks

XIII. Consultation and Coordination With Indian Tribal Governments

XIV. Environmental Impacts

XV. Summary and Explanation of the Standards

Scope

Definitions

Specified Exposure Control Methods

Alternative Exposure Control Methods

Permissible Exposure Limit

Exposure Assessment

Regulated Areas

Methods of Compliance

Respiratory Protection

Housekeeping

Written Exposure Control Plan

Medical Surveillance

Communication of Respirable Crystalline Silica Hazards to Employees

Recordkeeping

Dates

Authority and Signature

Citation Method

In the docket for the respirable crystalline silica rulemaking, found at http://www.regulations.gov, every submission was assigned a document identification (ID) number that consists of the docket number (OSHA-2010-0034) followed by an additional four-digit number. For example, the document ID number for OSHA's Preliminary Economic Analysis and Initial Regulatory Flexibility Analysis is OSHA-2010-0034-

1720. Some document ID numbers include one or more attachments, such as the National Institute for Occupational Safety and Health (NIOSH) prehearing submission (see Document ID OSHA 2010-0034-2177).

When citing exhibits in the docket, OSHA includes the term ``Document ID'' followed by the last four digits of the document ID number, the attachment number or other attachment identifier, if applicable, page numbers (designated ``p.'' or ``Tr.'' for pages from a hearing transcript), and in a limited number of cases a footnote number (designated ``Fn''). In a citation that contains two or more document ID numbers, the document ID numbers are separated by semi-colons. For example, a citation referring to the NIOSH prehearing comments and NIOSH testimony obtained from the hearing transcript would be indicated as follows: (Document ID 2177, Attachment B, pp. 2-3; 3579, Tr. 132). In some sections, such as Section V, Health Effects, author names and year of study publication are included before the document ID number in a citation, for example: (Hughes et al., 2001, Document ID 1060; McDonald et al., 2001, 1091; McDonald et al., 2005, 1092; Rando et al., 2001, 0415).

I. Executive Summary

This final rule establishes a permissible exposure limit (PEL) for respirable crystalline silica of 50 mug/m\3\ as an 8-hour time-

weighted average (TWA) in all industries covered by the rule. In addition to the PEL, the rule includes provisions to protect employees such as requirements for exposure assessment, methods for controlling exposure, respiratory protection, medical surveillance, hazard communication, and recordkeeping. OSHA is issuing two separate standards--one for general industry and maritime, and the other for construction--in order to tailor requirements to the circumstances found in these sectors. There are, however, numerous common elements in the two standards.

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The final rule is based on the requirements of the Occupational Safety and Health Act (OSH Act) and court interpretations of the Act. For health standards issued under section 6(b)(5) of the OSH Act, OSHA is required to promulgate a standard that reduces significant risk to the extent that it is technologically and economically feasible to do so. See Section II, Pertinent Legal Authority, for a full discussion of OSH Act legal requirements.

OSHA has conducted an extensive review of the literature on adverse health effects associated with exposure to respirable crystalline silica. OSHA has also developed estimates of the risk of silica-related diseases, assuming exposure over a working lifetime, at the preceding PELs as well as at the revised PEL and action level. Comments received on OSHA's preliminary analysis, and the Agency's final findings, are discussed in Section V, Health Effects, and Section VI, Final Quantitative Risk Assessment and Significance of Risk. OSHA finds that employees exposed to respirable crystalline silica at the preceding PELs are at an increased risk of lung cancer mortality and silicosis mortality and morbidity. Occupational exposures to respirable crystalline silica also result in increased risk of death from other nonmalignant respiratory diseases including chronic obstructive pulmonary disease (COPD), and from kidney disease. OSHA further concludes that exposure to respirable crystalline silica constitutes a significant risk of material impairment to health and that the final rule will substantially lower that risk. The Agency considers the level of risk remaining at the new PEL to be significant. However, based on the evidence evaluated during the rulemaking process, OSHA has determined a PEL of 50 mug/m\3\ is appropriate because it is the lowest level feasible for all affected industries.

OSHA's examination of the technological and economic feasibility of the rule is presented in the Final Economic Analysis and Final Regulatory Flexibility Analysis (FEA), and is summarized in Section VII of this preamble. OSHA concludes that the PEL of 50 mug/m\3\ is technologically feasible for most operations in all affected industries, although it will be a technological challenge for several affected sectors and will require the use of respirators for a limited number of job categories and tasks.

OSHA developed quantitative estimates of the compliance costs of the rule for each of the affected industry sectors. The estimated compliance costs were compared with industry revenues and profits to provide a screening analysis of the economic feasibility of complying with the rule and an evaluation of the economic impacts. Industries with unusually high costs as a percentage of revenues or profits were further analyzed for possible economic feasibility issues. After performing these analyses, OSHA finds that compliance with the requirements of the rule is economically feasible in every affected industry sector.

The final rule includes several major changes from the proposed rule as a result of OSHA's analysis of comments and evidence received during the comment periods and public hearings. The major changes are summarized below and are fully discussed in Section XV, Summary and Explanation of the Standards.

Scope. As proposed, the standards covered all occupational exposures to respirable crystalline silica with the exception of agricultural operations covered under 29 CFR part 1928. OSHA has made a final determination to exclude exposures in general industry and maritime where the employer has objective data demonstrating that employee exposure to respirable crystalline silica will remain below 25 mug/m\3\ as an 8-hour TWA under any foreseeable conditions. OSHA is also excluding exposures in construction where employee exposure to respirable crystalline silica will remain below 25 mug/m\3\ as an 8-

hour TWA under any foreseeable conditions. In addition, OSHA is excluding exposures that result from the processing of sorptive clays from the scope of the rule. The standard for general industry and maritime also allows employers to comply with the standard for construction in certain circumstances.

Specified Exposure Control Methods. OSHA has revised the structure of the standard for construction to emphasize the specified exposure control methods for construction tasks that are presented in Table 1 of the standard. Unlike in the proposed rule, employers who fully and properly implement the controls listed on Table 1 are not separately required to comply with the PEL, and are not subject to provisions for exposure assessment and methods of compliance. The entries on Table 1 have also been revised extensively.

Protective Clothing. The proposed rule would have required use of protective clothing in certain limited situations. The final rule does not include requirements for use of protective clothing to address exposure to respirable crystalline silica.

Housekeeping. The proposed rule would have prohibited use of compressed air, dry sweeping, and dry brushing to clean clothing or surfaces contaminated with crystalline silica where such activities could contribute to employee exposure to respirable crystalline silica that exceeds the PEL. The final rule allows for use of compressed air, dry sweeping, and dry brushing in certain limited situations.

Written Exposure Control Plan. OSHA did not propose a requirement for employers to develop a written exposure control plan. The final rule includes a requirement for employers covered by the rule to develop a written exposure control plan, and the standard for construction includes a provision for a competent person (i.e., a designated individual who is capable of identifying crystalline silica hazards in the workplace and who possesses the authority to take corrective measures to address them) to implement the written exposure control plan.

Regulated Areas. OSHA proposed to provide employers covered by the rule with the alternative of either establishing a regulated area or an access control plan to limit access to areas where exposure to respirable crystalline silica exceeds the PEL. The final standard for general industry and maritime requires employers to establish a regulated area in such circumstances. The final standard for construction does not include a provision for regulated areas, but includes a requirement that the written exposure control plan include procedures used to restrict access to work areas, when necessary, to minimize the numbers of employees exposed to respirable crystalline silica and their level of exposure. The access control plan alternative is not included in the final rule.

Medical Surveillance. The proposed rule would have required employers to make medical surveillance available to employees exposed to respirable crystalline silica above the PEL for 30 or more days per year. The final standard for general industry and maritime requires that medical surveillance be made available to employees exposed to respirable crystalline silica at or above the action level of 25 mug/

m\3\ as an 8-hour TWA for 30 or more days per year. The final standard for construction requires that medical surveillance be made available to employees who are required by the standard to use respirators for 30 or more days per year.

The rule requires the employer to obtain a written medical opinion from physicians or other licensed health care professionals (PLHCPs) for medical

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examinations provided under the rule but limits the information provided to the employer to the date of the examination, a statement that the examination has met the requirements of the standard, and any recommended limitations on the employee's use of respirators. The proposed rule would have required that such opinions contain additional information, without requiring employee authorization, such as any recommended limitations upon the employee's exposure to respirable crystalline silica, and any referral to a specialist. In the final rule, the written opinion provided to the employer will only include recommended limitations on the employee's exposure to respirable crystalline silica and referral to a specialist if the employee provides written authorization. The final rule requires a separate written medical report provided to the employee to include this additional information, as well as detailed information related to the employee's health.

Dates. OSHA proposed identical requirements for both standards: an effective date 60 days after publication of the rule; a date for compliance with all provisions except engineering controls and laboratory requirements of 180 days after the effective date; a date for compliance with engineering controls requirements, which was one year after the effective date; and a date for compliance with laboratory requirements of two years after the effective date.

OSHA has revised the proposed compliance dates in both standards. The final rule is effective 90 days after publication. For general industry and maritime, all obligations for compliance commence two years after the effective date, with two exceptions: The obligation for engineering controls commences five years after the effective date for hydraulic fracturing operations in the oil and gas industry; and the obligation for employers in general industry and maritime to offer medical surveillance commences two years after the effective date for employees exposed above the PEL, and four years after the effective date for employees exposed at or above the action level. For construction, all obligations for compliance commence one year after the effective date, with the exception that certain requirements for laboratory analysis commence two years after the effective date.

Under the OSH Act's legal standard directing OSHA to set health standards based on findings of significant risk of material impairment and technological and economic feasibility, OSHA does not use cost-

benefit analysis to determine the PEL or other aspects of the rule. It does, however, determine and analyze costs and benefits for its own informational purposes and to meet certain Executive Order requirements, as discussed in Section VII. Summary of the Final Economic Analysis and Final Regulatory Flexibility Analysis and in the FEA. Table I-1--which is derived from material presented in Section VII of this preamble--provides a summary of OSHA's best estimate of the costs and benefits of the rule using a discount rate of 3 percent. As shown, the rule is estimated to prevent 642 fatalities and 918 moderate-to-severe silicosis cases annually once it is fully effective, and the estimated cost of the rule is $1,030 million annually. Also as shown in Table I-1, the discounted monetized benefits of the rule are estimated to be $8.7 billion annually, and the rule is estimated to generate net benefits of approximately $7.7 billion annually.

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GRAPHIC TIFF OMITTED TR25MR16.000

II. Pertinent Legal Authority

The purpose of the Occupational Safety and Health Act (29 U.S.C. 651 et seq.) (``the Act'' or ``the OSH Act''), is ``to assure so far as possible every working man and woman in the Nation safe and healthful working conditions and to preserve our human resources'' (29 U.S.C. 651(b)). To achieve this goal Congress authorized the Secretary of Labor (``the Secretary'') ``to set mandatory occupational safety and health standards applicable to businesses affecting interstate commerce'' (29 U.S.C. 651(b)(3); see 29 U.S.C. 654(a) (requiring employers to comply with OSHA standards), 655(a) (authorizing summary adoption of existing consensus and federal standards within two years of the Act's enactment), and 655(b) (authorizing promulgation, modification or revocation of standards pursuant to notice and comment)). The primary statutory provision relied upon by the Agency in promulgating health standards is section 6(b)(5) of the Act; other sections of the OSH Act, however, authorize the Occupational Safety and Health Administration (OSHA) to require labeling and other appropriate forms of warning, exposure assessment, medical examinations, and recordkeeping in its standards (29 U.S.C. 655(b)(5), 655(b)(7), 657(c)).

The Act provides that in promulgating standards dealing with toxic materials or harmful physical agents, such as respirable crystalline silica, the Secretary shall set the standard which ``most adequately assures, to the extent feasible, on the basis of the best available evidence, that no employee will suffer material impairment of health . . . even if such employee has regular exposure to the hazard dealt with by such standard for the period of his working life'' (29 U.S.C. 655(b)(5)). Thus, ``when Congress passed the Occupational Safety and Health Act in 1970, it chose to place pre-eminent value on assuring employees a safe and healthful working environment, limited only by the feasibility of achieving such an environment'' (American Textile Mfrs. Institute, Inc. v. Donovan, 452 US 490, 541 (1981) (``Cotton Dust'')).

OSHA proposed this new standard for respirable crystalline silica and conducted its rulemaking pursuant to

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section 6(b)(5) of the Act ((29 U.S.C. 655(b)(5)). The preceding silica standard, however, was adopted under the Secretary's authority in section 6(a) of the OSH Act (29 U.S.C. 655(a)), to adopt national consensus and established Federal standards within two years of the Act's enactment (see 29 CFR 1910.1000 Table Z-1). Any rule that ``differs substantially from an existing national consensus standard'' must ``better effectuate the purposes of this Act than the national consensus standard'' (29 U.S.C. 655(b)(8)). Several additional legal requirements arise from the statutory language in sections 3(8) and 6(b)(5) of the Act (29 U.S.C. 652(8), 655(b)(5)). The remainder of this section discusses these requirements, which OSHA must consider and meet before it may promulgate this occupational health standard regulating exposure to respirable crystalline silica.

Material Impairment of Health

Subject to the limitations discussed below, when setting standards regulating exposure to toxic materials or harmful physical agents, the Secretary is required to set health standards that ensure that ``no employee will suffer material impairment of health or functional capacity . . .'' (29 U.S.C. 655(b)(5)). OSHA has, under this section, considered medical conditions such as irritation of the skin, eyes, and respiratory system, asthma, and cancer to be material impairments of health. What constitutes material impairment in any given case is a policy determination on which OSHA is given substantial leeway. ``OSHA is not required to state with scientific certainty or precision the exact point at which each type of harm becomes a material impairment'' (AFL-CIO v. OSHA, 965 F.2d 962, 975 (11th Cir. 1992)). Courts have also noted that OSHA should consider all forms and degrees of material impairment--not just death or serious physical harm (AFL-

CIO, 965 F.2d at 975). Thus the Agency has taken the position that ``subclinical'' health effects, which may be precursors to more serious disease, can be material impairments of health that OSHA should address when feasible (43 FR 52952, 52954 (11/14/78) (Preamble to the Lead Standard)).

Significant Risk

Section 3(8) of the Act requires that workplace safety and health standards be ``reasonably necessary or appropriate to provide safe or healthful employment'' (29 U.S.C. 652(8)). The Supreme Court, in its decision on OSHA's benzene standard, interpreted section 3(8) to mean that ``before promulgating any standard, the Secretary must make a finding that the workplaces in question are not safe'' (Indus. Union Dep't, AFL-CIO v. Am. Petroleum Inst., 448 U.S. 607, 642 (1980) (plurality opinion) (``Benzene'')). The Court further described OSHA's obligation as requiring it to evaluate ``whether significant risks are present and can be eliminated or lessened by a change in practices'' (Benzene, 448 U.S. at 642). The Court's holding is consistent with evidence in the legislative record, with regard to section 6(b)(5) of the Act (29 U.S.C. 655(b)(5)), that Congress intended the Agency to regulate unacceptably severe occupational hazards, and not ``to establish a utopia free from any hazards'' or to address risks comparable to those that exist in virtually any occupation or workplace (116 Cong. Rec. 37614 (1970), Leg. Hist. 480-82). It is also consistent with Section 6(g) of the OSH Act, which states that, in determining regulatory priorities, ``the Secretary shall give due regard to the urgency of the need for mandatory safety and health standards for particular industries, trades, crafts, occupations, businesses, workplaces or work environments'' (29 U.S.C. 655(g)).

The Supreme Court in Benzene clarified that OSHA has considerable latitude in defining significant risk and in determining the significance of any particular risk. The Court did not specify a means to distinguish significant from insignificant risks, but rather instructed OSHA to develop a reasonable approach to making its significant risk determination. The Court stated that ``it is the Agency's responsibility to determine, in the first instance, what it considers to be a `significant' risk'' (Benzene, 448 U.S. at 655), and it did not ``express any opinion on the . . . difficult question of what factual determinations would warrant a conclusion that significant risks are present which make promulgation of a new standard reasonably necessary or appropriate'' (Benzene, 448 U.S. at 659). The Court stated, however, that the section 6(f) (29 U.S.C. 655(b)(f)) substantial evidence standard applicable to OSHA's significant risk determination does not require the Agency ``to support its finding that a significant risk exists with anything approaching scientific certainty'' (Benzene, 448 U.S. at 656). Rather, OSHA may rely on ``a body of reputable scientific thought'' to which ``conservative assumptions in interpreting the data . . . '' may be applied, ``risking error on the side of overprotection'' (Benzene, 448 U.S. at 656; see also United Steelworkers of Am., AFL-CIO-CLC v. Marshall, 647 F.2d 1189, 1248 (D.C. Cir. 1980) (``Lead I'') (noting the Benzene Court's application of this principle to carcinogens and applying it to the lead standard, which was not based on carcinogenic effects)). OSHA may thus act with a ``pronounced bias towards worker safety'' in making its risk determinations (Bldg & Constr. Trades Dep't v. Brock, 838 F.2d 1258, 1266 (D.C. Cir. 1988) (``Asbestos II'').

The Supreme Court further recognized that what constitutes ``significant risk'' is ``not a mathematical straitjacket'' (Benzene, 448 U.S. at 655) and will be ``based largely on policy considerations'' (Benzene, 448 U.S. at 655 n.62). The Court gave the following example:

If . . . the odds are one in a billion that a person will die from cancer by taking a drink of chlorinated water, the risk clearly could not be considered significant. On the other hand, if the odds are one in a thousand that regular inhalation of gasoline vapors that are 2% benzene will be fatal, a reasonable person might well consider the risk significant . . . (Benzene, 448 U.S. at 655).

Following Benzene, OSHA has, in many of its health standards, considered the one-in-a-thousand metric when determining whether a significant risk exists. Moreover, as ``a prerequisite to more stringent regulation'' in all subsequent health standards, OSHA has, consistent with the Benzene plurality decision, based each standard on a finding of significant risk at the ``then prevailing standard'' of exposure to the relevant hazardous substance (Asbestos II, 838 F.2d at 1263). Once a significant risk of material impairment of health is demonstrated, it is of no import that the incidence of the illness may be declining (see Nat'l Min. Assoc. v. Sec'y, U.S. Dep't of Labor, Nos. 14-11942, 14-12163, slip op. at 80 (11th Cir. Jan. 25, 2016) (interpreting the Mine Act, 30 U.S.C. 811(a)(6)(A), which contains the same language as section 6(b)(5) of the OSH Act requiring the Secretary to set standards that assure no employee will suffer material impairment of health)).

The Agency's final risk assessment is derived from existing scientific and enforcement data and its final conclusions are made only after considering all evidence in the rulemaking record. Courts reviewing the validity of these standards have uniformly held the Secretary to the significant risk standard first articulated by the Benzene plurality and have generally upheld the Secretary's significant risk determinations as supported by substantial evidence and ``a reasoned explanation for his policy

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assumptions and conclusions'' (Asbestos II, 838 F.2d at 1266).

Once OSHA makes its significant risk finding, the ``more stringent regulation'' (Asbestos II, 838 F.2d at 1263) it promulgates must be ``reasonably necessary or appropriate'' to reduce or eliminate that risk, within the meaning of section 3(8) of the Act (29 U.S.C. 652(8)) and Benzene (448 U.S. at 642) (see Asbestos II, 838 F.2d at 1269). The courts have interpreted section 6(b)(5) of the OSH Act as requiring OSHA to set the standard that eliminates or reduces risk to the lowest feasible level; as discussed below, the limits of technological and economic feasibility usually determine where the new standard is set (see UAW v. Pendergrass, 878 F.2d 389, 390 (D.C. Cir. 1989)). In choosing among regulatory alternatives, however, ``the determination that one standard is appropriate, as opposed to a marginally more or less protective standard, is a technical decision entrusted to the expertise of the agency. . . '' (Nat'l Mining Ass'n v. Mine Safety and Health Admin., 116 F.3d 520, 528 (D.C. Cir. 1997)) (analyzing a Mine Safety and Health Administration (``MSHA'') standard under the Benzene significant risk standard). In making its choice, OSHA may incorporate a margin of safety even if it theoretically regulates below the lower limit of significant risk (Nat'l Mining Ass'n, 116 F.3d at 528 (citing American Petroleum Inst. v. Costle, 665 F.2d 1176, 1186 (D.C. Cir. 1982))).

Working Life Assumption

The OSH Act requires OSHA to set the standard that most adequately protects employees against harmful workplace exposures for the period of their ``working life'' (29 U.S.C. 655(b)(5)). OSHA's longstanding policy is to define ``working life'' as constituting 45 years; thus, it assumes 45 years of exposure when evaluating the risk of material impairment to health caused by a toxic or hazardous substance. This policy is not based on empirical data that most employees are exposed to a particular hazard for 45 years. Instead, OSHA has adopted the practice to be consistent with the statutory directive that ``no employee'' suffer material impairment of health ``even if'' such employee is exposed to the hazard for the period of his or her working life (see 74 FR 44796 (8/31/09)). OSHA's policy was given judicial approval in a challenge to an OSHA standard that lowered the permissible exposure limit (PEL) for asbestos (Asbestos II, 838 F.2d at 1264-1265). In that case, the petitioners claimed that the median duration of employment in the affected industry sectors was only five years. Therefore, according to petitioners, OSHA erred in assuming a 45-year working life in calculating the risk of health effects caused by asbestos exposure. The D.C. Circuit disagreed, stating,

Even if it is only the rare worker who stays with asbestos-

related tasks for 45 years, that worker would face a 64/1000 excess risk of contracting cancer; Congress clearly authorized OSHA to protect such a worker (Asbestos II, 838 F.2d at 1264-1265).

OSHA might calculate the health risks of exposure, and the related benefits of lowering the exposure limit, based on an assumption of a shorter working life, such as 25 years, but such estimates are for informational purposes only.

Best Available Evidence

Section 6(b)(5) of the Act requires OSHA to set standards ``on the basis of the best available evidence'' and to consider the ``latest available scientific data in the field'' (29 U.S.C. 655(b)(5)). As noted above, the Supreme Court, in its Benzene decision, explained that OSHA must look to ``a body of reputable scientific thought'' in making its material harm and significant risk determinations, while noting that a reviewing court must ``give OSHA some leeway where its findings must be made on the frontiers of scientific knowledge'' (Benzene, 448 U.S. at 656). The courts of appeals have afforded OSHA similar latitude to issue health standards in the face of scientific uncertainty. The Second Circuit, in upholding the vinyl chloride standard, stated:

. . . the ultimate facts here in dispute are `on the frontiers of scientific knowledge', and, though the factual finger points, it does not conclude. Under the command of OSHA, it remains the duty of the Secretary to act to protect the workingman, and to act even in circumstances where existing methodology or research is deficient (Society of the Plastics Industry, Inc. v. OSHA, 509 F.2d 1301, 1308 (2d Cir. 1975) (quoting Indus. Union Dep't, AFL-CIO v. Hodgson, 499 F.2d 467, 474 (D.C. Cir. 1974) (``Asbestos I''))).

The D.C. Circuit, in upholding the cotton dust standard, stated: ``OSHA's mandate necessarily requires it to act even if information is incomplete when the best available evidence indicates a serious threat to the health of workers'' (Am. Fed'n of Labor & Cong. of Indus. Orgs. v. Marshall, 617 F.2d 636, 651 (D.C. Cir. 1979), aff'd in part and vacated in part on other grounds, American Textile Mfrs. Inst., Inc. v. Donovan, 452 U.S. 490 (1981)).

When there is disputed scientific evidence, OSHA must review the evidence on both sides and ``reasonably resolve'' the dispute (Pub. Citizen Health Research Grp. v. Tyson, 796 F.2d 1479, 1500 (D.C. Cir. 1986)). In Public Citizen, there was disputed scientific evidence regarding whether there was a threshold exposure level for the health effects of ethylene oxide. The Court noted that, where ``OSHA has the expertise we lack and it has exercised that expertise by carefully reviewing the scientific data,'' a dispute within the scientific community is not occasion for it to take sides about which view is correct (Pub. Citizen Health Research Grp., 796 F.2d at 1500). ``Indeed, Congress did `not intend that the Secretary be paralyzed by debate surrounding diverse medical opinions' '' (Pub. Citizen Health Research Grp., 796 F.2d at 1497 (quoting H.R.Rep. No. 91-1291, 91st Cong., 2d Sess. 18 (1970), reprinted in Legislative History of the Occupational Safety and Health Act of 1970 at 848 (1971))).

A recent decision by the Eleventh Circuit Court of Appeals upholding a coal dust standard promulgated by MSHA emphasized that courts should give ``an extreme degree of deference to the agency when it is evaluating scientific data within its technical expertise'' (Nat'l Min. Assoc. v. Sec'y, U.S. Dep't of Labor, Nos. 14-11942, 14-

12163, slip op. at 43 (11th Cir. Jan. 25, 2016) (quoting Kennecott Greens Creek Min. Co. v. MSHA, 476 F.3d 946, 954-955 (D.C. Cir. 2007) (internal quotation marks omitted)). The Court emphasized that because the Mine Act, like the OSH Act, ``evinces a clear bias in favor of health and safety,'' the agency's responsibility to use the best evidence and consider feasibility should not be used as a counterweight to the agency's duty to protect the lives and health of workers (Nat'l Min. Assoc., Nos. 14-11942, 14-12163, slip op. at 43 (11th Cir. Jan. 25, 2016)).

Feasibility

The OSH Act requires that, in setting a standard, OSHA must eliminate the risk of material health impairment ``to the extent feasible'' (29 U.S.C. 655(b)(5)). The statutory mandate to consider the feasibility of the standard encompasses both technological and economic feasibility; these analyses have been done primarily on an industry-by-

industry basis (Lead I, 647 F.2d at 1264, 1301) in general industry. The Agency has also used application groups, defined by common tasks, as the structure for its feasibility analyses in construction (Pub. Citizen Health Research Grp. v. OSHA, 557 F.3d 165, 177-179 (3d Cir. 2009) (``Chromium (VI)''). The Supreme Court has broadly defined feasible as ``capable of being

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done'' (Cotton Dust, 452 U.S. at 509-510).

Although OSHA must set the most protective PEL that the Agency finds to be technologically and economically feasible, it retains discretion to set a uniform PEL even when the evidence demonstrates that certain industries or operations could reasonably be expected to meet a lower PEL. OSHA health standards generally set a single PEL for all affected employers; OSHA exercised this discretion most recently in its final rule on occupational exposure to chromium (VI) (71 FR 10100, 10337-10338 (2/28/2006); see also 62 FR 1494, 1575 (1/10/97) (methylene chloride)). In its decision upholding the chromium (VI) standard, including the uniform PEL, the Court of Appeals for the Third Circuit addressed this issue as one of deference, stating ``OSHA's decision to select a uniform exposure limit is a legislative policy decision that we will uphold as long as it was reasonably drawn from the record'' (Chromium (VI), 557 F.3d at 183 (3d Cir. 2009)); see also Am. Iron & Steel Inst. v. OSHA, 577 F.2d 825, 833 (3d Cir. 1978)). OSHA's reasons for choosing one chromium (VI) PEL, rather than imposing different PELs on different application groups or industries, included: Multiple PELs would create enforcement and compliance problems because many workplaces, and even workers, were affected by multiple categories of chromium (VI) exposure; discerning individual PELs for different groups of establishments would impose a huge evidentiary burden on the Agency and unnecessarily delay implementation of the standard; and a uniform PEL would, by eliminating confusion and simplifying compliance, enhance worker protection (Chromium (VI), 557 F.3d at 173, 183-184). The Court held that OSHA's rationale for choosing a uniform PEL, despite evidence that some application groups or industries could meet a lower PEL, was reasonably drawn from the record and that the Agency's decision was within its discretion and supported by past practice (Chromium (VI), 557 F.3d at 183-184).

Technological Feasibility

A standard is technologically feasible if the protective measures it requires already exist, can be brought into existence with available technology, or can be created with technology that can reasonably be expected to be developed (Lead I, 647 F.2d at 1272; Amer. Iron & Steel Inst. v. OSHA, 939 F.2d 975, 980 (D.C. Cir. 1991) (``Lead II'')). While the test for technological feasibility is normally articulated in terms of the ability of employers to decrease exposures to the PEL, provisions such as exposure measurement requirements must also be technologically feasible (Forging Indus. Ass'n v. Sec'y of Labor, 773 F.2d 1436, 1453 (4th Cir. 1985)).

OSHA's standards may be ``technology forcing,'' i.e., where the Agency gives an industry a reasonable amount of time to develop new technologies, OSHA is not bound by the ``technological status quo'' (Lead I, 647 F.2d at 1264); see also Kennecott Greens Creek Min. Co. v. MSHA, 476 F.3d 946, 957 (D.C. Cir. 2007) (MSHA standards, like OSHA standards, may be technology-forcing); Nat'l Petrochemical & Refiners Ass'n v. EPA, 287 F.3d 1130, 1136 (D.C. Cir. 2002) (agency is ``not obliged to provide detailed solutions to every engineering problem,'' but only to ``identify the major steps for improvement and give plausible reasons for its belief that the industry will be able to solve those problems in the time remaining.'').

In its Lead decisions, the D.C. Circuit described OSHA's obligation to demonstrate the technological feasibility of reducing occupational exposure to a hazardous substance.

Within the limits of the best available evidence . . . OSHA must prove a reasonable possibility that the typical firm will be able to develop and install engineering and work practice controls that can meet the PEL in most of its operations . . . The effect of such proof is to establish a presumption that industry can meet the PEL without relying on respirators . . . Insufficient proof of technological feasibility for a few isolated operations within an industry, or even OSHA's concession that respirators will be necessary in a few such operations, will not undermine this general presumption in favor of feasibility. Rather, in such operations firms will remain responsible for installing engineering and work practice controls to the extent feasible, and for using them to reduce . . . exposure as far as these controls can do so (Lead I, 647 F.2d at 1272).

Additionally, the D.C. Circuit explained that ``feasibility of compliance turns on whether exposure levels at or below the PEL can be met in most operations most of the time . . .'' (Lead II, 939 F.2d at 990).

Courts have given OSHA significant deference in reviewing its technological feasibility findings.

So long as we require OSHA to show that any required means of compliance, even if it carries no guarantee of meeting the PEL, will substantially lower . . . exposure, we can uphold OSHA's determination that every firm must exploit all possible means to meet the standard (Lead I, 647 F.2d at 1273).

Even in the face of significant uncertainty about technological feasibility in a given industry, OSHA has been granted broad discretion in making its findings (Lead I, 647 F.2d at 1285).

OSHA cannot let workers suffer while it awaits . . . scientific certainty. It can and must make reasonable technological feasibility predictions on the basis of `credible sources of information,' whether data from existing plants or expert testimony (Lead I, 647 F.2d at 1266 (quoting Am. Fed'n of Labor & Cong. of Indus. Orgs., 617 F.2d at 658)).

For example, in Lead I, the D.C. Circuit allowed OSHA to use, as best available evidence, information about new and expensive industrial smelting processes that had not yet been adopted in the U.S. and would require the rebuilding of plants (Lead I, 647 F.2d at 1283-1284). Even under circumstances where OSHA's feasibility findings were less certain and the Agency was relying on its ``legitimate policy of technology forcing,'' the D.C. Circuit approved of OSHA's feasibility findings when the Agency granted lengthy phase-in periods to allow particular industries time to comply (Lead I, 647 F.2d at 1279-1281, 1285).

OSHA is permitted to adopt a standard that some employers will not be able to meet some of the time, with employers limited to challenging feasibility at the enforcement stage (Lead I, 647 F.2d at 1273 & n. 125; Asbestos II, 838 F.2d at 1268). Even when the Agency recognized that it might have to balance its general feasibility findings with flexible enforcement of the standard in individual cases, the courts of appeals have generally upheld OSHA's technological feasibility findings (Lead II, 939 F.2d at 980; see Lead I, 647 F.2d at 1266-1273; Asbestos II, 838 F.2d at 1268). Flexible enforcement policies have been approved where there is variability in measurement of the regulated hazardous substance or where exposures can fluctuate uncontrollably (Asbestos II, 838 F.2d at 1267-1268; Lead II, 939 F.2d at 991). A common means of dealing with the measurement variability inherent in sampling and analysis is for the Agency to add the standard sampling error to its exposure measurements before determining whether to issue a citation (e.g., 51 FR 22612, 22654 (06/20/86) (Preamble to the Asbestos Standard)).

Economic Feasibility

In addition to technological feasibility, OSHA is required to demonstrate that its standards are economically feasible. A reviewing court will examine the cost of compliance with an OSHA standard ``in relation to the financial health and

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profitability of the industry and the likely effect of such costs on unit consumer prices . . .'' (Lead I, 647 F.2d at 1265 (omitting citation)). As articulated by the D.C. Circuit in Lead I,

OSHA must construct a reasonable estimate of compliance costs and demonstrate a reasonable likelihood that these costs will not threaten the existence or competitive structure of an industry, even if it does portend disaster for some marginal firms (Lead I, 647 F.2d at 1272).

A reasonable estimate entails assessing ``the likely range of costs and the likely effects of those costs on the industry'' (Lead I, 647 F.2d at 1266). As with OSHA's consideration of scientific data and control technology, however, the estimates need not be precise (Cotton Dust, 452 U.S. at 528-29 & n.54) as long as they are adequately explained. Thus, as the D.C. Circuit further explained:

Standards may be economically feasible even though, from the standpoint of employers, they are financially burdensome and affect profit margins adversely. Nor does the concept of economic feasibility necessarily guarantee the continued existence of individual employers. It would appear to be consistent with the purposes of the Act to envisage the economic demise of an employer who has lagged behind the rest of the industry in protecting the health and safety of employees and is consequently financially unable to comply with new standards as quickly as other employers. As the effect becomes more widespread within an industry, the problem of economic feasibility becomes more pressing (Asbestos I, 499 F.2d. at 478).

OSHA standards therefore satisfy the economic feasibility criterion even if they impose significant costs on regulated industries so long as they do not cause massive economic dislocations within a particular industry or imperil the very existence of the industry (Lead II, 939 F.2d at 980; Lead I, 647 F.2d at 1272; Asbestos I, 499 F.2d. at 478). As with its other legal findings, OSHA ``is not required to prove economic feasibility with certainty, but is required to use the best available evidence and to support its conclusions with substantial evidence'' (Lead II, 939 F.2d at 980-981) (citing Lead I, 647 F.2d at 1267)). Granting industries additional time to comply with new PELs may enhance the economic, as well as technological, feasibility of a standard (Lead I, 647 F.2d at 1265).

Because section 6(b)(5) of the Act explicitly imposes the ``to the extent feasible'' limitation on the setting of health standards, OSHA is not permitted to use cost-benefit analysis to make its standards-

setting decisions (29 U.S.C. 655(b)(5)).

Congress itself defined the basic relationship between costs and benefits, by placing the ``benefit'' of worker health above all other considerations save those making attainment of this ``benefit'' unachievable. Any standard based on a balancing of costs and benefits by the Secretary that strikes a different balance than that struck by Congress would be inconsistent with the command set forth in Sec. 6(b)(5) (Cotton Dust, 452 U.S. at 509).

Thus, while OSHA estimates the costs and benefits of its proposed and final rules, these calculations do not form the basis for the Agency's regulatory decisions; rather, they are performed in acknowledgement of requirements such as those in Executive Orders 12866 and 13563.

Structure of OSHA Health Standards

OSHA's health standards traditionally incorporate a comprehensive approach to reducing occupational disease. OSHA substance-specific health standards generally include the ``hierarchy of controls,'' which, as a matter of OSHA's preferred policy, mandates that employers install and implement all feasible engineering and work practice controls before respirators may be used. The Agency's adherence to the hierarchy of controls has been upheld by the courts (ASARCO, Inc. v. OSHA, 746 F.2d 483, 496-498 (9th Cir. 1984); Am. Iron & Steel Inst. v. OSHA, 182 F.3d 1261, 1271 (11th Cir. 1999)). In fact, courts view the legal standard for proving technological feasibility as incorporating the hierarchy:

OSHA must prove a reasonable possibility that the typical firm will be able to develop and install engineering and work practice controls that can meet the PEL in most of its operations. . . . The effect of such proof is to establish a presumption that industry can meet the PEL without relying on respirators (Lead I, 647 F.2d at 1272).

The hierarchy of controls focuses on removing harmful materials at their source. OSHA allows employers to rely on respiratory protection to protect their employees only when engineering and work practice controls are insufficient or infeasible. In fact, in the control of ``those occupational diseases caused by breathing air contaminated with harmful dusts, fogs, fumes, mists, gases, smokes, sprays, or vapors,'' the employers' primary objective ``shall be to prevent atmospheric contamination. This shall be accomplished as far as feasible by accepted engineering control measures (for example, enclosure or confinement of the operation, general and local ventilation, and substitution of less toxic materials). When effective engineering controls are not feasible, or while they are being instituted, appropriate respirators shall be used pursuant to this section'' (29 CFR 1910.134).

The reasons supporting OSHA's continued reliance on the hierarchy of controls, as well as its reasons for limiting the use of respirators, are numerous and grounded in good industrial hygiene principles (see Section XV, Summary and Explanation of the Standards, Methods of Compliance). Courts have upheld OSHA's emphasis on engineering and work practice controls over personal protective equipment in challenges to previous health standards, such as chromium (VI): ``Nothing in . . . any case reviewing an airborne toxin standard, can be read to support a technological feasibility rule that would effectively encourage the routine and widespread use of respirators to comply with a PEL'' (Chromium (VI), 557 F.3d at 179; see Am. Fed'n of Labor & Cong. of Indus. Orgs. v. Marshall, 617 F.2d 636, 653 (D.C. Cir. 1979) cert. granted, judgment vacated sub nom. Cotton Warehouse Ass'n v. Marshall, 449 U.S. 809 (1980) and aff'd in part, vacated in part sub nom. Am. Textile Mfrs. Inst., Inc. v. Donovan, 452 U.S. 490 (1981) (finding ``uncontradicted testimony in the record that respirators can cause severe physical discomfort and create safety problems of their own'')).

In health standards such as this one, the hierarchy of controls is augmented by ancillary provisions. These provisions work with the hierarchy of controls and personal protective equipment requirements to provide comprehensive protection to employees in affected workplaces. Such provisions typically include exposure assessment, medical surveillance, hazard communication, and recordkeeping. This approach is recognized as effective in dealing with air contaminants such as respirable crystalline silica; for example, the industry standards for respirable crystalline silica, ASTM E 1132-06, Standard Practice for Health Requirements Relating to Occupational Exposure to Respirable Crystalline Silica, and ASTM E 2626-09, Standard Practice for Controlling Occupational Exposure to Respirable Crystalline Silica for Construction and Demolition Activities, take a similar comprehensive approach (Document ID 1466; 1504).

The OSH Act compels OSHA to require all feasible measures for reducing significant health risks (29 U.S.C. 655(b)(5); Pub. Citizen Health Research Grp., 796 F.2d at 1505 (``if in fact a STEL short-term exposure limit would further reduce a significant

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health risk and is feasible to implement, then the OSH Act compels the agency to adopt it (barring alternative avenues to the same result)''). When there is significant risk below the PEL, as is the case with respirable crystalline silica, the DC Circuit indicated that OSHA should use its regulatory authority to impose additional requirements on employers when those requirements will result in a greater than de minimis incremental benefit to workers' health (Asbestos II, 838 F.2d at 1274). The Supreme Court alluded to a similar issue in Benzene, pointing out that ``in setting a permissible exposure level in reliance on less-than-perfect methods, OSHA would have the benefit of a backstop in the form of monitoring and medical testing'' (Benzene, 448 U.S. at 657). OSHA believes that the ancillary provisions in this final standard provide significant benefits to worker health by providing additional layers and types of protection to employees exposed to respirable crystalline silica.

Finally, while OSHA is bound by evidence in the rulemaking record, and generally looks to its prior standards for guidance on how to structure and specify requirements in a new standard, it is not limited to past approaches to regulation. In promulgating health standards, ``whenever practicable, the standard promulgated shall be expressed in terms of objective criteria and of the performance desired'' (29 U.S.C. 655(b)(5)). In cases of industries or tasks presenting unique challenges in terms of assessing and controlling exposures, it may be more practicable and provide greater certainty to require specific controls with a demonstrated track record of efficacy in reducing exposures and, therefore, risk (especially when supplemented by appropriate respirator usage). Such an approach could more effectively protect workers than the traditional exposure assessment-and-control approach when exposures may vary because of factors such as changing environmental conditions or materials, and an assessment may not reflect typical exposures associated with a task or operation. As discussed at length in Section XV, Summary and Explanation of the Standards, the specified exposure control measures option in the construction standard (i.e., Table 1, in paragraph (c)(1)) for respirable crystalline silica represents the type of innovative, objective approach available to the Secretary when fashioning a rule under these circumstances.

III. Events Leading to the Final Standards

The Occupational Safety and Health Administration's (OSHA's) previous standards for workplace exposure to respirable crystalline silica were adopted in 1971, pursuant to section 6(a) of the Occupational Safety and Health Act (29 U.S.C. 651 et seq.) (``the Act'' or ``the OSH Act'') (36 FR 10466 (5/29/71)). Section 6(a) (29 U.S.C. 655(a)) authorized OSHA, in the first two years after the effective date of the Act, to promulgate ``start-up'' standards, on an expedited basis and without public hearing or comment, based on national consensus or established Federal standards that improved employee safety or health. Pursuant to that authority, OSHA in 1971 promulgated approximately 425 permissible exposure limits (PELs) for air contaminants, including crystalline silica, which were derived principally from Federal standards applicable to government contractors under the Walsh-Healey Public Contracts Act, 41 U.S.C. 35, and the Contract Work Hours and Safety Standards Act (commonly known as the Construction Safety Act), 40 U.S.C. 333. The Walsh-Healey Act and Construction Safety Act standards had been adopted primarily from recommendations of the American Conference of Governmental Industrial Hygienists (ACGIH).

For general industry (see 29 CFR 1910.1000, Table Z-3), the PEL for crystalline silica in the form of respirable quartz was based on two alternative formulas: (1) A particle-count formula, PELmppcf=250/(% quartz + 5) as respirable dust; and (2) a mass formula proposed by ACGIH in 1968, PEL=(10 mg/m3)/(% quartz + 2) as respirable dust. The general industry PELs for crystalline silica in the form of cristobalite and tridymite were one-

half of the value calculated from either of the above two formulas for quartz. For construction (see 29 CFR 1926.55, Appendix A) and shipyards (see 29 CFR 1915.1000, Table Z), the formula for the PEL for crystalline silica in the form of quartz (PELmppcf=250/(% quartz + 5) as respirable dust), which requires particle counting, was derived from the 1970 ACGIH threshold limit value (TLV).\1\ Based on the formulas, the PELs for quartz, expressed as time-weighted averages (TWAs), were approximately equivalent to 100 mug/m3 for general industry and 250 mug/m3 for construction and shipyards. The PELs were not supplemented by additional protective provisions--such as medical surveillance requirements--as are included in other OSHA standards. OSHA believes that the formula based on particle-counting technology used in the general industry, construction, and shipyard PELs has been rendered obsolete by respirable mass (gravimetric) sampling.

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\1\ The Mineral Dusts tables that contain the silica PELs for construction and shipyards do not clearly express PELs for cristobalite and tridymite. 29 CFR 1926.55; 29 CFR 1915.1000. This lack of textual clarity likely results from a transcription error in the Code of Federal Regulations. OSHA's final rule provides the same PEL for quartz, cristobalite, and tridymite in general industry, maritime, and construction.

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In 1974, the National Institute for Occupational Safety and Health (NIOSH), an agency within the Department of Health and Human Services created by the OSH Act and designed to carry out research and recommend standards for occupational safety and health hazards, evaluated crystalline silica as a workplace hazard and issued criteria for a recommended standard (29 U.S.C. 669, 671; Document ID 0388). NIOSH recommended that occupational exposure to crystalline silica be controlled so that no worker is exposed to a TWA of free (respirable crystalline) silica greater than 50 mug/m3 as determined by a full-shift sample for up to a 10-hour workday over a 40-hour workweek. The document also recommended a number of ancillary provisions for a standard, such as exposure monitoring and medical surveillance.

In December 1974, OSHA published an Advance Notice of Proposed Rulemaking (ANPRM) based on the recommendations in the NIOSH criteria document (39 FR 44771 (12/27/74)). In the ANPRM, OSHA solicited ``public participation on the issues of whether a new standard for crystalline silica should be issued on the basis of the NIOSH criteria or any other information, and, if so, what should be the contents of a proposed standard for crystalline silica'' (39 FR at 44771). OSHA also set forth the particular issues of concern on which comments were requested. The Agency did not issue a proposed rule or pursue a final rule for crystalline silica at that time.

As information on the health effects of silica exposure developed during the 1980s and 1990s, national and international classification organizations came to recognize crystalline silica as a human carcinogen. In June 1986, the International Agency for Research on Cancer (IARC), which is the specialized cancer agency within the World Health Organization, evaluated the available evidence regarding crystalline silica carcinogenicity and concluded, in 1987, that crystalline silica is probably carcinogenic to

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humans (http://monographs.iarc.fr/ENG/Monographs/suppl7/Suppl7.pdf). An IARC working group met again in October 1996 to evaluate the complete body of research, including research that had been conducted since the initial 1986 evaluation. IARC concluded, more decisively this time, that ``crystalline silica inhaled in the form of quartz or cristobalite from occupational sources is carcinogenic to humans'' (Document ID 2258, Attachment 8, p. 211). In 2012, IARC reaffirmed that ``Crystalline silica in the form of quartz or cristobalite dust is carcinogenic to humans'' (Document ID 1473, p. 396).

In 1991, in the Sixth Annual Report on Carcinogens, the U.S. National Toxicology Program (NTP), within the U.S. Department of Health and Human Services, concluded that respirable crystalline silica was ``reasonably anticipated to be a human carcinogen'' (as referenced in Document ID 1417, p. 1). NTP reevaluated the available evidence and concluded, in the Ninth Report on Carcinogens, that ``respirable crystalline silica (RCS), primarily quartz dust occurring in industrial and occupational settings, is known to be a human carcinogen, based on sufficient evidence of carcinogenicity from studies in humans indicating a causal relationship between exposure to RCS and increased lung cancer rates in workers exposed to crystalline silica dust'' (Document ID 1417, p. 1). ACGIH listed respirable crystalline silica (in the form of quartz) as a suspected human carcinogen in 2000, while lowering the TLV to 0.05 mg/m3 (50 mug/m3) (Document ID 1503, p. 15). ACGIH subsequently lowered the TLV for crystalline silica to 0.025 mg/m3 (25 mug/m3) in 2006, which is ACGIH's current recommended exposure limit (Document ID 1503, pp. 1, 15).

In 1989, OSHA established 8-hour TWA PELs of 0.1 mg/m3 (100 mug/m3) for quartz and 0.05 mg/m3 (50 mug/m3) for cristobalite and tridymite, as part of the Air Contaminants final rule for general industry (54 FR 2332 (1/19/89)). OSHA stated that these limits presented no substantial change from the Agency's former formula limits, but would simplify sampling procedures. In providing comments on the proposed rule, NIOSH recommended that crystalline silica be considered a potential carcinogen.

In 1992, OSHA, as part of the Air Contaminants proposed rule for maritime, construction, and agriculture, proposed the same PELs as for general industry, to make the PELs consistent across all the OSHA-

regulated sectors (57 FR 26002 (6/12/92)). However, the U.S. Court of Appeals for the Eleventh Circuit vacated the 1989 Air Contaminants final rule for general industry (Am. Fed'n of Labor and Cong. of Indus. Orgs. v. OSHA, 965 F.2d 962 (1992)), and also mooted the proposed rule for maritime, construction, and agriculture. The Court's decision to vacate the rule forced the Agency to return to the original 1971 PELs for all compounds, including silica, adopted as section 6(a) standards.

In 1994, OSHA initiated a process to determine which safety and health hazards in the U.S. needed the most attention. A priority planning committee included safety and health experts from OSHA, NIOSH, and the Mine Safety and Health Administration (MSHA). The committee reviewed available information on occupational deaths, injuries, and illnesses and communicated extensively with representatives of labor, industry, professional and academic organizations, the States, voluntary standards organizations, and the public. The OSHA National Advisory Committee on Occupational Safety and Health and the Advisory Committee on Construction Safety and Health (ACCSH) also made recommendations. Rulemaking for crystalline silica exposure was one of the priorities designated by this process. OSHA indicated that crystalline silica would be added to the Agency's regulatory agenda as other standards were completed and resources became available.

In 1996, OSHA instituted a Special Emphasis Program (SEP) to step up enforcement of the crystalline silica standards. The SEP was intended to reduce worker silica dust exposures that can cause silicosis and lung cancer. It included extensive outreach designed to educate and train employers and employees about the hazards of silica and how to control them, as well as inspections to enforce the standards. Among the outreach materials available were slides presenting information on hazard recognition and crystalline silica control technology, a video on crystalline silica and silicosis, and informational cards for workers explaining crystalline silica, health effects related to exposure, and methods of control. The SEP provided guidance for targeting inspections of worksites that had employees at risk of developing silicosis. The inspections resulted in the collection of exposure data from the various worksites visited by OSHA's compliance officers.

As a follow-up to the SEP, OSHA undertook numerous non-regulatory actions to address silica exposures. For example, in October of 1996, OSHA launched a joint silicosis prevention effort with MSHA, NIOSH, and the American Lung Association (see https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=NEWS_RELEASES&p_id=14110). This public education campaign involved distribution of materials on how to prevent silicosis, including a guide for working safely with silica and stickers for hard hats to remind workers of crystalline silica hazards. Spanish language versions of these materials were also made available. OSHA and MSHA inspectors distributed materials at mines, construction sites, and other affected workplaces. The joint silicosis prevention effort included a National Conference to Eliminate Silicosis in Washington, DC, in March of 1997, which brought together approximately 650 participants from labor, business, government, and the health and safety professions to exchange ideas and share solutions regarding the goal of eliminating silicosis (see https://industrydocuments.library.ucsf.edu/documentstore/s/h/d/p//shdp0052/shdp0052.pdf).

In 1997, OSHA announced in its Unified Agenda under Long-Term Actions that it planned to publish a proposed rule on crystalline silica

. . . because the agency has concluded that there will be no significant progress in the prevention of silica-related diseases without the adoption of a full and comprehensive silica standard, including provisions for product substitution, engineering controls, training and education, respiratory protection and medical screening and surveillance. A full standard will improve worker protection, ensure adequate prevention programs, and further reduce silica-

related diseases (62 FR 57755, 57758 (10/29/97)).

In November 1998, OSHA moved ``Occupational Exposure to Crystalline Silica'' to the pre-rule stage in the Regulatory Plan (63 FR 61284, 61303-61304 (11/9/98)). OSHA held a series of stakeholder meetings in 1999 and 2000 to get input on the rulemaking. Stakeholder meetings for all industry sectors were held in Washington, Chicago, and San Francisco. A separate stakeholder meeting for the construction sector was held in Atlanta.

OSHA initiated Small Business Regulatory Enforcement Fairness Act (SBREFA) proceedings in 2003, seeking the advice of small business representatives on the proposed rule (68 FR 30583, 30584 (5/27/03)). The SBREFA panel, including representatives from OSHA, the Small Business Administration's Office of Advocacy, and the Office of Management and Budget (OMB), was

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convened on October 20, 2003. The panel conferred with small entity representatives (SERs) from general industry, maritime, and construction on November 10 and 12, 2003, and delivered its final report, which included comments from the SERs and recommendations to OSHA for the proposed rule, to OSHA's Assistant Secretary on December 19, 2003 (Document ID 0937).

In 2003, OSHA examined enforcement data for the years 1997 to 2002 and identified high rates of noncompliance with the OSHA respirable crystalline silica PELs, particularly in construction. This period covers the first five years of the SEP. These enforcement data, presented in Table III-1, indicate that 24 percent of silica samples from the construction industry and 13 percent from general industry were at least three times the then-existing OSHA PELs. The data indicate that 66 percent of the silica samples obtained during inspections in general industry were in compliance with the PEL, while only 58 percent of the samples collected in construction were in compliance.

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In an effort to expand the 1996 SEP, on January 24, 2008, OSHA implemented a National Emphasis Program (NEP) to identify and reduce or eliminate the health hazards associated with occupational exposure to crystalline silica (CPL-03-007 (1/24/08)). The NEP targeted worksites with elevated exposures to crystalline silica and included new program evaluation procedures designed to ensure that the goals of the NEP were measured as accurately as possible, detailed procedures for conducting inspections, updated information for selecting sites for inspection, development of outreach programs by each Regional and Area Office emphasizing the formation of voluntary partnerships to share information, and guidance on calculating PELs in construction and shipyards. In each OSHA Region, at least two percent of inspections every year are silica-related inspections. Additionally, the silica-

related inspections are conducted at a range of facilities reasonably representing the distribution of general industry and construction work sites in that region.

A more recent analysis of OSHA enforcement data from January 2003 to December 2009 (covering the period of continued implementation of the SEP and the first two years of the NEP) shows that considerable noncompliance with the then-existing PELs continued to occur. These enforcement data, presented in Table III-2, indicate that 14 percent of silica samples from the construction industry and 19 percent for general industry were at least three times the OSHA PEL during this period. The data indicate that 70 percent of the silica samples obtained during inspections in general industry were in compliance with the PEL, and 75 percent of the samples collected in construction were in compliance.

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Both industry and worker groups have recognized that a comprehensive standard is needed to protect workers exposed to respirable crystalline silica. For example, ASTM International (originally known as the American Society for Testing and Materials) has published voluntary consensus standards for addressing the hazards of crystalline silica, and the Building and Construction Trades Department, AFL-CIO also has recommended a comprehensive program standard. These recommended standards include provisions for methods of compliance, exposure monitoring, training, and medical surveillance. The National Industrial Sand Association has also developed an occupational exposure program for crystalline silica that addresses exposure assessment and medical surveillance.

Throughout the crystalline silica rulemaking process, OSHA has presented information to, and consulted with, ACCSH and the Maritime Advisory Committee on Occupational Safety and Health. In December of 2009, OSHA representatives met with ACCSH to discuss the rulemaking and receive their comments and recommendations. On December 11, 2009, ACCSH passed motions supporting the concept of Table 1 in the draft proposed construction rule, recognizing that the controls listed in Table 1 are effective. As discussed with regard to paragraph (f) of the proposed standard for construction (paragraph (c) of the final standard for construction), Table 1 presents specified control measures for selected construction tasks. ACCSH also recommended that OSHA maintain the protective clothing provision found in the SBREFA panel draft regulatory text and restore the ``competent person'' requirement and responsibilities to the proposed rule. Additionally, the group recommended that OSHA move forward expeditiously with the rulemaking process.

In January 2010, OSHA completed a peer review of the draft Health Effects Analysis and Preliminary Quantitative Risk Assessment following procedures set forth by OMB in the Final Information Quality Bulletin for Peer Review, published on the OMB Web site on December 16, 2004 (see 70 FR 2664 (1/14/05)). Each peer reviewer submitted a written report to OSHA. The Agency revised its draft documents as appropriate and made the revised documents available to the public as part of its Notice of Proposed Rulemaking (NPRM). OSHA also made the written charge to the peer reviewers, the peer reviewers' names, the peer reviewers' reports, and the Agency's response to the peer reviewers' reports publicly available with publication of the proposed rule (Document ID 1711; 1716). Five of the seven original peer reviewers submitted post-

hearing reports, commenting on OSHA's disposition of their original peer review comments in the proposed rule, as well as commenting on written and oral testimony presented at the silica hearing (Document ID 3574).

On August 23, 2013, OSHA posted its NPRM for respirable crystalline silica on its Web site and requested comments on the proposed rule. On September 12, 2013, OSHA published the NPRM in the Federal Register (78 FR 56273 (9/12/13)). In the NPRM, the Agency made a preliminary determination that employees exposed to respirable crystalline silica at the current PELs face a significant risk to their health and that promulgating the proposed standards would substantially reduce that risk. The NPRM required commenters to submit their comments by December 11, 2013. In response to stakeholder requests, OSHA extended the comment period until January 27, 2014 (78 FR 65242 (10/31/13)). On January 14, 2014, OSHA held a web chat to provide small businesses and other stakeholders an additional opportunity to obtain information from the Agency about the proposed rule. Subsequently, OSHA further extended the comment period to February 11, 2014 (79 FR 4641 (1/29/14)).

As part of the instructions for submitting comments, OSHA requested (but did not require) that parties submitting technical or scientific studies or research results and those submitting comments or testimony on the Agency's analyses disclose the nature of financial relationships with (e.g., consulting agreement), and extent of review by, parties interested in or

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affected by the rulemaking (78 FR 56274). Parties submitting studies or research results were also asked to disclose sources of funding and sponsorship for their research. OSHA intended for the disclosure of such information to promote the transparency and scientific integrity of evidence submitted to the record and stated that the request was consistent with Executive Order 13563.

The Agency received several comments related to this request. For example, an industrial hygiene engineer supported the disclosure of potential conflict of interest information (Document ID 2278, p. 5). Other commenters, such as congressional representatives and industry associations, opposed the request, asserting that it could lead to prejudgment or questioning of integrity, in addition to dissuading participation in the rulemaking; some also questioned the legality of such a request or OSHA's interpretation of Executive Order 13563 (e.g., Document ID 1811, p. 2; 2101, pp. 2-3). A number of stakeholders from academia and industry submitted information related to the request for funding, sponsorships, and review by interested parties (e.g., Document ID 1766, p. 1; 2004, p. 2; 2211, p. 2; 2195, p. 17). OSHA emphasizes that it reviewed and considered all evidence submitted to the record.

An informal public hearing on the proposed standards was held in Washington, DC from March 18 through April 4, 2014. Administrative Law Judges Daniel F. Solomon and Stephen L. Purcell presided over the hearing. The Agency heard testimony from over 200 stakeholders representing more than 70 organizations, such as public health groups, trade associations, and labor unions. Chief Administrative Law Judge Stephen L. Purcell closed the public hearing on April 4, 2014, allowing 45 days--until May 19, 2014--for participants who filed a notice of intention to appear at the hearings to submit additional evidence and data, and an additional 45 days--until July 3, 2014--to submit final briefs, arguments, and summations (Document ID 3589, Tr. 4415-4416). After the hearing concluded, OSHA extended the deadline to give those participants who filed a notice of intention to appear at the hearings until June 3, 2014 to submit additional information and data to the record, and until July 18, 2014 to submit final briefs and arguments (Document ID 3569). Based upon requests from stakeholders, the second deadline was extended, and parties who filed a notice of intention to appear at the hearing were given until August 18, 2014, to submit their final briefs and arguments (Document ID 4192).

OSHA provided the public with multiple opportunities to participate in the rulemaking process, including stakeholder meetings, the SBREFA panel, two comment periods (pre- and post-hearing), and a 14-day public hearing. Commenters were provided more than five months to comment on the rule before the hearing, and nearly as long to submit additional information, final briefs, and arguments after the hearing. OSHA received more than 2,000 comments on the silica NPRM during the entire pre-and post-hearing public participation period. In OSHA's view, therefore, the public was given sufficient opportunities and ample time to fully participate in this rulemaking.

The final rule on occupational exposure to respirable crystalline silica is based on consideration of the entire record of this rulemaking proceeding, including materials discussed or relied upon in the proposal, the record of the hearing, and all written comments and exhibits timely received. Thus, in promulgating this final rule, OSHA considered all comments in the record, including those that suggested that OSHA withdraw its proposal and merely enforce the existing silica standards, as well as those that argued the proposed rule was not protective enough. Based on this comprehensive record, OSHA concludes that employees exposed to respirable crystalline silica are at significant risk of developing silicosis and other non-malignant respiratory disease, lung cancer, kidney effects, and immune system effects. The Agency concludes that the PEL of 50 mug/m\3\ reduces the significant risks of material impairments of health posed to workers by occupational exposure to respirable crystalline silica to the maximum extent that is technologically and economically feasible. OSHA's substantive determinations with regard to the comments, testimony, and other information in the record, the legal standards governing the decision-making process, and the Agency's analysis of the data resulting in its assessments of risks, benefits, technological and economic feasibility, and compliance costs are discussed elsewhere in this preamble.

IV. Chemical Properties and Industrial Uses

Silica is a compound composed of the elements silicon and oxygen (chemical formula SiO2). Silica has a molecular weight of 60.08, and exists in crystalline and amorphous states, both in the natural environment and as produced during manufacturing or other processes. These substances are odorless solids, have no vapor pressure, and create non-explosive dusts when particles are suspended in air (Document ID 3637, pp. 1-3).

Silica is classified as part of the ``silicate'' class of minerals, which includes compounds that are composed of silicon and oxygen and which may also be bonded to metal ions or their oxides. The basic structural units of silicates are silicon tetrahedrons (SiO4), pyramidal structures with four triangular sides where a silicon atom is located in the center of the structure and an oxygen atom is located at each of the four corners. When silica tetrahedrons bond exclusively with other silica tetrahedrons, each oxygen atom is bonded to the silicon atom of its original ion, as well as to the silicon atom from another silica ion. This results in a ratio of one atom of silicon to two atoms of oxygen, expressed as SiO2. The silicon-oxygen bonds within the tetrahedrons use only one-half of each oxygen's total bonding energy. This leaves negatively charged oxygen ions available to bond with available positively charged ions. When they bond with metal and metal oxides, commonly of iron, magnesium, aluminum, sodium, potassium, and calcium, they form the silicate minerals commonly found in nature (Document ID 1334, p. 7).

In crystalline silica, the silicon and oxygen atoms are arranged in a three-dimensional repeating pattern. Silica is said to be polymorphic, as different forms are created when the silica tetrahedrons combine in different crystalline structures. The primary forms of crystalline silica are quartz, cristobalite, and tridymite. In an amorphous state, silicon and oxygen atoms are present in the same proportions but are not organized in a repeating pattern. Amorphous silica includes natural and manufactured glasses (vitreous and fused silica, quartz glass), biogenic silica, and opals, which are amorphous silica hydrates (Document ID 2258, Attachment 8, pp. 45-50).

Quartz is the most common form of crystalline silica and accounts for almost 12% by volume of the earth's crust. Alpha quartz, the quartz form that is stable below 573 degC, is the most prevalent form of crystalline silica found in the workplace. It accounts for the overwhelming majority of naturally found silica and is present in varying amounts in almost every type of mineral. Alpha quartz is found in igneous, sedimentary, and metamorphic rock, and all soils contain at least a trace amount of quartz (Document ID 1334, p.

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9). Alpha quartz is used in many products throughout various industries and is a common component of building materials (Document ID 1334, pp. 11-15). Common trade names for commercially available quartz include: CSQZ, DQ 12, Min-U-Sil, Sil-Co-Sil, Snowit, Sykron F300, and Sykron F600 (Document ID 2258, Attachment 8, p. 43).

Cristobalite is a form of crystalline silica that is formed at high temperatures (>1470 degC). Although naturally occurring cristobalite is relatively rare, volcanic eruptions, such as Mount St. Helens, can release cristobalite dust into the air. Cristobalite can also be created during some processes conducted in the workplace. For example, flux-calcined diatomaceous earth is a material used as a filtering aid and as a filler in other products (Document ID 2258, Attachment 8, p. 44). It is produced when diatomaceous earth (diatomite), a geological product of decayed unicellular organisms called diatoms, is heated with flux. The finished product can contain between 40 and 60 percent cristobalite. Also, high temperature furnaces are often lined with bricks that contain quartz. When subjected to prolonged high temperatures, this quartz can convert to cristobalite.

Tridymite is another material formed at high temperatures (>870 degC) that is associated with volcanic activity. The creation of tridymite requires the presence of a flux such as sodium oxide. Tridymite is rarely found in nature and rarely reported in the workplace (Document ID 1424 pp. 5, 14).

When heated or cooled sufficiently, crystalline silica can transition between the polymorphic forms, with specific transitions occurring at different temperatures. At higher temperatures the linkages between the silica tetrahedrons break and reform, resulting in new crystalline structures. Quartz converts to cristobalite at 1470 degC, and at 1723 degC cristobalite loses its crystalline structure and becomes amorphous fused silica. These high temperature transitions reverse themselves at extremely slow rates, with different forms co-

existing for a long time after the crystal cools (Document ID 2258, Attachment 8, p. 47).

Other types of transitions occur at lower temperatures when the silica-oxygen bonds in the silica tetrahedron rotate or stretch, resulting in a new crystalline structure. These low-temperature, or alpha to beta, transitions are readily and rapidly reversed as the crystal cools. At temperatures encountered by workers, only the alpha form of crystalline silica exists (Document ID 2258, Attachment 8, pp. 46-48).

Crystalline silica minerals produce distinct X-ray diffraction patterns, specific to their crystalline structure. The patterns can be used to distinguish the crystalline polymorphs from each other and from amorphous silica (Document ID 2258, Attachment 8, p. 45).

The specific gravity and melting point of silica vary between polymorphs. Silica is insoluble in water at 20 degC and in most acids, but its solubility increases with higher temperatures and pH, and it dissolves readily in hydrofluoric acid. Solubility is also affected by the presence of trace metals and by particle size. Under humid conditions water vapor in the air reacts with the surface of silica particles to form an external layer of silinols (SiOH). When these silinols are present the crystalline silica becomes more hydrophilic. Heating or acid washing reduces the amount of silinols on the surface area of crystalline silica particles. There is an external amorphous layer found in aged quartz, called the Beilby layer, which is not found on freshly cut quartz. This amorphous layer is more water soluble than the underlying crystalline core. Etching with hydrofluoric acid removes the Beilby layer as well as the principal metal impurities on quartz (Document ID 2258, Attachment 8, pp. 44-49).

Crystalline silica has limited chemical reactivity. It reacts with alkaline aqueous solutions, but does not readily react with most acids, with the exception of hydrofluoric acid. In contrast, amorphous silica and most silicates react with most mineral acids and alkaline solutions. Analytical chemists relied on this difference in acid reactivity to develop the silica point count analytical method that was widely used prior to the current X-ray diffraction and infrared methods (Document ID 2258, Attachment 8, pp. 48-51; 1355, p. 994).

Crystalline silica is used in industry in a wide variety of applications. Sand and gravel are used in road building and concrete construction. Sand with greater than 98% silica is used in the manufacture of glass and ceramics. Silica sand is used to form molds for metal castings in foundries, and in abrasive blasting operations. Silica is also used as a filler in plastics, rubber, and paint, and as an abrasive in soaps and scouring cleansers. Silica sand is used to filter impurities from municipal water and sewage treatment plants, and in hydraulic fracturing for oil and gas recovery (Document ID 1334, p. 11). Silica is also used to manufacture artificial stone products used as bathroom and kitchen countertops, and the silica content in those products can exceed 85 percent (Document ID 1477, pp. 3 and 11; 2178, Attachment 5, p. 420).

There are over 30 major industries and operations where exposures to crystalline silica can occur. They include such diverse workplaces as foundries, dental laboratories, concrete products and paint and coating manufacture, as well as construction activities including masonry cutting, drilling, grinding and tuckpointing, and use of heavy equipment during demolition activities involving silica-containing materials. A more detailed discussion of the industries affected by the proposed standard is presented in Section VII, Summary of the Final Economic Analysis and Final Regulatory Flexibility Analysis. Crystalline silica exposures can also occur in mining (which is under the jurisdiction of the Mine Safety and Health Administration), and in agriculture during plowing and harvesting.

V. Health Effects

  1. Introduction

    As discussed more thoroughly in Section II of this preamble, Pertinent Legal Authority, section 6(b)(5) of the Occupational Safety and Health Act (OSH Act or Act) requires the Secretary of Labor, in promulgating standards dealing with toxic materials or harmful physical agents, to ``set the standard which most adequately assures, to the extent feasible, on the basis of the best available evidence, that no employee will suffer material impairment of health or functional capacity even if such employee has regular exposure to the hazard dealt with by such standard for the period of his working life'' (29 U.S.C. 655). Thus, in order to set a new health standard, the Secretary must determine that there is a significant risk of material impairment of health at the existing PEL and that issuance of a new standard will significantly reduce or eliminate that risk.

    The Secretary's significant risk and material impairment determinations must be made ``on the basis of the best available evidence'' (29 U.S.C. 655(b)(5)). Although the Supreme Court, in its decision on OSHA's Benzene standard, explained that OSHA must look to ``a body of reputable scientific thought'' in making its material harm and significant risk determinations, the Court added that a reviewing court must ``give OSHA some leeway where its findings must be made on the frontiers

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    of scientific knowledge'' (Indus. Union Dep't, AFL-CIO v. Am. Petroleum Inst., 448 U.S. 607, 656 (1980) (plurality opinion) (``Benzene'')). Thus, while OSHA's significant risk determination must be supported by substantial evidence, the Agency ``is not required to support the finding that a significant risk exists with anything approaching scientific certainty'' (Benzene, 448 U.S. at 656).

    This section provides an overview of OSHA's material harm and significant risk determinations: (1) Summarizing OSHA's preliminary methods and findings from the proposal; (2) addressing public comments dealing with OSHA's evaluation of the scientific literature and methods used to estimate quantitative risk; and (3) presenting OSHA's final conclusions, with consideration of the rulemaking record, on the health effects and quantitative risk estimates associated with worker exposure to respirable crystalline silica. The quantitative risk estimates and significance of those risks are then discussed in detail in Section VI, Final Quantitative Risk Assessment and Significance of Risk.

  2. Summary of Health and Risk Findings

    As discussed in detail throughout this section and in Section VI, Final Quantitative Risk Assessment and Significance of Risk, OSHA finds, based upon the best available evidence in the published, peer-

    reviewed scientific literature, that exposure to respirable crystalline silica increases the risk of silicosis, lung cancer, other non-

    malignant respiratory disease (NMRD), and renal and autoimmune effects. In its Preliminary Quantitative Risk Assessment (QRA), OSHA used the best available exposure-response data from epidemiological studies to estimate quantitative risks. After carefully reviewing stakeholder comments on the Preliminary QRA and new information provided to the rulemaking record, OSHA finds there to be a clearly significant risk at the previous PELs for respirable crystalline silica (equivalent to approximately 100 mug/m\3\ for general industry and between 250 and 500 mug/m\3\ for construction/shipyards), with excess lifetime risk estimates for lung cancer mortality, silicosis mortality, and NMRD mortality each being much greater than 1 death per 1,000 workers exposed for a working life of 45 years. Cumulative risk estimates for silicosis morbidity are also well above 1 case per 1,000 workers exposed at the previous PELs. At the revised PEL of 50 mug/m\3\ respirable crystalline silica, these estimated risks are substantially reduced. Thus, OSHA concludes that the new PEL of 50 mug/m\3\ provides a large reduction in the lifetime and cumulative risk posed to workers exposed to respirable crystalline silica.

    These findings and conclusions are consistent with those of the World Health Organization's International Agency for Research on Cancer (IARC), the U.S. Department of Health and Human Services' (HHS) National Toxicology Program (NTP), the National Institute for Occupational Safety and Health (NIOSH), and many other organizations and individuals, as evidenced in the rulemaking record and further discussed below. Many other scientific organizations and governments have recognized the strong body of scientific evidence pointing to the health risks of respirable crystalline silica and have deemed it necessary to take action to reduce those risks. As far back as 1974, NIOSH recommended that the exposure limit for crystalline silica be reduced to 50 mug/m\3\ (Document ID 2177b, p. 2). In 2000, the American Conference of Governmental Industrial Hygienists (ACGIH), a professional society that has recommended workplace exposure limits for six decades, revised their Threshold Limit Value (TLV) for respirable crystalline silica to 50 mug/m\3\ and has since further lowered its TLV for respirable crystalline silica to 25 mug/m\3\. OSHA is setting its revised PEL at 50 mug/m\3\ based on consideration of the body of evidence describing the health risks of crystalline silica as well as on technological feasibility considerations, as discussed in Section VII of this preamble and Chapter IV of the Final Economic Analysis and Final Regulatory Flexibility Analysis (FEA).

    To reach these conclusions, OSHA performed an extensive search and review of the peer-reviewed scientific literature on the health effects of inhalation exposure to crystalline silica, particularly silicosis, lung cancer, other NMRD, and renal and autoimmune effects (Document ID 1711, pp. 7-265). Based upon this review, OSHA preliminarily determined that there was substantial evidence that exposure to respirable crystalline silica increases the risk of silicosis, lung cancer, NMRD, and renal and autoimmune effects (Document ID 1711, pp. 164, 181-208, 229). OSHA also found there to be suitable exposure-response data from many well-conducted epidemiological studies that permitted the Agency to estimate quantitative risks for lung cancer mortality, silicosis and NMRD mortality, renal disease mortality, and silicosis morbidity (Document ID 1711, p. 266).

    As part of the preliminary quantitative risk assessment, OSHA calculated estimates of the risk of silica-related diseases assuming exposure over a working life (45 years) to 25, 50, 100, 250, and 500 mug/m\3\ respirable crystalline silica (corresponding to cumulative exposures over 45 years to 1.125, 2.25, 4.5, 11.25, and 22.5 mg/m\3\-

    yrs) (see Bldg & Constr. Trades Dep't v. Brock, 838 F.2d 1258, 1264-65 (D.C. Cir. 1988) approving OSHA's policy of using 45 years for the working life of an employee in setting a toxic substance standard). To estimate lifetime excess mortality risks at these exposure levels, OSHA used, for each key study, the exposure-response risk model(s) and regression coefficient from the model(s) in a life table analysis that accounted for competing causes of death due to background causes and cumulated risk through age 85 (Document ID 1711, pp. 360-378). For these analyses, OSHA used lung cancer, NMRD, or renal disease mortality and all-cause mortality rates to account for background risks and competing risks (U.S. 2006 data for lung cancer and NMRD mortality in all males, 1998 data for renal disease mortality, obtained from cause-

    specific death rate tables published by the National Center for Health Statistics (2009, Document ID 1104)). The mortality risk estimates were presented in terms of lifetime excess risk per 1,000 workers for exposure over an 8-hour working day, 250 days per year, and a 45-year working lifetime. For silicosis morbidity, OSHA based its risk estimates on the cumulative risk model(s) used in each study to develop quantitative exposure-response relationships. These models characterized the risk of developing silicosis, as detected by chest radiography, up to the time that cohort members, including both active and retired workers, were last examined (78 FR 56273, 56312 (9/12/13)).

    OSHA then combined its review of the health effects literature and preliminary quantitative risk assessment into a draft document, entitled ``Occupational Exposure to Respirable Crystalline Silica--

    Review of Health Effects Literature and Preliminary Quantitative Risk Assessment,'' and submitted it to a panel of scientific experts \2\ for independent peer review,

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    in accordance with the Office of Management and Budget's (OMB) ``Final Information Quality Bulletin for Peer Review'' (Document ID 1336). The peer reviewers reviewed OSHA's draft Review of Health Effects Literature and Preliminary QRA. The peer-review panel responded to nearly 20 charge questions from OSHA and commented on various aspects of OSHA's analysis (Document ID 1716).

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    \2\ OSHA's contractor, Eastern Research Group, Inc. (ERG), conducted a search for nationally recognized experts in occupational epidemiology, biostatistics and risk assessment, animal and cellular toxicology, and occupational medicine who had no actual or apparent conflict of interest. ERG chose seven of the applicants to be peer reviewers based on their qualifications and the necessity of ensuring a broad and diverse panel in terms of scientific and technical expertise (see Document ID 1711, pp. 379-381). The seven peer reviewers were: Bruce Allen, Bruce Allen Consulting; Kenneth Crump, Ph.D., Louisiana Tech University Foundation; Murray Finkelstein, MD, Ph.D., McMaster University, Ontario; Gary Ginsberg, Ph.D., Connecticut Department of Public Health; Brian Miller, Ph.D., Institute of Occupational Medicine (IOM) Consulting Ltd., Scotland; Andrew Salmon, Ph.D., private consultant; and Noah Seixas, Ph.D., University of Washington, Seattle (Document ID 1711, p. 380).

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    Overall, the peer reviewers found that OSHA was very thorough in its review of the literature and was reasonable in its interpretation of the studies with regards to the various endpoints examined, such that the Agency's conclusions on health effects were generally well founded (Document ID 1711, p. 381). The reviewers had various comments on OSHA's draft Preliminary QRA (Document ID 1716, pp. 107-218). OSHA provided a response to each comment in the Review of Health Effects Literature and Preliminary QRA and, where appropriate, made revisions (Document ID 1711, pp. 381-399). The Agency then placed the Review of Health Effects Literature and Preliminary QRA into the rulemaking docket as a background document (Document ID 1711). With the publication of the Notice of Proposed Rulemaking (78 FR 56723 on 9/12/

    13), all aspects of the Review of Health Effects Literature and Preliminary QRA were open for public comment.

    Following the publication of the proposed rule (78 FR 56273 (9/12/

    13)) and accompanying revised Review of Health Effects Literature and Preliminary QRA (Document ID 1711), the peer reviewers were invited to review the revised analysis, examine the written comments in the docket, and attend the public hearing to listen to oral testimony as it applied to the health effects and quantitative risk assessment. Five peer reviewers were available and attended. In their final comments, provided to OSHA following the hearings, all five peer reviewers indicated that OSHA had adequately addressed their original comments (Document ID 3574). The peer reviewers also offered additional comments on concerns raised during the hearing. Many of the reviewers commented on the difficulty of evaluating exposure-response thresholds, and responded to public comments regarding causation and other specific issues (Document ID 3574). OSHA has incorporated many of the peer reviewers' additional comments into its risk assessment discussion in the preamble. Thus, OSHA believes that the external, independent peer-

    review process supports and lends legitimacy to its risk assessment methods and findings.

    OSHA also received substantial public comment and testimony from a wide variety of stakeholders supporting its Review of Health Effects Literature and Preliminary QRA. In general, supportive comments and testimony were received from NIOSH (Document ID 2177; 3998; 4233), the public health and medical community, labor unions, affected workers, private citizens, and others.

    Regarding health effects, NIOSH commented that the adverse health effects of exposure to respirable crystalline silica are ``well-known, long lasting, and preventable'' (Document ID 2177b, p. 2). Darius Sivin, Ph.D., of the UAW, commented, ``occupational exposure to silica has been recognized for centuries as a serious workplace hazard'' (Document ID 2282, Attachment 3, p. 4). Similarly, David Goldsmith, Ph.D., testified:

    There have been literally thousands of research studies on exposure to crystalline silica in the past 30 years. Almost every study tells the occupational research community that workers need better protection to prevent severe chronic respiratory diseases, including lung cancer and other diseases in the future. What OSHA is proposing to do in revising the workplace standard for silica seems to be a rational response to the accumulation of published evidence (Document ID 3577, Tr. 865-866).

    Franklin Mirer, Ph.D., CIH, Professor of Environmental and Occupational Health at CUNY School of Public Health, on behalf of the American Federation of Labor and Congress of Industrial Organizations (AFL-CIO), reiterated that silica ``is a clear and present danger to workers health at exposure levels prevailing now in a large number of industries. Workers are at significant risk for mortality and illnesses including lung cancer and non-malignant respiratory disease including COPD, and silicosis'' (Document ID 2256, Attachment 3, p. 3). The AFL-

    CIO also noted that there is ``overwhelming evidence in the record that exposure to respirable crystalline silica poses a significant health risk to workers'' (Document ID 4204, p. 11). The Building and Construction Trades Department, AFL-CIO, further commented that the rulemaking record ``clearly supports OSHA's risk determination'' (Document ID 4223, p. 2). Likewise, the Sorptive Minerals Institute, a national trade association, commented, ``It is beyond dispute that OSHA has correctly determined that industrial exposure to certain types of silica can cause extremely serious, sometimes even fatal disease. In the massive rulemaking docket being compiled by the Agency, credible claims to the contrary are sparse to non-existent'' (Document ID 4230, p. 8). OSHA also received numerous comments supportive of the revised standard from affected workers and citizens (e.g., Document ID 1724, 1726, 1731, 1752, 1756, 1759, 1762, 1764, 1787, 1798, 1800, 1802).

    Regarding OSHA's literature review for its quantitative risk assessment, the American Public Health Association (APHA) and the National Consumers League (NCL) commented, ``OSHA has thoroughly reviewed and evaluated the peer-reviewed literature on the health effects associated with exposure to respirable crystalline silica. OSHA's quantitative risk assessment is sound. The agency has relied on the best available evidence and acted appropriately in giving greater weight to those studies with the most robust designs and statistical analyses'' (Document ID 2178, Attachment 1, p. 1; 2373, p. 1).

    Dr. Mirer, who has served on several National Academy of Sciences committees setting risk assessment guidelines, further commented that OSHA's risk analysis is ``scientifically correct, and consistent with the latest thinking on risk assessment,'' (Document ID 2256, Attachment 3, p. 3), citing the National Academies' National Research Council's Science and Decisions: Advancing Risk Assessment (Document ID 4052), which makes technical recommendations on risk assessment and risk-based decision making (Document ID 3578, Tr. 935-936). In post-hearing comments expanding on this testimony, the AFL-CIO also noted that OSHA's risk assessment methodologies are transparent and consistent with practices recommended by the National Research Council in its publication, Risk Assessment in the Federal Government: Managing the Process, and with the Environmental Protection Agency's Guidelines for Carcinogenic Risk Assessment (Document ID 4204, p. 20). Similarly, Kyle Steenland, Ph.D., Professor in the Department of Environmental Health at Rollins School of Public Health, Emory University, one of the researchers on whose studies OSHA relied, testified that ``OSHA has

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    done a very capable job in conducting the summary of the literature and doing its own risk assessment'' (Document ID 3580, Tr. 1235). Collectively, these comments and testimony support OSHA's use of the best available evidence and methods to estimate quantitative risks of lung cancer mortality, silicosis and NMRD mortality, renal disease mortality, and silicosis morbidity from exposure to respirable crystalline silica.

    Based on OSHA's Preliminary QRA, many commenters recognized that reducing the permissible exposure limit is necessary to reduce significant risks presented by exposure to respirable crystalline silica (Document ID 4204, pp. 11-12; 2080, p. 1; 2339, p. 2). For example, the AFL-CIO stated that ``OSHA based its proposal on more than adequate evidence, but more recent publications have described further the risk posed by silica exposure, and further justify the need for new silica standards'' (Document ID 4204, pp. 11-12). Similarly, the American Society of Safety Engineers (ASSE) remarked that ``while some may debate the science underlying the findings set forth in the proposed rule, overexposure to crystalline silica has been linked to occupational illness since the time of the ancient Greeks, and reduction of the current permissible exposure limit (PEL) to that recommended for years by the National Institute for Occupational Safety and Health (NIOSH) is long overdue'' (Document ID 2339, p. 2).

    Not every commenter agreed, however, as OSHA also received critical comments and testimony from various employers and their representatives, as well as some organizations representing affected industries. In general, these comments were critical of the underlying studies on which OSHA relied for its quantitative risk assessment, or with the methods used by OSHA to estimate quantitative risks. Some commenters also presented additional studies for OSHA to consider. OSHA thoroughly reviewed these and did not find them adequate to alter OSHA's overall conclusions of health risk, as discussed in great detail in the sections that follow.

    After considering the evidence and testimony in the record, as discussed below, OSHA affirms its approach to quantify health risks related to exposure to respirable crystalline silica and the Agency's preliminary conclusions. In the final risk assessment that is now presented as part of this final rule in Section VI, Final Quantitative Risk Assessment and Significance of Risk, OSHA concludes that there is a clearly significant risk at the previous PELs for respirable crystalline silica, with excess lifetime risk estimates for lung cancer mortality, silicosis mortality, and NMRD mortality each being much greater than 1 death per 1,000 workers as a result of exposure for 45 working years (see Section VI, Final Quantitative Risk Assessment and Significance of Risk). At the revised PEL of 50 microg/m\3\ respirable crystalline silica, OSHA finds the estimated risks to be substantially reduced. Cumulative risk estimates for silicosis morbidity are also well above 1 case per 1,000 workers at the previous PELs, with a substantial reduction at the revised PEL (see Section VI, Final Quantitative Risk Assessment and Significance of Risk, Table VI-

    1).

    The health effects associated with silica exposure are well-

    established and supported by the record. Based on the record evidence, OSHA concludes that exposure to respirable crystalline silica causes silicosis and is the only known cause of silicosis. This causal relationship has long been accepted in the scientific and medical communities. In fact, the Department of Labor produced a video in 1938 featuring then Secretary of Labor Frances Perkins discussing the occurrence of silicosis among workers exposed to silica (see https://www.osha.gov/silica/index.html). Silicosis is a progressive disease induced by the inflammatory effects of respirable crystalline silica in the lung, which leads to lung damage and scarring and, in some cases, progresses to complications resulting in disability and death (see Section VI, Final Quantitative Risk Assessment and Significance of Risk). OSHA used a weight-of-evidence approach to evaluate the scientific studies in the literature to determine their overall quality and whether there is substantial evidence that exposure to respirable crystalline silica increases the risk of a particular health effect.

    For lung cancer, OSHA reviewed the published, peer-reviewed scientific literature, including 60 epidemiological studies covering more than 30 occupational groups in over a dozen industrial sectors (see Document ID 1711, pp. 77-170). Based on this comprehensive review, and after considering the rulemaking record as a whole, OSHA concludes that the data provide ample evidence that exposure to respirable crystalline silica increases the risk of lung cancer among workers (see Document ID 1711, p. 164). OSHA's conclusion is consistent with that of IARC, which is the specialized cancer agency that is part of the World Health Organization and utilizes interdisciplinary (e.g., biostatistics, epidemiology, and laboratory sciences) experts to comprehensively identify the causes of cancer. In 1997, IARC classified respirable crystalline silica dust, in the form of quartz or cristobalite, as Group 1, i.e., ``carcinogenic to humans,'' following a thorough expert committee review of the peer-reviewed scientific literature (Document ID 2258, Attachment 8, p. 211). OSHA notes that IARC classifications and accompanying monographs are well recognized in the scientific community, having been described as ``the most comprehensive and respected collection of systematically evaluated agents in the field of cancer epidemiology'' (Demetriou et al., 2012, Document ID 4131, p. 1273). For silica, IARC's overall finding was based on studies of nine occupational cohorts that it considered to be the least influenced by confounding factors (see Document ID 1711, p. 76). OSHA included these studies in its review, in addition to several other studies (Document ID 1711, pp. 77-170).

    Since IARC's 1997 determination that respirable crystalline silica is a Group 1 carcinogen, the scientific community has reaffirmed the soundness of this finding. In March of 2009, 27 scientists from eight countries participated in an additional IARC review of the scientific literature and reaffirmed that respirable crystalline silica dust is a Group 1 human carcinogen (Document ID 1473, p. 396). Additionally, in 2000, the NTP, which is a widely-respected interagency program under HHS that evaluates chemicals for possible toxic effects on public health, also concluded that respirable crystalline silica is a known human carcinogen (Document ID 1164, p. 1).

    For NMRD other than silicosis, based on its review of several studies and all subsequent record evidence, OSHA concludes that exposure to respirable crystalline silica increases the risk of emphysema, chronic bronchitis, and pulmonary function impairment (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, pp. 181-208). For renal disease, OSHA reviewed the epidemiological literature and finds that a number of epidemiological studies reported statistically significant associations between occupational exposure to silica dust and chronic renal disease, subclinical renal changes, end-stage renal disease morbidity, chronic renal disease mortality, and granulomatosis with polyangitis (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, p. 228). For autoimmune effects, OSHA reviewed

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    epidemiological information in the record suggesting an association between respirable crystalline silica exposure and increased risk of systemic autoimmune diseases, including scleroderma, rheumatoid arthritis, and systemic lupus erythematosus (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, p. 229). Therefore, OSHA concludes that there is substantial evidence that silica exposure increases the risks of renal and of autoimmune disease (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, p. 229).

    OSHA also finds there to be suitable exposure-response data from many well-conducted studies that permit the Agency to estimate quantitative risks for lung cancer mortality, silicosis and NMRD mortality, renal disease mortality, and silicosis morbidity (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, p. 266). OSHA believes the exposure-response data in these studies collectively represent the best available evidence for use in estimating the quantitative risks related to silica exposure. For lung cancer mortality, OSHA relies upon a number of published studies that analyzed exposure-response relationships between respirable crystalline silica and lung cancer. These included studies of cohorts from several industry sectors: Diatomaceous earth workers (Rice et al., 2001, Document ID 1118), Vermont granite workers (Attfield and Costello, 2004, Document ID 0285), North American industrial sand workers (Hughes et al., 2001, Document ID 1060), and British coal miners (Miller and MacCalman, 2009, Document ID 1306). These studies are scientifically sound due to their sufficient size and adequate years of follow-up, sufficient quantitative exposure data, lack of serious confounding by exposure to other occupational carcinogens, consideration (for the most part) of potential confounding by smoking, and absence of any apparent selection bias (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, p. 165). They all demonstrated positive, statistically significant exposure-response relationships between exposure to crystalline silica and lung cancer mortality. Also compelling was a pooled analysis (Steenland et al., 2001a, Document ID 0452) of 10 occupational cohorts (with a total of 65,980 workers and 1,072 lung cancer deaths), which was also used as a basis for IARC's 2009 reaffirmation of respirable crystalline silica as a human carcinogen. This analysis by Steenland et al. found an overall positive exposure-

    response relationship between cumulative exposure to crystalline silica and lung cancer mortality (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, pp. 269-292). Based on these studies, OSHA estimates that the lifetime lung cancer mortality excess risk associated with 45 years of exposure to respirable crystalline silica ranges from 11 to 54 deaths per 1,000 workers at the previous general industry PEL of 100 microg/m\3\ respirable crystalline silica, and 5 to 23 deaths per 1,000 workers at the revised PEL of 50 microg/m\3\ respirable crystalline silica (see Section VI, Final Quantitative Risk Assessment and Significance of Risk, Table VI-1). These estimates exceed by a substantial margin the one in a thousand benchmark that OSHA has generally applied to its health standards following the Supreme Court's Benzene decision (448 U.S. 607, 655 (1980)).

    For silicosis and NMRD mortality, OSHA relies upon two published, peer-reviewed studies: A pooled analysis of silicosis mortality data from six epidemiological studies (Mannetje et al., 2002b, Document ID 1089), and an exposure-response analysis of NMRD mortality among diatomaceous earth workers (Park et al, 2002, Document ID 0405) (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, p. 292). The pooled analysis had a total of 18,634 subjects, 150 silicosis deaths, and 20 deaths from unspecified pneumoconiosis, and demonstrated an increasing mortality rate with silica exposure (Mannetje et al., 2002b, Document ID 1089; see also 1711, pp. 292-295). To estimate the risks of silicosis mortality, OSHA used the model described by Mannetje et al. but used rate ratios that were estimated from a sensitivity analysis conducted by ToxaChemica, Inc. that was expected to better control for age and exposure measurement uncertainty (2004, Document ID 0469; 1711, p. 295). OSHA's estimate of lifetime silicosis mortality risk is 11 deaths per 1,000 workers at the previous general industry PEL, and 7 deaths per 1,000 workers at the revised PEL (see Section VI, Final Quantitative Risk Assessment and Significance of Risk, Table VI-1).

    The NMRD analysis by Park et al. (2002, Document 0405) included pneumoconiosis (including silicosis), chronic bronchitis, and emphysema, since silicosis is a cause of death that is often misclassified as emphysema or chronic bronchitis (see Document ID 1711, p. 295). Positive exposure-response relationships were found between exposure to crystalline silica and excess risk for NMRD mortality (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, pp. 204-206, 295-297). OSHA's estimate of excess lifetime NMRD mortality risk, calculated using the results from Park et al., is 85 deaths per 1,000 workers at the previous general industry PEL of 100 microg/m\3\ respirable crystalline silica, and 44 deaths per 1,000 workers at the revised PEL (see Section VI, Final Quantitative Risk Assessment and Significance of Risk, Table VI-1).\3\

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    \3\ The risk estimates for silicosis and NMRD are not directly comparable, as the endpoint for the NMRD analysis (Park et al., 2002, Document ID 0405) was death from all non-cancer lung diseases, including silicosis, pneumoconiosis, emphysema, and chronic bronchitis, whereas the endpoint for the silicosis analysis (Mannetje et al., 2002b, Document ID 1089) was deaths coded as silicosis or other pneumoconiosis only (Document ID 1711, pp. 297-

    298).

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    For renal disease mortality, Steenland et al. (2002a, Document ID 0448) conducted a pooled analysis of three cohorts (with a total of 13,382 workers) that found a positive exposure-response relationship for both multiple-cause mortality (i.e., any mention of renal disease on the death certificate) and underlying cause mortality. OSHA used the Steenland et al. (2002a, Document ID 0448) pooled analysis to estimate risks, given its large number of workers from cohorts with sufficient exposure data (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, pp. 314-315). OSHA's analysis for renal disease mortality shows estimated lifetime excess risk of 39 deaths per 1,000 workers at the previous general industry PEL of 100 microg/m\3\ respirable crystalline silica, and 32 deaths per 1,000 workers exposed at the revised PEL of 50 microg/m\3\ (see Section VI, Final Quantitative Risk Assessment and Significance of Risk, Table VI-

    1). OSHA acknowledges, however, that there are considerably less data for renal disease mortality, and thus the findings based on them are less robust than those for silicosis, lung cancer, and NMRD mortality (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, p. 229). For autoimmune disease, there were no quantitative exposure-response data available for a quantitative risk assessment (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, p. 229).

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    For silicosis morbidity, OSHA reviewed the principal studies available in the scientific literature that have characterized the risk to exposed workers of acquiring silicosis, as detected by the appearance of opacities on chest radiographs (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, p. 357). The most reliable estimates of silicosis morbidity came from five studies that evaluated radiographs over time, including after workers left employment: The U.S. gold miner cohort studied by Steenland and Brown (1995b, Document ID 0451); the Scottish coal miner cohort studied by Buchanan et al. (2003, Document ID 0306); the Chinese tin mining cohort studied by Chen et al. (2001, Document ID 0332); the Chinese tin, tungsten, and pottery worker cohorts studied by Chen et al. (2005, Document ID 0985); and the South African gold miner cohort studied by Hnizdo and Sluis-Cremer (1993, Document ID 1052) (see Section VI, Final Quantitative Risk Assessment and Significance of Risk; Document ID 1711, pp. 316-343). These studies demonstrated positive exposure-response relationships between exposure to crystalline silica and silicosis risk. Based on the results of these studies, OSHA estimates a cumulative risk for silicosis morbidity of between 60 and 773 cases per 1,000 workers for a 45-year exposure to the previous general industry PEL of 100 microg/m\3\ respirable crystalline silica depending upon the study used, and between 20 and 170 cases per 1,000 workers exposed at the new PEL of 50 microg/m\3\ depending upon the study used (see Section VI, Final Quantitative Risk Assessment and Significance of Risk, Table VI-1). Thus, like OSHA's risk estimates for other health endpoints, the risk is substantially lower, though still significant, at the revised PEL.

    In conclusion, OSHA finds, based on the best available evidence and methods to estimate quantitative risks of disease resulting from exposure to respirable crystalline silica, that there are significant risks of material health impairment at the former PELs for respirable crystalline silica, which would be substantially reduced (but not entirely eliminated) at the new PEL of 50 mug/m\3\. In meeting its legal burden to estimate the health risks posed by respirable crystalline silica, OSHA has used the best available evidence and methods to estimate quantitative risks of disease resulting from exposure to respirable crystalline silica. As a result, the Agency finds that the lifetime excess mortality risks (for lung cancer, NMRD and silicosis, and renal disease) and cumulative risk (silicosis morbidity) posed to workers exposed to respirable crystalline silica over a working life represent significant risks that warrant mitigation, and that these risks will be substantially reduced at the revised PEL of 50 mug/m\3\ respirable crystalline silica.

  3. Summary of the Review of Health Effects Literature and Preliminary QRA

    As noted above, a wide variety of stakeholders offered comments and testimony in this rulemaking on issues related to health and risk. Many of these comments were submitted in response to OSHA's preliminary risk and material impairment determinations, which were presented in two background documents, entitled ``Occupational Exposure to Respirable Crystalline Silica--Review of Health Effects Literature and Preliminary Quantitative Risk Assessment'' (Document ID 1711) and ``Supplemental Literature Review of Epidemiological Studies on Lung Cancer Associated with Exposure to Respirable Crystalline Silica'' (Document ID 1711, Attachment 1), and summarized in the proposal in Section V, Health Effects Summary, and Section VI, Summary of OSHA's Preliminary Quantitative Risk Assessment.

    In this subsection, OSHA summarizes the major findings of the two background documents. The Agency intends for this subsection to provide the detailed background necessary to fully understand stakeholders' comments and OSHA's responses.

    1. Background

    As noted above, OSHA's Review and Supplemental Review of Health Effects Literature and Preliminary Quantitative Risk Assessment (Document ID 1711; 1711, Attachment 1) were the result of the Agency's extensive search and review of the peer-reviewed scientific literature on the health effects of inhalation exposure to crystalline silica, particularly silicosis, lung cancer and cancer at other sites, non-

    malignant respiratory diseases (NMRD) other than silicosis, and renal and autoimmune effects. The purposes of this detailed search and scientific review were to determine the nature of the hazards presented by exposure to respirable crystalline silica, and to evaluate whether there was an adequate basis, with suitable data availability, for quantitative risk assessment.

    Much of the scientific evidence that describes the health effects and risks associated with exposure to crystalline silica consisted of epidemiological studies of worker populations; OSHA also reviewed animal and in vitro studies. OSHA used a weight-of-evidence approach in evaluating this evidence. Under this approach, OSHA evaluated the relevant studies to determine their overall quality. Factors considered in assessing the quality of studies included: (1) The size of the cohort studied and the power of the study to detect a sufficiently low level of disease risk; (2) the duration of follow-up of the study population; (3) the potential for study bias (e.g., selection bias in case-control studies or survivor effects in cross-sectional studies); and (4) the adequacy of underlying exposure information for examining exposure-response relationships. Studies were deemed suitable for inclusion in OSHA's Preliminary Quantitative Risk Assessment (QRA) where there was adequate quantitative information on exposure and disease risks and the study was judged to be sufficiently high quality according to these criteria.

    Based upon this weight-of-evidence approach, OSHA preliminarily determined that there is substantial evidence in the peer-reviewed scientific literature that exposure to respirable crystalline silica increases the risk of silicosis, lung cancer, other NMRD, and renal and autoimmune effects. The Preliminary QRA indicated that, for silicosis and NMRD mortality, lung cancer mortality, and renal disease mortality, there is a significant risk at the previous PELs for respirable crystalline silica, with excess lifetime risk estimates substantially greater than 1 death per 1,000 workers as a result of exposure over a working life (45 years, from age 20 to age 65). At the revised PEL of 50 mug/m\3\ respirable crystalline silica, OSHA estimated that these risks would be substantially reduced. Cumulative risk estimates for silicosis morbidity were also well above 1 case per 1,000 workers at the previous PELs, with a substantial reduction at the revised PEL.

    2. Summary of the Review of Health Effects Literature

    In its Review of Health Effects Literature, OSHA identified the adverse health effects associated with the inhalation of respirable crystalline silica (Document ID 1711). OSHA covered the following topics: Silicosis (including relevant data from U.S. disease surveillance efforts), lung cancer and cancer at other sites, non-

    malignant respiratory diseases (NMRD) other than silicosis, renal and autoimmune effects, and physical factors affecting the toxicity of crystalline silica. Most of the evidence that described the health risks associated with exposure to silica

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    consisted of epidemiological studies of worker populations; animal and in vitro studies on mode of action and molecular toxicology were also described. OSHA focused solely on those studies associated with airborne exposure to respirable crystalline silica due to the lack of evidence of health hazards from dermal or oral exposure. The review was further confined to issues related to the inhalation of respirable dust, which is generally defined as particles that are capable of reaching the pulmonary region of the lung (i.e., particles less than 10 microns (mum) in aerodynamic diameter), in the form of either quartz or cristobalite, the two forms of crystalline silica most often encountered in the workplace.

    a. Silicosis

    i. Types

    Silicosis is an irreversible, progressive disease induced by the inflammatory effects of respirable crystalline silica in the lung, leading to lung damage and scarring and, in some cases, progressing to complications resulting in disability and death. Exposure to respirable crystalline silica is the only known cause of silicosis. Three types of silicosis have been described: An acute form following intense exposure to respirable dust of high crystalline silica content for a relatively short period (i.e., a few months or years); an accelerated form, resulting from about 5 to 15 years of heavy exposure to respirable dusts of high crystalline silica content; and, most commonly, a chronic form that typically follows less intense exposure of more than 20 years (Becklake, 1994, Document ID 0294; Balaan and Banks, 1992, 0289). In both the accelerated and chronic forms of the disease, lung inflammation leads to the formation of excess connective tissue, or fibrosis, in the lung. The hallmark of the chronic form of silicosis is the silicotic islet or nodule, one of the few agent-specific lesions in pathology (Balaan and Banks, 1992, Document ID 0289). As the disease progresses, these nodules, or fibrotic lesions, increase in density and can develop into large fibrotic masses, resulting in progressive massive fibrosis (PMF). Once established, the fibrotic process of chronic silicosis is thought to be irreversible (Becklake, 1994, Document ID 0294). There is no specific treatment for silicosis (Davis, 1996, Document ID 0998; Banks, 2005, 0291).

    Chronic silicosis is the most frequently observed type of silicosis in the U.S. today. Affected workers may have a dry chronic cough, sputum production, shortness of breath, and reduced pulmonary function. These symptoms result from airway restriction and/or obstruction caused by the development of fibrotic scarring in the alveolar sacs and lower region of the lung. Prospective studies that follow the exposed cohort over a long period of time with periodic examinations can provide the best information on factors affecting the development and progression of silicosis, which has a latency period (the interval between beginning of exposure to silica and the onset of disease) from 10 to 30 years after first exposure (Weissman and Wagner, 2005; Document ID 0481).

    ii. Diagnosis

    The scarring caused by silicosis can be detected by chest x-ray or computerized tomography (CT) when the lesions become large enough to appear as visible opacities. The clinical diagnosis of silicosis has three requirements: Recognition by the physician that exposure to crystalline silica has occurred; the presence of chest radiographic abnormalities consistent with silicosis; the absence of other illnesses that could resemble silicosis on a chest radiograph (e.g., pulmonary fungal infection or tuberculosis) (Balaan and Banks, 1992, Document ID 0289; Banks, 2005, 0291). A standardized system to classify opacities seen in chest radiographs was developed by the International Labour Organization (ILO) to describe the presence and severity of silicosis on the basis of size, shape, and density of opacities, which together indicate the severity and extent of lung involvement (ILO, 1980, Document ID 1063; ILO, 2002, 1064; ILO, 2011, 1475; Merchant and Schwartz, 1998, 1096; NIOSH, 2011, 1513). The density of opacities seen on chest radiographs is classified on a 4-point category scale (0, 1, 2, or 3), with each category divided into three, giving a 12-

    subcategory scale between 0/0 and 3/+. For each subcategory, the top number indicates the major category that the profusion most closely resembles, and the bottom number indicates the major category that was given secondary consideration. Category 0 indicates the absence of visible opacities and categories 1 to 3 reflect increasing profusion of opacities and a concomitant increase in severity of disease. The bottom number can deviate from the top number by 1. At the extremes of the scale, a designation of 0/- or 3/+ may be used. Subcategory 0/- represents a radiograph that is obviously absent of small opacities. Subcategory 3/+ represents a radiograph that shows much greater profusion than depicted on a standard 3/3 radiograph.

    To address the low sensitivity of chest x-rays for detecting silicosis, Hnizdo et al. (1993, Document ID 1050) recommended that radiographs consistent with an ILO category of 0/1 or greater be considered indicative of silicosis among workers exposed to a high concentration of silica-containing dust. In like manner, to maintain high specificity, chest x-rays classified as category 1/0 or 1/1 should be considered as a positive diagnosis of silicosis. A biopsy is not necessary to make a diagnosis and a diagnosis does not require that chest x-ray films or digital radiographic images be rated using the ILO system (NIOSH, 2002, Document ID 1110).

    iii. Review of Occupation-Based Epidemiological Studies

    The causal relationship between exposure to crystalline silica and silicosis has long been accepted in the scientific and medical communities. OSHA reviewed a large number of cross-sectional and retrospective studies conducted to estimate the quantitative relationship between exposure to crystalline silica and the development of silicosis (e.g., Kreiss and Zhen, 1996, Document ID 1080; Love et al., 1999, 0369; Ng and Chan, 1994, 0382; Rosenman et al., 1996, 0423; Churchyard et al., 2003, 1295; Churchyard et al., 2004, 0986; Hughes et al., 1998, 1059; Muir et al., 1989a, 1102; Muir et al., 1989b, 1101; Park et al., 2002, 0405; Chen et al., 2001, 0332; Chen et al., 2005, 0985; Hnizdo and Sluis-Cremer, 1993, 1052; Miller et al., 1998, 0374; Buchanan et al., 2003, 0306; Steenland and Brown, 1995b, 0451). In general, these studies, particularly those that included retirees, found a risk of radiological silicosis (usually defined as x-ray films classified as ILO major category 1 or greater) among workers exposed near the range of cumulative exposures permitted by current exposure limits. The studies' methods and findings are presented in detail in the Preliminary QRA (Document ID 1711, pp. 316-340); those studies on which OSHA relied for its risk estimates are also discussed in the Summary of the Preliminary QRA, below.

    OSHA's review of the silicosis literature also focused on specific issues associated with the factors that affect the progression of the disease and the relationship between the appearance of radiological abnormalities indicative of silicosis and pulmonary function decline. From its review of the health literature, OSHA made a number of preliminary findings. First, the size of opacities apparent on initial x-ray films is a determinant of future disease

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    progression, with subjects exhibiting large opacities more likely to experience progression than those having smaller opacities (Hughes et al., 1982, Document ID 0362; Lee et al., 2001, 1086; Ogawa et al., 2003, 0398). Second, continued exposure to respirable crystalline silica following diagnosis of radiological silicosis increases the probability of disease progression compared to those who are not further exposed (Hessel et al., 1988, Document ID 1042), although there remains a likelihood of progression even absent continued exposure (Hessel et al., 1988, Document ID 1042; Miller et al., 1998, 0374; Ogawa et al., 2003, 0398; Yang et al., 2006, 1134).

    With respect to the relationship between radiological silicosis and pulmonary function declines, literature findings are mixed. A number of studies have reported pulmonary function declines among workers exhibiting a degree of small-opacity profusion consistent with ILO categories 2 and 3 (e.g., Ng and Chan, 1992, Document ID 1107). However, although some studies have not found pulmonary function declines associated with silicosis scored as ILO category 1, a number of other studies have documented declines in pulmonary function in persons exposed to silica and whose radiograph readings are in the major ILO category 1 (i.e., 1/0, 1/1, 1/2), or even before changes were seen on chest x-ray (Cowie, 1998, 0993; Cowie and Mabena, 1991, 0342; Ng et al., 1987(a), 1108; Wang et al., 1997, 0478). Thus, OSHA preliminarily concluded that at least some individuals will develop pulmonary function declines absent radiological changes indicative of silicosis. The Agency posited that this may reflect the relatively poor sensitivity of x-ray films in detecting silicosis or may be due to pulmonary function declines related to silica-induced chronic obstructive pulmonary disease (see Document ID 1711, pp. 49-75).

    iv. Surveillance

    Unlike most occupational diseases, surveillance statistics are available on silicosis mortality and morbidity in the U.S. The most comprehensive and current source of surveillance data in the U.S. related to occupational lung diseases, including silicosis, is the National Institute for Occupational Safety and Health (NIOSH) Work-

    Related Lung Disease (WoRLD) Surveillance System (NIOSH, 2008c, Document ID 1308). Other sources are detailed in the Review of Health Effects Literature (Document ID 1711). Mortality data are compiled from death certificates reported to state vital statistics offices, which are collected by the National Center for Health Statistics (NCHS), an agency within the Centers for Disease Control and Prevention (e.g., CDC, 2005, Document ID 0319).

    Silicosis-related mortality has declined in the U.S. over the time period for which these data have been collected. From 1968 to 2005, the annual number of silicosis deaths decreased from 1,157 to 161 (NIOSH, 2008c, Document ID 1308; http://wwwn.cdc.gov/eworld). The CDC cited two main factors that were likely responsible for the declining trend in silicosis mortality since 1968 (CDC, 2005, Document ID 0319). First, many deaths during the early part of the study period were among workers whose main exposure to respirable crystalline silica probably occurred before introduction of national silica standards established by OSHA and the Mine Safety and Health Administration (MSHA) (i.e., permissible exposure limits (PELs)); these standards likely led to reduced silica dust exposure beginning in the 1970s. Second, employment has declined in heavy industries (e.g., foundries) where silica exposure was prevalent (CDC, 2005, Document ID 0319).

    Despite this decline, silicosis deaths among workers of all ages result in significant premature mortality; between 1996 and 2005, a total of 1,746 deaths resulted in a total of 20,234 years of life lost from life expectancy, with an average of 11.6 years of life lost. For the same period, among 307 decedents who died before age 65 (the end of a working life), there were 3,045 years of life lost up to age 65, with an average of 9.9 years of life lost from a working life (NIOSH, 2008c, Document ID 1308).

    Surveillance data on silicosis morbidity, primarily from hospital discharge records, are available only from the few states that have administered disease surveillance programs for silicosis. For the reporting period 1993-2002, these states recorded 879 cases of silicosis (NIOSH 2008c, Document ID 1308). Nationwide hospital discharge data compiled by NIOSH (2008c, Document ID 1308) and the Council of State and Territorial Epidemiologists (CSTE, 2005, Document ID 0996) indicate that, for the years 1970 to 2004, there were at least 1,000 hospitalizations that were coded for silicosis each year, except one.

    Relying exclusively on such passive case-based disease surveillance systems that depend on the health care community to generate records is likely to understate the prevalence of diseases associated with respirable crystalline silica (Froines et al., 1989, Document ID 0385). In order to diagnose occupational diseases, health care professionals must have information about occupational histories and must be able to recognize occupational diseases (Goldman and Peters, 1981, Document ID 1027; Rutstein et al., 1983, 0425). The first criterion to be met in diagnosing silicosis is knowing a patient's history of exposure to crystalline silica. In addition to the lack of information about exposure histories, difficulty in recognizing occupational illnesses like silicosis, that manifest themselves long after initial exposure, contributes to under-recognition and underreporting by health care providers. Based on an analysis of data from Michigan's silicosis surveillance activities, Rosenman et al. (2003, Document ID 0420) estimated that silicosis mortality and morbidity were understated by a factor of between 2.5 and 5, and estimated that between 3,600 and 7,300 new cases of silicosis likely occurred in the U.S. annually between 1987 and 1996.

    b. Lung Cancer

    i. International Agency for Research on Cancer (IARC) Classification

    In 1997, the IARC determined that there was sufficient evidence to regard crystalline silica as a human carcinogen (IARC, 1997, Document ID 1062). This finding was based largely on nine studies of cohorts in four industry sectors that IARC considered to be the least influenced by confounding factors (sectors included quarries and granite works, gold mining, ceramic/pottery/refractory brick industries, and the diatomaceous earth industry). NIOSH also determined that crystalline silica is a human carcinogen after evaluating updated literature (2002, Document ID 1110).

    ii. Review of Occupation-Based Epidemiological Studies

    OSHA conducted an independent review of the epidemiological literature on exposure to respirable crystalline silica and lung cancer, covering more than 30 occupational groups in over a dozen industrial sectors. OSHA's review included approximately 60 primary epidemiological studies. Based on this review, OSHA preliminarily concluded that the human data provides ample evidence that exposure to respirable crystalline silica increases the risk of lung cancer among workers.

    The strongest evidence for carcinogenicity came from studies in five industry sectors:

    Diatomaceous Earth Workers (Checkoway et al., 1993, Document ID 0324; Checkoway et al., 1996, 0325; Checkoway et al., 1997, 0326;

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    Checkoway et al., 1999, 0327; Seixas et al., 1997, 0431);

    British Pottery Workers (Cherry et al., 1998, Document ID 0335; McDonald et al., 1995, 0371);

    Vermont Granite Workers (Attfield and Costello, 2004, Document ID 0285; Graham et al., 2004, 1031; Costello and Graham, 1988, 0991; Davis et al., 1983, 0999);

    North American Industrial Sand Workers (Hughes et al., 2001, Document ID 1060; McDonald et al., 2001, 1091; McDonald et al., 2005, 1092; Rando et al., 2001, 0415; Sanderson et al., 2000, 0429; Steenland and Sanderson, 2001, 0455); and

    British Coal Miners (Miller et al., 2007, Document ID 1305; Miller and MacCalman, 2009, 1306).

    OSHA considered these studies as providing the strongest evidence for several reasons. They were all retrospective cohort or case-control studies that demonstrated positive, statistically significant exposure-

    response relationships between exposure to crystalline silica and lung cancer mortality. Except for the British pottery studies, where exposure-response trends were noted for average exposure only, lung cancer risk was found to be related to cumulative exposure. In general, these studies were of sufficient size and had adequate years of follow up, and had sufficient quantitative exposure data to reliably estimate exposures of cohort members. As part of their analyses, the authors of these studies also found positive exposure-response relationships for silicosis, indicating that underlying estimates of worker exposures were not likely to be substantially misclassified. Furthermore, the authors of these studies addressed potential confounding due to other carcinogenic exposures through study design or data analysis.

    In the diatomaceous earth industry, Checkoway et al. developed a ``semi-quantitative'' cumulative exposure estimate that demonstrated a statistically significant positive exposure-response trend between duration of employment or cumulative exposure and lung cancer mortality (1993, Document ID 0324). The quartile analysis with a 15-year lag showed an increasing trend in relative risks (RR) of lung cancer mortality, with the highest exposure quartile having a RR of 2.74 for lung cancer mortality. Checkoway et al. conducted a re-analysis to address criticisms of potential confounding due to asbestos and again demonstrated a positive exposure-response risk gradient when controlling for asbestos exposure and other variables (1996, Document ID 0325). Rice et al. (2001, Document ID 1118) conducted a re-analysis and quantitative risk assessment of the Checkoway et al. (1997, Document ID 0326) study, finding that exposure to crystalline silica was a significant predictor of lung cancer mortality. OSHA included this re-analysis in its Preliminary QRA (Document ID 1711).

    In the British pottery industry, excess lung cancer risk was found to be associated with crystalline silica exposure among workers in a proportionate mortality ratio (PMR) study \4\ (McDonald et al., 1995, Document ID 0371) and in a cohort and nested case-control study \5\ (Cherry et al., 1998, Document ID 0335). In the former, elevated PMRs for lung cancer were found after adjusting for potential confounding by asbestos exposure. In the study by Cherry et al., odds ratios for lung cancer mortality were statistically significantly elevated after adjusting for smoking. Odds ratios were related to average, but not cumulative, exposure to crystalline silica.

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    \4\ A PMR is the number of deaths within a population due to a specific disease (e.g., lung cancer) divided by the total number of deaths in the population during some time period.

    \5\ A cohort study is a study in which the occurrence of disease (e.g., lung cancer) is measured in a cohort of workers with potential for a common exposure (e.g., silica). A nested case-

    control study is a study in which workers with disease are identified in an occupational cohort, and a control group consisting of workers without disease is selected (independently of exposure status) from the same cohort to determine whether there is a difference in exposure between cases and controls. A number of controls are matched to each case to control for potentially confounding factors, such as age, gender, etc.

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    In the Vermont granite cohort, Costello and Graham (1988, Document ID 0991) and Graham et al. (2004, Document ID 1031) in a follow-up study found that workers employed prior to 1930 had an excess risk of lung cancer. Lung cancer mortality among granite workers hired after 1940 (post-implementation of controls), however, was not elevated in the Costello and Graham study and was only somewhat elevated (not statistically significant) in the Graham et al. study. Graham et al. (2004, Document ID 1031) concluded that their results did not support a causal relationship between granite dust exposure and lung cancer mortality.

    Looking at the same population, Attfield and Costello (2004, Document ID 0285) developed a quantitative estimate of cumulative exposure (8 exposure categories) adapted from a job exposure matrix developed by Davis et al. (1983, Document ID 0999). They found a statistically significant trend between lung cancer mortality and log-

    transformed cumulative exposure to crystalline silica. Lung cancer mortality rose reasonably consistently through the first seven increasing exposure groups, but fell in the highest cumulative exposure group. With the highest exposure group omitted, a strong positive dose-

    response trend was found for both untransformed and log-transformed cumulative exposures. The authors explained that the highest exposure group would have included the most unreliable exposure estimates being reconstructed from exposures 20 years prior to study initiation when exposure estimation was less precise. OSHA expressed its belief that the study by Attfield and Costello (2004, Document ID 0285) was of superior design in that it used quantitative estimates of exposure and evaluated lung cancer mortality rates by exposure group. In contrast, the findings by Graham et al. (2004, Document ID 1031) were based on a dichotomous comparison of risk among high- versus low-exposure groups, where date-of-hire before and after implementation of ventilation controls was used as a surrogate for exposure. Consequently, OSHA used the Attfield and Costello study in its Preliminary QRA (Document ID 1711). In its Supplemental Literature Review of Epidemiological Studies on Lung Cancer Associated with Exposure to Respirable Crystalline Silica, OSHA also discussed a more recent study of Vermont granite workers by Vacek et al. (2011, Document ID 1486) that did not find an association between silica exposure and lung cancer mortality (Document ID 1711, Attachment 1, pp. 2-5). (OSHA examines this study in great length in Section V.F, Comments and Responses Concerning Lung Cancer Mortality.)

    In the North American industrial sand industry, studies of two overlapping cohorts found a statistically significant increased risk of lung cancer mortality with increased cumulative exposure in both categorical and continuous analyses (Hughes et al., 2001, Document ID 1060; McDonald et al., 2001, 1091; McDonald et al., 2005, 1092; Rando et al., 2001, 0415; Sanderson et al., 2000, 0429; Steenland and Sanderson, 2001, 0455). McDonald et al. (2001, Document ID 1091) examined a cohort that entered the workforce, on average, a decade earlier than the cohorts that Steenland and Sanderson (2001, Document ID 0455) examined. The McDonald cohort, drawn from eight plants, had more years of exposure in the industry (19 versus 8.8 years). The Steenland and Sanderson (2001, Document ID 0455) cohort worked in 16 plants, 7 of which overlapped with the McDonald, et al.

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    (2001, Document ID 1091) cohort. McDonald et al. (2001, Document ID 1091), Hughes et al. (2001, Document ID 1060), and Rando et al. (2001, Document ID 0415) had access to smoking histories, plant records, and exposure measurements that allowed for historical reconstruction and the development of a job exposure matrix. The McDonald et al. (2005, Document ID 1092) study was a later update, with follow-up through 2000, of both the cohort and nested case-control studies. Steenland and Sanderson (2001, Document ID 0455) had limited access to plant facilities, less detailed historic exposure data, and used MSHA enforcement records for estimates of recent exposure. These studies (Hughes et al., 2001, Document ID 1060; McDonald et al., 2005, 1092; Steenland and Sanderson, 2001, 0455) showed very similar exposure-

    response patterns of increased lung cancer mortality with increased exposure. OSHA included the quantitative exposure-response analysis from the Hughes et al. (2001, Document ID 1060) study in its Preliminary QRA, as it allowed for individual job, exposure, and smoking histories to be taken into account.

    OSHA noted that Brown and Rushton (2005a, Document ID 0303; 2005b, 0304) found no association between risk of lung cancer mortality and exposure to respirable crystalline silica among British industrial sand workers. However, a large portion of the cohort had relatively short service times in the industry, with over one-half the cohort deaths and almost three-fourths of the lung cancer mortalities having had less than 10 years of service. Considering the apparent high turnover in this industry and the absence of prior occupational histories, exposures from work experience other than in the industrial sand industry could be a significant confounder (Document ID 1711, p. 131). Additionally, as Steenland noted in a letter review (2005a, Document ID 1313), the cumulative exposures of workers in the Brown and Ruston (2005b, Document ID 0304) study were over 10 times lower than the cumulative exposures experienced by the cohorts in the pooled analysis that Steenland et al. (2001a, Document ID 0452) performed. The low exposures experienced by this cohort would have made detecting a positive association with lung cancer mortality even more difficult.

    In British coal miners, excess lung cancer mortality was reported in a large cohort study, which examined the mortality experience of 17,800 miners through the end of 2005 (Miller et al., 2007, Document ID 1305; Miller and MacCalman, 2009, 1306). By that time, the cohort had accumulated 516,431 person years of observation (an average of 29 years per miner), with 10,698 deaths from all causes. Overall lung cancer mortality was elevated (SMR = 115.7, 95% C.I. 104.8-127.7), and a positive exposure-response relationship with crystalline silica exposure was determined from Cox regression after adjusting for smoking history. Three of the strengths of this study were the detailed time-

    exposure measurements of both quartz and total mine dust, detailed individual work histories, and individual smoking histories. For lung cancer, analyses based on Cox regression provided strong evidence that, for these coal miners, although quartz exposures were associated with increased lung cancer risk, simultaneous exposures to coal dust did not cause increased lung cancer risk. Because of these strengths, OSHA included this study in its Preliminary QRA (Document ID 1711).

    In addition to the studies in these cohorts, OSHA also reviewed studies of lung cancer mortality in metal ore mining populations. Many of these mining studies, which showed mixed results, were subject to confounding due to exposure to other potential carcinogens such as radon and arsenic. IARC noted that only a few ore mining studies accounted for confounding from other occupational carcinogens and that, when confounding was absent or accounted for, an association between silica exposure and lung cancer was absent (1997, Document ID 1062). Many of the studies conducted since IARC's review, however, more strongly implicate crystalline silica as a human carcinogen (1997, Document ID 1062). Pelucchi et al. (2006, Document ID 0408), in a meta-

    analysis of studies conducted since IARC's (1997, Document ID 1062) review, reported statistically significantly elevated relative risks of lung cancer mortality in underground and surface miners in three cohort and four case-control studies. Cassidy et al., in a pooled case-control analysis, showed a statistically significant increased risk of lung cancer mortality among miners (OR = 1.48), and demonstrated a linear trend of increasing odds ratios with increasing exposures (2007, Document ID 0313).

    OSHA also preliminarily determined that the results of the studies conducted in three industry sectors (foundry, silicon carbide, and construction sectors) were confounded by the presence of exposures to other carcinogens. Exposure data from these studies were not sufficient to distinguish between exposure to silica dust and exposure to other occupational carcinogens. IARC previously made a similar determination in reference to the foundry industry. However, with respect to the construction industry, Cassidy et al. (2007, Document ID 0313), in a large European community-based case-control study, reported finding a clear linear trend of increasing odds ratios with increasing cumulative exposure to crystalline silica (estimated semi-quantitatively) after adjusting for smoking and exposure to insulation and wood dusts.

    In addition, an analysis of 4.8 million death certificates from 27 states within the U.S. for the years 1982 to 1995 showed statistically significant excesses in lung cancer mortality, silicosis mortality, tuberculosis, and NMRD among persons with occupations involving medium and high exposure to respirable crystalline silica (Calvert et al., 2003, Document ID 0309). A national records and death certificate study was also conducted in Finland by Pukkala et al., who found a statistically significant excess of lung cancer incidence among men and women with estimated medium and heavy exposures (2005, Document ID 0412).

    One of the more compelling studies OSHA evaluated and used in the Preliminary QRA (Document ID 1711) was Steenland et al.'s (2001a, Document ID 0452) pooled analysis of 10 occupational cohorts (5 mines and 5 industrial facilities), which demonstrated an overall positive exposure-response relationship between cumulative exposure to crystalline silica and lung cancer mortality. These 10 cohorts included 65,980 workers and 1,072 lung cancer deaths, and were selected because of the availability of raw data on exposure to crystalline silica and health outcomes. The investigators found lung cancer risk increased with increasing cumulative exposure, log cumulative exposure, and average exposure. Exposure-response trends were similar between mining and non-mining cohorts.

    iii. Confounding

    Smoking is known to be a major risk factor for lung cancer. However, OSHA maintained in the Preliminary QRA that it is unlikely that smoking explained the observed exposure-response trends in the studies described above (Document ID 1711). Studies by Hnizdo et al. (1997, Document ID 1049), McLaughlin et al. (1992, Document ID 0372), Hughes et al. (2001, Document ID 1060), McDonald et al. (2001, Document ID 1091; 2005, 1092), Miller and MacCalman (2009, Document ID 1306), and Cassidy et al. (2007, Document ID 0313) had detailed smoking histories with sufficiently large

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    populations and a sufficient number of years of follow-up time to quantify the interaction between crystalline silica exposure and cigarette smoking. In a cohort of white South African gold miners (Hnizdo and Sluis-Cremer, 1991, Document ID 1051) and in the follow-up nested case-control study (Hnizdo et al., 1997, Document ID 1049), the combined effect of exposure to respirable crystalline silica and smoking was greater than additive, suggesting a multiplicative effect. This effect appeared to be greatest for miners with greater than 35 pack-years of smoking and higher cumulative exposure to silica. In the Chinese nested case-control studies (McLaughlin et al., 1992, Document ID 0372), cigarette smoking was associated with lung cancer, but control for smoking did not influence the association between silica and lung cancer in the mining and pottery cohorts studied. The studies of industrial sand workers (Hughes et al., 2001, Document ID 1060) and British coal workers (Miller and MacCalman, 2009, Document ID 1306) found positive exposure-response trends after adjusting for smoking histories, as did Cassidy et al. (2007, Document ID 0313) in their community-based case-control study of exposed European workers.

    Given these findings of investigators who have accounted for the impact of smoking, OSHA preliminarily determined that the weight of the evidence reviewed identified respirable crystalline silica as an independent risk factor for lung cancer mortality. OSHA also determined that its finding was further supported by animal studies demonstrating that exposure to silica alone can cause lung cancer (e.g., Muhle et al., 1995, Document ID 0378).

    iv. Lung Cancer and Silicosis

    Animal and in vitro studies have demonstrated that the early steps in the proposed mechanistic pathways that lead to silicosis and lung cancer seem to share some common features (see Document ID 1711, pp. 171-172). This has led some researchers to suggest that silicosis is a prerequisite to lung cancer. Some have suggested that any increased lung cancer risk associated with silica may be a consequence of inflammation (and concomitant oxidative stress) and increased epithelial cell proliferation associated with the development of silicosis. However, other researchers have noted additional genotoxic and non-genotoxic mechanisms that may also be involved in carcinogenesis induced by silica (see Section V.H, Mechanisms of Silica-Induced Adverse Health Effects, and Document ID 1711, pp. 230-

    239). IARC also noted that a direct genotoxic mechanism from silica to induce a carcinogenic effect cannot be ruled out (2012, Document ID 1473). Thus, OSHA preliminarily concluded that available animal and in vitro studies do not support the hypothesis that development of silicosis is necessary for silica exposure to cause lung cancer.

    In general, studies of workers with silicosis, as well as meta-

    analyses that include these studies, have shown that workers with radiologic evidence of silicosis have higher lung cancer risk than those without radiologic abnormalities or mixed cohorts. Three meta-

    analyses attempted to look at the association of increasing ILO radiographic categories of silicosis with increasing lung cancer mortality. Two of these analyses (Kurihara and Wada, 2004, Document ID 1084; Tsuda et al., 1997, 1127) showed no association with increasing lung cancer mortality, while Lacasse et al. (2005, Document ID 0365) demonstrated a positive dose-response for lung cancer with increasing ILO radiographic category. A number of other studies found increased lung cancer risk among exposed workers absent radiological evidence of silicosis (Cassidy et al., 2007, Document ID 0313; Checkoway et al., 1999, 0327; Cherry et al., 1998, 0335; Hnizdo et al., 1997, 1049; McLaughlin et al., 1992, 0372). For example, the diatomaceous earth study by Checkoway et al. showed a statistically significant exposure-

    response relationship for lung cancer among persons without silicosis (1999, Document ID 0327). Checkoway and Franzblau, reviewing the international literature, found that all epidemiological studies conducted to that date were insufficient to conclusively determine the role of silicosis in the etiology of lung cancer (2000, Document ID 0323). OSHA preliminarily concluded that the more recent pooled and meta-analyses do not provide compelling evidence that silicosis is a necessary precursor to lung cancer.

    c. Non-Malignant Respiratory Diseases (Other Than Silicosis)

    In addition to causing silicosis, exposure to crystalline silica has been associated with increased risks of other non-malignant respiratory diseases (NMRD), primarily chronic obstructive pulmonary disease (COPD), chronic bronchitis, and emphysema. COPD is a disease state characterized by airflow limitation that is usually progressive and not fully reversible. In patients with COPD, either chronic bronchitis or emphysema may be present or both conditions may be present together.

    As detailed in the Review of Health Effects Literature, OSHA reviewed several studies of NMRD morbidity and preliminarily concluded that exposure to respirable crystalline silica may increase the risk of emphysema, chronic bronchitis, and pulmonary function impairment, regardless of whether signs of silicosis are present (Document ID 1711). Smokers may be at an increased risk relative to nonsmokers.

    OSHA also reviewed studies of NMRD mortality that focused on causes of death other than silicosis. Wyndham et al. found a significant excess mortality for chronic respiratory diseases in a cohort of white South African gold miners (1986, Document ID 0490). A case-referent analysis found that, although the major risk factor for chronic respiratory disease was smoking, there was a statistically significant additional effect of cumulative exposure to silica-containing dust. A multiplicative effect of smoking and cumulative dust exposure on mortality from COPD was found in another study of white South African gold miners (Hnizdo, 1990, Document ID 1045). Analysis of various combinations of dust exposure and smoking found a trend in odds ratios that indicated this synergism. There was a statistically significant increasing trend for dust particle-years and for cigarette-years of smoking.

    Park et al. (2002, Document ID 0405) analyzed the California diatomaceous earth cohort data originally studied by Checkoway et al. (1997, Document ID 0326), consisting of 2,570 diatomaceous earth workers employed for 12 months or more from 1942 to 1994, to quantify the relationship between exposure to cristobalite and mortality from chronic lung disease other than cancer (LDOC). Diseases in this category included pneumoconiosis (which included silicosis), chronic bronchitis, and emphysema, but excluded pneumonia and other infectious diseases. Smoking information was available for about 50 percent of the cohort and for 22 of the 67 LDOC deaths available for analysis, permitting at least partial adjustment for smoking. Using the exposure estimates developed for the cohort by Rice et al. (2001, Document ID 1118) in their exposure-response study of lung cancer risks, Park et al. (2002, Document 0405) evaluated the quantitative exposure-response relationship for LDOC mortality and found a strong positive relationship with exposure to respirable crystalline silica. OSHA found this study particularly compelling because of the strengths of the study design and availability of smoking history data on part of the cohort, as well as the high-

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    quality exposure and job history data. The study authors noted:

    Data on smoking, collected since the 1960s in the company's radiographic screening programme, were available for 1171 of the subjects (50%). However, smoking habits were unknown for 45 of the 67 workers that died from LDOC (67%). Our Poisson regression analyses for LDOC, stratified on smoking, have partially rectified the confounding by smoking issue. Furthermore, analyses performed without control for smoking produced slightly smaller and less precise estimates of the effects of silica, suggesting that smoking is a negative confounder. In their analysis of this cohort, Checkoway et al. applied the method of Axelson concluding that it was very unlikely that cigarette smoking could account for the association found between mortality from LDOC and cumulative exposure to silica (Document ID 0405, p. 41).

    Consequently, OSHA used this study in its Preliminary QRA (Document ID 1711, pp. 295-298).

    Based on this evidence, and the other studies discussed in the Review of Health Effects Literature, OSHA preliminarily concluded that respirable crystalline silica increases the risk for mortality from non-malignant respiratory disease (not including silicosis) in an exposure-related manner. The Agency also preliminarily concluded that the risk is strongly influenced by smoking, and opined that the effects of smoking and silica exposure may be synergistic.

    d. Renal Disease and Autoimmune Diseases

    In its Review of Health Effects Literature, OSHA described the available experimental and epidemiological data evaluating respirable crystalline silica exposure and renal and/or autoimmune effects (Document ID 1711). In addition to a number of case reports, epidemiological studies have found statistically significant associations between occupational exposure to silica dust and chronic renal disease (Calvert et al., 1997, Document ID 0976), subclinical renal changes (Ng et al., 1992c, Document ID 0386), end-stage renal disease morbidity (Steenland et al., 1990, Document ID 1125), chronic renal disease mortality (Steenland et al., 2001b, Document ID 0456; 2002a, 0448), and granulomatosis with polyangitis, a condition that can affect the kidneys (Nuyts et al., 1995, Document ID 0397). In other findings, silica-exposed individuals, both with and without silicosis, had an increased prevalence of abnormal renal function (Hotz et al., 1995, Document ID 0361), and renal effects have been reported to persist after cessation of silica exposure (Ng et al., 1992c, Document ID 0386). Possible mechanisms suggested for silica-induced renal disease include a direct toxic effect on the kidney, deposition of immune complexes (IgA) in the kidney following silica related pulmonary inflammation, and an autoimmune mechanism (Calvert et al., 1997, Document ID 0976; Gregorini et al., 1993, 1032).

    In a pooled cohort analysis, Steenland et al. (2002a, Document ID 0448) combined the industrial sand cohort from Steenland et al. (2001b, Document ID 0456), the gold mining cohort from Steenland and Brown (1995a, Document ID 0450), and the Vermont granite cohort studies by Costello and Graham (1988, Document ID 0991). In all, the combined cohort consisted of 13,382 workers with exposure information available for 12,783. The analysis demonstrated statistically significant exposure-response trends for acute and chronic renal disease mortality with quartiles of cumulative exposure to respirable crystalline silica. In a nested case-control study design, a positive exposure-response relationship was found across the three cohorts for both multiple-cause mortality (i.e., any mention of renal disease on the death certificate) and underlying cause mortality. Renal disease risk was most prevalent among workers with cumulative exposures of 500 microg/m\3\ or more (Steenland et al., 2002a, Document ID 0448).

    OSHA noted that other studies failed to find an excess renal disease risk among silica-exposed workers. Davis et al. (1983, Document ID 0999) found elevated, but not statistically significant, mortality from diseases of the genitourinary system among Vermont granite shed workers. There was no observed relationship between mortality from this cause and cumulative exposure. A similar finding was reported by Koskela et al. (1987, Document ID 0363) among Finnish granite workers, where there were 4 deaths due to urinary tract disease compared to 1.8 expected. Both Carta et al. (1994, Document ID 0312) and Cocco et al. (1994, Document ID 0988) reported finding no increased mortality from urinary tract disease among workers in an Italian lead mine and zinc mine. However, Cocco et al. (1994, Document ID 0988) commented that exposures to respirable crystalline silica were low, averaging 7 and 90 microg/m\3\ in the two mines, respectively, and that their study in particular had low statistical power to detect excess mortality.

    OSHA expressed its belief that there is substantial evidence, particularly the 3-cohort pooled analysis conducted by Steenland et al. (2002a, Document ID 0448), on which to base a finding that exposure to respirable crystalline silica increases the risk of renal disease mortality and morbidity. The pooled analysis by Steenland et al. involved a large number of workers from three cohorts with well-

    documented, validated job-exposure matrices; it found a positive, monotonic increase in renal disease risk with increasing exposure for both underlying and multiple cause data (2002a, Document ID 0448). However, there are considerably less data available for renal disease than there are for silicosis mortality and lung cancer mortality. The findings based on these data are, therefore, less robust. Nevertheless, OSHA preliminarily concluded that the underlying data are sufficient to provide useful estimates of risk and included the Steenland et al. (2002a, Document ID 0448) analysis in its Preliminary QRA.

    For autoimmune effects, OSHA reviewed epidemiological information suggesting an association between respirable silica exposure and autoimmune diseases, including scleroderma (Sluis-Cremer et al., 1985, Document ID 0439), rheumatoid arthritis (Klockars et al., 1987, Document ID 1075; Rosenman and Zhu, 1995, 0424), and systemic lupus erythematosus (Brown et al., 1997, Document ID 0974). However, there were no quantitative exposure-response data available on which to base a quantitative risk assessment for autoimmune diseases.

    e. Physical Factors Affecting Toxicity of Crystalline Silica

    OSHA also examined evidence on the comparative toxicity of the silica polymorphs (quartz, cristobalite, and tridymite). A number of animal studies appear to suggest that cristobalite and tridymite are more toxic to the lung than quartz and more tumorigenic (e.g., King et al., 1953, Document ID 1072; Wagner et al., 1980, 0476). However, in contrast to these findings, several authors have reviewed the studies done in this area and concluded that cristobalite and tridymite are not more toxic than quartz (e.g., Bolsaitis and Wallace, 1996, Document ID 0298; Guthrie and Heaney, 1995, 1035). Furthermore, a difference in toxicity between cristobalite and quartz has not been observed in epidemiological studies (tridymite has not been studied) (NIOSH, 2002, Document ID 1110). In an analysis of exposure-response for lung cancer, Steenland et al. found similar exposure-response trends between cristobalite-exposed workers and other cohorts

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    exposed to quartz (2001a, Document ID 0452).

    OSHA also discussed other physical factors that may influence the toxicologic potency of crystalline silica. A number of animal studies compared the toxicity of freshly fractured silica to that of aged silica (Porter et al., 2002, Document ID 1114; Shoemaker et al., 1995, 0437; Vallyathan et al., 1995, 1128). These studies have demonstrated that although freshly fractured silica is more toxic than aged silica, aged silica still retains significant toxicity. There have been no studies comparing workers exposed to freshly fractured silica to those exposed to aged silica. However, similarities between the results of animal and human studies involving freshly fractured silica suggest that the animal studies involving aged silica may also apply to humans. For example, studies of workers exposed to freshly fractured silica have demonstrated that these workers exhibit the same cellular effects as seen in animals exposed to freshly fractured silica (Castranova et al., 1998, Document ID 1294; Goodman et al., 1992, 1029). Animal studies also suggest that pulmonary reactions of rats to short-duration exposure to freshly fractured silica mimic those seen in acute silicosis in humans (Vallyathan et al., 1995, Document ID 1128).

    Surface impurities, particularly metals, have been shown to alter silica toxicity. Iron, depending on its state and quantity, has been shown to either increase or decrease toxicity (see Document ID 1711, pp. 247-258). Aluminum has been shown to decrease toxicity (Castranova et al., 1997, Document ID 0978; Donaldson and Borm, 1998, 1004; Fubini, 1998, 1016). Silica coated with aluminosilicate clay exhibits lower toxicity, possibly as a result of reduced bioavailability of the silica particle surface (Donaldson and Borm, 1998, Document ID 1004; Fubini, 1998, 1016). Aluminum as well as other metal ions are thought to modify silanol groups on the silica surface, thus decreasing the membranolytic and cytotoxic potency and resulting in enhanced particle clearance from the lung before damage can take place (Fubini, 1998, Document ID 1016). An epidemiological study found that the risk of silicosis was less in pottery workers than in tin and tungsten miners (Chen et al., 2005, Document ID 0985; Harrison et al., 2005, 1036), possibly reflecting that pottery workers were exposed to silica particles having less biologically-available, non-clay-occluded surface area than was the case for miners.

    Although it is evident that a number of factors can act to mediate the toxicological potency of crystalline silica, it is not clear how such considerations should be taken into account to evaluate lung cancer and silicosis risks to exposed workers. After evaluating many in vitro studies that investigated the surface characteristics of crystalline silica particles and their influence on fibrogenic activity, NIOSH concluded that further research is needed to associate specific surface characteristics that can affect toxicity with specific occupational exposure situations and consequent health risks to workers (2002, Document ID 1110). Thus, OSHA preliminarily concluded that while there was considerable evidence that several environmental influences can modify surface activity to either enhance or diminish the toxicity of silica, the available information was insufficient to determine in any quantitative way how these influences may affect disease risk to workers in any particular workplace setting.

    3. Summary of the Preliminary QRA

    OSHA presented in the Preliminary QRA estimates of the risk of silica-related diseases assuming exposure over a working life (45 years, from age 20 to age 65) to the revised 8-hour time-weighted average (TW

  4. PEL of 50 microg/m\3\ respirable crystalline silica, the new action level of 25 microg/m\3\, and the previous PELs. OSHA's previous general industry PEL for respirable quartz was expressed both in terms of a particle count formula and a gravimetric concentration formula; the previous construction and shipyard employment PELs for respirable quartz were only expressed in terms of a particle count formula. For general industry, as the quartz content increases, the gravimetric PEL approached a limit of 100 microg/m\3\ respirable quartz. For construction and shipyard employment, OSHA's previous PELs used a formula that limits exposure to respirable dust, depending upon the quartz content, expressed as a respirable particle count concentration. There was no single mass concentration equivalent for the construction and shipyard employment PELs; OSHA reviewed several studies that suggest that the previous construction/shipyard PEL likely was between 250 and 500 microg/m\3\ respirable quartz. In general industry, for both the gravimetric and particle count PELs, OSHA's previous PELs for cristobalite and tridymite were half the value for quartz. Based upon these previous PELs and the new action level, OSHA presented risk estimates associated with exposure over a working life to 25, 50, 100, 250, and 500 microg/m\3\ respirable silica (corresponding to cumulative exposures over 45 years to 1.125, 2.25, 4.5, 11.25, and 22.5 mg/m\3\-yrs).

    To estimate lifetime excess mortality risks at these exposure levels, OSHA implemented each of the risk models in a life table analysis that accounted for competing causes of death due to background causes and cumulated risk through age 85. For these analyses, OSHA used lung cancer, NMRD, or renal disease mortality and all-cause mortality rates to account for background risks and competing risks (U.S. 2006 data for lung cancer and NMRD mortality in all males, 1998 data for renal disease mortality, obtained from cause-specific death rate tables published by the National Center for Health Statistics (2009, Document ID 1104)). OSHA calculated these risk estimates assuming occupational exposure from age 20 to age 65. The mortality risk estimates were presented in terms of lifetime excess risk per 1,000 workers for exposure over an 8-hour working day, 250 days per year, and a 45-year working life.

    For silicosis morbidity, OSHA based its risk estimates on cumulative risk models used by various investigators to develop quantitative exposure-response relationships. These models characterized the risk of developing silicosis (as detected by chest radiography) up to the time that cohort members (including both active and retired workers) were last examined. Thus, risk estimates derived from these studies represented less-than-lifetime risks of developing radiographic silicosis. OSHA did not attempt to estimate lifetime risk (i.e., up to age 85) for silicosis morbidity because the relationships between age, time, and disease onset post-exposure have not been well characterized.

    a. Silicosis and NMRD Mortality

    i. Exposure-Response Studies

    In the Preliminary QRA, OSHA relied upon two published quantitative risk studies of silicosis and NMRD mortality (Document ID 1711). The first, Mannetje et al. (2002b, Document ID 1089) conducted a pooled analysis of silicosis mortality in which there were 18,634 subjects, 150 silicosis deaths, and 20 deaths from unspecified pneumoconiosis. Rates for silicosis adjusted for age, calendar time, and study were estimated by Poisson regression and increased nearly monotonically with deciles of cumulative exposure, from a mortality rate of 5/100,000 person-years in the lowest exposure category (0-0.99

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    mg/m\3\-yrs) to 299/100,000 person-years in the highest category (>28.10 mg/m\3\-yrs).

    As previously discussed, the second, Park et al. (2002, Document ID 0405) analyzed the California diatomaceous earth cohort data from Checkoway et al. (1997, Document ID 0326), and examined mortality from chronic lung disease other than cancer (LDOC; also known as non-

    malignant respiratory disease (NMRD)). Smoking information was available for about 50 percent of the cohort and for 22 of the 67 LDOC deaths available for analysis, permitting Park et al. (2002, Document ID 0405) to partially adjust for smoking. Estimates of LDOC mortality risks were derived via Poisson and Cox proportional hazards models; a variety of relative rate model forms were fit to the data, with a linear relative rate model selected for estimating risks.

    ii. Risk Estimates

    As silicosis is only caused by exposure to respirable crystalline silica (i.e., there is no background rate of silicosis in the unexposed population), absolute risks of silicosis mortality rather than excess risks were calculated for the Mannetje et al. pooled analysis (2002b, Document ID 1089). These risk estimates were derived from the rate ratios incorporating simulated measurement error reported by ToxaChemica (Document ID 0469). OSHA's estimate of lifetime risk of silicosis mortality, for 45 years of exposure to the previous general industry PEL, was 11 deaths per 1,000 workers for the pooled analysis (Document ID 1711). At the revised PEL, the risk estimate was 7 deaths per 1,000.

    OSHA also calculated preliminary risk estimates for NMRD mortality. These estimates were derived from Park et al. (2002, Document ID 0405). For 45 years of exposure to the previous general industry PEL, OSHA preliminarily estimated lifetime excess risk at 83 deaths per 1,000 workers. At the revised PEL, OSHA estimated 43 deaths per 1,000 workers.

    OSHA noted that, for exposures up to 250 microg/m\3\, the mortality risk estimates based on Park et al. (2002, Document ID 0405) are about 5 to 11 times as great as those calculated for the pooled analysis of silicosis mortality (Mannetje et al., 2002b, Document ID 1089). These two sets of risk estimates, however, are not directly comparable, as the endpoint for the Park et al. (2002, Document ID 0405) analysis was death from all non-cancer lung diseases, including pneumoconiosis, emphysema, and chronic bronchitis, whereas the pooled analysis by Mannetje et al. (2002b, Document ID 1089) included only deaths coded as silicosis or other pneumoconiosis. Less than 25 percent of the LDOC deaths in the Park et al. analysis were coded as silicosis or other pneumoconiosis (15 of 67), suggesting that silicosis as a cause of death may be misclassified as emphysema or chronic bronchitis. Thus, Mannetje et al.'s (2002b, Document ID 1089) selection of deaths may tend to underestimate the true risk of silicosis mortality, and Park et al.'s (2002, Document ID 0405) analysis may more completely capture the total respiratory mortality risk from all non-malignant causes.

    Since the time of OSHA's analysis, NCHS has released updated all-

    cause mortality and NMRD mortality background rates from 2011 (http://wonder.cdc.gov/ucd-icd10.html); OSHA's final risk estimates for NMRD mortality, which incorporate these updated rates (ICD10 codes J40-J47, chronic lower respiratory diseases; J60-J66, J68, pneumoconiosis and chemical effects), are available in Section VI, Final Quantitative Risk Assessment and Significance of Risk.

    b. Lung Cancer Mortality

    i. Exposure-Response Studies

    In 1997, when IARC determined that there was sufficient evidence to regard crystalline silica as a human carcinogen, it also noted that some epidemiological studies did not demonstrate an excess risk of lung cancer and that exposure-response trends were not always consistent among studies that were able to describe such trends (Document ID 1062). These findings led Steenland et al. (2001a, Document ID 0452) to conduct a comprehensive exposure-response analysis--the IARC multi-

    center study--of the risk of lung cancer associated with exposure to crystalline silica. This study relied on all available cohort data from previously-published epidemiological studies for which there were adequate quantitative data on worker silica exposures to derive pooled estimates of disease risk. In addition, as discussed previously, OSHA identified four more recent studies suitable for quantitative risk assessment: (1) An exposure-response analysis by Rice et al. (2001, Document ID 1118) of a cohort of diatomaceous earth workers primarily exposed to cristobalite; (2) an analysis by Attfield and Costello (2004, Document ID 0285) of U.S. granite workers; (3) an exposure-

    response analysis by Hughes et al. (2001, Document ID 1060) of U.S. industrial sand workers; and (4) a risk analysis by Miller et al. (2007, Document ID 1305) and Miller and MacCalman (2009, Document ID 1306) of British coal miners. OSHA thoroughly described each of these studies in its Preliminary QRA (Document ID 1711); a brief summary of the exposure-response models used in each study is provided here.

    The Steenland et al. pooled exposure-response analysis was based on data obtained from ten cohorts of silica-exposed workers (65,980 workers, 1,072 lung cancer deaths) (2001a, Document ID 0452). The pooled analysis cohorts included U.S. gold miners (Steenland and Brown, 1995a, Document ID 0450), U.S. diatomaceous earth workers (Checkoway et al., 1997, Document ID 0326), Australian gold miners (de Klerk and Musk, 1998, Document ID 0345), Finnish granite workers (Koskela et al., 1994, Document ID 1078), U.S. industrial sand employees (Steenland and Sanderson, 2001, Document ID 0455), Vermont granite workers (Costello and Graham, 1988, Document ID 0991), South African gold miners (Hnizdo and Sluis-Cremer, 1991, Document ID 1051; Hnizdo et al.,1997, 1049), and Chinese pottery workers, tin miners, and tungsten miners (Chen et al., 1992, Document ID 0329).

    Steenland et al. (2001a, Document ID 0452) performed a nested case-

    control analysis via Cox regression. There were 100 controls chosen for each case randomly from among cohort members who survived past the age at which the case died; controls were matched on age (the time variable in Cox regression), study, race/ethnicity, sex, and date of birth within 5 years. Steenland et al. found that the use of any of the following continuous exposure variables in a log linear relative risk model resulted in positive statistically significant (p 2000 mug/m\3\) quartz concentrations. OSHA chose to use this model to estimate the risk of radiological silicosis consistent with an ILO category 2/1+ chest x-ray for several exposure scenarios; in each, it assumed 45 years of exposure, 2000 hours/year of exposure, and no exposure above a concentration of 2000 mug/m\3\. The results showed that occupational exposures to the revised PEL of 50 mug/m\3\ led to an estimated risk of 55 cases per 1,000 workers. Exposure at the previous general industry PEL of 100 mug/m\3\ increased the estimate to 301 cases per 1,000 workers. At higher exposure levels the risk estimates rose quickly to near certainty.

    Chen et al. (2001, Document ID 0332) reported the results of a retrospective study of a Chinese cohort of 3,010 underground miners who had worked in tin mines at least one year between 1960 and 1965. They were followed through 1994, by which time 2,426 (80.6 percent) workers had either retired or died, and only 400 (13.3 percent) remained employed at the mines. Annual radiographs were taken beginning in 1963 and cohort members continued to have chest x-rays taken every 2 or 3 years after leaving work. Silicosis was diagnosed when at least 2 of 3 radiologists classified a radiograph as being a suspected case or at Stage I, II, or III under the 1986 Chinese pneumoconiosis roentgen diagnostic criteria, which the authors reported agreed closely with ILO categories 0/1, Category 1, Category 2, and Category 3, respectively. Silicosis was observed in 33.7 percent of the group; 67.4 percent of the cases developed after exposure ended.

    Chen et al. (2001, Document ID 0332) found that a Weibull model provided the best fit to relate cumulative silicosis risk to eight categories of cumulative total dust exposure. The risk of silicosis was strongly related to cumulative silica exposure. The investigators predicted a 55-percent risk of silicosis associated with 45 years of exposure to 100 mug/m\3\. The paper did not report the risk associated with a 45-year exposure to 50 mug/m\3\, but OSHA estimated the risk to be about 17 percent (based on the parameters of the Weibull model).

    In a later study, Chen et al. (2005, Document ID 0985) investigated silicosis morbidity risks among three cohorts to determine if the risk varied among workers exposed to silica dust having different characteristics. The cohorts consisted of 4,547 pottery workers, 4,028 tin miners, and 14,427 tungsten miners, all employed after January 1, 1950 and selected from a total of 20 workplaces. The approximate

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    mean cumulative exposures to respirable silica for pottery, tin, and tungsten workers were 6.4 mg/m\3\-yrs, 2.4 mg/m\3\-yrs, and 3.2 mg/

    m\3\-yrs, respectively. Measurement of particle surface occlusion (presence of a mineral coating that may affect the biological availability of the quartz component) indicated that, on average, 45 percent of the surface area of respirable particles collected from pottery factory samples was occluded, compared to 18 percent of the particle surface area for tin mine samples and 13 percent of particle surface area for tungsten mines. When cumulative silica exposure was adjusted to reflect exposure to surface-active quartz particles (i.e., not occluded), the estimated cumulative risk among pottery workers more closely approximated those of the tin and tungsten miners, suggesting to the authors that alumino silicate occlusion of the crystalline particles in pottery factories at least partially explained the lower risk seen among pottery workers, despite their having been more heavily exposed. Based on Chen et al. (2005, Document ID 0985), OSHA estimated the cumulative silicosis risk associated with 45 years of exposure to 100 mug/m\3\ respirable crystalline silica to be 6 percent for pottery workers, 12 percent for tungsten miners, and 40 percent for tin miners. For 45 years of exposure to 50 mug/m\3\, cumulative silicosis morbidity risks were estimated to be 2 percent for pottery workers, 2 percent for tungsten miners, and 10 percent for tin miners.

    ii. Risk Estimates

    OSHA's risk estimates for silicosis morbidity ranged between 60 and 773 per 1,000 workers for a 45-year exposure to the previous general industry PEL of 100 mug/m\3\, and between 20 and 170 per 1,000 workers for a 45-year exposure to the revised PEL of 50 mug/m\3\, depending upon the study used. OSHA recognizes that actual risk, to the extent that workers are exposed for less than 45 years or intermittently, is likely to be lower, but also recognizes that silicosis can progress for years after exposure ends. Also, given the consistent finding of a monotonic exposure-response relationship for silicosis morbidity with cumulative exposure in the studies reviewed, OSHA continues to find that cumulative exposure is a reasonable exposure metric upon which to base risk estimates in the exposure range of interest.

  5. Comments and Responses Concerning Silicosis and Non-Malignant Respiratory Disease Mortality and Morbidity

    In this section, OSHA focuses on comments pertaining to the literature used by the Agency to assess risk for silicosis and non-

    malignant respiratory disease (NMRD) mortality and morbidity. As discussed in the Review of Health Effects Literature and Preliminary QRA (Document ID 1711) and in Section V.C, Summary of the Review of Health Effects Literature and Preliminary QRA, of this preamble, OSHA used two studies (ToxaChemica, 2004, Document ID 0469; Park et al., 2002, 0405) to determine lifetime risk for silicosis and NMRD mortality and five studies (Buchanan et al., 2003, Document ID 0306; Chen et al., 2001, 0332; Chen et al., 2005, 0985; Hnizdo and Sluis-Cremer, 1993, 1052; and Steenland and Brown, 1995b, 0451) to determine cumulative risk for silicosis morbidity. OSHA discussed the reasons for selecting these scientific studies for quantitative risk assessment in its Review of Health Effects Literature and Preliminary QRA (Document ID 1711, pp. 340-342). Briefly, OSHA concluded that the aforementioned studies used scientifically accepted techniques to measure silica exposures and health effects in order to determine exposure-response relationships. The Agency believed, and continues to believe, that these studies, as a group, provide the best available evidence of the exposure-response relationships between silica exposure and silicosis morbidity, silicosis mortality, and NMRD mortality and that they constitute a solid and reliable foundation for OSHA's final risk assessment.

    OSHA received both supportive and critical comments and testimony regarding these studies. Comments largely focused on how the authors of these studies analyzed their data, and concerns expressed by commenters generally focused on exposure levels and measurement, potential biases, confounding, statistical significance of study results, and model forms. This section does not include extensive discussion on exposure measurement error, potential biases, thresholds, confounding factors, and the use of the cumulative exposure metric, which are discussed in depth in other sections of this preamble, including V.J Comments and Responses Concerning Biases in Key Studies and V.K Comments and Responses Concerning Exposure Estimation Error and ToxaChemica's Uncertainty Analysis. OSHA addresses comments on general model form and various other issues here and concludes that these comments do not meaningfully affect OSHA's reliance on the studies discussed herein or the results of the Agency's final risk assessment.

    1. Silicosis and NMRD Mortality

    There are two published studies that report quantitative risk assessments of silicosis and NMRD mortality (see Document ID 1711, pp. 292-298). The first is an exposure-response analysis of diatomaceous earth (DE) workers (Park et al., 2002, Document ID 0405). Park et al. quantified the relationship between cristobalite exposure and mortality caused by NMRD, which includes silicosis, pneumoconiosis, emphysema, and chronic bronchitis (Park et al. refers to these conditions as ``lung disease other than cancer (LDOC),'' while OSHA uses the term ``NMRD''). Because NMRD captures much of the silicosis misclassification that results in underestimation of the disease and includes risks from other lung diseases associated with crystalline silica exposures, OSHA believes the risk estimates derived from the Park et al. study reasonably reflect the risk of death from silica-

    related respiratory diseases, including silicosis (Document ID 1711, pp. 297-298). The second study (Mannetje et al. 2002b, Document ID 1089) is a pooled analysis of six epidemiological studies that were part of an IARC effort. OSHA's contractor ToxaChemica later conducted a reanalysis and uncertainty analysis using these data (ToxaChemica, 2004, Document ID 0469). OSHA believes that the estimates from the pooled study represent credible estimates of mortality risk from silicosis across a range of industrial workplaces, but are likely to understate the actual risk because silicosis is under-reported as a cause of death.

    a. Park et al. (2002)

    The American Chemistry Council (ACC) submitted several comments pertaining to the Park et al. (2002, Document ID 0405) study, including comments on the cohort's exposure concentrations. In its post-hearing brief, the ACC noted that the mean crystalline silica exposure in Park's DE cohort was estimated to be more than three times the former general industry PEL of 100 mug/m\3\ and the mean estimated exposure of the workers with silicosis could have been close to 10 times that level. According to the ACC, extrapolating risks from the high exposure levels in this cohort to the much lower levels relevant to OSHA's risk assessment (the previous general industry PEL of 100

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    mug/m\3\ and the revised PEL of 50 mug/m\3\) is ``fraught with uncertainty'' (Document ID 4209, pp. 84-85).

    OSHA acknowledges that there is some uncertainty in using models heavily influenced by exposures above the previous PEL due to potential deviance at areas of the relationship with fewer data points. However, OSHA believes that the ACC's characterization of exposures in the Park et al. (2002) study as vastly higher than the final and former PELs is incorrect. The ACC focused on mean exposure concentrations, reported by Park et al. as 290 mug/m\3\, to make this argument (Document ID 0405, p. 37). However, in the Park et al. study, the mean cumulative exposure of the cohort was 2.16 mg/m\3\-yrs, lower than what the final rule would permit over 45 years of exposure (2.25 mg/m\3\-yrs) (Document ID 0405, p. 37). Thus, whereas some participants in the Park et al. study had higher average-8-hour exposures than were typical under the previous PEL, they were quite comparable to the exposures workers might accumulate over their working lives under the final PEL of 50 mug/

    m\3\. In addition, as discussed in Section V.M, Comments and Responses Concerning Working Life, Life Tables, and Dose Metric, OSHA believes that the evidence in the rulemaking record, including comments and testimony from NIOSH (Document ID 3579, Tr. 127), Kyle Steenland, Ph.D. (Document ID 3580, Tr. 1227), and OSHA peer reviewer Kenneth Crump, Ph.D. (Document ID 1716, p. 166), points to cumulative exposure as a reasonable and appropriate dose metric for deriving exposure-response relationships. In sum, OSHA does not agree that the Park study should be discounted based on the ACC's concerns about the estimated exposure concentrations in the diatomaceous earth cohort.

    The ACC also criticized the Park study for its treatment of possible confounding by smoking and exposure to asbestos. The ACC commented in its pre-hearing brief that data on smoking was available for only half of the cohort (Document ID 2307, Attachment A, p. 108). The Panel also wrote that, ``while Park et al. dismissed asbestos as a potential confounder and omitted asbestos exposure in their final models, the situation is not as clear-cut as they would have one believe'' (Document ID 2307, Attachment A, p. 109). The Panel highlighted that Checkoway et al. (1997), the study upon which Park relied to dismiss asbestos as a potential confounder, noted that ``misclassification of asbestos exposure may have hindered our ability to control for asbestos as a potential confounder'' (Document ID 0326, p. 685; 2307, Attachment A, p. 109).

    OSHA has reviewed the ACC's concerns, and maintains that Park et al. adequately addressed the issues of possible confounding by smoking and exposure to asbestos in this data set. Smoking habits of a third of the individuals who died from NMRD were known in the Park et al. (2002) study. Based on that partial knowledge of smoking habits, Park et al. presented analyses indicating that confounding by smoking was unlikely to significantly impact the observed relationship between cumulative exposure to crystalline silica and NMRD mortality (Document ID 0405, p. 41). Specifically, Park et al. (2002) performed internally standardized analyses, which tend to be less susceptible to confounding by smoking since they compare the mortality experience of groups of workers within the cohort rather than comparing the mortality experience of the cohort with an external population (such as by using national mortality rates); the authors found that the internally standardized models yielded only slightly lower exposure-response coefficients than externally adjusted models (Document ID 0405; 1711, p. 302). These results suggested that estimates of NMRD mortality risks based on this cohort are not likely to be exaggerated due to cohort members' smoking habits. Park et al. also stated that the authors' findings regarding possible confounding by smoking were consistent with those of Checkoway et al., who also concluded there it was ``very unlikely'' that smoking could explain the association between mortality from NMRD and silica exposure in this cohort (Document ID 0405, p. 41; 0326, p. 687). NIOSH noted that ``residual confounding from poorly characterized smoking could have an effect,'' but that effect could be either positive or negative (Document ID 4233, pp. 32-33). While OSHA agrees that comprehensive smoking data would be ideal, the Agency believes that the approach taken by Park et al. to address this issue was reasonable.

    Asbestos exposure was estimated for all workers in Park et al., which enabled the researchers to directly test confounding. They ``found no confounding by asbestos'' and, accordingly, omitted asbestos exposure in their final modeling (Document ID 0405, p. 41). As discussed in the Review of Health Effects Literature and Preliminary QRA (Document ID 1711, pp. 301-302), exposure to asbestos was particularly prevalent among workers employed prior to 1930; after 1930, asbestos was presumably no longer used in the process (Gibbs, 1998, Document ID 1024, p. 307; Checkoway et al., 1998, 0984, p. 309). Checkoway et al. (1998), who evaluated the issue of asbestos confounding for the same cohort used by Park et al., found that the risk ratio for the highest silica exposure group after excluding the workers employed before 1930 from the cohort (Relative Risk (RR) = 1.73) was almost identical to the risk ratio of the high-exposure group before excluding those same workers (RR = 1.74) (Document ID 0984, p. 309). In addition, Checkoway's reanalysis of the original cohort study (Checkoway et al., 1993) examined those members of the cohort for whom there was quantitative information on asbestos exposure, based on a mixture of historical exposure monitoring data, production records, and recorded quantities of asbestos included in mixed products of the plant (Checkoway et al., 1996, Document ID 0325). The authors found an increasing trend in lung cancer mortality with exposure to crystalline silica after controlling for asbestos exposure and found only minor changes in relative risk estimates after adjusting for asbestos exposure (1996, Document ID 0325). Finally, Checkoway et al. (1998) reported that the prevalence of pleural abnormalities (indicators of asbestos exposure) among workers hired before 1930 (4.2 percent) was similar to that of workers hired after 1930 who presumably had no asbestos exposure (4.9 percent), suggesting that asbestos exposure was not a confounder for lung abnormalities in this group of workers (Document ID 0984, p. 309). Therefore, Checkoway et al. (1998) concluded that asbestos was not likely to significantly confound the exposure-response relationship observed between lung cancer mortality and exposure to crystalline silica in diatomaceous earth workers.

    Rice et al. also utilized Checkoway's (1997, Document ID 0326) data to test for confounding by asbestos in their Poisson and Cox proportional hazards models. Finding no evidence of confounding, Rice et al. did not include asbestos exposure as a variable in the final models presented in their 2001 paper (Document ID 1118, p. 41). Based on these numerous assessments of the effects of exposure to asbestos in the diatomaceous earth workers cohort used by Park et al. (2002), OSHA concludes that concerns about asbestos confounding in this cohort have been adequately addressed and that the additional analyses performed by Park et al. on this issue confirmed the findings of prior researchers that

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    confounding by asbestos exposure was not likely to have a large effect on exposure-response relationships.

    The ACC also expressed concern about model selection. Louis Anthony Cox, Jr., Ph.D., of Cox Associates, on behalf of the ACC, was concerned that the linear relative rate model was not appropriate because it is not designed to test for exposure-response thresholds and, similarly, the ACC has argued that threshold models are appropriate for crystalline silica-related diseases (Document ID 2307, Attachment 4, pp. 91). The ACC claimed that the Park et al. (2002) study is ``fully consistent'' with a threshold above the 100 mug/m\3\ concentration for NMRD, including silicosis, mortality (Document ID 2307, Attachment A, p. 107).

    In its post-hearing comments, NIOSH explained that categorical analysis for NMRD indicated no threshold existed with cumulative exposure corresponding to 25 mug/m\3\ over 40 years of exposure, which is below the cumulative exposure equivalent to the new PEL over 45 years (Document ID 4233, p. 27). Park et al. did not estimate a threshold below that level because the data lacked the power needed to discern a threshold (Document ID 4233, p. 27). OSHA agrees with NIOSH's assessment. In addition, as discussed extensively in Section V.I, Comments and Responses Concerning Thresholds for Silica-Related Diseases, OSHA has carefully reviewed the issue of thresholds and has concluded, based on the best available evidence, that workers with cumulative and average exposure levels permitted under the previous PEL of 100 mug/m\3\ are at risk of silica-related disease (that is, there is unlikely to be an exposure-response threshold at or near 100 mug/

    m\3\). For these reasons, OSHA disagrees with Dr. Cox's criticism of Park et al.'s reliance on the linear relative rate model.

    The ACC then questioned the use of unlagged cumulative exposures as the metric in Park et al. (2002). Dr. Cox noted that ``unlagged models are not very biologically plausible for dust-related NMRD deaths (if any) caused by exposure concentrations in the range of interest. Unresolved chronic inflammation and degradation of lung defenses takes years to decades to manifest'' (Document ID 2307, Attachment 4, p. 92). OSHA considers this criticism overstated. Park et al. considered a range of lag periods, from two years to 15. They found that ``unlagged models seemed to provide the best fit to the data in Poisson analyses although lagged models performed almost as well'' (Document ID 0405, p. 37). Based on those findings, as well as acknowledgments that NMRD effects other than silicosis (e.g., chronic bronchitis) may be observable without a relatively long lag time (unlike cancer) and that the majority of deaths observed in the cohort were indeed NMRD other than silicosis, the researchers decided to use an unlagged model. Because Park found the differences between the lagged and unlagged models for this cohort and the NMRD endpoint to be insignificant, OSHA finds that Park's final choice to use an unlagged model does not detract from OSHA's decision to utilize lagged models in its risk assessment.

    The ACC was also concerned about the truncation of cumulative exposures in the Park et al. (2002) paper. Peter Morfeld, Dr. rer. medic, stated that Park et al.:

    suffers from a methodological drawback. . . . The authors truncated the cumulative RCS dust exposures before doing the final analyses based on their observation of where the cases were found. The maximum in the study was 62.5 mg/m\3\-years but exposures were only used up to 32 mg/m\3\-years because no LDOC deaths occurred at exposures higher than that level. Such a selection distorts the estimated exposure-response relationship because it is based on the outcome of the study and on the exposure variable. Because high exposures with no effects were deliberately ignored, the exposure-

    response effect estimates are biased upward (Document ID 2307, Attachment 2, p. 27).

    OSHA acknowledges this concern about the truncation of data in the study, and asked Mr. Park about it at the public hearing. Mr. Park testified that there were good reasons to truncate the part of the exposed workforce at the high end of cumulative exposure. He noted several plausible reasons for the drop-off in the number of cases at high exposures (attenuation), including random variance in susceptibility to disease among different people and the healthy worker survivor effect \6\ (Document ID 3579, Tr. 242-243). He also stated that this attenuation is a common occurrence in studies of workers (Document ID 3579, Tr. 242). Mr. Park then emphasized that how one describes the higher end of the exposure-response relationship is inconsequential for the risk assessment process because the relationship at the lower end of the spectrum, where the PEL was determined, is more important for rulemaking (Document ID 3579, Tr. 242-243). He also stated, in a post-hearing comment, that ``for the purpose of low exposure extrapolation, adding a quadratic term to better describe the entirety of the exposure-response relationship would result in loss of precision with no advantage gained over truncation of high cumulative exposure observation time'' (Document ID 4233, p. 26). To summarize, Mr. Park stated that there are good scientific reasons to expect attenuation of exposure-response at the high end of the cumulative exposure range and that use of higher-

    exposure data affected by healthy worker survivor effect or other issues could reduce precision of the exposure-response model at the lower exposures that are more relevant to the final silica standard. OSHA finds that Mr. Park's approach in his study, along with his explanations in the rulemaking record, are reasonable and that he has fully responded to the concerns of the ACC.

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    \6\ Briefly, if individuals cease working due to illness, then those individuals will not be represented in cohort subgroups having the highest cumulative exposures. That exclusion may enable individuals with greater physiological resilience to silica exposures to be overrepresented in cohorts exposed to greater amounts of silica. Further discussion on the healthy worker survivor effect can be found in Section V.F, Comments and Responses on Lung Cancer Mortality.

    ---------------------------------------------------------------------------

    Dr. Morfeld also noted that alternative techniques that do not require truncation are available to account for a healthy worker survivor effect (Document ID 2307, Attachment 2, pp. 27-28). OSHA believes such techniques, such as g-estimation, to be relatively new or not yet in standard use in occupational epidemiology. As discussed above, OSHA finds Mr. Park's approach in his study to be reasonable.

    Finally, Dr. Cox stated in his comments that:

    key studies relied on by OSHA, such as Park et al. (2002), do not correct for biases in reported ER exposure-response relations due to residual confounding by age (within age categories), i.e., the fact that older workers may tend to have both higher lung cancer risks and higher values of occupational exposure metrics, even if one does not cause the other. This can induce a non-causal association between the occupational exposure metrics and the risk of cancer (Document ID 2307, Attachment 4, p. 29).

    Confounding occurs in an epidemiological study when the contribution of a causal factor cannot be separated from the effect of another variable (e.g., age) not accounted for in the analysis. Residual confounding occurs when attempts to control for confounding are not precise enough (e.g., controlling for age by using groups with age spans that are too wide), or subjects are misclassified with respect to confounders (Document ID 3607, p. 1). However, the Park et al. (2002) study of non-malignant respiratory disease mortality, which Dr. Cox cited as not

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    considering residual confounding by age, actually addressed this issue by using 13 five-year age groups (9.58 mg/m\3\-yrs) (possibly due to a healthy worker survivor effect, as explained above), OSHA notes that the 95 percent confidence intervals reported do not contradict the presence of a monotonic relationship (Document ID 1089). First, the confidence intervals of the lower exposed groups did not overlap with those of the higher exposed groups in that study (Document ID 1089). Second, even if they did, overlap in confidence intervals does not mean that there is not a significant difference between those groups. While it is true that, if 95 percent confidence intervals do not overlap, the represented populations are statistically significantly different, the converse--

    that, if confidence intervals do overlap, there is no statistically significant difference--is not always true (Nathaniel Schenker and Jane F. Gentleman. ``On Judging the Significance of Differences by Examining the Overlap Between Confidence Intervals.'' The American Statistician. 55(3): 2001. 182-186. (http://www.tandfonline.com/doi/abs/10.1198/000313001317097960).

    Finally, as discussed above and in detail in Section V.K, Comments and Responses Concerning Exposure Estimation Error and ToxaChemica's Uncertainty Analysis, the ToxaChemica et al. (2004) re-analysis of the corrected Mannetje et al. (2002b) data adjusting for two sources of measurement error resulted in a monotonic relationship for the risk ratios (Document ID 0469).

    2. Silicosis Morbidity

    OSHA relied on five studies for determining risk for silicosis morbidity: Buchanan et al., 2003 (Document ID 0306), Chen et al., 2001 (Document ID 0332), Chen et al., 2005 (Document ID 0985), Hnizdo and Sluis-Cremer, 1993 (Document ID 1052), and Steenland and Brown, 1995b (Document ID 0451). OSHA finds that the most reliable estimates of silicosis morbidity, as detected by chest radiographs, come from these five studies because they evaluated radiographs over time, included post-employment radiographic evaluations, and derived cumulative or lifetime estimates of silicosis disease risk. OSHA received several comments about these studies.

    a. Buchanan et al. (2003)

    Buchanan et al. (2003) reported on a cohort of Scottish coal workers (Document ID 0306). The authors found a statistically significant relationship

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    between silicosis and cumulative exposure acquired after 1964 (Document ID 0306). They also found that the risks of silicosis over a working lifetime can rise dramatically with exposure to high concentrations over a timescale of merely a few months (Document ID 0306). In the Preliminary QRA, OSHA considered this study to be of the highest overall quality of the studies relied upon to assess silicosis morbidity risks, in large measure because the underlying exposure data was based on modern exposure measurement methods and avoided the need to estimate historical exposures. The risk estimates derived from this study were lower than those derived from any of the other studies criticized by the ACC. One reason for this is because Buchanan et al. only included cases with chest x-ray findings having an ILO score of 2/

    1 or higher, whereas the other studies included cases with less damage, having a lower degree of perfusion on x-ray (ILO 1/0 or 1/1) (Document ID 0306). Thus, OSHA considered the risk estimates derived from the Buchanan et al. study to be more likely to understate risks.

    Dr. Cox commented that age needed to be included for modeling in Dr. Miller's 1998 paper, the data from which were used in the Buchanan et al. (2003) paper (Document ID 2307, Attachment 4, p. 97). However, the Miller et al. (1998) study explicitly states that age was one of several variables that were tried in the model but did not improve the model's fit, as was time spent working in the poorly characterized conditions before 1954 (Document ID 0374, p. 57). OSHA concludes that the original paper did assess these variables and how they related to the exposure-response relationship. Buchanan et al. (2003) also noted their own finding that differences in age and exposure both failed to improve fit, in agreement with Miller et al.'s conclusion (Document ID 0306, p. 161). OSHA therefore finds no credible reason that age should have been included as a variable in Miller et al. (1998).

    Dr. Cox also questioned the modeling methods in the Buchanan paper, which presented logistic regression in progressive stages to search for significance (Document ID 2307, Attachment 4, pp. 97-98; 0306, pp. 161-

    163). Dr. Cox claimed that this is an example of uncorrected multiple testing bias where the post hoc selection of data, variables, and models can make independent variables appear to be statistically significant in the prediction model. He suggested that corrections for bias are needed to determine if the reported significance is causal or statistical (Document ID 2307, Attachment 4, pp. 97-98). OSHA peer reviewer Brian Miller, Ph.D., stated that Dr. Cox's claim that the model was affected by multiple testing bias is unfounded (Document ID 3574, pp. 31-32). He noted that the model was based on a detailed knowledge of the history of exposures at that colliery, and represented the researchers' attempt to build ``a reality-driven and `best-fitting' model,'' (Document ID 3574, p. 31, quoting 2307, Attachment 4, p. 4). Furthermore, none of OSHA's peer reviewers raised any concerns about the approach taken by Buchanan et al. to develop their exposure-

    response model and none suggested that corrections needed to be made for multiple testing bias; all of them supported the study's inclusion in OSHA's risk assessment (Document ID 3574). Finally, the cumulative risk for silicosis morbidity derived from this study is similar to values from other papers reported in the QRA (see OSHA's Final Quantitative Risk Assessment in Section VI). Therefore, for the reasons discussed above, OSHA is not convinced by Dr. Cox's arguments and finds no credible reason to remove Buchanan et al. (2003) from consideration.

    b. Chen et al. (2001, 2005), Steenland and Brown (1995), and Hnizdo and Sluis-Cremer (1993)

    The ACC also commented on several other studies used by OSHA to estimate silicosis morbidity risks; these were the studies by Chen et al. (2001, Document ID 0332; 2005, 0985), Steenland and Brown (1995b, Document ID 0451), and Hnizdo and Sluis-Cremer (1993, Document ID 1052). The ACC's comments focus on uncertainties in estimating the historical exposures of cohort members (Document ID 2307, Attachment A, pp. 117-122, 124-130, 132-136). Section V.K, Comments and Responses Concerning Exposure Estimation Error and ToxaChemica's Uncertainty Analysis, discusses the record in detail with respect to the general issue of uncertainties in estimating historical exposures to respirable crystalline silica in epidemiological studies. The issues specific to the studies relied upon by OSHA in its risk estimates for silicosis morbidity will be discussed below.

    In the Chen et al. studies, which focused on mining (i.e., tin, tungsten) and pottery cohorts, high volume area samplers collected dust and the respirable crystalline silica concentration was determined from those samples (2001, Document ID 0332; 2005, 0985). However, according to the ACC, the rest of the collected dust was not assessed for chemicals that potentially could also cause radiographic opacities (Document ID 2307, Attachment A, pp. 132-135). Neither study expressed reason to be concerned about the non-silica portion of the dust samples. OSHA recognizes that uncertainty about potential unknown exposures exists in retrospective studies, which describes most epidemiological research. However, OSHA emphasizes that the risk values derived from the Chen et al. studies do not differ remarkably from other silicosis morbidity studies used in the risk assessment (Document ID 0306, 1052, 0451). Therefore, OSHA concludes that it is unlikely that an unknown compound significantly impacted the exposure-response relationships reported in both Chen studies.

    The study on gold miners (Steenland and Brown, 1995b, Document ID 0451), which found that cumulative exposure was the best disease predictor, followed by duration of exposure and average exposure, was also criticized by the ACC, which alleged that the exposure assessment suffered from ``enormous uncertainty'' (Document ID 2307, Attachment A, pp. 146-147). The ACC noted that exposure measurements were not available for the years prior to 1937 or after 1975 and that this limitation of the exposure information may have resulted in an underestimation of exposures (Document ID 2307, Attachment A, pp. 124-

    126). OSHA agrees that these are potential sources of uncertainty in the exposure estimates, but recognizes exposure uncertainty to be a common occurrence in occupational epidemiology studies. OSHA believes that the authors used the best measurement data available to them in their study.

    The ACC also took issue with Steenland and Brown's conversion factor for converting particle count to respirable silica mass (10 mppcf = 100 mug/m\3\), which was somewhat higher than that used in the Vermont granite worker studies (10 mppcf = 75 mug/m\3\) (Document ID 2307, Attachment A, p. 126). OSHA notes that the study's reasoning for adopting that specific particle count conversion factor was to address the higher percentage of silica found in the gold mine samples applicable to their cohort in comparison to the Vermont granite study (Document ID 0451, p. 1373). OSHA finds this decision, which was based on the specific known exposure conditions of this cohort, to be reasonable.

    With respect to the Hnizdo and Sluis-Cremer (1993, Document ID 1052)

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    study, which found that silicosis risk increased exponentially with cumulative exposure to respirable dust (Document ID 1052, p. 447), the ACC questioned three assumptions the study made about exposures. First, exposures were assumed to be static from the 1930s to the 1960s, based on measurements from the late 1950s to mid-1960s, an assumption that, according to the ACC, might underestimate exposure for workers employed before the late 1950s (Document ID 2307, Attachment A, pp. 117-119). Second, although respirable dust, by definition, includes particles up to 10 mum, the study only considered particles sized between 0.5 and 5 mum in diameter (Document ID 1052, p. 449). The ACC contends this exclusion may have resulted in underestimated exposure and overestimated risk (Document ID 2307, Attachment A, p. 119). OSHA agrees that uncertainty in exposure estimates is an important issue in the silica risk assessment, and generally discusses the issue of exposure measurement uncertainty in depth in a quantitative uncertainty analysis described in Section V.K, Comments and Responses Concerning Exposure Estimation Error and ToxaChemica's Uncertainty Analysis. As discussed there, after accounting for the likely effects of exposure measurement uncertainty in the risk assessment, OSHA affirms the conclusion of the risk assessment that there is significant risk of silicosis to workers exposed at the previous PELs.

    Thirdly, the ACC challenged the authors' estimate of the quartz content of the dust as 30 percent when it should have been 54 percent (Document ID 1052, p. 450; 2307, Attachment A, p. 120). According to the ACC, the 30 percent estimate was based on an incorrect assumption that the samples had been acid-washed (resulting in a reduction in silica content) before the quartz content was measured (Document ID 2307, Attachment A, pp. 120-122). This assumption would greatly underestimate the exposures of the cohort and the exposures needed to cause adverse effects, thus overestimating actual risk (Document ID 2307, Attachment A, pp. 121-122). The ACC recommended that the quartz content in the Hnizdo and Sluis-Cremer study be increased from 30 to 54 percent, based on the Gibbs and Du Toit study (2002, Document ID 1025, p. 602).

    OSHA considered this issue in the Preliminary QRA (Document ID 1711, p. 332). OSHA noted that the California Environmental Protection Agency's Office of Environmental Health Hazard Assessment reviewed the source data for Hnizdo and Sluis-Cremer, located in the Page-Shipp and Harris (1972, Document ID 0583) study, and compared them to the quartz exposures calculated by Hnizdo and Sluis-Cremer (OEHHA, 2005, Document ID 1322, p. 29). OEHHA concluded after analyzing the data that the samples likely were not acid-washed and that the Hnizdo and Sluis-

    Cremer paper erred in describing that aspect of the samples. Additionally, OEHHA reported data that suggests that the 30 percent quartz concentration may actually overestimate the exposure. It noted that recent investigations found the quartz content of respirable dust in South African gold mines to be less than 30 percent (Document ID 1322). In summary, OSHA concludes that no meaningful evidence was submitted to the rulemaking record that changes OSHA's original decision to include the Hnizdo and Sluis-Cremer study in its risk assessment.

    Despite the uncertainties inherent in estimating the exposures of occupational cohorts in silicosis morbidity studies, the resulting estimates of risk for the previous general industry PEL of 100 mug/

    m\3\ are in reasonable agreement and indicate that lifetime risks of silicosis morbidity at this level, and, by extension, risks at the higher previous PELs for maritime and construction (see section VI, Final Quantitative Risk Assessment and Significance of Risk) are in the range of hundreds of cases per 1,000 workers. Even in the unlikely event that exposure estimates underlying all of these studies were systematically understated by several fold, the magnitude of resulting risks would likely still be such that OSHA would determine them to be significant.

    3. Conclusion

    After carefully considering all of the comments on the studies relied on by OSHA to estimate silicosis and NMRD mortality and silicosis morbidity risks, OSHA concludes that the scientific evidence used in its quantitative risk assessment substantially supports the Agency's finding of significant risk for silicosis and non-malignant respiratory disease. In its risk estimates in the Preliminary QRA, OSHA acknowledged the uncertainties raised by the ACC and other commenters, but the Agency nevertheless concluded that the assessment was sufficient for evaluating the significance of the risk. After evaluating the evidence in the record on this topic, OSHA continues to conclude that its risk assessment (see Final Quantitative Risk Assessment in Section VI.C of this preamble) provides a reasonable and well-supported estimate of the risk faced by workers who are exposed to respirable crystalline silica.

  6. Comments and Responses Concerning Surveillance Data on Silicosis Morbidity and Mortality

    As discussed above in this preamble, OSHA has relied on epidemiological studies to assess the risk of silicosis, a debilitating and potentially fatal occupationally-related lung disease caused by exposure to respirable crystalline silica. In the proposed rule (78 FR 56273, 56298; also Document ID 1711, pp. 31-49), OSHA also discussed data from silicosis surveillance programs that provide some information about the number of silicosis-associated deaths or the extent of silicosis morbidity in the U.S. (78 FR at 56298). However, as OSHA explained, the surveillance data are not sufficient for estimating the risks of health effects associated with exposure to silica, nor are they sufficient for estimating the benefits of any potential regulatory action. This is because silicosis-related surveillance data are only available from a few states and do not provide exposure data that can be matched to surveillance data. Consequently, there is no way of knowing how much silica a person was exposed to before developing fatal silicosis (78 FR at 56298).

    In addition, the available data likely understate the resulting death and disease rates in U.S. workers exposed to crystalline silica (78 FR 56298). This understatement is due in large part to: (1) The passive nature of these surveillance systems, which rely on healthcare providers' awareness of a reporting requirement and submission of the appropriate information on standardized forms to health departments; (2) the long latency period of silicosis; (3) incomplete occupational exposure histories, and (4) other factors that result in a lack of recognition of silicosis by healthcare providers, including the low sensitivity, or ability of chest x-rays to identify cases of silicosis (78 FR 56298). Specific to death certificate data, information on usual industry and occupation are available from only 26 states for the period 1985 to 1999, and those codes are not verifiable (Document ID 1711). Added to these limitations is the ``lagging'' nature of surveillance data; it often takes years for cases to be reported, confirmed, and recorded. Furthermore, in many cases, the available surveillance systems lack information about actual exposures or even information about the usual occupation or industry of the deceased individual, which could provide some information about occupational

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    exposure (see 78 FR at 56298). Therefore, the Agency did not use these surveillance data to estimate the risk of silicosis for the purpose of meeting its legal requirements to prove a significant risk of material impairment of health (see 29 U.S.C. 655(b)(5); Benzene, 448 U.S. 607, 642 (1980)).

    Comments and testimony focusing on the silicosis surveillance data alleged that OSHA should have used the surveillance data in its risk estimates. Stakeholders argued that the declining numbers of reported silicosis deaths prove the lack of necessity for a new silica standard. Commenters also claimed that the surveillance data prove that OSHA overestimated both the risks at the former permissible exposure limits (PELs) and the benefits of the new rule.

    After reviewing the rulemaking record, OSHA maintains its view that these silicosis surveillance data, although useful for providing context and an illustration of a significant general trend in the reduction of deaths associated with silicosis over the past 4-5 decades, are not sufficient for estimating the magnitude of the risk or the expected benefits. In the case of silicosis, surveillance data are useful for describing general trends nationally and a few states have the ability to use the data at the local or state level to identify ``sentinel events'' that would justify initiating an inspection of a workplace, for example. The overall data, however, are inadequate and inappropriate for estimating risks or benefits associated with various exposure levels, as is required of OSHA's regulatory process, in part because they significantly understate the extent of silicosis in workers in the United States and because they lack information about exposure levels, exposure sources (e.g., type of job), controls, and health effects that is necessary to examine the effects of lowering the PEL. Thus, for these reasons and the ones discussed below, OSHA has continued to rely on epidemiological data to meet its burden of demonstrating that workers exposed to respirable crystalline silica at the previous PELs face a significant risk of developing silicosis and that risk will be reduced when the new limit is fully implemented. Another related concern identified by stakeholders is the apparent inconsistency between surveillance data and risk and benefits estimates derived from modeling epidemiological data (Document ID 4194, pp. 7-10; 4209, pp. 3-4). However, this difference is not an inconsistency, but the result of comparing two distinctly different items. Surveillance data, primarily death certificate data, are known to be under-reported and lack associated exposure data necessary to model relationships between various exposure levels and observance of health effects. For these reasons, OSHA relied on epidemiologic studies with detailed exposure-response relationships to evaluate the significance of risk at the preceding and new PELs. Thus, the silicosis mortality data derived from death certificates and estimates of silica-related mortality risks derived from well-conducted epidemiologic studies cannot be directly compared in any meaningful way. With respect to silicosis morbidity, OSHA notes that the estimates by Rosenman et al. (2003, Document ID 0420) of the number of cases of silicosis estimated to occur in the U.S. (between 2,700 and 5,475 estimated to be in OSHA's jurisdiction (i.e., excluding miners)) each year is in reasonable agreement with the estimates derived from epidemiologic studies, assuming either a 13-year or 45-year working life (see Chapter VII, Table VII-2 of the FEA).

    1. Surveillance Data on Silicosis Mortality

    The principal source of data on annual silicosis mortality in the U.S. is the National Institute for Occupational Safety and Health (NIOSH) Work-Related Lung Disease (WoRLD) Surveillance System (e.g., NIOSH, 2008c, Document ID 1308), which compiles cause-of-death data from death certificates reported to state vital statistics offices and collected by the National Center for Health Statistics (NCHS). Paper copies were published in 2003 and 2008 (Document ID 1307; 1308) and data are updated periodically in the electronic version on the CDC Web site (http://www.cdc.gov/eworld). NIOSH also developed and manages the National Occupational Respiratory Mortality System (NORMS), a data-

    storage and interactive data retrieval system that reflects death certificate data compiled by NCHS (http://webappa.cdc.gov/ords/norms.html).

    From 1968 to 2002, silicosis was recorded as an underlying or contributing cause of death on 16,305 death certificates; of these, a total of 15,944 (98 percent) deaths occurred in males (CDC, 2005, Document ID 0319). Over time, silicosis-related mortality has declined in the U.S., but has not been eliminated. Based on the death certificate data, the number of recognized and coded deaths for which silicosis was an underlying or contributing cause decreased from 1,157 in 1968 to 161 in 2005, corresponding to an 86-percent decline (Document ID 1711, p. 33; 1308, p. 55) (http://wwwn.cdc.gov/eworld). The crude mortality rate, expressed as the number of silicosis deaths per 1,000,000 general population (age 15 and higher) fell from about 8.9 per million to about 0.5 per million over that same time frame, a decline of 94 percent (Document ID 1711, p. 33; 1308, p. 55) (http://wwwn.cdc.gov/eworld).

    OSHA's Review of Health Effects Literature and Preliminary QRA included death certificate statistics for silicosis up to and including 2005 (Document ID 1711, p. 33). OSHA has since reviewed the more recent NORMS and NCHS data, up to and including 2013, which appear to show a general downward trend in mortality, as presented in Table V-1.

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    However, more detailed examination of the most recent data collected through NCHS (Table V-2) indicates that the decline in the number of deaths with silicosis as an underlying or contributing cause has leveled off in more recent years, suggesting that the number of silicosis deaths being recorded and captured by death certificates may be stabilizing after 30 or more years of decline.

    GRAPHIC TIFF OMITTED TR25MR16.004

    Robert Cohen, M.D., representing the American Thoracic Society, noted this apparent plateau effect, testifying that ``the data from the NIOSH work-related lung disease surveillance report and others show a plateau in silicosis

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    mortality since the 1990s, and we are concerned that that has been the same without any further reduction for more than 20 years. So we think that we still have work to do'' (Document ID 3577, p. 775).

    Some commenters raised the question about whether decedents who died more recently were exposed to high levels of silica (pre-1970s) and therefore wouldn't necessarily reflect mortalities relevant to the current OSHA standard (Document ID 4194, p. 9; 4209, pp. 7-8). OSHA has no information on the age of these decedents, or the timing of their exposure to silica. If we assume that workers born in 1940-1950 would have started working around 1960, at the earliest, and into the 1970's, and life expectancy in general of 70 years, or 60-70 years to account for years of life lost due to silicosis, most of these workers' working life would have been spent after the 1971 PEL went into effect. It is likely that some of the more recent decedents were exposed to silica prior to 1971; however, it is less likely that all were exposed prior to 1971. At the end of the day, there is no actual exposure information on these decedents, and this generalization does not account for overexposures, which have persisted over time.

    2. Surveillance Data on Silicosis Morbidity

    There is no nation-wide system for collecting silicosis morbidity case data. The data available are from three sources: (1) The National Hospital Discharge Survey (Document ID 1711, p. 40-43); (2) the Agency for Healthcare Research and Quality's (AHRQ) Nationwide Inpatient Survey (Document ID 3425, p. 2; https://www.hcup-us.ahrq.gov/nisoverview.jsp); and (3) states that administer silicosis and/or pneumoconiosis disease surveillance (see Document ID 1711, p. 40-43; http://www.cdc.gov/niosh/topics/surveillance/ords/StateBasedSurveillance/stateprograms.html).

    Both of the first two sources of data on silicosis morbidity cases are surveys that provide estimates of hospital discharges. The first is the National Hospital Discharge Survey (NHDS), which was conducted annually from 1965-2010. The NHDS was a national probability survey designed to meet the need for information on characteristics of inpatients discharged from non-Federal short-stay hospitals in the United States (see http://www.cdc.gov/nchs/nhds.htm). Estimates of silicosis listed as a diagnosis on hospital discharge records are available from the NHDS for the years 1985 to 2010 (see http://www.cdc.gov/nchs/nhds.htm). National estimates were rounded to the nearest 1,000, and the NHDS has consistently reported approximately 1,000 discharges/hospitalizations annually since 1980 (e.g., Document ID 1307; 1308). The second survey, the National (Nationwide) Inpatient Sample (NIS), is conducted annually by the AHRQ. Dr. Kenneth Rosenman, Division Chief and Professor of Medicine at Michigan State University and who oversees one of the few occupational disease surveillance systems in the U.S., testified that data from the NIS indicated that the nationwide number of hospitalizations where silicosis was one of the discharge diagnoses has remained constant, with 2,028 hospitalizations reported in 1993 and 2,082 in 2011 (Document ID 3425, p. 2).

    Morbidity data are also available from the states that administer silicosis and/or pneumoconiosis disease surveillance. These programs rely primarily on hospital discharge records and also may get some reports of cases from the medical community and workers' compensation programs. Currently, NIOSH funds the State-Based Occupational Safety and Health Surveillance cooperative agreements (Document ID 1711, p. 40-41; http://www.cdc.gov/niosh/topics/surveillance/ords/StateBasedSurveillance.html). All states funded under a cooperative agreement conduct population-based surveillance for pneumoconiosis (hospitalizations and mortality), and a few states (currently Michigan and New Jersey) have expanded surveillance specifically for silicosis (Document ID 1711, p. 40-42; http://www.cdc.gov/niosh/topics/surveillance/ords/StateBasedSurveillance/stateprograms.html).

    State-based hospital discharge data are a useful population-based surveillance data source for quantifying pneumoconiosis (including silicosis), even though only a small number of individuals with pneumoconiosis are hospitalized for that condition (Document ID 0996), and the data refer to hospitalizations with a diagnosis of silicosis, and not specific people. In addition to mortality data, NIOSH has updated its WoRLD Surveillance System with some state-based morbidity case data (http://wwwn.cdc.gov/eworld/Grouping/Silicosis/94). State-

    based surveillance systems can provide more detailed information on a few cases of silicosis.

    NIOSH has published aggregated state case data in its WoRLD Reports (Document ID 1308; 1307) for two ten-year periods that overlap, 1989 to 1998 and 1993 to 2002. State morbidity case data are compiled and evaluated by variables such as ascertainment source, primary industry, and occupations. For the time period 1989 to 1998, Michigan reported 589 cases of silicosis, New Jersey 191 cases, and Ohio 400 cases (Document ID 1307, p. 69). In its last published report, for the later and partially overlapping time period 1993 to 2002, Michigan reported 465 cases, New Jersey 135, and Ohio 279 (Document ID 1308, p. 72). Data for the years 2003 to 2011, from the CDC/NIOSH electronic report, eWoRld, show a modest decline in the number of cases of silicosis in these three states; however, decreases are not nearly as substantial as are those seen in the mortality rates (see Table V-3). Annual averages for the two ten-year periods and the nine-year time period were calculated by OSHA solely for the purpose of comparing cases of silicosis reported over time.

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    3. Critical Comments Received on Surveillance Data

    Industry representatives, including ACC's Crystalline Silica Panel and Dr. Jonathan Borak, representing the Chamber of Commerce (Chamber), contended that the steep decline seen in the number and rate of silicosis deaths since 1968 proves that OSHA cannot meet its burden of demonstrating that a more protective standard is necessary (e.g., Document ID 4209, p. 10; 2376, p. 8; 4016, p. 9). Similarly, other commenters, such as the American Petroleum Institute, the Independent Petroleum Association of America, the National Mining Association, the American Foundry Society (AFS), the National Utility & Excavating Contractors Association, Acme Brick, the National Ready Mixed Concrete Association, and the Small Business Administration's Office of Advocacy stated that surveillance data demonstrate that the previous OSHA PEL was sufficiently effective in reducing the number of deaths from silicosis (Document ID 3589, Tr. 4041; 4122; 2301, pp. 3, 7-9; 2211, p. 2; 2379, pp. 23-25; 2171, p. 1; 3730, p. 5; 3586, Tr. 3358-3360; 3589, Tr. 4311; 2349, pp. 3-4). Industry commenters also argued that the number of recorded silicosis-related deaths in recent years, as reflected in the surveillance data, is far lower than the number of lives that OSHA projected would be saved by a more stringent rule, indicating that OSHA's risk assessment is flawed (e.g., Document ID 3578, Tr. 1074-1075; 4209, p. 3-4).

    The Chamber, along with others, declared that OSHA ignored steep declines in silicosis mortality, which in its view indicates that there is no further need to reduce the PEL (Document ID 4194, pp. 7-8). OSHA has not ignored the fact that the available surveillance data indicate a decline in silicosis mortality. As discussed above and in the proposal, the Agency has acknowledged that the available surveillance data do show a decline in the silicosis mortality since 1968. Furthermore, OSHA has no information on whether underreporting has increased or decreased over time, and does not believe that differing rates of reporting and underreporting of silicosis on death certificates explains the observed decline in silicosis mortality. OSHA believes that the reductions in deaths attributable to silicosis are real, and not a statistical artifact. However, OSHA disagrees with commenters' argument that this trend shows the lack of a need for this new rule. First, as explained above, there is strong evidence that the death certificate data do not capture the entirety of silicosis mortality that actually exists, due to underreporting of silicosis as a cause of death. Second, the stakeholders' argument assumes that mortality will continue to decline, even in the absence of a stronger silica standard, and that OSHA and workers should wait for this decline to hit bottom (e.g., Document ID 4209, p. 7). However, testimony in the record suggests that the decline in the number of deaths has leveled off since 2000, probably because of the deaths of those historically exposed to higher levels of silica occurred before then (e.g., Document ID 3577, p. 775).

    Third, the decline in silicosis deaths recorded over the past several decades cannot be solely explained by improved working conditions, but also reflects the decline in employment in industries that historically were associated with high workplace exposures to crystalline silica. One of OSHA's peer reviewers for the Review of Health Effects Literature and Preliminary QRA, Bruce Allen, commented that the observed decline in mortality ``. . . in no way adjusts for the declining employment in jobs with silica exposure,'' making ``its interpretation problematic. To emphasize the contribution of historic declines in exposure as the underlying cause is spurious; no information is given to allow one to account for declining employment'' (Document ID 3574, p. 7). The CDC/NIOSH also identified declining employment in heavy industries where silica exposure was prevalent as a ``major factor'' in the reduction over time in silicosis mortality (Document ID 0319, p. 2). As discussed below, however, some silica-

    generating operations or industries are new or becoming more prevalent.

    In his written testimony, Dr. Rosenman pointed out that there are ``two aspects to the frequency of occurrence of disease (1) . . . the risk of disease based on the level of exposure and (2) the number of individuals at risk'' (Document ID 3425, pp. 3-4). Dr. Rosenman estimated the decline in the number of workers in Michigan foundries (75 percent) and the number of abrasive blasting companies in Michigan (71 percent), and then compared these percentages to the percentage decline in the number of recorded silicosis deaths (80 percent) over a similar time period. The similarities in these values led him to attribute ``almost all'' of the decrease in silicosis deaths to a decrease in the population at risk (Document ID 3425, pp. 3-4).

    Finally, OSHA's reliance on epidemiological data for its risk assessment purposes does not suggest that the Agency ignored the available surveillance data. As discussed above, the data are inadequate and inappropriate for estimating risks or benefits associated with various exposure levels, as is required of OSHA's regulatory process. Even in the limited cases where surveillance data are available, OSHA generally relies on epidemiological data, to the extent they include sufficiently detailed information on exposures, exposure sources (e.g., type of job), and health effects, to satisfy its statutory requirement to use the best available evidence to evaluate the significance of risk associated with exposure to hazardous substances.

    Some stakeholders provided comments to the rulemaking record consistent with OSHA's assessment. For example, Dr. Borak stated that the surveillance data ``provide little or no basis'' (Document ID 2376, p. 8) for OSHA to evaluate the protectiveness of the previous PELs. Similarly, NIOSH asserted that relying on the surveillance data to show that there is no need for a lower PEL or that there is no significant risk at 100 mug/m\3\ would be ``a misuse of surveillance data'' (Document ID 3579, Tr. 167). NIOSH also added that, because the surveillance data do not include information about exposures, it is not the kind of data that could be used for a quantitative risk assessment. NIOSH concluded that surveillance data are, in fact, ``really not germane to the risk assessment'' (Document ID 3579, Tr. 248). OSHA agrees with both Dr. Borak and NIOSH that the surveillance data cannot and do not inform the Agency on the need for a lower PEL, nor is there a role for surveillance data in making its significant risk findings. Therefore, for its findings of significant risk at the current PEL, the Agency relied on evidence derived from detailed exposure-response relationships from well-conducted epidemiologic studies, and not surveillance data, which have no associated exposure information. In this case, epidemiologic data provided the best available evidence.

    In its testimony, the AFL-CIO pointed out that a recent U.S. Government Accountability Office (GAO) report on the Mine Safety and Health Administration's (MSHA) proposed coal dust standard references the National Academy of Sciences (NAS) conclusion that risk assessments based on epidemiological data, not surveillance data, were an appropriate means to assess risk for coal-dust exposures (Document ID 4204, p. 21; 4072, Attachment 48, pp. 7-8). The NAS

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    emphasized that the surveillance data available to MSHA did not include individual miners' levels of exposure to coal mine dust and, therefore, could not be used for the purpose of estimating disease risk for miners. ``Based on principles of epidemiology and statistical modeling, measures of past exposures to coal mine dust are critical to assessing the relationship between miners' cumulative coal mine dust exposure and their risk of developing pneumoconiosis'' (Document ID 4072, Attachment 48, p. 8). The same rationale applies here. Thus, OSHA's decision to rely on epidemiological data is well supported by the record.

    Commenters from companies and industry groups also argued that they had no knowledge of workers acquiring silicosis in their companies or industry (e.g., Document ID 2384, p. 2; 2338, p. 3; 2365, p. 2; 2185, p. 3; 2426, p. 1). OSHA received similar comments as part of a letter campaign in which over 100 letters from brick industry representatives claimed there to be little or no silicosis observed in the industry despite historical exposures above the PEL (e.g., Document ID 2009). OSHA considered these comments and believes that many companies, including companies in the brick industry, may not have active medical surveillance programs for silicosis. Silicosis may not develop until after retirement as a result of its long latency period. In addition, silica exposures in some workplaces may be well below the final PEL as a result of the environment in which workers operate, including existing controls. Thus, OSHA believes that it is difficult to draw conclusions about the rate of silicosis morbidity in specific workplaces without having detailed information on medical surveillance, silica exposures, and follow-up. This is why OSHA relies heavily on epidemiological studies with detailed exposure data and extended follow-up, and uses these data to evaluate exposure-response relationships to assess health risks at the preceding and new PELs.

    Commenters also argued that, due to the long latency of the disease, silicosis cases diagnosed today are the result of exposures that occurred before the former PELs were adopted, and thus reflect exposures considerably higher than the previous PELs (e.g., Document ID 2376, p. 3; 2307, p. 12; 4194, p. 9; 3582, Tr. 1935). OSHA notes that the evidence shows that the declining trend in silicosis mortality does not provide a complete picture with regard to silicosis trends in the United States. Although many silicosis deaths reported today are likely the result of higher exposures (both magnitude and duration), some of which may have occurred before OSHA adopted the previous PELs, silicosis cases continue to occur today--some in occupations and industries where exposures are new and/or increasing. For example, five states reported cases of silicosis in dental technicians for the years 1994 to 2000 (CDC, MMWR Weekly, 2004, 53(09), pp. 195-197), for the first time. For the patients described in this report, the only identified source of crystalline silica exposure was their work as dental technicians. Exposure to respirable crystalline silica in dental laboratories can occur during procedures that generate airborne dust (e.g., mixing powders, removing castings from molds, grinding and polishing castings and porcelain, and using silica sand for abrasive blasting). In 2015, the CDC reported the first case of silicosis (progressive massive fibrosis) associated with exposure to quartz surfacing materials (countertop fabrication and installation) in the U.S. The patient was exposed to dust for 10 years from working with conglomerate or quartz surfacing materials containing 70%-90% crystalline silica. Cases had previously been reported in Israel, Italy and Spain (MMWR, 2015, 64(05); 129-130). Recently, hazardous silica exposures have been newly documented during hydraulic fracturing of gas and oil wells (Bang et al., MMWR, 2015, 64(05); 117-120).

    Dr. Rosenman's testimony provides support for this point. He testified that newer industries with high silica exposures may also be under-recognized because workers in those industries have not yet begun to be diagnosed with silicosis due to the latency period (Document ID 3577, p. 858). Dr. Rosenman submitted to the record a study by Valiante et al. (2004, Document ID 3926) that identified newly exposed construction workers in the growing industry of roadway repair, which began using current methods for repair in the 1980s. These methods use quick-setting concrete that generates dust containing silica above the OSHA PEL when workers perform jackhammering, and sawing and milling concrete operations. State surveillance systems identified 576 confirmed silicosis cases in New Jersey, Michigan, and Ohio that were reported to NIOSH for the years 1993 through 1997. Of these, 45 (8 percent) cases were in construction workers, three of which had been engaged in highway repair.

    Sample results for this study indicated a significant risk of overexposure to crystalline silica for workers who performed the five highway repair tasks involving concrete. Sample results in excess of the OSHA PEL were found for operating a jackhammer (88 percent of samples), sawing concrete and milling concrete tasks (100 percent of samples); cleaning up concrete tasks (67 percent of samples); and drilling dowels (100 percent of samples). No measured exposures in excess of the PEL were found for milling asphalt and cleaning up asphalt; however, of the eight samples collected for milling asphalt, six (55 percent) results approached the OSHA PEL, and one was at 92 percent of the PEL. No dust-control measures were in place during the sampling of these highway repair operations.

    The authors pointed out that surveillance systems such as those implemented by these states are limited in their ability to detect diseases with long latencies in highway repair working populations because of the relatively short period of time that modern repair methods had been in use when the study was conducted. Nevertheless, a few cases were identified, although the authors explain that the work histories of these cases were incomplete, and the authors recommended ongoing research to evaluate the silicosis disease potential among this growing worker population (Document ID 3926, pp. 876-880). In construction, use of equipment such as blades used on handheld saws to dry-cut masonry materials have increased both efficiency and silica exposures for workers over the past few decades (Document ID 4223, p. 11-13). Exposure data collected by OSHA as part of its technological feasibility analysis demonstrates that exposures frequently exceed previous exposure limits for these operations when no dust controls are used (see Chapter IV of the FEA). Another operation seeing new and increasing exposures to respirable crystalline silica is hydraulic fracturing in the oil and gas industry (Document ID 3588, p. 3773). Information in the record from medical professionals noted that lung diseases caused by silica exposures are ``not relics of the past,'' and that they continue to see cases of silicosis and other related diseases, even among younger workers who entered the workforce after the former PEL was enacted (see Document ID 3577, Tr. 773).

    Furthermore, the general declining trend seen in the death certificate data is considerably more modest in silicosis morbidity data. In his written testimony, Dr. Rosenman stated that the nationwide number of hospitalizations where silicosis was one of the discharge diagnoses has remained constant, with 2,028 hospitalizations reported in 1993

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    and 2,082 in 2011 (Document ID 3425, p. 2). It is the opinion of medical professionals including the American Thoracic Society and the American College of Chest Physicians that these hospitalizations likely represent ``the tip of the iceberg'' (of silicosis cases) since milder cases are not likely to be admitted to the hospital (Document ID 2175, p. 3). Again, this evidence shows that the declining trend observed in silicosis mortality statistics does not provide a complete picture with regard to silicosis trends in the United States. While silicosis mortality has decreased substantially since records were first available in 1968, the number of silicosis related deaths appears to have leveled off (see Table V-2; Document ID 3577, Tr. 775). Workers are still dying from silicosis today, and new cases are being identified by surveillance systems, where they exist.

    Based on the testimony and evidence described above, OSHA finds that the surveillance data describing trends in silicosis mortality and morbidity provide useful evidence of a continuing problem, but are not suitable for evaluating either the adequacy of the previous PELs or whether a more protective standard is needed. In fact, it would not be possible to derive estimates of risk at various exposure levels from the available surveillance data for silica. OSHA therefore appropriately continues to rely on epidemiological data and its quantitative risk assessment to support the need to reduce the previous PELs in its final rule.

    Commenters also argued that OSHA has failed to prove that a new standard is necessary because silica-associated deaths are due to existing exposures in excess of the previous PELs; therefore, the Agency should focus on better enforcing the previous PELs, rather than enacting a new standard (e.g., Document ID 2376, p. 8; 2307, p. 12; 4016, pp. 9-10; 3582, Tr. 1936). OSHA does not find this argument persuasive. First, many of the commenters used OSHA's targeted enforcement data to make this point. These data were obtained during inspections where OSHA suspected that exposures would be above the previous PELs. Consequently, the data by their very nature are skewed in the direction of exceeding the previous PELs, and such enforcement serves a deterrence function, encouraging future compliance with the PEL.

    Second, not all commenters agreed that overexposures were ``widespread.'' A few other commenters (e.g., AFS) thought that OSHA substantially overstated the number of workers occupationally exposed above 100 mug/m\3\ in its PEA (Document ID 2379, p. 25). However OSHA's risk analyses evaluated various exposure levels in determining risks to workers, and did not rely on surveillance data, which rarely have associated exposure data. Although OSHA relied on exposure data from inspections to assess technological feasibility, it did not rely on inspection data for its risk assessment because these exposure data are not tied to specific health outcomes. Instead, the exposure data used for risk assessment purposes is found in the scientific studies discussed throughout this preamble section.

    The surveillance data are also not comparable to OSHA's estimate of deaths avoided by the final rule because, as is broadly acknowledged, silicosis is underreported as a cause of death on death certificates. Thus, the surveillance data capture only a portion of the actual silicosis mortality. This point was raised by several rulemaking participants, including Dr. Rosenman; Dr. James Cone, MD, MPH, Occupational Medicine Physician at the New York City Department of Health, the AFL-CIO; and the American Thoracic Society (ATS) (Document ID 3425, p. 2; 3577, Tr. 855, 867; 4204, p. 17; 2175, p. 3; 3577, Tr. 772).

    The rulemaking record includes one study that evaluated underreporting of silicosis mortality. Goodwin et al. (2003, Document ID 1030) estimated, through radiological confirmation, the prevalence of unrecognized silicosis in a group of decedents presumed to be occupationally exposed to silica, but whose causes of death were identified as respiratory diseases other than silicosis. In order to assess whether silicosis had been overlooked and under-diagnosed by physicians, the authors looked at x-rays of decedents whose underlying cause of death was listed as tuberculosis, cor pulmonale, chronic bronchitis, emphysema, or chronic airway obstruction, and whose usual industry was listed as mining, construction, plastics, soaps, glass, cement, concrete, structural clay, pottery, miscellaneous mineral/

    stone, blast furnaces, foundries, primary metals, or shipbuilding and repair.

    Any decedent found to have evidence of silicosis on chest x-ray with a profusion score of 1/0 was considered to be a missed diagnosis. Of the 177 individuals who met study criteria, radiographic evidence of silicosis was found in 15 (8.5 percent). The authors concluded that silicosis goes undetected even when the state administers a case-based surveillance system. Goodwin et al. (2003, Document ID 1030) also cites mortality studies of Davis et al. (1983, Document ID 0999) and Hughes (1982, Document ID 0362) who reported finding decedents with past chest x-ray records showing evidence of silicosis but no mention of silicosis on the death certificate.

    The Goodwin et al. (2003) study illustrates the importance of information about the decedent's usual occupation and usual industry on death certificates. Yet for the years 1985 to 1999, only 26 states coded this information for inclusion on death certificates. If no occupational information is available, recognizing exposure to silica, which is necessary to diagnose silicosis, becomes even more difficult, further contributing to possible underreporting.

    Dr. Rosenman, a physician, epidemiologist and B-reader, testified that in his research he found silicosis recorded on only 14 percent of the death certificates of individuals with confirmed silicosis (Document ID 3425, p. 2; 3577, Tr. 854; see also 3756, Attachment 11). This means that as much as 86 percent of deaths related to silicosis are missing from the NIOSH WoRLD database, substantially compromising the accuracy of the surveillance information. Dr. Rosenman also found that silicosis is listed as the cause of death in a small percentage of individuals who have an advanced stage of silicosis; 18 percent in those with progressive massive fibrosis (PMF) and 10 percent in those with category 3 profusion.

    As noted above, factors that contribute to underreporting by health care providers include lack of information about exposure histories and difficulty recognizing occupational illnesses that have long latency periods, like silicosis (e.g., Document ID 4214, p. 13; 3584, Tr. 2557). Dr. Rosenman's testimony indicated that many physicians are unfamiliar with silicosis and this lack of recognition is one factor that contributes to the low recording rate for silicosis on death certificates (Document ID 3577, Tr. 855). In order to identify cases of silicosis, a health care provider must be informed of the patient's history of occupational exposure to dust containing respirable silica, a critical piece of information in identifying and reporting cases of silicosis. However, information on a decedent's usual occupation and/or industry is often not available at the time of death or is too general to be useful. If the physician completing the death certificate is unaware of the decedent's occupational exposure history to crystalline silica, and does not have that information available to her/him on a medical record, a diagnosis of silicosis on the death certificate is

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    unlikely. According to a study submitted by the Laborers' Health and Safety Fund of North America, (Wexelman et al., 2010), a sample of physician residents surveyed in New York City did not believe that cause of death reporting is accurate; this was a general finding, and not specific to silicosis (Document ID 3756, Attachment 7).

    The ATS and the American College of Chest Physicians commented that physicians often fail to recognize or misdiagnose silicosis as another lung disease on the death certificate, leading to under-reporting on death certificates (3577, Tr. 821, 826-827) and under-recognize and underreport cases of silicosis (Document ID 2175, p. 3). As Dr. Weissman from NIOSH responded:

    . . . it's well known that death certificates don't capture all of the people that have a condition when they pass away, and so there would be many that probably would not be captured if the silicosis didn't directly contribute to the death and depending on who filled out the death certificate, and the conditions of the death and all those kinds of things. So it's an under-representation of people who die with the condition . . . . (Document ID 3579, pp. 166-167).

    Although there is little empirical evidence describing the extent to which silicosis is underreported as a cause of death, OSHA finds, based on this evidence as well as on testimony in the record, that the available silicosis surveillance data are likely to significantly understate the number of deaths that occur in the U.S. where silicosis is an underlying or contributing cause. This is in large part due to physicians and medical residents who record causes of death not being familiar or having access to the patient's work or medical history (see Wexelman et al., 2010, Document ID 3756, Attachment 7; Al-Samarri et al., Prev. Chronic Dis. 10:120210,2013). According to Goodwin et al. (2003, Document ID 1030, p. 310), most primary care physicians do not take occupational histories, nor do they receive formal training in occupational disease. They further stated that, since it is likely that a person would not retain the same health care provider over many years, even if the presence of silicosis in a patient might have been known by a physician who cared for them, it would not necessarily be known by another physician or resident who recorded cause of death years or decades later and who did not have access to the patient's medical or work history. OSHA finds the testimony of Dr. Rosenman compelling, who found that silicosis was not recorded as an underlying or contributing cause of death even where there was chest x-ray evidence of progressive massive fibrosis related to exposure to crystalline silica.

    Some commenters stated that the decline in silicosis mortality demonstrates that there is a threshold for silicosis above the prior PEL of 100 mug/m\3\ (Document ID 4224, p. 2-5; 3582, Tr. 1951-1963). OSHA finds this argument irrelevant as the threshold concept does not apply to historical surveillance data. As noted above and discussed in Section V.I, Comments and Responses Concerning Threshold for Silica-

    Related Diseases, OSHA believes that surveillance data should not be used for quantitative risk analysis (including determination of threshold effects) because it lacks an exposure characterization based on sampling. Thus, the surveillance data cannot demonstrate the existence of a population threshold.

    There is also evidence in the record that silicosis morbidity statistics reviewed earlier in this section are underreported. This can be due, in part, to the relative insensitivity of chest roentgenograms for detecting lung fibrosis. Hnizdo et al. (1993) evaluated the sensitivity, specificity and predictive value of radiography by correlating radiological and pathological (autopsy) findings of silicosis. ``Sensitivity'' and ``specificity'' refer to the ability of a test to correctly identify those with the disease (true positive rate), and those without the disease (true negative). Because pathological findings are the most definitive for silicosis, findings on biopsy and autopsy provide the best comparison for determining sensitivity and specificity of chest imaging.

    The study used three readers and defined a profusion score of 1/1 as positive for silicosis. Sensitivity was defined as the probability of a positive radiological reading (ILO category >1/1) given that silicotic nodules were found in the lungs at autopsy. Specificity was defined as the probability of a negative radiological reading (ILO category =150 mug/m\3\ for any risk of silica-related renal disease mortality'' (Document ID 2307, Attachment A, p. 147).

    OSHA finds the ACC's suggestion of a threshold to be unpersuasive, as the ACC provided no analysis to indicate a threshold in this study. OSHA addresses the Steenland and Brown (1995a, Document ID 0450) exposure assessment in Section V.D, Comments and Responses Concerning Silicosis and Non-Malignant Respiratory Disease Mortality and Morbidity. The ACC also

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    ignored the alternative explanation, that elevated chronic renal disease mortality may have only been seen in the workers hired prior to 1930 because they had a higher cumulative exposure than workers hired later, not because there was necessarily a threshold.

    The ACC had a similar criticism of the Steenland et al. (2001b, Document ID 0456) study of North American industrial sand workers. The ACC posited that the exposure estimates were highly uncertain and likely to be understated (Document ID 2307, Attachment A, p. 149). The ACC noted that these exposure estimates, developed by Sanderson et al. (2000, Document ID 0429), were considerably lower than those developed by Rando et al. (2001, Document ID 0415) for another study of North American industrial sand workers (Document ID 2307, Attachment A, p. 149). After discussing several differences between these two exposure assessments, the ACC pointed to OSHA's discussion in the lung cancer section of the preamble to the Proposed Rule (78 FR at 56302) in which the Agency acknowledged that McDonald et al. (2001, Document ID 1091), Hughes et al. (2001, Document ID 1060) and Rando et al. (2001, Document ID 0415) had access to smoking histories, plant records, and exposure measurements that allowed for the development of a job exposure matrix, while Steenland and Sanderson (2001, Document ID 0455) had limited access to plant facilities, less detailed historic exposure data, and used MSHA enforcement records for estimates of recent exposure (Document ID 2307, Attachment A, pp. 149-151). The ACC then noted that the McDonald et al. study (2005, Document ID 1092), using the Rando et al. (2001, Document ID 0415) exposure assessment, found no association between end-stage renal disease or renal cancer and cumulative silica exposure (Document ID 2307, Attachment A, pp. 149, 152).

    The ACC also noted that, based on underlying cause of death, the SMR for acute renal death in the Steenland et al. (2001b, Document ID 0456) study was not significant (95% confidence interval: 0.70-9.86), and the SMR for chronic renal disease was barely significant (95% confidence interval: 1.06-4.08) (Document ID 2307, Attachment A, p. 151). In light of this, the ACC maintained that Steenland et al. based their exposure-response analyses on multiple-cause mortality data, using all deaths with any mention of renal disease on the death certificate even if it was not listed as the underlying cause. The ACC asserted that ``only the underlying cause data involve actual deaths from renal disease'' (Document ID 2307, Attachment A, p. 152).

    OSHA does not find this criticism persuasive. For regulatory purposes, multiple-cause mortality data is, if anything, more relevant because renal disease constitutes the type of material impairment of health that the Agency is authorized to protect against through regulation regardless of whether it is determined to be the underlying cause of a worker's death. Moreover, the discrepancy in the renal disease mortality findings is a moot point, as only the model in the pooled study with renal disease as an underlying cause was used to estimate risks in the Preliminary QRA (Document ID 1711, p. 316). In any event, OSHA notes an important difference between the Steenland et al. study (2001b, Document ID 0456) and the McDonald study (2005, Document ID 1092): They did not look at the same cohort of North American industrial sand workers. Steenland et al. (2001b) examined a cohort of 4,626 workers from 18 plants; the average year of first employment was 1967, with follow-up through 1996 (Document ID 0456, pp. 406-408). McDonald et al. (2005) examined a cohort of 2,452 workers employed between 1940 and 1979 at eight plants, with follow-up through 2000 (Document ID 1092, p. 368). Although there was overlap of about six plants in the studies (Document ID 1711, p. 127), these were clearly two fairly different cohorts of industrial sand workers. These differences in the cohorts might explain the discrepancy in the studies' results. In addition, OSHA notes that McDonald et al. (2005, Document ID 1092) observed statistically significant excess mortality from nephritis/nephrosis in their study that was not explained by the findings of their silica exposure-response analyses (Document ID 1092, p. 369).

    The ACC further argued that the Steenland et al. (2002a, Document ID 0448) pooled study is inferior to the Vacek et al. (2011, Document ID 2340) study of Vermont granite workers, which found no association between cumulative silica exposure and mortality from either kidney cancer or non-malignant kidney disease and which it contended has better mortality and exposure data (Document ID 2307, Attachment A, p. 154) (citing Vacek et al. (2011, Document ID 2340). In particular, it argued that the Vacek et al. study is more reliable for this purpose than the unpublished Attfield and Costello data (2004, Document ID 0285) on Vermont granite workers, which Steenland et al. relied on in finding an association between silica exposure and renal disease.

    OSHA notes that Steenland et al. acknowledged in their pooled study that that unpublished data had not undergone peer review (Document ID 0448, p. 5). Despite this limitation, OSHA is also unpersuaded that the Vacek et al. study, although it observed no increased kidney disease mortality (Document ID 2340, Table 3, p. 315), negates Steenland et al.'s overall conclusions. OSHA discussed several substantial differences between these two studies in Section V.F, Comments and Responses Concerning Lung Cancer Mortality.

    3. Additional Studies

    The ACC also submitted to the record several additional studies that did not show a statistically significant association between exposure to crystalline silica and renal disease mortality. These included the aforementioned studies by McDonald et al. (2005, Document ID 1092) and Vacek et al. (2011, Document ID 2340), as well as studies by Davis et al. (1983, Document ID 0999), Koskela et al. (1987, Document ID 0363), Cherry et al. (2012, article included in Document ID 2340), Birk et al. (2009, Document ID 1468), Mundt et al. (2011, Document ID 1478), Steenland et al. (2002b, Document ID 0454), Rosenman et al. (2000, Document ID 1120), and Calvert et al. (2003, Document ID 0309) (Document ID 2307, Attachment A, pp. 140-145). In light of its assertions on the limitations of the three studies in the pooled analysis, and because the three studies ``run counter to a larger number of studies in which a causal association between silica exposure and renal disease was not found,'' the ACC concluded that ``the three studies relied on by OSHA do not provide a reliable or supportable basis for projecting any risk of renal disease mortality from silica exposure'' (Document ID 4209, p. 94). Similarly, the AFS argued that renal disease was only ``found in a couple of selected studies and not observed in most others,'' including no foundry studies (Document ID 2379, Attachment 1, pp. 1-3).

    In light of the analysis contained in the Review of Health Effects Literature and Preliminary QRA, and OSHA's confirmation of its preliminary findings through examination of the record, OSHA finds these claims to be lacking in merit (Document ID 1711, pp. 211-229). In the Review of Health Effects Literature and Preliminary QRA, OSHA presented a comprehensive analysis of several studies that showed an association between crystalline silica

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    and renal disease, as well as discussing other studies that did not (Document ID 1711, pp. 211-229). Based upon its overall analysis of the literature, including the negative studies, OSHA concluded that there was substantial evidence suggesting an association between exposure to crystalline silica and increased risks of renal disease. This conclusion was supported by a number of case reports and epidemiological studies that found statistically significant associations between occupational exposure to silica dust and chronic renal disease (Calvert et al., 1997, Document ID 0976), subclinical renal changes (Ng et al., 1992c, Document ID 0386), end-stage renal disease morbidity (Steenland et al., 1990, Document ID 1125), end-stage renal disease incidence (Steenland et al. 2001b, Document ID 0456), chronic renal disease mortality (Steenland et al., 2002a, 0448), and granulomatosis with polyangitis (Nuyts et al., 1995, Document ID 0397). In other findings, silica-exposed individuals, both with and without silicosis, had an increased prevalence of abnormal renal function (Hotz et al., 1995, Document ID 0361), and renal effects were reported to persist after cessation of silica exposure (Ng et al., 1992c, Document ID 0386). While the mechanism of causation is presently unknown, possible mechanisms suggested for silica-induced renal disease included a direct toxic effect on the kidney, deposition in the kidney of immune complexes (IgA) following silica-related pulmonary inflammation, or an autoimmune mechanism (Calvert et al., 1997, Document ID 0976; Gregorini et al., 1993, 1032).

    From this review of the studies on renal disease, OSHA concluded that there were considerably less data, and thus the findings based on them were less robust, than the data available for silicosis and NMRD mortality, lung cancer mortality, or silicosis morbidity. Nevertheless, OSHA concluded that the Steenland et al. (2002a, Document ID 0448) pooled study had a large number of workers and validated exposure information, such that it was sufficient to provide useful estimates of risk of renal disease mortality. With regard to the additional negative studies presented by the ACC, OSHA notes that it discussed the Birk et al. (2009, Document ID 1468) and Mundt et al. (2011, Document ID 1478) studies in the Supplemental Literature Review of the Review of Health Effects Literature and Preliminary QRA, noting the short follow-up period as a limitation, which makes it unlikely to observe the presence of renal disease (Document ID 1711, Supplement, pp. 6-12). OSHA likewise discussed the Vacek et al. (2011, Document ID 2340) study earlier in this section, and notes that Cherry et al. reported a statistically significant excess of non-malignant renal disease mortality in the cohort for the period 1985-2008, with an unexplained cause (2012, p. 151, article included in Document ID 2340). Although these latter two studies did not find a significant association between silica exposure and renal disease mortality, OSHA does not believe that they substantially change its conclusions on renal disease mortality from the Preliminary QRA, given the number of positive studies presented and the limitations of those two studies.

    Thus, OSHA recognizes that the renal risk estimates are less robust and have more uncertainty than those for the other health endpoints for which there is a stronger case for causality (i.e., lung cancer mortality, silicosis and NMRD mortality, and silicosis morbidity). But, for the reasons stated above, OSHA believes that the evidence supporting causality regarding renal risk outweighs the evidence casting doubt on that conclusion. Scientific certainty is not the legal standard under which OSHA acts. OSHA is setting the standard based upon the clearly significant risks of lung cancer mortality, silicosis and NMRD mortality, silicosis morbidity, and renal disease mortality at the previous PELs; even if the risk of renal disease mortality is discounted, the conclusion would not change that regulation is needed to reduce the significant risk of material impairment of health (see Society of the Plastics Industry, Inc. v. OSHA, 509 F.2d 1301, 1308 (2d Cir. 1975)).

  7. Mechanisms of Silica-Induced Adverse Health Effects

    In this section, OSHA describes the mechanisms by which silica exposure may cause silica-related health effects, and responds to comments criticizing the Agency's analysis on this topic. In the proposal as well as this final rule, OSHA relied principally on epidemiological studies to establish the adverse health effects of silica exposure. The Agency also, however, reviewed animal studies (in vivo and in vitro) as well as in vitro human studies that provide information about the mechanisms by which respirable crystalline silica causes such effects, particularly silicosis and lung cancer. OSHA's review of this material can be found in the Review of Health Effects Literature and Preliminary Quantitative Risk Assessment (QRA), which provided background and support for the proposed rule (Document ID 1711, pp. 229-261).

    As described in the Review of Health Effects Literature, OSHA performed an extensive evaluation of the scientific literature pertaining to inhalation of respirable crystalline silica (Document ID 1711, pp. 7-265). Due to the lack of evidence of health hazards from dermal or oral exposure, the Agency focused solely on the studies addressing the inhalation hazards of respirable crystalline silica. OSHA determined, based on the best available scientific information, that several cellular events, such as cytotoxicity (i.e., cellular damage), oxidative stress, genotoxicity (i.e., damage to cellular DNA), cellular proliferation, and inflammation can contribute to a range of neoplastic (i.e., tumor-forming) and non-neoplastic health effects in the lung. While the exact mechanisms have yet to be fully elucidated, they are likely initiated by damage to lung cells from interaction directly with the silica particle itself or through silica particle activation of alveolar macrophages following phagocytosis (i.e., engulfing particulate matter in the lung for the purpose of removing or destroying foreign particles). The crystalline structure and unusually reactive surface properties of the silica particle appear to cause the early cellular effects. Silicosis and lung cancer share common features that arise from these early cellular interactions but OSHA, in its Review of Health Effects Literature and Preliminary QRA, ``preliminarily concluded that available animal and in vitro studies have not conclusively demonstrated that silicosis is a prerequisite for lung cancer in silica-exposed individuals'' (Document ID 1711, p. 259). Although the health effects associated with inhalation of respirable crystalline silica are seen primarily in the lung, other observed health effects include kidney and immune dysfunctions.

    Below, OSHA reviews the record evidence and responds to comments it received on the mechanisms underlying respirable crystalline silica-

    induced lung cancer and silicosis. The Agency also addresses comments regarding the use of animal studies to characterize adverse health effects in humans caused by exposure to respirable crystalline silica.

    1. Mechanisms for Silica-Related Health Effects

    In 2012, IARC reevaluated the available scientific information regarding respirable crystalline silica and lung cancer and reaffirmed that crystalline silica is carcinogenic to

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    humans, i.e., a Group 1 carcinogen (Document ID 1473, p. 396). OSHA's review of all the evidence now in the rulemaking record, including the results of IARC's reevaluation, indicates that silica may lead to increased risk of lung cancer in humans by a multistage process that involves a combination of genotoxic (i.e., causing damage to cellular DNA) and non-genotoxic (i.e., not involving damage to DNA) mechanisms. Respirable crystalline silica may cause genotoxicity as a result of reactive oxygen species (ROS) produced by activated alveolar macrophages and other lung cells exposed to crystalline silica particles during phagocytosis. ROS have been shown to damage DNA in human lung cells in vitro (see Document ID 1711, pp. 236-239). This genotoxic mechanism is believed to contribute to neoplastic transformation and silica-induced carcinogenesis. ROS is not only produced during the early cellular interaction with crystalline silica but also produced by PMNs (polymorphonuclear leukocytes) and lymphocytes recruited during the inflammatory response to crystalline silica. In addition to genotoxicity contributed by ROS, it is also plausible that reactive molecules on the surface of crystalline silica itself may bind directly to DNA and result in genotoxicity (Document ID 1711, p. 236). It should be noted that the mechanistic evidence summarized above suggests that crystalline silica may cause early genotoxic events that are independent of the advanced chronic inflammatory response and silicosis (Document ID 1473, pp. 391-392).

    Non-genotoxic mechanisms are also believed to contribute to the lung cancer caused by respirable crystalline silica. Phagocytic activation as well as silica-induced cytotoxicity trigger release of the aforementioned ROS, cytokines (e.g., TNFalpha), and growth factors (see Document ID 1711, pp. 233-235). These agents are able to cause cellular proliferation, loss of cell cycle regulation, activation of oncogenes (genes that have the potential to cause cancer), and inhibition of tumor suppressor genes, all of which are non-genotoxic mechanisms known to promote the carcinogenic process. It is plausible that these mechanisms may be involved in silica-induced tumorigenesis. The biopersistence and cytotoxic nature of crystalline silica leads to a cycle of cell death (i.e., cytotoxicity), activation of alveolar macrophages, recruitment of inflammatory cells (e.g., PMNs, leukocytes), and continual release of the non-genotoxic mediators (i.e., ROS, cytokines) able to promote carcinogenesis. The non-

    genotoxic mechanisms caused by early cellular responses (e.g., phagocytic activation, cytotoxicity) are regarded, along with genotoxicity, as important potential pathways that lead to the development of tumors (Document ID 1711, pp. 232-239; 1473, pp. 394-

    396).

    The same non-genotoxic processes that may cause lung cancer from respirable crystalline silica exposure are also believed to lead to chronic inflammation, lung scarring, fibrotic lesions, and eventually silicosis. This would occur when inflammatory cells move from the alveolar space through the interstitium of the lung as part of the clearance process. In the interstitium, respirable crystalline silica-

    laden cells--macrophages and neutrophils--release ROS and TNF-alpha, as well as other cytokines, stimulating the proliferation of fibroblasts (i.e., the major lung cell type in silicosis). Proliferating fibroblasts deposit collagen and connective tissue, inducing the typical scarring that is observed with silicosis. Alternatively, alveolar epithelial cells containing respirable crystalline silica die and may be replaced by fibroblasts due to necrosis of the epithelium. This allows for uninhibited growth of fibroblasts and formation of connective tissue where scarring proliferates (i.e., silicosis). As scarring increases, there is a reduction in lung elasticity concomitant with a reduction of the lung surface area capable of gas exchange, thus reducing pulmonary function and making breathing more difficult (Document ID 0314; 0315). It should be noted that silicosis involves many of the same mechanisms that occur during the early cellular interaction with crystalline silica. Therefore, it is plausible that development of silicosis may also potentially contribute to silica-induced lung cancer. However, the relative contributions of silicosis-dependent and silicosis-independent pathways are not known.

    Although it is clear that exposure to respirable crystalline silica increases the risk of lung cancer in exposed workers (see Section VI, Final Quantitative Risk Assessment and Significance of Risk), some commenters claimed that such exposure cannot cause lung cancer independently of silicosis (i.e., only those workers who already have silicosis can get lung cancer) (Document ID 2307, Attachment A, p. 53). This claim is inconsistent with the credible scientific evidence presented above that genotoxic and non-genotoxic mechanisms triggered by early cellular responses to crystalline silica prior to development of silicosis may contribute to crystalline silica-induced carcinogenesis. OSHA finds, based on its review of all the evidence in the rulemaking record, that workers without silicosis, as well as those with silicosis, are at risk of lung cancer if regularly exposed to respirable crystalline silica at levels permitted under the previous and new PELs. The Agency also emphasizes that, regardless of the mechanism by which respirable crystalline silica exposure increases lung cancer risk, the fact remains that workers exposed to respirable crystalline silica continue to be diagnosed with lung cancer at a higher rate than the general population. Therefore, as discussed in section VI, Final Quantitative Risk Assessment and Significance of Risk, OSHA has met its burden of proving that workers exposed to previously allowed levels of respirable crystalline silica are at significant risk, by one or more of these mechanisms, of serious and life-threatening health effects, including both silicosis and lung cancer.

    2. Relevance of Animal Models to Humans

    Animal data has been used for decades to evaluate hazards and make inferences regarding causal relationships between human health effects and exposure to toxic substances. The National Academies of Science has endorsed the use of well-conducted animal studies to support hazard evaluation in the risk assessment process (Document ID 4052, p. 81) and OSHA's policy has been to rely on such studies when regulating carcinogens. In the case of respirable crystalline silica, OSHA has used evidence from animal studies, along with human epidemiology and other relevant information, to establish that occupational exposure is associated with silicosis, lung cancer, and other non-malignant respiratory diseases, as well as renal and autoimmune effects (Document ID 1711, pp. 261-266). Exposure to various forms of respirable crystalline silica by inhalation and intratracheal instillation has consistently caused lung cancer in rats (IARC, 1997, Document ID 1062, pp. 150-163). These results led IARC and NTP to conclude that there is sufficient evidence in experimental animals to demonstrate the carcinogenicity of crystalline silica in the form of quartz dust. IARC also concluded that there is sufficient evidence in human studies for the carcinogenicity of crystalline silica in the form of quartz or cristobalite.

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    In its pre-hearing comments and post-hearing brief, the ACC noted that increased lung cancer risks from exposure to respirable crystalline silica have not been found in animal species other than rats, and questioned the relevance of the rat model for evaluating potential lung carcinogenicity in humans (Document ID 2307, Attachment A, p. 30; 4209, p. 32). Specifically, the ACC highlighted studies by Holland (1995) and Saffiotti et al. (1996) indicating that bioassays in respirable crystalline silica-exposed mice, guinea pigs, and Syrian hamsters have not found increased lung cancer (Document ID 2307, Attachment A, p. 30, f. 51).

    The ACC proposed that the increased lung cancer risk in respirable crystalline silica-exposed rats is due to a particle overload phenomenon, in which lung clearance of nonfibrous durable particles initiates a non-specific response that results in intrapulmonary lung tumors (Document ID 2307, Attachment A, p. 30, n. 51). Dr. Cox, on behalf of the ACC, citing Mauderly (1997, included in Document ID 3600), Oberdorster (1996, Document ID 3969), and Nikula et al. (1997, included in Document ID 3600), likewise commented that rats are ``uniquely sensitive to particulate pollution, for species-specific reasons that do not generalize to other rodents or mammals, including humans'' (Document ID 2307, Attachment 4, p. 83). OSHA reviewed the three studies referenced by Dr. Cox and notes that two actually appear to support the use of the rat model and the third does not reject it. Mauderly (1997) noted that the rat model was the only one to correctly predict carcinogenicity after inhalation exposure to several types of asbestos, and highlighted the shortcomings of other models, such as those using hamsters, which are highly insensitive to particle-induced lung cancers (article included in Document ID 3600, pp. 1339-1343). While Mauderly (1997) advised caution when using the rat because it is the most sensitive rodent species for lung cancer, he concluded that ``there is evidence supporting continued use of rats in exploration of carcinogenic hazards of inhaled particles,'' and that the other test species are problematic because they provide too many false negatives to be predictive (article included in Document ID 3600, p. 1343). Similarly, Oberdorster (1996), in discussing particle parameters used in the evaluation of exposure-dose-relationships of inhaled particles, stated that ``the rat model should not be dismissed prematurely'' (Document ID 3969, p. 73). Oberdorster (1996) postulated that humans and rats have very similar responses to particle-induced effects when analyzing the exposure-response relationship using particle surface area, rather than particle mass, as the exposure metric. Oberdorster concluded that there simply was not enough known regarding exact mechanisms to reject the model outright (Document ID 3969, pp. 85-87). The remaining paper cited by Dr. Cox, Nikula et al. (1997), evaluated the anatomical differences between primate and rodent responses to inhaled particulate matter and the role of clearance patterns and physiological responses to inhaled toxicants. The study noted that the differences between primate clearance patterns and rat clearance patterns may play a role in the pathogenesis from inhaled poorly soluble particles but did not dismiss the rat model as irrelevant to humans (Nikula, 1997, included in Document ID 3600, pp. 83, 93, 97).

    Thus, OSHA finds that the Mauderly (1997) and Oberdorster (1996) articles generally support the rat as an appropriate model for qualitatively assessing the hazards associated with particle inhalation. OSHA likewise notes that the rat model is a common and well-accepted toxicological model used to assess human health effects from toxicant inhalation (ILSI, 2000, Document ID 3906, pp. 2-9). OSHA evaluated the available studies in the record, both positive and non-

    positive, and believes that it is appropriate to regard positive findings in experimental studies using rats as supportive evidence for the carcinogenicity of crystalline silica. This determination is consistent with that of IARC (Document ID 1473, p. 388) and NTP (Document ID 1164, p. 1), which also regarded the significant increases in incidence of malignant lung tumors in rats from multiple studies by both inhalation and intratracheal instillation of crystalline silica to be sufficient evidence of carcinogenicity in experimental animals and, therefore, to contribute to the evidence for carcinogenicity in humans.

    3. Hypothesis That Lung Cancer Is Dependent on Silicosis

    The ACC asserted in its comments that ``if it exists at all, silica-related carcinogenicity most likely arises through a silicosis pathway or some other inflammation-mediated mechanism, rather than by means of a direct genotoxic effect'' (Document ID 2307, Attachment A, p. 52; 4209, p. 51; 2343, Attachment 1, pp. 40-44). It explained that the ``silicosis pathway'' means that lung cancer stems from chronic inflammatory lung damage, which in turn, ``implies that there is a threshold for any causal association between silica exposure and risk of lung cancer'' (Document ID 2307, Attachment A, pp. 52-53). The ACC went on to state that a mechanism that involves ROS, growth factors, and inflammatory cytokines from alveolar macrophages is ``most consistent'' with development of advanced chronic inflammation (e.g., epithelial hyperplasia, lung tissue damage, fibrosis, and silicosis). According to this hypothesis, silica-related lung cancer is restricted to people who have silicosis (Document ID 2307, Attachment 2, p. 7). Regarding this hypothesis, the ACC concluded, ``this view of the likely mechanism for silica-related lung cancer is widely accepted in the scientific community, including by OSHA's primary source of silica-

    related health risk estimates, Dr. Kyle Steenland. OSHA appears to share this view as well'' (Document ID 2307, Attachment A, p. 54).

    The ACC statement regarding acceptance by OSHA and the scientific community is inaccurate. It implies scientific consensus, as well as OSHA's concurrence, that the chronic inflammation from silicosis is the only mechanism by which crystalline silica exposure results in lung cancer. The ACC has over-simplified and neglected the findings of the mechanistic studies that show activation of phagocytic and epithelial cells to be an early cellular response to crystalline silica prior to chronic inflammation (see Document ID 1711, pp. 234-238). As discussed previously, alveolar macrophage activation leads to initial production of ROS and release of cytokine growth factors that could contribute to silica-induced carcinogenicity through both genotoxic and non-genotoxic mechanisms. The early cellular response does not require chronic inflammation and silicosis to be present, as postulated by the ACC. It is possible that the early mechanistic influences that increase cancer risk may be amplified by a later severe chronic inflammation or silicosis, if such a condition develops. However, as Brian Miller, Ph.D., stated ``this issue of silicosis being a precursor for lung cancer is unanswerable, given that we cannot investigate for early fibrotic lesions in the living, but must rely on radiographs.'' (Document ID 3574, Tr. 31).

    In pre-hearing comments the ACC commented, as proof of silicosis being linked to lung cancer, that fibrosis was linked to adenocarcinomas (Document ID 2307, Attachment A, p. 61). This statement is misleading. As explained

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    earlier, silicosis results from stimulation of fibroblast cells that cause lung fibrosis. Adenocarcinomas, a hallmark tumor type in respirable crystalline silica-induced lung cancer, are tumors that arise not from fibroblasts, but exclusively from lung epithelial cells (IARC, 2012, Document ID 1473, pp. 381-389, 392). These tumors may be linked to the genotoxic and non-genotoxic mechanisms that occur prior to fibrosis, not secondary to the fibrotic process itself.

    OSHA also received some comments that questioned the existence of a direct genotoxic mechanism. Jonathan Borak, M.D., on behalf of the U.S. Chamber of Commerce, commented, ``there is no direct evidence that silica causes cancer by means of a directly DNA-reactive mechanism'' (Document ID 2376, p. 21). Dr. Peter Morfeld, on behalf of the ACC, as well as Peter Valberg, Ph.D., and Christopher M. Long, Sc.D., of Gradient Corporation, on behalf of the U.S. Chamber of Commerce, cited a scientific article by Borm et al. (2011, included in Document ID 3573) which reported finding evidence against a genotoxic mechanism and in favor of a mechanism secondary to chronic inflammation (Document ID 3458, pp. 5-7; 4016, pp. 5-6; 4209, p. 51). Borm et al. (2011, included in Document ID 3573) analyzed 245 published studies from 1996 to 2008 identified using the search terms ``quartz'' and `toxicity'' in conjunction with ``surface,'' ``inflammation,'' ``fibrosis,'' and ``genotoxicity.'' The authors then estimated the lowest dose (in units of micrograms per cell surface area) to consistently induce DNA damage or induce markers of inflammation (e.g., IL-8 upregulation) in in vitro studies. They adjusted the in vitro doses for the lung surface area encountered in vivo and found the crystalline silica dose that produced primary genotoxicity was 60-120 times higher than the dose that produced inflammatory cytokines (Borm et al., 2011, included in Document ID 3573, p. 762). Drs. Valberg and Long concluded that Borm et al. demonstrated that genotoxicity was a secondary response to chronic inflammation, except at very high exposures at which genotoxicity independent of inflammation might occur. They also maintained that lung cancer as a secondary response to chronic inflammation is considered to have a threshold (Document ID 4016, p. 6).

    OSHA reviewed the Borm et al. study (2011, Document ID 3889), and notes several limitations. The authors examined the findings from various genotoxic assays (comet assay, 8-OH-dG, micronucleus test) (Borm et al., 2011, 3889, p. 758). They reported that 40 mug/cm\2\ was the lowest dose in vitro to produce significant direct DNA damage from crystalline silica. This genotoxic dose appears to be principally obtained from a study of a specific quartz sample (i.e., DQ12) in a single human alveolar epithelial cell line (i.e., A549 cells), even though Appendix Table 3 cited in vitro studies using other cells (e.g., fibroblasts) and other types of quartz (e.g., MinUsil) that produced direct genotoxic effects at lower doses (Borm et al., 2011, Document ID 3889, pp. 760, 769-770). This is especially pertinent since Borm et al. state that in vitro systems utilizing single-cell cultures are generally much less sensitive than in vivo systems, especially if attempting to determine oxidative stress-induced effects, since many cell culture systems use reagents that can scavenge ROS (Borm et al. 2011, Document ID 3889, p. 760). There was no indication that the authors accounted for this deficiency. They go on to conclude that their work shows a large-scale variation in hazard across different forms of quartz with regard to effects such as DNA breakage (e.g., genotoxicity) and inflammation (Borm et al. 2011, Document ID 3889, p. 762).

    The extreme variation in response along with reliance on an insensitive genotoxicity test system could overestimate the appropriate genotoxic dose in human lung cells in vivo. In addition, Borm et al. used the dose sufficient to initiate production of an inflammatory cytokine (i.e., IL-8) in the A549 cell-line as the threshold for inflammation. It is not clear that an early cellular response, such as IL-8 production necessarily reflects a sustained inflammatory response. In summary, OSHA finds inconsistencies in this analysis, leaving some questions regarding the study's conclusion that silica induces genotoxicity only as a secondary response to an inflammation-driven mechanism. While the in vitro dose comparisons in this study fail to demonstrate that genotoxicity is secondary to the inflammatory response, the study findings do indicate that cellular responses to crystalline silica that drive inflammation may also lead to tumorigenesis through both genotoxic and non-genotoxic mechanisms.

    Dr. Morfeld, in his hearing testimony on behalf of the ACC, referred to the paper by Borm et al. (2011) as reaching the conclusion that the mechanism of silica-related lung cancer is secondary inflammation-driven genotoxicity. As summarized by the ACC in post-

    hearing comments, he observed that ``there are no crystalline silica particles found in the nucleus of the cells. There is nothing going on with particles in the epithelial cells inside the lung'' (Document ID 4209, p. 52). In hearing testimony, however, Dr. Morfeld acknowledged that the Borm paper had limitations on extrapolating from in vitro to in vivo and cited a study by Donaldson et al. (2009), which discussed some of the limitations and the need for caution in extrapolating from in vitro to in vivo (Document ID 3582, Tr. 2076-2077; 3894, pp. 1-2). In considering this testimony, OSHA notes that the Donaldson et al. (2009) study, which includes the same authors as the Borm et al. (2011) study, acknowledged that direct interaction between respirable crystalline silica and epithelial cellular membranes induces intracellular oxidative stress which is capable of being genotoxic (Document ID 3894, p. 3). This is consistent with the OSHA position as well as the most recent IARC reevaluation of the cancer hazard from crystalline silica dust. As IARC stated in its most recent evaluation of the carcinogenicity of respirable crystalline silica under a section on direct genotoxicity and cell transformation (Document ID 1473, section 4.2.2, pp. 391-393):

    Reactive oxygen species are generated not only at the particle surface of crystalline silica, but also by phagocytic and epithelial cells exposed to quartz particles. . . . Oxidants generated by silica particles and by the respiratory burst of silica-activated phagocytic cells may cause cellular and lung injury, including DNA damage (Document ID 1473, p. 391).

    Given the IARC determination as well as the animal and in vitro studies reviewed herein, OSHA finds that there is no conclusive evidence that silica-related lung cancer only occurs as a secondary response to chronic inflammation, or that silicosis is a necessary prerequisite for lung cancer. Instead, OSHA finds support in the scientific literature for a conclusion that tumors may form through genotoxic as well as non-genotoxic mechanisms that result from respirable crystalline silica interaction with alveolar macrophages and other lung cells prior to onset of silicosis.

    4. Hypothesis That Crystalline Silica-Induced Lung Disease Exhibits a Threshold

    It is well established that silicosis arises from an advanced chronic inflammation of the lung. As noted above, a common hypothesis is that pathological conditions that depend on chronic inflammation may have a threshold. The exposure level at which silica-induced health effects might begin

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    to appear, however, is poorly characterized in the literature (see Section V.I, Comments and Responses Concerning Thresholds for Silica-

    Related Diseases). The threshold exposure level required for a sustained inflammatory response is dependent upon multiple pro- and anti-inflammatory factors that can be quite variable from individual to individual and from species to species (Document ID 3896).

    Discounting or overlooking the evidence that respirable crystalline silica may be genotoxic in the absence of chronic inflammation, Drs. Valberg and Long commented that crystalline silica follows a threshold paradigm for poorly soluble particles (PSPs). PSPs are defined generally as nonfibrous particles of low acute toxicity, which are not directly genotoxic (ILSI, 2000, Document ID 3906, p. 1). Specifically, Drs. Valberg and Long stated:

    Mechanisms whereby lung cells respond to retention of a wide variety of PSPs, including crystalline silica, follow a generally accepted threshold paradigm, where the initiation of a chronic inflammatory response is a necessary step in the disease process, and the inflammatory response does not become persistent until particle retention loads become sufficient to overwhelm lung defense mechanisms. This overall progression from increased but controlled pulmonary inflammation across a threshold exposure that leads to lung damage has been described by a number of investigators (Mauderly and McCunney, 1995; ILSI, 2000; Boobis et al., 2009; Porter et al. 2004) (Document ID 2330, p. 19).

    Similarly, Dr. Cox, in his post-hearing comments, discussed his 2011 article describing a quantifiable exposure-response threshold for lung diseases induced by inhalation of respirable crystalline silica (Document ID 4027, p. 29). Dr. Cox hypothesized the existence of an exposure threshold such that exposures to PSPs, which he described as including titanium dioxide, carbon black, and crystalline silica, must be intense enough and last long enough to disrupt normal homeostasis (i.e., normal cellular functions) and overwhelm normal repair processes. Under the scenario he described, a persistent state of chronic, unresolved inflammation results in a disruption of macrophage and neutrophil ability to clear silica and other foreign particles from the lung (Document ID 1470, pp. 1548-1551, 1555-1556).

    OSHA disagrees with these characterizations about exposure thresholds because, among other reasons, respirable crystalline silica is not generally considered to be in the class of substances defined as PSPs.\7\ Specifically, regarding the comments of Drs. Valberg and Long, OSHA notes that the two cited documents (Mauderly and McCunney, 1995, and ILSI, 2000) summarizing workshops on PSPs did not include crystalline silica in the definition of PSP and the lung ``overload'' concept, instead highlighting silica's cytotoxic and genotoxic mechanisms. Mauderly and McCunney (1995) stated, ``it is generally accepted that the term `overload' should be used in reference to particles having low cytotoxicity, which overload clearance mechanisms by virtue of the mass, volume, or surface area of the deposited material (Morrow, 1992)'' (p. 3, article cited in Document ID 2330, p. 19). Mauderly specifically cited quartz as a cytotoxic particle that may fall outside this definition (p. 24, article cited in Document ID 2330, p. 19). The International Life Science Institute's (ILSI) Workshop Report (2000) intended only to address particles of ``low acute toxicity,'' such as carbon black, coal dust, soot, and titanium dioxide (Document ID 3906, p. 1). OSHA believes that the cytotoxic nature of crystalline silica would exclude it from the class of rather nonreactive, non-toxic particles mentioned above. Therefore, the Agency concludes that most scientific experts would not include crystalline silica in the class of substances known as PSPs, nor intend for findings regarding PSPs to be extrapolated to crystalline silica.

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    \7\ OSHA notes that crystalline silica has many mechanistic features in common with asbestos. They are both durable, biopersistent mineral forms where there is sufficient evidence of an association with lung cancer (i.e., IARC Group 1 carcinogens), chronic lung inflammation, and severe pulmonary fibrosis (i.e., silicosis and asbestosis) in humans. Like crystalline silica, asbestos has reactive surfaces or other physiochemical properties able to hinder phagocytosis and activate macrophages to release reactive oxygen species, cytokines, and growth factors that lead to DNA damage, cytotoxicity, cell proliferation and an inflammatory response responsible for the disease outcomes mentioned above (see IARC 2012, Document ID 1473, pp. 283-290). Crystalline silica and asbestos can trigger phagocytic activation well below the high mass burdens required to ``overload'' the lung and impair pulmonary clearance that is typical of carbon black and other low acute-

    toxicity PSPs.

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    During the public hearing, OSHA questioned Dr. Morfeld about the relevance of the rat overload response and whether he considered crystalline silica to be like other PSPs such as carbon black. Dr. Morfeld replied that he was well aware of the literature and indicated that crystalline silica was not considered one of the PSPs (specifically not like carbon black) that these reports reviewed (Document ID 3582, Tr. 2072-2074). OSHA also notes a report of the European Centre for Ecotoxicology and Toxicology of Chemicals (ECETOC), which was cited by the ACC (Document ID 4209, p. 32) and stated that ``particles exhibiting significant surface related (cyto)toxicity like crystalline silica (quartz) and/or other specific toxic properties do not fall under this definition of PSPs'' (Document ID 3897, p. 5).

    Respirable crystalline silica differs from PSPs because it does not require particle overload to induce the same response typical of PSPs. ``Overload'' refers to the consequence of exposure that results in a retained lung burden of particles that is greater than the steady-state burden predicted from deposition rates and clearance kinetics (Document ID 4174, p. 20). This is a result of a volumetric over-exposure of dust in the lung, which overwhelms macrophage function. Respirable crystalline silica does not operate on this mechanism since macrophage function is inhibited by the cytotoxic nature of respirable crystalline silica rather than a volumetric overload (Oberdorster, 1996, Document ID 3969). Therefore, respirable crystalline silica does not require particle overload to induce the same response. Studies have found that the respirable crystalline silica exposure levels required to induce tumor formation in some animal studies are similar to those observed in human studies, whereas studies involving PSPs tend to show responses at much higher levels of exposure (Muhle et al., 1991, Document ID 1284; Muhle et al., 1995, 0378; Saffiotti and Ahmed, 1995, 1121).

    A study by Porter et al. (2004) demonstrated that pulmonary fibrosis induction does not require silica particle overload (Document ID 0410, p. 377). The ACC cited this study in its post-hearing brief, stating, ``Porter . . . noted that the response of the rat lung to inhaled crystalline silica particles is biphasic, with a below-

    threshold phase characterized by increased but controlled pulmonary inflammation'' (Document ID 4209, p. 52). OSHA notes that this biphasic response is due in part to the cytotoxic nature of crystalline silica, which disrupts macrophage clearance of silica particles leading to a chronic inflammatory response at less than overload conditions. While there are some mechanistic similarities, OSHA believes that the argument that crystalline silica operates on the basis of lung overload is erroneous and based on false assumptions that ignore toxicological properties unique to crystalline silica, such as cytotoxicity and the generation of intracellular ROS (Porter et al., 2002, Document ID 1114; Porter et al., 2004, 0410). As previously discussed, the generation of ROS could

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    potentially damage cellular DNA by a genotoxic mechanism that may not exhibit a threshold.

    OSHA thoroughly reviewed Dr. Cox's 2011 article (Document ID 1470), in which he proposed a threshold for crystalline silica, in its Supplemental Literature Review (Document ID 1711, Attachment 1, pp. 37-

    39). OSHA concluded that the evidence used to support Cox's assertion that the OSHA PEL was below a threshold for lung disease in humans was not supported by the evidence presented (Document ID 1470, p. 1543; 1711, Attachment 1). Specifically, Cox (2011) modelled a threshold level for respirable crystalline silica using animal studies of PSPs. This approach, according to the ILSI report (2000) and ECETOC report (2013), is clearly not appropriate since the cytotoxic nature of crystalline silica is not consistent with the low-toxicity PSPs (Document ID 3906, p. 1; 3897, p. 5). Dr. Cox (2011) categorized crystalline silica incorrectly as a PSP and ignored the evidence for cytotoxicity and genotoxicity associated with crystalline silica. He further failed to consider or include studies indicating a tumor response at exposure levels below that leading to an excessive chronic inflammatory response, such as Porter et al. (2002) and Muhle et al. (1995) (Document ID 1114; 0378). Thus, OSHA considers the threshold model designed by Dr. Cox (2011, Document ID 1470) and referenced by Drs. Valberg and Long (Document ID 2330) to be contradicted by the best available evidence regarding the toxicological properties of respirable crystalline silica. Although OSHA acknowledges the possible existence of a threshold for an inflammatory response, the Agency believes that the threshold is likely much lower than that advocated by industry representatives such as the ACC and the Chamber of Commerce (see Section V.I, Comments and Responses Concerning Thresholds for Silica-

    Related Diseases).

    OSHA concludes that a better estimate of a threshold effect for inflammation and carcinogenesis was done by Kuempel et al. (2001, Document ID 1082). These researchers studied the minimum human exposures necessary to achieve adverse functional and pathological evidence of inflammation. They employed a physiologically-based lung dosimetry model, included more relevant studies, and considered a genotoxic effect for lung cancer (Kuempel et al., 2001, Document ID 1082; see 1711, pp. 231-232). Briefly, Kuempel et al. evaluated both linear and nonlinear (threshold) models and determined that the average minimum critical quartz lung burden (Mcrit) in rats associated with reduced pulmonary clearance and increased neutrophil inflammation was 0.39 mg quartz/g lung tissue. Mcrit is based on the lowest observed adverse effect level in a study in rats (Kuempel, 2001, Document ID 1082, pp. 17-23). A human lung dosimetry model, developed from respirable coal mine dust and quartz exposure and lung burden data in UK coal miners (Tran and Buchanan, 2001, Document ID 1126), was then used to estimate the human-equivalent working lifetime exposure concentrations associated with lung doses. An 8-hour time-weighted average (TWA) concentration of 0.036 mg/m\3\ (36 mug/

    m\3\) over a 45-year working lifetime was estimated to result in a human-equivalent lung burden to the average Mcrit in rats (Document ID 1082, pp. 24-26). OSHA peer reviewer Gary Ginsburg, Ph.D., summarized, ``the Kuempel et al. (2001, 2001b) rat analysis of lung threshold loading and extrapolation to human dosimetry leads to the conclusion that in the median case this threshold is approximately 3 times below the current now former OSHA PEL'' (Document ID 3574, pp. 23). This estimated threshold would be significantly below the final PEL of 50 mug/m\3\.

    In pre-hearing comments, ACC stated that some health organizations suggested a silicosis-dependent threshold exists for lung cancer (ACC, Document ID 2307, Attachment A, pp. 60-62). Specifically, ACC cited Environment and Health Canada as stating:

    Although the mechanism of induction for the lung tumours has not been fully elucidated, there is sufficient supportive mode of action evidence from the data presented to demonstrate that a threshold approach to risk assessment is appropriate based on an understanding of the key events in the pathogenesis of crystalline silica induced lung tumours (pp. 49-51 as cited by ACC, Document ID 2307, p. 62).

    In addition to the statement submitted by ACC, Environment and Health Canada also stated that:

    While there is sufficient evidence to support key events in a threshold mode of action approach for lung tumours, the molecular mechanism is still not fully elucidated. Also, despite the fact that the effects seen in rats parallel the effects observed in human studies, additional mechanistic studies could further clarify why lung tumours are not seen in all experimental animals . . . Thus, the question of whether silica exposure, in the absence of silicotic response, results in lung tumours remains unanswered.'' (pp. 51-52 as cited by ACC, Document ID 2307, pp. 59-61).

    It should be noted that the Environment and Health Canada report was to determine general population risk of exposure to respirable crystalline silica as a fraction of PM10. Environment and Health Canada found that levels 0.1-2.1 mug/m\3\ respirable crystalline silica were sufficiently protective for the general population because they represented a margin of exposure (MOE) 23-500 times lower than the 50 mug/m\3\ quartz concentration associated with silicosis in humans (pp. 50-51 as cited by ACC, Document ID 2307, pp. 59-61).

    A report by Mossman and Glenn (2013) reviewed the findings from several international OEL setting panels (Document ID 4070). The report cites findings from the European Commission's Scientific Committee on Occupational Exposure Limits for respirable crystalline silica. The findings ``acknowledged a No Observed Adverse Exposure Level (NOAEL) for respirable crystalline silica in the range below 0.020 mg/m\3\, but stated that a clear threshold for silicosis could not be identified'' (Mossman and Glen, 2013; Document ID 4070, p. 655). The report went on to state that SCOEL (2002) recommended that an OEL should lie below 50 mug/m\3\ (Document ID 4070, p. 655). Therefore, even if silica-

    induced lung cancer were limited only to a mechanism that involved an inflammation-dependent threshold, OSHA concludes that exposure threshold would likely be lower than the final PEL.

    5. Renal Disease and Autoimmunity

    While mechanistic data is limited, other observed health effects from inhalation of respirable crystalline silica include kidney and autoimmune effects. Translocation of particles through the lymphatic system and filtration through the kidneys may induce effects in the immune and renal systems similar to the types of changes observed in the lung (Miller, 2000, Document ID 4174, pp. 40-45). A review of the available literature indicates that respirable crystalline silica most likely induces an oxidative stress response in the renal and immune cells similar to that described above (Donaldson et al., 2009, Document ID 3894).

    6. Conclusion

    OSHA has reviewed and responded to the comments received on the mechanistic studies of respirable crystalline silica-induced lung cancer and silicosis, as well as comments that the mechanistic data imply the existence of an exposure threshold. OSHA concludes that: (1) Lung cancer likely results from both genotoxic and non-genotoxic mechanisms that arise during early cellular responses as well

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    as during chronic inflammation from exposure to crystalline silica; (2) there is not convincing data to demonstrate that silicosis is a prerequisite for lung cancer; (3) experimental studies in rats are relevant to humans and provide supporting evidence for carcinogenicity; (4) crystalline silica does not behave like PSPs such as titanium dioxide; and (5) any threshold for an inflammatory response to respirable crystalline silica is likely several times below the final PEL of 50 mug/m\3\. Thus, the best available evidence on this issue supports OSHA's findings that respirable crystalline silica increases the risk of lung cancer in humans, even in the absence of silicosis, and that lung cancer risk can be increased by exposure to crystalline silica at or below the new OSHA PEL of 50 mug/m\3\.

    I. Comments and Responses Concerning Thresholds for Silica-Related Diseases

    In this section, OSHA discusses comments focused on the issue of exposure-response thresholds for silica exposure. In the comments received by OSHA on this topic, an exposure-response ``threshold'' for silica exposure typically refers to a level of exposure such that no individual whose exposure is below that level would be expected to develop an adverse health effect. Commenters referred to thresholds both in terms of concentration and cumulative exposure (i.e., a level of cumulative exposure below which an individual would not be expected to develop adverse health effects). In addition to individual thresholds, some commenters referred to a ``population average threshold,'' that is, the mean or median value of individual thresholds across a population of workers. There is significant scientific controversy over whether any such thresholds exist for silicosis and lung cancer, as well as the cumulative exposure level or concentration at which a threshold effect may occur and whether certain statistical modeling approaches can be used to identify threshold effects.

    OSHA has reviewed the evidence in the record pertaining to thresholds, and has determined that the best available evidence supports the Agency's use of non-threshold exposure-response models in its risk assessments for silicosis and lung cancer. The voluminous scientific record accrued by OSHA in this rulemaking supports lowering the existing PEL to 50 mug/m\3\. Rather than indicating a threshold of risk that starts above the previous general industry PEL, the weight of this evidence, including OSHA's own risk assessment models, supports a conclusion that there continues to be significant, albeit reduced, risk at the 50 mug/m\3\ exposure limit. OSHA's evaluation of the best available evidence on thresholds indicates that there is considerable uncertainty about whether there is any threshold below which silica exposure causes no adverse health effects; but, in any event, the weight of evidence supports the view that, if there is a threshold of exposure for the health effects caused by respirable crystalline silica, it is likely lower than the new PEL of 50 mug/m\3\. Commenters have not provided convincing evidence of a population threshold (e.g., an exposure level safe for all workers) above the revised PEL. In addition, OSHA's final risk assessment demonstrates that achieving this limit--which OSHA separately concludes is overall the lowest feasible level for silica-generating operations--will result in significant reductions in mortality and morbidity from occupational exposure to respirable crystalline silica.

    1. Thresholds--General

    In the Preliminary Quantitative Risk Assessment (QRA) (Document ID 1711, pp. 275, 282-285), OSHA reviewed evidence on thresholds from a lung dosimetry model developed by Kuempel et al. (2001, Document ID 1082) and from epidemiological analyses conducted by Steenland and Deddens (2002, Document ID 1124). As discussed in the Preliminary QRA, Kuempel et al. (2001) used kinetic lung models for both rats and humans to relate lung burden of crystalline silica and estimate a minimum critical lung burden (Mcrit) of quartz above which particle clearance begins to decline and lung inflammation begins to increase (early steps in the process of developing silica-related disease). The Mcrit would be achieved by a human equivalent airborne exposure to 36 mug/m\3\ for 45 years, based on the authors' rat-to-

    human lung model conversion. Exposures below this level would not lead to an excess lung cancer risk in the average individual, if it were assumed that cancer is strictly a secondary response to persistent inflammation. OSHA notes, however, that if some of the silica-related lung cancer risk occurs as a result of direct genotoxicity from early cellular interaction with respirable silica particles, then this threshold value may not be applicable. Since silicosis is caused by persistent lung inflammation, this exposure level could be viewed as a possible average threshold level for that disease as well (Document ID 1711, p. 284). As 36 mug/m\3\ is well below the previous general industry PEL of 100 mug/m\3\ and below the final PEL of 50 mug/

    m\3\, the Kuempel et al. study showed no evidence of an exposure-

    response threshold high enough to impact OSHA's choice of PEL.

    Steenland and Deddens (2002, Document ID 1124) examined a pooled lung cancer study originally conducted by Steenland et al. (2001a). They found that a threshold model based on the log of cumulative dose (15-year lag) fit better than a no-threshold model, with the best threshold at 4.8 log mg/m\3\-days (representing an average exposure of 10 mug/m\3\ over a 45-year working lifetime). OSHA preliminarily concluded that, in the Kuempel et al. (2001) study and among the studies evaluated by Steenland et al. (2001a) in the pooled analysis, there was no empirical evidence of a threshold for lung cancer in the exposure range represented by the previous and final PELs (i.e., at 50 mug/m\3\ or higher) (Document ID 1711, pp. 275, 284). Thus, based on these two studies, workers exposed at or below the new PEL of 50 mug/

    m\3\ over a working lifetime still face a risk of developing silicosis and lung cancer because their exposure would be above the supposed exposure threshold.

    In its prehearing comments, the ACC argued that OSHA's examination of the epidemiological evidence, along with animal studies and mechanistic considerations, ``has not shown that reducing exposures below currently permitted exposure levels would create any additional health benefits for workers. OSHA's analysis and the studies on which it relies have not demonstrated the absence of an exposure threshold above 100 mug/m\3\ for the various adverse health effects considered in the QRA'' (Document ID 2307, Attachment A, p. 26; also 2348, Attachment 1, p. 33). According to the ACC, an exposure threshold above OSHA's previous general industry PEL of 100 mug/m\3\ means that workers exposed below that level will not get sick, negating the need to lower the PEL (Document ID 2307, Attachment A, p. 91).

    Members of OSHA's peer review panel for the Review of Health Effects Literature and Preliminary Quantitative Risk Assessment (Document ID 1711) rejected the ACC's comments as unsupportable. Peer reviewer Mr. Bruce Allen stated: ``it is essentially impossible to distinguish between dose-response patterns that represent a threshold and those that do not'' in epidemiological data (Document ID 3574, p. 8). Peer reviewer Dr. Kenneth Crump similarly commented:

    OSHA is on very solid ground in the Preliminary QRA's statement that ``available information cannot firmly establish a threshold exposure for silica-

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    related effects'' . . . the hypothesis that a particular dose response does not have a threshold is not falsifiable. Similarly, the hypothesis that a particular dose response does have a threshold is not falsifiable (Document ID 3574, p. 17).

    Dr. Cox, representing the ACC, agreed with Dr. Crump that ``it's impossible to prove a negative, empirically . . . you could never rule out that possibility'' of a threshold at a low level of exposure (Document ID 3576, Tr. 402). However, he contended that it is possible to rule out a threshold in the higher-level range of observed exposures based on observed illness: ``I think that there are plenty of chemicals for which the hypothesis of a threshold existing at or above current standards could be ruled out because you see people getting sick at current levels'' (Document ID 3576, Tr. 403). Other commenters stated their belief that workers recently diagnosed with silicosis must have had exposures above the previous general industry PEL and, based on this supposition, concluded that OSHA has not definitively proven risk to workers exposed below the previous general industry PEL (Document ID 4224, pp. 2-5; Tr. 3582, pp. 1951-1963).

    OSHA agrees with Dr. Cox that observation of workers ``getting sick at current levels'' can rule out a threshold effect at those levels. As is discussed below, there is evidence that workers exposed to silica at cumulative or average exposure levels permitted under the previous PELs have become ill and died as a result of their exposure. OSHA thus strongly disagrees with any implication from commenters that the Agency should postpone reducing a PEL until it has extensive documentation of sick and dying workers to demonstrate that the current PEL is not sufficiently protective (see Section II, Pertinent Legal Authority, and Section VI, Final Quantitative Risk Assessment and Significance of Risk).

    The ACC's and Chamber's comments on this issue essentially argue that the model OSHA used to assess risk was inadequate to assess whether a threshold of risk exists and, if one does exist, at what level (Document ID 2307, Attachment A, pp. 52-65; 2376, pp. 20-22; 2330, pp. 17-21). According to OSHA peer reviewer Dr. Crump, however, the analytical approach taken by OSHA in the Preliminary QRA was appropriate. Considering the inherent limitations of epidemiological data:

    an attempt to distinguish between threshold and non-threshold dose responses is not even a scientific exercise . . . The best that can be done is to attempt to place bounds on the amount of risk at particular exposures consistent with the available data, which is what OSHA had done in their risk assessment (Document ID 3574, p. 17).

    A further source of uncertainty in investigating thresholds was highlighted by Dr. Mirer, on behalf of the AFL-CIO (Document ID 3578, Tr. 988-989) and by peer reviewer Dr. Andrew Salmon, who stated:

    many of the so-called thresholds seen in epidemiological studies represent thresholds of observability rather than thresholds of disease incidence . . . studies (and anecdotal observations) with less statistical power and shorter post-exposure followup (or none) will necessarily fail to see the less frequent and later-appearing responses at lower doses. This creates an apparent threshold which is higher in these studies than the apparent threshold implied by studies with greater statistical power and longer follow-up (Document ID 3574, p. 37).

    Peer reviewer Dr. Gary Ginsberg suggested that, recognizing these inherent limitations, OSHA should characterize the body of evidence and argument surrounding thresholds by discussing the following factors related to whether a threshold for silica-related health effects exists at exposure levels above the previous general industry PEL:

    the choices relative to the threshold concept for the silica dose response . . . including specific dose response datasets that are consistent with a linear or a threshold-type model, if a threshold seems likely, where was it seen relative to the current and proposed PEL, and a general discussion of mechanism of action, measurement error and population variability as concepts that can help us understand silica dose response for cancer and non-cancer endpoints (Document ID 3574, p. 24).

    Following Dr. Ginsberg's suggestion, OSHA has, in its final health and risk analysis, considered the epidemiological evidence relevant to possible threshold effects for silicosis and lung cancer. As discussed below, first in ``Thresholds--Silicosis and NMRD'' and then in ``Thresholds--Lung Cancer,'' OSHA has carefully considered comments about statistical methods, exposure measurement uncertainty, and variability as they pertain to threshold effects. The discussion addresses the epidemiological evidence with respect to both cumulative and concentration thresholds. For reference, a working lifetime (45 years) of exposure to silica at the previous general industry PEL (100 mug/m\3\) and the final PEL (50 mug/m\3\) yield cumulative exposures of 4.5 mg/m\3\-yrs and 2.25 mg/m\3\-yrs, respectively. Other sections with detailed discussions pertinent to threshold issues include Section V.H, Mechanisms of Silica-Induced Adverse Health Effects, and Section V.K, Comments and Responses Concerning Exposure Estimation Error and ToxaChemica's Uncertainty Analysis.

    2. Thresholds--Silicosis and NMRD

    OSHA has determined that the studies most relevant to the threshold issue in this rulemaking are those of workers who have cumulative exposures or average exposure concentrations below the levels associated with the previous general industry PEL (100 mug/m\3\, or cumulative exposure of 4.5 mg/m\3\-yrs). Contrary to comments that OSHA only relied on studies involving exposures far above the levels of interest to OSHA in this rulemaking, and then extrapolated exposure-

    response relationships down to relevant levels (e.g., Document ID 2307, Attachment A, pp. 94-95; 4226, p. 2), a number of silicosis studies included workers who were exposed at levels close to or below the previous OSHA PEL for general industry. For example, four of the six cohorts of workers in the pooled silicosis mortality risk analysis conducted by Mannetje et al. (2002) had median cumulative exposures below 2.25 mg/m\3\-yrs., and three had median silica concentrations below 100 mug/m\3\ (Mannetje et al., 2002, Document ID 1089, p. 724). Other silicosis studies with significant numbers of relatively low-

    exposed workers include analyses of German pottery workers (Birk et al., 2009, Document ID 4002, Attachment 2; Mundt et al., 2011, 1478; Morfeld et al., 2013, 3843), Vermont granite workers (Attfield and Costello, 2004, Document ID 0285; Vacek et al., 2011, 1486), and industrial sand workers (McDonald et al., 2001, Document ID 1091; Hughes et al., 2001, 1060; McDonald et al., 2005, 1092). In this section, OSHA will discuss each of them in relationship to whether they suggest the existence of a threshold above 100 mug/m\3\, the previous PEL for general industry.

    a. Mannetje et al. Pooled Study and Related Analyses

    Mannetje et al. (2002b, Document ID 1089) estimated excess lifetime risk of silicosis based on six of the ten cohorts that were part of the IARC multi-center exposure-response study (Steenland et al., 2001a, Document ID 0452). The six cohorts were U.S. diatomaceous earth (DE) workers, Finnish granite workers, U.S. granite workers, U.S. industrial sand workers, U.S. gold miners, and Australian gold miners. Together, the cohorts included 18,634 subjects and 170 silicosis deaths. All cohorts except the Finnish granite workers and Australian gold miners had significant numbers of workers with median

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    cumulative and/or average exposures below the levels associated with OSHA's previous general industry PEL. Checking for nonlinearities in their exposure-response model, Mannetje et al. found that a five-knot cubic spline model (which allows for deviations, such as thresholds, from a linear relationship) did not fit the data better than the linear model used in their main analysis. The result of this attempt to check for nonlinearities suggests that there is no threshold effect in the relationship between cumulative silica exposure and silicosis risk in the study. Significantly, NIOSH stated that the results of Mannetje et al.'s analysis ``suggest the absence of threshold at the lowest cumulative exposure analyzed . . . in fact, the trend for silicosis mortality risk extends down almost linearly to the lowest cumulative exposure stratum'', in which ``the average cumulative exposure is the equivalent of 45 years of exposure at 11.1 mug/m\3\ silica'' (Document ID 4233, pp. 34-35). This level is significantly below the new OSHA PEL of 50 mug/m\3\.

    As discussed in Section V.K, Comments and Responses Concerning Exposure Estimation Error and ToxaChemica's Uncertainty Analysis, OSHA commissioned Drs. Kyle Steenland and Scott Bartell to examine the potential effects of exposure measurement error on the mortality risk estimates derived from the pooled studies of lung cancer (Steenland et al., 2001, Document ID 0452) and silicosis (Mannetje et al., 2002b, Document ID 1089). Their analysis of the pooled data, using a variety of standard statistical techniques (e.g., regression analysis), also found the data either consistent with the absence of a threshold or inconsistent with the existence of a threshold \8\ (Document ID 0469). Thus, neither Mannetje et al. nor Steenland and Bartell's analyses of the pooled cohorts suggested the existence of a cumulative exposure threshold effect; in fact, they suggested the absence of a threshold. Given the predominance in these studies of cohorts where at least half of the workers had cumulative exposures below 4.5 mg/m\3\-yrs, OSHA believes these results constitute strong evidence against an exposure threshold above the level of cumulative exposure resulting from long-

    term exposure at the previous PEL of 100 mug/m\3\.

    ---------------------------------------------------------------------------

    \8\ This analysis included a log-cumulative logistic regression model, as well as a categorical analysis and five-knot restricted cubic spline analysis using log-cumulative exposure. Had the spline analysis shown a better-fitting model with a flat exposure-response at low cumulative exposure levels, it might have suggested a threshold effect for cumulative exposure. However, no significant difference was observed between the parametric model and the two other models, which had greater flexibility in the shape of the exposure-response (Document ID 0469, p. 50, Figure 5).

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    b. Vermont Granite Workers

    As discussed in the Supplemental Literature Review of Epidemiological Studies, Vacek et al. (2011, Document ID 1486) examined exposures from 1950 to 1999 for a group of 7,052 workers in the Vermont granite industry (Document ID 1711, Attachment 1, pp. 2-5). The exposure samples show relatively low exposures for the worker population. For the period 1950 to 2004, Verma et al. (2012), who developed the job exposure matrix used by Vacek et al., estimated that average exposure concentrations in 21 of 22 jobs were below 100 mug/

    m\3\, and 11 of the 22 job classes were at 50 mug/m\3\ or below. The remaining job category, laborer, had an estimated average exposure concentration of exactly 100 mug/m\3\ (Verma et al., 2011, Document ID 1487, p. 75).

    Six of the 5,338 cohort members hired in or after 1940, when Vermont's dust control program was in effect, were identified as having died of silicosis by the end of the follow-up period (Vacek et al., Document ID 1486, p. 314). The frequency of observed silicosis mortality in the population is significant by OSHA standards (1.1 per 1,000 workers), and may be underestimated due to under-reporting of silicosis as a cause of death (see Section V.E, Comments and Responses Concerning Surveillance Data on Silicosis Morbidity and Mortality). This observed silicosis mortality shows that deaths from silicosis occurred among workers hired after silica concentrations were reduced below OSHA's previous general industry PEL. It therefore demonstrates that a threshold for silicosis above 100 mug/m\3\ is unlikely.

    In terms of morbidity, Graham et al.'s study of radiographic evidence of silicosis among retired Vermont granite workers found silicosis in 5.7 percent of workers hired after 1940 (equivalent to 57/

    1,000 workers) (Graham et al., 2004, Document ID 1031, p. 465). OSHA concludes that these studies of low-exposed workers in the Vermont granite industry show significant risk of silicosis--both mortality and morbidity--at concentrations below the previous PELs. These studies also indicate that a threshold at an exposure concentration significantly above the previous PEL for general industry, as posited by industry representatives, is unlikely.

    c. U.S. Industrial Sand Workers

    In an exposure-response study of 4,027 workers in 18 U.S. industrial sand plants, Steenland and Sanderson (2001) reported that approximately three-quarters of the workers with complete work histories had cumulative exposures below 1.28 mg/m\3\-yrs, well below the cumulative exposure of 2.25 mg/m\3\-yrs associated with a working lifetime of exposure at the final PEL of 50 mug/m\3\ (Document ID 0455, p. 700). The study identified fourteen deaths from silicosis and unspecified pneumoconiosis (~3.5 per 1,000 workers) (Document ID 0455, p. 700), of which seven occurred among workers with cumulative exposures below 1.28 mg/m\3\-yrs. As with other reports of silicosis mortality, this figure may underestimate the true rate of silicosis mortality in this worker population.

    Hughes et al. (2001) reported 32 cases of silicosis mortality in a cohort of 2,670 workers at nine North American industrial sand plants (~12 per 1,000) (Document ID 1060, p. 203). The authors developed a job-exposure matrix based on exposure samples collected by the companies and by MSHA between 1973 and 1994, along with the 1946 exposure survey used by Steenland and Sanderson (2001, Document ID 0455; 2307, Attachment 7, p. 6). Job histories were available for 29 workers who died of silicosis. Of these, fourteen had estimated cumulative exposure less than or equal to 5 mg/m\3\-yrs, and seven had cumulative exposures less than or equal to 1.5 mg/m\3\-yrs (Document ID 1060, p. 204). Both studies clearly showed silicosis risk among workers whose cumulative exposures were comparable to those that workers could experience under the final PEL (Document ID 0455, p. 700; 1060, p. 204), indicating that a threshold above this level of cumulative exposure is unlikely.

    d. German Porcelain Workers

    A series of papers by Birk et al. (2009, Document ID 4002, Attachment 2; 2010, Document ID 1467), Mundt et al. (2011, Document ID 1478), and Morfeld et al. (2013, Document ID 3843) examined silicosis mortality and morbidity in a population of over 17,000 workers in the German porcelain industry. Cohort members' annual average concentrations of respirable quartz dust were reconstructed from detailed work histories and dust measurements collected in the industry from 1951 onward (Birk et al., 2009, Document ID 4002, Attachment 2, pp. 374-375). Morfeld et al. observed 40 silicosis morbidity cases (ILO profusion category 1/1 or greater), and noted that additional

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    follow-up of the cohort might be necessary due to the long latency period of silicosis (2013, Document ID 3843, p. 1032).

    Follow-up time is a critical factor for detection of silicosis, which has a typical latency of 20-30 years (see Morfeld et al., 2013, Document ID 3843, p. 1028). As stated in Section V.C, Summary of the Review of Health Effects Literature and Preliminary QRA, the disease latency for silicosis can extend to around 30 years. Follow-up was extremely limited in the German porcelain workers silicosis morbidity analysis, with a mean of 7.5 years of follow up for the study population (Document ID 3843). Despite the limited follow-up time, the cohort showed evidence of silicosis morbidity among low-exposed workers: 17.5 percent of cases occurred among workers whose highest average silica exposure in any year (``highest annual'') was estimated by the authors to be less than 250 mug/m\3\, and 12.5 percent of cases occurred among workers whose highest annual silica exposure was estimated at less than 100 mug/m\3\ (Document ID 3843).

    The lead author of the study, Dr. Peter Morfeld, testified at the public hearings on behalf of the ACC Crystalline Silica Panel. In his post-hearing comments, Dr. Morfeld stated that ``mechanistic considerations imply that we should not expect to see a threshold for cumulative exposure'' in silicosis, but that the question of whether a threshold concentration level may exist remains (Document ID 4003, p. 3). The study by Morfeld et al. ``focused on the statistical estimation of a concentration threshold . . . and simultaneously took into account the cumulative exposure to respirable crystalline silica dust as a driving force of the disease'' (Document ID 4003, p. 3). Morfeld et al. applied a technique developed by Ulm et al. (1989, 1991) to estimate a concentration threshold. In this method a series of candidate exposure concentration values are subtracted from the estimated annual mean concentration data. Using the recalculated exposure estimates for the study population, regression analyses for each candidate are run to identify the best fitting model, using the Akaike Information Criterion (AIC) to evaluate model fit (Document ID 3843, p. 1029). According to Morfeld, the best fitting model in their study estimated a threshold concentration of 250 mug/m\3\ (AIC = 488.3) with a 95 percent confidence interval of 160 to 300 mug/m\3\. A second model with very similar fit (AIC = 488.8) estimated a threshold concentration of 200 mug/m\3\ with a 95 percent confidence interval of 57 mug/m\3\ to 270 mug/m\3\. A third model with a poorer fit (AIC=490.6) estimated a threshold concentration of 80 mug/

    m\3\ with a 95 percent confidence interval of 0.2 mug/m\3\ to 210 mug/m\3\ (Document ID 3843, Table 3, p. 1031).

    In the Final Peer Review Report, Dr. Crump stated that Morfeld et al.'s modeling approach, like ``all such attempts statistically to estimate a threshold,'' is ``not reliable because the threshold estimates so obtained are highly unstable'' (Document ID 3574, p. 17). Dr. Morfeld's co-author, Dr. Mundt, stated in the public hearings:

    I'll be the first one to tell you there is a lot of imprecision and, therefore, say confidence intervals or uncertainty should be respected, and that the--I'm hesitant to just focus on a single point number like the .25 250 mug/m\3\, and prefer that you encompass the broader range that was reported in the Morfeld, on which I was an author and consistently brought this point to the table (Document ID 3577, Tr. 645).

    NIOSH submitted post-hearing comments on the analysis in Morfeld et al. (2013). NIOSH pointed out that the exposure measurements in the analysis were based on German dust samplers, which for pottery have been shown to collect approximately twice as much dust as U.S. samplers. Therefore, ``when Dr. Morfeld cited 0.15 mg/m\3\ (150 mug/

    m\3\) as the lower 95% confidence limit for the threshold, that would convert to 0.075 mg/m\3\ (75 mug/m\3\) in terms of equivalent measurements made with a U.S. sampler'' (Document ID 4233, p. 21). Similarly, the U.S. equivalent of each of the other threshold estimates and confidence limits presented in Morfeld et al.'s analysis would be about half the reported exposure levels. NIOSH also commented that Morfeld et al.'s analysis appears to be consistent with both threshold and non-threshold models (Document ID 4233, p. 55). Furthermore, NIOSH observed that Morfeld et al. did not account for uncertainty in the values of one of their model parameters (egr); therefore their reported threshold confidence limits of 0.16-0.30 are too narrow (Document ID 4233, p. 56). More generally, NIOSH noted that Morfeld et al. did not quantitatively evaluate how uncertainty in exposure estimates may have impacted the results of the analysis; Morfeld agreed that he had not performed a ``formal uncertainty analysis'' (Document ID 4233, p. 58; 3582, Tr. 2078-2079). NIOSH concluded, ``it is our firm recommendation to discount results based on the model specified in Morfeld et al. Eq. 3 . . . including all results related to a threshold'' (Document ID 4233, p. 58). OSHA has evaluated NIOSH's comments on the analysis and agrees that the issues raised by NIOSH raise serious questions about Morfeld et al.'s conclusions regarding a silica threshold.

    OSHA's greater concern with Dr. Morfeld's estimate of 250 mug/

    m\3\ as a threshold concentration for silicosis is the fact that a substantial proportion of workers with silicosis in Dr. Morfeld's study had no estimated exposure above the threshold suggested by the authors; this threshold was characterized by commenters, including the Chamber of Commerce (Chamber), as a concentration ``below which the lung responses did not progress to silicosis'' (Document ID 4224, Attachment 1, p. 3). This point was emphasized by Dr. Brian Miller in the Final Peer Review Report (Document ID 3574, p. 57) and by NIOSH (Document ID 4233, p. 57). In the study, 17.5 percent of workers with silicosis were classified as having no exposure above Morfeld et al.'s estimated threshold of 250 mug/m\3\, (Document ID 3843, p. 1031) and 12.5 percent of these workers were classified as having no exposure above 100 mug/m\3\. OSHA believes the presence of these low-exposed workers with silicosis clearly contradicts the authors' estimate of 250 mug/

    m\3\ as a level of exposure below which no worker will develop silicosis (see Document ID 4233, p. 57).

    In a post-hearing comment, Dr. Morfeld offered a different interpretation of his results, describing his threshold estimate as a ``population average'' which would not be expected to characterize risk for all individuals in a population. Rather, according to Dr. Morfeld ``we expect to see differences in response thresholds among subjects'' (Document ID 4003, p. 5). OSHA agrees with this interpretation, which was similarly expressed in several comments from OSHA's peer reviewers on the subject of thresholds (e.g., Document ID 3574, pp. 13, 21-22). Consistent with its peer reviewers' opinions, OSHA draws the conclusion from the data and discussion concerning population averages that these ``differences in response thresholds among subjects'' support setting the PEL at 50 mug/m\3\ in order to protect the majority of workers in the population of employees exposed to respirable crystalline silica. OSHA's review of the Morfeld et al. data on German porcelain workers thus reinforces its view that reducing exposures to this level will benefit the many workers who would develop silicosis at exposure levels below that of the ``average'' worker.

    Dr. Morfeld's discussion of his estimate as a ``population average'' among workers with different individual responses to silica exposure

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    echoes several comments from OSHA's peer reviewers on the subject of thresholds. In the Final Peer Review Report, Dr. Ginsberg observed that a linear exposure-response model may reflect a distribution of individual ``thresholds,'' such that ``the population can be characterized as having a distribution of vulnerability. This distribution may be due to differences in levels of host defenses that come with differences in age, co-exposure to other chemicals, the presence of interacting background disease processes, non-chemical stressors, and a variety of other host factors'' (Document ID 3574, p. 21). Given the number of factors that may influence vulnerability to certain diseases in a population of workers, Dr. Ginsberg continued:

    it is logical for OSHA to strongly consider inter-subject variability . . . as the reason for linearly-appearing regression slopes in silica-related non-cancer and cancer studies. This explanation does not imply an artifact that is, a false appearance of linear exposure-response but that the linear (or log linear) regression coefficient extending down to low dose reflects the inherent variability in susceptibility such that the effect of concern . . . may occur in some individuals at doses well below what might be a threshold in others (Document ID 3574, pp. 21-22).

    Peer reviewer Mr. Bruce Allen agreed that ``it makes no sense to discuss a single threshold value . . . Given, then, that thresholds must be envisioned as a distribution in the population, then there is substantial population-level risk even at the mean threshold value, and unacceptably high risk levels at exposures far below the mean threshold.'' He further stated:

    It is NOT, therefore, inappropriate to model the population-

    level observations using a non-threshold model . . . In fact, I would claim that it is inappropriate to include ANY threshold models (i.e., those that assume a single threshold value) when modeling epidemiological data. A non-threshold model for characterizing the population dose-response behavior is theoretically and practically the optimal approach (Document ID 3574, p. 13).

    OSHA concludes that this German porcelain workers cohort shows evidence of silicosis among workers exposed at levels below the previous PELs, and that continued follow-up of this cohort would be likely to show greater silicosis risk among low-exposed workers due to the short follow-up time. Furthermore, the Chamber's characterization of Dr. Morfeld's result as ``a threshold concentration of 250 mug/

    m\3\ below which the lung responses did not progress to silicosis'' (Document ID 4224, p. 3) is plainly inaccurate, as the estimated exposures of a substantial proportion of the workers with silicosis in the data set did not exceed this level.

    e. Park et al. (2002)

    The ACC submitted comments on the Park et al. (2002, Document ID 0405) study which examined silicosis and lung disease other than cancer (i.e., NMRD) in a cohort of diatomaceous earth workers. The ACC's comments on this study are discussed in detail in Section V.D, Comments and Responses Concerning Silicosis and Non-Malignant Respiratory Disease Mortality and Morbidity, including comments relating to exposure-response thresholds in this study. Briefly, the ACC claimed that the Park et al. (2002) study is ``fully consistent'' with Morfeld's estimate of a threshold above the 100 mug/m\3\ concentration for NMRD, including silicosis, mortality (Document ID 2307, Attachment A, p. 107). However, NIOSH explained in its post-

    hearing brief that categorical analysis for NMRD indicated no threshold existed at or above a cumulative exposure corresponding to 25 mug/

    m\3\ over 40 years of exposure, which is below the cumulative exposure equivalent to the new PEL over 45 years (Document ID 4233, p. 27). Park et al. did not attempt to estimate a threshold below that level because the data lacked the power needed to discern a threshold (Document ID 4233, p. 27). OSHA agrees with NIOSH's assessment, which indicates that, if there is a cumulative exposure threshold for NMRD, including silicosis, it is significantly below the final PEL of 50 mug/m\3\.

    f. Conclusion--Silicosis and NMRD

    OSHA concludes that the body of epidemiological literature clearly demonstrates risk of silicosis and NMRD morbidity and mortality among workers who have been exposed to cumulative exposures or average exposure concentrations at or below the levels associated with the previous general industry PEL (100 mug/m\3\, or cumulative exposure of 4.5 mg/m\3\-yrs). Thus, OSHA does not agree with commenters who have stated that the previous general industry PEL is fully protective and that reducing it will yield no health benefits to silica-exposed workers (e.g., Document ID 4224, p. 2-5; Tr. 3582, pp. 1951-1963). Instead, the Agency finds that the evidence is at least as consistent with a finding that no threshold is discernible as it is with a finding that a threshold exists at some minimal level of exposure. The best available evidence also demonstrates silicosis morbidity and mortality below the previous PEL of 100 mug/m\3\, indicating that any threshold for silicosis (understood as an exposure level below which no one would develop disease), if one exists, is below that level. Even if the conclusion reached by Dr. Morfeld that a population average threshold exists above the level of the previous PEL is accurate, there will still be a substantial portion of the population who will develop silicosis from exposures below the identified ``threshold.'' These findings support OSHA's action in lowering the PEL to 50 mug/m\3\.

    3. Thresholds--Lung Cancer

    OSHA's Preliminary QRA and supplemental literature review included several studies that provide information on possible threshold effects for lung cancer. OSHA has determined that the epidemiological studies most relevant to the threshold issue are those with workers who have cumulative exposures or average exposure concentrations below the levels associated with the previous general industry PEL (100 mug/

    m\3\, or cumulative exposure of 4.5 mg/m\3\-yrs). As with the silicosis studies previously discussed, contrary to comments that OSHA only relied on studies involving exposures far above the levels of interest to OSHA in this rulemaking (e.g., Document ID 2307, Attachment A, pp. 94-95; 4226, p. 2), a number of lung cancer studies included workers who were exposed at levels close to or below the previous general industry PEL. Five of the 10 cohorts of workers in the pooled lung cancer risk analysis conducted by Steenland et al. (2001a) had median cumulative exposures below 4.5 mg/m\3\-yrs (the cumulative level associated with a working lifetime of exposure at the previous general industry PEL); four were also below 2.25 mg/m\3\-yrs (the cumulative level associated with a working lifetime of exposure at the revised PEL) and three had median silica concentrations below 100 mug/m\3\ (Document ID 0452, p. 775). Other lung cancer studies with significant numbers of relatively low-exposed workers include analyses of the Vermont granite workers (Attfield and Costello, 2004, Document ID 0285; Vacek et al., 2011, 1486) and industrial sand workers (McDonald et al., 2001, Document ID 1091; Hughes et al., 2001, 1060; McDonald et al., 2005, 1092) described in the previous discussion on silicosis. In addition to the epidemiological studies discussed here, in Section V.H, Mechanisms of Silica-Induced Adverse Health Effects, OSHA discussed studies that have shown direct genotoxic mechanisms by which exposure to crystalline silica at any level, with no threshold effect, may lead to lung cancer.

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    a. Steenland et al. Pooled Lung Cancer Study and Related Analyse

    Steenland et al. (2001a) estimated excess lifetime risk of lung cancer based on a 10-cohort pooled study, which included several cohorts with significant numbers of workers with median cumulative and average exposures below those allowed by the previous general industry PEL (Document ID 0452). Results indicated that 45 years of exposure at 0.1 mg/m\3\ (100 mug/m\3\) would result in a lifetime risk of 28 excess lung cancer deaths per 1,000 workers (95% confidence interval (CI) 13-46 per 1,000). An alternative (non-linear) model yielded a lower risk estimate of 17 per 1,000 (95% CI 2-36 per 1,000).

    A follow-up letter by Steenland and Deddens (2002, Document ID 1124) addressed the possibility of an exposure threshold effect in the pooled lung cancer analysis conducted by Steenland et al. in 2001. According to Dr. Steenland, ``We further investigated whether there was a level below which there was no increase in risk, the so-called threshold. So we fit models that had a threshold versus those that didn't, and we explored various thresholds that might apply'' (Document ID 3580, Tr. 1229). Threshold models using average exposure and cumulative exposure failed to show a statistically significant improvement in fit over models without a threshold. However, the authors found that when they used the log of cumulative exposure (a transformation commonly used to reduce the influence of high exposure points on a model), a threshold model with a 15-year lag fit better than a no-threshold model. The authors reported the best threshold estimate at 4.8 log mg/m\3\-days (Document ID 1124, p. 781), or an average exposure of approximately 10 mug/m\3\ over a 45-year working lifetime, one-fifth of the final PEL. Dr. Steenland explained what his analysis indicated regarding a cumulative exposure threshold for lung cancer: ``we found, in fact, that there was a threshold model that fit better than a no-threshold model, not enormously better but better statistically, but that threshold was extremely low . . . far below the . . . silica standard proposed by OSHA'' (Document ID 3580, Tr. 1229).

    In response to comments from ACC Panel members Dr. Valberg and Dr. Long that the analysis presented by Steenland et al. showed a clear threshold at a level of cumulative exposure high enough to bear on OSHA's choice of PEL (Document ID 2330, p. 20), Dr. Steenland explained that their conclusion was based on a misreading of an illustration in his study:

    If you look at the figure, you see that the curve of the spline a flexible, nonlinear exposure-response model starts to go up around four on the log scale of microgram per meter cubed days. And if you transform that from the log to the regular scale, that is quite consistent with the threshold we got when we did a formal analysis using the log transform model discussed above (Document ID 3580, Tr. 1255).

    The ACC representatives' comments do appear to be based on a misunderstanding of the figure in question, due to an error in Dr. Steenland's 2001 publication in which the axis of the figure under discussion was incorrectly labeled. This error was later corrected in an erratum (Document ID 3580, Tr. 1257; Steenland et al., 2002, Erratum. Cancer Causes Control, 13:777).

    In addition, at OSHA's request, Drs. Steenland and Bartell (ToxaChemica, 2004, Document ID 0469) conducted a quantitative uncertainty analysis to examine the effects of possible exposure measurement error on the pooled lung cancer study results (see Section V.K, Comments and Responses Concerning Exposure Estimation Error and ToxaChemica's Uncertainty Analysis). These analyses showed no evidence of a threshold effect for lung cancer at the final or previous PELs. Based on Dr. Steenland's work, therefore, OSHA believes that no-

    threshold models are appropriate for evaluating the exposure-response relationship between silica exposure and lung cancer. Even if commenters are correct that threshold models are preferable, the threshold is likely at a level of cumulative exposure significantly below what a worker would accumulate in 45 years of exposure at the final PEL, and is therefore immaterial to this rulemaking (see Document ID 1124, p. 781).

    b. Vermont Granite Workers

    In the Preliminary QRA and supplemental literature review, OSHA reviewed several studies on lung cancer among silica-exposed workers in the Vermont granite industry, whose exposures were reduced to relatively low levels due to a program for dust control initiated in 1938-1940 by the Vermont Division of Industrial Hygiene (Document ID 1711, pp. 97-102; 1711, Attachment 1, pp. 2-5; 1487, p. 73). As discussed above, Verma et al. (2012) reported that all jobs in the industry had average exposure concentrations at or below 100 mug/

    m\3\--most of them well below this level--in the time period 1950-2004 after implementation of exposure controls (Document ID 1487, Table IV, p. 75).

    Attfield and Costello (2004) examined a cohort of 5,414 Vermont granite workers, including 201 workers who died of lung cancer (Document ID 0285, pp. 130, 134). In this study, cancer risk was elevated at cumulative exposure levels below 4.5 mg/m\3\-yrs, the amount of exposure that would result from a 45-year working lifetime of exposure at the previous PEL. The authors reported elevated lung cancer in all exposure groups, observing statistically significant elevation among workers with cumulative exposures between 0.5 and 1 mg/m\3\-yrs (p 50-100 mug/m\3\ and 2.4 (95% CI 1.1-5.2) for average annual exposure group >150-200 mug/m\3\, controlling for age, smoking, and duration of employment. In contrast, the HRs for lung cancer mortality associated with cumulative exposure were not statistically elevated after controlling for age and smoking.

    The authors suggested the possibility of a threshold for lung cancer mortality. However, no formal threshold analysis for lung cancer was conducted in this study or in the follow-up threshold analysis conducted on this population by Morfeld et al. for silicosis (2013, Document ID 4175). Having reviewed this study carefully, OSHA believes it is inconclusive on the issue of thresholds due to the elevated risk of lung cancer seen among low-exposed workers (for example, those with average exposures of 50-100 mug/m\3\), which is inconsistent with the ACC's claim that a threshold exists at or above the previous PEL of 100 mug/m\3\, and due to several limitations which may preclude detection of a relationship between cumulative exposure and lung cancer in this cohort. As discussed in the Preliminary QRA, these include: (1) A strong healthy worker effect observed for lung cancer; (2) Mundt et al. did not follow the typical convention of considering lagged exposures to account for disease latency; and (3) the relatively young age of this cohort (median age 56 years old at time of silicosis determination) (Document ID 1478, p. 288) and limited follow-up period (average of 19 years per subject) (Birk et al. 2009, Document ID 4002, Attachment 2, p. 377). Only 9.2 percent of the cohort was deceased by the end of the follow up period. Mundt et al. (2011) acknowledged this limitation, stating that the lack of increased risk of lung cancer was a preliminary finding (Document ID 1478, p. 288).

    f. German Uranium Miners

    In pre-hearing comments, Dr. Morfeld described a study of 58,677 German uranium miners by Sogl et al. (2012,

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    Document ID 3842; 2307, Attachment 2, p. 11). Dr. Morfeld noted that the study was based on a detailed exposure assessment of respirable crystalline silica (RCS) dust. According to Dr. Morfeld, Sogl et al. ``showed that no lung cancer excess risk was observed at RCS dust exposure levels below 10 mg/m\3\-years'' (Document ID 2307, Attachment 2, p. 11). OSHA's review of this publication confirmed that the authors reported a spline function with a single knot at 10 mg/m\3\-yrs, which Morfeld interprets to suggest a threshold for lung cancer of approximately 250 mug/m\3\ average exposure concentration for workers exposed over the course of 40 years. However, the authors also noted that an increase in risk below this level could not be ruled out due to strong confounding with radon, resulting in possible over-adjustment (Sogl et al., Document ID 3842, p. 9). That is, because workers with high exposures to silica would also have had high exposures to the lung carcinogen radon, the models used by Sogl et al. may have been unable to detect a relationship between silica and lung cancer in the presence of radon. As described previously, excess lung cancer has been observed among workers with lower cumulative exposures than the Sogl et al. ``threshold'' in other studies which do not suffer from confounding from potent lung carcinogens other than silica (for example, industrial sand workers), and which are, therefore, likely to provide more reliable evidence on the issue of thresholds. OSHA concludes that the Sogl et al. study does not provide convincing evidence of a cumulative exposure threshold for lung cancer.

    g. U.S. Diatomaceous Earth Workers

    Checkoway et al. (1997) investigated the risk of lung cancer among diatomaceous earth (DE) workers exposed to respirable cristobalite (a type of silica found in DE) (Document ID 0326; 1711, pp. 139-143). Exposure samples were collected primarily at one of the two plants in the study by plant industrial hygienists over a 40-year timeframe from 1948 to 1988 and used to estimate exposure for each individual in the cohort (Seixas et al., 1997, Document ID 0431, p. 593). Based on 77 deaths from cancer of the trachea, lung, and bronchus, the standardized mortality ratios (SMR) were 129 (95% CI 101-161) and 144 (95% CI 114-

    180) based on rates for U.S. and local county males, respectively (Document ID 0326, pp. 683-684). The authors found a positive, but not monotonic, exposure-response trend for lung cancer. The risk ratios for lung cancer with increasing quintiles of respirable crystalline silica exposure were 1.00, 0.96, 0.77, 1.26 and 2.15 with a 15-year exposure lag. Lung cancer mortality was thus elevated for workers with cumulative exposures greater than 2.1 mg/m\3\-yrs, but was only statistically significantly elevated for the highest exposure category (RR = 2.15; 95% CI 1.08-4.28) (Document ID 0326, p. 686). OSHA notes that this highest exposure category includes cumulative exposures only slightly higher than 4.5 mg/m\3\-yrs, the level of cumulative exposure resulting from a 45-year working lifetime at the previous PEL of 100 mug/m\3\. OSHA does not believe that the appearance of a statistically significantly elevated lung cancer risk in the highest category should be interpreted as evidence of an exposure-response threshold, especially in light of the somewhat elevated risk seen at lower exposure levels. OSHA believes it is more likely to reflect limited power to detect excess risk at lower exposure levels, a common issue in epidemiological studies which was emphasized by peer reviewer Dr. Andrew Salmon in relation to purported thresholds (Document ID 3574, p. 37).

    h. Finnish Nationwide Job Exposure Matrix

    OSHA reviewed Pukkala et al. (2005, Document ID 0412) in the Review of Health Effects Literature and Preliminary Quantitative Risk Assessment (Document ID 1711, pp. 153-154). As discussed there, Pukkala et al. (2005) evaluated the occupational silica exposure among all Finns born between 1906 and 1945 who participated in a national population census on December 31, 1970. Follow-up of the cohort was through 1995. Between 1970 and 1995, there were 30,137 cases of incident lung cancer among men and 3,527 among women. Exposure data from 1972 to 2000 was collected by the Finnish Institute of Occupational Health (FIOH). Cumulative exposure categories for respirable quartz were defined as: 10 mg/m\3\-yrs (high). For men, over 18 percent of the 30,137 lung cancer cases worked in occupations with potential exposure to silica dust. The cohort showed statistically significantly increased lung cancer among men in the lowest occupationally exposed group (those with less than 1.0 mg/m\3\-yrs cumulative silica exposure), as well as for men with exposures in the two higher groups (1.0-9.9 mg/m\3\-yrs and >10 mg/m\3\-yrs). For women, the cohort showed statistically significantly increased lung cancer among women with at least 1.0 mg/m\3\-yrs cumulative silica exposure. Given these results, it is unclear why ACC stated that Pukkula's results suggest that ``excess risk of lung cancer is mainly attributable to . . . cumulative exposure exceeding 10 mg/m\3\-years'' (Document ID 4209, p. 54). Indeed, Pukkula's analysis appears to show excess risk of lung cancer among men with any level of occupational exposure and among women whose cumulative exposures were quite low (at least equivalent to about 25 mug/m\3\ over 45 years). It does not support the ACC's contention that lung cancer is seen primarily in workers with exposures greater than 200 mug/m\3\ (Document ID 4209, p. 54), but rather suggests that any threshold for lung cancer risk would likely be well below 100 mug/m\3\.

    i. U.S. National (27 states) Case-Control Study

    As discussed in the Review of Health Effects Literature and Preliminary Quantitative Risk Assessment (Document ID 1711, pp. 152-

    153), Calvert et al. (2003, Document ID 3890) conducted a case-control study using 4.8 million death certificates from the National Occupational Mortality Surveillance data set. Death certificates were collected from 27 states covering the period from 1982 to 1995. Cases were persons who had died from any of several diseases of interest: Silicosis, tuberculosis, lung cancer, chronic obstructive pulmonary disease (COPD), gastrointestinal cancers, autoimmune-related diseases, or renal disease. Worker exposure to crystalline silica was categorized as no/low, medium, high, or super-high based on their industry and occupation. The authors acknowledged the potential for confounding by higher smoking rates for cases compared to controls, and partially controlled for this by eliminating white-collar workers from the control group in the analysis. Following this adjustment, the authors reported weak, but statistically significantly elevated, lung cancer mortality odds ratios (OR) of 1.07 (95% CI 1.06-1.09) and 1.08 (95% CI 1.01-1.15) for the high- and super-high exposure groups, respectively (Calvert et al., 2003, Document ID 3890, p. 126). Upon careful review of this study, OSHA maintains its position that it should not be used for quantitative risk analysis (including determination of threshold effects) because it lacks an exposure characterization based on sampling. Any determination regarding the existence or location of a threshold based on Calvert et al. (2003) must, therefore, be considered highly speculative.

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    j. Conclusion--Lung Cancer

    In conclusion, OSHA has determined that the best available evidence on the issue of a threshold for silica-related lung cancer does not support the ACC's contention that an exposure-response threshold, below which respirable crystalline silica exposure is not expected to cause cancer, exists at or above the previous general industry PEL of 100 mug/m3. While there are some studies that claim to point to thresholds above the previous general industry PEL, multiple studies contradict this evidence, most convincingly through evidence that cohort members with low cumulative silica exposures suffered from lung cancer as a result of their exposure. These studies indicate that there is either no threshold for silica-related lung cancer, or that this threshold is at such a low level that workers cumulatively exposed at or below the level allowed by the new PEL of 50 mug/m3 will still be at risk of developing lung cancer. Thus, OSHA does not agree with commenters who have stated that the previous general industry PEL is fully protective and that reducing it will yield no health benefits to silica-exposed workers (e.g., Document ID 4224, p. 2-5; Tr. 3582, pp. 1951-1963).

    4. Exposure Uncertainty and Thresholds

    In his pre-hearing comments, Dr. Cox stated that the observation of a positive and monotonic exposure-response relationship in epidemiological studies ``does not constitute valid evidence against the hypothesis of a threshold,'' and that OSHA's findings of risk at exposures below the previous PEL for general industry ``could be due simply to exposure misclassification'' in studies of silica-related health effects in exposed workers (Document ID 2307, Attachment 4, pp. 41-42). His statements closely followed his analyses from a 2011 paper, in which Cox presented a series of simulation analyses designed to show that common concerns in epidemiological analyses, such as uncontrolled confounding, errors in exposure estimates, and model specification errors, can obscure evidence of an exposure-response threshold, if such a threshold exists (Document ID 3600, Attachment 7). Dr. Cox concluded that the currently available epidemiological studies ``do not provide trustworthy information about the presence or absence of thresholds in exposure-response relations'' with respect to an exposure concentration threshold for lung cancer (Document ID 3600, Attachment 7, p. 1548).

    OSHA has reviewed Dr. Cox's comments and testimony, and concludes that uncertainty about risk due to exposure estimation and confounding cannot be resolved through the application of the statistical procedures recommended by Dr. Cox. (Similar comments from Dr. Cox about alleged biases in the studies relied upon are addressed in the next section, where OSHA reaches similar conclusions). A reviewer on the independent peer review panel, Dr. Ginsberg, commented that:

    epidemiology studies will always have issues of exposure misclassification or other types of error that may create uncertainty when it comes to model specification. However, these types of error will also bias correlations to the null such that if they were sufficiently influential to obscure a threshold they may also substantially weaken regression results and underestimate the true risk (Document ID 3574, p. 23).

    OSHA agrees with Dr. Ginsberg. As discussed in Section V.K, Comments and Responses Concerning Exposure Estimation Error and ToxaChemica's Uncertainty Analysis, a ``gold standard'' exposure sample is not available for the epidemiological studies in the silica literature, so it is not possible to determine the direction or magnitude of the effects of exposure misclassification on OSHA's risk estimates. The silica literature is not unique in this sense. As stated by Mr. Robert Park of NIOSH, ``modeling exposure uncertainty as described by Dr. Cox . . . is infeasible in the vast majority of retrospective observational studies. Nevertheless, mainstream scientific thought holds that valid conclusions regarding disease causality can still be drawn from such studies'' (Document ID 4233, p. 32).

    For the reasons discussed throughout this analysis of the scientific literature, OSHA concludes that, even acknowledging a variety of uncertainties in the studies relied upon, these uncertainties are, for the most part, typical or inherent in these types of studies. OSHA therefore finds that the weight of evidence in these studies, representing the best available evidence on the health effects of silica exposure, strongly supports the findings of significant risk from silicosis, NMRD, lung cancer, and renal disease discussed in this section and in the quantitative risk assessment that follows in the next section (see Benzene, 448 U.S. at 656 (``OSHA is not required to support its finding that a significant risk exists with anything approaching scientific certainty. Although the Agency's findings must be supported by substantial evidence, 29 U.S.C. 655(f), 6(b)(5) specifically allows the Secretary to regulate on the basis of the `best available evidence.' '')).

    5. Conclusion

    In summary, OSHA acknowledges that common issues with epidemiological studies limit the Agency's ability to determine whether and where a threshold effect exists for silicosis and lung cancer. However, as shown in the foregoing discussion, there is evidence in the epidemiological literature that workers exposed to silica at concentrations and cumulative levels allowable under the previous general industry PEL not only develop silicosis, but face a risk of silicosis high enough to be significant ( >1 per 1,000 exposed workers). Although the evidence is less clear for lung cancer, studies nevertheless show excess cases of lung cancer among workers with cumulative exposures in the range of interest to OSHA. Furthermore, the statistical model-based approaches proposed in public comments do not demonstrate the existence or location of a ``threshold'' level of silica exposure below which silica exposure is harmless to workers. The above considerations lead the Agency to conclude that any possible exposure threshold is likely to be at a low level, such that some workers will continue to suffer the health effects of silica exposure even at the new PEL of 50 mug/m3.

    There is a great deal of argument and analysis directed at the question of thresholds in silica exposure-response relationships, but nothing like a scientific consensus about the appropriate approach to the question has emerged. If OSHA were to accept the ACC's claim that exposure to 100 mug/m3 silica is safe for all workers (due to a threshold at or above an exposure concentration of 100 mug/

    m3) and set a PEL at 100 mug/m3 for all industry sectors, and if that claim is in fact erroneous, the consequences of that error to silica-exposed workers would be grave. A large population of workers would remain at significant risk of serious occupational disease despite feasible options for exposure reduction.

  8. Comments and Responses Concerning Biases in Key Studies

    OSHA received numerous comments and testimony, particularly from representatives of the ACC, regarding biases in the data that the Agency relied upon to conduct its Preliminary Quantitative Risk Assessment (Preliminary QRA). In this section, OSHA focuses on these comments regarding biases, particularly with respect to how such biases may have affected the data and findings from the

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    key peer-reviewed, published studies that OSHA relied upon in its Preliminary QRA.

    The data utilized by OSHA to conduct its Preliminary QRA came from published studies in the peer-reviewed scientific literature. When developing health standards, OSHA is not required or expected to conduct original research or wait for better data or new studies (see 29 U.S.C. 655(b)(5); e.g., United Steelworkers v. Marshall, 647 F.2d 1189, 1266 (D.C. Cir. 1980), cert. denied, 453 U.S. 913 (1981)). Generally, OSHA bases its determinations of significant risk of material impairment of health on the cumulative evidence found in a number of studies, no one of which may be conclusive by itself (see Public Citizen Health Research Group v. Tyson, 796 F.2d 1479, 1495 (D.C. Cir. 1986) (reviewing courts do not ``seek a single dispositive study that fully supports the Administrator's determination . . . Rather, OSHA's decision may be fully supportable if it is based . . . on the inconclusive but suggestive results of numerous studies.''). OSHA's critical reading and interpretation of scientific studies is thus appropriately guided by the instructions of the Supreme Court's Benzene decision that ``so long as they are supported by a body of reputable scientific thought, OSHA is free to use conservative assumptions in interpreting the data with respect to carcinogens, risking error on the side of overprotection rather than underprotection'' (Industrial Union Dep't v. American Petroleum Inst., 448 U.S. 607, 656 (1980)).

    Since OSHA is not a research agency, it draws from the best available existing data in the scientific literature to conduct its quantitative risk assessments. In most cases, with the exception of certain risk and uncertainty analyses prepared for OSHA by its contractor ToxaChemica, OSHA had no involvement in the data generation or analyses reported in those studies. Thus, in calculating its risk estimates, OSHA used published regression coefficients or equations from key peer-reviewed, published studies, but had no control over the actual published data; nor did the Agency have access to the raw data from such studies.

    As discussed throughout Section V of this preamble, the weight of scientific opinion indicates that respirable crystalline silica is a human carcinogen that causes serious, life-threatening disease at the previously-permitted exposure levels. Under its statutory mandate, the Agency can and does take into account the potential for statistical and other biases to skew study results in either direction. However, the potential biases of concern to the commenters are well known among epidemiologists. OSHA therefore believes that the scientists who conduct the studies and subject them to peer review before publication have taken the potential for biases into account in evaluating the quality of the data and analysis. As discussed further below, OSHA heard testimony from David Goldsmith, Ph.D., describing how scientists use ``absolutely the best evidence they can lay their hands on'' and place higher value on studies that are the least confounded by other factors that, if unaccounted for, could contribute to the effect (e.g., lung cancer mortality). (Document ID 3577, Tr. 894-895). Dr. Goldsmith also testified that many of the assertions of biases put forth in the rulemaking docket are speculative in nature, with no actual evidence presented (Document ID 3577, Tr. 901). Thus, while taking seriously the critiques of the ``body of reputable scientific thought'' OSHA has used to support this final silica standard, the Agency finds no reason, as discussed below, to consider discredited in any material way its key conclusions regarding causation or significant risk of harm.

    In his pre-hearing comments, Dr. Cox, on behalf of the ACC, claimed that the Preliminary QRA did not address a number of sources of potential bias:

    The Preliminary QRA and the published articles that it relies on do not correct for well-known biases in modeling statistical associations between exposures and response. (These include study, data, and model selection biases; model form specification and model over-fitting biases; biases due to residual confounding, e.g., because age is positively correlated with both cumulative exposure and risk of lung diseases within each age category (typically 5 or more years long); and biases due to the effects of errors in exposure estimates on shifting apparent thresholds to lower concentrations). As a result, OSHA has not demonstrated that there is any non-random association between crystalline silica exposure and adverse health responses (e.g., lung cancer, non-malignant respiratory disease, renal disease) at exposure levels at or below 100 microg/m\3\. The reported findings of such an association, e.g., based on significantly elevated relative risks or statistically significant positive regression coefficients for exposed compared to unexposed workers, are based on unverified modeling assumptions and on ignoring uncertainty about those assumptions (Document ID 2307, Attachment 4, pp. 1-2).

    These biases, according to Dr. Cox, nearly always result in false positives, i.e., finding that an exposure-response relationship exists when there really is no such relationship (Document ID 3576, Tr. 380). Although his comments appear to be directed to all published, peer-

    reviewed studies relied upon by OSHA in estimating risks, Dr. Cox admitted at the hearing that his statements about false positives were based on his review of the Preliminary QRA with relation to lung cancer only, and that he ``didn't really know'' whether the same allegations of bias he directed at the lung cancer studies are relevant to the studies of silica's other health risks (Document ID 3576, Tr. 426). In his comments, Dr. Cox discussed each source of bias in detail; OSHA will address them in turn. The concerns expressed by commenters, including Dr. Cox, about exposure uncertainty--another potential source of bias--are addressed in Section V.K, Comments and Responses Concerning Exposure Estimation Error and ToxaChemica's Uncertainty Analysis.

    1. Model Specification Bias

    Dr. Cox stated that model specification error occurs when the model form, such as the linear absolute risk model, does not correctly describe the data (Document ID 2307, Attachment 4, p. 21). Using a simple linear regression example from Wikipedia, Dr. Cox asserted that common indicators of goodness-of-fit, including sum of square residuals and correlation coefficients, can be weak in identifying ``nonlinearities, outliers, influential single observations, and other violations of modeling assumptions'' (Document ID 2307, Attachment 4, pp. 52-53). He advocated for the use of diagnostic tests to check that a model is a valid and robust choice, stating, ``unfortunately, OSHA's Preliminary QRA and the underlying papers and reports on which it relies are not meticulous in reporting the results of such model diagnostics, as good statistical and epidemiological practice requires'' (Document ID 2307, Attachment 4, p. 21). In his post-hearing brief, Dr. Cox further described these diagnostic tests to include plots of residuals, quantification of the effects of removing outliers and influential observations, and comparisons of alternative model forms using model cross-validation (Document ID 4027, p. 2). He also suggested using Bayesian Model Averaging (BMA) or other model ensemble methods to quantify the effects of model uncertainty (Document ID 4027, p. 3).

    OSHA believes that guidelines for which diagnostic procedures should be performed, and whether and how they are reported in published papers, are best determined by the scientific community through the pre-publication peer review process. Many studies in

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    the silica literature did not report the results of diagnostic tests. For example, the Vacek et al. (2009) study of lung cancer and silicosis mortality, which was submitted to the rulemaking record by the ACC to support its position, made no mention of the results of model diagnostic tests; rather, the authors simply stated that models were fitted by maximum likelihood, with the deviance used to examine model fitting (Document ID 2307, Attachment 6, pp. 11-12). As illustrated by this example, authors of epidemiological studies do not normally report the results of diagnostic tests; nor do such authors publish their raw data. Therefore, there is no data readily available to OSHA with which it could perform the diagnostic analysis that Dr. Cox states is necessary. If the suggestion is that no well-conducted epidemiological study that failed to report a battery of diagnostic tests or disclose what they showed should be relied upon for regulatory purposes, there would be virtually no body of scientific study left for OSHA to consider, raising the legal standard for issuing toxic substance standards far above what the Benzene decision requires. Despite this, OSHA maintains that, given the large number of peer-reviewed studies in the published scientific literature on crystalline silica, subjecting each model in each study to diagnostic testing along the lines advocated by Dr. Cox would not fundamentally change the collective conclusions when examining the literature base as a whole. Despite Dr. Cox's criticisms, the scientific literature that OSHA reviewed to draw its conclusions regarding material impairment of health and used in its quantitative risk assessment, constitutes the best available evidence upon which to base this toxic substance standard, in accordance with 29 U.S.C. 655(b) and the Benzene decision and subsequent case law.

    Dr. Cox's other suggested approach to addressing model uncertainty, BMA, can be used to construct a risk estimate based on multiple exposure-response models. Unlike BMA, standard statistical practice in the epidemiological literature is to evaluate multiple possible models, identify the model that best represents the observations in the data set, and use this model to estimate risk. In some cases, analysts may report the results of two or more models, along with their respective fit statistics and other information to aid model selection for risk assessment and show the sensitivity of the results to modeling choices (e.g., Rice et al., 2001, Document ID 1118). These standard approaches were used in each of the studies relied on by OSHA in its Preliminary QRA.

    In contrast, BMA is a probabilistic approach designed to account for uncertainty inherent in the model selection process. The analyst begins with a set of possible models (Mi) and assigns each a prior probability (PrMi) that reflects the analyst's initial belief that model Mi represents the true exposure-

    response relationship. Next, a data set is used to update the probabilities assigned to the models, generating the posterior probability for each model. Finally, the models are used in combination to derive a risk estimate that is a composite of the risk estimates from each model, weighted by each model's posterior probability (see Viallefont et al., 2001, Document ID 3600, Attachment 34, pp. 3216-

    3217). Thus, BMA combines multiple models, and uses quantitative weights accounting for the analyst's belief about the plausibility of each model, to generate a single weighted-average risk estimate. These aspects of BMA are regarded by some analysts as improvements to the standard approaches to exposure-response modeling.

    However, Kyle Steenland, Ph.D., Professor, Department of Environmental Health, Rollins School of Public Health, Emory University, the principal author of a pooled study that OSHA heavily relied upon, noted that BMA is not a standard method for risk assessment. ``Bayesian model averaging, to my knowledge, has not been used in risk assessment ever. And so, sure, you could try that. You could try a million things. But I think OSHA has correctly used standard methods to do their risk assessment and BMA is not one of those standard methods'' (Document ID 3580, Tr. 1259).

    Indeed, BMA is a relatively new method in risk analysis. Because of its novelty, best practices for important steps in BMA, such as defining the class of models to include in the analysis, and choosing prior probabilities, have not been developed. Until best practices for BMA are established, it would be difficult for OSHA to conduct and properly evaluate the quality of BMA analyses. Evaluation of the quality of available analyses is a key step in the Agency's identification of the best available evidence on which to base its significant risk determination and benefits analysis.

    OSHA also emphasizes that, as noted by Dr. Steenland, scientifically accepted and standard practices were used to estimate risk from occupational exposure to crystalline silica (Document ID 3580, Tr. 1259). Thus OSHA has decided that it is not necessary to use BMA in its QRA, and that the standard statistical methods used in the studies it relies upon to estimate risk are appropriate as a basis for risk estimation. OSHA notes that it is possible to incorporate risk estimates based on more than one model in its risk assessment by presenting ranges of risk, a strategy often used by OSHA when the best available evidence includes more than one model, analytical approach, or data set. In its Preliminary QRA, OSHA presented ranges of risks for silica-related lung cancer and silicosis based on different data sets and models, thus further lessening the utility of using more complex techniques such as BMA. OSHA continued this practice in its final risk assessment, presented in Section VI, Final Quantitative Risk Assessment and Significance of Risk.

    2. Study Selection Bias

    Another bias described by Dr. Cox is study selection bias, which he stated occurs when only studies that support a positive exposure-

    response relationship are included in the risk assessment, and when criteria for the inclusion and exclusion of studies are not clearly specified in advance (Document ID 2307, Attachment 4, pp. 22-23). Dr. Cox noted the criteria used by OSHA to select studies, as described in the Supplemental Literature Review of Epidemiological Studies on Lung Cancer Associated with Exposure to Respirable Crystalline Silica (Supplemental Literature Review) (Document ID 1711, Attachment 1, p. 29). Dr. Cox, however, claimed that OSHA did not apply these criteria consistently, in that there may still be exposure misclassification or confounding present in the studies OSHA relied upon to estimate the risk of the health effects evaluated by the Agency (Document ID 2307, Attachment 4, pp. 24-25). Similarly, the American Foundry Society (AFS), in its post-hearing brief, asserted that, ``No formal process is described for search criteria or study selection'' and that OSHA's approach of identifying studies based upon the IARC (1997) and NIOSH (2002) evaluations of the literature ``is a haphazard approach that is not reproducible and is subject to bias. Moreover it appears to rely primarily on information that is more than 10 years old'' (Document ID 4229, p. 4).

    OSHA disagrees with the arguments presented by Dr. Cox and the AFS, as did some commenters. The American Public Health Association (APHA), in its post-hearing brief, expressed strong

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    support for OSHA's study selection methods. Dr. Georges Benjamin, Executive Director, wrote, ``APHA recognizes that OSHA has thoroughly reviewed and evaluated the peer-reviewed literature on the health effects associated with exposure to respirable crystalline silica. OSHA's quantitative risk assessment is sound. The agency has relied on the best available evidence and acted appropriately in giving greater weight to those studies with the most robust designs and statistical analyses'' (Document ID 2178, Attachment 1, p. 1). Similarly, Dr. Steenland testified that ``OSHA has done a very capable job in conducting the summary of the literature'' (Document ID 3580, Tr. 1235).

    In response to the criticisms by Dr. Cox and the AFS, OSHA notes that the silica literature was exhaustively reviewed by IARC in 1997 and NIOSH in 2002 (Document ID 1062; 1110). As a result, there was no need for OSHA to initiate a new review of the historical literature. Instead, OSHA used the IARC and NIOSH reviews as a starting point for its own review. As recognized by the APHA, OSHA evaluated and summarized many of the studies referenced in the IARC and NIOSH reviews, and then performed literature searches to identify new studies published since the time of the IARC and NIOSH reviews. OSHA clearly described this process in its Review of Health Effects Literature: ``OSHA has included in its review all published studies that the Agency deems relevant to assessing the hazards associated with exposure to respirable crystalline silica. These studies were identified from numerous scientific reviews that have been published previously such as the IARC (1997) and NIOSH (2002) evaluations of the scientific literature as well as from literature searches and contact with experts and stakeholders'' (Document ID 1711, p. 8). For its Preliminary QRA, OSHA relied heavily on the IARC pooled exposure-response analyses and risk assessment for lung cancer in 10 cohorts of silica-exposed workers (Steenland et al., 2001a, Document ID 0452) and multi-center study of silicosis mortality (Mannetje et al., 2002b, Document ID 1089). As stated in the Review of Health Effects Literature, these two studies ``relied on all available cohort data from previously published epidemiological studies for which there were adequate quantitative data on worker exposures to crystalline silica to derive pooled estimates of disease risk'' (Document ID 1711, p. 267).

    In addition to relying on these two pooled IARC multi-center studies, OSHA also identified single cohort studies with sufficient quantitative information on exposures and disease incidence and mortality rates. As pointed out by Dr. Cox, OSHA described the criteria used for selection of the single cohort studies of lung cancer mortality:

    OSHA gave studies greater weight and consideration if they (1) included a robust number of workers; (2) had adequate length of follow-up; (3) had sufficient power to detect modest increases in lung cancer incidence and mortality; (4) used quantitative exposure data of sufficient quality to avoid exposure misclassification; (5) evaluated exposure-response relationships between exposure to silica and lung cancer; and (6) considered confounding factors including smoking and exposure to other carcinogens (Document ID 1711, Attachment 1, p. 29).

    Using these criteria, OSHA identified four single-cohort studies of lung cancer mortality that were suitable for quantitative risk assessment; two of these cohorts (Attfield and Costello, 2004, Document ID 0285; Rice et al., 2001, 1118) were included among the 10 used in the IARC multi-center study and two appeared later (Hughes et al., 2001, Document ID 1060; Miller and MacCalman, 2009, 1306) (Document ID 1711, p. 267). For NMRD mortality, in addition to the IARC multi-center study (Mannetje et al., 2002b, Document ID 1089), OSHA relied on Park et al. (2002) (Document ID 0405), who presented an exposure-response analysis of NMRD mortality (including silicosis and other chronic obstructive pulmonary diseases) among diatomaceous earth workers (Document ID 1711, p. 267). For silicosis morbidity, several single-

    cohort studies with exposure-response analyses were selected (Chen et al., 2005, Document ID 0985; Hnizdo and Sluis-Cremer, 1993, 1052; Steenland and Brown, 1995b, 0451; Miller et al., 1998, 0374; Buchanan et al., 2003, 0306) (Document ID 1711, p. 267).

    With respect to Dr. Cox's claim that OSHA did not apply its criteria consistently, on the basis that there may still be exposure misclassification or confounding present, OSHA notes that it selected studies that best addressed the criteria; OSHA did not state that it only selected studies that addressed all of the criteria. Given the fact that some of the epidemiological studies concern exposures of worker populations dating back to the 1930's, there is always some potential for exposure misclassification or the absence of information on smoking. When this was the case, OSHA discussed these limitations in its Review of Health Effects Literature and Preliminary QRA (Document ID 1711). For example, OSHA discussed the lack of smoking information for cases and controls in the Steenland et al. (2001a, Document ID 0452) pooled lung cancer analysis (Document ID 1711, pp. 150-151).

    With respect to the AFS's claim that OSHA relied on studies that were more than 10 years old, OSHA again notes that it reviewed, in its Review of Health Effects Literature and its Supplemental Literature Review, the studies in the silica literature and selected the ones that best met the criteria described above (Document ID 1711; 1711, Attachment 1). It would be improper to only select the most recent studies, particularly if the older studies are of higher quality based on the criteria. Furthermore, the studies OSHA relied upon in its Preliminary QRA were published between 1993 and 2009; the claim that OSHA primarily relied on older studies is thus misleading, when the studies were of relatively recent vintage and determined to be of high quality based on the criteria described above. The AFS also suggested that OSHA examine several additional foundry studies of lung cancer (Document ID 2379, Attachment 2, p. 24); OSHA retrieved all of these suggested studies, added them to the rulemaking docket following the informal public hearings, and discusses them in Section V.F, Comments and Responses Concerning Lung Cancer Mortality.

    3. Data Selection Bias

    A related bias presented by Dr. Cox is data selection bias, which he stated occurs when only a subset of the data is used in the analysis ``to guarantee a finding of a positive'' exposure-response relationship (Document ID 2307, Attachment 4, p. 26). He provided an example, the Attfield and Costello (2004, Document ID 0285) study of lung cancer mortality, which excluded data as a result of attenuation observed in the highest exposure group (Document ID 2307, Attachment 4, pp. 26-27). Attenuation of response means the exposure-response relationship leveled off or decreased in the highest exposure group. Referring to another study of the same cohort, Vacek et al. (2009, Document ID 2307, Attachment 6; 2011, 1486), Dr. Cox stated, ``OSHA endorses the Attfield and Costello findings, based on dropping cases that do not support the hypothesis of an ER exposure-response relation for lung cancer, while rejecting the Vacek et al. study that included more complete data (that was not subjected to post hoc subset selection) but that did not find a significant ER exposure-response

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    relation'' (Document ID 2307, Attachment 4, pp. 26-27).

    OSHA believes there are very valid reasons for the observance of attenuation of response in the highest exposure group that would justify the exclusion of data in Attfield and Costello (2004, Document ID 0285) and other studies. This issue was discussed by Gary Ginsberg, Ph.D., an OSHA peer reviewer from the Connecticut Department of Public Health, in his post-hearing comments. Dr. Ginsberg noted that several epidemiological studies have found an attenuation of response at higher doses, with possible explanations including: (1) Measurement error, which arises from the fact that the highest doses are associated with the oldest datasets, which are most prone to measurement error; (2) ``intercurrent causes of mortality'' from high dose exposures that result in death to the subject prior to the completion of the long latency period for cancer; and (3) the healthy worker survivor effect, which occurs when workers with ill health leave the workforce early (Document ID 3574, p. 24). As discussed in Section V.F, Comments and Responses Concerning Lung Cancer Mortality, OSHA disagrees strongly with Dr. Cox's assertion that data were excluded to ensure a positive exposure-response relationship (Document ID 2307, Attachment 4, p. 26). In addition, as detailed in Section VI, Final Quantitative Risk Assessment and Significance of Risk, OSHA calculated quantitative risk estimates for lung cancer mortality from several other studies that did not rely on a subset of the data (Rice et al., 2001, Document ID 1118; Hughes et al., 2001, 1060; Miller and MacCalman, 2009, 1306; ToxaChemica, 2004, 0469; 1711, p. 351). These studies also demonstrated positive exposure-response relationships.

    4. Model Selection Bias

    Another selection bias presented by Dr. Cox is model selection bias, which he said occurs when many different combinations of models, including alternative exposure metrics, different lags, alternative model forms, and different subsets of data, are tried with respect to their ``ability to produce `significant'-looking regression coefficients'' (Document ID 2307, Attachment 4, p. 27). This is another aspect of model specification error, as discussed above under model averaging. Dr. Cox wrote:

    This type of multiple testing of hypotheses and multiple comparisons of alternative approaches, followed by selection of a final choice based on the outcomes of these multiple attempts, completely invalidates the claimed significance levels and confidence intervals reported for the final ER exposure-response associations. Trying in multiple ways to find a positive association, and then selecting a combination that succeeds in doing so and reporting it as `significant,' while leaving the nominal (reported) statistical significance level of the final selection unchanged (typically at p=0.05), is a well-known recipe for producing false-positive associations (Document ID 2307, Attachment 4, p. 28).

    Dr. Cox further stated that unless methods of significance level reduction (i.e., reducing the nominal statistical significance level of the final selection) are used, the study is biased towards false-

    positive results (Document ID 2307, Attachment 4, p. 28).

    During the informal public hearings, counsel for the ACC asked Mr. Park of NIOSH's Risk Evaluation Branch about this issue, i.e., trying a number of modeling choices, including exposure metrics, log-

    transformations, lag periods, and model subsets (Document ID 3579, Tr. 149-150). Mr. Park's reply supports the use of multiple modeling choices in the risk assessment as a form of sensitivity analysis:

    Investigations like this look at a number of options. They come into the study not totally naiumlve. They, in fact, have some very strong preference even before looking at the data based on prior knowledge. So cumulative exposure, for example, is a generally very high confidence choice in a metric. Trying different lags is interesting. It helps validate the study because you know what it ought to look like sort of. And in many cases, the choice does not make a lot of difference. So it's kind of a robust test, and similarly, the choice of the final model is not just coming in naiumlve. A linear exposure response has a lot of biological support in many different contexts, but it could be not the best choice (Document ID 3579, Tr. 150-151).

    ACC counsel further asked, ``And does one at the end of this process, though, make any adjustment in what you consider to be the statistically significant relationship in light of the fact that you've looked at so many different models and arrangements?'' (Document ID 3579, Tr. 151-152). Mr. Park replied, ``No, I don't think that's a legitimate application of a multiple comparison question'' (Document ID 3579, Tr. 152). OSHA agrees with Mr. Park that significance level reduction is not appropriate in the context of testing model forms for risk estimation, and notes that, in the Agency's experience, significance level reduction is not typically performed in the occupational epidemiology literature. In addition, OSHA notes that, in many of the key studies relied upon by the Agency to estimate quantitative risks, the authors presented the results of multiple models that showed statistically significant exposure-response relationships. For example, Rice et al. (2001) presented the results of six model forms, with all except one being significant (Table 1, Document ID 1118, p. 41). Attfield and Costello (2004) presented the results of their model with and without a 15-year lag and log transformation, with many results being significant (Table VII, Document ID 0285, p. 135). Thus, OSHA concludes that model selection bias is not a problem in its quantitative risk assessment.

    Furthermore, OSHA disagrees with Dr. Cox's assertion that modeling choices are used to ``produce `significant'-looking regression coefficients'' (Document ID 2307, Attachment 4, p. 27). OSHA believes that the investigators of the studies it relied upon in its Preliminary, and now final, QRA made knowledgeable modeling choices based upon the exposure distribution and health outcome being examined. For example, in long-term cohort studies, such as those of lung cancer mortality relied upon by OSHA, most authors relied upon cumulative exposure (mg/m\3\-yrs or mg/m\3\-days), i.e., the concentration of crystalline silica exposure (mg/m\3\) multiplied by the duration of exposure (years or days), as an exposure metric. Consistent with standard statistical techniques used in epidemiology, the cumulative exposure metric may then be log-transformed to account for an asymmetric distribution with a long right tail, or attenuation, and the metric may be lagged by several years to account for the long latency period between the exposure and the development of lung cancer. When investigators use subsets of the data, they typically explain the rationale and the effect of using the subset in the analysis. These choices all have important justifications and are not used purely to produce the authors' desired results, as Dr. Cox suggested (Document ID 2307, Attachment 4, p. 27).

    5. Model Uncertainty Bias

    Related to model selection bias is Dr. Cox's assertion of model uncertainty bias, which he said occurs when many different models are examined and then one is selected on which to base risk calculations; this approach ``treats the finally selected model as if it were known to be correct, for purposes of calculating confidence intervals and significance levels. But, in reality, there remains great uncertainty about what the true causal relation between exposure and response looks like (if there is one)'' (Document ID 2307,

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    Attachment 4, pp. 28-29). He further stated that ignoring this bias leads to artificially narrow confidence intervals, which bias conclusions towards false-positive findings. He then cited a paper (Piegorsch, 2013, included in Document ID 3600) describing statistical methods for overcoming this bias by ``including multiple possible models in the calculation of results'' (Document ID 2307, Attachment 4, p. 29). OSHA concludes this bias is really an extension of model specification error and model selection bias, previously discussed, and maintains that best practices for model averaging have not yet been established, making it difficult for the Agency to conduct and properly evaluate the quality of BMA analyses.

    6. Model Over-Fitting Bias

    Next, Dr. Cox discussed model over-fitting bias, which he said occurs when the same data set is used both to fit a model and to assess the fit; this ``leads to biased results: Estimated confidence intervals are too narrow (and hence lower confidence limits on estimated ER exposure-response slopes are too high); estimated significance levels are too small (i.e., significance is exaggerated); and estimated measures of goodness-of-fit overstate how well the model fits the data'' (Document ID 2307, Attachment 4, p. 39). He suggested using appropriate statistical methods, such as ``k-fold cross-validation,'' to overcome the bias (Document ID 2307, Attachment 4, p. 39).

    OSHA does not agree that using the same data set to fit and assess a model necessarily results in an over-fitting bias. The Agency understands over-fitting to occur when a model is excessively complex relative to the amount of data available such that there are a large number of predictors relative to the total number of observations available. For survival models, it is the number of events, i.e., deaths, that is relevant, rather than the size of the entire sample (Babyak, 2004, included in Document ID 3600, p. 415). If the number of predictors (e.g., exposure, age, gender) is small relative to the number of events, then there should be no bias from over-fitting. In an article cited and submitted to the rulemaking docket by Dr. Cox, Babyak (2004) discussed a simulation study that found, for survival models, an unacceptable bias when there were fewer than 10 to 15 events per independent predictor (included in Document ID 3600, p. 415). In the studies that OSHA relied on in its Preliminary QRA, there were generally a large number of events relative to the small number of predictors. For example, in the Miller and MacCalman (2009) study of British coal miners, in the lung cancer model using both quartz and coal dust exposures, there was a large number of events (973 lung cancer deaths) relative to the few predictors in the model (quartz exposure, coal dust exposure, cohort entry date, smoking habits at entry, cohort effects, and differences in regional background cause-

    specific rates) (Document ID 1306, pp. 6, 9). Thus, OSHA does not agree the studies it relied upon were substantially influenced by over-

    fitting bias. OSHA also notes that k-fold cross-validation, as recommended by Dr. Cox, is not typically reported in published occupational epidemiology studies, and that the studies the Agency relied upon in the Preliminary QRA were published in peer-reviewed journals and used statistical techniques typically used in the field of occupational epidemiology and epidemiology generally.

    7. Residual Confounding Bias

    Dr. Cox also asserted a bias due to residual confounding by age. Bias due to confounding occurs in an epidemiological study, in very general terms, when the effect of an exposure is mixed together with the effect of another variable (e.g., age) not accounted for in the analysis. Residual confounding occurs when additional confounding factors are not considered, control of confounding is not precise enough (e.g., controlling for age by using groups with age spans that are too wide), or subjects are misclassified with respect to confounders (Document ID 3607, p. 1). Dr. Cox stated in his comments that:

    key studies relied on by OSHA, such as Park et al. (2002), do not correct for biases in reported ER exposure-response relations due to residual confounding by age (within age categories), i.e., the fact that older workers may tend to have both higher lung cancer risks and higher values of occupational exposure metrics, even if one does not cause the other. This can induce a non-causal association between the occupational exposure metrics and the risk of cancer (Document ID 2307, Attachment 4, p. 29).

    The Park et al. (2002) study of non-malignant respiratory disease mortality, which Dr. Cox cited as not considering residual confounding by age, used 13 five-year age groups (3 PEL, provide no cause to doubt OSHA's determination that significant risk exists at both the previous and the revised PEL.

    An additional concern raised by Dr. Cox was based on his misunderstanding that the equation used to characterize the relationship between true and observed exposure in Drs. Steenland and Bartell's simulation, ``Exposuretrue = Exposureobserved + E'', concerned cumulative exposure. Dr. Cox stated that the equation is ``inappropriate for cumulative exposures because both the mean and the variance of actual cumulative exposure received typically increase in direct proportion to duration'' (Document ID 2307, Attachment 4, p. 45). That is, the longer period of time over which a cumulative exposure is acquired, the higher variance is likely to be, because cumulative exposure is the sum of the randomly varying exposures received on different days. However, the exposures referred to in the equation are the mean job-specific concentrations recorded in the job-

    exposure matrix (Exposureobserved) and individuals' actual exposure concentrations from each job worked (Exposuretrue), not their cumulative exposures (Document ID 0469, p. 11). Therefore, Dr. Cox's criticism is unfounded.

    Dr. Cox additionally criticized the simulation analysis on the basis that ``the usual starting point for inhalation exposures is with the random number of particles inhaled per breath modeled as a time-varying (non-homogenous) Poisson process . . . It is unclear why ToxaChemica decided to assume (and why OSHA accepted the assumption) of an underdispersed distribution . . . rather than assuming a Poisson distribution'' (Document ID 2307, Attachment 4, pp. 45-46). OSHA believes this criticism also reflects a misunderstanding of Drs. Steenland and Bartell's analysis. While it could be pertinent to an analysis of workers' silica dose (the amount of silica that enters the body), the analysis addresses the concentration of silica in the air near a worker's breathing zone, not internal dose. The worker's airborne concentration is the regulated exposure endpoint and the exposure of interest for OSHA's risk assessment. Thus, the uncertainty analysis does not need to

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    account for the number of particles inhaled per breath.

    More broadly, Dr. Cox asserted that the Monte Carlo analysis ``is an inappropriate tool for analyzing the effects of exposure measurement error on estimated exposure-response data,'' citing a paper by Gryparis et al. (2009) (Document ID 2307, Attachment 4, p. 44). This paper indicates that by randomly simulating exposure measurement error, the Monte Carlo approach can introduce classical error (Document ID 3870, p. 262). Peer reviewer Dr. Noah Seixas similarly commented that ``the typical Monte Carlo simulation, which is what appears to have been done, would introduce classical error,'' that is, error which is independent of the unobserved variable (in this case, the true exposure value). He explained that, as a result, ``the estimated risks from the simulation analyses are most likely to be underestimates, or conservatively estimating risk. This is an important aspect of measurement error with significant implications for risk assessment and should not be overlooked.'' (Document ID 3574, pp. 116-117). Addressing Dr. Cox's broader point, Dr. Seixas in his peer review stated that the ``simulation of exposure measurement error in assessing the degree of bias that may have been present is a reasonable approach to assessing this source of uncertainty'' (Document ID 3574, pp. 116). Dr. Crump similarly characterized the uncertainty analysis used in the Steenland and Bartell study as ``a strong effort'' that ``appropriately applied'' this method (Document ID 3574, pp. 161-162). In this regard, OSHA generally notes that the advantages and limitations of various methods to address exposure measurement error in exposure-response models is an area of ongoing investigation in risk assessment. As shown by the comments of OSHA's peer reviewers above, there is no scientific consensus to support Dr. Cox's opinion that the Monte Carlo analysis is an inappropriate approach to analyze the effects of exposure measurement error.

    In conclusion, through use of high quality studies and modeling, performance of an uncertainty analysis, and submission of the results of that analysis to peer review, OSHA maintains that it has relied upon the best available evidence. In addition, OSHA has carefully considered the public comments criticizing ToxaChemica's uncertainty analysis and has concluded that exposure estimation error did not substantially affect the results in the majority of studies examined (Document ID 1711, pp. 299-314). As a result, it was not necessary to conduct additional analyses modifying the approach adopted by Drs. Steenland and Bartell. Accordingly, OSHA reaffirms its determination that the conclusions of the Agency's risk assessment are correct and largely unaffected by potential error in exposure measurement.

    L. Comments and Responses Concerning Causation

    As discussed in Section V.C, Summary of the Review of Health Effects Literature and Preliminary QRA, OSHA finds, based upon the best available evidence in the published, peer-reviewed scientific literature, that exposure to respirable crystalline silica increases the risk of silicosis, lung cancer, other non-malignant respiratory disease (NMRD), and renal and autoimmune effects. Exposure to respirable crystalline silica causes silicosis and is the only known cause of silicosis. For other health endpoints like lung cancer that have both occupational and non-occupational sources of exposure, OSHA used a comprehensive weight-of-evidence approach to evaluate the published, peer-reviewed scientific studies in the literature to determine their overall quality and whether there is substantial evidence that exposure to respirable crystalline silica increases the risk of a particular health effect. For example, with respect to lung cancer, OSHA reviewed 60 epidemiological studies covering more than 30 occupational groups in over a dozen industrial sectors and concluded that exposure to respirable crystalline silica increases the risk of lung cancer (Document ID 1711, pp. 77-170). This conclusion is consistent with that of the World Health Organization's International Agency for Research on Cancer (IARC), HHS' National Toxicology Program (NTP), the National Institute for Occupational Safety and Health (NIOSH), and many other organizations and individuals, as evidenced in the rulemaking record and discussed throughout this section.

    In spite of this, and in addition to asserting that OSHA's Preliminary QRA was affected by many biases, Dr. Cox, on behalf of the ACC, argued that OSHA failed to conduct statistical analyses of causation, which led to inaccurate conclusions about causation. He specifically challenged OSHA's reliance upon the IARC determination of carcinogenicity, as discussed in Section V.F, Comments and Responses Concerning Lung Cancer Mortality, and its use of the criteria for evaluating causality developed by the noted epidemiologist Bradford Hill (Document ID 2307, Attachment 4, pp. 13-14; 4027, p. 28). The Hill criteria are nine aspects of an association that should be considered when examining causation: (1) The strength of the association; (2) the consistency of the association; (3) the specificity of the association; (4) the temporal relationship of the association; (5) the biological gradient (i.e., dose-response curve); (6) the biological plausibility of the association; (7) coherency; (8) experimentation; and (9) analogy (Document ID 3948, pp. 295-299).

    Instead, Dr. Cox suggested that OSHA use the methods listed in Table 1 of his 2013 paper, ``Improving causal inferences in risk analysis,'' which he described as ``the most useful study designs and methods for valid causal analysis and modeling of causal exposure-

    response (CER) relations'' (Document ID 2307, Attachment 4, p. 11). Because OSHA did not use these methods, Dr. Cox maintained that the Agency's Preliminary QRA ``asserts causal conclusions based on non-

    causal studies, data, and analyses'' (Document ID 2307, Attachment 4, p. 3). He also contended that OSHA ``had conflated association and causation, ignoring the fact that modeling choices can create findings of statistical associations that do not predict correctly the changes in health effects (if any) that would be caused by changes in exposures'' (Document ID 2307, Attachment 4, p. 3). He claimed that ``this lapse all by itself invalidates the Preliminary QRA's predictions and conclusions'' (Document ID 2307, Attachment 4, p. 3). As discussed below, since OSHA's methodology and conclusions regarding causation are based on the best available evidence, they are sound. Consequently, Dr. Cox's contrary position is unpersuasive.

    1. IARC Determination

    Dr. Cox asserted that OSHA erred in its reliance on the IARC determination of carcinogenicity for crystalline silica inhaled in the forms of quartz or cristobalite. He believed OSHA only relied on the IARC findings because they aligned with the Agency's opinion, noting that the ``IARC analysis involved some of the same researchers, same methodological flaws, and same gaps in explicit, well-documented derivations of benefits and conclusions as OSHA's own preliminary QRA'' (Document ID 2307, Attachment 4, pp. 13-14). OSHA, however, relied on IARC's determination to include lung cancer in its quantitative risk assessment because it constitutes the best available evidence. For this reason, Dr. Cox's position is without merit and OSHA's

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    findings are supported by substantial evidence in the record and reasonable.

    As discussed in Section V.F, Comments and Responses Concerning Lung Cancer Mortality, the IARC classifications and accompanying monographs are well recognized in the scientific community, and have been described by scientists as ``the most comprehensive and respected collection of systematically evaluated agents in the field of cancer epidemiology'' (Demetriou et al., 2012, Document ID 4131, p. 1273). IARC's conclusions resulted from a thorough expert committee review of the peer-reviewed scientific literature, in which crystalline silica dust, in the form of quartz or cristobalite, was classified as Group 1, ``carcinogenic to humans,'' in 1997 (Document ID 2258, Attachment 8, p. 210). Since the publication of these conclusions, the scientific community has reaffirmed their soundness. In March of 2009, 27 scientists from eight countries participated in an additional IARC review of the scientific literature and reaffirmed that crystalline silica dust is a Group 1 carcinogen, i.e., ``carcinogenic to humans'' (Document ID 1473, p. 396). Additionally, the HHS' U.S. National Toxicology Program also concluded that respirable crystalline silica is a known human carcinogen (Document ID 1164, p. 1).

    Further supporting OSHA's reliance on IARC's determination of carcinogenicity for its quantitative risk assessment is testimony offered by scientists during the informal public hearings. This testimony highlighted IARC's carcinogenicity determinations as very thorough examinations of the scientific literature that demonstrate that exposure to respirable crystalline silica causes lung cancer. For example, when asked about Dr. Cox's causation claims during the informal public hearings, David Goldsmith, Ph.D., noted that causation was very carefully examined by IARC. He believed that IARC, in its 1997 evaluation of evidence for cancer and silica, ``. . . chose . . . the best six studies that were the least confounded for inability to control for smoking or other kinds of hazardous exposures like radiation and asbestos and arsenic . . .'' (Document ID 3577, Tr. 894-

    896). He also believed it ``. . . crucial . . . that we pay attention to those kinds of studies, that we pay attention to the kinds of studies that were looked at by the IARC cohort that Steenland did from 2001. That's where they had the best evidence'' (Document ID 3577, Tr. 894-896).

    Regarding IARC's evaluation of possible biases and confounders in epidemiological studies, as well as its overall determination, Frank Mirer, Ph.D., of CUNY School of Public Health, representing the AFL-

    CIO, testified:

    IARC has active practicing scientists review--I've been on two IARC monographs, but not these monographs, monograph working groups. It's been dealt with. It's been dealt with over a week of intense discussion between the scientists who are on these committees, as to whether there's chance bias in confounding which might have led to these results, and by 1987 for foundries and 1997 for silica, and it's been decided and reaffirmed.

    So people who don't believe it are deniers, pure and simple. This is the scientific consensus. I was on the NTP Board of Scientific Counselors when we reviewed the same data. Known to be a human carcinogen. Once you know it's a human carcinogen from studies in humans, you can calculate risk rates (Document ID 3578, Tr. 937).

    That OSHA relied on the best available evidence to draw its conclusions was also affirmed by Dr. Cox's inability to provide additional studies that would have cast doubt on the Agency's causal analysis. Indeed, during the informal public hearings, Kenneth Crump, Ph.D., an OSHA peer reviewer from the Louisiana Tech University Foundation, asked Dr. Cox if he could identify ``any causal studies of silica that they OSHA should have used but did not use?'' Dr. Cox responded: ``I think OSHA could look at a paper from around 2007 of Brown's, on some of the issues and causal analysis, but I think the crystalline silica area has been behind other particulate matter areas . . . in not using causal analysis methods. So no, I can't point to a good study that they should have included but didn't'' (Document ID 3576, Tr. 401-402). In light of the above, OSHA maintains that in relying on IARC's determination of carcinogenicity, its conclusions on causation are rooted in the best available evidence.

    2. Bradford Hill Criteria and Causality

    Dr. Cox also challenged OSHA's use of Hill's criteria for causation. He claimed that the Bradford Hill considerations were neither necessary nor sufficient for establishing causation, which was his reason for failing to include them in the statistical methods listed in Table 1 of his written comments for objectively establishing evidence about causation (Document ID 4027, p. 28). As explained below, based on its review of the record, OSHA finds this position meritless, as it is unsupported by the best available evidence.

    As a preliminary matter, Hill's criteria for causation (Document ID 3948) are generally accepted as a gold standard for causation in the scientific community. Indeed, OSHA heard testimony during the informal public hearings and received post-hearing comments indicating that Dr. Cox's assertion that statistical methods should be used to establish causality is not consistent with common scientific practice. For example, Andrew Salmon, Ph.D., an OSHA peer reviewer, wrote:

    The identification of causality as opposed to statistical association is, as described by Bradford Hill in his well-known criteria, based mainly on non-statistical considerations such as consistence, temporality and mechanistic plausibility: the role of statistics is mostly limited to establishing that there is in fact a quantitatively credible association to which causality may (or may not) be ascribed. OSHA correctly cites the substantial body of evidence supporting the association and causality for silicosis and lung cancer following silica exposure, and also quotes previous expert reviews (such as IARC). The causal nature of these associations has already been established beyond any reasonable doubt, and OSHA's analysis sufficiently reflects this (Document ID 3574, p. 38).

    Similarly, Kyle Steenland, Ph.D., Professor, Department of Environmental Health, Rollins School of Public Health, Emory University, in response to a question about Dr. Cox's testimony on causation from Darius Sivin, Ph.D., of the UAW Health and Safety Department, stated that the Bradford Hill criteria are met for lung cancer and silicosis:

    Most of the Bradford Hill criteria apply here. You know you can never prove causality. But when the evidence builds up to such an extent and you have 100 studies and they tend to be fairly consistent, that's when we draw a causal conclusion. And that was the case for cigarette smoke in lung cancer. That was the case for asbestos in lung cancer. And when the evidence builds up to a certain point, you say, yeah, it's a reasonable assumption that this thing causes, X causes Y (Document ID 3580, pp. 1243-1244).

    As a follow-up, OSHA asked if Dr. Steenland felt that the Bradford Hill criteria were met for silica health endpoints. Dr. Steenland replied, ``For silicosis or for lung cancer. I had said they're met for both'' (Document ID 3580, p. 1262).

    Gary Ginsberg, Ph.D., an OSHA peer reviewer, agreed with Dr. Steenland, remarking to Dr. Cox during questioning, ``I'm a little dumbfounded about the concern over causality, given all the animal evidence'' (Document ID 3576, Tr. 406). Mr. Park from NIOSH's Risk Evaluation Branch, in his question to Dr. Cox, echoed the sentiments of Dr. Ginsberg, stating:

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    It's ludicrous to hear someone question causality. There's 100 years of research in occupational medicine, in exposure assessment. People here even in industry would agree that silica they say causes silicosis, which causes lung cancer. There's some debate about whether the middle step is required. There's no question that there's excess lung cancer in silica-exposed populations. We look at literature, and we identify what we call good studies. Good studies are ones that look at confounding, asbestos, whatever. We make judgments. If there's data that allows one to control for confounding, that's part of the analysis. If there is confounding that we can't control for, we evaluate it. We ask how bad could it be? There's a lot of empirical judgment from people who know these populations, know these exposures, know these industries, who can make very good judgments about that. We aren't stupid. So I don't know where you're coming from (Document ID 3576, Tr. 410-411).

    Indeed, Kenneth Mundt, Ph.D., testifying on behalf of the International Diatomite Producers Association (part of the ACC Crystalline Silica Panel, which included Dr. Cox), and whose research study was the basis for the Morfeld et al. (2013, Document ID 3843) paper that reportedly identified a high exposure threshold for silicosis, also appeared to disagree with Dr. Cox's view of causation. Dr. Mundt testified that while he thought he could appreciate Dr. Cox's testimony, at some point there is sufficiently accumulated evidence of a causal association; he concluded, ``I think here, over time, we've had the advantage with the reduction of exposure to see reduction in disease, which I think just makes it a home run that the diseases are caused by, therefore can be prevented by appropriate intervention'' (Document ID 3577, Tr. 639-640).

    OSHA notes that Dr. Cox, upon further questioning by Mr. Park, appeared to concede that exposure to respirable crystalline silica causes silicosis; Dr. Cox stated, ``I do not question that at sufficiently high exposures, there are real effects'' (Document ID 3576, Tr. 412). Later, when questioned by Anne Ryder, an attorney in the Solicitor of Labor's office, he made a similar statement: ``I do take it as given that silica at sufficiently high and prolonged exposures causes silicosis'' (Document ID 3576, Tr. 426). Based upon this testimony of Dr. Cox acknowledging that silica exposure causes silicosis, OSHA interprets his concern with respect to silicosis to be not one of causation, but rather a concern with whether there is a silicosis threshold (i.e., that exposure to crystalline silica must generally be above some level in order for silicosis to occur). Indeed, OSHA peer reviewer Brian Miller, Ph.D., noted in his post-hearing comments that Dr. Cox, when challenged, accepted that silica was causal for silicosis, ``but questioned whether there was evidence for increased risks at low concentrations; i.e. whether there was a threshold'' (Document ID 3574, p. 31). Thresholds for silicosis are addressed in great detail in Section V.I, Comments and Responses Concerning Thresholds for Silica-Related Diseases.

    Based on the testimony and written comments of numerous scientists representing both public health and industry--all of whom agree that causation is established by applying the Bradford Hill criteria and examining the totality of the evidence--OSHA strongly disagrees with Dr. Cox's claims that the Bradford Hill criteria are inadequate to evaluate causation in epidemiology and that additional statistical techniques are needed to establish causation. OSHA defends its reliance on the IARC determination of 1997 and re-determination of 2012 that crystalline silica is a causal agent for lung cancer. OSHA's own Review of Health Effects Literature further demonstrates the totality of the evidence supporting the causality determination (Document ID 1711). Indeed, other than Dr. Cox representing the ACC, no other individual or entity questioned causation with respect to silicosis. Even Dr. Cox's questioning of causation for silicosis appears to be more of a question about thresholds, which is discussed in Section V.I, Comments and Responses Concerning Thresholds for Silica-Related Diseases.

    3. Dr. Cox's Proposed Statistical Methods

    OSHA reviewed the statistical methods provided by Dr. Cox in Table 1 of his 2013 paper, ``Improving causal inferences in risk analysis,'' (Document ID 2307, Attachment 4, p. 11), and explains below why the Agency did not adopt them. For example, Intervention Time Series Analysis (ITSA), as proposed by Dr. Cox in his Table 1, is a method for assessing the impact of an intervention or shock on the trend of outcomes of interest (Gilmour et al., 2006, cited in Document ID 2307, Attachment 4, p. 11). Implementing ITSA requires time series data before and after the intervention for both the dependent variable (e.g., disease outcome) and independent variables (e.g., silica exposure and other predictors), as well as the point of occurrence of the intervention. Although time-series data are frequently available in epidemiological studies, for silica we do not have a specific ``intervention point'' comparable to the implementation of a new OSHA standard that can be identified and analyzed. Rather, changes in exposure controls tend to be iterative and piecemeal, gradually bringing workers' exposures down over the course of a facility's history and affecting job-specific exposures differently at different points in time. Furthermore, individual workers' exposures change continually with new job assignments and employment. In addition, in a situation where the intervention really reduces the adverse outcome to a low level, such as 1/1000 lifetime excess risk, ITSA would require an enormous observational database in order to be able to estimate the actual post-intervention level of risk. OSHA believes the standard risk analysis approach of estimating an exposure-response relationship based on workers' exposures over time and using this model to predict the effects of a new standard on risk appropriately reflects the typical pattern of multiple and gradual changes in the workers' exposures over time found in most industrial facilities.

    Another method listed in Dr. Cox's Table 1, marginal structural models (MSM), was introduced in the late 1990s (Robins, 1998, cited in Document ID 2307, Attachment 4, p. 11) to address issues that can arise in standard modeling approaches when time-varying exposure and/or time-

    dependent confounders are present.\10\ These methods are actively being explored in the epidemiological literature, but have not yet become a standard method in occupational epidemiology. As such, OSHA faces some of the same issues with MSM as were previously noted with BMA: Published, peer-reviewed studies using this approach are not available for the silica literature, and best practices are not yet well established. Thus, the incorporation of MSM in the silica risk assessment is not possible using the currently available literature and would be premature for OSHA's risk assessment generally.

    ---------------------------------------------------------------------------

    \10\ A time-dependent confounder is a covariate whose post-

    baseline value is a risk factor for both the subsequent exposure and the outcome.

    ---------------------------------------------------------------------------

    In addition, in his post-hearing brief, Dr. Cox contended that ``a well-done QRA should explicitly address the causal fraction (and explain the value used), rather than tacitly assuming that it is 1'' (Document ID 4027, p. 4). However, this claim is without grounds. OSHA understands Dr. Cox's reference to the ``causal fraction'' to mean that,

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    when estimating risk from an exposure-response model, only a fraction of the total estimated risk should be attributed to disease caused by the occupational exposure of interest. The Agency notes that the ``causal fraction'' of risk is typically addressed through the use of life table analyses, which incorporate background rates for the disease in question. Such analyses, which OSHA used in its Preliminary QRA, calculate the excess risk, over and above background risk, that is solely attributable to the exposure in question. Thus, there is no need to estimate a causal fraction due to exposure. These approaches are further discussed in Section V.M, Comments and Responses Concerning Working Life, Life Tables, and Dose Metric. Furthermore, nowhere in the silica epidemiological literature has the use of an alternative ``causal fraction'' approach to ascribing the causal relationship between silica exposure and silicosis and lung cancer been deemed necessary to reliably estimate risk.

    4. The Assertion That the Silica Scientific Literature May Be False

    Dr. Cox also asserted that the same biases and issues with causation in OSHA's Quantitative Risk Assessment (QRA) were likewise present in the silica literature. He wrote, ``In general, the statistical methods and causal inferences described in this literature are no more credible or sound than those in OSHA's Preliminary QRA, and for the same reasons'' (Document ID 2307, Attachment 4, p. 30).

    The rulemaking record contains evidence that contradicts Dr. Cox's claims with respect to the scientific foundation of the QRA. Such evidence includes scientific testimony and the findings of many expert bodies, including IARC, the HHS National Toxicology Program, and NIOSH, concluding that exposure to respirable crystalline silica causes lung cancer. At the public hearing, Dr. Steenland, Professor at Emory University, testified that the body of evidence pertaining to silica was of equal quality to that of other occupational health hazards (Document ID 3580, pp. 1245-1246). Dr. Goldsmith similarly testified:

    Silica dust . . . is like asbestos and cigarette smoking in that exposure clearly increases the risk of many diseases. There have been literally thousands of research studies on exposure to crystalline silica in the past 30 years. Almost every study tells the occupational research community that workers need better protection to prevent severe chronic respiratory diseases, including lung cancer and other diseases in the future. What OSHA is proposing to do in revising the workplace standard for silica seems to be a rational response to the accumulation of published evidence (Document ID 3577, Tr. 865-866).

    OSHA agrees with these experts, whose positive view of the science supporting the need for better protection from silica exposures stands in contrast to Dr. Cox's claim regarding what he believes to be the problematic nature of the silica literature. Dr. Cox asserted in his written statement:

    Scientists with subject matter expertise in areas such as crystalline silica health effects epidemiology are not necessarily or usually also experts in causal analysis and valid causal interpretation of data, and their causal conclusions are often mistaken, with a pronounced bias toward declaring and publishing findings of `significant' effects where none actually exists (false positives). This has led some commentators to worry that `science is failing us,' due largely to widely publicized but false beliefs about causation (Lehrer, 2012); and that, in recent times, `Most published research findings are wrong' (Ioannadis, 2005), with the most sensational and publicized claims being most likely to be wrong. (Document ID 2307, Attachment 4, pp. 15-16).

    Moreover, during the public hearing, Dr. Cox stated that, with respect to lung cancer in the context of crystalline silica, the literature base may be false:

    MR. PERRY OSHA Director of the Directorate of Standards and Guidance: So as I understand it, you basically think there's a good possibility that the entire literature base, with respect to lung cancer now, I'm talking about, is wrong?

    DR. COX: You mean with respect to lung cancer in the context of crystalline silica?

    MR. PERRY: Yes, sir.

    DR. COX: I think that consistent with the findings of Lauer Lehrer and Ioannidis and others, I think that it's very possible and plausible that there is a consistent pattern of false positives in the literature base, yes. And that implies, yes, they are wrong. False positives are false (Document ID 3576, Tr. 423).

    The Ioannidis paper (Document ID 3851) used mathematical constructs to purportedly demonstrate that most claimed research findings are false, and then provided suggestions for improvement (Document ID 3851, p. 0696). Two of his suggestions appear particularly relevant to the silica literature: ``Better powered evidence, e.g., large studies or low-bias meta-analyses, may help, as it comes closer to the unknown `gold' standard. However, large studies may still have biases and these should be acknowledged and avoided''; and ``second, most research questions are addressed by many teams, and it is misleading to emphasize the statistically significant findings of any single team. What matters is the totality of the evidence'' (Document ID 3851, pp. 0700-0701). OSHA finds no merit in the claim that most claimed research findings are false. Instead, it finds that the silica literature for lung cancer is overall trustworthy, particularly because the ``totality of the evidence'' characterized by large studies demonstrates a causal relationship between crystalline silica exposure and lung cancer, as IARC determined in 1997 and 2012 (Document ID 2258, Attachment 8, p. 210; 1473, p. 396).

    OSHA likewise notes that there was disagreement on Ioannidis' methods and conclusions. Jonathan D. Wren of the University of Oklahoma, in a correspondence to the journal that published the paper, noted that Ioannidis, ``after all, relies heavily on other studies to support his premise, so if most (i.e., greater than 50%) of his cited studies are themselves false (including the eight of 37 that pertain to his own work), then his argument is automatically on shaky ground'' (Document ID 4087, p. 1193). In addition, Steven Goodman of Johns Hopkins School of Medicine and Sander Greenland of the University of California, Los Angeles, performed a substantive mathematical review (Document ID 4081) of the Ioannidis models and concluded in their correspondence to the same journal that ``the claims that the model employed in this paper constitutes `proof' that most published medical research claims are false, and that research in `hot' areas is most likely to be false, are unfounded'' (Document ID 4095, p. 0773).

    Christiana A. Demetriou, Imperial College London, et al. (2012), analyzed this issue of potential false positive associations in the field of cancer epidemiology (Document ID 4131). They examined the scientific literature for 509 agents classified by IARC as Group 3, ``not classifiable as to its carcinogenicity to humans'' (Document ID 4131). Of the 509 agents, 37 had potential false positive associations in the studies reviewed by IARC; this represented an overall frequency of potential false positive associations between 0.03 and 0.10 (Document ID 4131). Regarding this overall false positive frequency of about 10 percent, the authors concluded, ``In terms of public health care decisions, given that the production of evidence is historical, public health care professionals are not expected to react immediately to a single positive association. Instead, they are likely to wait for further support or enough evidence to reach a consensus, and if a hypothesis is repeatedly tested, then any initial false-positive results will be quickly undermined'' (Document ID 4131, p. 1277). The

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    authors also cautioned that ``Reasons for criticisms that are most common in studies with false-positive findings can also underestimate an association and in terms of public health care, false-negative results may be a more important problem than false-positives'' (Document ID 4131, pp. 1278-1279). Thus, this study suggested that the false positive frequency in published literature is actually rather low, and stressed the importance of considering the totality of the literature, rather than a single study.

    Given these responses to Ioannidis, OSHA fundamentally rejects the claim that most published research findings are false. The Agency concludes that, most likely, where, as here, there are multiple, statistically significant positive findings of an association between silica and lung cancer made by different researchers in independent studies looking at distinct cohorts, the chances that there is a consistent pattern of false positives are small; OSHA's mandate is met when the weight of the evidence in the body of science constituting the best available evidence supports such a conclusion.

  9. Comments and Responses Concerning Working Life, Life Tables, and Dose Metric

    As discussed in Section V.C, Summary of the Review of Health Effects Literature and Preliminary QRA, OSHA presented risk estimates associated with exposure over a working lifetime to 25, 50, 100, 250, and 500 mug/m\3\ respirable crystalline silica (corresponding to cumulative exposures over 45 years to 1.125, 2.25, 4.5, 11.25, and 22.5 mg/m\3\-yrs). For mortality from silica-related disease (i.e., lung cancer, silicosis and non-malignant respiratory disease (NMRD), and renal disease), OSHA estimated lifetime risks using a life table analysis that accounted for background and competing causes of death. The mortality risk estimates were presented as excess risk per 1,000 workers for exposures over an 8-hour working day, 250 days per year, and a 45-year working lifetime. This is a legal standard that OSHA typically uses in health standards to satisfy the statutory mandate to ``set the standard which most adequately assures, to the extent feasible, that no employee will suffer material impairment of health or functional capacity even if such employee has regular exposure to the hazard dealt with by such standard for the period of his working life.'' 29 U.S.C. 655(b)(5). For silicosis morbidity, OSHA based its risk estimates on cumulative risk models used by various investigators to develop quantitative exposure-response relationships. These models characterized the risk of developing silicosis (as detected by chest radiography) up to the time that cohort members (including both active and retired workers) were last examined. Thus, risk estimates derived from these studies represent less-than-lifetime risks of developing radiographic silicosis. OSHA did not attempt to estimate lifetime risk (i.e., up to age 85) for silicosis morbidity because the relationships between age, time, and disease onset post-exposure have not been well characterized.

    OSHA received critical comments from representatives of the ACC and the Chamber. These commenters expressed concern that (1) the working lifetime exposure of 45 years was not realistic for workers, (2) the use of life tables was improper and alternative methods should be used, and (3) the cumulative exposure metric does not consider the exposure intensity and possible resulting dose-rate effects. OSHA examines these comments in detail in this section, and shows why they do not alter its conclusion that the best available evidence in the rulemaking record fully supports the Agency's use of a 45-year working life in a life table analysis with cumulative exposure as the exposure metric of concern.

    1. Working Life

    The Chamber commented that 45-year career silica exposures do not exist in today's working world, particularly in ``short term work-site industries'' such as construction and energy production (Document ID 4194, p. 11; 2288, p. 11). The Chamber stated that careers in these jobs are closer to 6 years, pointing out that OSHA's contractor, ERG, estimated a 64 percent annual turnover rate in the construction industry. Referring to Section 6(b)(5) of the Occupational Safety and Health (OSH) Act of 1970, the Chamber concluded, ``OSHA improperly inflates risk estimates with its false 45-year policy, contradicting the Act, which requires standards based on actual, `working life' exposures--not dated hypotheticals'' (Document ID 4194, pp. 11-12; 2288, pp. 11-12).

    As stated previously, OSHA believes that the 45-year exposure estimate satisfies its statutory obligation to evaluate risks from exposure over a working life, and notes that the Agency has historically based its significance-of-risk determinations on a 45-year working life from age 20 to age 65 in each of its substance-specific rulemakings conducted since 1980. The Agency's use of a 45-year working life in risk assessment has also been upheld by the DC Circuit (Bldg & Constr. Trades Dep't v. Brock, 838 F.2d 1258, 1264-65 (D.C. Cir. 1988)) (also see Section II, Pertinent Legal Authority). Even if most workers are not exposed for such a long period, some will be, and OSHA is legally obligated to set a standard that protects those workers to the extent such standard is feasible. For reasons explained throughout this preamble, OSHA has set the PEL for this standard at 50 microg/m\3\ TWA. In setting the PEL, the Agency reasoned that while this level does not eliminate all risk from 45 years of exposures for each employee, it is the lowest level feasible for most operations.

    In addition, OSHA heard testimony and received several comments with accompanying data that support a 45-year working life in affected industries. For example, six worker representatives of the International Union of Bricklayers and Allied Craftworkers (BAC), which represents a portion of the unionized masonry construction industry (Document ID 4053, p. 2), raised their hands in the affirmative when asked if they had colleagues who worked for longer than 40 years in their trade (Document ID 3585, Tr. 3053). Following the hearings, BAC reviewed its International Pension Fund and counted 116 members who had worked in the industry for 40 years or longer. It noted that this figure was likely an understatement, as many workers had previous experience in the industry prior to being represented by BAC, and many BAC affiliates did not begin participation in the Fund until approximately a decade after its establishment in 1972 (Document ID 4053, p. 2).

    OSHA heard similar testimony from representatives of other labor groups and unions. Appearing with the Laborers' Health and Safety Fund of North America (LHSFNA), Eddie Mallon, a long-time member of the New York City tunnel workers' local union, testified that he had worked in the tunnel business for 50 years, mainly on underground construction projects (Document ID 3589, Tr. 4209). Appearing with the United Steelworkers, Allen Harville, of the Newport News Shipbuilding Facility and Drydock, testified that there are workers at his shipyard with more than 50 years of experience. He also believed that 15 to 20 percent of workers had 20 to 40 years of experience (Document ID 3584, Tr. 2571).

    In addition, several union representatives appearing with the Building and Construction Trades Department (BCTD) of the American Federation of Labor and Congress of Industrial Organizations (AFL-CIO) also

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    commented on the working life exposure estimate. Deven Johnson, of the Operative Plasterers' and Cement Masons' International Association, testified that he thought 45 years was relevant, as many members of his union had received gold cards for 50 and 60 years of membership; he also noted that there was a 75-year member in his own local union (Document ID 3581, Tr. 1625-1626). Similarly, Sarah Coyne, representing the International Union of Painters and Allied Trades, testified that 45 years was adequate, as ``we have many, many members who continue to work out in the field with the 45 years'' (Document ID 3581, Tr. 1626). Charles Austin, of the International Association of Sheet Metal, Air, Rail and Transportation Workers, added that thousands of workers in the union's dust screening program have been in the field for 20 to 30 years (Document ID 3581, Tr. 1628-1629).

    In its post-hearing comment, the BCTD submitted evidence on behalf of the United Association of Plumbers, Fitters, Welders and HVAC Service Techs, which represents a portion of the workers in the construction industry. A review of membership records for this association revealed 35,649 active members with 45 years or more of service as a member of the union. Laurie Shadrick, Safety and Health National Coordinator for the United Association, indicated that this membership figure is considered an underestimate, as many members had previous work experience in the construction industry prior to joining the union, or were not tracked by the union after transitioning to other construction trades (Document ID 4073, Attachment 1b). The post-

    hearing comment of the BCTD also indicated a trend of an aging workforce in the construction industry, with workers 65 years of age and older predicted to increase from 5 percent in 2012 to 8.3 percent in 2022 (Document ID 4073, Attachment 1a, p. 1). This age increase is likely due to the fact that few construction workers have a defined benefit pension plan, and the age for collecting Social Security retirement benefits has been increasing; as a result, many construction workers are staying employed for longer in the industry (Document ID 4073, Attachment 1a, p. 1). Thus, the BCTD expressed its support for using a 45-year working life in the construction industry for risk assessment purposes (Document ID 4073, Attachment 1a, p. 1).

    In addition to BAC and BCTD, OSHA received post-hearing comments on the 45-year working life from the International Union of Operating Engineers (IUOE) and the American Federation of State, County and Municipal Employees (AFSCME). The IUOE reviewed records of the Central Pension Fund, in which IUOE construction and stationary local unions participate, and determined that the average years of service amongst all retirees (75,877 participants) was 21.34 years, with a maximum of 49.93 years of active service. Of these retirees, 15,836 participants recorded over 30 years of service, and 1,957 participants recorded over 40 years of service (Document ID 4025, pp. 6-7). The IUOE also pointed to the testimony of Anthony Bodway, Special Projects Manager at Payne & Dolan, Inc. and appearing with the National Asphalt Pavement Association (NAPA), who indicated that some workers in his company's milling division had been with the company anywhere from 35 to 40 years (Document ID 3583, Tr. 2227, 2228). Similarly, the AFSCME reported that, according to its 2011 poll, 49 percent of its membership had over 10 years of experience, and 21 percent had over 20 years (Document ID 3760, p. 2).

    The rulemaking record on this topic of the working life thus factually refutes the Chamber's assertion that ``no such 45-year career silica exposures exist in today's working world, particularly in construction, energy production, and other short term work-site industries'' (Document ID 4194, p. 11; 2288, p. 11). Instead, OSHA concludes that the rulemaking record demonstrates that the Agency's use of a 45-year working life as a basis for estimating risk is legally justified and factually appropriate.

    2. Life Tables

    Dr. Cox, on behalf of the ACC, commented that OSHA should use ``modern methods,'' such as Bayesian competing-risks analyses, expectation-maximization (EM) methods, and copula-based approaches that account for subdistributions and interdependencies among competing risks (Document ID 2307, Attachment 4, p. 61). Such methods, according to Dr. Cox, are needed ``to obtain risk estimates . . . that have some resemblance to reality, and that overcome known biases in the naiumlve life table method used by OSHA'' (Document ID 2307, Attachment 4, p. 61). Dr. Cox then asserted that the life table method used in the following studies to estimate mortality risks is also incorrect: Steenland et al. (2001a, Document ID 0452), Rice et al. (2001, Document ID 1118), and Attfield and Costello (2004, Document ID 0285) (Document ID 2307, Attachment 4, pp. 61-63).

    OSHA does not agree that the life table method it used to estimate mortality risks is incorrect or inappropriate. Indeed, the Agency's life table approach is a standard method commonly used to estimate the quantitative risks of mortality. As pointed out by Rice et al. (2001), the life table method was developed by the National Research Council's BEIR IV Committee on the Biological Effects of Ionizing Radiations (BEIR), Board of Radiation Effects Research, in its 1988 publication on radon (Document ID 1118, p. 40). OSHA notes that the National Research Council is the operating arm of the National Academy of Sciences and the National Academy of Engineering, and is highly respected in the scientific community. As further described by Rice et al., an ``advantage of this actuarial method is that it accounts for competing causes of death which act to remove a fraction of the population each year from the risk of death from lung cancer so that it is not necessary to assume that all workers would survive these competing causes to a given age'' (Document ID 1118, p. 40). Because this life table method is generally accepted in the scientific community and has been used in a variety of peer-reviewed, published journal articles, including some of the key studies relied upon by the Agency in its Preliminary QRA (e.g., Rice et al., 2001, Document ID 1118, p. 40; Park et al., 2002, 0405, p. 38), OSHA believes it is appropriate here.

    Regarding the alternative methods proposed by Dr. Cox, OSHA believes that these methods are not widely used in the occupational epidemiology community. In addition, OSHA notes that Dr. Cox did not provide any alternate risk estimates to support the use of his proposed alternative methods, despite the fact that the Agency made its life table data available in the Review of Health Effects Literature and Preliminary QRA (Document ID 1711, pp. 360-378). Thus, for these reasons, OSHA disagrees with Dr. Cox's claim that the life table method used by the Agency to estimate quantitative risks was inappropriate.

    3. Exposure Metric

    In its risk assessment, OSHA uses cumulative exposure, i.e., average exposure concentration multiplied by duration of exposure, as the exposure metric to quantify exposure-response relationships. It uses this metric because each of the key epidemiological studies on which the Agency relied to estimate risks used cumulative exposure as the exposure metric to quantify exposure-response relationships, although some

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    also reported significant relationships based on exposure intensity (Document ID 1711, p. 342). As noted in the Review of Health Effects Literature, the majority of studies for lung cancer and silicosis morbidity and mortality have consistently found significant positive relationships between risk and cumulative exposure (Document ID 1711, p. 343). For example, nine of the ten epidemiological studies included in the pooled analysis by Steenland et al. (2001a, Document ID 0452) showed positive exposure coefficients when exposure was expressed as cumulative exposure (Document ID 1711, p. 343).

    Commenting on this exposure metric, the ACC argued that cumulative exposure undervalues the role of exposure intensity, as some studies of silicosis have indicated a dose-rate effect, i.e., short-term exposure to high concentrations results in greater risk than longer-term exposure to lower concentrations at an equivalent cumulative exposure level (Document ID 4209, p. 58; 2307, Attachment A, pp. 93-94). The ACC added that, given that silica-related lung cancer and silicosis may both involve an inflammation-mediated mechanism, a dose-rate effect would also be expected for lung cancer (Document ID 4209, p. 58). It concluded that ``assessments of risk based solely on cumulative exposure do not account adequately for the role played by intensity of exposure and, accordingly, do not yield reliable estimates of risk'' (Document ID 4209, p. 68). Patrick Hessel, Ph.D., representing the Chamber, pointed to the initial comments of OSHA peer reviewer Kenneth Crump, Ph.D., who stated that ``not accounting for a dose-rate effect, if one exists, could overestimate risk at lower concentrations'' (Document ID 4016, p. 2, citing 1716, pp. 165-167).

    OSHA acknowledges these concerns regarding the exposure metric and finds them to have some merit. However, it notes that the best available studies use cumulative exposure as the exposure metric, as in common in occupational epidemiological studies. As discussed below, there is also substantial good evidence in the record supporting the use of cumulative exposure as the exposure metric for crystalline silica risk assessment.

    Paul Schulte, Ph.D., of NIOSH testified that ``cumulative exposure is a standard and appropriate metric for irreversible effects that occur soon after actual exposure is experienced. For lung cancer and nonmalignant respiratory disease, NMRD mortality, cumulative exposure lagged for cancer is fully justified . . . For silicosis risk assessment purposes, cumulative exposure is a reasonable and practical choice'' (Document ID 3579, Tr. 127). NIOSH also conducted a simulated dose rate analysis for silicosis incidence with data from a Chinese tin miners cohort and, in comparing exposure metrics, concluded that the best fit to the data was cumulative exposure with no dose-rate effect (Document ID 4233, pp. 36-39). This finding is consistent with the testimony of Dr. Steenland, who stated, ``Cumulative exposure, I might say, is often the best predictor of chronic disease in general, in epidemiology'' (Document ID 3580, Tr. 1227). OSHA also notes that using a cumulative exposure metric (e.g., mg/m\3\-yrs) factors in both exposure intensity and duration, while using only an exposure intensity metric (e.g., mug/m\3\) ignores the influence of exposure duration. Dr. Crump's comment that ``estimating risk based on an `incomplete' exposure metric like average exposure is not recommended . . . . Exposure to a particular air concentration for one week is unlikely to carry the same risk as exposure to that concentration for 20 years, although the average exposures are the same'' also supports the use of a cumulative exposure metric (Document ID 1716, p. 166).

    With regard to a possible dose-rate effect, OSHA agrees with Dr. Crump that if one exists and is unaccounted for, the result could be an overestimation of risks at lower concentrations (Document ID 1716, pp. 165-167). OSHA is aware of two studies discussed in its Review of Health Effects Literature and Preliminary QRA that examined dose-rate effects on silicosis exposure-response (Document ID 1711, pp. 342-344). Neither study found a dose-rate effect relative to cumulative exposure at silica concentrations near the previous OSHA PEL (Document ID 1711, pp. 342-344). However, they did observe a dose-rate effect in instances where workers were exposed to crystalline silica concentrations far above the previous PEL (i.e., several-fold to orders of magnitude above 100 mug/m\3\) (Buchanan et al., 2003, Document ID 0306; Hughes et al., 1998, 1059). For example, the Hughes et al. (1998) study of diatomaceous earth workers found that the relationship between cumulative silica exposure and risk of silicosis was steeper for workers hired prior to 1950 and exposed to average concentrations above 500 microg/m\3\ compared to workers hired after 1950 and exposed to lower average concentrations (Document ID 1059). Similarly, the Buchanan et al. (2003) study of Scottish coal miners adjusted the cumulative exposure metric in the risk model to account for the effects of exposures to high concentrations where the investigators found that, at concentrations above 2000 microg/m\3\, the risk of silicosis was about three times higher than the risk associated with exposure to lower concentrations but at the same cumulative exposure (Document ID 0306, p. 162). OSHA concluded that there is little evidence that a dose-rate effect exists at concentrations in the range of the previous PEL (100 microg/m\3\) (Document ID 1711, p. 344). However, at the suggestion of Dr. Crump, OSHA used the model from the Buchanan et al. study in its silicosis morbidity risk assessment to account for possible dose-rate effects at high average concentrations (Document ID 1711, pp. 335-342). OSHA notes that the risk estimates in the exposure range of interest (25-500 mug/m\3\) derived from the Buchanan et al. (2003) study were not appreciably different from those derived from the other studies of silicosis morbidity (see Section VI, Final Quantitative Risk Assessment and Significance of Risk, Table VI-1.).

    In its post-hearing brief, NIOSH also added that a ``detailed examination of dose rate would require extensive and real time exposure history which does not exist for silica (or almost any other agent)'' (Document ID 4233, p. 36). Similarly, Dr. Crump wrote, ``Having noted that there is evidence for a dose-rate effect for silicosis, it may be difficult to account for it quantitatively. The data are likely to be limited by uncertainty in exposures at earlier times, which were likely to be higher'' (Document ID 1716, p. 167). OSHA agrees with Dr. Crump, and believes that it has used the best available evidence to estimate risks of silicosis morbidity and sufficiently accounted for any dose-

    rate effect at high silica average concentrations by using the Buchanan et al. (2003) study.

    For silicosis/NMRD mortality, the ACC noted that Vacek et al. (2009, Document ID 2307, Attachment 6) reported that, in their categorical analysis of the years worked at various levels of exposure intensity, only years worked at >200 microg/m\3\ for silicosis and >300 microg/m\3\ for NMRD were associated with increased mortality (Document ID 2307, Attachment A, p. 93, citing 2307, Attachment 6, pp. 21, 23). However, OSHA believes it to be inappropriate to consider these results in isolation from the other study findings, and notes that Vacek et al. (2009) also reported statistically significant associations of silicosis mortality with cumulative exposure, exposure duration, and average exposure intensity in their

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    continuous analyses with univariate models; for NMRD mortality, there were statistically significant associations with cumulative exposure and average exposure intensity (Document ID 2307, Attachment 6, pp. 21, 23).

    In addition, OSHA notes that Vacek et al. (2009) did not include both an exposure intensity term and a cumulative exposure term in the multivariate model, after testing for correlation between cumulative exposure and years at particular exposure intensity; such a model would indicate how exposure intensity affects any relationship with cumulative exposure. As Dr. Crump stated in his comments:

    To demonstrate evidence for a dose-rate effect that is not captured by cumulative exposure, it would be most convincing to show some effect of dose rate that is in addition to the effect of cumulative exposure. To demonstrate such an effect one would need to model both cumulative exposure and some effect of dose rate, and show that adding the effect of dose rate makes a statistically significant improvement to the model over that predicted by cumulative exposure alone (Document ID 1716, p. 166).

    Indeed, both Buchanan et al. (2003, Document ID 0306) and Hughes et al. (1998, Document ID 1059), when examining possible dose-rate effects for silicosis morbidity, specifically included both cumulative exposure and exposure intensity in their multivariate models. Additionally, as described in the lung cancer section of this preamble, the Vacek et al. study may be affected by both exposure misclassification and the healthy worker survivor effect. Both of these biases may flatten an exposure-response relationship, obscuring the relationship at lower exposure levels, which could be the reason why a significant effect was not found at the lower exposure levels in the Vacek et al. (2009, Document ID 2307, Attachment 6) multivariate analysis.

    Regarding lung cancer mortality, the ACC pointed out that Steenland et al. (2001a, Document ID 0452) acknowledged that duration of exposure did not fit the data well in their pooled lung cancer study. The ACC indicated that exposure intensity should be considered (Document ID 2307, Attachment A, p. 93; 4209, p. 58, citing 0452, p. 779). OSHA interpreted the results of the Steenland et al. (2001, Document ID 0452) study to simply mean that duration of exposure alone was not a good predictor for lung cancer mortality, where a lag period may be important between the exposure and the development of disease. Indeed, Steenland et al. found the model with logged cumulative exposure, with a 15-year lag, to be a strong predictor of lung cancer (Document ID 0452, p. 779). Additionally, no new evidence of a dose-rate effect in lung cancer studies was submitted to the record.

    For these reasons, OSHA does not believe there to be any persuasive data in the record that supports a dose-rate effect at exposure concentrations near the revised or previous PELs. OSHA concludes that cumulative exposure is a reasonable exposure metric on which to base estimates of risk to workers exposed to crystalline silica in the exposure range of interest (25 to 500 mug/m\3\).

  10. Comments and Responses Concerning Physico-Chemical and Toxicological Properties of Respirable Crystalline Silica

    As discussed in the Review of Health Effects Literature and Preliminary Quantitative Risk Assessment (Document ID 1711, pp. 344-

    350), the toxicological potency of crystalline silica is influenced by a number of physical and chemical factors that affect the biological activity of the silica particles inhaled in the lung. The toxicological potency of crystalline silica is largely influenced by the presence of oxygen free radicals on the surfaces of respirable particles; these chemically-reactive oxygen species interact with cellular components in the lung to promote and sustain the inflammatory reaction responsible for the lung damage associated with exposure to crystalline silica. The reactivity of particle surfaces is greatest when crystalline silica has been freshly fractured by high-energy work processes such as abrasive blasting, rock drilling, or sawing concrete materials. As particles age in the air, the surface reactivity decreases and exhibits lower toxicologic potency (Porter et al., 2002, Document ID 1114; Shoemaker et al., 1995, 0437; Vallyathan et al., 1995, 1128). In addition, surface impurities have been shown to alter silica toxicity. For example, aluminum and aluminosilicate clay on silica particles has been shown to decrease toxicity (Castranova et al., 1997, Document ID 0978; Donaldson and Borm, 1998, 1004; Fubini, 1998, 1016; Donaldson and Borm, 1998, Document ID 1004; Fubini, 1998, 1016).

    In the preamble to the proposed standard, OSHA preliminarily concluded that although there is evidence that several environmental influences can modify surface activity to either enhance or diminish the toxicity of silica, the available information was insufficient to determine to what extent these influences may affect risk to workers in any particular workplace setting (Document 1711, p. 350). NIOSH affirmed OSHA's preliminary conclusion regarding the silica-related risks of exposure to clay-occluded quartz particles, which was based on what OSHA believed to be the best available evidence. NIOSH stated:

    NIOSH concurs with this assessment by OSHA. Currently available information is not adequate to inform differential quantitative risk management approaches for crystalline silica that are based on surface property measurements. Thus, NIOSH recommends a single PEL for respirable crystalline silica without consideration of surface properties (Document ID 4233, p. 44).

    Two rulemaking participants, the Brick Industry Association (BIA), which represents distributors and manufacturers of clay brick, and the Sorptive Minerals Institute (SMI), which represents many industries that process and mine sorptive clays for consumer products and commercial and industrial applications, provided comment and supporting evidence that the crystalline silica encountered in their workplace environments presents a substantially lower risk of silica-related disease than that reflected in the Agency's Preliminary QRA.

    BIA argued that the quartz particles found in clays and shales used in clay brick are occluded in aluminum-rich clay coatings. BIA submitted to the record several studies indicating reduced toxicity and fibrogenicity from exposure to quartz in aluminum-rich clays (Document ID 2343, Attachment 2, p. 2). It purported that ``OSHA lacks the statutory authority to impose the proposed rule upon the brick and structural clay manufacturing industry because employees in that industry do not face a significant risk of material impairment of health or functional capacity'' (Document ID 2242, pp. 2-3). BIA concluded that its industry should be exempted from the rule, stating: ``OSHA should exercise its discretion to exempt the brickmaking industry from compliance with the proposed rule unless and until it determines how best to take into account the industry's low incidence of adverse health effects from silica toxicity'' (Document ID 2242, p. 11).

    SMI argued that silica in sorptive clays exists as either amorphous silica or as geologically ancient, occluded quartz, ``neither of which pose the health risk identified and studied in OSHA's risk assessment'' (Document ID 4230, p. 2). SMI further contended that OSHA's discussion of aged silica ``does not accurately reflect the risk of geologically ancient, (occluded) silica formed millions of years ago found in

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    sorptive clays'' (Document ID 4230, p. 2). Additionally, SMI noted that clay products produced by the sorptive minerals industry are not heated to high temperatures or fractured, making them different from brick and pottery clays (Document ID 2377, p. 7). In support of its position, SMI submitted to the record several toxicity studies of silica in sorptive clays. It stated that the evidence does not provide the basis for a finding of a significant risk of material impairment of health from exposure to silica in sorptive clays (Document ID 4230, p. 2). Consequently, SMI concluded that the application of a reduced PEL and comprehensive standard is not warranted.

    Having considered the evidence SMI submitted to the record, OSHA finds that although quartz originating from bentonite deposits exhibits some biological activity, it is clear that it is considerably less toxic than unoccluded quartz. Moreover, evidence does not exist that would permit the Agency to evaluate the magnitude of the lifetime risk resulting from exposure to quartz in bentonite-containing materials and similar sorptive clays. This finding does not extend to the brick industry, where workers are exposed to silica through occluded quartz in aluminum rich clays. The Love et al. study (1999, Document ID 0369), which BIA claimed would be of useful quality for OSHA's risk assessment, shows sufficient cases of silicosis to demonstrate significant risk within the meaning used by OSHA for regulatory purposes. In addition, OSHA found a reduced, although still significant, risk of silicosis morbidity in the study of pottery workers (Chen et al., 2005, Document ID 0985) that BIA put forth as being representative of mortality in the brick industry (Document ID 3577, Tr. 674). These findings are discussed in detail below.

    1. The Clay Brick Industry

    BIA did not support a reduction in the PEL because although brick industry employees are exposed to crystalline silica-bearing materials, BIA believes silicosis is virtually non-existent in that industry. It contended that silica exposure in the brick industry does not cause similar rates of disease as in other industries because brick industry workers are exposed to quartz occluded in aluminum-rich layers, reducing the silica's toxicity. BIA concluded that ``no significant workplace risk for brick workers from crystalline silica exposure exists at the current exposure limit'' (Document ID 3577, Tr. 654) and that reducing the PEL would have no benefit to workers in the brick industry (Document ID 2300, p. 2). These concerns were also echoed by individual companies in the brick industry, such as Acme Brick (Document ID 2085, Attachment 1), Belden Brick Company (Document ID 2378), and Riverside Brick & Supply Company, Inc. (Document ID 2346, Attachment 1). In addition, OSHA received over 50 letters as part of a letter campaign from brick industry representatives referring to BIA's comments on the lack of silicosis in the brick industry (e.g., Document ID 2004).

    The Tile Council of North America, Inc., also noted that ``clay raw materials used in tile manufacturing are similar to those used in brick and sanitary ware manufacturing'' and also suggested that aluminosilicates decrease toxicity (Document ID 3528, p. 1). OSHA agrees with the Tile Council of North America, Inc., that their concerns mirror those of the BIA and, therefore, the Agency's consideration and response to BIA also applies to the tile industry.

    a. Evidence on the Toxicity of Silica in Clay Brick.

    On behalf of BIA, Mr. Robert Glenn presented a series of published and unpublished studies (Document ID 3418), also summarized by BIA (Document ID 2300, Attachment 1) as evidence that ``no significant workplace risk for brick workers from crystalline silica exposure exists at the current exposure limit'' (Document ID 3577, Tr. 654). Most of these studies, including an unpublished report on West Virginia brick workers (West Virginia State Health Department, 1939), a study of North Carolina brick workers (Trice, 1941), a study of brick workers in England (Keatinge and Potter, 1949), a study of Canadian brick workers (Ontario Health Department, 1972), two studies of North Carolina brick workers (NIOSH, 1978 and NIOSH, 1980), a study of English and Scottish brick workers (Love et al., 1999, Document ID 0369), and an unpublished study commissioned by BIA of workers at 13 of its member companies (BIA, 2006), reported little or no silicosis among the workers examined (Document ID 3418; 3577, Tr. 655-669).

    Based on its review of the record evidence, OSHA finds that there are many silica-containing materials (e.g., other clays, sand, etc.) in brick and concludes that BIA's position is not supported by the best available evidence. The analysis contained in the studies Mr. Glenn presents does not meet the rigorous standards used in the studies on which OSHA's risk assessment relies. Indeed the studies cited by Mr. Glenn and BIA do not adequately support their contention that silicosis is ``essentially non-existent.'' Several studies were poorly designed and applied inappropriate procedures for evaluating chest X-rays (Document ID 3577, Tr. 682-685). Dr. David Weissman of NIOSH underscored the significance of such issues, stating: ``It's very important, for example, to use multiple B readers to evaluate chest X-rays and medians of readings, and it is very important for people to be blinded to how readings are done'' (Document ID 3577, Tr. 682). Also problematic was Mr. Glenn's failure to provide key information on the length of exposure or time since the first exposure in any of the studies he presented, which examined only currently employed workers. Information on duration of exposure or time since first exposure is essential to evaluating risk of silicosis because silicosis typically develops slowly and becomes detectable between 10 years and several decades following a worker's first exposure. In the hearing, Dr. Ken Rosenman also noted inadequacies related to silicosis latency, testifying that ``we know that silicosis occurs 20, 30 years after . . . first exposure . . . if people have high exposure but short duration, short latency, you are not going to see positive x-rays even if silicosis is developing and so it's not going to be useful'' (Document ID 3577, Tr. 688-689).

    Mr. Glenn acknowledged shortcomings in the studies he submitted for OSHA's consideration, agreeing with Dr. Weissman's points about quality assurance for X-ray interpretation and study design (e.g., Document ID 3577, Tr. 683). In response to Dr. Rosenman's concerns about silicosis latency, he reported that no information on worker tenure or time since first exposure was presented in Trice (1941), Keatings and Potter (1949), Rajhans and Buldovsky (1972), the NIOSH studies (1978, 1980), or Love et al. (1999), and that more than half of the West Virginia brick workers studied by NIOSH (1939) had a tenure of less than 10 years (Document ID 4021, pp. 5-6), a time period that OSHA believes is too short to see development of most forms of silicosis. He suggested that high exposures in two areas of the West Virginia facilities could trigger accelerated or acute silicosis, which could be observed in less than 10 years, if the toxicity of the silica in clay brick was comparable to silica found in other industries (post-hearing comments, p. 5). However, OSHA notes that a cross-sectional report on actively employed workers would not necessarily capture cases of accelerated or acute silicosis,

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    which are associated with severe symptoms that compromise individuals' ability to continue work, and therefore would result in a survivor effect where only unaffected workers remain at the time of study.

    Mr. Glenn further argued that the Agency should assess risk to brick workers based on studies from that industry because the incidence of silicosis among brick workers appears to be lower than among workers in other industries (Document ID 3577, Tr. 670). For the reasons discussed above, OSHA does not believe the studies submitted by Mr. Glenn provide an adequate basis for risk assessment. In addition, studies presented did not: (1) Include retired workers; (2) report the duration of workers' exposure to silica; (3) employ, in most cases, quality-assurance practices for interpreting workers' medical exams; or (4) include estimates of workers' silica exposures. Furthermore, Mr. Glenn acknowledged in the informal public hearing that the Love et al. (1999, Document ID 0369) study of 1,925 workers employed at brick plants in England and Scotland in 1990-1991 is the only available study of brick workers that presented exposure-response information (Document ID 3577, Tr. 692). He characterized the results of that study as contradictory to OSHA's risk assessment for silicosis morbidity because the authors concluded that frequency of pneumoconiosis is low in comparison to other quartz-exposed workers (Document ID 4021, p. 2). He also cited an analysis by Miller and Soutar (Document ID 1098) (Dr. Soutar is a co-author of the Love et al. study) that compared silicosis risk estimates derived from Love et al. and those from Buchanan et al.'s study of Scottish coal workers exposed to silica, and concluded that silicosis risk among the coal workers far exceeded that among brick workers (Document ID 3577, Tr. 671). He furthermore concluded that the Love et al. study is ``the only sensible study to be used for setting an exposure limit for quartz in brick manufacturing.'' (Document ID 3577, Tr. 679).

    Based on review of the Love et al. study (Document ID 0369), OSHA agrees with Mr. Glenn's claim that the silicosis risk among workers in clay brick industries appears to be somewhat lower than might be expected in other industries. However, OSHA is unconvinced by Mr. Glenn's argument that risk to workers exposed at the previous PEL is not significant because the cases of silicosis reported in this study are sufficient to show significant risk within the meaning used by OSHA for regulatory purposes (1 in 1,000 workers exposed for a working lifetime).

    Love et al. reported that 3.7 percent of workers with radiographs were classified as ILO Category 0/1 (any signs of small opacities) and 1.4 percent of workers were classified as ILO Category 1/0 (small radiographic opacities) or greater. Furthermore, among workers aged 55 and older, the age category most likely to have had sufficient time since first exposure to develop detectable lung abnormalities from silicosis exposure, Love et al. reported prevalences of abnormal radiographs ranging from 2.9 percent (cumulative exposure below 0.5 mg/

    yr-m\3\) to 16.4 percent (exposure at least 4 mg/yr-m\3\) (Love et al. 1999, Document ID 0369, Table 4, p. 129). According to the study authors, these abnormalities ``are the most likely dust related pathology--namely, silicosis'' (Document ID 0369, p. 132). Given that OSHA considers a lifetime risk of 0.1 percent (1 in 1,000) to clearly represent a significant risk, OSHA considers the Love et al. study to have demonstrated a significant risk to brick workers even if only a tiny fraction of the abnormalities observed in the study population represent developing silicosis (see Benzene, 448 U.S. 607, 655 n. 2). According to the study authors, ``the estimated exposure-response relation for quartz suggests considerable risks of radiological abnormality even at concentrations of 0.1 mg/m\3\ 100 mug/m\3\ of quartz'' (Document ID 0369, p. 132).

    OSHA concludes that, despite the possibly lower toxicity of silica in the clay brick industry compared to other forms, and despite the Love et al. study's likely underestimation of risk due to exclusion of retired workers, the study demonstrates significant risk among brick workers exposed at the previous general industry PEL. It also suggests that the silicosis risk among brick workers would remain significant even at the new PEL. Furthermore, OSHA is unconvinced by Mr. Glenn's argument that the Agency should develop a quantitative risk assessment based on the Love et al. study, because that study excluded retired workers and had inadequate worker follow-up. As explained earlier in this section, adequate follow-up time and inclusion of retired workers is extremely important to allow for latency in the development of silicosis. Therefore, OSHA relied on studies including retired workers in its QRA for silicosis morbidity.

    Mr. Glenn additionally argued that the risk of lung cancer from silica exposure among brick workers is likely to be lower than among workers exposed to silica in other work settings. Mr. Glenn acknowledged that ``there are no published mortality studies of brick workers that look at cause of death or lung cancer death'' (Document ID 3577, Tr. 674). However, he stated that ``pottery clays are similar to the structural clays used in brickmaking in that the quartz is occluded in aluminum-rich layers of bentonite, kaolinite, and illite,'' and that OSHA should consider studies of mortality among pottery workers as representative of the brick industry (Tr. 674). Mr. Glenn cited the Chen et al. (2005) study of Chinese pottery workers, which reported a weak exposure-response relationship between silica exposure and lung cancer mortality, and which appeared to be affected by PAH-related confounding. He concluded that the Chen et al. study ``provides strong evidence for aluminum-rich clays suppressing any potential carcinogenesis from quartz'' (Document ID 3577, Tr. 675).

    OSHA acknowledges that occlusion may weaken the carcinogenicity of silica in the brick clay industry, but does not believe that the Chen et al. study provides conclusive evidence of such an effect. This is because of the relatively low carcinogenic potential of silica and the difficulty involved in interpreting one cohort with known issues of confounding (see Section V.F, Comments and Responses Concerning Lung Cancer Mortality). OSHA also notes, however, that it estimated risks of silicosis morbidity from the cited Chen et al. (2005, Document ID 0985) study, and found the risk among pottery workers to be significant, with 60 deaths per 1,000 workers at the previous PEL of 100 mug/

    m3 and 20 deaths per 1,000 workers at the revised PEL of 50 mug/m3 (as indicated in Section VI, Final Quantitative Risk Assessment and Significance of Risk, Table VI-1). Thus, given Mr. Glenn's assertion that pottery clays are similar to the clays used in brickmaking, OSHA believes that while the risk of silicosis morbidity may be lower than that seen in other industry sectors, it is likely to still be significant in the brickmaking industry.

    Thus, OSHA concludes that the BIA's position is not supported by the best available evidence. The studies cited by Mr. Glenn to support his contention that brick workers are not at significant risk of silica-related disease do not have the same standards as those studies used by OSHA in its quantitative risk assessment. Furthermore, in the highest-quality study brought forward by Mr. Glenn (Love et al. 1999, Document ID 0369), there are sufficient cases of silicosis to demonstrate significant risk within the meaning used by OSHA for

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    regulatory purposes. Even if the commenters' arguments that silica in clay brick is less toxic were, to some extent, legitimate, this would not significantly affect OSHA's own estimates from the epidemiological evidence of the risks of silicosis.

    2. Sorptive Minerals (Bentonite Clay) Processing

    SMI asserted that the physico-chemical form of respirable crystalline silica in sorptive clays reduces the toxicologic potency of crystalline silica relative to the forms of silica common to most studies relied on in OSHA's Preliminary QRA. In other words, the risk associated with exposure to silica in sorptive clays is assertedly lower than the risk associated with exposure to silica in other materials. SMI based this view on what it deemed the ``best available scientific literature,'' epidemiological, in vitro, and animal evidence OSHA had not previously considered. It believed the evidence showed reduced risk from exposure to occluded quartz found in the sorptive clays and that occluded quartz does not create a risk similar to that posed by freshly fractured quartz (Document ID 2377, p. 7). Based on this, SMI contended that the results of OSHA's Preliminary QRA were not applicable to the sorptive minerals industry, and a more stringent standard for crystalline silica is ``neither warranted nor legally permissible'' (Document ID 4230, p. 1). As discussed below, OSHA reviewed the evidence submitted by SMI and finds that although the studies provide evidence of some biological activity in quartz originating from bentonite deposits, there is not quantitative evidence that would permit the Agency to evaluate the magnitude of the lifetime risk resulting from exposure to quartz in bentonite-containing materials and similar sorptive clays.

    a. Evidence on the Toxicity of Silica in Sorptive Minerals

    SMI submitted a number of studies to the rulemaking record. First, it summarized a retrospective study by Waxweiler et al. (Document ID 3998, Attachment 18e) of attapulgite clay workers in Georgia in which the authors concluded that there was a significant deficit of non-

    malignant respiratory disease mortality and no clear excess of lung cancer mortality among these workers. It used the study as the basis for its recommendation to OSHA that the study ``be cited and that exposures in the industry be recognized in the final rule as not posing the same hazard as those in industries with reactive crystalline silica'' (Document ID 2377, p. 10).

    Based on its review of the rulemaking record, OSHA concludes that the Waxweiler et al. study is of limited value for assessing the hazard potential of quartz in bentonite clay because of the low airborne levels of silica to which the workers were exposed. The Agency's conclusion is supported by NIOSH's summary of the time-weighted average (TWA) exposures calculated for each job category in Waxweiler et al. (1988, Document ID 3998, Attachment 18e), which were found to be ``within the acceptable limits as recommended by NIOSH (i.e., 3 50 mug/m3) . . . and most were substantially lower'' (Document ID 4233, p. 41). It cannot be known to what extent the low toxicity of the dust or the low exposures experienced by the workers each contributed to the lack of observed disease.

    SMI also presented a World Health Organization (WHO) document (2005, Document ID 3929), which recognized that ``studies of workers exposed to sorptive clays have not identified significant silicosis risk'' (Document ID 2377, p. 10). However, although WHO did find that there were no reported cases of fibrotic reaction in humans exposed to montmorillonite minerals in the absence of crystalline silica (Document ID 3929, p. 130), the WHO report does discuss the long-term effects from exposure to crystalline silica, including silicosis and lung cancer. In fact, with respect to evaluating the hazards associated with exposure to bentonite clay, WHO regarded silica as a potential confounder (Document ID 3929, p. 136). Thus, WHO did not specifically make any findings with respect to the hazard potential of quartz in the bentonite clay mineral matrix but instead recognized the hazard presented by exposure to crystalline silica generally.

    Additionally, the WHO (Document ID 3929, pp. 114, 118) cited two case/case series reports of bentonite-exposed workers, one demonstrating increasing prevalence of silicosis with increasing exposure to bentonite dust (Rombola and Guardascione, 1955, Document ID 3998, Attachment 18) and another describing cases of silicosis among workers exposed to bentonite dust (Phibbs et al. 1971, Document ID 3998, Attachment 18b). Rombola and Guardascione (1955) found silicosis prevalences of 35.5 and 12.8 percent in two bentonite processing factories, and 6 percent in a bentonite mine. In the factory where the highest exposures occurred, 10 of the 26 cases found were severe and all cases developed with seven or fewer years of exposure, indicating that exposure levels were extremely high (Document ID 4233, p. 42, citing 3998, Attachment 18). Phibbs et al. (1971) reviewed chest x-rays of 32 workers in two bentonite plants, of which x-ray films for 14 indicated silicosis ranging from minimal to advanced. Although the exposure of affected workers to respirable dust or quartz is not known, industrial hygiene surveys conducted in four bentonite plants showed some areas having particle counts in excess of 3 to 11 times the ACGIH particle count limit (Document ID 3998, Attachment 18b, p. 4). This is roughly equivalent to exposure levels between 8 and 28 times OSHA's former general industry PEL of 100 mug/m3 (given that the particle count limit is about 2.5 or more times higher than the gravimetric limit for respirable quartz (see Section V.C, Summary of the Review of Health Effects Literature and Preliminary QRA). Exposures of this magnitude are considerably higher than those experienced by worker cohorts of the studies relied on by OSHA in its Final Risk Assessment and discussed in Section V.C, Summary of the Review of Health Effects Literature and Preliminary QRA. For example, the median of average exposures reported in the ten cohort studies used by Steenland et al. (2001, Document ID 0684, p. 775) ranged from about one-half to six times the former general industry PEL.

    The lack of specific exposure information on bentonite workers found with silicosis, combined with the extraordinary exposures experienced by workers in the bentonite plants studied by Phibbs et al. (1971), make this study, while concerning, unsuitable for evaluating risks in the range of the former and final rule PELs. OSHA notes that the WHO report also concluded that available data were inadequate to conclusively establish a dose-response relationship or even a cause-

    and-effect relationship for bentonite dust, and that its role in inducing pneumoconiosis remains uncertain.

    SMI also presented evidence from animal and in vitro studies that it believes shows that respirable crystalline quartz present in sorptive clays exists in a distinct occluded form, which significantly mitigates adverse health effects due to the physico-chemical characteristics of the occluded quartz. As discussed below, based on careful review of the studies SMI cited, OSHA believes these studies indicate that silica in bentonite clay is of lower toxicologic potency than that found in other industry sectors.

    SMI submitted two studies: an animal study (Creutzenberg et al. 2008,

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    Document ID 3891) and a study of the characteristics of quartz samples isolated from bentonite (Miles et al. 2008, Document ID 4173). SMI contended that these studies demonstrate the low toxicity potential of geologically ancient occluded quartz found in sorptive clays (Document ID 2377, pp. 8-9).

    Creutzenberg et al. (2008) summarized the findings from a rat study aimed at ``characterizing the differences in biological activity between crystalline ground reference quartz (DQ12) and a quartz with occluded surfaces (quartz isolate) obtained from a clay deposit formed 110-112 million years ago'' (Document ID 3891, p. 995). Based on histopathological assessment of the lungs in each treatment group, Creutzenberg et al. (2008, Document ID 3891) found that the DQ12 reference quartz group exhibited a significantly stronger inflammatory reaction than the quartz isolate, which showed a slight but still statistically significant inflammatory response compared to the control group. The increased inflammatory response was observed at day 3 but not at 28 or 90 days. Thus, reaction elicited by the quartz isolate, thought to have similar properties to bentonite, was considered by the investigators to represent a moderate effect that did not progress. In light of this, the implications of this study for development of silicosis are unclear.

    SMI also cited Miles et al. (2008, Document ID 4173), who studied the mineralogical and chemical characteristics of quartz samples isolated from bentonite, including the quartz isolate used by Creutzenberg et al. (2008) in their animal study. Their evaluation identified several differences in the chemical and physical properties of the quartz isolates and unoccluded quartz that could help explain the observed differences in toxicity (Document ID 4173); these included differences in crystal structure, electrical potential of particle surfaces, and, possibly, differences in the reactivity of surface-free radicals owing to the presence of iron ions in the residual clay material associated with the quartz isolates.

    With respect to the two studies just discussed, animal evidence cited by SMI demonstrates that quartz in bentonite induces a modest inflammatory reaction in the lung that does not persist (Creutzenberg et al., 2008, Document ID 3891). Such a reaction is notably different from the persistent and stronger response seen with standard experimental quartz material without surface occlusion (Creutzenberg et al., 2008, Document ID 3891). Physical and chemical characteristics of quartz from bentonite deposits have been shown to differ from standard experimental quartz in ways that can explain its reduced toxicity (Miles et al., 2008, Document ID 4173). However, the animal studies cited by SMI are not suitable for risk assessment since they were short-term (90 days), single-dose experiments.

    In sum, human evidence on the toxicity of quartz in bentonite clay includes one study cited by SMI that did not find an excess risk of respiratory disease (Waxweiller et al., Document ID 3998, Attachment 18e). However, because exposures experienced by the workers were low with most less than that of the final rule PEL, the lack of an observed effect cannot be solely attributed to the nature of the quartz particles. Two studies of bentonite workers found a high prevalence of silicosis based on x-ray findings (Rombola and Guardascione, 1955, Document ID 3998, Attachment 18; Phibbs et al., 1971, Document ID 3998, Attachment 18b). Limited exposure data provided in the studies as well as the relatively short latencies seen among cases of severe silicosis make it clear that the bentonite workers were exposed to extremely high dust levels. Neither of these studies can be relied on to evaluate disease risk in the exposure range of the former and revised respirable crystalline silica PELs.

    OSHA finds that the evidence for quartz originating from bentonite deposits indicates some biological activity, but also indicates lower toxicity than standard experimental quartz (which has similar characteristics to quartz encountered in most workplaces where exposures occur). For regulatory purposes, however, OSHA finds that the evidence does not exist that would permit the Agency to evaluate the magnitude of the lifetime risk resulting from exposure to quartz in sorptive clays at the 100 mug/m\3\ PEL. Instead, OSHA finds that the record provides no sound basis for determining the significance of risk for exposure to sorptive clays containing respirable quartz. Thus, OSHA is excluding sorptive clays (as described specifically in the Scope part of Section XV, Summary and Explanation) from the scope of the rule, until such time that sufficient science has been developed to permit evaluation of the significance of the risk. However, in excluding sorptive clays from the rule, the general industry PEL, as described in 29 CFR 1910.1000 Table Z-3, will continue to apply.

    VI. Final Quantitative Risk Assessment and Significance of Risk

  11. Introduction

    To promulgate a standard that regulates workplace exposure to toxic materials or harmful physical agents, OSHA must first determine that the standard reduces a ``significant risk'' of ``material impairment.'' Section 6(b)(5) of the OSH Act, 29 U.S.C. 655(b). The first part of this requirement, ``significant risk,'' refers to the likelihood of harm, whereas the second part, ``material impairment,'' refers to the severity of the consequences of exposure. Section II, Pertinent Legal Authority, of this preamble addresses the statutory bases for these requirements and how they have been construed by the Supreme Court and federal courts of appeals.

    It is the Agency's practice to estimate risk to workers by using quantitative risk assessment and determining the significance of that risk based on the best available evidence. Using that evidence, OSHA identifies material health impairments associated with potentially hazardous occupational exposures, and, when possible, provides a quantitative assessment of exposed workers' risk of these impairments. The Agency then evaluates whether these risks are severe enough to warrant regulatory action and determines whether a new or revised rule will substantially reduce these risks. For single-substance standards governed by section 6(b)(5) of the OSH Act, 29 U.S.C. 655(b)(5), OSHA sets a permissible exposure limit (PEL) based on that risk assessment as well as feasibility considerations. These health and risk determinations are made in the context of a rulemaking record in which the body of evidence used to establish material impairment, assess risks, and identify affected worker population, as well as the Agency's preliminary risk assessment, are placed in a public rulemaking record and subject to public comment. Final determinations regarding the standard, including final determinations of material impairment and risk, are thus based on consideration of the entire rulemaking record.

    In this case, OSHA reviewed extensive toxicological, epidemiological, and experimental research pertaining to the adverse health effects of occupational exposure to respirable crystalline silica, including silicosis, other non-malignant respiratory disease (NMRD), lung cancer, and autoimmune and renal diseases. Using the information collected during this review, the Agency

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    developed quantitative estimates of the excess risk of mortality and morbidity attributable to the previously allowed and revised respirable crystalline silica PELs; these estimates were published with the proposed rule. The Agency subsequently reexamined these estimates in light of the rulemaking record as a whole, including comments, testimony, data, and other information, and has determined that long-

    term exposure at and above the previous PELs would pose a significant risk to workers' health, and that adoption of the new PEL and other provisions of the final rule will substantially reduce this risk. Based on these findings, the Agency is adopting a new PEL of 50 mug/m\3\.

    Even though OSHA's risk assessment indicates that a significant risk also exists at the revised action level of 25 mug/m\3\, the Agency is not adopting a PEL below the revised 50 mug/m\3\ limit because OSHA must also consider the technological and economic feasibility of the standard in determining exposure limits. As explained in the Summary and Explanation for paragraph (c), Permissible Exposure Limit (PEL), of the general industry/maritime standard (paragraph (d) for construction), OSHA has determined that, with the adoption of additional engineering and work practice controls, the revised PEL of 50 mug/m\3\ is technologically and economically feasible in most operations in the affected general industrial and maritime sectors and in the construction industry, but that a lower PEL of 25 mug/m\3\ is not technologically feasible for most of these operations (see Section VII, Summary of the Final Economic Analysis and Final Regulatory Flexibility Analysis (FEA) and Chapter IV, Technological Feasibility, of the FEA). Therefore, OSHA concludes that by establishing the 50 mug/m\3\ PEL, the Agency has reduced significant risk to the extent feasible.

  12. OSHA's Findings of Material Impairments of Health

    As discussed below and in OSHA's Review of Health Effects Literature and Preliminary QRA (Document ID 1711, pp. 7-229), there is convincing evidence that inhalation exposure to respirable crystalline silica increases the risk of a variety of adverse health effects, including silicosis, NMRD (such as chronic bronchitis and emphysema), lung cancer, kidney disease, immunological effects, and infectious tuberculosis (TB). OSHA considers each of these conditions to be a material impairment of health. These diseases make it difficult or impossible to work and result in significant and permanent functional limitations, reduced quality of life, and sometimes death. When these diseases coexist, as is common, the effects are particularly debilitating (Rice and Stayner, 1995, Document ID 0418; Rosenman et al., 1999, 0421). Based on these findings and on the scientific evidence that respirable crystalline silica substantially increases the risk of each of these conditions, OSHA has determined that exposure to respirable crystalline silica increases the risk of ``material impairment of health or functional capacity'' within the meaning of the Occupational Safety and Health Act.

    1. Silicosis

    OSHA considers silicosis, an irreversible and potentially fatal disease, to be a clear material impairment of health. The term ``silicosis'' refers to a spectrum of lung diseases attributable to the inhalation of respirable crystalline silica. As described more fully in the Review of Health Effects Literature (Document ID 1711, pp. 16-71), the three types of silicosis are acute, accelerated, and chronic. Acute silicosis can occur within a few weeks to months after inhalation exposure to extremely high levels of respirable crystalline silica. Death from acute silicosis can occur within months to a few years of disease onset, with the affected person drowning in his or her own lung fluid (NIOSH, 1996, Document ID 0840). Accelerated silicosis results from exposure to high levels of airborne respirable crystalline silica, and disease usually occurs within 5 to 10 years of initial exposure (NIOSH, 1996, Document ID 0840). Both acute and accelerated silicosis are associated with exposures that are substantially above the previous general industry PEL, although no precise information on the relationships between exposure and occurrence of disease exists.

    Chronic silicosis is the most common form of silicosis seen today, and is a progressive and irreversible condition characterized as a diffuse nodular pulmonary fibrosis (NIOSH, 1996, Document ID 0840). Chronic silicosis generally occurs after 10 years or more of inhalation exposure to respirable crystalline silica at levels below those associated with acute and accelerated silicosis. Affected workers may have a dry chronic cough, sputum production, shortness of breath, and reduced pulmonary function. These symptoms result from airway restriction caused by the development of fibrotic scarring in the lower regions of the lungs. The scarring can be detected in chest x-ray films when the lesions become large enough to appear as visible opacities. The result is a restriction of lung volumes and decreased pulmonary compliance with concomitant reduced gas transfer. Chronic silicosis is characterized by small, rounded opacities that are symmetrically distributed in the upper lung zones on chest radiograph (Balaan and Banks, 1992, Document ID 0289, pp. 347, 350-351).

    The diagnosis of silicosis is based on a history of exposure to respirable crystalline silica, chest radiograph findings, and the exclusion of other conditions that appear similar. Because workers affected by early stages of chronic silicosis are often asymptomatic, the finding of opacities in the lung is key to detecting silicosis and characterizing its severity. The International Labour Organization (ILO) International Classification of Radiographs of Pneumoconioses (ILO, 1980, Document ID 1063; 2002, 1064) is the currently accepted standard against which chest radiographs are evaluated for use in epidemiological studies, medical surveillance, and clinical evaluation. The ILO system standardizes the description of chest x-rays, and is based on a 12-step scale of severity and extent of silicosis as evidenced by the size, shape, and density of opacities seen on the x-

    ray film. Profusion (frequency) of small opacities is classified on a 4-point major category scale (0-3), with each major category divided into three, giving a 12-point scale between 0/- and 3/+. Large opacities are defined as any opacity greater than 1 cm that is present in a film (ILO, 1980, Document ID 1063; 2002, 1064, p. 6).

    The small rounded opacities seen in early stage chronic silicosis (ILO major category 1 profusion) may progress (through ILO major categories 2 and/or 3) and develop into large fibrotic masses that destroy the lung architecture, resulting in progressive massive fibrosis (PMF). This stage of advanced silicosis is usually characterized by impaired pulmonary function, permanent disability, and premature death. In cases involving PMF, death is commonly attributable to progressive respiratory insufficiency (Balaan and Banks, 1992, Document ID 0289).

    Patients with ILO category 2 or 3 background profusion of small opacities are at increased risk, compared to those with category 1 profusion, of developing the large opacities characteristic of PMF. In one study of silicosis patients in Hong Kong, Ng and Chan (1991, Document ID 1106, p. 231) found the risk of PMF increased by 42 and 64 percent among patients whose chest x-

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    ray films were classified as ILO major category 2 or 3, respectively. Research has shown that people with silicosis advanced beyond ILO major category 1 have reduced life expectancy compared to the general population (Infante-Rivard et al., 1991, Document ID 1065; Ng et al., 1992a, 0383; Westerholm, 1980, 0484).

    Silicosis is the oldest known occupational lung disease and is still today the cause of significant premature mortality. As discussed further in Section V.E, Comments and Responses Concerning Surveillance Data on Silicosis Morbidity and Mortality, in 2013, there were 111 deaths in the U.S. where silicosis was recorded as an underlying or contributing cause of death on a death certificate (NCHS data). Between 1996 and 2005, deaths attributed to silicosis resulted in an average of 11.6 years of life lost by affected workers (NIOSH, 2007, Document ID 1362). In addition, exposure to respirable crystalline silica remains an important cause of morbidity and hospitalizations. National inpatient hospitalization data show that in the year 2011, 2,082 silicosis-related hospitalizations occurred, indicating that silicosis continues to be a significant health issue in the U.S. (Document ID 3577, Tr. 854-855). Although there is no national silicosis disease surveillance system in the U.S., a published analysis of state-based surveillance data from the time period 1987-1996 estimated that between 3,600-7,000 new cases of silicosis occurred in the U.S. each year (Rosenman et al., 2003, Document ID 1166).

    It has been widely reported that available statistics on silicosis-

    related mortality and morbidity are likely to be understated due to misclassification of causes of death (for example, as tuberculosis, chronic bronchitis, emphysema, or cor pulmonale), lack of occupational information on death certificates, or misdiagnosis of disease by health care providers (Goodwin et al., 2003, Document ID 1030; Windau et al., 1991, 0487; Rosenman et al., 2003, 1166). Furthermore, reliance on chest x-ray findings may miss cases of silicosis because fibrotic changes in the lung may not be visible on chest radiograph; thus, silicosis may be present absent x-ray signs or may be more severe than indicated by x-ray (Hnizdo et al., 1993, Document ID 1050; Craighhead and Vallyahan, 1980, 0995; Rosenman et al., 1997, 4181).

    Although most workers with early-stage silicosis (ILO categories 0/

    1 or 1/0) typically do not experience respiratory symptoms, the primary risk to the affected worker is progression of disease with progressive decline of lung function. Several studies of workers exposed to crystalline silica have shown that, once silicosis is detected by x-

    ray, a substantial proportion of affected workers can progress beyond ILO category 1 silicosis, even after exposure has ceased (e.g., Hughes, 1982, Document ID 0362; Hessel et al., 1988, 1042; Miller et al., 1998, 0374; Ng et al., 1987a, 1108; Yang et al., 2006, 1134). In a population of coal miners whose last chest x-ray while employed was classified as major category 0, and who were examined again 10 years after the mine had closed, 20 percent had developed opacities consistent with a classification of at least 1/0, and 4 percent progressed further to at least 2/1 (Miller et al., 1998, Document ID 0374). Although there were periods of extremely high exposure to respirable quartz in the mine (greater than 2,000 mug/m\3\ in some jobs between 1972 and 1976, and more than 10 percent of exposures between 1969 and 1977 were greater than 1,000 mug/m\3\), the mean cumulative exposure for the cohort over the period 1964-1978 was 1.8 mg/m\3\-yrs, corresponding to an average silica concentration of 120 mug/m\3\. In a population of granite quarry workers exposed to an average respirable silica concentration of 480 mug/m\3\ (mean length of employment was 23.4 years), 45 percent of those diagnosed with simple silicosis (i.e., presence of small opacities only on chest x-ray films) showed radiological progression of disease after 2 to 10 years of follow up (Ng et al., 1987a, Document ID 1108). Among a population of gold miners, 92 percent progressed in 14 years; exposures of high-, medium-, and low-exposure groups were 970, 450, and 240 mug/m\3\, respectively (Hessel et al., 1988, Document ID 1042). Chinese mine and factory workers categorized under the Chinese system of x-ray classification as ``suspected'' silicosis cases (analogous to ILO 0/1) had a progression rate to stage I (analogous to ILO major category 1) of 48.7 percent, and the average interval was about 5.1 years (Yang et al., 2006, Document ID 1134).

    The risk of silicosis carries with it an increased risk of reduced lung function as the disease irreversibly progresses. There is strong evidence in the literature for the finding that lung function deteriorates more rapidly in workers exposed to silica, especially those with silicosis, than what is expected from a normal aging process (Cowie, 1988, Document ID 0993; Hughes et al., 1982, 0362; Malmberg et al., 1993, 0370; Ng and Chan, 1992, 1107). The rates of decline in lung function are greater in those whose disease showed evidence of radiologic progression (Begin et al., 1987, Document ID 0295; Cowie, 1988, 0993; Ng and Chan, 1992, 1107; Ng et al., 1987a, 1108). Additionally, the average deterioration of lung function exceeds that in smokers (Hughes et al., 1982, Document ID 0362).

    Several studies have reported no decrease in pulmonary function with an ILO category 1 level of profusion of small opacities but found declines in pulmonary function with categories 2 and 3 (Ng et al., 1987a, Document ID 1108; Begin et al., 1988, 0296; Moore et al., 1988, 1099). However, one study found a statistically significantly greater annual loss in forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) among those with category 1 profusion compared to category 0 (Cowie, 1988, Document ID 0993). In another study, the degree of profusion of opacities was associated with reductions in several pulmonary function metrics (Cowie and Mabena, 1991, Document ID 0342). Some studies have reported no associations between radiographic silicosis and decreases in pulmonary function (Ng et al., 1987a, Document ID 1108; Wiles et al., 1972, 0485; Hnizdo, 1992, 1046), while other studies (Ng et al., 1987a, Document ID 1108; Wang et al., 1997, 0478) have found that measurable changes in pulmonary function are evident well before the changes seen on chest x-

    ray. Findings of pulmonary function decrements absent radiologic signs of silicosis may reflect the general insensitivity of chest radiography in detecting lung fibrosis, or may also reflect that exposure to respirable silica has been shown to increase the risk of non-malignant respiratory disease (NMRD) and its attendant pulmonary function losses (see Section V.C, Summary of the Review of Health Effects Literature and Preliminary QRA).

    Moreover, exposure to respirable crystalline silica in and of itself, with or without silicosis, increases the risk that latent tuberculosis infection can convert to active disease. Early descriptions of dust diseases of the lung did not distinguish between TB and silicosis, and most fatal cases described in the first half of this century were a combination of silicosis and TB (Castranova et al., 1996, Document ID 0314). More recent findings demonstrate that exposure to silica, even without silicosis, increases the risk of infectious (i.e., active) pulmonary TB (Sherson and Lander, 1990, Document ID 0434; Cowie, 1994, 0992; Hnizdo and Murray, 1998, 0360; teWaterNaude et al., 2006, 0465). Both conditions together can

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    hasten the development of respiratory impairment and increase mortality risk even beyond that experienced by persons with active TB who have not been exposed to respirable crystalline silica (Banks, 2005, Document ID 0291).

    Based on the information presented above and in its review of the health literature, OSHA concludes that silicosis remains a significant cause of early death and of serious illness, despite the existence of an enforceable exposure limit over the past 40 years. Silicosis in its later stages of progression (i.e., with chest x-ray findings of ILO category 2 or 3 profusion of small opacities, or the presence of large opacities) is characterized by the likely appearance of respiratory symptoms and decreased pulmonary function, as well as increased risk of progression to PMF, disability, and early mortality. Early-stage silicosis, although without symptoms among many who are affected, nevertheless reflects the formation of fibrotic lesions in the lung and increases the risk of progression to later stages, even after exposure to respirable crystalline silica ceases. In addition, the presence of silicosis increases the risk of pulmonary infections, including conversion of latent TB infection to active TB. Silicosis is not a reversible condition, and there is no specific treatment for the disease, other than administration of drugs to alleviate inflammation and maintain open airways, or administration of oxygen therapy in severe cases. Based on these considerations, OSHA finds that silicosis of any form, and at any stage of progression, is a material impairment of health and that fibrotic scarring of the lungs represents loss of functional respiratory capacity.

    2. Lung Cancer

    OSHA considers lung cancer, an irreversible and frequently fatal disease, to be a clear material impairment of health (see Homer et al., 2009, Document ID 1343). According to the National Cancer Institute (SEER Cancer Statistics Review, 2006, Document ID 1343), the five-year survival rate for all forms of lung cancer is only 15.6 percent, a rate that has not improved in nearly two decades. After reviewing the record as a whole, OSHA finds that respirable crystalline silica exposure substantially increases the risk of lung cancer. This finding is based on the best available toxicological and epidemiological data, reflects substantial supportive evidence from animal and mechanistic research, and is consistent with the conclusions of other government and public health organizations, including the International Agency for Research on Cancer (1997, Document ID 1062; 2012, Document ID 1473), the HHS National Toxicology Program (2000, Document ID 1417), the CDC's National Institute for Occupational Safety and Health (2002, Document ID 1110), the American Thoracic Society (1997, Document ID 0283), and the American Conference of Governmental Industrial Hygienists (2010, Document ID 0515).

    The Agency's primary evidence comes from evaluation of more than 50 studies of occupational cohorts from many different industry sectors in which exposure to respirable crystalline silica occurs, including: Granite and stone quarrying; the refractory brick industry; gold, tin, and tungsten mining; the diatomaceous earth industry; the industrial sand industry; and construction. In addition, the association between exposure to respirable crystalline silica and lung cancer risk was reported in a national mortality surveillance study (Calvert et al., 2003, Document ID 0309) and in two community-based studies (Pukkala et al., 2005, Document ID 0412; Cassidy et al., 2007, 0313), as well as in a pooled analysis of 10 occupational cohort studies (Steenland et al., 2001a, Document ID 0452). Toxicity studies provide supportive evidence of the carcinogenicity of crystalline silica, in that they demonstrate biologically plausible mechanisms by which crystalline silica in the deep lung can give rise to biochemical and cellular events leading to tumor development (see Section V.H, Mechanisms of Silica-Induced Adverse Health Effects).

    3. Non-Malignant Respiratory Disease (NMRD) (Other Than Silicosis)

    Although many of the stakeholders in this rule have focused their attention on the evidence related to silicosis and lung cancer, the available evidence shows that exposure to respirable crystalline silica also increases the risk of developing NMRD, in particular chronic bronchitis and emphysema. OSHA has determined that NMRD, which results in loss of pulmonary function that restricts normal activity in individuals afflicted with these conditions (see American Thoracic Society, 2003, Document ID 1332), constitutes a material impairment of health. Both chronic bronchitis and emphysema can occur in conjunction with the development of silicosis. Several studies have documented increased prevalence of chronic bronchitis and emphysema among silica-

    exposed workers even absent evidence of silicosis (see Document ID 1711, pp. 182-192; NIOSH, 2002, 1110; American Thoracic Society, 2003, 1332). There is also evidence that smoking may have an additive or synergistic effect on silica-related NMRD morbidity or mortality (Hnizdo, 1990, Document ID 1045; Hnizdo et al., 1990, 1047; Wyndham et al., 1986, 0490; NIOSH, 2002, 1110). In a study of diatomaceous earth workers, Park et al. (2002, Document ID 0405) found a positive exposure-response relationship between exposure to respirable cristobalite (a form of silica) and increased mortality from NMRD.

    Decrements in pulmonary function have often been found among workers exposed to respirable crystalline silica absent radiologic evidence of silicosis. Several cross-sectional studies have reported such findings among granite workers (Theriault et al., 1974a, Document ID 0466; Wallsh, 1997, 0477; Ng et al., 1992b, 0387; Montes II et al., 2004b, 0377), gold miners (Irwig and Rocks, 1978, Document ID 1067; Hnizdo et al., 1990, 1047; Cowie and Mabena, 1991, 0342), gemstone cutters (Ng et al., 1987b, Document ID 1113), concrete workers (Meijer et al., 2001, Document ID 1243), refractory brick workers (Wang et al., 1997, Document ID 0478), hard rock miners (Manfreda et al., 1982, Document ID 1094; Kreiss et al., 1989, 1079), pottery workers (Neukirk et al., 1994, Document ID 0381), slate workers (Surh, 2003, Document ID 0462), and potato sorters exposed to silica in diatomaceous earth (Jorna et al, 1994, Document ID 1071).

    OSHA also evaluated several longitudinal studies where exposed workers were examined over a period of time to track changes in pulmonary function. Among both active and retired granite workers exposed to an average of 60 mug/m \3\, Graham et al. did not find exposure-related decrements in pulmonary function (1981, Document ID 1280; 1984, 0354). However, Eisen et al. (1995, Document ID 1010) did find significant pulmonary decrements among a subset of granite workers (termed ``dropouts'') who left work and consequently did not voluntarily participate in the last of a series of annual pulmonary function tests. This group of workers experienced steeper declines in FEV1 compared to the subset of workers who remained at work and participated in all tests (termed ``survivors''), and these declines were significantly related to dust exposure. Thus, in this study, workers who had left work had exposure-related declines in pulmonary function to a greater extent than did workers who remained on the job, clearly demonstrating a survivor effect among the active

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    workers. Exposure-related changes in lung function were also reported in a 12-year study of granite workers (Malmberg, 1993, Document ID 0370), in two 5-year studies of South African miners (Hnizdo, 1992, Document ID 1046; Cowie, 1988, 0993), and in a study of foundry workers whose lung function was assessed between 1978 and 1992 (Hertzberg et al., 2002, Document ID 0358).

    Each of these studies reported their findings in terms of rates of decline in any of several pulmonary function measures, such as FVC, FEV1, and FEV1/FVC. To put these declines in perspective, Eisen et al. (1995, Document ID 1010) reported that the rate of decline in FEV1 seen among the dropout subgroup of Vermont granite workers was 4 ml per mg/m\3\-yrs of exposure to respirable granite dust; by comparison, FEV1 declines at a rate of 10 ml/year from smoking one pack of cigarettes daily. From their study of foundry workers, Hertzberg et al., reported finding a 1.1 ml/year decline in FEV1 and a 1.6 ml/year decline in FVC for each mg/m\3\-yrs of respirable silica exposure after controlling for ethnicity and smoking (2002, Document ID 0358, p. 725). From these rates of decline, they estimated that exposure to the previous OSHA general industry quartz standard of 100 microg/m\3\ for 40 years would result in a total loss of FEV1 and FVC that is less than but still comparable to smoking a pack of cigarettes daily for 40 years. Hertzberg et al. also estimated that exposure to the current standard for 40 years would increase the risk of developing abnormal FEV1 or FVC by factors of 1.68 and 1.42, respectively (2002, Document ID 0358, pp. 725-726). OSHA believes that this magnitude of reduced pulmonary function, as well as the increased morbidity and mortality from non-malignant respiratory disease (NMRD) that has been documented in the studies summarized above, constitute material impairments of health and loss of functional respiratory capacity.

    4. Renal and Autoimmune Effects

    Finally, OSHA's review of the literature reflects substantial evidence that exposure to crystalline silica increases the risk of renal and autoimmune diseases, both of which OSHA considers to be material impairments of health (see Section V.C, Summary of the Review of Health Effects Literature and Preliminary QRA). Epidemiological studies have found statistically significant associations between occupational exposure to silica dust and chronic renal disease (e.g., Calvert et al., 1997, Document ID 0976), subclinical renal changes including proteinurea and elevated serum creatinine (e.g., Ng et al., 1992c, Document ID 0386; Rosenman et al., 2000, 1120; Hotz, et al., 1995, 0361), end-stage renal disease morbidity (e.g., Steenland et al., 1990, Document ID 1125), chronic renal disease mortality (Steenland et al., 2001b, Document ID 0456; 2002a, 0448), and granulomatosis with polyangitis (Nuyts et al., 1995, Document ID 0397). Granulomatosis with polyangitis is characterized by inflammation of blood vessels, leading to damaging granulomatous formation in the lung and damage to the glomeruli of the kidneys, a network of capillaries responsible for the first stage of blood filtration. If untreated, this condition often leads to renal failure (Nuyts et al., 1995, Document ID 0397, p. 1162). Possible mechanisms for silica-induced renal disease include a direct toxic effect on the kidney and an autoimmune mechanism (see Section V.H, Mechanisms of Silica-Induced Adverse Health Effects; Calvert et al., 1997, Document ID 0976; Gregorini et al., 1993, 1032). Steenland et al. (2002a, Document ID 0448) demonstrated a positive exposure-

    response relationship between exposure to respirable crystalline silica and end-stage renal disease mortality.

    In addition, there are a number of studies that show exposure to be related to increased risks of autoimmune disease, including scleroderma (e.g., Sluis-Cremer et al., 1985, Document ID 0439), rheumatoid arthritis (e.g., Klockars et al., 1987, Document ID 1075; Rosenman and Zhu, 1995, 0424), and systemic lupus erythematosus (e.g., Brown et al., 1997, Document ID 0974). Scleroderma is a degenerative disorder that leads to over-production of collagen in connective tissue that can cause a wide variety of symptoms including skin discoloration and ulceration, joint pain, swelling and discomfort in the extremities, breathing problems, and digestive problems. Rheumatoid arthritis is characterized by joint pain and tenderness, fatigue, fever, and weight loss. Systemic lupus erythematosus is a chronic disease of connective tissue that can present a wide range of symptoms including skin rash, fever, malaise, joint pain, and, in many cases, anemia and iron deficiency. OSHA considers chronic renal disease, end-stage renal disease mortality, granulomatosis with polyangitis, scleroderma, rheumatoid arthritis, and systemic lupus erythematosus clearly to be material impairments of health.

  13. OSHA's Final Quantitative Risk Estimates

    To evaluate the significance of the health risks that result from exposure to hazardous chemical agents, OSHA relies on epidemiological and experimental data, as well as statistical methods. The Agency uses these data and methods to characterize the risk of disease resulting from workers' exposure to a given hazard over a working lifetime at levels of exposure reflecting both compliance with previous standards and compliance with the new standard. In the case of respirable crystalline silica, the previous general industry, construction, and shipyard PELs were formulas that limit 8-hour TWA exposures to respirable dust; the limit on exposure decreased with increasing crystalline silica content of the dust. OSHA's previous general industry PEL for respirable quartz was expressed both in terms of a particle count and a gravimetric concentration, while the previous construction and shipyard employment PELs for respirable quartz were only expressed in terms of a particle count formula. For general industry, the gravimetric formula PEL for quartz approaches 100 microg/m\3\ of respirable crystalline silica when the quartz content of the dust is about 10 percent or greater. The previous PEL's particle count formula for the construction and shipyard industries is equal to a range of about 250 mug/m\3\ to 500 mug/m\3\ expressed as respirable quartz. In general industry, the previous PELs for cristobalite and tridymite, which are forms (polymorphs) of silica, were one-half the PEL for quartz.

    In this final rule, OSHA has established a uniform PEL for respirable crystalline silica by revising the PELs applicable to general industry, construction, and maritime to 50 mug/m\3\ TWA of respirable crystalline silica. OSHA has also established an action level of 25 microg/m\3\ TWA. In this section of the preamble, OSHA presents its final estimates of health risks associated with a working lifetime (45 years) of exposure to 25, 50, and 100 microg/m\3\ respirable crystalline silica. These levels represent the risks associated with exposure over a working lifetime to the new action level, new PEL, and previous general industry PEL, respectively. OSHA also presents estimates associated with exposure to 250 and 500 microg/m\3\ to represent a range of risks likely to be associated with exposure to the former construction and shipyard PELs. Risk estimates are presented for mortality due to lung cancer, silicosis and other non-malignant respiratory disease (NMRD),

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    and end-stage renal disease, as well as silicosis morbidity. These estimates are the product of OSHA's risk assessment, following the Agency's consideration of new data introduced into the rulemaking record and of the numerous comments in the record that raised questions about OSHA's preliminary findings and analysis.

    After reviewing the evidence and testimony in the record, OSHA has determined that it is appropriate to base its final risk estimates on the same studies and models as were used in the NPRM (see Section V.C, Summary of the Review of Health Effects Literature and Preliminary QRA). For mortality risk estimates, OSHA used the models developed by various investigators and employed a life table analysis to implement the models using the same background all-cause mortality data and consistent assumption for length of lifetime (85 years). The life table is a technique that allows estimation of excess risk of disease mortality factoring in the probability of surviving to a particular age assuming no exposure to the agent in question and given the background probability of dying from any cause at or before that age (see Section V.M, Comments and Responses Concerning Working Life, Life Tables, and Dose Metric). Since the time of OSHA's preliminary analysis, the National Center for Health Statistics (NCHS) released updated all-cause mortality background rates from 2011; these rates are available in an internet web-based query by year and 2010 International Classification of Diseases (ICD) code through the Centers of Disease Control and Prevention (CDC) Wonder database (http://wonder.cdc.gov/udc-icd10.html). Using these updated statistics, OSHA revised its life table analyses to estimate lifetime risks of mortality that result from 45 years of exposure to respirable crystalline silica. OSHA's final quantitative mortality risk estimates are presented in Table VI-1 below.

    For silicosis morbidity risk estimates, OSHA relied on the cumulative risk models developed by investigators of five studies who conducted studies relating cumulative disease risk to cumulative exposure to respirable crystalline silica (see footnotes to Table VI-

    1). Of these, only one, the study by Steenland and Brown (1995) of U.S. gold miners, employed a life-table analysis. Table VI-1 also presents OSHA's final quantitative estimates of silicosis morbidity risks.

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    OSHA notes that the updated risk estimates are not substantially different from those presented in the Preliminary QRA; for example, for exposure at the previous general industry PEL approaching 100 mug/

    m\3\, the excess lung cancer mortality risk ranged from 13 to 60 deaths per 1,000 workers using the original 2006 background data, and from 11 to 54 deaths per 1,000 workers using the updated 2011 background data. For exposure at the revised PEL of 50 mug/m\3\, the risk estimates ranged from 6 to 26 deaths per 1,000 workers using the 2006 background data, and 5 to 23 deaths per 1,000 workers using the 2011 background data. Similarly, the updated risk estimates for NMRD are not substantially different; for example, for exposure for 45 working years at the previous general industry PEL approaching 100 mug/m\3\, the excess NMRD mortality risk, using the Park et al. (2002, Document 0405) model was 83 deaths per 1,000 workers using the original 2006 background data, and 85 deaths per 1,000 workers using the updated 2011 background data. For exposure at the revised PEL of 50 mug/m\3\, the risk estimate was 43 deaths per 1,000 workers using the 2006 background data, and 44 deaths per 1,000 workers using the 2011 background data.

    OSHA also presents in the table the excess lung cancer mortality risk associated with 45 years of exposure to the previous construction/

    shipyard PEL (in the range of 250 to 500 microg/m\3\). It should be noted, however, that exposure to 250 or 500 microg/m\3\ over 45 years represents cumulative exposures of 11.25 and 22.5 mg/m\3\-yrs, respectively, which are well above the median cumulative exposure for most of the cohorts used in the risk assessment. Estimating excess risks over this higher range of cumulative exposures required some degree of extrapolation, which adds uncertainty. In addition, at cumulative exposures as high as permitted by the previous construction and maritime PELs, silica-related causes of mortality will compete with each other and it is difficult to determine the risk of any single cause of mortality in the face of such competing risks.

    OSHA's final risk estimates for renal disease reflect the 1998 background all-cause mortality and renal mortality rates for U.S. males, rather than the 2011 rates used for lung cancer and NMRD, as updated in the previous sections. Background rates were not adjusted for the renal disease risk estimates because the CDC significantly changed the classification of renal diseases after 1998; they are now inconsistent with those used by Steenland et al. (2002a, Document ID 0448), the study relied on by OSHA, to ascertain the cause of death of workers in their study. OSHA notes that the change in classification system, from ICD-9 to ICD-10, did not materially affect background rates for diseases grouped as lung cancer or NMRD. The findings from OSHA's final risk assessment are summarized below.

    OSHA notes that the key studies in its final risk assessment were composed of

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    cohorts with cumulative exposures relevant to those permitted by the preceding General Industry PEL (45 years of exposure at 100 mug/m\3\ equals 4.5 mg/m\3\-yrs). Table VI-2 provides the reported cumulative exposure information for each of the cohorts of the key studies. Most of these cohorts had mean or median cumulative exposures below 4.5 mg/

    m\3\-yrs. Based on this data, OSHA concludes that the cumulative exposures experienced by the cohorts are relevant and reasonable for use in the Agency's final risk assessment.

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    1. Summary of Excess Risk Estimates for Lung Cancer Mortality

    For estimates of lung cancer risk from crystalline silica exposure, OSHA has relied upon studies of exposure-response relationships presented in a pooled analysis of 10 cohort studies (Steenland et al., 2001a, Document ID 0452; ToxaChemica, Inc., 2004, 0469) as well as on individual studies of granite (Attfield and Costello, 2004, Document ID 0543), diatomaceous earth (Rice et al., 2001, Document ID 1118), and industrial sand (Hughes et al., 2001, Document ID 1060) worker cohorts, and a study of coal miners exposed to respirable crystalline silica (Miller et al., 2007, Document ID 1305; Miller and MacCalman, 2009, 1306). OSHA found these studies to have been suitable for use to quantitatively characterize health risks to exposed workers because: (1) Study populations were of sufficient size to provide adequate statistical power to detect low levels of risk; (2) sufficient quantitative exposure data were available over a sufficient span of time to characterize cumulative exposures of cohort members to respirable crystalline silica; (3) the studies either adjusted for or otherwise adequately addressed confounding factors such as smoking and exposure to other carcinogens; and (4) investigators developed quantitative assessments of exposure-response relationships using appropriate statistical models or otherwise provided sufficient information that permits OSHA to do so. OSHA implemented all risk models in its own life table analysis so that the use of background lung cancer rates and assumptions regarding length of exposure and lifetime were consistent across each of the models, and so OSHA could estimate lung cancer risks associated with exposure to specific levels of silica of interest to the Agency.

    The Steenland et al. (2001a, Document ID 0452) study consisted of a pooled exposure-response analysis and risk assessment based on raw data obtained for ten cohorts of silica-exposed workers (65,980 workers, 1,072 lung cancer deaths). The cohorts in this pooled analysis include U.S. gold miners (Steenland and Brown, 1995a, Document ID 0450), U.S. diatomaceous earth workers (Checkoway et al., 1997, Document ID 0326), Australian gold miners (de Klerk and Musk, 1998, Document ID 0345), Finnish granite workers (Koskela et al., 1994, Document ID 1078), South African gold miners (Hnizdo et al., 1997, Document ID 1049), U.S. industrial sand workers (Steenland et al., 2001b, Document ID 0456), Vermont granite workers (Costello and Graham, 1988, Document ID 0991), and Chinese pottery workers, tin miners, and tungsten miners (Chen et al., 1992, Document ID 0329). To determine the exposure-response relationship between silica exposures and lung cancer, the investigators used a nested case-control design with cases and controls matched for race, sex, age (within five years), and study; 100 controls were matched for each case. An extensive exposure assessment for this pooled analysis was developed and published by Mannetje et al. (2002a, Document ID 1090).

    Using ToxaChemica's study (2004, Document ID 0469) of this pooled data, the estimated excess lifetime lung cancer risk associated with 45 years of exposure to 100 mug/m\3\ (about equal to the previous general industry PEL) is between 20 and 26 deaths per 1,000 workers. The estimated excess lifetime risk associated with 45 years of exposure to silica concentrations in the range of 250 and 500 mug/m\3\ (about equal to the previous construction and shipyard PELs) is between 24 and 33 deaths per 1,000. At the final PEL of 50 mug/m\3\, the estimated excess lifetime risk ranges from 16 to 23 deaths per 1,000, and, at the action level of 25 mug/m\3\, from 10 to 21 deaths per 1,000.

    In addition to the pooled cohort study, OSHA's Final Quantitative Risk Assessment presents risk estimates in Table VI-1 derived from four individual studies where investigators presented either lung cancer risk estimates or exposure-response coefficients. Two of these studies, one on diatomaceous earth workers (Rice et al., 2001, Document ID 1118) and one on Vermont granite workers (Attfield and Costello, 2004, Document ID 0543), were included in the 10-cohort pooled study (Steenland et al., 2001a, Document ID 0452; ToxaChemica Inc., 2004, 0469). The other two were of British coal miners (Miller et al., 2007, Document ID 1305; Miller and MacCalman, 2009,1306) and North American industrial sand workers (Hughes et al., 2001, Document ID 1060).

    Rice et al. (2001, Document ID 1118) presented an exposure-response analysis of the diatomaceous worker cohort studied by Checkoway et al. (1993, Document ID 0324; 1996, 0325; 1997, 0326), who found a significant relationship between exposure to respirable cristobalite and increased lung cancer mortality. From this cohort the estimates of the excess risk of lung cancer mortality are 30, 15, and 8 deaths per 1,000 workers for 45 years of exposure to 100, 50, and 25 mug/m\3\, respectively. For exposures in the range of the current construction and shipyard PELs over 45 years, estimated risks lie in a range between 72 and 137 excess deaths per 1,000 workers.

    Somewhat higher risk estimates are derived from the analysis presented by Attfield and Costello (2004, Document ID 0543) of Vermont granite workers. OSHA's use of this analysis yielded a risk estimate of 54 excess deaths per 1,000 workers for 45 years of exposure to the previous general industry PEL of 100 mug/m\3\, 22 excess deaths per 1,000 for 45 years of exposure to the final PEL of 50 mug/m\3\, and 10 excess deaths per 1,000 for 45 years of exposure at the action level of 25 mug/m\3\. Estimated excess risks associated with 45 years of exposure at the current construction PEL range from 231 to 657 deaths per 1,000.

    Hughes et al. (2001, Document ID 1060) conducted a study of industrial sand workers in the U.S. and Canada. Using this study, OSHA estimated cancer risks of 33, 14, and 7 deaths per 1,000 for 45 years exposure to the previous general industry PEL of 100 mug/m\3\, the final PEL of 50 mug/m\3\, and the final action level of 25 mug/m\3\ respirable crystalline silica, respectively. For 45 years of exposure to the previous construction PEL, estimated risks range from 120 to 407 deaths per 1,000 workers.

    Miller and MacCalman (2010, Document ID 1306; also reported in Miller et al., 2007, Document ID 1305) presented a study of miners from 10 coal mines in the U.K. Based on this study, OSHA estimated the lifetime lung cancer mortality risk to be 11 per 1,000 workers for 45 years of exposure to 100 mug/m\3\ respirable crystalline silica. For the final PEL of 50 mug/m\3\ and action level of 25 mug/m\3\, the lifetime risks are estimated to be 5 and 3 deaths per 1,000, respectively. The range of risks estimated to result from 45 years of exposure to the previous construction and shipyard PELs is from 33 to 86 deaths per 1,000 workers.

    2. Summary of Risk Estimates for Silicosis and Other Chronic Lung Disease Mortality

    OSHA based its quantitative assessment of silicosis mortality risks on a pooled analysis conducted by Mannetje et al. (2002b, Document ID 1089) of data from six of the ten epidemiological studies in the Steenland et al. (2001a, Document ID 0452) pooled analysis of lung cancer mortality that also included extensive data on silicosis. Cohorts included in the silicosis study were: U.S. diatomaceous earth workers (Checkoway et al., 1997, Document ID 0326); Finnish granite workers (Koskela

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    et al., 1994, Document ID 1078); U.S. granite workers (Costello and Graham, 1988, Document ID 0991); U.S. industrial sand workers (Silicosis and Silicate Disease Committee, 1988, Document ID 0455); U.S. gold miners (Steenland and Brown, 1995b, Document ID 0451); and Australian gold miners (de Klerk and Musk, 1998, Document ID 0345). These six cohorts contained 18,634 workers and 170 silicosis deaths, where silicosis mortality was defined as death from silicosis (ICD-9 502, n = 150) or from unspecified pneumoconiosis (ICD-9 505, n = 20). Although Mannetje et al, (2002b, Document ID 1089) estimated silicosis risks from a Poisson regression, a subsequent analysis was conducted by Steenland and Bartell (ToxaChemica, 2004, Document ID 0469) based on a case control design. Based on the Steenland and Bartell analysis, OSHA estimated that the lifetime risk of silicosis mortality associated with 45 years of exposure to the previous general industry PEL of 100 mug/

    m\3\ is 11 deaths per 1,000 workers. Exposure for 45 years to the final PEL of 50 mug/m\3\ results in an estimated 7 silicosis deaths per 1,000, and exposure for 45 years to the final action level of 25 mug/

    m\3\ results in an estimated 4 silicosis deaths per 1,000. Lifetime risks associated with exposure at the previous construction and shipyard PELs range from 17 to 22 deaths per 1,000 workers.

    To study non-malignant respiratory diseases (NMRD), of which silicosis is one, Park et al. (2002, Document ID 0405) analyzed the California diatomaceous earth cohort data originally studied by Checkoway et al. (1997, Document ID 0326). The authors quantified the relationship between exposure to cristobalite and mortality from NMRD. Diseases in this category included pneumoconiosis (which includes silicosis), chronic bronchitis, and emphysema, but excluded pneumonia and other infectious diseases. Because of the broader range of silica-

    related diseases examined by Park et al., OSHA's estimates of the lifetime chronic lung disease mortality risk based on this study are substantially higher than those that OSHA derived from the Mannetje et al. (2002b, Document ID 1089) silicosis analysis. For the previous general industry PEL of 100 mug/m\3\, exposure for 45 years is estimated to result in 85 excess deaths per 1,000 workers. At the final PEL of 50 mug/m\3\ and action level of 25 mug/m\3\, OSHA estimates the lifetime risk from 45 years of exposure to be 44 and 22 excess deaths per 1,000, respectively. The range of risks associated with exposure at the former construction and shipyard PELs over a working lifetime is from 192 to 329 excess deaths per 1,000 workers.

    3. Summary of Risk Estimates for Renal Disease Mortality

    OSHA's analysis of the health effects literature included several studies that have demonstrated that exposure to respirable crystalline silica increases the risk of renal and autoimmune disease (see Document ID 1711, Review of Health Effects Literature and Preliminary QRA, pp. 208-229). For autoimmune disease, there was insufficient data on which to base a quantitative risk assessment. OSHA's assessment of the renal disease risks that result from exposure to respirable crystalline silica is based on an analysis of pooled data from three cohort studies (Steenland et al., 2002a, Document ID 0448). The combined cohort for the pooled analysis (Steenland et al., 2002a, Document ID 0448) consisted of 13,382 workers and included industrial sand workers (Steenland et al., 2001b, Document ID 0456), U.S. gold miners (Steenland and Brown, 1995a, Document ID 0450), and Vermont granite workers (Costello and Graham, 1988, Document ID 0991). Exposure data were available for 12,783 workers and analyses conducted by the original investigators demonstrated monotonically increasing exposure-

    response trends for silicosis, indicating that exposure estimates were not likely subject to significant random misclassification. The mean duration of exposure, cumulative exposure, and concentration of respirable silica for the combined cohort were 13.6 years, 1.2 mg/m\3\-

    years, and 70 mug/m\3\, respectively. There were highly statistically significant trends for increasing renal disease mortality with increasing cumulative exposure for both multiple cause analysis of mortality (p 3 respirable crystalline silica, the Agency's estimate of excess lung cancer mortality, from 5 to 23 deaths per 1,000 workers, is still 3- to 15-fold higher than private industry's average fatal injury rate, given the same employment time, and substantially exceeds those rates found in lower-risk industries such as finance and educational and health services. Adding in the mortality from silicosis, NMRD, and renal disease would make these comparisons even more stark.

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    GRAPHIC TIFF OMITTED TR25MR16.009

    Because there is little available information on the incidence of occupational cancer across all industries, risk from crystalline silica exposure cannot be compared with overall risk from other workplace carcinogens. However, OSHA's previous risk assessments provide estimates of risk from exposure to certain carcinogens. These risk assessments, as with the current assessment for respirable crystalline silica, were based on animal or human data of reasonable or high quality and used the best information then available. Table VI-4 shows the Agency's best estimates of cancer risk from 45 years of occupational exposure to several carcinogens, as published in the preambles to final rules promulgated since the Benzene decision in 1980.

    Page 16393

    GRAPHIC TIFF OMITTED TR25MR16.010

    The estimated excess lung cancer mortality risks associated with respirable crystalline silica at the previous general industry PEL, 11-

    54 deaths per 1,000 workers, are comparable to, and in some cases higher than, the estimated excess cancer risks for many other workplace carcinogens for which OSHA made a determination of significant risk (see Table VI-4, ``Selected OSHA Risk Estimates for Prior and Current PELs''). The estimated excess lung cancer risks associated with exposure to the previous construction and shipyard PELs are even higher. The estimated risk from lifetime occupational exposure to respirable crystalline silica at the final PEL of 50 mug/m\3\ is 5-23 excess lung cancer deaths per 1,000 workers, a range still higher than the risks from exposure to many other carcinogens regulated by OSHA.

    OSHA's risk assessment also shows that reduction of the PELs for respirable crystalline silica to the final level of 50 mug/m\3\ will result in substantial reduction in risk, although quantitative estimates of that reduction vary depending on the statistical models used. Risk models that reflect attenuation of the risk with increasing exposure, such as those relating risk to a log transformation of cumulative exposure, will result in lower estimates of risk reduction compared to linear risk models. Thus, for lung cancer risks, the assessment based on the 10-cohort pooled analysis by Steenland et al. (2001, Document ID 0455; also 0469; 1312) suggests risk will be reduced by about 14 percent from the previous general industry PEL and by 28-41 percent from the previous construction/shipyard PEL (based on the midpoint of the ranges of estimated risk derived from the three models used for the pooled cohort data). These risk reduction estimates, however, are much lower than those derived from the single cohort studies (Rice et al., 2001, Document ID 1118; Attfield and Costello, 2004, 0543; Hughes et al., 2001, 1060; Miller and MacCalman 2009, 1306). These single cohort studies suggest that reducing the previous PELs to the final PEL will reduce lung cancer risk by more than 50 percent in general industry and by more than 80 percent in construction and shipyards.

    For silicosis mortality, OSHA's assessment indicates that risk will be reduced by 36 percent and by 58-68 percent as a result of reducing the previous general industry and construction/shipyard PELs, respectively. NMRD mortality risks will be reduced by 48 percent and by 77-87 percent as a result of reducing the general industry and construction/shipyard PELs, respectively, to the new PEL. There is also a substantial reduction in renal disease mortality risks; an 18-percent reduction associated with reducing the previous general industry PEL and a 38-49 percent reduction associated with reducing the previous construction/shipyard PEL.

    Thus, OSHA believes that the final PEL of 50 mug/m\3\ respirable crystalline silica will substantially reduce the risk of material health impairments associated with exposure to silica. However, even at this final PEL, as well as the action level of 25 mug/m\3\, the risk posed to workers with 45 years of

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    regular exposure to respirable crystalline silica is greater than 1 per 1,000 workers and is still clearly significant.

    2. Silicosis Morbidity Risks

    OSHA's Final Quantitative Risk Assessment also characterizes the risk of developing silicosis, defined as developing lung fibrosis detected by chest x-ray. For 45 years of exposure at the previous general industry PEL of 100 mug/m\3\, OSHA estimates that the risk of developing lung fibrosis consistent with an ILO category 1+ degree of small opacity profusion ranges from 60 to 773 cases per 1,000. For exposure at the previous construction and shipyard PELs, the risk approaches 100 percent. The wide range of risk estimates derived from the underlying studies relied on for the risk assessment may reflect differences in the relative toxicity of quartz particles in different workplaces; nevertheless, OSHA finds that each of these risk estimates clearly represents a significant risk of developing fibrotic lesions in the lung. Exposure to the final PEL of 50 mug/m\3\ respirable crystalline silica for 45 years yields an estimated risk of between 20 and 170 cases per 1,000 for developing fibrotic lesions consistent with an ILO category of 1+. These risk estimates indicate that the final PEL will result in a reduction in risk by about two-thirds or more, which the Agency finds is a substantial reduction of the risk of developing abnormal chest x-ray findings consistent with silicosis.

    One study of coal miners also permitted the agency to evaluate the risk of developing lung fibrosis consistent with an ILO category 2+ degree of profusion of small opacities (Buchanan et al., 2003, Document ID 0306). This level of profusion has been shown to be associated with a higher prevalence of lung function decrement and an increased rate of early mortality (Ng et al., 1987a, Document ID 1108; Begin et al., 1988, 0296; Moore et al., 1988, 1099; Ng et al., 1992a, 0383; Infante-

    Rivard, 1991, 1065). From this study, OSHA estimates that the risk associated with 45 years of exposure to the previous general industry 100 mug/m\3\ PEL is 301 cases per 1,000 workers, again a clearly significant risk. Exposure to the final PEL of 50 mug/m\3\ respirable crystalline silica for 45 years yields an estimated risk of 55 cases per 1,000 for developing lesions consistent with an ILO category 2+ degree of small opacity profusion. This represents a reduction in risk of over 80 percent, again a clearly substantial reduction of the risk of developing radiologic silicosis consistent with ILO category 2+.

    3. Sources of Uncertainty and Variability in OSHA's Risk Assessment

    Throughout the development of OSHA's risk assessment for silica-

    related health effects, sources of uncertainty and variability have been identified by the Agency, peer reviewers, interagency reviewers, stakeholders, scientific experts, and the general public. This subsection reviews and summarizes several general areas of uncertainty and variability in OSHA's risk assessment. As used in this section, ``uncertainty'' refers to lack of knowledge about factors affecting exposure or risk, and ``variability'' refers to heterogeneity, for example, across people, places, or time. For more detailed discussion and evaluation of sources of uncertainty in the risk assessment and a comprehensive review of comments received by OSHA on the risk assessment, (see discussions provided throughout the previous section, Section V, Health Effects).

    As shown in Table VI-1, OSHA's risk estimates for lung cancer are a range derived from a pooled analysis of 10 cohort studies (Steenland et al., 2001a, Document ID 0452; ToxaChemica, Inc., 2004, 0469), a study of granite workers (Attfield and Costello, 2004, Document ID 0543), a study of diatomaceous earth workers (Rice et al., 2001, Document ID 1118), a multi-cohort study of industrial sand workers (Hughes et al., 2001, Document ID 1060), and a study of coal miners exposed to respirable crystalline silica (Miller et al., 2007, Document ID 1305; Miller and MacCalman, 2009, 1306). Similarly, a variety of studies in several different working populations was used to derive risk estimates of silicosis mortality, silicosis morbidity, and renal disease mortality. The ranges of risks presented in Table VI-1 for silica mortality and the other health endpoints thus reflect silica exposure-

    response across a variety of industries and worker populations, which may differ for reasons such as the processes in which silica exposure occurs and the various kinds of minerals that co-exist with crystalline silica in the dust particles (see discussion on variability in toxicological potency of crystalline silica later in this section). The ranges presented in Table VI-1 do not reflect statistical uncertainty (e.g., 95% confidence intervals) or model uncertainty (e.g., the slope of the exposure-response curve at exposures higher or lower than the exposures of the study population) but do reflect variability in the sources of data for the different studies.

    The risks presented in Table VI-1, however, do not reflect variability in the consistency, duration or frequency of workers' exposures. As discussed previously in this section, OSHA's final estimates of health risks represent risk associated with exposure to an 8-hour time weighted average of 25, 50, 100, 250 and 500 mug/m\3\ respirable crystalline silica. These levels represent the risks associated with continuous occupational exposure over a working lifetime of 45 years to the new action level, new PEL, previous general industry PEL, and the range in exposure (250-500 mug/m\3\) that approximates the previous construction and shipyard PELs, respectively. OSHA estimates risks assuming exposure over a working life so that it can evaluate the significance of the risk associated with exposure at the previous PELs in a manner consistent with Section 6(b)(5) of the Act, which requires OSHA to set standards that substantially reduce these risks to the extent feasible even if workers are exposed over a full working lifetime. However, while the risk assessment is based on the assumed working life of 45 years, OSHA recognizes that risks associated with shorter-term or intermittent exposures at a given airborne concentration of silica will be less than the risk associated with continuous occupational exposure at the same concentration over a working lifetime. OSHA thus also uses alternatives to the 45-year full-

    time exposure metric in its projections of the benefits of the final rule (Section VII of this preamble and the FEA) that reflect the reduction in silica-related disease that the Agency expects will result from implementation of the revised standard, using the various estimates of workers' typical exposure levels and patterns.

    The remainder of this discussion reviews several general areas of uncertainty and variability in OSHA's risk assessment that are not quantitatively reflected in the risk estimates shown in Table VI-1, but that provide important context for understanding these estimates, including differences in the degree of uncertainty among the estimates. These areas include exposure estimation error, dose-rate effects, model form uncertainty, variability in toxicological potency of crystalline silica, and additional sources of uncertainty specific to particular endpoints, (e.g., the small number of cases in the renal disease analysis), differing conclusions in the literature on silica as a causative factor in renal disease and lung cancer, and reporting error in silicosis mortality and morbidity. These different sources of uncertainty have varying effects that can lead either to under- or over-

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    estimation of risks. OSHA has taken these sources of uncertainty into account in concluding that the body of scientific literature supports the finding that there is significant risk at existing levels of exposure. The Agency is not required to support the finding that a ``significant risk exists with anything approaching scientific certainty'' (Benzene, 448 U.S. at 656).

    a. Exposure Estimation Error

    As discussed in Section V, OSHA identified exposure estimation error as a key source of uncertainty in most of the studies and thus the Agency's risk assessment. OSHA's contractor, ToxaChemica, Inc., commissioned Drs. Kyle Steenland and Scott Bartell to perform an uncertainty analysis to examine the effect of uncertainty due to exposure estimation error in the pooled studies (Steenland et al., 2001a, Document ID 0452; Mannetje 2002b, 1089) on the lung cancer and silicosis mortality risk estimates (ToxaChemica, Inc., 2004, Document ID 0469). Drs. Steenland and Bartell addressed two main sources of error in the silica exposure estimates. The first arises from the assignment of individual workers' exposures based either on exposure measurements for a sample of workers in the same job or estimated exposure levels for specific jobs in the past when no measurements were available, via a job-exposure matrix (JEM) (Mannetje et al., 2002a, Document ID 1090). The second arises from the conversion of historically-available dust measurements, typically particle count concentrations, to gravimetric respirable silica concentrations. ToxaChemica, Inc. conducted an uncertainty analysis using the raw data from the IARC multi-centric study to address these sources of error (2004, Document ID 0469).

    To explore the potential effects of both kinds of uncertainty described above, ToxaChemica, Inc. (2004, Document ID 0469) used the distributions representing the error in job-specific exposure assignment and the error in converting exposure metrics to generate 50 exposure simulations for each cohort. A study-specific coefficient and a pooled coefficient were fit for each new simulation. The results indicated that the only lung cancer cohort for which the mean of the exposure coefficients derived from the simulations differed substantially from the previously calculated exposure coefficient was the South African gold cohort (simulation mean of 0.181 vs. original coefficient of 0.582). This suggests that the results of exposure-

    response analyses conducted using the South African cohort are sensitive to error in exposure estimates; therefore, there is greater uncertainty due to potential exposure estimation error in an exposure-

    response model based on this cohort than is the case for the other nine cohorts in Steenland et al's analysis (or, put another way, the exposure estimation for the other nine cohorts was less sensitive to the effects of exposure measurement uncertainty).

    For the pooled analysis, the mean coefficient estimate from the simulations was 0.057, just slightly lower than the previous estimate of 0.060. Based on these results, OSHA concluded that random error in the underlying exposure estimates in the Steenland et al. (2001a, Document ID 0452) pooled cohort study of lung cancer is not likely to have substantially influenced the original findings.

    Following the same procedures described above for the lung cancer analysis, ToxaChemica, Inc. (2004, Document ID 0469) combined both sources of random measurement error in a Monte Carlo analysis of the silicosis mortality data from Mannetje et al. (2002b, Document ID 1089). The silicosis mortality dataset appeared to be more sensitive to possible error in exposure measurement than the lung cancer dataset, for which the mean of the simulation coefficients was virtually identical to the original. To reflect this exposure measurement uncertainty, OSHA's final risk estimates derived from the pooled analysis (Mannetje et al., 2002b, Document ID 1089), incorporated ToxaChemica, Inc.'s simulated measurement error (2004, Document ID 0469).

    b. Uncertainty Related to Dose-Rate Effects

    OSHA received comments citing uncertainty in its risk assessment related to possible dose-rate effects in the silica exposure-response relationships, particularly for silicosis. For example, the ACC commented that extrapolating risks from the high mean exposure levels in the Park et al. 2002 cohort (Document ID 0405) to the much lower mean exposure levels relevant to OSHA's risk assessment contributes uncertainty to the analysis (Document ID 4209, pp. 84-85), because of the possibility that risk accrues differently at different exposure concentrations. The ACC thus argued that the risk associated with any particular level of cumulative exposure may be higher for exposure to a high concentration of respirable crystalline silica over a short period of time than for an equivalent cumulative exposure resulting from exposure to a low concentration of respirable crystalline silica over a long period of time (Document ID 4209, p. 58; 2307, Attachment A, pp. 93-94). These and similar comments on dose-rate effects questioned OSHA's use of workers' cumulative exposure levels to estimate risk, as the cumulative exposure metric does not capture dose-rate effects. Thus, according to the ACC, if there are significant dose-rate effects in the exposure-response relationship for a disease or other health endpoint, use of the cumulative exposure metric could lead to error in risk estimates.

    The rationale for OSHA's reliance on a cumulative exposure metric to assess the risks of respirable crystalline silica is discussed in Section V. With respect to this issue of uncertainty related to dose-

    response effects, OSHA finds limited evidence in the record to either support or refute the effects hypothesized by the ACC. As such, OSHA acknowledges some uncertainty. Furthermore, use of an alternative metric such as concentration would not provide assurance that uncertainties would be mitigated or reduced.

    Two studies discussed in OSHA's Review of Health Effects Literature and Preliminary QRA examined dose-rate effects on silicosis exposure-

    response (Document ID 1711, pp. 342-344). Neither study found a dose-

    rate effect relative to cumulative exposure at silica concentrations near the previous OSHA PEL (Document ID 1711, pp. 342-344). However, they did observe a dose-rate effect in instances where workers were exposed to crystalline silica concentrations far above the previous PEL (i.e., several-fold to orders of magnitude above 100 mug/m\3\) (Buchanan et al., 2003, Document ID 0306; Hughes et al., 1998, 1059). The Hughes et al. (1998) study of diatomaceous earth workers found that the relationship between cumulative silica exposure and risk of silicosis was steeper for workers hired prior to 1950 and exposed to average concentrations above 500 microg/m\3\ compared to workers hired after 1950 and exposed to lower average concentrations (Document ID 1059). Hughes et al. reported that subdivisions for workers with exposure to concentrations below 500 mug/m\3\ were examined, but that no differences were observed across these groups (Document ID 1059, p. 809). It is unclear whether sparse data at the low end of the concentration range contributed to this finding, as the authors did not provide detailed information on the distribution of exposures in the study population.

    The Buchanan et al. (2003) study of Scottish coal miners adjusted the cumulative exposure metric in the risk model to account for the effects of exposures to high concentrations where

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    the investigators found that, at concentrations above 2000 mug/m\3\, the risk of silicosis was about three times higher than the risk associated with exposure to lower concentrations but at the same cumulative exposure (Document ID 0306, p. 162). Buchanan et al. noted that only 16 percent of exposure hours among the workers in the study occurred at levels below 10 mug/m\3\ (Document ID 0306, p. 161), and cautioned that insufficient data are available to predict effects at very low concentrations where data are sparse (Document ID 0306, p. 163). However, 56 percent of hours occurred at levels between 10 and 100 mug/m\3\. Detailed information on the hours worked at concentrations within this range was not provided.

    Based on its review of these studies, OSHA concluded that there is little evidence that a dose-rate effect exists at concentrations in the range of the previous PEL (100 mug/m\3\) (Document ID 1711, p. 344). However, there remains some uncertainty related to dose-rate effects in the Agency's silicosis risk assessment. Even if a dose-rate effect exists only at concentrations far higher than the previous PEL, it is possible for the dose-rate effect to impact model form if not properly accounted for in study populations with high-concentration exposures. This is one reason that OSHA presents a range of risk estimates based on a variety of study populations exposed under different working conditions. For example, as OSHA noted in its Review of Health Effects Literature and Preliminary QRA (Document ID 1711, pp. 355-356), the Park et al. study is complemented by the Mannetje et al. multi-cohort silicosis mortality pooled study. Mannetje et al.'s study included several cohorts that had exposure concentrations in the range of interest for this rulemaking and also showed clear evidence of significant risk of silicosis mortality at the previous general industry and construction PELs (2002b, Document ID 1089). In addition, OSHA used the model from the Buchanan et al. study in its silicosis morbidity risk assessment to account for possible dose-rate effects at high average concentrations (Document ID 1711, pp. 335-342). OSHA notes that the risk estimates in the exposure range of interest (25-500 mug/m\3\) derived from the Buchanan et al. (2003) study were not appreciably different from those derived from the other studies of silicosis morbidity (see Table VI-1).

    c. Model Form Uncertainty

    Another source of uncertainty in OSHA's risk analysis is uncertainty with respect to the form of the statistical models used to characterize the relationship between exposure level and risk of adverse health outcomes. As discussed in Section V, some commenters expressed concern that studies relied on by OSHA may not have considered all potential exposure-response relationships and might be unable to discern differences between monotonic and non-monotonic characteristics (e.g., Document ID 2307, Attachment A, p. 113-114).

    OSHA acknowledges that the possibility of error in selection of exposure-response model forms is a source of uncertainty in the silica risk assessment. To address this uncertainty, the Agency included studies in the risk assessment that explored a variety of model forms. For example, as discussed in Section V, the ToxaChemica reanalyses of the Mannetje et al. silicosis mortality dataset and the Steenland et al. lung cancer mortality data set examined several model forms including a five-knot restricted spline analysis, which is a highly flexible model form able to capture a variety of exposure-response shapes (Document ID 0469, p. 50). The ToxaChemica reanalysis addresses the issue of model form uncertainty by finding similar exposure-

    response relationships regardless of the type of model used.

    d. Uncertainty Related to Silica Exposure as a Risk Factor for Lung Cancer

    As discussed in Section V, OSHA has reviewed the best available evidence on the relationship between silica exposure and lung cancer mortality, and has concluded that the weight of evidence supports the finding that exposure to silica at the preceding and new PELs increases the risk of lung cancer. However, OSHA acknowledges that not every study in the literature on silica-related lung cancer reached the same conclusions. This variability is to be expected in epidemiology, as there are different cohorts, measurements, study designs, and analytical methods, among other factors. OSHA further acknowledges that there is uncertainty with respect to the magnitude of the risk of lung cancer from silica exposure. In the case of silica, the exposure-

    response relationship with lung cancer may be easily obscured, as crystalline silica is a comparably weaker carcinogen (i.e., the increase in risk per unit exposure is smaller) than other well-studied, more potent carcinogens such as hexavalent chromium (Steenland et al., 2001, Document ID 0452, p. 781) and tobacco smoke, a common co-exposure in silica-exposed populations.

    A study by Vacek et al. (2011) illustrates the uncertainties involved in evaluating risk of lung cancer from silica exposure. This study found no significant association between respirable silica exposure and lung cancer mortality in a cohort of Vermont granite workers (Document ID 1486, pp. 75-81). Some commenters criticized OSHA's preliminary risk assessment for rejecting the Vacek et al. (2011) study and instead relying upon the Attfield and Costello (2004, Document ID 0284) study of Vermont granite workers (Document ID 2307, Attachment A, pp. 36-47; 4209, pp. 34-36). As discussed in detail in Section V, OSHA reviewed the Vacek et al. study and all comments received by the Agency on this issue, and has decided not to reject the Attfield and Costello (2004) study in favor of the Vacek et al. (2011) study as a basis for risk assessment. OSHA acknowledges that comprehensive studies, such as those of Attfield and Costello (2004) and Vacek et al. (2011), in the Vermont granite industry have shown conflicting results with respect to lung cancer mortality (Document ID 0284; 1486). Although OSHA believes that the Attfield and Costello (2004) study is the most appropriate Vermont granite study to use in its QRA, it also relied upon other studies, and that the risk estimates for lung cancer mortality based on those studies (i.e., Document ID 0543, 1060, 1118, 1306) still provide substantial evidence that respirable crystalline silica poses a significant risk of lung cancer to exposed workers.

    e. Uncertainty Related to Renal Disease

    As discussed in Section V, OSHA acknowledges that there are considerably less data for renal disease mortality than those for silicosis, lung cancer, and non-malignant respiratory disease (NMRD) mortality. Although the Agency believes the renal disease risk findings are based on credible data, the risk findings based on them are less robust than the findings for silicosis, lung cancer, and NMRD.

    Based upon its overall analysis of the literature, including the negative studies, OSHA has concluded that there is substantial evidence suggesting an association between exposure to crystalline silica and increased risks of renal disease. This conclusion is supported by a number of case reports and epidemiological studies that found statistically significant associations between occupational exposure to silica dust and chronic renal disease (Calvert et al., 1997, Document ID 0976), subclinical renal changes (Ng et al., 1992c, Document ID 0386), end-stage renal disease morbidity (Steenland et

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    al., 1990, Document ID 1125), end-stage renal disease incidence (Steenland et al., 2001b, Document ID 0456), chronic renal disease mortality (Steenland et al., 2002a, 0448), and granulomatosis with polyangitis (Nuyts et al., 1995, Document ID 0397). However, as discussed in the Review of Health Effects Literature and Preliminary QRA, the studies reviewed by OSHA included a number of studies that did not show an association between crystalline silica and renal disease (Document ID 1711, pp. 211-229). Additional negative studies by Birk et al. (2009, Document ID 1468), and Mundt et al. (2011, Document ID 1478) were reviewed in the Supplemental Literature Review of the Review of Health Effects Literature and Preliminary QRA, which noted the short follow-up period as a limitation, which reduces the likelihood that an increased incidence of renal mortality would have been detected (Document ID 1711, Supplement, pp. 6-12). Comments submitted to OSHA by the ACC additionally cited several studies that did not show a statistically significant association between exposure to crystalline silica and renal disease mortality, including McDonald et al. (2005, Document ID 1092), Vacek et al. (2011, Document ID 2340), Davis et al. (1983, Document ID 0999), Koskela et al. (1987, Document ID 0363), Cherry et al. (2012, article included in Document ID 2340), Steenland et al. (2002b, Document ID 0454), Rosenman et al. (2000, Document ID 1120), and Calvert et al. (2003, Document ID 0309) (Document ID 2307, Attachment A, pp. 140-145).

    As discussed in detail in Section V, OSHA concludes that the evidence supporting causality regarding renal risk outweighs the evidence casting doubt on that conclusion, but acknowledges this divergence in the renal disease literature as a source of uncertainty.

    OSHA estimated quantitative risks for renal disease mortality (Document ID 1711, pp. 314-316) using data from a pooled analysis of renal disease, conducted by Steenland et al. (2002a, Document ID 0448). The data set included 51 deaths from renal disease as an underlying cause, which the authors of the pooled study, Drs. Kyle Steenland and Scott Bartell, acknowledged to be insufficient to provide robust estimates of risk (Document ID 2307, Attachment A, p. 139, citing 0469, p. 27). OSHA agrees with Dr. Steenland and acknowledges, as it did in its Review of Health Effects Literature and Preliminary QRA (Document ID 1711, p. 357), that its quantitative risk estimates for renal disease mortality are less robust than those for the other health effects examined (i.e., lung cancer mortality, silicosis and NMRD mortality, and silicosis morbidity).

    f. Uncertainty in Reporting and Diagnosis of Silicosis Mortality and Silicosis Morbidity

    OSHA's final quantitative risk assessment includes risk estimates for silicosis mortality and morbidity. Silicosis mortality is ascertained by analysis of death certificates for cause of death, and morbidity is ascertained by the presence of chest radiographic abnormalities consistent with silicosis among silica-exposed workers. Each of these kinds of studies are associated with uncertainties in case ascertainment and use of chest roentgenograms to detect lung scarring due to silicosis.

    For silicosis mortality, OSHA's analysis includes a pooled analysis of six epidemiological studies first published by Mannetje et al. (2002b, Document ID 1089) and re-analyzed by OSHA's contractor ToxaChemica (2004, Document ID 0469). OSHA finds that the estimates from Mannetje et al. and ToxaChemica's analyses are likely to understate the actual risk because silicosis is under-reported as a cause of death, as discussed in Sections VC.2.iv and V.E in the context of silicosis disease surveillance systems. To help address this uncertainty, OSHA's risk analysis also included an exposure-response analysis of diatomaceous earth (DE) workers (Park et al., 2002, Document ID 0405), which better captures the totality of silica-related respiratory disease than do the datasets analyzed by Mannetje et al. and ToxaChemica. Park et al.. quantified the relationship between cristobalite exposure and mortality caused by NMRD, which includes silicosis, pneumoconiosis, emphysema, and chronic bronchitis. Because NMRD captures much of the silicosis misclassification that results in underestimation of the disease and includes risks from other lung diseases associated with crystalline silica exposures, OSHA finds the risk estimates derived from the Park et al. study are important to include as part of OSHA's range of estimates of the risk of death from silica-related respiratory diseases, including silicosis. (Document ID 1711, pp. 297-298). OSHA concludes that the range of silicosis and NMRD risks presented in the final risk assessment, based on both the ToxaChemica reanalysis of Mannetje et al.'s silicosis mortality data and Park et al.'s study of NMRD mortality, provide a credible range of estimates of mortality risk from silicosis and NMRD across a range of industrial workplaces. The upper end of this range, based on the Park et al. study, is less likely to underestimate risk as a result of under-reporting of silicosis mortality, but cannot be directly compared to risk estimates from studies that focused on cohorts of workers from different industries.

    OSHA's estimates of silicosis morbidity risks are based on studies of active and retired workers for which exposure histories could be constructed and chest x-ray films could be evaluated for signs of silicosis. There is evidence in the record that chest x-ray films are relatively insensitive to detecting lung fibrosis. Hnizdo et al. (1993, Document ID 1050) found chest x-ray films to have low sensitivity for detecting lung fibrosis related to silicosis, compared to pathological examination at autopsy. To address the low sensitivity of chest x-rays for detecting silicosis, Hnizdo et al. (1993, Document ID 1050) recommended that radiographs consistent with an ILO category of 0/1 or greater be considered indicative of silicosis among workers exposed to a high concentration of silica-containing dust. In like manner, to maintain high specificity, chest x-rays classified as category 1/0 or 1/1 should be considered as a positive diagnosis of silicosis. Studies relied on in OSHA's risk assessment typically used an ILO category of 1/0 or greater to identify cases of silicosis. According to Hnizdo et al., they are unlikely to include many false positives (diagnoses of silicosis where there is none), but may include false negatives (failure to identify cases of silicosis). Thus, the use of chest roentgenograms to ascertain silicosis cases in the morbidity studies relied on by OSHA in its risk assessment could lead to an underestimation of risk given the low sensitivity of chest roentgenograms for detecting silicosis.

    g. Variability in Toxicological Potency of Crystalline Silica

    As discussed in Section V, the toxicological potency of crystalline silica is influenced by a number of physical and chemical factors that affect the biological activity of inhaled silica particles. The toxicological potency of crystalline silica is largely influenced by the presence of oxygen free radicals on the surfaces of respirable particles. These chemically-reactive oxygen species interact with cellular components in the lung to promote and sustain the inflammatory reaction responsible for the lung damage associated with exposure to crystalline silica. The reactivity of particle surfaces is greatest when crystalline silica has been freshly fractured by high-energy

    Page 16398

    work processes such as abrasive blasting, rock drilling, or sawing concrete materials. As particles age in the air, the surface reactivity decreases and exhibits lower toxicologic potency (Porter et al., 2002, Document ID 1114; Shoemaker et al., 1995, 0437; Vallyathan et al., 1995, 1128). In addition, surface impurities have been shown to alter silica toxicity. For example, aluminum and aluminosilicate clay on silica particles has been shown to decrease toxicity (Castranova et al., 1997, Document ID 0978; Donaldson and Borm, 1998, 1004; Fubini, 1998, 1016; Donaldson and Borm, 1998, Document ID 1004; Fubini, 1998, 1016).

    In the preamble to the proposed standard, OSHA preliminarily concluded that although there is evidence that several environmental influences can modify surface activity to either enhance or diminish the toxicity of silica, the available information was insufficient to determine to what extent these influences may affect risk to workers in any particular workplace setting (Document 1711, p. 350). OSHA acknowledges that health risks are probably in the low end of the range for workers in the brick manufacturing industry, although the evidence still indicates that there is a significant risk at the previous general industry PEL for those workers. OSHA also acknowledges that there was a lack of evidence for a significant risk in the sorbent minerals industry due to the nature of crystalline silica present in those operations; as a result, it decided to exclude sorptive clay processing from this rule. Furthermore, Dudley and Morriss (2015) raise concerns about the whether the exposures reflected in the historical cohorts used in the risk assessment are sufficiently reflective of rapidly changing working conditions over the last 45 years.\11\ However, the risk estimates presented in Table VI-1 are based on studies from a variety of industries, such that the risk ranges presented are likely to include estimates appropriate to most working populations. Thus, in OSHA's view, its significant risk finding is well supported by the weight of best available evidence, notwithstanding uncertainties that may be present to varying degrees in the numerous studies relied upon and the even greater number of studies that the Agency considered.

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    \11\ Dudley, S. E. and Morriss, A. P. (2015), Will the Occupational Safety and Health Administration's Proposed Standards for Occupational Exposure to Respirable Crystalline Silica Reduce Workplace Risk?. Rish Analysis, 35: 1191-1196. doi:10.1111/

    risa.12341

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    4. OSHA's Response to Comments on Significant Risk of Material Impairment

    OSHA received several comments pertaining to the Agency's determination of a significant risk of material impairment of health posed to workers exposed for a working life to the previous PELs. Although many of these comments were supportive of OSHA's conclusions regarding the significance of risk, others were critical or suggested that OSHA has an obligation to further reduce the risk below that estimated to remain at the revised PEL.

    Referring to the previous PELs for respirable crystalline silica, the AFL-CIO commented that ``workers face a significant risk of harm from silica exposure at the current permissible exposure limits,'' and that ``there is overwhelming evidence in the record that exposure to respirable crystalline silica poses a significant health risk to workers'' (Document ID 4204, pp. 10-11). The AFL-CIO noted that OSHA's mortality risk estimates well exceeded the benchmark of 1/1,000 excess risk over a working lifetime of exposure to the previous PELs, and also highlighted the risks of silicosis morbidity (Document ID 4204, p. 13). The AFL-CIO further pointed out that there is no cure for silicosis, and quoted oral testimony from workers at the informal public hearings demonstrating that ``silica-related diseases are still destroying workers' lives and livelihoods'' (Document ID 4204, p. 19).

    Both the UAW and the Building and Construction Trades Department (BCTD) concurred with the AFL-CIO that the previous PEL needs to be lowered to adequately protect workers. Referring to the previous PEL, the BCTD stated that ``the record supports OSHA's determination that exposures at the current PEL present a significant risk'' (Document ID 4223, p. 6). Although supportive of OSHA's proposed standard, the UAW also suggested the adoption of a PEL of 25 microg/m\3\ or lower where feasible (Document ID 2282, Attachment 3, p.1), noting that a PEL set at this level ``will significantly reduce workers' exposure to deadly silica dust and prevent thousands of illnesses and deaths every year'' (Document ID 2282, Attachment 3, p. 25). Similarly, Charles Gordon, a retired occupational safety and health attorney, commented that the revised PEL ``leaves a remaining risk of 97 deaths per 1,000 workers from silicosis, lung cancer, and renal disease combined'' (Document ID 4236, p. 2). Again, it should be noted that these risk estimates are not additive because some individuals may suffer from multiple diseases caused by exposure to silica. Instead, OSHA presents risk estimates for each health endpoint.

    As discussed above, OSHA acknowledges that there remains a significant risk of material impairment of health at the revised PEL; a further reduction in the PEL, however, is not currently technologically feasible (see Section VII, Summary of the Final Economic Analysis and Final Regulatory Flexibility Analysis, in which OSHA summarizes its assessment of the technological feasibility of the revised PEL). Despite this, the final PEL will provide a very substantial reduction in the risk of material impairment of health to silica-exposed workers, as described in the Benzene decision (Benzene, 448 U.S. at 642).

    In contrast to the foregoing comments from labor groups contending that OSHA would be setting the PEL too high if it made a final determination to lower the preceding PELs to 50 microg/m\3\, critical comments came from industry groups including the American Chemistry Council (ACC), which disagreed with OSHA's determination of a significant risk of material impairment of health at the previous PELs. The ACC stated, ``OSHA's assessment of these risks is flawed, and its conclusions that the risks are significant at a PEL of 100 microg/

    m\3\ and would be substantially reduced by lowering the PEL to 50 microg/m\3\ are unsupported'' (Document ID 4209, p. 12). The ACC then asserted several ``fundamental shortcomings'' in OSHA's QRA on which OSHA based its significant risk determination (Document ID 4209, pp. 16-17), including a variety of purported biases in the key studies on which OSHA relied. OSHA addresses the ACC's concerns in detail in Section V of this preamble dealing with the key studies relied upon by the Agency for each health endpoint, as well as separate sections addressing the issues of biases, causation, thresholds, the uncertainty analysis, and the life table and exposure assumptions used in the QRA. As more fully discussed in those sections, OSHA finds these concerns to be unpersuasive. As discussed in Section V, the scientific community and regulators in other advanced industrial societies agree on the need for a PEL of at most 50 microg/m\3\ based on demonstrated health risks, and OSHA has used the best available evidence in the scientific literature to estimate quantitative risks of silica-related illnesses and thereby reach the same conclusion. OSHA's preliminary review of the health effects literature and OSHA's preliminary QRA were, further, examined by an independent, external peer review panel of

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    accomplished scientists, which lent credibility to the Agency's methods and findings and led to some adjustments in the analysis that strengthened OSHA's final risk assessment. There is, additionally, widespread support for the Agency's methods and conclusions in the rulemaking record. As such, OSHA is confident in its conclusion that there is a significant risk of material impairment of health to workers exposed to respirable crystalline silica at the levels of exposure permitted under the previous PELs and under this final standard, and finds no merit in broad assertions purporting to debunk this conclusion.

    In summary, as discussed throughout Section V and this final rule, OSHA concludes, based on the best available evidence in the scientific literature, that workers' exposure to respirable crystalline silica at the previous PELs results in a clearly significant risk of material impairment of health. The serious, and potentially fatal, health effects suffered by exposed workers include silicosis, lung cancer, NMRD, renal disease, and autoimmune effects. OSHA finds that the risk is substantially decreased, though still significant, at the new PEL of 50 microg/m\3\ and below, including at the new action level of 25 microg/m\3\. The Agency is constrained, however, from lowering the PEL further by its finding that a lower PEL would be infeasible in many operations across several industries. Given the significant risks faced by workers exposed to respirable crystalline silica under the previously-existing exposure limits, OSHA believes that it is imperative that it issue this final standard pursuant to its statutory mandate under the OSH Act.

    VII. Summary of the Final Economic Analysis and Final Regulatory Flexibility Analysis

  14. Introduction

    OSHA's Final Economic Analysis and Final Regulatory Flexibility Analysis (FEA) addresses issues related to the costs, benefits, technological and economic feasibility, and the economic impacts (including impacts on small entities) of this final respirable crystalline silica rule and evaluates regulatory alternatives to the final rule. Executive Orders 13563 and 12866 direct agencies to assess all costs and benefits of available regulatory alternatives and, if regulation is necessary, to select regulatory approaches that maximize net benefits (including potential economic, environmental, and public health and safety effects; distributive impacts; and equity). Executive Order 13563 emphasized the importance of quantifying both costs and benefits, of reducing costs, of harmonizing rules, and of promoting flexibility. The full FEA has been placed in OSHA rulemaking docket OSHA-2010-0034. This rule is an economically significant regulatory action under Sec. 3(f)(1) of Executive Order 12866 and has been reviewed by the Office of Information and Regulatory Affairs in the Office of Management and Budget, as required by executive order.

    The purpose of the FEA is to:

    Identify the establishments and industries potentially affected by the final rule;

    Estimate current exposures and the technologically feasible methods of controlling these exposures;

    Estimate the benefits resulting from employers coming into compliance with the final rule in terms of reductions in cases of silicosis, lung cancer, other forms of chronic obstructive pulmonary disease, and renal failure;

    Evaluate the costs and economic impacts that establishments in the regulated community will incur to achieve compliance with the final rule;

    Assess the economic feasibility of the final rule for affected industries; and

    Assess the impact of the final rule on small entities through a Final Regulatory Flexibility Analysis (FRFA), to include an evaluation of significant regulatory alternatives to the final rule that OSHA has considered.

    Significant Changes to the FEA Between the Proposed Standards and the Final Standards

    OSHA changed the FEA for several reasons:

    Changes to the rule, summarized in Section I of this preamble and discussed in detail in the Summary and Explanation;

    Comments on the Preliminary Economic Analysis (PEA);

    Updates of economic data; and

    Recognition of errors in the PEA.

    OSHA revised its technological and economic analysis in response to these changes and to comments received on the NPRM. The FEA contains some costs that were not included in the PEA and updates data to use more recent data sources and, in some cases, revised methodologies. Detailed discussions of these changes are included in the relevant sections throughout the FEA.

    The FEA contains the following chapters:

    Chapter I. Introduction

    Chapter II. Market Failure and the Need for Regulation

    Chapter III. Profile of Affected Industries

    Chapter IV. Technological Feasibility

    Chapter V. Costs of Compliance

    Chapter VI. Economic Feasibility Analysis and Regulatory Flexibility Determination

    Chapter VII. Benefits and Net Benefits

    Chapter VIII. Regulatory Alternatives

    Chapter IX. Final Regulatory Flexibility Analysis

    Chapter X. Environmental Impacts

    Table VII-1 provides a summary of OSHA's best estimate of the costs and estimated benefits of the final rule using a discount rate of 3 percent. As shown, the final rule is estimated to prevent 642 fatalities and 918 silica-related illnesses annually once it is fully effective, and the estimated cost of the rule is $1,030 million annually. Also as shown in Table VII-1, the discounted monetized benefits of the final rule are estimated to be $8.7 billion annually, and the final rule is estimated to generate net benefits of $7.7 billion annually. Table VII-1 also presents the estimated costs and estimated benefits of the final rule using a discount rate of 7 percent.

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    The remainder of this section (Section VII) of the preamble is organized as follows:

  15. Market Failure and the Need for Regulation

  16. Profile of Affected Industries

  17. Technological Feasibility

  18. Costs of Compliance

  19. Economic Feasibility Analysis and Regulatory Flexibility Determination

  20. Benefits and Net Benefits

  21. Regulatory Alternatives

    I. Final Regulatory Flexibility Analysis.

  22. Market Failure and the Need for Regulation

    Employees in work environments addressed by the final silica rule are exposed to a variety of significant hazards that can and do cause serious injury and death. As described in Chapter II of the FEA in support of the final rule, OSHA concludes there is a failure of private markets to protect workers from exposure to unnecessarily high levels of respirable crystalline silica and that private markets, as well as information dissemination programs, workers' compensation systems, and

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    tort liability options, each may fail to protect workers from silica exposure, resulting in the need for a more protective OSHA silica rule.

    After carefully weighing the various potential advantages and disadvantages of using a regulatory approach to improve upon the current situation, OSHA concludes that, in the case of silica exposure, the final mandatory standards represent the best choice for reducing the risks to employees. In addition, rulemaking is necessary in this case in order to replace older existing standards with updated, clear, and consistent health standards.

  23. Profile of Affected Industries

    Introduction

    Chapter III of the FEA presents profile data for industries potentially affected by the final silica rule. The discussion below summarizes the findings in that chapter. As a first step, OSHA identifies the North American Industrial Classification System (NAICS) industries, both in general industry and maritime and in the construction sector, with potential worker exposure to silica. Next, OSHA provides summary statistics for the affected industries, including the number of affected entities and establishments, the number of workers whose exposure to silica could result in disease or death (``at-risk workers''), and the average revenue for affected entities and establishments.\12\ Finally, OSHA presents silica exposure profiles for at-risk workers. These data are presented by sector and job category. Summary data are also provided for the number of workers in each affected industry who are currently exposed above the final silica PEL of 50 mug/m\3\, as well as above an alternative PEL of 100 mug/

    m\3\ for economic analysis purposes.

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    \12\ The Census Bureau defines an establishment as a single physical location at which business is conducted or services or industrial operations are performed. The Census Bureau defines a business firm or entity as a business organization consisting of one or more domestic establishments in the same state and industry that were specified under common ownership or control. The firm and the establishment are the same for single-establishment firms. For each multi-establishment firm, establishments in the same industry within a state will be counted as one firm; the firm employment and annual payroll are summed from the associated establishments. (US Census Bureau, Statistics of US Businesses, Definitions. 2015, http://www.census.gov/econ/susb/definitions.html?cssp=SERP).

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    The methodological basis for the industry and at-risk worker data presented in this chapter comes from the PEA, the Eastern Research Group (ERG) analysis supporting the PEA (2007a, 2007b, 2008a, and 2008b),\13\ and ERG's analytic support in preparing the FEA. The data used in this chapter come from the rulemaking record (Docket OSHA-2010-

    0034), the technological feasibility analyses presented in Chapter IV of the FEA, and from OSHA (2016), which updated its earlier spreadsheets to reflect the most recent industry data available. To do so, ERG first matched the BLS Occupational Employment Statistics (OES) survey occupational titles with the at-risk job categories, by NAICS industry. ERG then calculated the percentages of production employment represented by each at-risk job title within industry (see OSHA, 2016 for details on the calculation of employment percentages and the mapping of at-risk job categorizations into OES occupations).\14\ ERG's expertise for identifying the appropriate OES occupations and calculating the employment percentages enabled OSHA to estimate the number of employees in the at-risk job categories by NAICS industry (Id.).

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    \13\ Document ID, 1709, 1608, 1431, and 1365, respectively.

    \14\ Production employment includes workers in building and grounds maintenance; forestry, fishing, and farming; installation and maintenance; construction; production; and material handling occupations.

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    In the NPRM and PEA, OSHA invited the public to submit additional information and data that might help improve the accuracy and usefulness of the preliminary industry profile; the profile presented here and in Chapter III of the FEA reflects public comment.

    Selection of NAICS Industries for Analysis

    The technological feasibility analyses presented in Chapter IV of the FEA identify the general industry and maritime sectors and the construction activities potentially affected by the final silica standard.

    General Industry and Maritime

    Employees engaged in various activities in general industry and maritime routinely encounter crystalline silica as a molding material, as an inert mineral additive, as a component of fluids used to stimulate well production of oil or natural gas, as a refractory material, as a sandblasting abrasive, or as a natural component of the base materials with which they work. Some industries use various forms of silica for multiple purposes. As a result, employers are faced with the challenge of limiting worker exposure to silica in dozens of job categories throughout the general industry and maritime sectors.

    Job categories in general industry and maritime were selected for analysis based on data from the technical industrial hygiene literature, evidence from OSHA Special Emphasis Program (SEP) results, and, in several cases, information from ERG site visit reports and public comment submitted into the record. These data sources provided evidence of silica exposures in numerous sectors. While the available data are not entirely comprehensive, OSHA believes that silica exposures in other sectors are quite limited.

    The industry subsectors in the overall general industry and maritime application groups that OSHA identified as being potentially affected by the final silica standard are as follows:

    Asphalt Paving Products

    Asphalt Roofing Materials

    Hydraulic Fracturing

    Industries with Captive Foundries

    Concrete Products

    Cut Stone

    Dental Equipment and Supplies

    Dental Laboratories

    Flat Glass

    Iron Foundries

    Jewelry

    Mineral Processing

    Mineral Wool

    Nonferrous Sand Casting Foundries

    Non-Sand Casting Foundries

    Other Ferrous Sand Casting Foundries

    Other Glass Products

    Paint and Coatings

    Porcelain Enameling

    Pottery

    Railroads

    Ready-Mix Concrete

    Refractories

    Refractory Repair

    Shipyards

    Structural Clay

    In some cases, affected industries presented in the technological feasibility analysis have been disaggregated to facilitate the cost and economic impact analysis. In particular, flat glass, mineral wool, and other glass products are subsectors of the glass industry described in Chapter IV, Section IV-9, of the FEA, and captive foundries,\15\ iron foundries, nonferrous sand casting foundries, non-sand cast foundries, and other ferrous sand casting foundries are subsectors of the

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    overall foundries industry presented in Chapter IV, Section IV-8, of the FEA.

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    \15\ Captive foundries include establishments in other industries with foundry processes incidental to the primary products manufactured. ERG (2008b, Document ID 1365) provides a discussion of the methodological issues involved in estimating the number of captive foundries and in identifying the industries in which they are found. Since the 2008 ERG report, through comment in the public record and the public hearings, OSHA has gained additional information on the presence of captive foundries throughout general industry.

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    As described in ERG (2008b, Document ID 1365) and updated in OSHA (2016), OSHA identified the six-digit NAICS codes for these subsectors to develop a list of industries potentially affected by the final silica standard. Table VII-2 presents the sectors listed above with their corresponding six-digit NAICS industries. The NAICS codes and associated industry definitions in the FEA are consistent with the 2012 NAICS edition.

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    Construction

    The construction sector is an integral part of the nation's economy, accounting for approximately 4.5 percent of total private sector employment. Establishments in this industry are involved in a wide variety of activities, including land development and subdivision, homebuilding, construction of nonresidential buildings and other structures, heavy construction work (including roadways and bridges), and a myriad of special trades such as plumbing, roofing, electrical, excavation, and demolition work.

    Construction activities were selected for analysis based on historical data of recorded samples of construction worker exposures from the OSHA Integrated Management Information System (IMIS) and the National Institute for Occupational Safety and Health (NIOSH). In addition, OSHA reviewed the industrial hygiene literature across the full range of construction activities and focused on dusty operations where silica sand was most likely to be fractured or abraded by work operations. These physical processes have been found to cause the silica exposures that pose the greatest risk of silicosis for workers.

    The construction activities, by equipment or task, that OSHA identified as being potentially affected by the final silica standard are as follows:

    Earth drilling

    Heavy Equipment Operators and Ground Crew Laborers--I (Abrading or fracturing silica containing materials or demolishing concrete or masonry structures)

    Heavy Equipment Operators and Ground Crew Laborers--II (Grading and Excavating)

    Hole Drillers Using Handheld or Stand-Mounted Drills

    Jackhammers and Other Powered Handheld Chipping Tools

    Masonry and Concrete Cutters Using Portable Saws--I (Handheld power saws)

    Masonry and Concrete Cutters Using Portable Saws--II (Handheld power saws for cutting fiber-cement board)

    Masonry and Concrete Cutters Using Portable Saws--III (Walk-

    behind saws)

    Masonry and Concrete Cutters Using Portable Saws--IV (Drivable or ride-on concrete saws)

    Masonry and Concrete Cutters Using Portable Saws--V (Rig-

    mounted core saws or drills)

    Masonry Cutters Using Stationary Saws

    Millers Using Portable or Mobile Machines--I (Walk-behind milling machines and floor grinders)

    Millers Using Portable or Mobile Machines--II (Small drivable milling machine (less than half-lane))

    Millers Using Portable or Mobile Machines--III (Milling machines (half-lane and larger with cuts of any depth on asphalt only and for cuts of four inches in depth or less on any other substrate))

    Rock and Concrete Drillers--I (Vehicle-mounted drilling rigs for rock and concrete)

    Rock and Concrete Drillers--II (Dowel drilling rigs for concrete)

    Mobile Crushing Machine Operators and Tenders

    Tuckpointers and Grinders--I (Handheld grinders for mortar removal (e.g., tuckpointing))

    Tuckpointers and Grinders--II (Handheld grinders for uses other than mortar removal)

    As shown in OSHA (2016) and in Chapter IV of the FEA, these construction activities occur in the following industries and governmental bodies, accompanied by their four-digit NAICS codes: \16\ \17\

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    \16\ ERG and OSHA used the four-digit NAICS codes for the construction sector both because the BLS's Occupational Employment Statistics survey only provides data at this level of detail ad because, unlike the case in general industry and maritime, job categories in the construction sector are task-specific, not industry-specific. Furthermore, as far as economic impacts are concerned, IRS data on profitability are reported only at the four-

    digit NAICS code level of detail.

    \17\ Some public employees in state and local governments are exposed to elevated levels of respirable crystalline silica. These exposures are included in the construction sector because they are the result of construction activities.

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    2361 Residential Building Construction

    2362 Nonresidential Building Construction

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    2371 Utility System Construction

    2372 Land Subdivision

    2373 Highway, Street, and Bridge Construction

    2379 Other Heavy and Civil Engineering Construction

    2381 Foundation, Structure, and Building Exterior Contractors

    2382 Building Equipment Contractors

    2383 Building Finishing Contractors

    2389 Other Specialty Trade Contractors

    2211 Electric Utilities

    9992 State Government

    9993 Local Government

    Characteristics of Affected Industries

    Table VII-3 provides an overview of the industries and estimated number of workers affected by the final rule. Included in Table VII-3 are summary statistics for each of the affected industries, subtotals for construction and for general industry and maritime, and grand totals for all affected industries combined.

    The first five columns in Table VII-3 identify the NAICS code for each industry in which workers are routinely exposed to respirable crystalline silica and the name or title of the industry, followed by the total number of entities, establishments, and employees for that industry. Note that, while the industries are characterized by such exposure, not every entity, establishment, and employee in these affected industries engage in activities involving silica exposure.

    The next three columns in Table VII-3 show, for each affected industry, the number of entities and establishments in which workers are actually exposed to silica and the total number of workers exposed to silica. The number of affected establishments was set equal to the total number of establishments in an industry (based on Census data) unless the number of affected establishments would exceed the number of affected employees in the industry. In that case, the number of affected establishments in the industry was set equal to the number of affected employees, and the number of affected entities in the industry was reduced so as to maintain the same ratio of entities to establishments in the industry.\18\

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    \18\ OSHA determined that removing this assumption would have a negligible impact on total costs and would reduce the cost and economic impact on the average affected establishment or entity.

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    As shown in Table VII-3, OSHA estimates that a total of 652,600 entities (586,800 in construction; 65,900 in general industry and maritime), 675,800 establishments (600,700 in construction; 75,100 in general industry and maritime), and 2.3 million workers (2.0 million in construction; 0.3 million in general industry and maritime) would be affected by the final silica rule. Note that only 67 percent of the entities and establishments, and about 21 percent of the workers in affected industries,

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    actually engage in activities involving silica exposure.\19\

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    \19\ It should be emphasized that these percentages vary significantly depending on the industry sector and, within an industry sector, depending on the NAICS industry. For example, about 35 percent of the workers in construction, but only 6 percent of workers in general industry, actually engage in activities involving silica exposure. As an example within construction, about 35 percent of workers in highway, street, and bridge construction, but only 3 percent of workers in state and local governments, actually engage in activities involving silica exposure.

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    The ninth column in Table VII-3, with data only for construction, shows for each affected NAICS construction industry the number of full-

    time-equivalent (FTE) affected workers that corresponds to the total number of affected construction workers in the previous column.\20\ This distinction is necessary because affected construction workers may spend large amounts of time working on tasks with no risk of silica exposure. As shown in Table VII-3, the 2.0 million affected workers in construction converts to approximately 387,700 FTE affected workers. In contrast, OSHA based its analysis of the affected workers in general industry and maritime on the assumption that they were engaged full time in activities with some silica exposure.

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    \20\ FTE affected workers becomes a relevant variable in the estimation of control costs in the construction industry. The reason is that, consistent with the costing methodology, control costs depend only on how many worker-days there are in which exposures are above the PEL. These are the worker-days in which controls are required. For the derivation of FTEs, see Tables IV-8 and IV-22 and the associated text in ERG (2007a, Document ID 1709).

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    The last three columns in Table VII-3 show combined total revenues for all entities (not just affected entities) in each affected industry, and the average revenue per entity and per establishment in each affected industry. Because OSHA did not have data to distinguish revenues for affected entities and establishments in any industry, average revenue per entity and average revenue per affected entity (as well as average revenue per establishment and average revenue per affected establishment) are estimated to be equal in value.

    Silica Exposure Profile of At-Risk Workers

    The technological feasibility analyses presented in Chapter IV of the FEA contain data and discussion of worker exposures to silica throughout industry. Exposure profiles, by job category, were developed from individual exposure measurements that were judged to be substantive and to contain sufficient accompanying description to allow interpretation of the circumstance of each measurement. The resulting exposure profiles show the job categories with current overexposures to silica and, thus, the workers for whom silica controls would be implemented under the final rule.

    Chapter IV of the FEA includes a section with a detailed description of the methods used to develop the exposure profile and to assess the technological feasibility of the final standard. The final exposure profiles take the exposure data that were used for the same purpose in OSHA's PEA and build upon them, using new data in the rulemaking record. The sampling data that were used to identify the affected industries and to develop the exposure profiles presented in the PEA were obtained from a comprehensive review of the following sources of information: OSHA compliance inspections conducted before 2011, OSHA contractor (ERG) site visits performed for this rulemaking, NIOSH site visits, NIOSH Health Hazard Evaluation reports (HHEs), published literature, submissions by individual companies or associations and, in a few cases, data from analogous operations (Document ID 1720, pp. IV-2-IV-3). The exposure profiles presented in the PEA were updated for the FEA using exposure measurements from the OSHA Information System (OIS) that were taken during compliance inspections conducted between 2011 and 2014 (Document ID 3958). In addition, exposure data submitted to the record by rulemaking participants were used to update the exposure profiles. The criteria used for determining whether to include exposure data in the exposure profiles are described in Section IV-2--Methodology in Chapter IV of the FEA. As explained there, some of the original data are no longer used in the exposure profiles based on those selection or screening criteria. OSHA considers the exposure data relied upon for its analysis to be the best available evidence of baseline silica exposure conditions.

    Table VII-4 summarizes, from the exposure profiles, the total number of workers at risk from silica exposure at any level, and the distribution of 8-hour TWA respirable crystalline silica exposures by job category for general industry and maritime sectors and for construction activities. Exposures are grouped into the following ranges: Less than 25 mug/m\3\; >= 25 mug/m\3\ and 50 mug/m\3\ and 100 mug/m\3\ and 25 percent (NIOSH Manual of Analytical Methods, http://www.cdc.gov/niosh/docs/95-117/). Their arguments include: (1) That there is sampling error attributed to bias against the particle-size selection criteria that defines the performance of the samplers and variation in performance between sampling devices; (2) that the accuracy and precision of the analytical method at the low levels of silica that would be collected at the revised PEL and action level is less than that in the range of the previous PELs for silica, particularly in the presence of interfering substances; and (3) variation between laboratories analyzing comparable samples adds an unacceptable degree of uncertainty. After considering all of the testimony and evidence in the record, OSHA rejects these arguments and, as discussed below, concludes that it is feasible to obtain measurements of respirable crystalline silica at the final rule's PEL and action level with reasonable accuracy.

    OSHA is basing its conclusions on the following findings, which are described in detail in this section. First, although there is variation in the performance of respirable dust samplers, studies have demonstrated that, for the majority of work settings, samplers will perform with an acceptable level of bias (as defined by international standards) as measured against internationally recognized particle-size selection criteria that define respirable dust samplers. This means that the respirable dust mass collected by the sampler will be reasonably close to the mass that would be collected by an ideal sampler that exactly matches the particle-size selection criteria. In addition, OSHA finds that the measure of precision of the analytical methods for samples collected at crystalline silica concentrations equal to the revised PEL and action level is only somewhat higher (i.e., somewhat less precise) than that for samples collected at concentrations equal to the previous, higher PELs. Further, the analytical methods can account for interferences such that, with few exceptions, the sensitivity and precision of the method are not significantly compromised. Studies of measurement variability between laboratories, as determined by proficiency testing, have demonstrated a significant decline in inter-laboratory variability in recent years. Improvements in inter-laboratory variability have been attributed to changes in proficiency test procedures as well as greater standardization of analytical procedures among laboratories. Finally, although measurement variability increases at low sample loads compared to sample loads in the range of the former PELs, OSHA finds, based on these studies, that the magnitude of this increase has also declined in recent years.

    Several rulemaking participants commented that OSHA's analysis of the feasibility of sampling and analytical methods for crystalline silica was well supported and sound (Document ID 2080, pp. 3-4; 2244, p. 3; 2371, Attachment 1, p. 5; 3578, Tr. 941; 3586, Tr. 3284; 3577, Tr. 851-852; 4214, pp. 12-13; 4223, pp. 30-33). Gregory Siwinski, CIH, and Dr. Michael Lax, Medical Director of Upstate Medical University, an occupational health clinical center, commented that current laboratory methods can measure respirable crystalline silica at the 50 mug/m\3\ PEL and 25 mug/m\3\ action level, and that they have measured exposures below the action level (Document ID 2244, p. 3). Dr. Celeste Montforton of the George Washington School of Public Health testified that ``industrial hygienists, company safety personnel, consultants, and government inspectors have been conducting for decades workplace sampling for respirable silica . . .'' and that some governments, such as Manitoba and British Columbia, are successfully collecting and analyzing samples to determine compliance with their occupational exposure limits of 25 mug/m\3\ (Document ID 3577, Tr. 851-852). Dr. Frank Mirer of the CUNY School of Public Health, formerly with the UAW and on behalf of the AFL-CIO, stated that ``air sampling is feasible at 25 mug/m\3\ and below for a full shift and even for part shift. It was dealt with adequately in the OSHA proposal'' (Document ID 3578, Tr. 941).

    The ACC, Chamber, and others base their argument that sampling and analytical methods for respirable crystalline silica are insufficiently precise on strict adherence to NIOSH's accuracy criterion of 25 percent at a 95-percent confidence level for chemical sampling and analysis methods (http://www.cdc.gov/niosh/docs/95-117/). The ACC pointed out that ``OSHA standards typically reflect the NIOSH Accuracy Criterion by requiring employers to use a method of monitoring and analysis that has an accuracy of plus or minus 25 percent . . . ,'' and cited a number of OSHA standards where the Agency has included such requirements (benzene, 29 CFR 1910.1028; lead (which requires a method accuracy of 20%), 29 CFR 1910.1025; cadmium, 29 CFR 1910.1027; chromium (VI), 29 CFR 1910.1026) (Document ID 4209, p. 129). However, the NIOSH accuracy criterion is not a hard, bright-line rule in the sense that a sampling and analytical method must be rejected if it fails to meet this level of accuracy, but is rather a goal or target to be used in methods development. Where evidence has shown that a method does not meet the accuracy criterion at the PEL or action level, OSHA has stipulated a less rigorous level of accuracy to be achieved. For example, OSHA's acrylonitrile standard requires use of a method that is accurate to 35 percent at the PEL and 50 percent at the action level (29 CFR 1910.1045), and several OSHA standards require that 35 percent accuracy be obtained at the action level (arsenic, 29 CFR 1910.1018; ethylene oxide, 29 CFR 1910.1047; formaldehyde, 29 CFR 1910.1048; 1,3-butadiene, 29 CFR 1910.1051; methylene chloride, 29 CFR 1910.1052). As discussed below, the precision of the sampling and analytical method for crystalline silica, as currently implemented using OSHA Method ID-142 for X-ray diffraction, is about 21 percent for quartz and cristobalite.

    In the remainder of this section, OSHA first describes available respirable dust sampling methods and

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    addresses comments and testimony related to the performance and accuracy of respirable dust samplers. Following that discussion, OSHA summarizes available analytical methods for measuring crystalline silica in respirable dust samples and addresses comments and evidence regarding analytical method precision, the presence of interfering materials, and reported variability between laboratories analyzing comparable samples.

    a. Respirable Dust Sampling Devices

    Respirable dust comprises particles small enough that, when inhaled, they are capable of reaching the pulmonary region of the lung where gas exchange takes place. Measurement of respirable dusts requires the separation of particles by size to assess exposures to the respirable fraction of airborne dusts. A variety of different industrial hygiene sampling devices, such as cyclones and elutriators, have been developed to separate the respirable fraction of airborne dust from the non-respirable fraction. Cyclones are the most commonly used size-selective sampling devices, or ``samplers,'' for assessing personal exposures to respirable dusts such as crystalline silica. The current OSHA (ID-142, revised December 1996, Document ID 0946) and NIOSH (Method 7500, Document ID 0901; Method 7602, 0903; Method 7603, http://www.cdc.gov/niosh/docs/2003-154/pdfs/7603.pdf) methods for sampling and analysis of crystalline silica specify the use of cyclones.

    Although respirable dust commonly refers to dust particles having an aerodynamic diameter of 10 mum (micrometer) or less, it is more precisely defined by the collection efficiency of the respiratory system as described by a particle collection efficiency model. These models are often depicted by particle collection efficiency curves that describe, for each particle size range, the mass fraction of particles deposited in various parts of the respiratory system. These curves serve as the ``yardsticks'' against which the performance of cyclone samplers should be compared (Vincent, 2007, Document ID 1456). Figure VII-1 below shows particle collection efficiency curves for two particle size selection criteria: The criteria specified in the 1968 American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV) for respirable dust, which was the basis for the prior OSHA general industry silica PEL, and an international specification by the International Organization for Standardization (ISO) and the Comiteacute Europeacuteen de Normalisation (CEN) known as the ISO/CEN convention, which was adopted by ACGIH in 1994 and is the basis for the definition of respirable crystalline silica in the final rule. In addition to the curves, which cover the full range of particle sizes that comprise respirable dust, particle size collection criteria are also often described by their 50-percent respirable ``cut size'' or ``cut point.'' This is the aerodynamic diameter at which 50 percent of the particle mass is collected, i.e., the particle size that the sampler can collect with 50-percent efficiency. Particles with a diameter smaller than the 50-percent cut point are collected with an efficiency greater than 50 percent, while larger-diameter particles are collected with an efficiency less than 50 percent. The cut point for the 1968 ACGIH specification is 3.5 mum and for the ISO/CEN convention is 4.0 mum (Lippman, 2001, Document ID 1446, pp. 107, 113).

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    For most workplace conditions, the change in the criteria for respirable dust in the final rule would theoretically increase the mass of respirable dust collected over that measured under the previous criteria by an amount that depends on the size distribution of airborne particles in the workplace. Soderholm (1991, Document ID 1661) examined these differences based on 31 aerosol size distributions measured in various industrial workplaces (e.g., coal mine, lead smelter, brass foundry, bakery, shielded metal arc SMA welding, spray painting, pistol range) and determined the percentage increase in the mass of respirable dust that would be collected under the ISO/CEN convention over that which would be collected under the 1968 ACGIH criteria. Soderholm concluded that, for all but three of the 31 size distributions that were evaluated, the increased respirable dust mass that would be collected using the ISO/CEN convention for respirable dust instead of the 1968 ACGIH criteria would be less than 30 percent, with most size distributions (25 out of the 31 examined, or 80 percent) resulting in a difference of between 0 and 20 percent (Document ID 1661, pp. 248-249, Figure 1). In the PEA, OSHA stated its belief that the magnitude of this effect does not outweigh the advantages of adopting the ISO/CEN convention. In particular, most respirable dust samplers on the market today are designed and calibrated to perform in a manner that closely conforms to the international ISO/CEN convention.

    Incorporating the ISO/CEN convention in the definition of respirable crystalline silica will permit employers to use any sampling device that conforms to the ISO/CEN convention. There are a variety of these cyclone samplers on the market, such as the Dorr-Oliver, Higgins-

    Dewell (HD), GK2.69, SIMPEDS, and SKC aluminum. In the PEA, OSHA reviewed several studies demonstrating that these samplers collect respirable particles with efficiencies that closely match the ISO/CEN convention (Document ID 1720, pp. IV-21--IV-24). In addition to cyclone samplers, there are also personal impactors available for use at flow rates from 2 to 8 L/min that have been shown to conform closely with the ISO/CEN convention (Document ID 1834, Attachment 1). Cyclones and impactors both separate particles by size based on inertia. When an airstream containing particles changes direction, smaller particles remain suspended in the airstream and larger ones impact a surface and are removed from the airstream. Cyclones employ a vortex to separate particles centrifugally, while impactors use a laminar airflow around a flat surface such that particles in the desired size range impact onto the surface.

    The current OSHA sampling method for crystalline silica, ID-142, is the method used by OSHA to enforce the silica PELs and is used by some employers as well. It specifies that a respirable sample be collected by drawing air at 1.7 0.2 liters/minute (L/min) through a Dorr-Oliver 10 millimeter (mm) nylon cyclone attached to a cassette containing a 5-mum pore-size, 37-mm diameter polyvinyl chloride (PVC) filter (Document ID 0946). NIOSH sampling and analysis methods for crystalline silica (Method 7500, Method 7602, Method 7603) have also adopted the ISO/CEN convention with flow rate specifications of 1.7 L/

    min for the Dorr-Oliver 10-mm nylon cyclone and 2.2 L/min for the HD cyclone (Document ID 0901; 0903). Method 7500 also allows for the use of an aluminum cyclone at 2.5 L/min. NIOSH is revising its respirable dust method to include any sampler designed to meet the ISO/CEN criteria (Document ID 3579, Tr. 218).

    The devices discussed above, when used at the appropriate flow rates, are capable of collecting a quantity of respirable crystalline silica that exceeds the quantitative detection limit for quartz (the principle form of crystalline silica) of 10 mug for OSHA's XRD method (Document ID 0946). For several scenarios based on using various devices and sampling times (8-hour, 4-hour, and 1-hour samples), OSHA calculated the amount of respirable quartz that would be collected at quartz concentrations equal to the existing general industry PEL, the proposed (and now final) rule's PEL, and the proposed (and now final) rule's action level. As seen in Table IV.3-A, computations show that the 10-mm nylon Dorr-Oliver operated at an optimized flow rate of 1.7 L/min, the aluminum cyclone operated at 2.5 L/min, the HD cyclone operated at 2.2 L/min, and the GK2.69 operated at 4.2 L/min will all collect enough quartz during an 8-hour or 4-hour sampling period to meet or exceed the 10 microg quartz limit of quantification for OSHA Method ID-142. Therefore, each of the commercially available cyclones is capable of collecting a sufficient quantity of quartz to exceed the limit of quantification when airborne concentrations are at or below the action level, provided that at least 4-hour air samples are taken. Table VII-7 also shows that the samplers can collect enough silica to meet the limit of quantification when the airborne respirable silica concentration is below the action level of 25 mug/m\3\, in one case as low as 5 mug/m\3\.

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    A comment from the National Rural Electric Cooperative Association (NRECA) stated that the current OSHA and NIOSH analytical methods require sampling to collect a minimum of 400 liters of air, and that at the flow rates specified for current samplers, sampling would have to be performed for approximately 2.5 to 4 hours; however, this is considerably longer than most construction tasks performed in electrical transmission and distribution work, which tend to last 2 hours or less (Document ID 2365, pp. 2, 6-7). OSHA does not view this discrepancy to be a problem. The minimum sampling times indicated in the OSHA and NIOSH methods contemplate that exposure occurs over most of the work shift. Construction operations frequently involve shorter-

    term tasks after which there is no further exposure to respirable crystalline silica. In those situations, OSHA often does not itself continue sampling during inspections and does not expect employers to continue sampling when there is no exposure to silica, and considers the sampling result that is obtained from shorter-term task sampling to be sufficient to represent a worker's 8-hour time-weighted-average (TWA) exposure, which can be calculated assuming no exposure for the period of the shift that is not sampled. If the airborne concentration of silica for the task is low, the sampling result would likely be below the limit of quantification. In that case, it would be safe for the employer to assume that the exposure is below the action level.

    Transition to ISO-CEN Criteria for Samplers

    In the final rule, OSHA is adopting the ISO/CEN particle size-

    selective criteria for respirable dust samplers used to measure exposures to respirable crystalline silica. Under the ISO/CEN convention, samplers should collect 50 percent of the mass of particles that are 4 mum in diameter (referred to as the cut point), with smaller particles being collected at higher efficiency and larger particles being collected at lower efficiency. Particles greater than 10 mum in diameter, which are not considered to be respirable, are to be excluded from the sample based on the ISO/CEN convention (Document ID 1446, pp. 112-113).

    Several rulemaking participants supported OSHA's proposed adoption of the ISO/CEN criteria for respirable dust samplers (Document ID 1730; 1969; 3576, Tr. 290; 3579, Tr. 218-219; 4233, p. 4). For example, a representative of SKC, Inc., which manufactures samplers used to collect respirable crystalline silica, stated that:

    Adoption of the ISO/CEN performance standard for respirable dust samplers by OSHA will bring the U.S. regulatory standards in line with standards/guidelines established by other occupational health and safety agencies, regulatory bodies, and scientific consensus organizations around the world. It will also align OSHA performance criteria for respirable dust samplers to that of NIOSH (Document ID 1730, pp. 1-2).

    As discussed above, OSHA's previous (and currently enforceable) general industry PEL for crystalline silica was based on a 1968 ACGIH definition, which specified a model with a cut point of 3.5 mum. Based on available studies conducted over 40 years ago, the Dorr-Oliver 10-mm cyclone was thought to perform closely to this specification. As such, it is the sampling device specified in OSHA's respirable dust sampling and analytical methods, including Method ID-142 for respirable crystalline silica (Document ID 0946). For most sizes of respirable particles, the ISO/CEN convention specifies a greater efficiency in particle collection than does the 1968 ACGIH model; consequently, samplers designed to meet the ISO/CEN convention will capture somewhat greater mass of airborne particle than would a sampler designed to the 1968 ACGIH model, with the magnitude of the increased mass dependent on the distribution of particle sizes in the air. For most particle size distributions encountered in workplaces, the increase in dust mass theoretically collected under the ISO/CEN convention compared to the ACGIH model would be 25 percent or less (Soderholm, 1991, Document ID 1661).

    Several rulemaking participants commented that moving from the 1968 ACGIH model to the ISO/CEN convention effectively decreased the PEL and action level below the levels intended, since more dust would be collected by samplers that conform to

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    the ISO/CEN convention than by those that conform to the 1968 ACGIH model (Document ID 2174; 2195, p. 30; 2285, pp. 3-4; 2307, Attachments 10, p. 19, and 12, p. 3; 2317, p. 2; 3456, p. 10; 4194, pp. 15-16). For example, the Chamber commented that adopting the ISO/CEN specification ``can result in citations for over exposure to quartz dust where none would have been issued prior to the adoption of this convention'' (Document ID 2288, p. 16). OSHA disagrees with this assessment because, based on more recent evaluations (Bartley et al., 1994, Document ID 1438, Attachment 2; Lee et al., 2010, 3616; 2012, 3615), the Dorr-

    Oliver 10-mm cyclone that has been used by the Agency for enforcement of respirable dust standards for decades has been found to perform reasonably closely (i.e., with an acceptable level of bias) to the ISO/

    CEN specification when operated at the 1.7 L/min flow rate specified by OSHA's existing method. Consequently, OSHA and employers can continue to use the Dorr-Oliver cyclone to evaluate compliance against the final PEL of 50 mug/m\3\ without having to change equipment or procedures, and thus would not be collecting a greater quantity of dust than before. Furthermore, OSHA notes that other ISO/CEN-compliant samplers, such as the SKC 10-mm aluminum cyclone and the HD cyclone specified in the NIOSH Method 7500, are already widely used by investigators and employers to evaluate exposures to respirable crystalline silica against benchmark standards. Therefore, the change from the ACGIH convention to the ISO/CEN convention is more a continuation of the status quo than a drastic change from prior practice.

    Other rulemaking participants argued that moving to the ISO/CEN convention effectively invalidates OSHA's risk and feasibility analyses since the exposure data that underlie these analyses were obtained using devices conforming to the 1968 ACGIH specification. For example, Thomas Hall, testifying for the Chamber, stated that moving to the ISO/

    CEN convention ``would produce a difference in current exposure results from . . . historical measurements that have been used in the risk assessments'' (Document ID 3576, Tr. 435). Similarly, in its pre-

    hearing comments, the ACC argued that:

    When OSHA conducted technological feasibility studies for attaining the proposed 50 mug/m\3\ PEL, the Agency based its decisions on samples collected using the current ACGIH method, not the proposed ISO/CEN method. Thus, the switch to the ISO/CEN definition will have two impacts on feasibility. First, it will add uncertainty regarding OSHA's technological feasibility determination because greater reductions in exposure will be required to achieve a 50 mug/m\3\ PEL measured by the ISO/CEN definition than by the ACGIH definition that OSHA applied. Second, OSHA's use of the ACGIH definition to estimate compliance costs causes the Agency to underestimate the costs of achieving the 50 mug/m\3\ PEL because OSHA did not account for the additional workers whose exposures would exceed the proposed PEL under the ISO/CEN definition but who would be exposed below the proposed PEL if measured under the ACGIH definition (Document ID 2307, Attachment 8, p. 9).

    OSHA rejects these arguments for the following reasons. First, with respect to the risk information relied on by the Agency, exposure data used in the various studies were collected from employer records reflecting use of several different methods. Some studies estimated worker exposures to silica from particle counts, for which the sampling method using impingers does not strictly conform to either the ACGIH or ISO/CEN conventions (e.g., Rice et al., Document ID 1118; Park et al., Document ID 0405; Attfield and Costello, Document ID 0285; Hughes et al., Document ID 1060). Other studies used measurements taken using cyclone samplers and modern gravimetric methods of silica analysis (e.g., Rice et al. and Park et al., data obtained from cyclone pre-

    separator up through 1988, Document ID 1118, 0405; Hughes et al., data from 10-mm nylon cyclone through 1998, Document ID 1060). OSHA believes it likely that exposure data collected using cyclones in these studies likely conformed to the ISO/CEN specification since flow rates recommended in the OSHA and NIOSH methods were most likely used. The studies by Miller and MacCalman (Document ID 1097) and by Buchanan et al. (Document ID 0306) used exposure measurements made with the MRE 113A dust sampler, which does conform reasonably well with the ISO/CEN specification (Gorner et al., Document ID 1457, p. 47). The studies by Chen et al. (2001, Document ID 0332; 2005, Document ID 0985) estimated worker exposures to silica from total dust measurements that were converted to respirable silica measurements from side-by-side comparisons of the total dust sampling method with samples taken using a Dorr-Oliver cyclone operated at 1.7 L/min, which is consistent with the ISO/CEN convention (see Section V, Health Effects, of this preamble and OSHA's Preliminary Review of Health Effects Literature and Preliminary Quantitative Risk Assessment, Document ID 1711). Thus, it is simply not the case that the exposure assessments conducted for these studies necessarily reflect results from dust samples collected with a device conforming to the 1968 ACGIH particle size-selective criteria, and OSHA finds that no adjustment of OSHA's risk estimates to reflect exposure measurements consistent with the ISO/CEN convention is warranted.

    Second, with respect to the feasibility analysis, OSHA relied on exposure data and constructed exposure profiles based principally on measurements made by compliance officers using the Dorr-Oliver cyclone operated at 1.7 L/min, as the Agency has done since Method ID-142 was developed in 1981, well before the 1990 cut-off date for data used to construct the exposure profiles. As explained earlier in the section, recent research shows that the Dorr-Oliver cyclone operated at this flow rate performs in a manner consistent with the ISO/CEN specification. Other data relied on by OSHA comes from investigations and studies conducted by NIOSH and others who used various cyclones that conform to the ISO/CEN specification. Thus, OSHA finds that the exposure profiles being relied on to evaluate feasibility and costs of compliance do not reflect sample results obtained using the 1968 ACGIH model. Instead, the vast majority of sample results relied upon were collected in a manner consistent with the requirements of the final rule. NIOSH supported this assessment, stating that, given the Dorr-

    Oliver sampler operated at a flow rate of 1.7 L/min conforms closely to the ISO/CEN convention, ``there is continuation with historic exposure data'' (Document ID 4233, p. 4). For these reasons, OSHA finds that it is appropriate to rely on the feasibility and cost analyses and underlying exposure data without adjustment to account for the final rule's adoption of the ISO/CEN specification for respirable dust samplers.

    Sampling Error

    Several commenters raised issues concerning the accuracy of respirable dust samplers in relation to the ISO/CEN criteria, asserting that sampling respirable dust is uncertain and inaccurate, and that there are numerous sources of error. Chief among these were Dr. Thomas Hall of Industrial Hygiene Specialty Resources, LLC, testifying for the Chamber, and Paul K. Scott of ChemRisk, testifying for the ACC.

    The Chamber's witnesses and others referenced studies showing that all samplers were biased against the ISO/CEN particle-size selection convention. This means that the sampler would collect more or less mass of respirable particulate than would an ideal sampler

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    that exactly conforms to the ISO/CEN convention. OSHA discussed this issue in the PEA, noting that most samplers tend to over-sample smaller particles and under-sample larger particles, compared to the ISO/CEN convention, at their optimized flow rates. This means that, for particle size distributions dominated by smaller particles, the sampler will collect more mass than would be predicted from an ideal sampler that exactly conforms to the ISO/CEN convention. For particle size distributions dominated by larger particles in the respirable range, less mass would be collected than predicted. In the PEA, OSHA evaluated several studies that showed that several cyclone samplers exhibited a bias of 10 percent or less for most particle size distributions encountered in the workplace. Some of these studies found biases as high as 20 percent but only for particle size distributions having a large mass median aerodynamic diameter (MMAD) (i.e., 20 microm or larger) and narrow distribution of particle sizes (i.e., a geometric standard deviation (GSD) of 2 or less) (Document ID 1720, pp. IV-21--IV-24). Such particle size distributions are infrequently seen in the workplace; for well-controlled environments, Frank Hearl of NIOSH testified that the GSD for typical particle size distributions would be about 2 (Document ID 3579, Tr. 187). Dr. Hall (Document ID 3576, Tr. 502) testified, similarly, that it would be around 1.8 to 3 for well-controlled environments and higher for uncontrolled environments (see also Liden and Kenny, 1993, Document ID 1450, p. 390, Figure 5; Soderholm, 1991,1661, p. 249, Figure 1). Furthermore, a particle size distribution with a large MMAD and small GSD would contain only a very small percentage (20 percent) against the ISO/CEN convention for nearly all particle size distributions having MMAD of 5 to 10 mum (Document ID 3616, pp. 704-706, Figure 3(b)). However, when the flow rate was adjusted to 4.4 L/min, bias exceeding 20 percent was found to occur primarily with particle size distributions having GSDs under 2.0 and MMAD greater than 10 mum (Document ID 3616, p. 707, Figure 5(a)). As discussed above, it is rare to encounter particle size distributions having relatively large MMADs and small GSDs, so the high variability attributed to high-flow samplers by Dr. Hall and Mr. Scott should not be of concern for most workplace settings. Further, sampler performance is considered acceptable if the bias and accuracy over at least 80 percent of the remaining portion of the bias map are within acceptable limits, which are no more than 10 and 30 percent, respectively (Document ID 1457, pp. 49, 52). The Lee et al. studies (2010 and 2012) concluded that the high-flow samplers tested met these international requirements for accuracy for sampling the ISO/CEN convention, and the Stacey et al. (2013) study found that their results compared favorably with those of Lee et al. (2012). Therefore, OSHA finds that the uncertainties characterized by Dr. Hall and Mr. Scott are exaggerated for most workplace situations, and that there is substantial evidence that high-flow samplers, in particular the GK2.69 cyclone, can be used to collect respirable crystalline silica air samples in most workplace settings without introducing undue bias.

    Mr. Scott, testifying for the ACC, was of the opinion that, although high-flow samplers have been evaluated by Gorner et al. (2001, Document ID 1457) and Lee et al. (2010, Document ID 3616; 2012, 3615) with respect to their sampling efficiencies as compared to the ISO/CEN convention and their performance compared to low-flow samplers, none of the studies evaluated the accuracy and precision using methods recommended in NIOSH's Guidelines for Air Sampling and Analytical Method Development and Evaluation (1995, http://www.cdc.gov/niosh/docs/95-117/) (Document ID 2308, Attachment 6, p. 18). OSHA understands Mr. Scott to contend that the sampler must be tested against a generated atmosphere of respirable crystalline silica and that the precision of the sampling and analytical method must be determined overall from these generated samples.

    OSHA does not agree with the implication that, until high-flow samplers have been evaluated according to the NIOSH (1995) protocol, the findings from the studies described above are not sufficient to permit an assessment of sampler performance. The NIOSH Guidelines cited by Mr. Scott state that ``an experimental design for the evaluation of sampling and analytical methods has been suggested. If these experiments are not applicable to the method under study, then a revised experimental design should be prepared which is appropriate to fully evaluate the method'' (http://www.cdc.gov/niosh/docs/95-117/, p. 1). These guidelines contemplate the development of entirely new sampling and analytical methods. Because the analytical portion of the sampling and analytical method for respirable crystalline silica was already fully evaluated before the GK2.69 was developed (Kenny and Gussman, 1997, Document ID 1444), it was only necessary to evaluate the performance of the GK2.69 high-flow sampler. As described above, the studies by Lee et al. (2010, Document ID 3616; 2012, 3615) and Stacey et al. (2013, Document ID 3618) reflect a collaborative effort between NIOSH in the U.S. and HSE in the U.K. to evaluate the performance of high-flow respirable dust samplers. The Lee et al. (2010, 2012) studies were conducted by NIOSH laboratories in Morgantown, West Virginia with peer review by HSE scientists, and the Stacey et al. (2013) study was conducted by HSE at the Health and Safety Laboratory at Buxton in the U.K. Both Lee et al. (2012) and Stacey et al. (2013) concluded that high-flow samplers studied, including the GK2.69, met the EN 13205 requirements for accuracy for sampling against the ISO/CEN convention, demonstrating that results from these two national laboratories compared favorably. OSHA concludes these peer-reviewed studies, performed by NIOSH and HSE scientists, meet the highest standards for effective methods evaluation and therefore does not agree with the suggestion that additional work following NIOSH's protocol is necessary. Comments submitted by NIOSH indicate that the Lee et al. (2010, 2012) and Stacy et al. (2013) studies are

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    sufficient to establish the GK2.69 high-flow sampler as acceptable for sampling respirable crystalline silica under the ISO/CEN convention (Document ID 2177, Attachment B; 4233, p. 4).

    URS Corporation, on behalf of the ACC, commented that precision will not be improved by the use of high-flow samplers because filter loadings of interferences will increase along with the amount of crystalline silica; this would, in URS's opinion, necessitate additional sample handling procedures, such as acid washing, that erode precision. URS also argued that such samples may require analysis of multiple peaks and that overall X-ray intensity may be diminished due to increased filter load (Document ID 2307, Attachment 12, p. 3). In its post-hearing brief, the ACC stated that the use of high-volume samplers ``in addition to traditional Dorr-Oliver sampler'' would reduce inter-laboratory precision (i.e., the extent to which different laboratories achieve similar results for the same sample) due to the use of multiple sampler types (Document ID 4209, p. 154).

    OSHA finds that these arguments are unsupported. Although the high-

    flow sampler will collect more dust than lower-flow samplers in the same environment, the relative proportion of any interfering materials collected to the amount of crystalline silica collected would remain unchanged. Thus, there should be no increased effect from the interfering materials relative to the silica. OSHA recognizes that, to prevent undue interference or diminished X-ray intensity, it is important to keep the dust load on the filter within reasonable limits. Both OSHA and NIOSH methods stipulate a maximum sample weight to be collected (3 mg for OSHA and 2 mg for NIOSH) (Document ID 0946, p. 5; 0901, p. 3), and in the event that excess sample is collected, the sample can be split into portions and each portion analyzed separately (Document ID 0946, p. 5). In environments where using a high-flow sampler is likely to collect more than the maximum sample size, use of a lower-flow sampler is advised. In response to the concern that permitting use of high-flow samplers will affect inter-laboratory variability, OSHA observes that employers are already using a variety of commercially available samplers, such as those listed in the NIOSH Method 7500, to obtain exposure samples; not everyone uses the Dorr-

    Oliver sampler. Thus, for the final rule, OSHA is permitting employers to use any sampling device that has been designed and calibrated to conform to the ISO/CEN convention, including higher-flow samplers such as the GK2.69. In effect, this is a continuation of well-studied current practice, not an untested departure from it.

    b. Laboratory Analysis of Crystalline Silica

    Crystalline silica is analyzed in the laboratory using either X-ray diffraction (XRD) or infrared spectroscopy (IR). A third method, colorimetric spectrophotometry, is no longer used (Document ID 3579, Tr. 211; Harper et al., 2014, 3998, Attachment 8, p. 1). This section describes crystalline silica analysis by XRD and IR and responds to comments and testimony on the precision and accuracy of these methods for measuring crystalline silica concentrations in the range of the final rule's PEL and action level. As discussed below, both XRD and IR methods can detect and quantify crystalline silica in amounts collected below the final rule's 25 microg action level.

    X-Ray Diffraction

    For XRD, a dust sample that has been collected by a sampler is deposited on a silver-membrane filter and scanned by the X-ray beam, where X-rays diffract at specific angles. A sensor detects these diffracted X-ray beams and records each diffracted beam as a diffraction peak. Unique X-ray diffraction patterns are created when the diffraction peaks are plotted against the angles at which they occur. The intensity of the diffracted X-ray beams depends on the amount of crystalline silica present in the sample, which can be quantified by comparing the areas of the diffraction peaks obtained with those obtained from scanning a series of calibration standards prepared with known quantities of an appropriate reference material. Comparing multiple diffraction peaks obtained from the sample with those obtained from the calibration standards permits both quantitative and qualitative confirmation of the amount and type of crystalline silica present in the sample (i.e., quartz or cristobalite). A major advantage of XRD compared with the other techniques used to measure crystalline silica is that X-ray diffraction is specific for crystalline materials. Neither non-crystalline silica nor the amorphous silica layer that forms on crystalline silica particles affects the analysis. The ability of this technique to quantitatively discriminate between different forms of crystalline silica and other crystalline or non-crystalline materials present in the sample makes this method least prone to interferences. Sample analysis by XRD is also non-destructive, meaning that samples can be reanalyzed if necessary (Document ID 1720, pp. IV-26--IV-27).

    The OSHA Technical Manual lists the following substances as potential interferences for the analysis of crystalline silica using XRD: Aluminum phosphate, feldspars (microcline, orthoclase, plagioclase), graphite, iron carbide, lead sulfate, micas (biotite, muscovite), montmorillonite, potash, sillimanite, silver chloride, talc, and zircon (https://www.osha.gov/dts/osta/otm/otm_ii/otm_ii_1.html, Chapter 1, III.K). The interference from other minerals usually can be recognized by scanning multiple diffraction peaks quantitatively. Diffraction peak-profiling techniques can resolve and discriminate closely spaced peaks that might interfere with each other. Sometimes interferences cannot be directly resolved using these techniques. However, many interfering materials can be chemically washed away in acids that do not dissolve the crystalline silica in the sample. Properly performed, these acid washes can dissolve and remove these interferences without appreciable loss of crystalline silica (Document ID 1720, p. IV-27).

    The nationally recognized analytical methods using XRD include OSHA ID-142, NIOSH 7500, and MSHA P-2 (Document ID 0946; 0901; 1458). All are based on the XRD of a redeposited thin-layered sample with comparison to standards of known concentrations (Document ID 0946, p. 1; 0901, p. 1; 1458, p. 1). These methods, however, differ on diffraction peak confirmation strategies. The OSHA and MSHA methods require at least three diffraction peaks to be scanned (Document ID 0946, p. 5; 1458, p. 13). The NIOSH method only requires that multiple peaks be qualitatively scanned on representative bulk samples to determine the presence of crystalline silica and possible interferences, and quantitative analysis of air samples is based on a single diffraction peak for each crystalline silica polymorph analyzed (Document ID 0901, pp. 3, 5).

    Infrared Spectroscopy

    Infrared spectroscopy is based on the principle that molecules of a material will absorb specific wavelengths of infrared electromagnetic energy that match the resonance frequencies of the vibrations and rotations of the electron bonds between the atoms making up the material. The absorption of IR radiation by the sample is compared with the IR absorption of calibration standards of known concentration to determine the amount of crystalline silica in the sample. Using IR can be efficient for routine analysis of samples that are well

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    characterized with respect to mineral content, and the technique, like XRD, is non-destructive, allowing samples to be reanalyzed if necessary. The three principle IR analytical methods for crystalline silica analyses are NIOSH 7602 (Document ID 0903), NIOSH 7603 (http://www.cdc.gov/niosh/docs/2003-54/pdfs/7603.pdf), and MSHA P-7 (Document ID 1462); NIOSH Method 7603 and MSHA P-7 were both specifically developed for the analysis of quartz in respirable coal dust. OSHA does not use IR for analysis of respirable crystalline silica.

    Interferences from silicates and other minerals can affect the accuracy of IR results. The electromagnetic radiation absorbed by silica in the infrared wavelengths consists of broad bands. In theory, no two compounds have the same absorption bands; however, in actuality, the IR spectra of silicate minerals contain silica tetrahedra and have absorption bands that will overlap. If interferences enhance the baseline measurement and are not taken into account, they can have a negative effect that might underestimate the amount of silica in the sample. Compared with XRD, the ability to compensate for these interferences is limited (Document ID 1720, pp. IV-29--IV-30).

    c. Sensitivity of Sampling and Analytical Methods

    The sensitivity of an analytical method or instrument refers to the smallest quantity of a substance that can be measured with a specified level of accuracy, and is expressed as either the LOD or the ``Limit of Quantification'' (LOQ). These two terms have different meanings. The LOD is the smallest amount of an analyte that can be detected with acceptable confidence that the instrument response is due to the presence of the analyte. The LOQ is the lowest amount of analyte that can be reliably quantified in a sample and is higher than the LOD. These values can vary from laboratory to laboratory as well as within a given laboratory between batches of samples because of variation in instrumentation, sample preparation techniques, and the sample matrix, and must be confirmed periodically by laboratories.

    At a concentration of 50 microg/m\3\, the final rule's PEL, the mass of crystalline silica collected on a full-shift (480 minute) air sample at a flow rate of 1.7 L/min, for a total of 816 L of air, is approximately 41 microg (see Table VII-7). At a concentration of 25 microg/m\3\, the final rule's action level, the mass collected is about 20 microg. The LOQ for quartz for OSHA's XRD method is 10 microg (Document ID 0946; 3764, p. 4), which is below the amount of quartz that would be collected from full-shift samples at the PEL and action level. Similarly, the reported LODs for quartz for the NIOSH and MSHA XRD and IR methods are lower than that which would be collected from full-shift samples taken at the PEL and action level (NIOSH Method 7500, Document ID 0901, p. 1; MSHA Method P-2, 1458, p. 2; NIOSH Method 7602, 0903, p. 1; NIOSH Method 7603, http://www.cdc.gov/niosh/docs/2003-154/pdfs/7603.pdf, p. 1; MSHA Method P-7, 1462, p. 1).

    The rule's 50 microg/m\3\ PEL for crystalline silica includes quartz, cristobalite, and tridymite in any combination. For cristobalite and tridymite, the previous general industry formula PEL was approximately 50 microg/m\3\, so the change in the PEL for crystalline silica does not represent a substantive change in the PEL for cristobalite or tridymite when quartz is not present. OSHA Method ID-142 (Document ID 0946) lists a 30-microg LOQ for cristobalite; however, because of technological improvements in the equipment, the current LOQ for cristobalite for OSHA's XRD method as implemented by the OSHA Salt Lake Technical Center (SLTC) is about 20 microg (Document ID 3764, p. 10).

    That XRD analysis of quartz from samples prepared from reference materials can achieve LODs and LOQs between 5 and 10 microg was not disputed in the record. Of greater concern to several rulemaking participants was the effect of interfering materials potentially present in a field sample on detection limits and on the accuracy of analytical methods at low filter loads when interferences are present. Although the Chamber's witness, Robert Lieckfield of Bureau Veritas Laboratories, did not dispute that laboratories could achieve this level of sensitivity (Document ID 3576, Tr. 485-486), the ACC took issue with this characterization of method sensitivity stating that ``the LOQ for real world samples containing interferences is likely to be higher than the stated LOQ's for analytical methods, which are determined using pure NIST samples with no interferences'' (Document ID 4209, p. 132). Both Mr. Lieckfield and Mr. Scott testified that the presence of interferences in samples can increase the LOQ and potential error of measurement at the LOQ (Document ID 2259, p. 7; 3460, p. 5).

    Mr. Scott (Document ID 2308, Attachment 6, p. 5) cited a laboratory performance study by Eller et al. (1999a, Document ID 1687), in which laboratories analyzing samples with and without interfering materials present reported a range of LOD's from 5 mug to 50 mug. Mr. Scott believed that this study provided evidence that interfering materials present in crystalline silica samples adversely affected laboratories' reported LODs. OSHA disagrees with this interpretation. The Agency reviewed this study in the PEA (Document ID 1720, p. IV-33) and believes that the variability in reported LODs reflected differences in laboratory practices with respect to instrument calibration and quality control procedures. These factors led Eller et al. (1999b, Document ID 1688, p. 24; 1720, p. IV-42) to recommend changes in such practices to improve laboratory performance. Thus, OSHA finds that the variation in reported LODs referred to by Mr. Scott cannot be attributed primarily to the presence of interfering materials on the samples.

    The presence of interferences can adversely affect the sensitivity and precision of the analysis, but typically only when the interference is so severe that quantification of crystalline silica must be made from secondary and tertiary diffraction peaks (Document ID 0946, p. 6). However, OSHA finds no evidence that interferences usually present serious quantification problems. First, there are standard protocols in the OSHA, NIOSH, and MSHA methods that deal with interferences. According to OSHA Method ID-142,

    Because of these broad selection criteria and the high specificity of the method for quartz, some of the listed interferences may only present a problem when a large amount of interferent is present. . . . Interference effects are minimized by analyzing each sample for confirmation using at least three different diffraction peaks so as to include peaks where the quartz and cristobalite results are in good agreement and where the interferent thus causes no problem. Bulk samples or a description of the process being sampled are useful in customizing a chemical cleanup procedure for any interference found difficult to resolve by software. Even so, the presence of an interference rarely jeopardizes the analysis (Document ID 0946, p. 5).

    Software developed by instrument manufacturers and techniques such as acid washing of the sample when interferences are suspected to be present are also useful in resolving interferences. The Chamber's expert witness, Mr. Lieckfield, acknowledged that it was also their practice at his lab to chemically treat samples from the start to remove interfering materials and to analyze multiple diffraction peaks to resolve interferences (Document ID 3576, Tr. 533, 542). According to OSHA's representative from the SLTC, it is ``nearly always possible'' to eliminate interferences and is it no more difficult to obtain precise measurements when

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    interferences are present than when they are not (Document ID 3579, Tr. 48).

    ACC also cites the results of a round-robin performance study that it commissioned, in which five laboratories were provided with crystalline silica samples with and without interfering materials (Document ID 4209, p. 132). These laboratories reported non-detectable levels of silica for 34 percent of the filters having silica loadings of 20 mug or more. However, as discussed below in the section on inter-laboratory variability (Section IV-3.2.5--Measurement Error Between Laboratories), OSHA has determined that this study is seriously flawed and, in particular, that there was systematic bias in the results, possibly due to sample loss. This could explain the high prevalence of reported non-detectable samples by the laboratories, rather than the presence of interferences per se.

    Furthermore, OSHA's review of the several hundred inspection reports relied on to evaluate the technological feasibility of the final rule's PEL in many industry sectors does not show that investigators have particular difficulty in measuring respirable crystalline silica concentrations below the PEL. Sections IV-4 and IV-5 of this chapter contain hundreds of exposure measurement results in a wide variety of workplace settings that were detected and reported by a laboratory as being above detectable limits but below the PEL or action level. If, as ACC suggests, interferences have a profound effect on the ability to measure concentrations in this range, many of these samples might have been reported as ``less than the LOD,'' with the reported LOD in the range of 25 mug to 50 mug. Examination of the exposure data described in Sections IV-4 and IV-5 of this chapter shows clearly that this is not the case (see exposure profiles for Concrete Products, Section IV-4.3; Cut Stone, Section IV-4.4; Foundries (Metal Casting), Section IV-4.8; Mineral Processing, Section IV-4.12; Porcelain Enameling, Section IV-4.14; Ready Mix Concrete, Section IV-4.17; Refractories, Section IV-4.18). In addition, the United Steelworkers reported receiving exposure data from 17 employers with samples in this same range, indicating that sampling of exposures below the final PEL and action level is feasible and already being utilized by employers (Document ID 4214, pp. 12-13; Document ID 4032, Attachment 3).

    Therefore, OSHA finds that the presence of interfering substances on field samples will not, most of the time, preclude being able to detect concentrations of respirable crystalline silica in the range of the PEL and action level, and that such instances where this might occur are rare. Accordingly, even when the presence of interfering substances is taken into account, worker exposure is capable of being measured with a reasonable degree of sensitivity and precision.

    d. Precision of Measurement

    All analytical methods have some random measurement error. The statistics that describe analytical error refer to the amount of random variation in measurements of replicate sets of samples containing the same quantity of silica. This variation is expressed as a standard deviation about the mean of the measurements. The relative standard deviation (RSD), a key statistic used to describe analytical error, is calculated by dividing the standard deviation by the mean for a data set. The RSD is also known as the coefficient of variation (CV).

    When random errors are normally distributed, a 95-percent confidence interval can be calculated as X (1.96 x CV), where X is the mean. This statistic is termed the ``precision'' of the analytical method and represents a 2-sided confidence interval in that, for a particular measurement, there is a 95-percent chance that the ``true'' value, which could be higher or lower than the measurement, lies within the confidence interval. The measure of analytical precision typically also includes a term to represent error in sampler pump flow, which is conventionally taken to be 5 percent. The better the precision of an analytical method, the lower its value (i.e., a method having a precision of 17 percent has better precision than one with a precision of 20 percent).

    OSHA also uses a statistic called the Sampling and Analytical Error (SAE) to assist compliance safety and health officers (CSHOs) in determining compliance with an exposure limit. The estimate of the SAE is unique for each analyte and analytical method, and must be determined by each laboratory based on its own quality control practices. At OSHA's Salt Lake Technical Center (SLTC), where analytical methods are developed and air samples taken for enforcement purposes are analyzed, the SAE is based on statistical analysis of results of internally prepared quality control samples. Sampling and analytical components are assessed separately, where CV1 reflects analytical error that is estimated from the analysis of quality control samples, and CV2 is the sampling error, assumed to be 5 percent due to variability in sampling pump flow rates that can affect sample air volume. Analytical error is combined with sampling pump error, and the SAE is calculated as a one-sided 95-

    percent confidence limit with the following formula:

    GRAPHIC TIFF OMITTED TR25MR16.178

    The current SLTC SAE for crystalline silica is approximately 0.17, according to testimony from a representative of SLTC (Document ID 3579, Tr. 95). OSHA uses the SAE in its enforcement of PELs, where the PEL times the SAE is added to the PEL for a substance and compared to a sample result (see Section II, Chapter 1 of the OSHA Technical Manual, https://www.osha.gov/dts/osta/otm/otm_toc.html). A sample result is considered to have definitively exceeded the PEL if the result is greater than the sum of the PEL and the PEL times the SAE. For example, with the PEL at 50 mug/m\3\ and an SAE of 17 percent, an air sample result would have to be greater than 58.5 mug/m\3\ (i.e., 50 + (50 x 0.17)) to be considered to have definitively exceeded the PEL. This policy gives employers the benefit of the doubt, as it assumes that the actual exposure was below the PEL even when the result is above the PEL but below the PEL plus the SAE; the effect is that OSHA does not cite an employer for an exposure above the PEL unless the Agency has obtained a sample measurement definitively above the PEL after accounting for sampling and analytical error.

    OSHA's quality control samples, which were prepared and analyzed at SLTC, demonstrate that the XRD method has acceptable precision, even at the low range of filter loads (50 mug). For the period April 2012 through April 2014, SLTC's analysis of 348 quality control samples, with a range of filter loads of about 50 to 250 mug crystalline silica, showed average recovery (i.e., the measurement result as compared to the reference mean value for the sample) of 0.98 with an RSD of 0.093 and precision of 20.8 percent (Document ID 3764, Attachment 1). Among those samples, there were 114 with a target filter load of 50 mug (range of actual filter load was 50 to 51.6 mug); these samples showed an average recovery of 1.00 with an RSD of 0.093 and precision of 20.7 percent (Document ID 3764, Attachment 1). Thus, OSHA's experience with quality control standards shows that the XRD method for quartz is as precise in the low range of method validation as it is over the full range.

    The ACC raised several questions regarding OSHA's Method ID-142 and

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    its validation. First, a paper they submitted by Sandra Wroblewski, CIH, of Computer Analytical Solutions notes that OSHA's stated Overall Analytical Error is 26 percent, higher than the 25-percent level ``OSHA states is necessary to ensure that a PEL can be feasibly measured,'' and that the method had not been validated for cristobalite (Document ID 2307, Attachment 10, pp. 13-14). In addition, the ACC stated that OSHA's method specifies a precision and accuracy validation range of 50-160 microg quartz per sample, above the quantity that would be collected at the PEL and action level (assuming use of a Dorr-Oliver sampler at 1.7 L/min) and that the method has not been tested for validation at a range corresponding to the PEL and action level (Document ID 2307, Attachment 10, p. 14). ACC also argued that OSHA's method does not comply with the Agency's Inorganic Methods Protocol, which requires the CV1 to be 0.07 or less and the detection limit to be less than 0.1 times the PEL (Document ID 2307, Attachment A, p. 202). The Edison Electric Institute (Document ID 2357, pp. 20-21) and Ameren Corporation (Document ID 2315, p. 2) expressed similar concerns about the detection limit.

    While OSHA's published Method ID-142 reports an Overall Analytical Error of 26 percent, OSHA no longer uses this statistic (it is in the process of revising Method ID-142); the Agency provides measures of precision and SAE instead. The Overall Analytical Error, which is described in Method ID-142, published in 1996, included a bias term that is now corrected for in the data used to determine method precision, so there is no longer a need to include a bias term in the estimation of analytical error. As described above, the precision of Method ID-142 is about 21 percent based on recent quality control samples.\24\ OSHA's Inorganic Methods Protocol, to which the ACC referred, has been replaced by evaluation guidelines for air sampling methods using spectroscopic or chromatographic analysis, published in 2005 (https://www.osha.gov/dts/sltc/methods/spectroguide/spectroguide.html) and 2010 (https://www.osha.gov/dts/sltc/methods/chromguide/chromguide.html), respectively. These more recent publications no longer reflect the guidance contained in the Inorganic Methods Protocol, and OSHA's Method ID-142 is consistent with these more recent guidelines. Finally, although the published method did not include validation data for filter loads below 50 mug or data for cristobalite, OSHA has conducted studies to characterize the precision that is achieved at low filter loads for quartz and cristobalite; these studies are in the rulemaking record (Document ID 1670, Attachment 1; 1847, Attachment 1; 3764, pp. 15-16) and are discussed further below.

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    \24\ OSHA also wishes to point out that the guideline for achieving a method precision of 25 percent was never an OSHA requirement for determining method feasibility, but is drawn from the NIOSH Accuracy Criterion (http://www.cdc.gov/niosh/docs/95-117/

    ), which was used for the purpose of developing and evaluating analytical methods. Nevertheless, OSHA's Method ID-142 now meets that guideline.

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    In comments submitted on behalf of the Chamber, Mr. Lieckfield cited the NIOSH Manual of Analytical Methods, Chapter R, as stating that ``current analysis methods do not have sufficient accuracy to monitor below current exposure standards'' (Document ID 2259, p. 1). However, this is contradicted by NIOSH's own post-hearing submission, which stated that, although method variability was assessed based on the exposure limits at that time (i.e., 1983, see Document ID 0901, pp. 1, 7), ``it was known from an intra-laboratory study that an acceptable variability would likely be at least 20 mug on-filter, and so 20 mug was given as the lower range of the analytical method'' (Document ID 4233, p. 3). Furthermore, in Chapter R of NIOSH's Manual, NIOSH goes on to say that the GK2.69 high-flow sampler ``has promise for potentially lowering the levels of silica that can be measured and still meet the required accuracy'' (http://www.cdc.gov/niosh/docs/2003-154/pdfs/chapter-r.pdf, p. 265). This chapter was published in 2003, well before the studies by Lee et al. (2010, 2012) and Stacey et al. (2013), discussed above, which demonstrate that the GK2.69 sampler has acceptable performance. NIOSH concluded in its post-hearing comment that ``current methods of sampling and analysis for respirable crystalline silica have variability that is acceptable to demonstrate compliance with the proposed PEL and action level'' (Document ID 4233, p. 4).

    At the time of the proposal, there was little data characterizing the precision of analytical methods for crystalline silica at filter loads in the range of the PEL and action level (i.e., with prepared samples of 40 mug and 20 mug crystalline silica, which are the amounts of silica that would be collected from full-shift sampling at the PEL and action level, respectively, assuming samples are collected with a Dorr-Oliver cyclone at a flow rate of 1.7 L/min). To characterize the precision of OSHA's Method ID-142 at low filter loads, SLTC conducted studies in 2010 and again in 2013 (the latter of which was presented in the PEA; see Document ID 1720, p. IV-35). For these studies, the lab prepared 10 replicate samples each of quartz and cristobalite from NIST standard reference material and determined the precision of the analytical method; a term representing pump flow rate error was included in the precision estimate. In the 2010 test (Document ID 1670, Attachment 1), the precision for quartz loads equating to the PEL and action level was 27 and 33 percent, respectively. For cristobalite loads equating to the PEL and action level, the precision was 23 and 27 percent, respectively. The results from the 2013 test (Document ID 1847, Attachment 1; 3764, pp. 15-16; Document ID 1720, p. IV-35) showed improvement in the precision; for quartz, precision at loads equating to the PEL and action level was 17 and 19 percent, respectively, and for cristobalite, precision at loads equating to the PEL and action level was 19 and 19 percent, respectively. Both the 2010 and 2013 tests were conducted using the same NIST standards, same instrumentation, and same sample preparation method (OSHA Method ID-142) with the exception that the 2013 test used automatic pipetting rather than manual pipetting to prepare the samples (Document ID 1847). OSHA believes it likely that this change in sample preparation reduced variation in the amount of silica loaded onto the filters, which would account for at least some of the increased precision seen between 2010 and 2013 (i.e., imprecision in preparing the samples would make the analytical precision for 2010 appear worse than it actually was). Based on these studies, particularly the 2013 study, OSHA preliminarily determined that the XRD method was capable of accurately measuring crystalline silica concentrations at the PEL and action level.

    The ACC believed that OSHA's reliance on the 2013 study was ``misplaced'' because the results were not representative of ``real world'' samples that contain interfering minerals that could increase analytical error, and because the studies did not account for inter-

    laboratory variability (Document ID 4209, pp. 135-137; 2308, Attachment 6, p. 10). The ACC also believed that variability would have been depressed in this study because the samples were analyzed in close temporal proximity by the same analyst and using the same instrument calibration, and the study involved only 10 samples at each filter load (Document ID 4209, pp. 137-138; 2308,

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    Attachment 6, p. 10). The ACC's witness, Mr. Scott, also commented that the study failed to take into account the effect of particle sizes on the analysis of crystalline silica and believed that SLTC's evaluation could not reflect differences in precision between the XRD and IR methods (Document ID 2308, Attachment 6, p. 10).

    Despite the criticism that OSHA's investigation involved a small number of samples analyzed at the same time, the results obtained were comparable to OSHA's analysis of quality control samples at somewhat higher filter loads (between 50 and 51.6 mug) analyzed over a two-

    year period (Document ID 3764, Attachment 1). These results, described above, showed a precision of 20.7 percent, compared to 17 and 19 percent for quartz filter loads of 40 and 20 mug, respectively (Document ID 1847, Attachment 1; Document ID 3764). From these results, OSHA concludes that any effect on analytical error from performing a single study using the same analyst and instrument calibration is modest.

    OSHA also concludes that Mr. Scott's argument that particle size effects were not taken into account is without merit. The samples prepared and analyzed in OSHA's study, like any laboratory's quality control samples, use standard materials that have a narrow range in particle size. Although large (non-respirable) size particles can result in an overestimate of crystalline silica content, in practice this is not typically a serious problem with air samples and is more of a concern with analyzing bulk samples. First, as discussed above, respirable dust samplers calibrated to conform to the ISO/CEN convention are collecting respirable particulate and excluding larger particles (Document ID 3579, Tr. 219). In analyzing field samples, OSHA uses microscopy to identify whether larger particles are present and, if they are, the results are reported as a bulk sample result so as not to be interpreted as an airborne exposure (Document ID 3579, Tr. 213). Additionally, OSHA's Method ID-142 calls for grinding and sieving bulk samples to minimize particle size effects in the analysis (Document ID 0946, p. 13). OSHA also notes that the Chamber's witness, Mr. Lieckfield, testified that his laboratory does not check for oversized particles (Document ID 3576, p. 483).

    With regard to interferences, as discussed above, there are procedures that have been in place for many years to reduce the effect of interfering materials in the analysis. The presence of interferences does not typically prevent an analyst from quantifying crystalline silica in a sample with reasonable precision. As to the claim regarding XRD versus IR, a recent study of proficiency test data, in which multiple laboratories are provided comparable silica samples, both with and without interfering materials added, did not find a meaningful difference in precision between laboratories using XRD and those using IR (Harper et al., 2014, Document ID 3998, Attachment 8). In addition, as discussed above, NIOSH's and OSHA's measures of precision of the XRD method at low filter loads were comparable, despite differences in equipment and sample preparation procedures. Therefore, OSHA finds that the studies it carried out to evaluate the precision of OSHA Method ID-

    142 at low filter loads provide a reasonable characterization of the precision of the method for analyzing air samples taken at concentrations equal to the final PEL and action level under the respirable crystalline silica rule.

    With respect to the ACC's and Mr. Scott's reference to inter-

    laboratory variation in silica sample results, OSHA discusses data and studies that have evaluated inter-laboratory variance in analytical results in the next section.

    e. Measurement Error Between Laboratories

    The sources of random and systematic error described above reflect the variation in sample measurement experienced by a single laboratory; this is termed intra-laboratory variability. Another source of error that affects the reliability of results obtained from sampling and analytical methods is inter-laboratory variability, which describes the extent to which different laboratories may obtain disparate results from analyzing the same sample. Inter-laboratory variability can be characterized by using data from proficiency testing, where laboratories analyze similarly-prepared samples and their results are compared. In practice, however, it is difficult to separate intra- and inter-laboratory variability because each laboratory participating in a proficiency test provides analytical results that reflect their own degree of intra-laboratory variability. Thus, use of proficiency test data to compare performance of laboratories in implementing an analytical method is really a measure of total laboratory variability.

    The best available source of data for characterizing total variability (which includes an inter-laboratory variability component) of crystalline silica analytical methods is the AIHA Industrial Hygiene Proficiency Analytical Testing (PAT) Program. The AIHA PAT Program is a comprehensive testing program that provides an opportunity for laboratories to demonstrate competence in their ability to accurately analyze air samples through comparisons with other labs. The PAT program is designed to help consumers identify laboratories that are deemed proficient in crystalline silica analysis.

    Crystalline silica (using quartz only) is one of the analytes included in the proficiency testing program. The AIHA PAT program evaluates the total variability among participating laboratories based on proficiency testing of specially prepared silica samples. The AIHA contracts the preparation of its crystalline silica PAT samples to an independent laboratory that prepares four PAT samples in the range of about 50 to 225 mug (Document ID 3586, Tr. 3279-3280) and one blank sample for each participating laboratory per round. Each set of PAT samples with the same sample number is prepared with as close to the same mass of crystalline silica deposited on the filter as possible. However, some variability occurs within each numbered PAT sample set because of small amounts of random error during sample preparation. Before the contract laboratory distributes the round, it analyzes a representative lot of each numbered set of samples to ensure that prepared samples are within 10 percent (Document ID 3586, Tr. 3276). The samples are distributed to the participating laboratories on a quarterly basis (Document ID 1720, p. IV-36). The PAT program does not specify the particular analytical method to be used. However, the laboratory is expected to analyze the PAT samples using the methods and procedures it would use for normal operations.

    The results of the PAT sample analysis are reported to the AIHA by the participating laboratories. For each PAT round, AIHA compiles the results and establishes upper and lower performance limits for each of the four sample results based on the mean and RSD of the sample results. For each of the four samples, a reference value is defined as the mean value from a selected set of reference laboratories. The RSD for each of the four samples is determined from the results reported by the reference labs after correcting for outliers (generally clear mistakes in analysis or reporting, particularly those that are order-

    of-magnitude errors) (Document ID 4188, p. 2). A participating laboratory receives a passing score if at least three out of the four sample results reported are within 20 percent of the reference mean for the sample (Document ID 3586, Tr. 3291).

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    Two or more results reported by a lab in a given round that are outside the limits results in the lab receiving an unsatisfactory rating. An unsatisfactory rating in 2 of the last 3 rounds results in revocation of the lab's AIHA accreditation for the analysis of crystalline silica. Participation in the PAT program is a prerequisite for accreditation through the AIHA Industrial Hygiene Laboratory Accreditation Program (IHLAP).

    In the PEA, OSHA presented PAT results from its SLTC for the period June 2005 through February 2010 (PAT Rounds 160-180) (Document ID 1720, pp. IV-40-41). The mean recovery was 99 percent, with a range of 55 to 165 percent. Eighty-one percent of the samples analyzed over this period were within 25 percent of the reference mean and the RSD for this set of samples was 19 percent, showing reasonable agreement with the reference mean. OSHA also evaluated PAT data from all participating laboratories for the period April 2004 through June 2006 (PAT Rounds 156-165) (Document ID 1720, pp. IV-37--IV-40). Overall, the mean lab RSD was 19.5 percent for the sample range of 49 to 165 mug. Beginning with Round 161, PAT samples were prepared by liquid deposition rather than by sampling a generated silica aerosol, in order to improve consistency and reduce errors in sample preparation. The improvement was reflected in the results, with the mean lab RSD declining from 21.5 percent to 17.2 percent after the change to liquid deposition, demonstrating the improved consistency between PAT samples.

    In the time since OSHA analyzed the PAT data, Harper et al. (2014, Document ID 3998, Attachment 8) evaluated more recent data. Specifically, Harper et al. (2014, Document ID 3998, Attachment 8, p. 3) evaluated PAT test results for the period 2003-2014 (Rounds 152 through 194) and found that variation in respirable crystalline silica analysis has improved substantially since the earlier data from 1990 to 1998 was studied by Eller et al. (1999a, Document ID 1687). A total of 9,449 sample results were analyzed after removing re-test results, results where the method of analysis was not identified, and results that were more than three standard deviations from the reference mean. There was a clear improvement in overall variation in the newer data set compared with that of Eller et al. (1999a, Document ID 1687), with the mean laboratory RSD declining from about 28.7 percent to 20.9 percent (Document ID 3998, Attachment 8, Figure 1). Both the older and newer data sets showed that analytical variation increased with lower filter loadings, but the more recent data set showed a much smaller increase than did the older. At a filter load of 50 mug, the mean lab RSD of the more recent data was less than 25 percent, whereas it was almost 35 percent with the older data set (Document ID 3998, Attachment 8, Figure 1). It was also clear that the change in sample preparation procedure (i.e., from aerosol deposition to liquid deposition starting in Round 161) explained at least some of the improvement seen in the more recent PAT results, with the mean lab RSD declining from 23.6 percent for all rounds combined to 19.9 percent for Rounds 162-194.

    Despite the improvement seen with the change in deposition method, it is important to understand that the observed variation in PAT results between labs still reflects some sample preparation error (limited to 10 percent as explained above), a source of error not reflected in the analysis of field samples. Other factors identified by the investigators that account for the improved performance include the phasing out of the colorimetric method among participating labs, use of more appropriate calibration materials (i.e., NIST standard reference material), calibration to lower mass loadings, stricter adherence to published method procedures, and possible improvements in analytical equipment. There was also only a small difference (2 percent) in mean lab RSD between labs using XRD and those using IR (Document ID 3998, Attachment 8, p. 9). The increase in variance seen with lower filter loads was not affected either by analytical method (XRD vs. IR) or by the composition of interfering minerals added to the matrix (Document ID 3998, Attachment 8, p. 4).

    OSHA finds that this study provides substantial evidence that employers will obtain reliable results from analysis of respirable crystalline silica most of the time for the purpose of evaluating compliance with the PEL. From Round 162 through 194 (after the deposition method was changed), and over the full range of PAT data, only about 7 out of the 128 (5 percent) lab RSD values reported were above 25 percent (Document ID 3404, Figure 2). For filter loads of 75 mug or less, only 3 lab RSD values out of about 30 reported, were above 25 percent. As stated above, the mean RSD at a filter load of 50 mug was less than 25 percent and agreement between labs improved substantially compared to earlier PAT data.

    Summary data for PAT samples having a target load of less than 62.5 mug were provided by AIHA in a post-hearing comment (Document ID 4188) and compared with the findings reported by Harper et al. (2014, Document ID 3998, Attachment 8). For PAT rounds 155-193 (from 1999 to 2013), there were 15 sets of samples in the range of 41.4 to 61.8 mug distributed to participating laboratories. Lab RSDs from results reported for these samples ranged from 11.2 to 26.4 percent, with an average RSD of 17.1 percent, just slightly above the average RSD of 15.9 percent for all samples across the entire range of filter loads from those rounds. Taken together, the results of the analysis performed by Harper et al. (2014, Document ID 3998, Attachment 8) and the summary data provided by AIHA (Document ID 4188) suggest that sample results from participating labs will be within 25 percent of the crystalline silica filter load most of the time.

    In its post hearing comments, the National Stone, Sand & Gravel Association (NSSGA) contended that analytical laboratories cannot provide adequately precise and accurate results of silica samples (Document ID 4232). NSSGA provided a detailed analysis of low-load samples from the same 15 PAT rounds as examined by AIHA (Document ID 4188) and concluded that ``employers and employees cannot rely on today's silica sampling and analytical industry for consistently accurate sample results necessary to achieve or surpass compliance requirements'' (Document ID 4232, p. 26). The NSSGA compared individual labs' sample results to the reference mean for each sample and found, from the AIHA PAT data, that 76-84 percent of the results were within 25 percent of the reference mean, and the range of results reported by laboratories included clear outliers, ranging from zero to several-fold above the target filter load (Document ID 4232, p. 8, Table 1, rows 1-

    6). NSSGA concluded from this that ``it is of little value to employers that a given lab's results meet the NIOSH Accuracy Criterion while other labs' results cannot, particularly since employers almost certainly won't know which labs fall into which category'' (Document ID 4232, p. 10). NSSGA's point appears to be that the outliers in the PAT data erode an employer's ability to determine if they are receiving accurate analytical results, without which they have little ability to determine their compliance status with respect to the PEL or action level. Further, NSSGA suggests that OSHA's analysis of the PAT data, discussed above, is not adequate to demonstrate the performance of an individual

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    laboratory that may be chosen by an employer.

    In response to NSSGA's criticism, OSHA points out that its analysis of the PAT data was part of its analysis of technological feasibility in which the Agency's legal burden is to show that employers can achieve compliance in most operations most of the time. It may be an unavoidable fact that lab results may be inaccurate some of the time, but that does not render the standard infeasible or unenforceable. OSHA contends that its analysis has satisfied that burden and nothing in the NSSGA's comments suggests otherwise.

    NSSGA further suggests that employers have no means of determining, based on a laboratory's PAT proficiency rating alone, whether that individual laboratory is likely to produce erroneously high or low results. OSHA concurs that selecting a laboratory based on accreditation, price, and turnaround time, as NSSGA suggests (Document ID 4232, p. 5), is common but may be inadequate to determine whether an individual laboratory is capable of producing results of consistently high quality. Employers and their industrial hygiene consultants can, and should, ask additional questions and request additional assurances of quality from the laboratories they consider using. For example, employers can ask to review the laboratory's individual PAT results over time, focusing on and questioning any significant outliers in the laboratory's results. While NSSGA suggests that the PAT results are treated as confidential by the AIHA-PAT program (Document ID 4232, p. 6), there is nothing stopping a laboratory from sharing its PAT data or any other information related to its accreditation with their clients or prospective clients.

    Further, laboratories routinely perform statistical analyses of their performance in the context of analyzing known samples they use for equipment calibration, and often perform statistical comparisons among the various technicians they employ. Review of these statistics can shed light on the laboratory's ability to provide consistent analysis. Finally, as employers conduct exposure monitoring over time, and come to understand what results are typically seen in their workplaces, clear outliers should become more identifiable; for example, if employee exposures are usually between the action level and PEL, and a sample result shows an exposure significantly above the PEL without any clear change in workplace conditions or operations, employers should question the result and ask for a reanalysis of the sample. Employers could also request gravimetric analysis for respirable dust against which to compare the silica result to confirm that the silica content of the dust is consistent with past experience. For example, if, over time, an employer's consistent results are that the silica content of respirable dust generated in its workplace is 20 percent silica, and subsequently receives a sample result that indicates a significantly higher or lower silica content, it would be appropriate for the employer to question the result and request reanalysis. Therefore, OSHA rejects the idea that employers are at the mercy of random chance and have to simply accept a high degree of uncertainty in exposure measurements; rather, there are positive steps they can take to reduce that uncertainty.

    Results from the AIHA PAT program were discussed at considerable length during the rulemaking proceeding. After considering all of the analyses of PAT data presented by Eller et al. (1999a, Document ID 1687), OSHA in its PEA, and Harper et al. (2014, Document ID 3404), the ACC concluded that ``PAT program results indicate that analytical variability as measured by precision is unacceptably high for silica loadings in the range of 50-250 mug'' and that the PAT data ``provide strong evidence that commercial laboratories will not be able to provide reliable measurements of . . . respirable crystalline silica exposures at the levels of the proposed PEL and action level'' (Document ID 4209, p. 144). OSHA disagrees with this assessment. First, OSHA's experience over the last 40 years in enforcing the preceding PEL that this standard supersedes is that analytical variability has not been an impediment to successful enforcement of the superseded PEL, and there have been few, if any, challenges to such enforcement actions based on variability. Nor has OSHA been made aware of concerns from employers that they have been unable to evaluate their own compliance with the former PEL or make reasonable risk management decisions to protect workers. In fact, the Chamber's expert, Mr. Lieckfield, admitted that analytical variability for asbestos, another substance that has been regulated by OSHA over the Agency's entire history, ``is worse'' than that for crystalline silica (Document ID 3576, Tr. 531).

    To support its contention that reliably measuring silica at the final rule's PEL and action level is not possible, the ACC cited Harper et al. (2014, Document ID 3998, Attachment 8) as stating that further increases in laboratory variance below the 40-50 mug range would have ``implications for the working range of the analytical methods,'' and that excessive variance might ``make it difficult to address for either method'' (Document ID 4209, p. 144). However, it is clear from Harper et al. (2014) that this is the basis for the authors' recommendation that the PAT program consider producing samples with filter loads as low as 20 mug to ``support the analysis of lower target concentration levels'' (Document ID 3404, p. 5). They also identify use of currently available higher-flow-rate sampling devices (discussed above) to increase the collected mass of silica, which would generate field samples in the filter load range currently used in the PAT program.

    Finally, the ACC sponsored a performance testing study to assess inter-laboratory variability at crystalline silica filter loads at 40 and 20 mug (i.e., the amount of silica collected at final rule's PEL and action level, respectively, assuming use of a Dorr-Oliver cyclone operated at a flow rate of 1.7 L/min) as well as at 80 mug (i.e., the amount collected at the preceding PEL) (Document ID 2307, Attachment 14; 3461; 3462). The study was blinded in that participating laboratories were not aware that they were receiving prepared samples, nor were they aware that they were involved in a performance study. For this study, each of five laboratories was sent three replicate rounds of samples; each round consisted of three filters prepared with respirable crystalline silica (Min-U-Sil 5) alone, three of silica mixed with kaolin, three of silica mixed with soda-feldspar, and one blank filter. The samples were prepared by RJ Lee Group and sent by a third party to the laboratories as if they were field samples. All laboratories were accredited by AIHA and analyzed the samples by XRD.

    The samples were initially prepared on 5 mum PVC filters; however, due to sample loss during preparation, RJ Lee changed to 0.8 mum PVC filters. It should be noted that the 2-propanol used to suspend the Min-U Sil sample for deposition onto the 0.8 mum filter dissolved between 50 and 100 mug of filter material, such that the amount of minerals deposited on the filter could not be verified from the post-deposition filter weights. In addition, two of the labs had difficulty dissolving these filters in tetrahydrofuran, a standard method used to dissolve PVC filters in order to redeposit the sample onto silver membrane filters for XRD analysis. These labs were replaced by two laboratories that used muffle furnaces to ash the filters before redeposition, as

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    did the other three labs originally selected.

    Results reported from the labs showed a high degree of both intra- and inter-laboratory variability as well as a systematic negative bias in measured vs. applied silica levels, with mean reported silica values more than 30 percent lower than the deposited amount. Across all laboratories, mean results reported for filter loads of 20, 40, and 80 mug were 13.36, 22.93, and 46.91 mug, respectively (Document ID 2307, Attachment 14, pp. 5-6). In addition, laboratories reported non-

    detectable results for about one-third of the silica samples (Document ID 2307, Attachment 14, p. 7) and two blank filters sent to the labs were reported to have silica present, in one case an amount of 52 mug (Document ID 2307, Attachment 14, pp. 9-10; 3582, Tr. 1995). Individual CVs for the labs ranged from 20 to 66 percent, up to more than 3 times higher than the CVs reported by OSHA or NIOSH for their respective methods. After examining variability in reported results, the investigators concluded that two-fold differences in filter load could not be reliably distinguished in the concentration range of 25 to 100 mug/m\3\ (Document ID 2307, Attachment 14, p. 14).

    OSHA identifies several deficiencies in this study; these deficiencies are sufficient to discredit the finding that high variability in silica results can be attributed to the inability of the analytical method to accurately measure crystalline silica at filter loads representative of concentrations at the action level and PEL set by this rule. Principally, the loss of filter material during deposition of the samples, combined with the lack of any verification of the actual amount of silica loaded onto the filters, makes it impossible to use the laboratory results to assess lab performance since the amount of silica on the filters analyzed by the labs cannot be known. The large negative bias in lab results compared to the target filter load implies that there was significant sample loss. In addition, the quality control employed by RJ Lee to ensure that filter loads were accurately known consisted only of an analysis of six separately prepared samples to evaluate the recovery from the 0.8 mum PVC filter and two sets of filters to evaluate recovery and test for shipping loss (Document ID 3461, Slides 8, 15, 16; 3582, Tr. 2090-

    2091). This is in stark contrast to the procedures used by the AIHA PAT program, which verifies its sample preparation by analyzing a statistically adequate number of samples prepared each quarter to ensure that sample variation does not exceed 10 percent (Document ID 3586, Tr. 3276-3277). RJ Lee's use of the 0.8 mum PVC copolymer filter (Document ID 4001, Attachment 1) is also contrary to the NIOSH Method 7500 (Document ID 0901), which specifies use of the 5 mum PVC filter, and may have introduced bias. As stated at the hearing by Mary Ann Latko of the AIHA Proficiency Analytical Testing Programs, ``any variance from the NIOSH method should not be considered valid unless there's a sufficient quality control data provided to demonstrate the reliability of the modified method'' (Document ID 3586, Tr. 3278).

    OSHA finds that the AIHA PAT data are a far more credible measure of inter-laboratory variation in crystalline silica measurement than the ACC-sponsored RJ Lee study. Strict procedures are used to prepare and validate sample preparation in accordance with ISO requirements for conformity assessment and competence of testing in calibration laboratories (Document ID 3586, Tr. 3275) and the database includes 200 rounds of silica testing since 2004, with 55 laboratories participating in each round (Document ID 3586, Tr. 3264-3265). By comparison, the RJ Lee study consisted of three rounds of testing among five laboratories.

    One of the goals of the RJ Lee study was to conduct a double-blind test so that laboratories would not know they were analyzing prepared samples for proficiency testing; according to Mr. Bailey, a laboratory's knowledge that they are participating in a performance study, such as is the case with the AIHA PAT program, ``can introduce bias into the evaluation from the very beginning'' (Document ID 3582, Tr. 1989; Document ID 4209, p. 147). However, OSHA doubts that such knowledge has a profound effect on laboratory performance. Accredited laboratories participating in the PAT program undergo audits to ensure that analytical procedures are applied consistently whether samples are received from the field or from the PAT program. According to testimony from Mr. Walsh:

    Site assessors for the AIHA accreditation program are very sensitive to how PAT samples are processed in the lab. It's a specific area that's examined, and if the samples are processed in any way other than a normal sample, the laboratory is cited as a deficiency (Document ID 3586, Tr. 3299-3300).

    Therefore, after considering the evidence and testimony on the RJ Lee study and AIHA PAT Program data, OSHA concludes that the AIHA PAT data are the best available data on which to evaluate inter-laboratory variability in measuring respirable crystalline silica. The data evaluated by Harper et al. (2014) showed that laboratory performance has improved in recent years resulting in greater agreement between labs; mean RSD for the period 2003-2013 was 20.9 percent (Document ID 3998, Attachment 8, Figure 1). In addition, across the range of PAT filter loadings, only about 5 percent of the samples resulted in lab RSDs above 25 percent. At lower filter loads, 75 mug or less, about 10 percent of samples resulted in RSDs above 25 percent Document ID 3998, Attachment 8, Figure 2). OSHA concludes that these findings indicate general agreement between laboratories analyzing PAT samples.

    Although laboratory performance has not been broadly evaluated at filter loads below 40 mug, particularly when interferences are present, OSHA's investigations show that the XRD method is capable of measuring crystalline silica at filter loads of 40 mug or less without appreciable loss of precision. The analysis of recent PAT data by Harper et al. (2014, Document ID 3998, Attachment 8) shows that the increase seen in inter-laboratory variation with lower filter loads (e.g., about 50 and 70 mug) is modest compared to the increase in variation seen in the past from earlier PAT data, and the summary data provided by AIHA (Document ID 4188) show that the average lab RSD for samples with low filter loads is only a few percentage points above average lab RSD across the full range of filter loads used in the PAT program since 1999. OSHA finds that the studies of recent PAT data demonstrate that laboratories have improved their performance in recent years, most likely as a result of improving quality control procedures such as were first proposed by Eller et al. (1999b, Document ID 1688, pp. 23-24). Such procedures, including procedures concerning equipment calibration, use of NIST standard reference material for calibration, and strict adherence to published analytical methods, are required by Appendix A of the final standards (29 CFR 1910.1053 and 29 CFR 1926.1153). According to Dr. Rosa Key-Schwartz, NIOSH's expert in crystalline silica analysis, NIOSH worked closely with the AIHA laboratory accreditation program to implement a silica emphasis program for site visitors who audit accredited laboratories to ensure that these quality control procedures are being followed (Document ID 3579, Tr. 153). With such renewed emphasis being placed on

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    tighter procedures for crystalline silica analysis, OSHA finds that exposure monitoring results being received from laboratories are more reliable than was the case in years past and thus are deserving of greater confidence from employers and workers.

    f. Conclusion

    Based on the record evidence reviewed in this section, OSHA finds that current methods to sample respirable dust and analyze samples for respirable crystalline silica by XRD and IR methods are capable of reliably measuring silica concentrations in the range of the final rule's PEL and action level. This finding is based on the following considerations: (1) Several sampling devices are available that conform to the ISO/CEN specification for particle-size selective samplers with a level of bias and accuracy deemed acceptable by international convention, and moving to the ISO/CEN convention will maintain continuity with past practice, (2) both the XRD and IR methods can measure respirable crystalline silica with acceptable precision at amounts that would be collected by samplers when airborne concentrations are at or around the PEL and action level, and (3) laboratory proficiency data demonstrate that there is reasonable agreement between laboratories analyzing comparable samples most of the time.

    There are several sampling devices that can collect respirable crystalline silica in sufficient quantity to be measured by laboratory analysis; some of these include the Dorr-Oliver nylon cyclone operated at 1.7 L/min air flow rate, the Higgins-Dewell cyclones (2.2 L/min), the SKC aluminum cyclone (2.5 L/min), and the GK2.69, which is a high-

    flow sampler (4.2 L/min). Each of these cyclones can collect the minimum amount of silica necessary, at the PEL and action level, for laboratories to measure when operated at their respective flow rates for at least four hours. In addition, each of these devices (as well as a number of others) has been shown to conform to the ISO/CEN convention with an acceptable bias and accuracy for a wide range of particle-size distributions encountered in the workplace. OSHA used the Dorr-Oliver at a flow rate of 1.7 L/min to enforce the previous PELs for respirable crystalline silica, so specifying the use of sampling devices conforming to the ISO/CEN convention does not reflect a change in enforcement practice. The modest error that is associated with using respirable dust samplers is independent of where the PEL is set, and these samplers have been used for decades both by OSHA, to enforce the preceding silica PEL (and other respirable dust PELs), and by employers in managing silica-related risks. Therefore, OSHA finds that these samplers are capable of and remain suitable for collecting respirable dust samples for crystalline silica analysis.

    Both XRD and IR analytical methods are capable of quantifying crystalline silica with acceptable precision when air samples are taken in environments where silica concentrations are around the PEL and action level. OSHA's quality control samples analyzed by XRD over the past few years show the precision to be about 20 percent over the range of filter loads tested (about one-half to twice the former PEL). OSHA conducted studies to characterize the precision of its Method ID-142 at low filter loads representing the amounts that would be captured using the Dorr-Oliver cyclone at the action level and PEL (i.e., 20 and 40 mug, respectively), and found the precision, for quartz and cristobalite, at both 20 and 40 mug to be comparable to the precision at the higher range of filter loads.

    Evaluation of data from AIHA's Proficiency Analytical Testing Program shows that results from participating laboratories are in agreement (i.e., within 25%) most of the time. Performance between laboratories has improved significantly in recent years, most likely due to adoption of many of the quality control practices specified by Appendix A of the final standards. Although precision declines as the amount of crystalline silica in samples declines, the rate of decline in precision with declining mass is less today than for prior years. OSHA expects that increasing emphasis on improved quality control procedures by the AIHA laboratory accreditation program (Document ID 3579, Tr. 153), the requirement in the final rule for employers to use laboratories that use XRD or IR analysis (not colorimetric) and that are accredited and conform to the quality control procedures of Appendix A of the final standards, and increased market pressure for laboratories to provide reliable results are likely to improve agreement in results obtained by laboratories in the future.

    Inter-laboratory variability has not been well characterized at filter loads below 50 mug, which is slightly more than would be collected by a Dorr-Oliver cyclone sampling a silica concentration at the PEL over a full shift. However, OSHA concludes that the studies conducted by SLTC show that acceptable precision can be achieved by the XRD method for filter loads obtained by collecting samples with the Dorr-Oliver and similar devices at the action level and PEL. If employers are concerned about the accuracy that their laboratory would achieve at filter loads this low, samplers with higher flow rates could be used to collect an amount of silica that falls within the working range of the OSHA method and within the range of filter loads currently used by the PAT program (i.e., 50 mug or more). For example, either the aluminum cyclone or HD will collect at least 50 microg or more of silica where concentrations are around the PEL, and the GK2.69 will collect a sufficient quantity of crystalline silica where concentrations are at least at the action level.

    Based on the information and evidence presented in this section, OSHA is confident that current sampling and analytical methods for respirable crystalline silica provide reasonable estimates of measured exposures. Employers should be able to rely on sampling results from laboratories meeting the specifications in Appendix A of the final standards to analyze their compliance with the PEL and action level under the new silica rule; employers can obtain assurances from laboratories or their industrial hygiene service providers that such requirements are met. Similarly, employees should be confident that those exposure results provide them with reasonable estimates of their exposures to respirable crystalline silica. Thus, OSHA finds that the sampling and analysis requirements under the final rule are technologically feasible.

    3. Feasibility Findings for the Final Permissible Exposure Limit of 50 mug/m\3\

    In order to demonstrate the technological feasibility of the final PEL, OSHA must show that engineering and work practices are capable of reducing exposures to the PEL or below for most operations most of the time. Substantial information was submitted to the record on control measures that can reduce employee exposures to respirable crystalline silica, including but not limited to LEV systems, which could include an upgrade of the existing LEV or installation of additional LEV; process enclosures that isolate the employee from the exposure; dust suppression such as wet methods; improved housekeeping; and improved work practices. Substantial information was also submitted to the record on the use of respiratory protection; while OSHA does not, as a rule, consider the use of respirators when deciding whether an operation is technologically

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    feasible, it does, when it finds a particular operation or task cannot achieve the PEL without respiratory protection, require appropriate respirator use as a supplementary control to engineering and work practice controls, when those controls are not sufficient alone to meet the PEL.

    OSHA finds that many engineering control options are currently commercially available to control respirable dust (e.g., Document ID 0199, pp. 9-10; 0943, p. 87; 1607, p. 10-19; 1720, p. IV-237; 3791, p. iii; 3585, p. 3073; 3585, p. 3072). These controls will reduce employees' exposures to respirable crystalline silica when the employees are performing the majority of tasks that create high exposures. OSHA's finding is based on numerous studies, conducted both in experimental settings in which the tools, materials and duration of the task are controlled by the investigator, and in observational field studies of employees performing their normal duties in the field. As detailed in Chapter IV of the FEA, more than 30 studies were submitted to the docket that report substantial reductions in exposure when using controls compared with uncontrolled situations. The specific reports that OSHA relied upon to estimate the range of reductions that can be achieved through the implementation of engineering controls are discussed in greater detail in the relevant sections of the technological feasibility analyses.

    Table VII-8 lists the general industry sectors included in the technological feasibility analysis and indicates the numbers of job categories in each sector for which OSHA has concluded that the final PEL of 50 mug/m\3\ is technologically feasible (see Chapter IV of the FEA). As this table shows, OSHA has determined that the final rule's PEL is feasible for all general industry sectors for the vast majority of operations in these affected industry sectors (87 out of 90). For only three general industry job categories, OSHA has concluded that exposures to silica will likely exceed the final rule's PEL even when all feasible controls are fully implemented; therefore, supplemental respiratory protection will be needed in addition to those controls to ensure that employees are not exposed in excess of the PEL for those three categories. Specifically, supplemental use of respiratory protection may be necessary for abrasive blasting operations in the concrete products industry sector, cleaning cement trucks in the ready mix concrete industry sector, and during abrasive blasting operations in shipyards. In addition, in foundries, while finding that compliance with the standard is overall feasible for all job categories, OSHA recognizes that supplemental use of respiratory protection may be necessary for the subset of employees who infrequently perform refractory lining repair; for the small percentage of shakeout operators, knockout operators, and abrasive blasters who work on large castings in circumstances where substitution to non-silica granular media is not feasible; and for maintenance operators performing refractory patching where reduced silica refractory patching products cannot be used.

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    GRAPHIC TIFF OMITTED TR25MR16.044

    OSHA has determined that some engineering controls are already commercially available for the hydraulic fracturing industry, and other controls that have demonstrated promise are currently being developed. OSHA recognizes, however, that engineering controls have not been widely implemented at hydraulic fracturing sites, and no individual PBZ results associated with controls have been submitted to the record.

    The available information indicates that controls for dust emissions occurring from the sand mover, conveyor, and blender hopper have been effective in reducing exposures. KSW Environmental reported that a commercially-available control technology reduced exposures in one test with all 12 samples below the NIOSH recommended exposure limit (REL) of 50 mug/m\3\ (Document ID 4204, p. 35, Fn. 21). KSW Environmental also stated that four additional customer tests resulted in 76 PBZ samples, all below 100 mug/m\3\ (Document ID 4204, p. 35, Fn. 21). Another manufacturer of a similar ventilation system (J&J Bodies) reported that there was significantly less

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    airborne dust during the loading of proppant onto the sand mover when its dust control system was used. This dust control system was used at 10 different hydraulic fracturing sites with reportedly good results (Document ID 1530, p. 5).

    These findings indicate that, with good control of the major dust emission sources at the sand mover and along the conveyor to the blender hopper, exposures can be reduced to at least 100 mug/m\3\. Use of other dust controls, including controlling road dust (reducing dust emissions by 40 to 95 percent), applying water misting systems to knock down dust released from partially-enclosed conveyors and blender hoppers (reducing dust emissions by more than half), providing filtered booths for sand operators (reducing exposure to respirable dust by about half), reducing drop height at transfer points and hoppers, and establishing regulated areas, will further reduce exposures to 50 mug/m\3\ or below. Additional opportunities for exposure reduction include use of substitute proppant, where appropriate, and development and testing of dust suppression agents for proppant, such as that developed by ARG (Document ID 4072, Attachment 35, pp. 9-10). OSHA anticipates that once employers come into compliance with the preceding PEL, the additional controls to be used in conjunction with those methodologies to achieve compliance with the PEL of 50 mug/m\3\ will be more conventional and readily available.

    Therefore, OSHA finds that the PEL of 50 mug/m\3\ can be achieved for most operations in the hydraulic fracturing industry most of the time. As shown in Table IV.4.22-B of the FEA, this level has already been achieved for almost one-third of all sampled workers (and nearly 1 in 5 sand fracturing workers, the highest exposed job category). OSHA expects that the growing availability of the controls needed to achieve the preceding PEL, along with further development of emerging technologies and better use and maintenance of existing controls, will reduce exposures to at or below the PEL for the remaining operations.

    The American Petroleum Institute (API), the Marcellus Shale Coalition (MSC), and Halliburton questioned whether the analysis of engineering controls presented in the PEA was sufficient to demonstrate the technological feasibility of reducing exposures to silica at hydraulic fracturing sites to levels at or below 50 mug/m\3\, in part because the analysis did not include industry-specific studies on the effectiveness of dust controls but largely relied instead on research from other industries (Document ID 2301, Attachment 1, pp. 29, 60-61; 2302, pp. 4-7; 2311, pp. 2-3). These stakeholders argued that OSHA needed to do significantly more data collection and analysis to show that the PEL of 50 mug/m\3\ is feasible for hydraulic fracturing operations.

    OSHA sought additional information on current exposures and dust control practices. Throughout the NPRM and hearings, OSHA, as well as other stakeholders, requested additional information on exposures and engineering controls (Document ID 3589, Tr. 4068-4070, 4074-4078, 4123-

    4124; 3576, Tr. 500, 534). Submissions to the record indicate that significant efforts are currently being made to develop more effective dust controls specifically designed for hydraulic fracturing (Document ID 1530; 1532; 1537; 1538; 1570; 4072, Attachments 34, 35, 36; 4204, p. 35, Fn. 21). However, industry representatives provided no additional sampling data to evaluate the effectiveness of current efforts to control exposures. Thus, NIOSH and OSHA provided the only detailed air sampling information for this industry, and summary data were provided by a few rulemaking participants (Document ID 4204, Attachment 1, p. 35, Fn. 21; 4020, Attachment 1, p. 4).

    When evaluating technological feasibility, OSHA can consider engineering controls that are under development. Under section 6(b)(5) of the OSH Act, 29 U.S.C. 655(b), OSHA is not bound to the technological status quo and can impose a standard where only the most technologically advanced companies can achieve the PEL even if it is only some of the operations some of the time. Lead I (United Steelworkers of Am., AFL-CIO-CLC v. Marshall, 647 F.2d 1189 (D.C. Cir. 1980)); Am. Iron & Steel Inst. v. OSHA, 577 F.2d 825 (3d Cir. 1978). Relying on these precedents, the D.C. Circuit reaffirmed that MSHA and OSHA standards may be ``technology-forcing'' in Kennecott Greens Creek Min. Co. v. MSHA, 476 F.3d 946, 957, 960 (D.C. Cir. 2007), and that ``the agency is `not obliged to provide detailed solutions to every engineering problem,' but only to `identify the major steps for improvement and give plausible reasons for its belief that the industry will be able to solve those problems in the time remaining.' '' Id. (finding that MSHA provided ``more than enough evidence,'' including ``identifying several types of control technologies that are effective at reducing . . . exposure,'' to conclude that the industry could comply with the two-year implementation date of a technology-

    forcing standard) (citing Nat'l Petrochemical & Refiners Ass'n v. EPA, 287 F.3d 1130, 1136 (D.C. Cir. 2002)).

    OSHA concluded that these technologies will enable the industry to comply within five years. OSHA has described technologies that have been developed and tested, and that have demonstrated that the PEL is obtainable. These technologies have been developed to reduce exposures to the preceding PEL, but some of them appear also to have the capability to reduce some exposures to the PEL of 50 microg/m\3\. KSW Environmental has provided data that indicate exposures can be achieved at or below the PEL (Document ID 1570, p. 22; 4204, Attachment 1, p. 35, Fn. 21; 4222, Attachment 2, p. 6), and NIOSH has presented concepts of ``mini-bag houses'' that can be retrofitted on existing equipment (Document ID 1537, p. 5; 1546, p. 10). SandBox Logistics, LLC, has developed a shipping container for bulk transport of sand specifically designed for hydraulic fracturing operations that eliminates the need for sand movers, a major source of exposure to silica at fracturing sites (Document ID 3589, Tr. 4148). OSHA views these and other advanced controls discussed above as on the ``horizon,'' but not currently widely available for operational use (Am. Fed'n of Labor & Cong. of Indus. Organizations v. Brennan, 530 F.2d 109, 121 (3d Cir. 1975)). Once they are deployed, as explained fully in Chapter IV of the FEA, more conventional adjustments and additional controls can be used with them to lower exposures to the new PEL or below.

    Evidence in the record shows widespread recognition of silica exposure hazards on hydraulic fracturing sites and industry's efforts to address them primarily through the efforts of the National Service, Transmission, Exploration & Production Safety (STEPS) network's Respirable Silica Focus Group. The STEPS network initiated action to address exposure to silica at hydraulic fracturing sites in 2010, when NIOSH first conducted air sampling and then publicized the severity of hazardous silica exposures as part of its Field Effort to Assess Chemical Exposures in Gas and Oil Workers (Document ID 1541). Recognition of silica exposures in the industry well above the preceding PEL of 100 microg/m\3\ prompted the development of engineering controls to reduce exposures to silica. While some companies in the hydraulic fracturing industry are able to obtain and implement controls to comply with the preceding PEL (e.g., Document ID 4204,

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    Attachment 1, p. 35, Fn. 21), the technology is not currently widely available. Given the progress that has been made since 2010, OSHA concluded that these technologies will become more widely available and enable the industry to comply with the final PEL within five years. As noted by Kenny Jordan, the Executive Director of the Association of Energy Service Companies (AESC), his organization's participation on the National Occupational Research Agenda (NOR

  24. NIOSH Oil and Gas Extraction Council enabled members to be ``at the forefront of building awareness of the silica at the well site issue, particularly among those working in fracking operations'' (Document ID 3589, Tr. 4059). In the five years since that time, the substantial progress in controlling silica exposures at fracking sites described above has occurred.

    In June 2012, the STEPS network, in which AESC and many other industry, educational and regulatory entities participate, launched a respirable silica focus group to spread awareness, better characterize on-site silica exposures, and facilitate and evaluate the development of engineering controls (Document ID 3589, Tr. 4059; 1537). This enabled several manufacturers of engineering controls, such as KSW Environmental (formerly Frac Sand Dust Control and Dupre) who had developed a working model in 2009 (Document ID 1520), to collaborate and share information on various engineering controls. As a consequence, the silica control field has grown significantly during this period, including the development, testing and, in some cases, deployment of new technologies, including those from KSW Environmental, J&J Truck Bodies, SandBox Logistics, and NIOSH's baghouse. For example, John Oren, the co-inventor of the SandBox Logistics technology, said it had taken his company only three years to develop the product and make it commercially available (Document ID 3589, Tr. 4148). OSHA concludes that an additional five years will be more than enough time for these and other firms to complete development and increase manufacturing and sales capacity, and, simultaneously, for hydraulic fracturing employers to test, adopt and adapt these emerging technologies to their workplaces. Indeed, in light of the progress that has already been made, it may be more accurate to call the standard ``market-

    accelerating'' than ``technology-forcing.''

    During the rulemaking, API touted the efforts of this industry to develop technology to protect workers against the hazards of silica (Document ID 4222, Attachment 2, p. 9). OSHA agrees with API that these efforts have been noteworthy and that more time is warranted to allow for continued development, commercialization, and implementation of these innovative technologies. OSHA is confident that with the innovation displayed by this industry to date, the hydraulic fracturing industry can further reduce worker exposures to the PEL if sufficient time is provided. Therefore, OSHA is providing an extra three years from the effective date of the standard--for a total of five years--to implement engineering controls for the hydraulic fracturing industry. OSHA concludes that this is ample time for this highly technical and innovative industry to come into compliance with the final PEL. This is consistent with, but longer than, the time frame OSHA granted for implementation of engineering controls for hexavalent chromium, where OSHA provided four years to allow sufficient time for some industries to coordinate efforts with other regulatory compliance obligations as well as gain experience with new technology and learn more effective ways to control exposures (71 FR 10100, 10372, Feb. 28, 2006). Thus, with the extra time provided for this industry to come into compliance, OSHA finds that the final PEL of 50 microg/m\3\ is feasible for the hydraulic fracturing industry.

    In the two years leading up to the effective date, the hydraulic fracturing industry will continue to be subject to the preceding PEL in 29 CFR 1910.1000 (Table Z). In order to meet the preceding PEL of 100 microg/m\3\ during this interim period, such compliance will include adoption of the new engineering controls discussed above as they become widely available for field use.\25\ As a result, OSHA expects many exposures in hydraulic fracturing to be at or near the 50 microg/m\3\ level ahead of the five-year compliance date due to the expected efficacy of this new technology. Thus, with the extra time provided for this industry to come into compliance, OSHA finds that the standard is feasible for most workers in the Hydraulic Fracturing industry most of the time.

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    \25\ Compliance with Table Z requires implementing all feasible engineering and administrative controls to achieve the PEL before using protective equipment such as respirators. 29 CFR 1910.1000(e). OSHA acknowledges that the technologies to meet the PEL in Table Z are not currently widely available in the quantities needed for the entire industry to achieve compliance. Accordingly, as employers work toward implementing controls during the interim period, supplemental respiratory protection may be necessary to comply with the PEL of 100 microg/m\3\. Likewise, during the additional three-

    year phase-in period, OSHA anticipates that many employers may need to use supplemental respiratory protection to comply with the PEL of 50 microg/m\3\.

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    OSHA has determined that a PEL of 50 microg/m\3\ is technologically feasible for the maritime industry. Although it is not feasible to reduce painters' exposures to 50 microg/m\3\ when conducting abrasive blasting operations most of the time without the use of respirators, evidence in the record demonstrates that it is feasible to reduce painters' helpers' exposure to 50 microg/m\3\ most of the time with HEPA-filtered vacuums. As noted in Chapter IV of the FEA, workers in the maritime industry may also be exposed during foundry activities; as explained in FEA Chapter IV. Section 4.8.4--

    Captive Foundries, OSHA has determined that it is feasible to reduce exposures during most operations in captive foundries to 50 microg/

    m\3\, most of the time. The record evidence indicates that shipyard foundries face similar issues controlling silica as other typical small foundries (e.g., cleaning the cast metal) and that shipyard foundries cast items in a range of sizes, from small items like a ship's plaque to large items like the bow structure for an aircraft carrier (Document ID 1145; 3584, Tr. 2607). OSHA did not receive comments indicating that foundries in shipyards would require any unique controls to reduce exposures, and therefore believes that exposures in shipyard foundries can also be reduced to 50 microg/m\3\ in most operations, most of the time. Accordingly, OSHA has determined that 50 microg/m\3\ is feasible for most silica-related activities performed in the maritime industry.

    Even if captive foundries are excluded from consideration, OSHA considers the standard to be feasible for shipyards with the use of respirators by painters doing abrasive blasting. OSHA recognizes that, consistent with its hierarchy of controls policy for setting methods of compliance, respirator use is not ordinarily taken into account when determining industry-wide feasibility. Neither this policy nor the ``most operations most of the time'' formulation for technological feasibility is meant to place OSHA in a ``mathematical straitjacket'' (Indus. Union Dep't, AFL-CIO v. Am. Petroleum Inst., 448 U.S. 607, 655 (1980) (``Benzene'') (stated with respect to the ``significant risk'' finding, which the Supreme Court recognized is ``based largely on policy considerations'' (Benzene, 448 U.S. at 655 n.62)). No court has been confronted with a situation where an industry has two operations (or any even number), of which one can achieve the PEL through

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    engineering controls and the other (or exactly half) can achieve it most of the time only with the use of respirators. However, the same court that formulated the ``most operations most of the time'' standard ``also noted that `insufficient proof of technological feasibility for a few isolated operations within an industry, or even OSHA's concession that respirators will be necessary in a few such operations, will not undermine' a showing that the standard is generally feasible'' (Amer. Iron & Steel Inst. v. OSHA, 939 F.2d 975, 980 (D.C. Cir. 1991) (Lead II), (quoting United Steelworkers of Am. AFL-CIO-CLC v. Marshall, 647 F.2d 1189, 1272 (D.C. Cir. 1980) (``Lead I'')). It further recognized the intended pragmatic flexibility of this standard by stating that ``for example, if `only the most technologically advanced plants in an industry have been able to achieve the standard--even if only in some of their operations some of the time,' then the standard is considered feasible for the entire industry'' (Lead II, 939 F. 2d at 980 (quoting Lead I, 647 F.2d at 1264)). In this instance, OSHA has determined that it makes sense to treat painters performing abrasive blasting in shipyards as an outlier for which the PEL established for all other covered industries is feasible, even conceding that respirators will be necessary. If abrasive blasting were the predominant activity that occurs in shipyards, there might be justification to set a separate, higher PEL for shipyards. But as in construction (for which supplemental respirator use is also contemplated for abrasive blasting operations), abrasive blasting is one of many activities that occurs; substitution of non-silica blasting materials is an option in many cases; few, if any, painters spend entire days or weeks doing blasting operations and thus needing respirators for the duration; and lowering the standard from 250 microg/m\3\ to 50 microg/m\3\ does not threaten the economic viability of the industry. Under these circumstances, OSHA concludes that it may find the standard feasible for shipyards rather than raise the PEL for this single industry because it can only achieve the uniform PEL with respirators or, alternatively, not be able to revise the previous PEL of 250 microg/m\3\ at all.

    Table VII-9 lists the construction application groups included in the technological feasibility analysis and indicates the numbers of tasks in each application group. As this table shows, OSHA has determined that the rule's PEL is feasible for the vast majority of tasks (19 out of 23) in the construction industry. For those construction tasks listed in Table 1 of paragraph (c) of the construction standard, OSHA has determined that the controls listed on Table 1 are either commercially available from tool and equipment manufacturers or, in the case of jackhammers, can be fabricated from readily available parts. Therefore, OSHA has determined that these control requirements are technologically feasible and will, with few exceptions, achieve exposures of 50 mug/m\3\ or less most of the time. Furthermore, Table 1 in paragraph (c) of the standard for construction acts as a ``safe harbor'' in the sense that full and proper implementation of the specified controls satisfies the employer's duty to achieve the PEL, and the employer is under no further obligation to do an exposure assessment or install additional, non-specified controls. Thus, OSHA finds the operations listed in Table 1 to be technologically feasible for the vast majority of employers who will be following the table.

    Where available evidence indicates that exposures will remain above this level after implementation of dust controls (see Chapter IV of the FEA), Table 1 requires that respiratory protection be used. OSHA has determined that available engineering and work practice controls cannot achieve exposure levels of 50 mug/m\3\ or less for only two activities: Handheld grinders used to remove mortar (i.e., tuckpointing) and dowel drilling in concrete. For a few other activities, OSHA concludes that respiratory protection will not generally be needed unless the task is performed indoors or in enclosed areas, or the task is performed for more than four hours in a shift. Table 1 requires use of respiratory protection when using handheld power saws indoors or outdoors more than four hours per shift; walk-

    behind saws indoors; dowel drills in concrete; jackhammers or handheld powered chipping tools indoors or outdoors more than four hours per shift; handheld grinders for mortar removal; and handheld grinders for uses other than mortar removal when used indoors for more than four hours per shift.

    OSHA has also evaluated the feasibility of three application groups that do not appear on Table 1: Underground construction, drywall finishing work, and abrasive blasting. For these operations, employers will be subject to the paragraph (d) requirements for alternative exposure control methods. Due in part to the complexity of excavating machines, dust controls, and the ventilation systems required to control dust for underground operations, OSHA decided not to include underground construction and tunneling operations in Table 1 of paragraph (c) of the construction standard. Nonetheless, OSHA has determined that the PEL is technologically feasible in underground construction because exposures can be reduced to 50 microg/m\3\ or less most of the time. Drywall finishing work was not included on Table 1 because silica-free drywall compounds are commercially available and can be used to eliminate exposure to silica when finishing drywall. In contrast to underground construction and drywall finishing, OSHA decided that abrasive blasting was not suited to the Table 1 approach because employers have several options in the control measures they can implement when abrasive blasting based on their particular application. For example, substitution to low-silica agent, use of wet blasting and process enclosures are all possible control options for abrasive blasting operations. Therefore, OSHA does not specify a specific control for abrasive blasting suitable for all applications, unlike the entries on Table 1 for tuckpointing and dowel drilling, where LEV is the only option accompanied by required supplemental respirator use. Furthermore, OSHA has existing requirements for abrasive blasting under the ventilation standard for construction (29 CFR 1926.57). In certain situations, that standard requires abrasive blasting operators to use abrasive blasting respirators approved by NIOSH for protection from dusts produced during abrasive blasting operations (29 CFR 1926.57(f)(5)(i) through (iii)). That standard also includes specifications for blast-cleaning enclosures (29 CFR 1926.57(f)(3)), exhaust ventilation systems (29 CFR 1926.57(f)(4)), air supply and air compressors (29 CFR 1926.57(f)(6)), and operational procedures (29 CFR 1926.57(f)(7)). OSHA also has similar requirements for abrasive blasting under the general industry standard (29 CFR 1910.94). Therefore, OSHA expects that respiratory protection will be required to be used during blasting operations under the paragraph (d) approach that employers must follow when employees are doing this task.

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    The American Chemistry Council's (ACC's) Crystalline Silica Panel contended that OSHA did not demonstrate that the proposed standard would be technologically feasible in all affected industry sectors because OSHA had failed to account for day-to-day environmental variability in exposures (Document ID 4209, Attachment 1, p. 97). ACC noted that OSHA enforces PELs as never-to-be-exceeded values and that an employer can be cited based

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    on a single measurement even if most exposures on most days are below the PEL. Therefore, they stated that to be ``reasonably confident of complying with OSHA's proposed PEL of 50 mug/m\3\, the long-term average exposure in most workplaces likely would have to be maintained at a level below 25 mug/m\3\ (or even below 20 mug/m\3\)'' (Document ID 4209, p. 97; 2307, Attachment A, pp. 23-24, 160). Representatives from the American Foundry Society (AFS) and the Asphalt Roofing Materials Association (ARMA) made similar arguments (Document ID 2291, p. 5; 3584, Tr. 2654-2655; 3580, Tr. 1282-1284, 1289).

    OSHA recognizes the existence of exposure variability due to environmental factors that can affect employee exposures, especially in the construction industry where work sites and weather conditions can change on a daily basis. OSHA has acknowledged this in past rulemakings where the same issue was raised (e.g., benzene, 52 FR 34534; asbestos, 53 FR 35609; lead in construction, 58 FR 26590; formaldehyde, 57 FR 22290; cadmium, 57 FR 42102; and chromium (VI), 71 FR 10099). However, not all exposure variation is due to random environmental factors; rather, many high exposures are the result of predictable causes that the employer can readily identify and address in efforts to improve exposure control. Several studies were submitted to the docket that used multivariate statistical models to identify factors associated with increased exposure to silica during various construction activities (Document ID 3608, 3803, 3956, 3998 Attachment 5h). These studies reported that as much as 80 percent of the variability in respirable quartz exposures could be attributed to various exposure determinants included in the models, clearly indicating that not all variability in exposure is uncontrollable. This was also attested to at the hearing by Dr. Frank Mirer:

    Exposures go up and down not by magic but by particular conditions, differences in work methods, differences in control efficiency, differences in adjacent operations (Document ID 3578, Tr. 971).

    OSHA concludes from the evidence in the record that the consistent use of engineering controls will reduce exposure variability. By improving or adding effective controls and work practices to reduce employee exposures to the PEL or below, employers will reduce exposure variability, and this reduction will provide employers with greater confidence that they are in compliance with the revised PEL. OSHA does, however, acknowledge that exposure controls cannot entirely eliminate variability. Some day-to-day variability in silica exposure measurements may remain, despite an employer's conscientious application and maintenance of all feasible engineering and work practice controls. Nonetheless, the legal standard for finding that a PEL is technologically feasible for an industry sector is whether most employers can implement engineering and work practice controls that reduce exposures to the PEL or below most of the time. As explained in Section XV, Summary and Explanation, in situations where exposure measurements made by OSHA indicate that exposures are above the PEL, and that result is clearly inconsistent with an employer's own exposure assessment, OSHA will use its enforcement discretion to determine an appropriate response. Moreover, for the vast majority of construction employers (and some general industry or maritime employers doing tasks that are ``indistinguishable'' from Table 1 tasks and choose to comply with the construction standard), full compliance with Table 1 will eliminate the risk that an employer will be subject to citation for exposures above the PEL, even when the employer has instituted all feasible controls that normally or typically maintain exposures below the PEL.

    OSHA also received a number of general comments on the feasibility of wet methods and LEV, as well as comments on challenges faced when employing these dust control strategies in specific work settings. In general industry, several commenters indicated for specific industries that there was no one control that could obtain the PEL of 50 mug/

    m\3\ (Document ID 2264, p. 36). CISC was also critical of several aspects of OSHA's feasibility analysis. CISC commented that OSHA failed to consider exposures from secondary or adjacent sources and that OSHA should factor this into its analysis (Document ID 2319, p. 30; 4217, p. 13). Dr. Mirer also stated that many employees' silica exposures are due to dust released from adjacent operations, but indicated that if these dust releases are controlled, the exposures of workers in adjacent areas will be substantially reduced (Document ID 4204, p. 104). In many industries, OSHA has shown that all sources of respirable crystalline silica should be controlled and that often a combination of controls may be needed to address potential sources of silica. Additionally, addressing each source of exposure also reduces exposures in adjacent areas, thus mitigating the concern about secondary exposures expressed by both industry and union stakeholders.

    Other commenters addressed the use of water on construction sites; several commenters asserted that it is not always possible for employers to use water for dust suppression. For example, in its post-

    hearing submission, CISC discussed what it believed to be ``significant obstacles'' to using wet dust suppression technologies on construction sites. Such obstacles include freezing weather, which contraindicates water use, and a lack of running water onsite, which requires employers to deliver water, a practice which, according to CISC, is both ``costly and time consuming'' (Document ID 4217, pp. 18-19). However, many other participants commented that these barriers can be overcome. For example, Phillip Rice, of Fann Contracting, Inc., uses water trucks to haul water to sites and includes the cost of doing so in his bids. He added that ``when someone says they can't get water on their project there is something wrong'' (Document ID 2116, Attachment 1, p. 33). Representatives of the International Union of Bricklayers and Allied Craftworkers pointed out that water is essential for work in the masonry trades and without it, no mortar can be mixed to set materials (Document ID 3585, Tr. 3059-3060). They testified that, in their experience, it was rare to work on sites that did not have water or electricity available, but when they do, they bring in water trucks and gas-powered generators to run saws (Document ID 3585, Tr. 3061-3063). With respect to weather conditions, heated water or heated shelters can be used if construction work is being performed in sub-freezing temperatures (Document ID 3585, Tr. 3095-3096).

    These comments and testimony indicate that the vast majority of the barriers to wet dust suppression raised by CISC have already been overcome in various construction settings. However, OSHA recognizes that there will be limited instances where the use of wet dust suppression is not feasible, particularly where its use can create a greater hazard. For example, water cannot be used for dust control in work settings where hot processes are present due to the potential for steam explosions (Document ID 2291, p. 13; 2298, p. 3), nor can it be used safely where it can increase fall hazards, such as on a roof (Document ID 2214, p. 2). Nevertheless, OSHA finds that many employers currently use wet dust suppression, that there are many commercially available products with integrated water systems for dust suppression, and that these products

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    can be used in most work settings to control exposures to respirable crystalline silica. In the limited cases where dust suppression is not feasible, OSHA discusses the use of alternative controls such as local exhaust ventilation and the supplemental use of respiratory protection, as needed.

    Some commenters questioned whether OSHA had adequately considered the difficulties in complying with the PEL for maintenance activities. The National Association of Manufacturers, for example, quoted one of its members, who stated:

    there are occasional conditions where maintenance cleaning is performed inside conveyor enclosures where the enclosure is ordinarily a part of the dust control systems. This is just one example of where a control would have to be breached in order to properly maintain it as well as the operating equipment. It is simply not technically feasible to establish engineering controls for all possible maintenance activities (Document ID 2380, Attachment 2, p. 1).

    OSHA has addressed maintenance activities in each sector's technological feasibility analysis, but the standard itself acknowledges the difficulties of some maintenance activities. Paragraph (g)(1)(ii) of the standard for general industry and maritime (paragraph (e)(1)(ii)(B) in construction) requires respiratory protection ``where exposures exceed the PEL during tasks, such as certain maintenance and repair tasks, for which engineering and work practice controls are not feasible'' (see the Summary and Explanation section on Respiratory Protection for more information).

    CISC submitted comments suggesting that the technological feasibility analysis was incomplete because it did not cover every construction-related task for which there is the potential for exposure to silica dust. It listed more than 20 operations, including cement mixing, cutting concrete pavers, demolishing drywall or plaster walls/

    ceilings, overhead drilling, demolition of concrete and masonry structures, and grouting floor and wall tiles, that it stated OSHA must examine in order to establish feasibility, in addition to the application groups already covered by OSHA's analysis (Document ID 2319, pp. 19-21). CISC asserted that, because of the many types of silica-containing materials used in the construction industry, as well as the presence of naturally occurring silica in soil, additional data collection and analysis by OSHA should be conducted before promulgating a final rule (Document ID 2319, pp. 25-26; 4217, p. 3).

    As explained in the NPRM, OSHA's analysis for construction focuses on tasks for which the available evidence indicates that significant levels of respirable crystalline silica may be created, due primarily to the use of powered tools or large equipment that generates visible dust. OSHA notes that many of the examples of tasks for which CISC requested additional analysis are tasks involving the tools and equipment already covered in this feasibility analysis. For example, overhead drilling is addressed in section IV-5.4 Hole Drillers Using Handheld or Stand-Mounted Drills, and the demolition of concrete and masonry structures is addressed in section IV-5.3 Heavy Equipment Operators. In other cases, such as for concrete mixing, there are no sampling data in the record to indicate that the task is likely to result in 8-hour TWA exposures above the action level. Exposure can occur when cleaning dried cement, and the feasibility of control measures to reduce exposures when cleaning out the inside of cement mixers is discussed in section IV-4.17 Ready Mix Concrete. Other tasks listed by CISC involve working with wet or intact concrete, which is unlikely to result in 8-hour TWA exposures above the action level. Further, CISC did not submit to the record any air monitoring data to support its assertion that these activities result in significant exposures. Therefore, OSHA has not added these additional activities to the feasibility analysis.

    4. Feasibility Findings for an Alternative Permissible Exposure Limit of 25 mug/m\3\

    In the NPRM, OSHA invited comment on whether it should consider a lower PEL because it determined there was still significant risk at the proposed PEL of 50 mug/m\3\ (78 FR 56288, September 12, 2013). OSHA has determined that the rule's PEL of 50 mug/m\3\ is the lowest exposure limit that can be found to be technologically feasible based on the rulemaking record. Specifically, OSHA has determined that the information in the rulemaking record either demonstrates that the proposed alternative PEL of 25 mug/m\3\ would not be achievable for most of the affected industry sectors and application groups or the information is insufficient to conclude that engineering and work practice controls can consistently reduce exposures to or below 25 mug/m\3\. Therefore, OSHA cannot find that the proposed alternative PEL of 25 mug/m\3\ is achievable for most operations in the affected industries, most of the time.

    The UAW submitted comments and data to the record, maintaining that a PEL of 25 mug/m\3\ is technologically feasible. As evidence, it submitted exposure data from a dental equipment manufacturing plant and two foundries (Document ID 2282, Attachment 3, pp. 7-8; 4031, pp. 3-8) showing that exposures to silica in these establishments were consistently below 25 mug/m\3\ TWA. However, OSHA cannot conclude that exposure data from three facilities is representative of the wide array of facilities affected by the rule or sufficient to constitute substantial record evidence that a PEL of 25 mug/m\3\ is technologically feasible in most operations most of the time.

    Although available exposure data indicate that exposures below 25 mug/m\3\ have already been achieved for most employees in some general industry sectors and construction application groups (e.g., dental laboratories, jewelry, and paint and coatings in general industry, and drywall finishers and heavy equipment operators performing excavation in construction), the relatively low exposures can be attributed to the effective control of the relatively small amounts of dust containing silica generated by employees in these industries and application groups. Further extrapolation to other sectors or groups with higher baseline exposures or more challenging control situations is not warranted, however.

    For most of the industries and application groups included in this analysis, a review of the sampling data indicates that an alternative PEL of 25 mug/m\3\ cannot be achieved with engineering and work practice controls. OSHA finds that engineering and work practice controls will not be able to consistently reduce and maintain exposures to an alternative PEL of 25 mug/m\3\ in the sectors that use large quantities of silica containing material, including foundries (ferrous, nonferrous, and non-sandcasting), concrete products, and hydraulic fracturing, or have high energy operations, such as jackhammering and crushing machines.

    For instance, in the ferrous foundry industry, the baseline median exposure in the profiles exceeds 50 mug/m\3\ for 6 of the 12 job categories analyzed: Sand system operators, shakeout operators, abrasive blasting operator, cleaning/finishing operators, maintenance operators, and housekeeping employees. OSHA concluded that engineering and work practice controls can reduce TWA exposures to 50 mug/m\3\ or less for most of these operations most of the time. However, because large amounts of silica-containing sand is transported, used, and recycled to create castings, OSHA cannot conclude that available controls can reduce exposures to or below 25 mug/m\3\ in any step of the

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    production process. Additionally, high energy operations in foundries can create concentrations of respirable silica above 25 mug/m\3\. For example, the shakeout process is a high energy operation using equipment that separates castings from mold materials by mechanically vibrating or tumbling the casting. The dust generated from this process causes elevated silica exposures for shakeout operators and often contributes to exposures for other employees in a foundry. The effectiveness of dust controls on shakeout operations was demonstrated at three foundries that implemented various dust controls in the shakeout area (e.g., shakeout enclosure added, ventilation system improved, conveyors enclosed and ventilated); full-shift samples taken by or for OSHA measured exposures for shakeout operators ranging from less than or equal to 13 mug/m\3\ to 41 mug/m\3\ (Document ID 1365, pp. 2-51; 1407, p. 20; 0511, p. 2). These readings were obtained in foundries that had made a systematic effort to identify and abate all sources of dust emission with the establishment of an abatement team consisting of an engineer, maintenance and production supervisors, and employees. TWA exposures for the shakeout operators were reduced to less than 50 mug/m\3\, but two of the four measurements in this well-

    controlled facility exceeded 25 mug/m\3\ (see Chapter IV 4.8.1 of the FEA). Other industry sectors that use substantial quantities of crystalline silica as a raw material include refractories, glass products, mineral processing, structural clay and cement products. OSHA finds that the available evidence on exposures at facilities in these industries in which controls have been implemented indicates most exposures are typically between 25 mug/m\3\ and 50 mug/m\3\.

    For other general industry sectors, OSHA has insufficient data to demonstrate that engineering and work practice controls will reduce exposures to or below 25 mug/m\3\ most of the time (see Chapter IV of the FEA). For example, it is not evident that exposures can be reduced to 25 mug/m\3\ for four out of five jobs analyzed in the pottery sector, for two out of three job categories in the structural clay sector, and for two jobs in the porcelain enameling sector.

    OSHA has also determined that application groups in construction that use large quantities of silica containing material or involve high energy operations will not be able to consistently achieve 25 mug/

    m\3\ (e.g. tuck pointing/grinding and rock and concrete drilling). These operations cause employees to have elevated exposures even when available engineering and work practice controls are used. Examples include using jackhammers during demolition of concrete and masonry structures, grinding concrete surfaces, using walk-behind milling machines, operating rock and concrete crushers, and using portable saws to cut concrete block. For instance, jackhammering is a high energy operation and OSHA finds that when employees perform this operation for four hours or less in a shift, most employees using jackhammers outdoors experience levels at or below 50 mug/m\3\ TWA but not reliably at or below 25 mug/m\3\. The use of portable cut-off saws (a type of handheld power saw) is also a high energy operation that can lead to exposures over 25 mug/m\3\. Due to energy applied to the material being cut from the rapid rotation of the circular blade, the dust generated can be difficult to control; available data indicate that exposures will often exceed 25 mug/m\3\ TWA, even when the portable cut-off saw is used with water for dust suppression. Evidence in the record indicates that, for most of the other construction operations examined, use of feasible engineering and work practice controls will still result in frequent exposures above 25 mug/m\3\. For other tasks in construction application groups, OSHA has insufficient data to demonstrate that engineering and work practice controls will reduce exposures to or below 25 mug/m\3\ most of the time (see Chapter IV of the FEA).

    Therefore, OSHA concludes that 50 mug/m\3\ as an 8-hour TWA is the lowest feasible exposure limit that the record demonstrates can be applied to most general industry, maritime, and construction operations without the excessive use of respirators. OSHA also concludes that it would hugely complicate both compliance and enforcement of the rule if it were to set a PEL of 25 mug/m\3\ for a minority of industries or operations where it would be technologically feasible and a PEL of 50 mug/m\3\ for the remaining industries and operations where technological feasibility at the lower PEL is either demonstrably unattainable, doubtful or unknown. OSHA is not under a legal obligation to issue different PELs for different industries or application groups, but may exercise discretion to issue a uniform PEL if it determines that the PEL is technologically feasible for all affected industries (if not for all affected operations) and that a uniform PEL would constitute better public policy (see Section II, Pertinent Legal Authority (discussing the chromium (VI) decision)). In declining to lower the PEL to 25 mug/m\3\ for any segment of the affected industries, OSHA has made that determination here.

  25. Costs of Compliance

    Overview

    This section assesses the costs to establishments in all affected industry sectors of reducing worker exposures to silica to an 8-hour time-weighted average (TWA) permissible exposure limit (PEL) of 50 mug/m\3\--or, alternatively, for employers in construction to meet the Table 1 requirements--and of complying with the standard's ancillary requirements. This cost assessment is based on OSHA's technological feasibility analysis presented in Chapter IV of the FEA; analyses of the costs of the standard conducted by OSHA's contractor, Eastern Research Group; testimony during the hearings; and the comments submitted to the docket as part of the rulemaking process.

    OSHA estimates that the standard will have a total cost of $1,029.8 million per year in 2012 dollars. Of that total, $370.8 million will be borne by the general industry and maritime sectors, and $659.0 million will be borne by the construction sector. Costs originally estimated for earlier years in the PEA were adjusted to 2012 dollars using the appropriate price indices. In general, all employee and supervisor wages (loaded) were from the 2012 BLS OES (Document ID 1560); medical costs were inflated to 2012 dollars using the medical services component of the Consumer Price Index; and, unless otherwise specified, all other costs were inflated using the GDP Implicit Price Deflator (Document ID 1666).

    All costs were annualized using a discount rate of 3 percent, which--along with 7 percent \26\--is one of the discount rates recommended by OMB. Annualization periods for expenditures on equipment are based on equipment life, while there is a 10-year annualization period for one-time costs. Note that the benefits of the standard, discussed in Section VII.G of this preamble and in Chapter VII of the FEA, were annualized over a 60-year period to reflect the time needed for benefits to reach steady-state values. Therefore, the time horizon of OSHA's complete analysis of this rule is 60 years. Employment and production in affected

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    industries are being held constant over this time horizon for purposes of the analysis. All non-annual costs are estimated to repeat every ten years over the 60-year time horizon, including one-time costs that recur because of changes in operations over time or because of new entrants that must comply with the standard.\27\ Table VII-10 shows, by affected industry in the sectors of general industry and maritime, annualized compliance costs for all establishments, all small entities (as defined by the Small Business Act and the Small Business Administration's (SBA's) implementing regulations; see 15 U.S.C. 632 and 13 CFR 121.201), and for all very small entities (those with fewer than 20 employees). Table VII-11 similarly shows, by affected industry in construction, annualized compliance costs for all entities, all small entities, and all very small entities. Note that the totals in these tables and all other tables in this chapter, as well as totals summarized in the text, may not precisely sum from underlying elements due to rounding.

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    \26\ Appendix V-D of the FEA presents costs by NAICS industry and establishment size category using, as alternatives, both a 7 percent discount rate and a 0 percent discount rate. In the sensitivity analysis presented in Chapter VII of the FEA, OSHA compares the estimated cost of the rule using the 3 percent discount rate to the estimated cost using these alternative discount rates.

    \27\ To the extent one-time costs do not recur, OSHA's cost estimates, when expressed as an annualization over a 10-year period, will overstate the cost of the standard.

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    OSHA's exposure profile, presented in Chapter III of the FEA, represents the Agency's best estimate of current exposures (i.e., baseline exposures). Except for compliance with Table 1 in construction, OSHA did not attempt to determine the extent to which current exposures in compliance with the new silica PEL are the result of baseline engineering controls or the result of other circumstances leading to low exposures. This information is not needed to estimate the costs of (additional) engineering controls needed to comply with the new PEL, but it is relevant to estimate the costs of complying with Table 1 in construction.

    For both construction and general industry/maritime, the estimated costs for the silica rule represent the additional costs necessary for employers to achieve full compliance with the new standard, assuming that all firms are compliant with the previous standard. Thus, the estimated costs do not include any costs necessary to achieve compliance with previous silica requirements, to the extent that some employers may not be fully complying with previously-applicable regulatory requirements. OSHA almost never assigns costs for reaching compliance with an already existing standard to a new standard addressing the same health issues. Nor are any costs associated with previously-achieved compliance with the new requirements included.

    Because of the severe health hazards involved, as well as current OSHA regulation, the Agency expects that the estimated 11,640 abrasive blasters in the construction sector and the estimated 3,038 abrasive blasters in the maritime sector are currently wearing respirators as required by OSHA's abrasive blasting provisions (29 CFR 1915.154 (referencing 29 CFR 1910.134)). Furthermore, an estimated 264,761 workers, including abrasive blasters, will need to use respirators at least once during a year to achieve compliance with the new silica rule in construction, and, based on the NIOSH/BLS respirator use survey (NIOSH/BLS, 2003, Document ID 1492), an estimated 56 percent of construction employees whose exposures are high enough that they will need respirators under the new rule currently use such respirators. OSHA therefore estimates that 56 percent of affected construction employees already use respirators in compliance with the respirator requirements of the final silica rule.

    Other than respiratory protection, OSHA did not assume baseline compliance with any other ancillary provision, even though some employers have reported that they currently monitor silica exposure, provide silica training, and conduct medical surveillance.

    The remainder of this chapter is organized as follows. First, unit and total costs by provision are presented for general industry and maritime and for construction. Following that, the chapter concludes with a summary of the estimated costs of the rule for all affected industries.

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    1. Engineering Controls

    a. General Industry and Maritime

    The engineering control section in Chapter V of the FEA covers OSHA's estimates of engineering control costs for general industry and maritime sectors. Oil and natural gas fracturing operations are addressed separately because OSHA used a different methodology to estimate engineering control costs for this application group. This section will address OSHA's overall methodology, the methodology for each category of costs (such as ventilation, housekeeping, conveyors), issues specific to small entities, and issues specific to the hydraulic fracturing industry. Within each of these discussions, this section summarizes the methodology used in the PEA to estimate engineering control costs, summarizes and responds to the comments on the PEA, and summarizes the changes made to the methodology used in the PEA for the FEA. Finally, the chapter presents OSHA's final estimates of engineering control costs.

    Introduction

    The PEA's technological feasibility analysis identified the types of engineering controls that affected industries or sectors would need in order to control worker exposures to at

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    or below the proposed PEL of 50 mug/m\3\. Through its contractor, Eastern Research Group (ERG), OSHA generated cost estimates for those controls using product and technical literature, equipment vendors, industrial engineers, industrial hygienists, and other sources, as relevant to each item. Wherever possible, objective cost estimates from recognized technical sources were used. Specific sources for each estimate were presented with the cost estimates.

    Table V-4 of the PEA provided a list of possible controls on an industry-by-industry basis and included details on control specifications and costs. The basic information for the types of controls needed was taken from the PEA's technological feasibility analysis. The following discussion explains how OSHA developed and used these estimates to prepare the aggregate costs of engineering controls presented in the PEA.

    In developing engineering control cost estimates for the PEA, OSHA made a variety of estimates about the size or scope of the engineering or work practice changes necessary to reduce silica exposures in accordance with the proposed rule. In some cases, OSHA estimated that employers would need to install all new engineering controls. In other cases, though, employers were expected to only need to add additional ventilation capacity or improve maintenance for existing equipment. In these cases, the costs were based on judgments of the amount of incremental change (either additional capacity or additional maintenance work) required per year. These estimates of the size or scope of the necessary engineering or work practice changes reflected representative conditions for the affected workers based on technical literature (including National Institute for Occupational Safety and Health (NIOSH) Health Hazard Evaluations), judgments of knowledgeable consultants and industry observers, and site visits. A detailed list of the specific costing assumptions and information sources for each control, grouped by job category or industry sector, was shown in PEA Appendix V-A, Table V-A-1.

    In order to estimate costs in a consistent manner, OSHA, in the PEA, estimated all costs on an annualized basis. For capital costs, OSHA calculated the annualized capital cost, using a three percent discount rate over the expected lifetime of the capital item. The capital costs for long-lasting capital items (such as ventilation system improvements) were annualized over ten years. OSHA estimated that, in the general industry and maritime sectors, any capital expenditure would also entail maintenance costs equal to ten percent of the value of the capital investment annually.

    General Methodology

    General Methodology: Per-Worker Basis and Treatment of Overexposures for Cost Calculations

    PEA Estimates

    OSHA, in the PEA, estimated control costs on a per-worker basis. Costs were related directly to the estimates of the number of workers needing controls (i.e., workers exposed over 50 mug/m\3\). OSHA divided engineering control costs into two categories: (1) Those only needed by establishments with employees exposed to levels of silica that exceeded the preceding general industry PEL of 100 mug/m\3\; and (2) those applicable to all establishments where workers were exposed to levels of silica above the proposed PEL (whether just above 50 mug/m\3\ or also above 100 mug/m\3\). It should be noted that the maritime sector has been subject to a different preceding PEL of 250 mug/m\3\. The PEA estimates were presented in the PEA cost analysis tables. The overwhelming majority of the costs (90 percent of all engineering control costs and 85 percent of costs associated with meeting the preceding PEL of 100 mug/m\3\) were associated with the second category (controls applicable to all establishments with exposures above the proposed or preceding PEL). Because OSHA is not accounting for the costs of controls necessary to reach the preceding PEL, the PEA focused on controls that may be needed to meet the new PEL. OSHA derived per-worker costs by examining the controls needed for each job category in each industry and dividing the cost of that control by the number of workers whose exposures would be reduced by that control. OSHA then multiplied the estimated per-worker control cost by the number of workers exposed between the proposed (new) PEL of 50 mug/m\3\ and the preceding PEL of 100 mug/m\3\. The numbers of workers in this category were based on the exposure profiles for at-

    risk occupations developed in the technological feasibility analysis in Chapter IV of the PEA and the estimates of the number of workers employed in these occupations were developed in the industry profile in Chapter III of the PEA. The exposure profile information was determined to be the best available data for estimating the need for incremental controls on a per-worker basis.

    In general, in the PEA, OSHA inferred the extent to which exposure controls were already in place from the distribution of overexposures among the affected workers. Thus, if most exposures in a facility were above the preceding PEL, OSHA broadly interpreted this as a sign of limited or no controls, and if most exposures were below the proposed (new) PEL of 50 mug/m\3\, this would be indicative of having adequate controls in place. OSHA calculated the costs of controls per exposed worker in each job category and assigned this cost to the total number of employees exposed between the proposed (new) PEL and the preceding PEL. For example, if a control cost $1,000 per year and covered 4 employees, the cost per employee would be $250 per year. If 100 employees in the job category were exposed between the preceding and proposed (new) PEL, then the total costs would be $250 times 100 employees or $25,000. No costs were estimated for employees currently exposed above the preceding PEL or below the proposed (new) PEL.

    OSHA determined that multiple controls would be needed for almost all jobs in general industry in order reduce exposures from baseline conditions to meeting the proposed (new) PEL of 50 mug/m\3\. Some of these controls cover a group of workers, while others might be individualized (such as daily housekeeping by each individual worker).

    Comments on the Per-Worker Basis and Proportionality of Costs

    URS, speaking for the American Chemistry Council (ACC), argued that OSHA's approach underestimated the costs of controls because it based costs on controls per worker instead of controls per facility (Document ID 2307, Attachment 8, p. 4). Since OSHA did not provide a distribution of exposures by facility or provide facility-specific information, URS used data in the record to create its own models to account for facility size. URS described its approach as follows:

    URS created three statistical binomial distributions of overexposed workers, one for each of the three facility sizes, using OSHA's estimate of the percentage of over-exposed workers for that job. The result was a binomial distribution curve indicating the percentage of overexposed workers for each job category for each size-specific ``model facility.''

    For each binomial distribution, the peak of the distribution curve centers on the average number of overexposed workers per facility for that job description according to OSHA's estimate (Document ID 2307, Attachment 8, p. 7).

    In taking this approach, URS erroneously assumed that the

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    distribution of overexposed workers per facility was random, as evidenced by its use of a binomial distribution to approximate overexposures per facility within each of three facility sizes (Document ID 2307, Attachment 8, p. 7). Examination of the spreadsheet URS provided shows that this approach approximately doubles the number of controls needed and, and for this reason, doubles the total cost of engineering controls (Document ID 2307, Attachment 26, Table 2A, URS Summary Worksheet).

    OSHA disagrees with URS's implicit conclusion that overexposures are random across facilities. It is not reasonable to assume that controls have no relation to exposure level as this approach assumes. As will be discussed later in the context of OSHA's treatment of the preceding PEL, the data underlying the exposure profile show that establishments with low exposures are much more likely to have controls in place than those with very high exposures.

    URS then assumed that if one worker in a job category is overexposed, then all controls listed by OSHA will be needed (Document ID 2307, Attachment 25, Engineering Costs). URS did not dispute that multiple controls would be needed for almost all jobs in general industry in order reduce exposures from baseline conditions to meeting the proposed (new) PEL of 50 mug/m\3\. The existence of multiple controls weakens the theory suggested by URS--that all controls are needed if even one worker is exposed at levels above the PEL--because as explained above, some controls are individualized while some protect groups of workers.

    The best possible approach to what engineering controls are needed might differ based on whether: (1) There are no controls for a job category in place at all and most workers are overexposed by a large margin; or (2) only some workers in a job category are overexposed by a small margin (i.e., a set of controls is already in place).

    In the first case, the most common approach would be to apply a relatively full set of controls, as explained in OSHA's technological feasibility analysis. This might start with enclosures and local exhaust ventilation (LEV), but, if exposures are high and the establishment is very dusty, it might also include initial cleaning or the introduction of ongoing routine housekeeping. In these situations, in which most employees are overexposed, OSHA estimated that the full set of controls listed in the technological feasibility analysis would be applied and, in these cases, there would be little difference in the results obtained using OSHA's approach and the results obtained using the approach suggested by URS.

    However, the approach to controlling silica exposures that OSHA believes to be typical when establishments are faced with the second situation would be quite different, and therefore different from what URS expected. Commenters from both labor (Document ID 4204, p. 40) and industry (Document ID 1992, p. 6) pointed out that when there are controls in place or only some workers are overexposed, the first step is to examine work practices. The AFL-CIO noted that exposures can be controlled through work practices, repositioning ventilation systems, and controlling fugitive emissions (carryover from adjacent silica emitting processes) (Document ID 4204, p. 40). Implementing these types of changes can be inexpensive. The principal cost of improving work practices may only be training or retraining workers in appropriate work practices. OSHA's proportional cost approach in the PEA may therefore overestimate costs for situations in which overexposures can be corrected with work practice changes because the Agency will have included costs for engineering controls when, in fact, none will be needed. The URS approach will always include the costs of all controls for a job category in any facility where anyone in a job category is overexposed, and will thus yield even higher estimates.

    As described in Chapter IV, Technological Feasibility, of the FEA, and summarized below, in situations in which there are LEV systems in place but the PEL is still not being met, employers would typically try many things short of removing the entire system and replacing it with a system with greater air flow velocities (and thus greater capacity and cost). The incremental solutions to controlling silica exposures include minor design modification of existing controls, better repair and maintenance of existing controls, adding additional LEV capacity to existing systems, improving housekeeping, modifying tools or machinery causing high levels of emissions, and reducing cross contamination.

    Some worksites might require a slightly different and readily modified design. For example, an OSHA special emphasis program inspection of a facility in the Concrete Products industry discovered that installing a more powerful fan motor, installing a new filter bag for the bag-filling machine LEV, and moving hoods closer to the packing operator's position reduced respirable dust exposure by 92 percent, to 11 mug/m\3\ (Document ID 0126, pp. 7-8). In an assessment of the Asphalt Roofing industry, NIOSH recommended repair and servicing of existing process enclosures and ventilation systems to eliminate leaks and poor hood capture but did not indicate that entirely new systems would need to be installed (Document ID 0889, pp. 12-13; 0891, pp. 3 and 11; 0890, p.14; 0893, p. 12).

    In other cases, better equipment repair and maintenance procedures can be the key to meeting the PEL when there are already controls in place. For example, as described in Chapter IV of the FEA, in the Concrete Products industry, OSHA obtained a sample of 116 mug/m\3\ for a material handler who operated a forklift to transport product between stations. The inspector noted that there were leaks in the silo bin chute and that some controls were not fully utilized. The report indicated that dust generated by various other processes in the facility was a contributing factor to the forklift operator's high level of exposure. In this case, the first course of action for the employer would be to correct the deficiencies in the existing systems. Similarly, at a site visit in the Paint and Coating industry, ERG monitored mixer operators' exposures and obtained results below the limit of detection while workers emptied 50-pound bags of powder into hoppers when dust control systems were working properly. These values are 95 percent lower than the 263 mug/m\3\ obtained during another shift, at the same plant, when the dust control systems malfunctioned (Document ID 0199, p. 9).

    In other cases, as pointed out by a foundry commenter, adding LEV capacity to existing systems for silica emissions not yet subject to any LEV control can be a good strategy for lowering exposures (Document ID 1992, p. 6). In one foundry, NIOSH investigators recommended installation of LEV over the coater and press areas, enclosure of the coating process, and/or repair and servicing of existing process enclosures and ventilation systems to eliminate leaks and poor hood capture (Document ID 0889, pp. 12-13; 0891, pp. 3 and 11; 0890, p. 14; 0893, p. 12).

    Various combinations of improved housekeeping, initial cleaning, and switching to High-Efficiency Particulate Air (HEPA) vacuums can also help employers meet the PEL. In the Structural Clay industry, professional cleaning in a brick manufacturing facility removed ``several inches'' of dust from floors, structural surfaces and equipment (Document ID 1365, pp. 3-19-3-20; 0571). These changes alone led

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    to a dramatic decrease in exposures, by as much as 90 percent, to below 50 mug/m\3\, for materials handlers. Similar results were observed for grinding operators (Document ID 0571). In one NIOSH evaluation, operators in a grinding area where good housekeeping practices were being implemented had substantially lower exposures than operators in a grinding room where the housekeeping practices were poor. The grinding room referred to as the ``C plant'' had 2 to 3 inches of settled dust on the floor and had an exposure result of 144 mug/m\3\. Grinding operators at the grinding room referred to as the ``B plant,'' where dust had been cleaned up, had substantially lower exposures (24 mug/

    m\3\) (Document ID 0235, pp. 6-7).

    Good housekeeping also increases the useful life of equipment. As discussed in Chapter IV of the FEA, dust clogs machines and reduces their useful life. As an example, regulating cotton dust was acknowledged to increase productivity by reducing down time. It also increased the useful life of looms (Document ID 2256, Attachment 4, p. 11). The Agency predicts that this is likely to be the case with silica controls as well. Dust being properly captured at the source can also result in cost savings in housekeeping activities because less dust needs to be cleaned up when it is captured at the source and not allowed to spread (Document ID 2256, Attachment 4, p. 11).

    In specific situations, there are a variety of other controls that may be useful. As discussed in the Technological Feasibility chapter of the FEA, Simcox et al. (1999) (Document ID 1146) found that Fabricators in the Cut Stone industry had a mean exposure of 490 mug/m\3\, which was reduced 88 percent to 60 mug/m\3\ when dry grinding tools used on granite were replaced or modified to be water-fed. Similar reductions were found at other facilities when wet grinding, polishing, and cutting methods were adopted (Document ID 1365, p. 11-20; 1146, p. 579). In the technological feasibility chapter, OSHA examined the work practices of cut stone splitters and chippers and found that a combination of wetting the floor at appropriate times, modifying ventilation directly from the top of the saws, and retrofitting splitting stations with LEV reduced exposures from a mean of 117 mug/

    m\3\ to a mean of 18 mug/m\3\, an 85 percent reduction (Document ID 1365, p. 11-22; 0180).

    Finally, in situations where there is cross contamination, employers may achieve the PEL for some workers without implementing any controls specific to that job category. As pointed out by the AFL-CIO, when this occurs, OSHA's costs may be overestimated (Document ID 4204, Attachment 1, p. 105).

    These examples show that in many situations, where there are already controls in place, or where exposures are only slightly above the PEL, the PEL can be met by a variety of mechanisms short of installing an entirely new set of controls. Since the record shows that, frequently, exposures can be controlled without installing new engineering controls, OSHA's approach of estimating costs based on the proportion of the workers exposed above the PEL is much more likely to be accurate than estimates based on URS's suggestion that all controls are needed whenever one worker is exposed above the PEL.

    The URS facility-based approach would require taking the costs of newly installing a full set of controls even if only one worker is exposed above the PEL. This approach assumes that (1) the existing exposure levels in a given facility have been achieved without the use of any controls; and (2) existing controls cannot be improved upon for less than the cost of installing an entirely new system of controls. These assumptions are unsupported by the URS comments and the nature of exposure control, as discussed above.

    OSHA, therefore, rejects URS's approach and is maintaining its per-

    worker basis for calculating costs for the FEA. Based on the evidence presented in this section, the Agency concludes that OSHA's proportional approach of assigning control costs to each worker based on the cost per worker of a complete set of controls is a better approach to commonly encountered exposure situations than to assume that any reading above the PEL triggers the need for a complete set of controls.

    The AFL-CIO argued that OSHA's proportional approach resulted in an over-estimation of costs because it involved adding costs for the exposed occupation wherever there was an overexposure, even when the overexposure was primarily or solely the result of cross contamination. The AFL-CIO recommended that OSHA ``identify operations which are unlikely to generate silica emissions, or background and bystander exposure measurements, and subtract those measured exposure levels from those operations which do emit silica'' (Document ID 4204, Attachment 1, pp. 31-32). OSHA has routinely included the elimination of cross contamination as a component of the controls needed for some job categories. As discussed in Chapter IV of the FEA, OSHA also believes that other controls will still be needed for many job categories in which cross contamination is common and as long as these additional controls are needed, overall costs will not decline as a result of controlling cross contamination. However, OSHA agrees that there may be situations in which correcting cross contamination alone would be sufficient. In this case, the commenter is right that OSHA may sometimes overestimate costs.

    General Methodological Issues--Comments on Costs Associated With Exposures Over the Preceding PEL

    Many commenters argued that OSHA should have attributed the costs of reaching the preceding PEL of 100 mug/m\3\ to this standard (Document ID 2307, Attachment 8b, p. 16; 2195, p. 33; 1819, p. 2; 2375, Attachment 2, p. 65; 2307, Attachment 1, p. 2; 2379, Attachment 2, p. 9). For example, Stuart Sessions of Environomics, commenting on behalf of the ACC, stated that of the workers currently exposed over 50 mug/

    m\3\, two-thirds are exposed over 100 mug/m\3\, and that OSHA erred in excluding the costs of reducing those exposures to 100 mug/m\3\ (Document ID 2307, Attachment C, pp. 2-3).

    OSHA's preliminary initial regulatory flexibility analysis (PIRFA) for the 2003 Small Business Advocacy Review (SBAR) panel included benefits and costs associated with future compliance with existing silica requirements on the basis that the rule would help improve compliance with the existing silica rules (OSHA, 2003a and 2003b) (Document ID 1685 and 0938, respectively). Upon further consideration, OSHA determined that a more fair and accurate measure of the benefits and costs of the proposed rule was to begin the analysis with a baseline of full compliance with existing requirements; OSHA has retained this approach for the final rule. The Agency offers three reasons in support of this approach. First, the obligation to comply with the preceding silica PEL is independent of OSHA's actions in this rulemaking. The benefits and costs associated with achieving compliance with the preceding silica rules are a function of those rules and do not affect the choice of PEL. The question before the Agency was whether to adopt new rules, and its analysis focused on the benefits and costs of those new rules. Second, the Agency's longstanding policy is to assume 100 percent compliance for purposes of estimating the costs and benefits of new rules, and to assume less than full compliance with the existing OSHA rules would be inconsistent with that policy. Finally, assuming full compliance with the existing rules is in keeping with standard OSHA practice in

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    measuring the incremental effects of a new rule against pre-existing legal obligations. Reliance on costs that assume full compliance with both the preceding and proposed (new) OSHA rules makes it easier to compare the two regulatory schemes.

    Some commenters also disagreed with the way OSHA attributed costs to employers whose workers were being exposed to silica at levels greater than the preceding PEL of 100 mug/m\3\ (Document ID 3251, p. 2; 3296, p. 2; 3333, p. 2; 3373, p.2; 2503, p.2; 2291, p. 16; 4209, p. 111). These commenters argued that OSHA did not attribute any costs to reaching 50 mug/m\3\ to employers whose employees were exposed above 100 mug/m\3\. They argued that OSHA instead assumed that the costs and controls necessary to reach 100 mug/m\3\ would also be sufficient to reach a level of 50 mug/m\3\, and as discussed above, that OSHA did not account for those costs because reducing exposures to the preceding PEL of 100 mug/m\3\ was already required before this rulemaking. The American Foundry Society (AFS) argued that OSHA reduced costs by two-thirds ``under the logic that employers must comply with the current PEL and the proposal does not add any existing obligation'' (Document ID 2379, Appendix 1, p. 10). AFS added that OSHA's underestimation of costs in this manner was particularly severe because OSHA used outdated data that showed more employees with exposures over 100 mug/m\3\, whereas more recent data would show fewer employees with exposures above 100 mug/m\3\ and more with exposures between 50 and 100 mug/m\3\. Had OSHA used this updated data, in AFS's estimation, the Agency would have identified more employers needing to install additional engineering controls and thus there would be additional costs that were not accounted for in the PEA (Document ID 2379, Attachment 3, pp. 9-10). ACC made a similar point, saying that as a result of OSHA's methodology, ``the exposure reduction costs for the estimated 81,000 workers now exposed above 100 mug/m\3\ are not taken into account by OSHA on either a full cost basis or an incremental cost basis'' (Document ID 2308, Attachment 9, pp. 2-3).

    In addition URS, among others, argued that ``OSHA fails to account for the non-linear costs associated with each incremental reduction in silica concentrations,'' meaning that URS believed that it is more costly to achieve additional reductions in exposure as exposures are lowered. For example, according to URS's contention, it would be more costly to reduce exposures from 75 mug/m\3\ to 50 mug/m\3\ than from 125 mug/m\3\ to 100 mug/m\3\ (Document ID 2308--Attachment 8, p. 11; 2291, p. 16; 4209, p. 11; 2307, Attachment 2, pp. 181-182; 2379, Attachment 2, p. 9; 3487, p. 13).

    OSHA has several responses to these criticisms. In response to the criticism that OSHA overestimated the number of workers with exposure levels above 100 mug/m\3\ as a result of using outdated data, the Agency has updated the exposure profile used to develop the final analysis of costs. This update is described previously in Chapters III and IV of the FEA. As a result of this update, OSHA found that, in the aggregate, the percentage of workers in general industry and maritime exposed to silica levels between 50 mug/m\3\ and 100 mug/m\3\ rose from 33 percent as estimated in the PEA to 42 percent. And, as the commenters noted would be the case, the percentage exposed at levels above 100 mug/m\3\ fell from 67 percent to 58 percent. OSHA has updated this analysis to incorporate these data and has estimated costs for these additional workers whose exposures fall between 50 mug/m\3\ and 100 mug/m\3\. The revised distribution also shows that of those workers with exposures above the new PEL, 41 percent are exposed between the new PEL and the preceding general industry PEL with an average exposure level of 70 mug/m\3\, 29 percent are exposed between the preceding PEL and 250 mug/m\3\ with an average exposure level of 156 mug/m\3\, and 30 percent are exposed above 250 mug/m\3\ with an average exposure level of 485 mug/m\3\. Where an industry submitted more recent exposure data or information about exposure distributions within their industry, OSHA was able to show that its final exposure distribution was roughly equivalent (see Chapter IV of the FEA).

    The technological feasibility analysis (presented in Chapter IV of the FEA) describes the controls necessary for reducing exposures from the highest levels observed in an industry's exposure profile to the new PEL. In all application groups except two (asphalt paving products and dental laboratories), the highest observed exposures were above the preceding PEL. With the exception of hydraulic fracturing,\28\ the technological feasibility analysis did not distinguish between the controls necessary to meet the preceding general industry PEL of 100 mug/m\3\ and those necessary to meet the new general industry PEL of 50 mug/m\3\. Instead, the technological feasibility analysis simply listed the controls necessary for those employers whose employees had the highest baseline exposures to significantly reduce exposures and, in most operations, meet the new PEL.

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    \28\ Due to an unusually rich data set, and the great similarity of different fracturing operations, both with respect to the equipment used and the current levels of control, OSHA was able to estimate which controls are necessary to go from an uncontrolled situation to the preceding PEL and which are necessary to get from the preceding PEL to the new PEL in the hydraulic fracturing industry.

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    It was not necessary for OSHA to distinguish between controls necessary to achieve the preceding PEL and those necessary to achieve the new PEL in order to demonstrate the technological feasibility of achieving a PEL of 50 mug/m\3\. Such a distinction would have been difficult because, from a baseline of uncontrolled exposures, the controls necessary to meet the preceding and new PELs are difficult to distinguish. For example, if there are two different controls necessary to fully meet the new PEL, then it is logically possible that two different establishments may achieve an exposure level at or below the preceding PEL in different ways. One establishment may have excellent housekeeping but poorly maintained LEV. Another may have well maintained LEV but poor housekeeping. For individual cases, there is not a simple demarcation of which controls of the total set of controls are necessary to achieve the new PEL when only the exposure level and not the controls already in place are known. Nor, as discussed above, is it the case that a control, once installed, will always provide identical protection. Two otherwise equal facilities may have the same installed controls but different exposure levels because of the quality of the maintenance of the system.

    For the purposes of costing engineering controls for general industry and maritime in the PEA, OSHA assigned all of the costs for meeting a PEL of 50 mug/m\3\--including the costs of controls necessary to meet the preceding PEL of 100 mug/m\3\--to all workers with exposure levels between 50 mug/m\3\ and 100 mug/m\3\. However, OSHA assigned no costs in the PEA to employees whose exposures exceeded the preceding PEL. This approach would be accurate for both those above and below the preceding PEL only if the exact same controls would be needed to control exposures in both situations and these controls would always yield an exposure level below the preceding PEL. However, as discussed in the previous section on proportionality of costs, OSHA has determined that this is not typically the case. There exist multiple kinds of controls and the actual application and operation of the control can differ. The approach applied in the PEA applied more controls than will typically be needed where exposures are below the preceding PEL and thus overestimates costs in these situations, but then assigns no costs for achieving

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    the new PEL where exposures are above the preceding PEL. In the latter situation, it can reasonably be expected that, in most cases, some costs would be incurred to meet the new PEL even after the preceding PEL is met and therefore the PEA methodology underestimated costs in those situations. Although these over- and under-estimates are partially offsetting, OSHA acknowledges that any over-estimates of cost do not necessarily offset the potential under-estimates of costs.

    OSHA has therefore decided to adopt an approach to the estimation of costs different from that adopted in the PEA. In the FEA, OSHA relied on data available in the rulemaking record to both correct the overestimate of costs for those below the preceding PEL and, as many industry commenters urged, estimate the costs necessary to meet the preceding PEL as well as the new PEL for those above the preceding PEL.

    To be clear, these data still do not enable OSHA to distinguish between the exact controls needed to get from uncontrolled exposures to the preceding PEL and those needed to get from the preceding PEL to the new PEL on an industry-by-industry and occupation-by-occupation basis. However, the data do enable OSHA to show that the majority of the costs of controlling silica exposures are incurred in order to reduce exposures from uncontrolled levels to the preceding PEL. OSHA will then assume that 50 percent of the costs incurred will be to implement the controls necessary to get from the uncontrolled situation to the preceding PEL and 50 percent to implement the controls necessary to go from the preceding PEL to meeting the new PEL. If, in fact, a majority of the costs are incurred in order to reduce exposures to the preceding PEL, the assumption that attributes 50 percent of costs to going from the preceding PEL to the new PEL will overestimate the true costs for establishments with exposures at the preceding PEL or between the preceding PEL and the new PEL.

    In order to assess whether the majority of the costs are necessary to meet the preceding PEL, OSHA first examined what kinds of exposures are associated with the uncontrolled situations that served as the starting point for the estimates of needed controls in the technological feasibility analysis. The average level of exposure across all of general industry for employees with exposure exceeding the preceding PEL is over 300 mug/m\3\. Thus, on average, across all industries the uncontrolled situation involves high levels of exposure, commonly more than 3 times the preceding PEL.\29\

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    \29\ To check that this was not the result of a very high exposures for a small number of employees or industries, OSHA examined the exposure profile presented in Table III-9 and found that in only 4 industries (with 1.1 percent of all employees exposed above the preceding PEL) were there no exposures above 250 mug/

    m\3\.

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    In general, to reduce exposures from over 2.5 times the preceding PEL to the preceding PEL, employers would have to implement some measure or measures, and those measures would be the ones that provide the greatest reduction in silica exposures and therefore control most of the silica exposures in the facility. In most cases this will be a working LEV system or some form of worker isolation. Measures like improved housekeeping cannot reduce exposures from the levels observed in uncontrolled exposure situations to the preceding PEL. OSHA reviewed industry-by-industry and occupation-by-occupation cost estimates for engineering controls and found that, on average 63 percent of the costs were for LEV, 23 percent were for housekeeping, and 16 percent were for other controls, most commonly wet methods (based on OSHA, 2016). In many cases, where wet methods were applicable, wet methods represented the majority of the costs and there were not significant LEV costs. As a result, 79 percent of the costs of controls, on average, are attributable to either wet methods or LEV. The combination of LEV or wet methods with some improvement in housekeeping (though not the improvements necessary to meet the new PEL) will constitute the majority of costs for virtually all occupational categories. Some improvement in housekeeping will typically also be required to meet even the preceding PEL.\30\ While employers can probably meet the preceding PEL with less than ideally maintained LEV systems, improvements in maintenance will not reverse the conclusion that the majority of the costs are incurred to meet the preceding PEL. This is the case because on average 63 percent of engineering control costs are necessary to reach the preceding PEL and some housekeeping costs will also be necessary, leaving a significant percentage of expenditures above 50 percent of the costs available for improved maintenance.

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    \30\ For example, in several industry sectors where workers are currently manually dumping silica-containing materials, the use of automated and ventilated dumping stations is needed to reduce exposures from over 250 mug/m\3\ to below the preceding PEL. However, once these controls are installed and in use, final exposures are often below the limit of detection or less than 12 mug/m\3\--well below the new PEL (see technological feasibility chapter for paint and coatings). However, to maintain these exposures below the new PEL, these industry sectors will need to ensure that ventilation systems are properly maintained and will need sufficient housekeeping to ensure against build-ups of dust.

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    To confirm the findings of this cost-spreadsheet-based analysis of where the majority of the costs are incurred, OSHA reviewed industries where good data are available on controls in both uncontrolled situations and situations with exposures between the new and the preceding PEL. OSHA examined the exposures and controls in eight ferrous sand casting foundry facilities. In these eight facilities, four had relatively few workers exposed above 50 mug/m\3\, and the other 4 had many exposures over 100 mug/m\3\. OSHA found that those facilities with most exposures over 100 mug/m\3\ generally had little or no LEV (relying instead on general ventilation), poor housekeeping, no enclosures for workers, and poor maintenance. The foundries where silica dust was better controlled generally had working LEV systems, good housekeeping that kept surfaces free of silica dust, and good maintenance practices. This indicates that LEV and some housekeeping are essential to meeting the preceding PEL. OSHA also examined data on all exposures with control descriptions. These data showed that exposures above 250 mug/m\3\ occurred in uncontrolled situations or situations in which controls, though installed, were not in use. In situations where exposures were between the preceding and new PELs, most exposures showed some controls in place, normally LEV, but not all controls recommended. In some cases there were no controls in place. These generally represented situations in which exposures were much lower than the typical uncontrolled situations and such facilities would not normally need the full controls necessary to go from very high levels of exposure to the new PEL (See Exhibit: Descriptions of Control, available in Docket OSHA-2010-0034 at www.regulations.gov).

    Based on these findings, OSHA determined that the majority of costs are incurred in order to implement controls necessary to get from an uncontrolled situation to the preceding PEL. However, OSHA developed cost estimates for engineering controls based on the conservative assumption that 50 percent of the total costs of going from an uncontrolled situation to the new PEL is incurred in order to reach the preceding PEL and the remaining 50 percent are incurred to reach the new

    Page 16474

    PEL.\31\ For example, in the cut stone industry 63 percent of those exposed above the new PEL are also above the preceding PEL and 37 percent are below the preceding PEL but above the new PEL. The total cost to the cut stone industry of going from uncontrolled exposure to the new PEL is $17.7 million. With OSHA's assumption that half of the costs of going from an uncontrolled situation to the new PEL is incurred in order to reach the preceding PEL, then the cost for those employers with employees exposed above the preceding PEL would be 63 percent of $17.5 million times 0.5, which equals $5.5 million. The cost for those below the preceding PEL would be 37 percent of $17.7 million times 0.5, which equal $3.3 million. The total cost of going from the preceding PEL to the new PEL in the cut stone industry is therefore the sum of these two calculations: $8.8 million. This will overestimate the costs of reaching the new PEL, given the majority of the costs are incurred to implement controls necessary to reach the preceding PEL.\32\

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    \31\ This approach was not applied to the two industries, dental laboratories and asphalt paving materials, where the exposure profile showed that there were no exposures above the preceding PEL.

    \32\ OSHA also notes that this approach shows rising incremental costs of control, which is consistent with some comments. This is because 50 percent of the costs are estimated to be incurred to go from levels of over 250 mug/m\3\ to 100 mug/m\3\ and equal costs are estimated to be incurred to go from 100 mug/m\3\ to 50 mug/

    m\3\.

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    As presented in more detail below, this approach results in a total annualized cost estimate for general industry and maritime engineering controls of $225 million. Fortunately, this cost estimate is not highly sensitive to the allocation percentage chosen. Each decrement of 5 percentage points changes the engineering control costs by approximately 5.5 percent. Thus, for example, if 65 percent of the costs are necessary to go from the preceding PEL to the new PEL, then the annualized cost estimate for engineering controls would rise to $261 million per year.\33\

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    \33\ A value of 100 percent would be totally implausible as it would imply that all establishments currently far above the preceding PEL could achieve that PEL without cost. Put another way, this would be equivalent to saying that, if OSHA had decided to adopt the alternative PEL of 100 mug/m\3\ (i.e., the same as the preceding general industry PEL), as some employer groups recommended, any employers currently above that PEL--regardless of how far above the PEL they were--would be able to meet a PEL of 100 mug/m\3\ without implementing any new engineering controls.

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    Accounting for Costs of Downtime

    Some commenters suggested that OSHA failed to account for the downtime that installing engineering controls or performing an initial through cleaning would require (e.g., Document ID 2368, p. 13 for engineering controls; Document ID 2379, Attachment 2, p. 16 for initial thorough cleaning).

    Almost all firms need downtime occasionally in order to perform general maintenance, inventory, or other tasks. In the final rule, OSHA has extended the compliance date for general industry from one year to two years. This will allow almost all employers to schedule work that might require downtime to install, improve, or maintain controls that they determine are necessary to meet the new PEL or to perform the initial thorough cleaning at times when they would already need scheduled downtime for other purposes. Therefore, OSHA has determined that there will be no additional costs incurred for downtime in order for employers to install engineering controls or to perform the initial thorough cleaning.

    Technological Change

    One commenter, Dr. Ruth Ruttenberg, testifying for the AFL-CIO, argued that OSHA had overestimated costs by failing to consider technological change:

    Technological improvements--both engineering and scientific--are constantly occurring, especially when the pressure of a pending or existing regulation provide a strong incentive to find a way to comply at a lower cost. . . . These improvements are well-documented following the promulgation of rules for vinyl chloride, coke ovens, lead, asbestos, lock-out/tag-out, ethylene oxide, and a host of others (Document ID 2256, Attachment 4, p. 2).

    Dr. Ruttenberg recognized that OSHA, in the PEA, already predicted some ``technological and cost-saving advances with silica,'' such as expanding the use of automated processes and developing more effective bag seals, but criticized OSHA for not accounting for those cost savings in its analysis:

    Technological improvements are as sure a reality--based on past experience and academic research--as overestimation of cost and underestimate of benefits are in an OSHA regulatory analysis. More than 40 years of OSHA history bear this out (Document ID 2256, Attachment 4, p. 3).

    When promulgating health standards, OSHA generally takes an approach in which cost estimates and economic feasibility analyses are based on the technologies specified in the technological feasibility analysis. This is a conservative approach to satisfying OSHA's legal obligations to show economic and technological feasibility. As a result, the Agency does not account for some factors that may reduce costs, such as technological changes that reduce the costs of controls over time and improvements in production that reduce the number of employees exposed. As pointed out in the PEA, and from the examples described in the ``Total Cost Summary'' at the end of this chapter, some past experience suggests that these factors tend to result in OSHA's costs being overestimated.\34\ OSHA considers the primary purpose of the cost estimate to be to provide a basis for evaluating the economic feasibility of the rule, and OSHA has determined that for this rulemaking, feasibility is most accurately demonstrated by using an approach that does not account for the potential impacts of future technological changes.

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    \34\ On the other hand, there is supplemental evidence from Harrington et al. (2000) Harrington, Winston, Richard D. Morgenstern and Peter Nelson. ``On the Accuracy of Regulatory Cost Estimates.'' Journal of Policy Analysis and Management, 19(2), 297-

    322, 2000 that OSHA does not systematically overestimate costs on a per-unit basis, and that the reason for overestimation of costs at the aggregate level has been a combination of difficulty with establishing baseline conditions and noncompliance. Nevertheless, several examples of OSHA's overestimation of costs reported in the article are due to technological improvements.

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    General Methodological Issues: Number of Workers Covered by a Control PEA Estimates

    The cost calculations in the PEA included estimates of the number of workers whose exposures are controlled by each engineering control. Because working arrangements vary within occupations and across facilities of different sizes, there are no definitive data on how many workers are likely to be covered by a given set of controls. In many small facilities, especially those that might operate only one shift per day, some controls will limit exposures for only a single worker. Also, small facilities might have only one worker in certain affected job categories. More commonly, however, and especially in the principal production operations, several workers are likely to derive exposure reductions from each engineering control.

    The PEA relied on case-specific judgments of the number of workers whose exposures are controlled by each engineering control (see Table 3-3 in ERG, 2007b, Document ID 1608). The majority of controls were estimated to benefit four workers, based on the judgment that there is often multi-shift work and that many work stations are shared by at least two workers per shift. The costs of some types of equipment that protect multiple employees, such as HEPA vacuums, were spread over larger groups of employees (e.g., six to eight workers). In the PEA, the average number of workers affected represented

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    an average across all establishments, large and small.

    Comments and Responses

    Some commenters questioned OSHA's estimate of the number of workers whose exposures could be controlled per newly added or enhanced control. OSHA's PEA most commonly estimated that four workers would have their exposures reduced for each new or enhanced engineering control. Dr. Ronald Bird, testifying for the Chamber of Commerce, argued that OSHA's estimates were simply arbitrary assumptions (Document ID 2368, p. 14). Stuart Sessions, testifying for the ACC, argued that the use of a single standard crew size of four led OSHA to underestimate costs and economic impacts for smaller establishments, at which, he argued, ``there are virtually never as many as four overexposed workers in any job category, and it is simply impossible that one application of a package of controls in this situation could protect as many as 4 overexposed workers on average'' (Document ID 4231, Attachment 1, p. 6).

    The approach OSHA used was intended to represent the average number of employees affected by a given set of controls. Larger establishments may have more than four workers whose exposures are reduced by a single control, and smaller establishments may have fewer than four. However, OSHA agrees that this approach may result in an underestimate of costs for the smallest establishments. Because it is particularly important to consider the costs to the smallest establishments, OSHA has reduced the number of employees whose exposures are reduced per control by half for establishments with fewer than twenty employees, so that in those small establishments a given control is assumed to reduce exposures for two workers instead of four as assumed in the PEA. Because larger establishments may have greater numbers of employees whose exposures are reduced per control, this change may result in an overall overestimation of costs. (In the PEA, the overestimation of costs for larger facilities was partially offset by the underestimation of costs for smaller establishments. This is no longer the case in the FEA.) OSHA nevertheless believes the revised approach used in the FEA is better than the approach used in the PEA for purposes of capturing economic impacts on smaller establishments, even though it may result in aggregate costs being overestimated.

    Variability

    Some commenters argued that both OSHA's technological feasibility and cost analyses were flawed because OSHA neglected to address the day-to-day variability of exposure measurements. By failing to address the issue of variability, these commenters argued, OSHA grossly underestimated the costs of engineering controls. These commenters reported that silica exposures would have to be controlled to levels considerably lower than the proposed (new) PEL in order to account for the variation in exposures across jobs and from day to day (e.g., Document ID 2307, Attachment 2, p. 202; 2308, Attachment 7, p. 2; 2308, Attachment 8, p. 6; 2379, Attachment 4, p. 1; 2291, p. 11; 2195, pp. 26-27; 2503, p. 2; 2222, Attachment 1, p. 1). For example, in response to a written question about the activities in which employers were able to achieve the proposed (new) PEL ``most of the time,'' AFS objected to the premise of the question, noting that ``several foundries have received citations for exposures above the current PEL on operations or tasks for which the proposed PEL is achieved most of the time'' (Document ID 2379, Appendix 1, p. 18). AFS argued that OSHA's non-

    compliance model of enforcement requires employers to reduce average exposures to half the PEL in order to have confidence that exposures will never exceed the PEL (Document ID 2379, Appendix 2, p. 29). The Asphalt Roofing Manufacturing Association (ARMA) made a similar point and said that the majority of asphalt roofing plants operated by its members have some exposures over the PEL of 50 mug/m\3\, even if it's a ``relatively small incidence'' (Document ID 2291, p. 11).

    Both AFS and ARMA offered estimates of the magnitude of this variability by measuring the statistical variance of exposures. AFS stated that to assure 84 percent confidence in compliance with the preceding PEL, the mean exposures in some specific jobs in specific foundries would need to be below half that PEL, and that the ``mean level necessary to achieve the 95 percent confidence of compliance could not be determined but is significantly below one half the PEL'' (Document ID 2379, Appendix 1, p. 23).

    ARMA examined the distribution of silica exposures in over 1,300 samples from 57 asphalt roofing facilities. These data showed that even though the median exposures for all jobs were below the new action level of 25 mug/m\3\, a total of 9 percent of all samples were above the new PEL of 50 mug/m\3\ (Document ID 2291, p. 5, Table 1). ARMA also provided an estimate of the ``lowest strictly achievable level'' (meaning a level not to be exceeded more than 5 percent of the time) which varied by job classification from 67 to 310 mug/m\3\ (Document ID 2291, p. 9, Table 2).

    One serious problem with the ARMA analysis is that the discussions of variability and the estimates of mathematical variance are based on results either from different facilities with potentially different levels of controls or from all job categories within one facility. The key issue for assessing the importance of variability is the variance within a given job category in a specific establishment with specific controls. The methodology employed is such that even if individual job categories or individual facilities had no variance, pooling data across facilities would create variance.

    ARMA estimated that sufficiently controlling variation would require investment in capture vents, duct work, and dust collection systems costing up to $2.1 million each in initial costs per manufacturing line (Document ID 2291, p. 12). AFS did not provide a cost estimate solely for sufficiently controlling variation.

    The AFL-CIO disagreed with industry's arguments and instead argued that the best way to reduce variability was not simply to add additional engineering controls because, as explained earlier in the discussion of URS's comments on the per-worker cost basis, overexposures are not random:

    The worker-to-worker variation is explainable and controllable: Workers use different methods, they may take different positions relative to ventilation systems, they may use different work practices, and they may be subject to fugitive emissions (carryover from adjacent silica emitting processes). These differences in conditions can be observed by the industrial hygienist collecting the air sample, compared to exposure levels, and changed. Day-to-day variation for the same worker is caused by variation in materials, ventilation systems, production rate, and adjacent sources showing such variation. Sometimes these variations can be large, based on breakdowns of ventilation, process upsets and blowouts (Document ID 4204, p. 40).

    OSHA's enforcement policies are discussed in Chapter IV of the FEA and in this preamble. Variability of exposures is potentially a cost issue when there are technologically feasible controls that have costs not otherwise accounted for that could further reduce environmental variability. If it is not technologically feasible to reduce variability then there will be no further costs. For example, if an employer has

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    installed all feasible controls, there are no additional costs for engineering controls because there are no additional controls to purchase, regardless of variability. On the other hand, an employer who has a median exposure level of 80 percent of the PEL with frequent excursions above and who could feasibly reduce variability would be required to do so.

    As noted above, those (AFS, ARMA) who argued that OSHA had underestimated costs by failing to account for exposure variability, in general, assumed that the best approach to reducing variability would be to increase the levels of LEV to reduce the average exposure level to half of the PEL or less, without examining the origin of the variability.

    OSHA agrees with the AFL-CIO that variability in exposure is likely controllable by examining the origins of the variability. One origin is poor work practices. To improve work practices, employers could observe work practices when monitoring takes place; determine which work practices are associated with high exposures; and modify those work practices found to lead to high exposures. Variability can also be the result of a failure of controls not functioning properly, either resulting from sudden failures or from gradual deterioration of performance over time. The latter can be prevented by good maintenance.

    Both in its cost assessment for the proposal and in the modifications made for this final rule, OSHA has taken account of the costs necessary to reduce unusual and exceptionally high exposure levels and thus reduce some sources of variation. As discussed in the cost of ancillary provisions, OSHA has estimated costs for exposure monitoring that include the time for observation of the worker. OSHA has also estimated costs for training to assure good work practices, and has increased the estimated length of training in general industry to ensure that the time is sufficient for training on work practices. In this section, OSHA has costed LEV, LEV maintenance, and the need for replacement LEV to assure that the LEV will function properly. OSHA has therefore already accounted for a variety of costs associated with steps that can be taken to reduce variability in exposures.

    Substitution of Low- or Non-Silica Inputs

    PEA Estimate

    For several industries, employers might lower silica exposures by substituting low- or non-silica inputs for existing inputs. While this option can be an extremely effective method for controlling silica exposures in many industries, OSHA did not cost this option in the PEA. OSHA determined that there were often complicating factors that restricted the potential for broad substitution of non-silica-

    containing inputs for silica-containing inputs throughout the affected industries. It is possible that the same product quality cannot be maintained without using silica. Some products made with substitute ingredients were judged to be inferior in quality and potentially not viable in the market. In addition, a substitute silica ingredient might introduce adverse health risks of its own. Further, in several instances, the availability of reasonably inexpensive alternative non-

    silica ingredients was well known but the alternative was not selected as a control option by most firms. In light of these concerns, OSHA decided not to include the option of non-silica substitutes in estimating the cost of the proposed rule.

    Comments and Responses on Substitution

    Some commenters complained that OSHA's analysis did not account for the costs of substitution (Document ID 2264, Attachment 1, p. 27; 2379, Attachment 2, p. 6; 3485, p. 25; 3487, p. 17).

    OSHA considered the comments on the issue but has decided to adhere to the approach taken in the PEA. OSHA did not take account of the costs of substituting other substances for silica, because, while such substitution might have substantial benefits and avoid the need for engineering controls, OSHA determined that, in most situations, substitution is not the least costly method of achieving the proposed or new PEL (Document ID 2379, Attachment 2, p. 6). As a result, OSHA's final cost analyses do not account for the possibility that firms would choose to substitute for substances other than silica. To the extent that substitutes are the least costly solution in some situations, OSHA has overestimated the costs.

    Cost of Air Quality Permit Notification

    The Agency received comments suggesting that foundries and other manufacturing plants would be required by the Environmental Protection Agency (EPA), or other federal or state environmental authorities, to incur an administrative cost to ensure their systems are compliant with relevant EPA regulations. Commenters expressed concern that the permitting process itself could be a major undertaking, made worse by difficult compliance deadlines. Given that the final rule provides extra time for planning and permitting, OSHA has examined the potential impacts of the new rule and finds that the commenters are overstating the potential for such costs. The argument for significant permitting costs was typically combined (e.g., Document ID 2379, Appendix 3) with an argument that the Agency underestimated the amount of ventilation required to comply with the final rule; comments on ventilation requirements are dealt with in great detail elsewhere in this chapter.

    Upon investigation, while OSHA agrees that it would be appropriate to recognize an administrative burden with respect to the interfacing environmental regulations, the Agency believes that many of the commenters' concerns were overstated. First, many control methods needed to comply with the final rule will not require alterations to existing ventilation systems. As discussed earlier in Chapter V of the FEA, work practices, housekeeping and maintenance are important components in controlling exposures; in many cases existing ventilation, as designed and permitted with the environmental authority, is adequate, but needs to be maintained better. In addition, most establishments, particularly smaller ones, will continue to have particulate emissions levels that fall below the level of EPA permit requirements. In the case of large facilities that do not, the changes will be on a sufficiently small scale that they will not require elaborate repermitting, but will only require minor incremental costs for notifying the environmental authorities, or in some cases, submitting a ``minor'' permit (see http://www2.epa.gov/nsr and http://www2.epa.gov/title-v-operating-permits). Taking into account the preceding silica PEL and the estimate that baghouses will capture 99 percent of silica emissions (Document ID 3641, p. VII-19), OSHA concludes that it is unlikely that facilities will encounter a need for significant air permit modifications.

    The Agency recognizes, however, that there will be minor incremental costs for notifying environmental authorities. While many establishments in the United States may have no requirement to do so, the Agency has conservatively assumed that all establishments with twenty or more employees in most industries will need to dedicate a certain amount of time to preparing a one-time notification to environmental authorities to ensure that their air permits accurately reflect current operating conditions. OSHA has determined that small establishments

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    would generally lack the large scale industrial facilities requiring permits, and that the few that might require such permits would be balanced out by the likely inclusion of medium establishments that do not actually require permits for their emissions. The industries excluded were those that generally lack large scale industrial facilities, or that do not produce a concentrated, as opposed to diverse or unconsolidated, emission source. The excluded industries were hydraulic fracturing, shipyards, dental equipment and labs, jewelry, railroads, and landscaping.

    To allow for adequate administrative time for creating and submitting the notification, at those facilities that could potentially incur costs, OSHA allocated 20 hours to establishments with 20 to 499 employees and 40 hours to establishments with 500 or more employees. A manager's loaded hourly wage rate of $74.97 was applied to estimate the cost to employers (BLS, OES, 2012, Document ID 1560). The costs per establishment were estimated at approximately $1,500 per medium establishment and $3,000 per large establishment. Because both new permit applications and permit modifications are minor administrative chores, OSHA's cost estimates are sufficient to cover either case.

    Costs for Specific Engineering Controls

    Ventilation Costs

    PEA Estimates

    In the PEA, OSHA determined that at many workstations, employers needed to improve ventilation to reduce silica exposures. The cost of ventilation enhancements estimated in the PEA generally reflected the expense of ductwork and other equipment for the immediate workstation or individual location and, potentially, the cost of incremental capacity system-wide enhancements and increased operating costs for the heating, ventilation, and air conditioning (HVAC) system for the facility.

    In considering the specific ventilation enhancements for given job categories the PEA estimated the type of LEV and the approximate quantity in cubic feet per minute (cfm) of air flow required to reduce worker exposures.

    To develop generally applicable ventilation cost estimates for the PEA, a set of workstation-specific and facility-wide ventilation estimates were defined using suggested ventilation approaches described in the American Conference of Governmental Industrial Hygienists (ACGIH) Industrial Ventilation Manual, 24th edition (Document ID 1607). With the assistance of industrial hygienists and plant ventilation engineering specialists, workstation estimates of cfm were derived from the ACGIH Ventilation Manual, and where not covered in that source, from expert judgements for the purpose of costing LEV enhancements (Document ID 1608, p. 29).

    Over a wide range of circumstances, ventilation enhancement costs, which included a cost factor for HEPA filters and baghouses, where needed, varied from roughly $9 per cfm to approximately $18 per cfm (Document ID 1608, p. 29). Because of a lack of detailed data to estimate the specific ventilation installation costs for a given facility, an estimate of the likely average capital cost per cfm was used and applied to all ventilation enhancements. Based on discussions with ventilation specialists, $12.83 per cfm was judged to be a reasonable overall estimate of the likely capital costs of ventilation enhancements (Document ID 3983, p. 1).

    OSHA applied the per-cfm capital cost estimate to estimated cfm requirements for each workstation. By using the unit value of $12.83 per cfm, the cost estimates for each ventilation enhancement included both the cost of the LEV enhancement at the workstation and the contribution of the enhancement to the overall facility ventilation system requirements. That is, each ventilation enhancement at a workstation was expected to generate costs to the building's general ventilation system either by requiring increased capacity to make up for the air removed by the LEV system or to filter the air before returning it to the workplace.

    For operating costs, engineering consultants analyzed the costs of heating and cooling system operation for 12 geographically (and therefore, climatologically) diverse U.S. cities. The analysis, presented in Table 3-2 in the ERG report (Document ID 1608, p. 30), showed the heating and cooling British Thermal Unit (BTU) requirements for 60-hours-a-week operation (12 hours a day, Monday through Friday) or for a continuous 24-hour-a-day, year-round operation, with and without recirculation of plant air. Facilities that recirculate air have much lower ventilation system operating costs because they do not need to heat or cool outside air to comfortable inside temperatures.

    In the PEA, ventilation operating costs were based on a weighted average of the costs of four operating scenarios: (1) No recirculated air, continuous operation; (2) no recirculated air, operating 60 hours per week; (3) recirculated HEPA filtered air, continuous operation; and (4) recirculated HEPA filtered air, operating 60 hours per week. These scenarios were chosen to reflect the various types of operating system characteristics likely to be found among affected facilities. The weights (representing the share of total facilities falling into each category) and operating costs per cfm for each of these scenarios are shown below in Table VII-11-1:

    Page 16478

    GRAPHIC TIFF OMITTED TR25MR16.051

    The national average annual operating cost per cfm was estimated to be $2.22. This estimate was a weighted average of the operating costs for facilities that recirculate air and those that require make-up air. The operating costs for HEPA-filter recirculated air were estimated at $0.50 per cfm for facilities operating 60 hours per week and $1.40 per cfm for those continuously operating 24 hours per day. The operating costs for facilities that do not recirculate air were $5.78 per cfm for those operating 60 hours per week and $15.55 per cfm for those operating continuously. In generating these estimates, it was judged that 80 percent of facilities would recirculate airflow and 20 percent would not, and that 75 percent within each group operate for 12 hours per day on weekdays, with the remainder operating continuously, year-

    round, for 24 hours a day.

    OSHA also added a maintenance factor to the operating cost estimates, which was 10 percent of the capital cost investments of $12.83 per cfm for ventilation systems. As a result, the total annual costs per cfm, excluding annualized capital costs, were estimated to be $3.50 (weighted average operating costs of $2.22 plus annual maintenance costs of 10 percent of $12.83).

    Underlying the cost results was the assumption that, over the course of the proposed one-year compliance period for engineering controls, employers would schedule installation of ventilation to minimize disruption of production, just as they would with any modification to their plants.

    Comments and Responses on Local Exhaust Ventilation Issues: Need for a Complete New System

    Local exhaust ventilation represents one of the major costs associated with engineering controls in both the PEA and in the FEA. Commenters raised issues both about OSHA's PEA estimates of the unit costs of LEV and about the adequacy of OSHA's estimates of the volume of LEV that would be needed to adequately control silica exposures.

    URS, testifying on behalf of ACC, argued that any firm that would be utilizing LEV to meet a PEL of 50 mug/m\3\ would need to remove any existing LEV and install an entirely new LEV system. Thus, in URS's estimation, there would be no incremental addition of LEV. In a discussion of the URS approach during OSHA's informal public hearings, OSHA asked the URS representative to confirm that his organization commented that when a majority of workers are exposed over the PEL, the existing controls must be replaced instead of enhanced:

    MR. BURT: I want to be sure I understand what that's saying. Let's say you encountered a situation in which there were four workers. Two were exposed at 35, two at 60. You would scrap all of the controls and start over again. That's what it seems to be saying.

    . . .

    MR. WAGGENER: Yes, that they would need to be replaced with a more adequate system (Document ID 3582, Tr. 2109-2110).

    OSHA's examination of the spreadsheets URS provided documenting its independently developed cost estimates shows that, in all cases where any employee in an establishment was exposed above 50 mug/m\3\, URS assumed that the employer would need to install a complete new LEV system and included the costs for installing and operating this entirely new system (Document ID 2308, Attachment 8, pp. 13-14).

    John Burke from OSCO Industries took a different approach to the question that better illustrates the options that OSHA believed to be available when it developed the PEA estimates:

    A single large dust collector is probably already handling the exhausting of the entire sand conditioning system. Most likely all the pick-up points referenced in the economic analysis already have suction being applied and yet there is still an overexposure. What do you do and how much is that going to cost? If the sand system operator is overexposed then you could first evaluate work practices controls. If work practice controls are unsuccessful and additional suction is needed, that suction is going to be very expensive! If your environmental operating permit allows it you may be able to tweak the performance of the dust collector. There may be some things you can

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    do to tweak the capacity of your existing dust collector to bring it up to exactly its permitted air volume or you might have to enlarge your dust collector (Document ID 1992, p. 6).

    OSHA agrees with Mr. Burke. As discussed above, there are usually a wide variety of ways to improve existing controls before removing and reinstalling an LEV system. As a result, OSHA finds the URS approach unrealistic and likely to significantly overestimate costs.

    Comments and Responses on the Volume of Controls Needed

    One commenter, URS, questioned OSHA's estimates of the volume of additional LEV that would be needed to comply with the standard. URS, testifying for ACC, reported that OSHA's estimates in the PEA were too low as compared to the recommendations in Table 6-2 of the ACGIH Ventilation Manual (28th Edition). They criticized OSHA's estimates saying that OSHA routinely underestimated required capture velocities by at least a factor of two for particles with high (conveyor loading, crushing) or very high (grinding, abrasive blasting, tumbling) energies of dispersion (Document ID 2308, Attachment 8, pp. 12 and 14). URS said that ``the capture velocities for LEV systems in OSHA's models were often based on the minimum recommended velocity,'' that OSHA's estimated additional LEV was too low because ``the ACGIH capture velocity values used by OSHA were first developed and published many years ago'' and were not sufficient to control dust to the levels OSHA is now proposing, and that ``the velocity values used in OSHA's cost model are most likely undersized by a factor of 2 or more'' (Document ID 2308, pp. 11-12). Other than its own supposition, URS did not identify an alternative source for OSHA to use as the basis for estimates of ventilation capacity necessary to control silica exposures.

    In response to these comments, and in order to determine whether ACGIH recommendations had changed between the 24th edition (which OSHA used to develop estimates in the PEA) and the more recent 28th edition, OSHA checked its estimated volumes against those in the more recent ACGIH Ventilation Manual (Chapter 13 in the 28th edition (Document ID 3883)). In the 24th edition of the Manual, ACGIH provided a single recommendation for ventilation capacity rather than a range. In the PEA, OSHA adopted this recommendation and did not choose a value from within a range of values. The 28th edition of the Manual provides more flexibility in system design and specification and incorporates a recommended range. However, OSHA determined that the ventilation capacity estimates did not change between the 24th edition of the Manual and the 28th edition. In most cases, OSHA's estimated volumes were identical to those recommended by ACGIH. The exceptions were situations in which ACGIH provided no recommendation (in which case OSHA relied on recommendations of industrial hygienists), and situations in which the technological feasibility analysis recommended additional volumes of LEV capacity above what employers were typically using. In the latter situations, OSHA estimated that an additional 25 percent of the ACGIH specification would be necessary to adequately control silica exposures (See Exhibit: Comparison of OSHA CFM Volumes to ACGIH Values, available in Docket OSHA-2010-0034 at www.regulations.gov).

    URS argued that silica was different from other substances LEV might be applied to in ways that would call for higher volumes of ventilation (Document ID 2308, Attachment 8, p. 14). However, in all cases involving silica (such as shake-out stations), the ACGIH Manual recommended the volumes used by OSHA and criticized by URS.

    OSHA's estimates of the ventilation capacity necessary to control silica exposures relied on a detailed set of recommendations provided by ACGIH while URS simply asserted that these values are ``most likely undersized by a factor of 2 or more'' without providing additional evidence to support this (Document ID 2308, Attachment 8, p. 12). Based on these findings, OSHA has determined that the ACGIH recommendations constitute the best available evidence and has maintained the estimates of ventilation capacity from the PEA for the FEA.

    Comments Providing Alternative Ventilation System Cost Estimates

    Other commenters provided much higher costs than OSHA's estimates but without providing any background to allow OSHA to put those costs in context. It is difficult for OSHA to evaluate a cost estimate without information on the size of the facility, the estimated volume of air, and the exposure levels before and after the LEV was installed.

    The Interlocking Concrete Pavement Institute (ICPI) commented that OSHA underestimated compliance costs because ``one ICP manufacturer reported that it could cost $150,000 to acquire and install highly efficient vacuum and water dust-control systems'' and other manufacturers reported similarly high costs (Document ID 2246, p. 11). At the public hearings, OSHA sought clarification on the assumptions underlying the ICPI cost estimate, and the ICPI representative stated that $150,000 was a mid-range estimate. The representative also confirmed that this was the cost of an entirely new system:

    MR. BLICKSILVER: Does this actually represent the incremental cost associated with complying with OSHA's proposed rule? . . . Or is this an overall cost for dust control in these manufacturing plants?

    MR. SMITH: The latter (Document ID 3589, Tr. 4407-4409).

    In a follow-up verbal exchange, OSHA requested that ICPI analyze its survey data to produce median values for the range of cost estimates and submit their analysis as a post-hearing comment (Document ID 3589, Tr. 4409). However, no ICPI comments appeared in the record following the Institute's testimony at the hearings.

    Similarly, OSHA asked Mr. Tom Slavin, testifying for AFS, for additional information from AFS on the many cost estimates for individual foundries that it had included in its comments:

    MR. BURT: You provide many examples of cost to specific foundries of specific activities. I would like to suggest that those can be most useful if we have data on the size of the firm in question, the type of foundry if that's appropriate, and what they were trying to accomplish with this effort.

    Were they at 400 and trying to get to 100, at 100 trying to get lower? Something that puts it in context would again make these many, many helpful quotes much more useful.

    Size is just critical, just because of the fact that when we don't know whether we're talking about 20 or 200 people in a foundry really affects what you want to do with those cost estimates. And that one's relatively simple, size of firm, type of foundry if you have it, what they were trying to do with that effort (Document ID 3584, Tr. 2773-2774).

    Later in the exchange, OSHA requested information on ``the components of AFS's estimated cost per cfm of additional ventilation that would be capital cost, installation cost, and then any other operating costs you have'' (Document ID 3584, Tr. 2784). OSHA received no response to this request.

    Unfortunately, it is almost impossible for OSHA to make use of commenters' estimates of costs or volume of LEV systems without information on the size of the facility and on what the resulting system accomplished in terms of reducing exposure levels. OSHA consistently requested this kind of

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    information, but did not receive it. As shown in the discussion of alternative estimates of costs by small entity representatives during the SBAR Panel (discussed below), even estimates that appear higher than OSHA's average costs can be consistent with those costs when the full context for the estimates is examined.

    Comments and Responses on Unit Cost per CFM

    Many commenters thought that OSHA's unit costs for ventilation were too low. With respect to the annualized value of the capital costs plus operating and maintenance costs of $5.33 that OSHA used in the PEA, AFS stated:

    The PEA uses an annual cost factor of $5.33 for ventilation, including ducting and bag house operation ... is far below foundry experience. A group of foundry ventilation managers and ventilation experts estimated the annual cost per CFM at $20 for exhaust alone and another $6-10 for makeup air critical to achieving the lower PEL. The cost to meet the new U.S. Environmental Protection Agency (EPA) dust loading criteria increases the exhaust annual cost to $25 per CFM. Any new installation would be expected to design to the new criteria even if not yet required to do so for that specific jurisdiction (Document ID 2379, Appendix 3, p. 9).

    URS, commenting on behalf of ACC, estimated the annualized cost of LEV to be $27 per cfm, and increased OSHA's original estimate of capital costs from $12.83 to $22 per cfm for the purpose of URS's cost estimate (Document ID 2308, Attachment 8, pp. 13-14).

    Many other commenters from industry suggested unit costs for additional LEV. For example, AFS provided independent estimates of annualized costs of $20 to $25 per cfm and URS estimated $22 to $27 capital costs per cfm (Document ID 2379, Appendix 1, p. 45; 2308, Attachment 8, p. 14; 2379, Appendix 2, p. 13; 2503, p. 2; 2119, Attachment 3, p. 4; 2248, p. 8; 3490, p. 3; 3584, Tr. 2779).

    OSHA agrees that there can be a wide range of both capital and operating costs associated with LEV. Capital costs will vary according to such factors as the exact nature of the ventilation (including the design of the slot, hood, or bagging station), the volume of materials to be handled by the ventilation, and the length of the ductwork necessary. OSHA also would like to clarify that, as shown in OSHA's spreadsheets (OSHA, 2016), where there are major structural changes associated with a control, such as automation, a new bagging station, or conveyor closure, these costs are estimated over and above the basic capital costs of LEV. Annual operating costs vary according to climate, hours of operation, and the extent to which air is recirculated. To examine these possible costs, OSHA reviewed the thoroughly documented LEV costs presented in its Final Economic Analysis for the Occupational Exposure to Hexavalent Chromium Standard (Document ID 3641). In that FEA, OSHA's estimates of the capital costs for LEV (updated to 2012 dollars) averaged more than $20 per cfm when major work station changes, such as automated bag slitting stations, were included in the cost of LEV. Ordinary additional LEV without major workstation changes was estimated to have an average capital cost of $9 per cfm in 2012 dollars. Operating costs in that rulemaking were estimated to be somewhat higher than estimated here, but combined annualized costs (capital plus operating costs) were approximately the same (See Exhibit: Analysis of LEV Costs from Hex Chrome, available in Docket OSHA-2010-0034 at www.regulations.gov).

    OSHA agrees that the capital costs of some kinds of LEV that involve significant workstation modifications or even automation can exceed $20 per cfm, but finds an average of $13.34 (in 2012 dollars) per cfm in capital costs to be reasonable given that some kinds of LEV installation can cost as little as $3 to $5 per cfm. OSHA also finds the operating cost estimates used in the FEA to be a reasonable average across a very wide variety of circumstances.

    Housekeeping and Dust Suppression Costs

    PEA Costs

    For a number of occupations, the technological feasibility analysis in the PEA indicated that improved housekeeping practices were needed to reduce silica exposures. The degree of incremental housekeeping depended upon how dusty the operations were and the appropriate equipment for addressing the dust problem. The incremental costs for most such occupations reflected labor associated with additional housekeeping efforts. Because incremental housekeeping labor was required on virtually every work shift by most of the affected occupations, the costs of housekeeping in the PEA were significant. The PEA also estimated that employers would need to purchase HEPA vacuums and to incur the ongoing costs of HEPA vacuum filters. The time needed for such housekeeping varied from five to twenty minutes per affected worker per day. Appendix V-A in the PEA provided detailed specifications on the application of housekeeping and other dust-

    suppression controls in each occupational category and the sources of OSHA's unit cost data for such controls.

    For some indoor dust suppression tasks, it was assumed that dust suppression mixes--often sawdust-based with oil or other material that adheres to dust and allows it to be swept up without becoming airborne--were spread over the areas to be swept. For these products, estimates were made of usage rates and the incremental times necessary to employ them in housekeeping tasks.

    For outdoor dust suppression, the PEA determined that workers must often spray water over storage piles and raw material receiving areas. The methods by which water is provided for these tasks can vary widely, from water trucks to available hoses. It was judged that most facilities would make hoses available for spraying and that spraying requires a materials-handling worker to devote part of the workday to lightly spray the area for dust control.

    The PEA did not include any costs for thorough cleaning designed to remove accumulated dust, either as a one-time cost or as an annual cost.

    Comments and Responses on Costs of Routine Housekeeping and Initial Cleaning

    Commenters had a number of issues with respect to how OSHA treated the costs of housekeeping, including the time and equipment needed for vacuuming, the need for professional floor to ceiling cleaning, and the costs of the ban on dry sweeping.

    Comments and Responses on Costs of Routine Housekeeping

    With respect to the use of HEPA vacuums, AFS commented that due to the volume of sand involved, foundries often use vacuum systems that cost $45,000 instead of the $3,500 estimated by OSHA in the PEA (Document ID 4229, Attachment 1, p. 23). Several commenters reported that HEPA semi-mobile central vacuum systems cost more than $40,000 to purchase and cost approximately $4,000 per year to maintain, and that sweeping compound costs approximately $4,000 per year (Document ID 2384, p. 7; 2114, Attachment 1, p. 4). Several others noted that acquiring HEPA vacuums and employee time for vacuuming would be expensive (Document ID 2301, Attachment 1, p. 74; 3300, pp. 4-5; 2114, Attachment 1, p. 4).

    OSHA's costs are for improved housekeeping, beyond the necessary tasks related to dealing with the large volumes of sand used in foundries. For this final rule, OSHA estimates the costs

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    of additional housekeeping as those necessary for overexposed workers to spend 10 minutes vacuuming their immediate work areas with a 15-

    gallon HEPA vacuum. It is possible that a large firm may find a dust handling system or a semi-mobile central vacuum system less expensive than having individual workers equipped with smaller capacity HEPA vacuums spend additional time performing housekeeping on each shift.

    With respect to the shipbuilding sector, OSHA found that it had not accounted for the costs of HEPA vacuums for abrasive blasting helpers. OSHA has added costs for the vacuums, but not for the time spent performing housekeeping as the vacuums replace dry sweeping.

    As to the possible costs of the ban on dry sweeping, OSHA has modified this prohibition in ways that should avoid significant costs in situations where dry sweeping is the only effective method of housekeeping.

    Comments and Responses on Costs of Initial Cleaning

    URS, testifying for ACC, questioned OSHA's omission of ``professional cleaning'' from its cost models for some industries, noting that professional cleaning was identified in the PEA as necessary for some industries to achieve the PEL (Document ID 2308, Attachment 8, p. 12). URS also provided estimates of the cost of professional cleaning:

    Based on communications with several industries, URS estimates that a thorough annual professional cleaning will cost about $1.00 per square foot of the facility process operations area.

    . . . A professional cleaning can take several days to accomplish . . . For square footage, URS assumed 20,000 square feet for very small facilities, 50,000 square feet for small facilities, and 200,000 square feet for large facilities (Document ID 2308, Attachment 8, p. 24).

    Initial thorough facility cleaning and rigorous housekeeping are supplemental controls and work practices addressed in the technological feasibility analysis for the following application groups: Concrete Products, Pottery, Structural Clay, Mineral Processing, Iron Foundries, Nonferrous Sand Foundries, and Captive Foundries. OSHA failed to include the costs of a thorough initial cleaning in the PEA, but has developed estimates of these costs for the FEA in response to the URS comment. The final standard sets the performance objective of achieving the PEL using engineering controls, work practices, and where necessary, respiratory protection, and, with respect to facility cleaning and housekeeping, the rule does not mandate that firms hire outside specialists. To estimate the final costs for initial thorough facility cleaning, OSHA first developed an analysis of average production floor space in square feet for two plant sizes based on data on plant floor space and employment for individual facilities reported in various NIOSH control technology and exposure assessment field studies (OSHA examined Document ID 215; 216; 268; 1373; 1383; 3786; 3996; and 4114. The analysis is in Exhibit: Analysis of Plant Floor Space, available in Docket OSHA-2010-0034 at www.regulations.gov).

    For the purpose of estimating cleaning costs, OSHA characterized establishments with fewer than twenty employees as very small establishments, and characterized establishments with twenty or more employees as larger establishments.

    OSHA determined, based on a review of the data in the NIOSH field studies, that production floor space averages 725 square feet per employee (See Exhibit: Analysis of Plant Floor Space).

    For very small establishments with fewer than 20 employees, OSHA used an average of 7 employees per establishment. For larger establishments, OSHA used an average of 80 employees. (These estimates of the number of employees are based on OSHA (2016), which shows that the average number of employees for establishments with fewer than 20 employees is 7 employees and that the average number of employees for establishments with more than 20 employees is 80 employees.) Based on these parameters, OSHA's floor space model found that the typical floor space for very small establishments is 5,075 square feet and for larger establishments is 58,000 square feet.

    ERG spoke with a representative of an upper-Midwestern firm specializing in the industrial cleaning of foundries and related facilities (Document ID 3817, p. 2). According to that representative, cleaning costs depend on numerous factors, such as the distance to the facility that needs to be cleaned, the size and number of machines and pieces of equipment present, the types of required cleaning activities, and the presence of confined spaces. The representative described one of his company's clients as a sand-casting foundry that produces 42,000 tons of gray and ductile iron castings per year in a 210,000 square foot facility. According to the representative, a crew of two technicians cleans the facility every 2 to 3 weeks at a cost of $2,200 to $3,500 per cleaning, which requires one day, or roughly $0.01 to $0.02 per square foot in 2014 dollars.

    For the FEA, OSHA is estimating, based on data from the ERG field interviews, that it will take 4 to 5 days to perform a one-time initial cleaning (remove all visible silica dust) and that if the same facility is cleaned every 2 to 3 weeks it will take 1 day to clean it. At a cost of $0.02 per day per square foot, and using a cleaning duration of 5 days, OSHA calculated a cost of $0.15 per square foot in 2012 dollars for an initial thorough cleaning. This value is derived from inflating the 2003 estimate of $0.10 per square foot ($0.02 per day per square foot over 5 days) to 2012 dollars, which raised the cost to $0.12 per square foot. OSHA also allowed for an additional allotment of 25 percent of the estimated cost of $0.12 per square foot (in 2012 dollars) to ensure that the cleaning was sufficiently thorough to achieve compliance, increasing the total from $0.12 to $0.15. OSHA judges that this is a reasonable average for the range of facilities to be covered, especially given that some annual cleaning is probably already occurring at most facilities and therefore the full cost of cleaning would not be attributable to this rule. The costs here are applied to represent an incremental cleaning beyond that employed for normal business purposes.

    As discussed earlier in this chapter, URS, an engineering consultant to ACC, estimated that a thorough annual professional cleaning will cost about $1.00 per square foot of a facility's process operations area. URS provided no specific reference for that unit estimate other than that it communicated with industry representatives (Document ID 2308, Attachment 8, p. 24). The data OSHA used to develop its cost estimates are based on interviews with a company that provides housekeeping services rather than companies that may or may not have purchased such services. OSHA's estimated costs for a thorough initial cleaning are over five times the costs of a thorough cleaning where there is just few weeks' worth of accumulated dust. Greater accumulations during an initial cleaning do not mean that the initial cleaning will cost 50 times the cost of a more basic/regular cleaning, as much of the cost of the initial cleaning will be due to the time spent going over the entire facility with the appropriate cleaning devices--a cost that is fixed by area and not by accumulation. OSHA therefore rejects the URS unit estimate of $1.00 per square foot as not representative of a typical cost for initial thorough facility cleaning, particularly for firms that choose to use in-house resources. Nonetheless, OSHA

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    acknowledges that unique circumstances may create higher unit costs than the value OSHA is using in the FEA. OSHA also acknowledges that the cost of cleaning per square foot probably declines as facility size increases (Document ID 4231, p. 4). The paucity of data on square footage for the affected facilities, however, did not allow for further modeling of cleaning costs.

    For this final analysis of costs for initial thorough facility cleaning, OSHA estimated that an upfront, one-time, extensive servicing (using vacuum and wash equipment) to rid the production area of respirable crystalline silica during plant turnaround or other downtime would cost $0.15 per square foot (including the additional allowance to ensure a sufficiently thorough cleaning) or $0.02 when annualized at 3 percent for 10 years, and OSHA applied that unit cost along with the average production floor space discussed above in OSHA's cost model (725 square feet per employee) to derive final costs for facility cleaning by application group. For the seven affected application groups, OSHA estimates that annualized initial thorough facility cleaning costs will range from just under $45,000 for Nonferrous Sand Foundries to $488,000 for Concrete Products. Across all seven affected application groups, OSHA estimates that annualized costs for initial thorough facility cleaning will total $2.8 million.

    Conveyor Covers

    The technological feasibility analysis in the PEA recommended reducing silica exposures by enclosing process equipment, such as conveyors, particularly where silica-containing materials were transferred (and notable quantities of dust can become airborne), or where dust is generated, such as in sawing or grinding operations. For the PEA, OSHA estimated the capital costs of conveyor covers as $20.73 (updated to 21012 dollars) per linear foot, based on Landola (2003, Document ID 0745) (as summarized in footnote a in Table V-3 of the PEA). OSHA estimated that each work crew of four affected workers would require 100 linear feet of conveyors. OSHA, based on ERG's estimates, calculated maintenance costs as 10 percent of capital costs. Based on the technological feasibility analysis, OSHA also included the cost of LEV on the vents of the conveyors for the structural clay, foundry, asphalt roofing, and mineral processing application groups, but not for the glass and mineral wool application groups.

    URS commented that OSHA underestimated the length of conveyors by using 100 linear feet in its estimate, and suggested that the estimate of 200 feet that it used as the basis for its estimates was still an underestimation for some foundries (Document ID 2307, Attachment 26, Control Basis and Control Changes tabs). URS maintained OSHA's estimate of $20.73 per linear foot in its own calculations. However, it appears that URS did not understand that OSHA estimated 100 linear feet of conveyors for every 4 workers, not 100 linear feet of conveyors for an entire affected establishment. Further, the URS comment indicated that 100 linear feet was an underestimate for ``medium and large foundries.'' But because OSHA's estimate of 100 linear feet is for every four workers, OSHA actually estimated much longer conveyor lengths for larger facilities with more workers. OSHA has determined that its estimate of 100 linear feet for every four workers at a cost of $20.73 per linear foot is a reasonable approach for estimating the costs of conveyor covers.

    Selected Control Options That Are Not Costed

    Consistent with ERG's cost model, in the PEA OSHA chose not to estimate costs for some control options mentioned in the accompanying technological feasibility analysis in Chapter IV of the PEA. In these cases, OSHA judged that other control options for a specific at-risk occupation were sufficient to meet the PEL. AFS identified several control options for which OSHA did not estimate costs:

    Substitution of non-silica sand (V-A-51)

    Pneumatic sand handling systems (V-A-51)

    Didion drum to clean scrap for furnace operators (V-A-52)

    Non-silica cores and core coatings (V-A-52)

    Professional cleaning costs and associated downtime (V-A-52)

    Physical isolation of pouring areas (V-A-52)

    Modify ventilation system to reduce airflow from other areas (V-A-52)

    Automation of a knockout process (V-A-53)

    Automated abrasive blast pre-cleaning of castings for finishing operators (V-A-54)

    Wet methods (V-A-54)

    Low silica refractory (V-A-55) (Document ID 2379, p. 16)

    Just because a control is mentioned in the technological feasibility analysis does not mean that OSHA has determined that its use is required--only that it represents a technologically feasible method for controlling exposures. The Agency developed cost estimates based on the lowest cost combination of controls that allows employers to move from an uncontrolled situation to meeting the new PEL. OSHA did not include the costs for possible controls that were either more expensive or were not necessary to achieve the PEL. OSHA (2016) describes in detail which controls were considered necessary to achieve the PEL. OSHA continues in the FEA to exclude costs for these kinds of more expensive possible controls.

    Railroads

    In its preliminary estimates, OSHA inadvertently applied the preceding general industry PEL of 100 mug/m\3\ in its analysis of the railroad industry. Silica exposures among railroad employees, however, result from ballast dumping, which is track work that is generally subject to OSHA's construction standard and covered by the preceding construction PEL of 250 mug/m\3\ (see discussion of railroads in Chapter III, Industry Profile). As a result, OSHA has changed its conclusion that there would be no incremental costs for railroads to meet the new PEL. OSHA has reassigned all costs previously assigned to meeting the preceding PEL to being incremental costs of meeting the new PEL. Although the railroad activities affected by the new silica rule will typically constitute construction work, OSHA has categorized all compliance costs for railroads with general industry costs under NAICS 482110 because the railroad industry is predominantly engaged in non-

    construction work and its NAICS code is not typically classified as a construction code.

    Costs of Engineering Controls for Hydraulic Fracturing in the PEA

    Both in the PEA and in the FEA, OSHA presented the methods of estimating the costs of controlling silica exposures during hydraulic fracturing separately from the engineering control costs for all other portions of general industry because there are some fundamental differences in the methodology OSHA used, and thus in the comments OSHA received on that methodology. In the PEA, OSHA began its analysis of hydraulic fracturing in the standard way of examining the set of engineering controls available to control employee exposures to silica. Unlike the way OSHA handled the rest of general industry, however, for hydraulic fracturing OSHA identified precisely which controls were necessary to go from current levels of exposure to the preceding general industry PEL of 100 mug/m\3\ and then what further

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    controls would be necessary to go from the preceding general industry PEL of 100 mug/m\3\ to the new PEL of 50 mug/m\3\. OSHA took a different approach for this sector because the data available for this industry, as a result of an extensive set of site visits, were adequate to make this type of determination. OSHA determined that a combination of wet methods, partial enclosure, and LEV controls would be sufficient to meet a PEL of 100 mug/m\3\ for hydraulic fracturing. OSHA then determined that LEV controls at thief hatches and operator enclosures would be sufficient to reduce exposures during hydraulic fracturing from 100 mug/m\3\ to 50 mug/m\3\. The costs of these additional engineering controls were shown in Tables A-14, A-15, and A-16 for large, medium, and small fleets, respectively, in the PEA (the full derivation of the results in these tables can be found in ERG, 2013, Document ID 1712).

    As discussed in the Industry Profile section of the FEA (Chapter III), the basic unit for analysis for this industry is the fleet rather than the establishment. Rather than allocating costs according to the proportion of workers above a given exposure level, as was done for the rest of general industry, for hydraulic fracturing the controls applied per fleet were judged to reduce the exposures of all workers associated with the fleet.

    Public Comments on OSHA's Preliminary Cost Estimates for Engineering Controls in Hydraulic Fracturing

    General Methodology

    Though there were extensive comments on OSHA's estimates of engineering control costs for hydraulic fracturing, no commenter objected to the differences in methodology compared to OSHA's treatment of the other general industry sectors (as outlined above). Halliburton Energy Services, Inc. commented that OSHA's analysis ``lacks data'' (Document ID 4211, p. 5). As discussed in Chapter IV Technological Feasibility, OSHA agrees that there is limited experience with many possible controls. For this reason, OSHA has allowed this industry an extended compliance deadline of five years before they have to meet the new PEL with engineering controls. However, OSHA does not agree that this adds significant uncertainty to the costs analysis. The costs of the controls OSHA has examined, and especially those needed to go from the preceding general industry PEL to the new PEL can readily be ascertained. It is possible that the cost of some controls that have not yet been tested and that OSHA has not costed could be much lower than the costs OSHA estimated in the PEA and in the FEA.

    Compliance Rate

    In the joint comments submitted by the American Petroleum Institute and the Independent Petroleum Association of America (API/IPAA or ``the Associations''), the Associations disagreed with OSHA's estimated current compliance rate for the use of engineering controls. In the PEA, OSHA estimated a compliance rate of ten percent for engineering controls in this industry. In their comments the Associations said that ``ERG assumed that 10% of all hydraulic fracturing firms already utilize: (1) Baghouse controls; (2) caps on fill ports; (3) dust curtains; (4) wetting methods; and (5) conveyor skirting systems'' (Document ID 2301, p. 40, fn. 148).

    While OSHA used a compliance rate of ten percent for all of these controls, it is not meant to represent that all prescribed controls are used in ten percent of firms. OSHA's compliance rates take into account that some well sites, as documented in Chapter IV of the FEA, were observed to be using a variety of controls that reduce dust levels, and as a result, those firms will not need to implement as many additional controls in order to achieve the new PEL. Further, as noted in Chapter IV of the FEA, the industry is constantly installing additional controls to reduce silica exposures. Thus the Agency sees no reason to change its estimate of current compliance. In any case, removing the assumption would make only a ten percent difference to the cost estimates, which would not be a change of large enough magnitude to threaten OSHA's conclusion that compliance with the final rule is economically feasible for the hydraulic fracturing industry.

    Maintenance Costs

    In the PEA, OSHA estimated that the life of most capital equipment would be ten years, and that maintenance and operating costs would range from ten to thirty percent of capital costs per year (ten percent being most common).

    API/IPAA argued that the hostile, sandy environment of the well site shortens the useful life of equipment and increases maintenance costs. The Associations estimated that the useful life of equipment ranges from 5 years to 7.5 years and that annual operating and maintenance costs range from 10 percent to 25 percent of capital costs. While OSHA agrees that the oilfield environment is challenging and dusty, there is no evidence in the record that these environments are more challenging than other industrial settings where equipment lives of 10 years and operating and maintenance costs of 10 to 30 percent have been used as reasonable estimates.

    Cost of Specific Controls

    Dust Booths

    In the PEA, OSHA estimated that there would need to be one dust booth for each sand moving machine, and that this would result in one dust booth for small fleets, three for medium fleets, and five for large fleets. In critiquing OSHA's cost analysis for hydraulic fracturing, API/IPAA disagreed with OSHA's estimates that only sand mover operators would need to utilize dust control booths in order to achieve the new PEL (Document ID 2301, p. 69). API/IPAA suggested that instead there would need to be one booth per affected worker and that only one worker could utilize a given booth. In the Associations' estimate this would mean that there would need to be 3, 8 and 12 booths for small, medium, and large fleets, respectively (Document ID 2301, Attachment 4, Dust Booths, row 9).

    As discussed in the technological feasibility chapter of the FEA, OSHA agrees that workers other than sand mover operators will need to use dust booths. However, OSHA does not agree that a booth can only accommodate a single person. These booths are places of refuge and are not assigned to specific individuals. The technological feasibility chapter in the FEA determined that dust booths can accommodate more than one person per booth. Because OSHA agrees that more employees than sand mover operators will need booths, OSHA has raised its estimates of booths needed by size class from 1, 4, and 5 booths to 3, 6, and 8 booths. While this estimate of the number of booths is lower than that recommended by API/IPAA, OSHA finds that these booths can accommodate 2 persons per booth and thus can accommodate more workers than API/IPAA suggested.

    In the PEA, OSHA estimated the transportation costs for booths as $37.25 per booth. API/IPAA disagreed. The Associations argued that a cost of $513 for a small fleet, which would only have one booth, would be more appropriate (Document ID 2301, p. 69). Most of the difference between API/IPAA's cost estimate for deploying dust control booths and OSHA's estimate is attributable to the fact that the Associations presented their cost per fleet and OSHA presented its cost per

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    booth. API/IPAA applied their estimate of the number of booths necessary at these worksites when deriving their estimate and they estimated about six times as many booths being necessary as OSHA did. However, after further examination of this cost, OSHA determined that the standard per-mile shipping rate that it used to estimate transportation costs in the PEA was applied incorrectly. This resulted in an estimate of transportation costs for booths in the PEA that was too low. OSHA has determined that the cost to transport dust booths presented by the Associations more completely captured the costs associated with transporting these booths. For the FEA, OSHA has accepted the Associations' per-fleet transportation cost of $513 for each booth and applied the cost to the Agency's estimate of the number of booths necessary to control silica exposures on well sites.

    Water Misting

    In the PEA, OSHA estimated that water misting system would be needed to control residual emissions from some releases from sand moving systems. These water misting systems were estimated to cost $60,000 per fleet to purchase and an additional 20 percent of the purchase cost for installation. API/IPAA incorrectly assumed that these water misting systems were intended to control all dust emission from truck traffic and other sources (Document ID 2301, pp. 69-70). This was not the case--dust suppression for truck and other traffic was costed at a much higher rate separately from water misting.

    OSHA's cost estimates for misting systems were based on conversations with a mining dust control specialist who indicated the price and efficacy of available water misting systems (Document ID 1571). While API/IPAA disagreed with OSHA's costs, they did not offer any data to show an alternative cost, instead simply carrying OSHA's estimate for water misting systems forward in their analysis to arrive at their cost estimate (Document ID 2301, Attachment 3, Water Misting, cells K:O6 and J8). OSHA has determined that the equipment that formed the basis for its cost estimates in the PEA may not be durable enough to stand up to the wear from frequent loading, unloading, and transportation. Therefore, the Agency, based on its own judgement, has increased the estimated cost of a water misting system by 33 percent in order to account for the need for a more durable system. Based on this, OSHA's final cost analysis for hydraulic fracturing includes costs of $79,800 per fleet to purchase the equipment plus installation costs of $15,960 for installation (20 percent of the purchase price) for water misting equipment to control residual dust emissions from sand moving systems.

    Costs of Transportation

    In developing the costs for hydraulic fracturing firms to comply with this rule in the PEA, it was determined that the baghouse controls that are commercially available are integrated into sandmover units and therefore should not present any logistical difficulties for transportation purposes. However, in examining the costs to transport, assemble, and disassemble the control equipment, API/IPAA noted potential difficulties in adding baghouse controls to sandmovers, which are often nearly at weight limits for road movement (Document ID 2301, p. 71).

    OSHA's determination about integrated units has not changed since the PEA. The existence of integrated units is further discussed in Chapter IV of the FEA, Technological Feasibility. OSHA notes that sandmover units are not the heaviest items transported by hydraulic fracturing firms, so the additional weight associated with baghouse controls would be insignificant in this context. These firms are highly experienced in moving the heavy, bulky equipment needed on well sites and including additional controls on this equipment is not expected to create a situation that exceeds the capabilities of these firms.

    Containerized Systems

    Commenting on OSHA's analysis of the cost of controls for hydraulic fracturing, API/IPAA expressed concern that OSHA was considering requiring the use of containerized systems. The Associations stated that these systems would be economically infeasible for small fleets and raised questions about whether these systems would be sufficient to allow fleets using them to achieve the PEL (Document ID 4222, p. 7). Neither in the PEA nor the FEA has OSHA's cost analysis reflected the use of containerized systems, nor does OSHA require their use. Instead, containerized systems represent a possible technological change that could potentially reduce the costs of silica control. OSHA has in no way quantitatively tried to estimate the effects of this possible reduction.

    Conveyor Skirting

    In the PEA, OSHA found that conveyor skirting systems with appropriate LEV would be needed to meet the new PEL, and included the cost of such controls in the incremental costs associated with the new PEL. As discussed in Chapter IV, Technological Feasibility, in the FEA, however, OSHA now finds that these conveyor skirting systems will be needed to meet the preceding PEL, but not to further lower exposures to the new PEL, so OSHA is not including costs for these controls as incremental costs associated with achieving the new PEL. As a result, the FEA does not include costs for conveyor skirting systems and LEV.

    Dust Suppression--Control of Dust Generated From Traffic

    On the other hand, dust suppression to control silica emissions generated by truck traffic, estimated in the PEA as necessary only to meet the preceding PEL, has now been determined to be necessary to meet the new PEL (see Chapter IV, Technological Feasibility in the FEA). As a result, in the FEA OSHA added the costs of dust suppression to control silica dust generated by truck traffic to the estimated incremental costs of meeting the new PEL. OSHA estimates that dust suppression is more expensive in the aggregate than conveyor skirting systems with appropriate LEV.

    OSHA made two additional changes to the costs of dust suppression from the PEA to the FEA. First, OSHA accepted the unit costs for dust suppression application provided by API/IPAA (Document ID 2301, Attachment 3, Dust Suppression). This unit cost is somewhat lower than the original estimate that OSHA adopted in the PEA (Document ID 1712). This seems reasonable to OSHA based on the costs of the most commonly used dust suppression materials. Second, OSHA has determined that these controls will be utilized to reduce exposures for ancillary support workers and remote/intermittent workers, 50 percent of whom work in situations that currently have exposures below the new PEL (as shown in the exposure profile in the section on hydraulic fracturing in Chapter IV, of the FEA, technological feasibility). As a result, instead of assigning dust suppression costs for all wells (as in the PEA), OSHA determined in the FEA that dust suppression costs would be incurred by 50 percent of wells. This aligns with a view that, in many cases, natural conditions (silica content of soils, dustiness, wetness and/or climate) are such that dust suppression is not needed.

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    Small Business Considerations

    Small Business Regulatory Enforcement Fairness Act (SBREF

  26. Comments on Compliance

    Costs in General Industry and Maritime

    Before publishing the NPRM, OSHA received comment on the accuracy of its unit costs through the Small Business Advocacy Review (SBAR) Panel process.

    The Small Entity Representatives (SERs) who participated in the 2003 SBAR Panel process on OSHA's draft standards for silica provided many comments on the estimated compliance costs OSHA presented in the Preliminary Initial Regulatory Flexibility Analysis (PIRFA) for general industry and maritime (Document ID 0938).

    In response to the SERs' comments, OSHA carefully reviewed its cost estimates and evaluated the alternative estimates and methodologies suggested by the SERs. OSHA updated all unit costs presented in the PIRFA to reflect the most recent cost data available and inflated all costs to 2009 dollars prior to publication of the proposed rule. However, the Agency generally determined that the control cost estimates in the PIRFA were based on sound methods and reliable data sources.

    For the PEA, OSHA reviewed the SERs' cost estimates for small entities in the foundry and structural clay industries. Given that those SERs did not report their own sizes, the Agency could not compare their estimates to the estimates in the PEA. OSHA concluded that the compliance costs reported by the SERs in general industry that did provide size data were not incompatible with OSHA's own estimates of the costs of engineering controls to comply with the PEL. As discussed above, for the FEA, OSHA has halved the number of workers assumed to be covered by each control for most controls in establishments with fewer than twenty employees, which results in a doubling of the engineering control costs for these establishments.

    Comments and Responses on Costs for Small Establishments

    Stuart Sessions, testifying on behalf of ACC, argued that OSHA had underestimated costs to small establishments for two reasons: (1) Small establishments may have higher exposures and therefore many need to spend more money installing controls to reduce those exposures; and (2) costs to small establishments may involve diseconomies of scale--

    whereby smaller facilities would have to pay more per unit to procure and install systems--that OSHA had not accounted for (Document ID 4231, Attachment 1, pp. 2-4).

    With respect to the issue about small establishments having higher exposures--the commenter simply asserted that this is the case without providing any evidence to support the claim. Mr. Sessions speculated that smaller businesses have a ``lesser ability to afford compliance expenditures and lesser ability to devote management attention to compliance responsibilities'' (Document ID 4231, Attachment 1, p. 2). While it is possible that very small establishments may not have the same controls already in place as large establishments, as asserted by the commenter, this does not necessarily mean that very small establishments will have higher exposures. Small and very small establishments typically only have one shift per day, so fewer shifts are being worked where there is a potential for exposure. They also may spend more time on activities not involving silica exposures. For example, a small art foundry that produces one or two castings a week will simply spend proportionally less time on activities that lead to silica exposure than a large production foundry.

    With respect to the issue of diseconomies of scale, OSHA has taken this phenomenon into account in its cost estimates in the FEA. First, in order to provide a conservative estimate of costs for the purposes of determining the impacts on very small employers, OSHA has revised what Mr. Sessions called ``the most inappropriate of OSHA's assumptions'' (Document ID 4231, Attachment 1, p. 6). In the PEA, OSHA estimated that a single control would reduce the exposures of four workers. For the FEA, OSHA has revised its estimates so that the number of workers whose exposures are reduced by a control are half that used in the PEA for establishments with fewer than 20 employees--reducing the number of workers covered by a control from four to two. OSHA made this adjustment even though there are ways in which small establishments may have lower costs per cfm than larger establishments. For capital costs, a major element of cost per cfm is the length of ductwork. Within the same industry, the length of ductwork will be much shorter in smaller establishments. For operating costs per cfm, length of operating time is a key element of costs.

    OSHA has continued to estimate that the exposures of four employees whose exposures would be reduced per control for establishments with more than twenty employees (even though it is likely that more than four workers have their exposures reduced per control in the largest establishments). This effectively means that very large establishments with hundreds of employees have been modeled as if their costs were equivalent to that of several 20-40 person establishments combined. Far from neglecting diseconomies of scale, in an effort to be conservative and adequately account for the challenges faced by smaller establishments, OSHA has instead neglected to account for economies of scale in larger establishments.

    Mr. Sessions calculated some higher overall costs for smaller establishments (Document ID 4231, Attachment 1, pp. 6-10). However, these costs are critically dependent on the assumptions already addressed and rejected by OSHA, such as that exposures are random and that any exposures require that all possible controls be installed to control those exposures.

    Final Control Costs

    Unit Control Costs

    Methodology

    For the FEA, OSHA used unit costs developed in the PEA for specific respirable crystalline silica control measures from product and technical literature, equipment vendors, industrial engineers, industrial hygienists, and other sources, as relevant to each item. Some PEA estimates were modified for the FEA based on comments in the record, and all costs were updated to 2012 dollars. Specific sources for each estimate are presented with the cost estimates. Wherever possible, objective cost estimates from recognized technical sources were used. Table V-4 in the FEA provides details on control specifications and data sources underlying OSHA's unit cost estimates.

    Summary of Control Costs for General Industry and Maritime

    Table V-5 in the FEA summarizes the estimated number of at-risk workers and the annualized silica control costs for each application group. Control costs in general industry and maritime for firms to achieve the PEL of 50 mug/m\3\ level are expected to total $238.1 million annually. As shown, application group-level costs exceed $15.0 million annually for concrete products, hydraulic fracturing, iron foundries, railroads, and structural clay.

    Table V-6 in the FEA shows aggregate annual control costs in general industry and maritime by NAICS industry. These costs reflect the disaggregation of

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    application group costs among the industries that comprise each group (see Table III-1 in Chapter III of the FEA on the profile of affected industries.)

    b. Control Costs in Construction

    In both the PEA and the FEA, OSHA determined that employers, in order to minimize exposure monitoring costs, would select appropriate controls from Table 1. The final estimate for control costs, however, includes Table 1 control costs for a larger number of employees than in the PEA. For the purpose of estimating control costs in the PEA, OSHA examined all of the employers with employees engaged in Table 1 tasks but judged that only a subset of those employers (those with workers exposed above the proposed silica PEL) would require additional engineering controls. For this final rule, OSHA has judged, for costing purposes, that all of the construction employers with employees performing any task covered in Table 1 will adopt the engineering controls for that task as specified in Table 1. Thus, in the FEA, OSHA took the more conservative approach--which may result in an overestimate of costs--of identifying the cost of controls for all employers with employees engaged in Table 1 tasks, not just the subset of employers with employees exposed above the PEL. However, as discussed in Chapter III of the FEA, OSHA did adjust control costs to reflect the 44 percent of workers in construction currently exposed at or below the PEL who are estimated to be in baseline compliance with the Table 1 requirements.

    OSHA is also likely overestimating the cost of controls for another reason. If the employer is able to demonstrate by objective data, or other appropriate means, that worker exposures would be below the action level under any foreseeable conditions, the employer would be excluded from the scope of the final rule. These employers would not require additional controls. OSHA did not have sufficient data to identify this group of employers and did not try to reduce the costs to reflect this group, so OSHA's estimate of costs is therefore overestimated by an amount equal to the costs for those employers engaged in covered construction tasks but excluded from the scope of the rule.

    A few tasks involving potentially hazardous levels of silica exposure are not covered in Table 1. Employers would have to engage in exposure monitoring for these tasks pursuant to paragraph (d) and use whatever feasible controls are necessary to meet the PEL specified in paragraph (d)(1). For example, tunnel boring and abrasive blasting are not covered by Table 1 and are therefore addressed separately in this cost analysis. Although several commenters identified various other activities that they believed were not covered by Table 1 that could result in crystalline silica exposure over the PEL (Document ID 2319, pp. 19-21; 2296, pp. 8-9), some of these activities were simply detailed particularized descriptions of included activities. For example, overhead drilling is addressed in the FEA, Chapter IV-5.4 Hole Drillers Using Handheld or Stand-Mounted Drills, and the demolition of concrete and masonry structures is addressed in the FEA, Chapter IV-5.3 Heavy Equipment Operators. For the remainder, the available exposure data did not indicate that these activities resulted in a serious risk of exposure to respirable crystalline silica (see FEA, Chapter III Industry Profile, Construction, Public Comments on the Preliminary Profile of Construction and Summary and Explanation, Scope and Application); furthermore, these other activities could be addressed using the controls identified in the FEA. Because OSHA did not have sufficient data to identify a significant number of silica exposures above the PEL of 50 mug/m\3\ for these activities, the Agency did not include costs for controlling silica exposures during these activities. Nevertheless, to the extent that employers find it necessary to implement controls for any activity that OSHA did not explicitly include in this analysis, the FEA shows that those controls are clearly economically feasible.

    The control costs for the construction standard are therefore based almost entirely on the tasks and controls specified in Table 1. Most of the remainder of this section is devoted to explaining the manner in which OSHA estimated the costs of applying appropriate engineering controls to construction activities as required by Table 1 of the final standard. These costs are generated by the application of known dust-

    reducing technology, such as the application of wet methods or ventilation systems, as detailed in the technological feasibility analysis in Chapter IV of the FEA. These costs are discussed first, and, following that, the control costs for tasks not specified in Table 1 are separately estimated.

    OSHA revised Table 1 between the PEA and the FEA. The entries included in the table have been modified with some tasks being added and some being removed.\35 \In addition, the methods of controlling exposures that Table 1 requires for certain tasks have changed in response to comments and additional analysis. Excluding changes to respirator requirements, which are addressed elsewhere in this preamble, significant and substantive revisions to Table 1 that have the potential to impact control costs include:

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    \35\ Additionally, the nomenclature changed from ``Operation'' in the NPRM to ``Equipment/Task'' in the final rule.

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    New entries on Table 1--

    cir Handheld power saws for cutting fiber-cement board (with blade diameter of 8 inches or less)

    cir Rig-mounted core saws and drills

    cir Dowel drilling rigs for concrete

    cir Small drivable milling machines (less than half-lane)

    cir Large drivable milling machines (half-lane and larger for cuts of any depth on asphalt only and for cuts of four inches in depth or less on any other substrate)

    cir Heavy equipment and utility vehicles used to abrade or fracture silica-containing materials (e.g., hoe-ramming, rock ripping) or used during demolition activities involving silica-containing materials.

    cir Heavy equipment and utility vehicles for tasks such as grading and excavating but not including: Demolishing, abrading, or fracturing silica-containing materials

    Removed entry for drywall finishing from Table 1

    Revised entries on Table 1--

    cir Drivable saw entry revised to permit outdoor use only.

    cir Portable walk-behind or drivable masonry saws divided into two entries--walk-behind saws and drivable saws.

    cir Handheld drills entry revised to include stand-mounted drills and overhead drilling.

    cir Combined entries for vehicle-mounted drilling rigs for rock and vehicle-mounted drilling rigs for concrete.

    cir Milling divided into three tasks--walk-behind milling machines and floor grinders; small drivable milling machines (less than half-lane); and large drivable milling machines (half-lane and larger with cuts of any depth on asphalt only and for cuts of four inches in depth or less on any other substrate).

    cir Heavy equipment used during earthmoving divided into two tasks--(1) heavy equipment and utility vehicles used to abrade or fracture silica-containing materials (e.g., hoe-ramming, rock ripping) or used during demolition activities involving silica-containing materials, and (2) use of heavy equipment and utility vehicles for tasks such as grading and excavating but not including: Demolishing, abrading, or fracturing silica-containing materials.

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    cir Revised crushing machines entry to require equipment designed to deliver water spray or mist for dust suppression and a ventilated booth or remote control station.

    In addition to the new and revised tasks in Table 1, some of the controls and specifications required by Table 1 were revised for this final rule, including removal of ``Notes/Additional Specifications'' from individual Table 1 entries and addition of substantive paragraphs after the table. Those revisions include:

    Revised or newly required controls/specifications for Table 1 tasks--

    cir Revised requirement to operate and maintain tools/machine/

    equipment in accordance with manufacturer's instructions to minimize dust emissions.

    cir Revised specifications for dust collectors to require they provide at least 25 cubic feet per minute (cfm) of air flow per inch of blade/wheel diameter (for some, but not all entries that include a dust collection system as a control method).

    cir Revised specification for dust collectors to require they provide the air flow recommended by the tool manufacturer, or greater, and have a filter with 99 percent or greater efficiency and a filter-

    cleaning mechanism (for some, but not all entries that include a dust collection system as a control method). The entries for handheld grinders for mortar removal (i.e., tuckpointing) and handheld grinders for uses other than mortar removal require a cyclonic pre-separator or filter-cleaning mechanism.

    cir Revised requirement for tasks indoors or in enclosed areas to provide a means of exhaust as needed to minimize the accumulation of visible airborne dust (paragraph (c)(2)(i)).

    cir Added requirement for wet methods to apply water at flow rates sufficient to minimize release of visible dust (paragraph (c)(2)(ii)).

    cir Revised specifications for enclosed cabs to require that cabs: (1) Are maintained as free as practicable from settled dust; (2) have door seals and closing mechanisms that work properly; (3) have gaskets and seals that are in good condition and working properly; (4) are under positive pressure maintained through continuous delivery of fresh air; (4) have intake air that is filtered through a filter that is 95% efficient in the 0.3-10.0 mum range (e.g., MERV-16 or better); and (5) have heating and cooling capabilities (paragraph (c)(2)(iii)).

    cir Added requirement to operate handheld grinders outdoors only for uses other than mortar removal, unless certain additional controls are implemented.

    cir Added wet methods option for use of heavy equipment and utility vehicles for tasks such as grading and excavating but not including: Demolishing, abrading, or fracturing silica-containing materials.

    cir Added requirement to use wet methods when employees outside of the cab are engaged in tasks with heavy equipment used to abrade or fracture silica-containing materials (e.g., hoe-ramming, rock ripping) or used during demolition activities involving silica-containing materials.

    Removed controls/specifications for Table 1 tasks--

    cir Removed requirements to change water frequently to avoid silt build-up in water.

    cir Removed requirements to prevent wet slurry from accumulating and drying.

    cir Removed requirements to operate equipment such that no visible dust is emitted from the process.

    cir Removed local exhaust dust collection system option and requirement to ensure that saw blade is not excessively worn from the entry for handheld power saws.

    cir Removed requirement to eliminate blowing or dry sweeping drilling debris from working surface from the entry for handheld and stand-mounted drills (including impact and rotary hammer drills).

    cir Removed additional specifications for dust collection systems for vehicle-mounted drilling rigs for concrete (e.g., use smooth ducts and maintain duct transport velocity at 4,000 feet per minute; provide duct clean-out points; install pressure gauges across dust collection filters; activate LEV before drilling begins and deactivate after drill bit stops rotating).

    cir Removed requirements to operate grinder for tuckpointing flush against the working surface and to perform the work against the natural rotation of the blade.

    cir Removed dust collection system option and requirement to use an enclosed cab from crushing machines.

    These and other changes to Table 1 are discussed in detail in Section XV: Summary and Explanation of this preamble. While Table 1 has changed with regard to the tasks included and the control methods required, OSHA's methodology used to estimate the costs of controls for the construction industry has remained basically the same as that explained in detail in the PEA, with steps added (and explained in the following discussion) to address cost issues raised during the comment period and the updates and revisions to Table 1. OSHA summarizes the methodology in the following discussion, but the PEA includes additional details about the methodology not repeated in the FEA.

    OSHA adopted the control cost methodology developed by ERG (2007a, Document ID 1709) for the PEA and subsequently for the FEA. In order to provide some guidance on that cost methodology, OSHA itemizes below the three major steps, with sub-tasks, used to estimate control costs in construction, with two additional steps added for the FEA to estimate the number of affected workers by industry and equipment category \36\ (numbered Step 3) and to estimate control costs for self-employed persons (numbered Step 5)--tables referenced below are in Chapter V of the FEA:

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    \36\ The term ``equipment category'' as used here matches the broad headings used in the Technological Feasibility analysis. Later on in this section, OSHA identifies which Table 1 tasks are included in each equipment category.

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    Step 1: Baseline daily costs, relative costs of controls, and labor share of value

    cir Use RSMeans (2008, Document ID 1331) estimates to estimate the baseline daily cost for every representative job associated with each silica equipment category (Table V-30) and unit labor and equipment costs (Table V-31).

    cir Use vendors' equipment prices and RSMeans estimates to estimate the unit cost of silica controls (Table V-32), and estimate the productivity impact for every silica control and representative job, to be added to the cost of the control applied to a particular job (Table V-33).\37\

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    \37\ This latter sub-step was performed in the PEA, but it was inadvertently omitted in the text summary.

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    cir Use the costs from Tables V-32 and V-33 to calculate the incremental productivity impact, labor cost, and equipment cost for each representative job when controls are in place (Table V-34).

    cir Using Tables V-30 and V-34, calculate the percentage incremental cost of implementing silica controls for each representative job (Table V-35).

    cir Calculate the weighted average incremental cost (in percentage terms) and labor share of total costs for each silica job category (outdoors and indoors estimated separately) using the assumed distribution of associated representative jobs (Tables V-36a and V-

    36b).

    Step 2: Total value of activities performed in all Table 1 silica equipment categories

    cir Match BLS Occupational Employment Statistics OES

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    occupational classifications for key and secondary workers with the labor requirements for each equipment category (Table V-37) and estimate the full-time-equivalent (FTE) number of employees by key and secondary occupations working on each silica task (Tables V-38a and V-

    38b).

    cir Based on the distribution of occupational employment by industry from OES, distribute the full-time-equivalent employment totals for each equipment category by NAICS construction industry (Table V-39).

    Step 3: Total affected employment by industry and equipment category

    cir Disaggregate construction industries into four distinct subsectors based on commonality of construction work (Table V-40a) and then estimate the percentage of affected workers by occupation, equipment category, and construction subsector (Table V-40b).

    cir Use the percentage of affected workers by occupation, equipment category, and construction subsector (Table V-40b) to obtain total affected employment by occupation (Table V-41) and total affected employment by industry and task (Table V-42).

    Step 4: Aggregate silica control costs (not including self-employed persons)

    cir Using the FTE employment totals for each task by NAICS construction industry (Table V-39) and the mean hourly wage data from OES, adjusted for fringe benefits, calculate the annual labor value of each Table 1 silica activity by NAICS construction industry (Table V-

    43).

    cir Using the labor share of value calculated for each activity performed in a silica-related equipment category (Table V-43), estimate the total value of each Table 1 equipment/task category by industry (Table V-44).

    cir Estimate the distribution of silica work by equipment type, duration of activity, and location of activity (Table V-45).

    cir Multiply the total value of Table 1 construction activities requiring controls (Table V-44) by the percentage incremental cost associated with the controls required for each activity that uses equipment in each equipment category (Tables V-36a and V-36b) and weighted by the percentage of tasks performed outdoors and indoors/

    within an enclosed space (Table V-45), to calculate the total control costs, adjusted for baseline compliance, by Table 1 equipment category and industry (Table V-46).

    cir Calculate engineering control costs for silica-generating construction activities not covered in Table 1 (Tables V-47a and V-

    47b).

    cir Combine the control costs for Table 1 construction activities (Table V-46) and the control costs for construction activities not covered in Table 1 (Tables V-47a and V-47b) to calculate the total control costs by equipment category and construction industry (Table V-

    48).

    Step 5: Adjust aggregate silica control costs to include self-employed persons

    cir Use data from the BLS Current Population Survey to estimate the ratio of the number of self-employed persons to the number of employees by occupation (Table V-49) and then redo the estimation after restricting self-employed persons to just those occupations covered by OSHA that potentially involve exposure to hazardous levels of respirable crystalline silica (Table V-50).

    cir Multiply the FTE rate for each occupation (from Tables V-38a and V-38b) by the number of self-employed workers and employees in that occupation (from Table V-50) to obtain the ratio of FTE self-employed persons to FTE employees and then reduce that ratio to reflect only self-employed persons working on a multi-employer worksite where the work of the self-employed person cannot be isolated in time or space (Table V-51).

    cir Increase the earlier estimate of control costs by equipment category and industry (Table V-48) by the adjusted FTE ratio of self-

    employed workers (Table V-40) to calculate total control costs by equipment category and industry with self-employed persons included (Table V-52).

    Baseline Costs of Representative Jobs

    Baseline Job Safety Practices

    OSHA's cost estimates address the extent to which current construction practices incorporate silica dust control measures. Thus, OSHA's baseline reflects such safety measures as are currently employed. To the limited extent that silica dust control measures are already being employed, OSHA has reduced the estimates of the incremental costs of silica control measures to comply with the new PEL. As discussed in Chapter III of the FEA and summarized in Tables III-A-1 and III-A-2, OSHA estimates that 44 percent of workers with exposures currently below the new PEL are using the controls required in Table 1.

    Representative Jobs

    Unlike the situation with the general industry/maritime standard, OSHA does not have extensive data identifying the number of employees engaged in Table 1 tasks or the duration of their exposure to respirable crystalline silica during those tasks. Therefore, ERG developed a model based on ``representative jobs'' for the purposes of identifying the control costs necessary to comply with Table 1. Using RSMeans Heavy Construction Cost Data (RSMeans, 2008, Document ID 1331), which is a data source frequently used in the construction industry to develop construction bids, ERG (2007a, Document ID 1709) defined representative jobs for each silica-generating activity described in the feasibility analysis. These activities and jobs are directly related to the silica-related construction activities described in the technological feasibility chapter of the FEA. ERG (2007a, Document ID 1709) specified each job in terms of the type of work being performed (e.g., concrete demolition), the makeup of the crew necessary to do the work, and the requisite equipment. For example, for the impact drilling activity, ERG defined three representative jobs for various types of demolition work. For each job, ERG derived crew composition and equipment requirement data from the RSMeans (2008,Document ID 1331) guide and then calculated the per-day baseline cost from the labor rates, equipment charges, material costs, and overhead and profit markups presented in the cost estimating guide.

    Table V-30 of the FEA shows the specifications for each representative job and the associated daily labor, equipment, and material costs. Table V-31 of the FEA provides a summary of the labor rates and equipment charges used to estimate the daily cost of each representative construction job in Table V-30 of the FEA. Note that the data on hourly wages with overhead and profit in Table V-31 of the FEA, obtained from RSMeans (2008, Document ID 1331), are employed here to be consistent with other RSMeans cost parameters to estimate the baseline costs of representative jobs. The RSMeans estimates are published for the purpose of helping contractors formulate job bids, so ERG relied on that data as an indicator of the amount of labor and time that would be required for each of the representative jobs in the cost model developed for this analysis. These RSMeans estimates are later used only to determine two ratios: The labor share of the costs of representative construction jobs and the percentage increase in the cost of each representative job due to the addition of controls to comply with the final rule. Everywhere else in the cost chapter, when the actual wages were important to the calculations and are expressed as

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    fixed amounts and not just ratios, OSHA used 2012 BLS wage data, which include fringe benefits but not overhead and profit.

    SBREFA Panel Comments on Cost Methodology for Construction

    Prior to the publication of the PEA, one SBREFA commenter criticized the methodology for estimating engineering control costs on the grounds that while RSMeans estimates were used to establish the marginal costs of new controls (as a percentage of baseline costs), average wage rates (including fringe benefits) from the BLS Occupational Employment Statistics Survey, 2000, were used to calculate the value of at-risk tasks without providing a justification for not using RSMeans wage data (Document ID 0968, p. 13). Since BLS wage rates are significantly lower than the RSMeans rates used by ERG in earlier parts of the analysis, the commenter argued that this would significantly lower the base to which the marginal cost factors are applied to estimate compliance costs (Id.). This SBREFA commenter further argued that the RSMeans estimates are likely to be on the high end of estimated wages because they only cover unionized labor and are therefore likely to lead to high estimates of impacts. The commenter then recommended that more appropriate indexed labor wage costs be computed and used consistently throughout the analysis (Document ID 0968, p. 14).

    First, the commenter's concern is misplaced because the choice of the RSMeans estimates source does not skew the results in the manner suggested by the commenter; nor does it even have a significant impact on the cost analysis. The RSMeans estimates were used only to develop the ratio of costs for the representative jobs to the total labor cost and then to determine the incremental compliance costs as a percentage of the total and the share (percentage) of estimate value with controls accounted for by labor. Because the RSMeans estimates are organized by project cost to assist contractors in bid planning, that data set is the logical choice for this purpose over BLS data, which provides wage data but does not provide comparable costs for projects. Dividing project labor value by the labor share of project value yields an estimate of total project value.

    The absolute level of the RSMeans wage and equipment cost levels do not directly affect the resultant aggregate compliance costs. While lower wage rates would lower the baseline costs of the representative jobs, it does not follow that control costs as a percent of baseline costs would also be lower. In fact, if lower wage rates are combined with the same equipment costs, the equipment part of incremental control costs would be a higher percentage of total baseline costs. Only the labor share (percentage) of baseline costs, along with the incremental compliance costs as a percent of baseline costs, are taken from the analysis of representative costs and used in the subsequent estimation of aggregate costs. The absolute levels of the wage rates and equipment costs taken from RSMeans do not directly enter the aggregate cost analysis.

    Second, OSHA notes that the BLS wage data, on which the aggregate compliance costs are based, are obtained from a statistically valid, national survey of employment and compensation levels and are the best available data characterizing national averages of wages by detailed occupation. For some of the reasons the commenter noted, OSHA believes that the BLS wage estimate provides a more accurate reflection of average wages.

    Another set of SBREFA commenters criticized OSHA's cost estimation methodology, arguing that fundamental errors resulted in serious underestimates of the costs of engineering controls. The commenters asserted without any significant explanation that the task-by-task incremental cost estimates (shown in Table V-23 of the PIRFA, Document ID 1720, p. 749) should have been multiplied by two factors: (1) ``The ratio of the RSMeans labor rate to the BLS wage and benefits rate,'' and (2) the inverse of the ``percentage in key occupations working on task'' from Table V-26 (also in the PIRFA, Document ID 1720, p. 766). Under this approach, the commenters argued that ``the cost of PEL controls for brickmasons, blockmasons, cement masons and concrete finishers performing grinding and tuckpointing would be approximately seventy-two (72.0) times the ERG estimate, and . . . the cost of PEL controls for drywall finishing (at the 50 mug/m\3\ PEL) would be approximately 7.2 times the ERG estimate'' (Document ID 0004).

    The rationalization for these calculations was not provided, and OSHA found these conclusions without merit. The incremental control costs shown in Table V-34 of the FEA were based on RSMeans estimates for labor and equipment costs. As shown in Table V-34, these cost estimates, after adjustments for productivity impacts, are used to calculate the percentage increase in baseline costs associated with each control. The RSMeans-based cost estimates shown in Table V-34 are also used to estimate the share of total baseline task/project costs accounted for by labor requirements. The averages of the percentage increase due to incremental control costs and the labor share (percentage) of total baseline costs are shown in Table V-37 of the FEA. These two percentages are used to extrapolate the aggregate control costs associated with each task. This extrapolation was based on (1) the full-time-equivalent employment in key and secondary occupations associated with each task, and (2) the value of the labor time as measured by the BLS occupational wage statistics, adjusted for fringe benefits.

    OSHA provided similar responses in the PEA and requested comment on its responses to the SBREFA comments, but received none (see PEA, p. V-

    131).

    The same set of SBREFA commenters further argued that OSHA's analysis contained five more ``fundamental errors'' (Document ID 0004). First, the commenters asserted that OSHA's calculations understate the actual cost because they are based on old data (1999 or 2000 data from RSMeans rather than RSMeans 2003 data). OSHA used the most recent available data at the time the initial preliminary analysis was completed and subsequently updated those data for the PEA (and the FEA) using RSMeans estimates from 2008 (Document ID 1331). However, as noted previously, the RSMeans estimates do not directly determine the absolute level of aggregate compliance costs, but rather the labor share (percentage) of project costs and incremental compliance costs as a percentage of baseline costs. This aspect of the analysis received no further comment and has been retained for the FEA.

    Second, the commenters asserted that there is no information to ``suggest much less substantiate the premise that the exposure monitoring data in Tables 3-1 and 3-2 in the ERG (2007a) report, Document ID 1709) (even if they were properly collected and analyzed) are in any way representative of current workplace exposures across the country'' (Document ID 0004). In response, OSHA points out that the profiles used to estimate the numbers of workers exposed in excess of each PEL option were, in fact, based on the extensively documented technological feasibility analysis with many of the data points in the exposure profiles being taken from the findings of OSHA inspections (and based on ERG, 2007a, Document ID 1709). OSHA is tasked with using the best available evidence to develop the analyses, and the data in the exposure profile represent the best available evidence on current workplace

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    exposures to respirable crystalline silica. More importantly, for estimating the cost of controls, Table 1 in the final rule is intended to be the default option for protecting workers performing covered tasks, regardless of actual exposure level. The FEA reflects this, while recognizing that a sizable minority of workers with exposures below the PEL have limited their exposures by using such controls currently.

    Third, the commenters claimed that there is ``is no information to suggest much less substantiate the premise that the exposure monitoring data in Tables 3-1 and 3-2 (even if they were representative of current workplace exposures) are in any way representative of the non-existent, theoretical jobs artificially created by the FTE full-time equivalent analysis so as to justify their use as the foundation for Table 4-12'' (Document ID 0004). However, OSHA notes that the representative jobs on which the cost analysis is based were designed to correspond directly to the tasks assessed in the technological feasibility analysis. Furthermore, Table 4-12 in ERG (2007a, Document ID 1709) was derived directly from Table 3-2 and is independent of the ``FTE analysis.''

    Fourth, the commenters argued that a more logical and appropriate methodology would assume that all FTEs were exposed above the PEL in the absence of controls, and the commenter could find ``no justification, and substantial support to the contrary, for an approach that artificially condenses actual exposures into far more highly concentrated exposures (by condensing all at-risk task hours into FTEs) and then assumes that, despite the impact of this change, the grab bag of exposure monitoring described in ERG Tables 3-1, 3-2 and 4-12 represents these FTEs'' (Document ID 0004). The commenters asserted that the effect in ERG (2007a, Document ID 1709) of ``first multiplying total project costs by the FTE percentage (from Table 4-8) and then by the `Percentage of Workers Requiring Controls' from Table 4-12 (and then by the average `Total Incremental Costs as % of Baseline Costs' by job category from Table 4-7) results in an unjustified double discounting of exposed workers in the incremental cost calculation'' (Document ID 0004).

    OSHA disagrees. The Agency notes that ERG (2007a, Document ID 1709) used the exposure profiles from the industry profile to estimate the number of full-time equivalent workers that are exposed above the PEL. In other words, this exposure profile is applicable if all exposed workers worked full time only at the specified silica-generating tasks. The actual number exposed above the PEL is represented by the adjusted FTE numbers (see Table 4-22 in ERG, 2007a, Document ID 1709). The adjusted FTE estimate takes into account that most workers, irrespective of occupation, spend some time working on jobs where no silica contamination is present. The control costs (as opposed to some program costs) are independent of the number of workers associated with these worker-days. OSHA noted in the PEA that the thrust of the comment about ``double discounting'' was unclear, but the commenters did not respond with clarification. Nothing is ``discounted'' in the estimation of aggregate control costs.

    Finally, the SBREFA commenters argued that the ``application of the FTE analysis to the additional equipment costs is based on the wholly unfounded assumption, contrary to actual experience, that this additional equipment could be used with perfect efficiency (i.e., never idle) so that it is only at a particular site during the time the at-

    risk tasks are being performed'' (Document ID 0004). In response, OSHA notes that its analysis does in fact assume some efficiency with respect to the use of additional equipment required for controls. However, many of the equipment costs are based on monthly equipment rental rates provided by RSMeans that already embody some degree of idleness over the course of a year (see ERG, 2007a, Table 4-3, Document ID 1709). In other cases, daily equipment costs were directly estimated based on equipment purchase costs, annualization factors, and assumed operating and maintenance costs.\38\ OSHA did receive further comment on the issue following the publication of the PEA (Document ID 4217, pp. 84-88), and, in response, the Agency developed prorated ownership costs (equivalent to twice the rental rates) for control equipment for tradespersons performing tasks involving short-term, intermittent silica work.

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    \38\ These were originally translated to daily costs on the assumption of full-time usage (240 days per year). However, in response to this comment, this rate was adjusted downward, assuming instead that equipment would be used 150 days per year (30 weeks), on average; OSHA applied this downward adjustment to equipment usage in the PEA and the effect of this change in equipment usage was to increase the daily cost of control equipment.

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    Public Comment on Engineering Control Costs in Construction

    Having already incorporated comments from small business in the SBREFA panel process, the Agency produced revised estimates for the PEA in support of the proposed silica rule. In the PEA, OSHA requested comments from rulemaking participants on the Agency's preliminary estimate of control costs in construction. Below are comments representative of the prominent issues that raised concerns.

    The most broad-based critique of the construction cost analysis came from the Construction Industry Safety Coalition (CISC), and its consultant Environomics (Document IDs 2319, 2320, and 4217). Several of their arguments regarding underestimation of costs related to an undercount of the affected construction population (for example, they believed OSHA should have accounted for the cost to control silica exposures for plumbers). OSHA agrees in part that there were some occupations--plumbers, plumber helpers, electricians, electrician helpers, roofers, roofer helpers, terrazzo workers and finishers, and sheet metal workers--that likely have exposure and should be included in this analysis, as they do perform some activities covered by Table 1. These are discussed in FEA Chapter III, Industry Profile.

    Owning Versus Renting Engineering Controls in Construction

    OSHA also received comments regarding the availability of control equipment. In its post-hearing brief, CISC commented:

    In the Agency's cost analysis, it has also made the entirely impractical assumption that controls (e.g., wet methods, LEV) for the tools that construction workers use in performing tasks that generate respirable silica need to be available only during the exact duration while a dusty task is performed. The CISC estimates costs instead to provide control equipment on an ``always available'' basis to workers who engage in dusty tasks. Control equipment must be available whenever a worker may need to perform an at-risk task, and not for only the very limited duration when the at-risk task is actually being performed. Costs for the engineering controls required to meet the reduced PEL in the proposed rule will be far higher than OSHA estimates (Document ID 4217, p. 29).

    While OSHA agrees that CISC's argument has merit, during hearing testimony CISC's representative acknowledged that its estimates did not initially take into account the economic life of a control. This is reflected in the following conversation between CISC's Stuart Sessions and OSHA's Robert Stone:

    MR. STONE: So returning to the methodology for costing, you pretty much used our numbers and you used our, presumably, like you mentioned the dust shroud that has a one-year life and, therefore,

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    after one year, you take the cost again the second year, is that right? And the third year, and so on? Okay. I think this is perhaps a problem with the way you've done your analysis. We used basically FTEs, full-time equivalents. You're using three percent of the time let's say for plumbers, as an example, you're applying it to three crews, all right? At the end of one year, you're having them buy another dust shroud. And my view . . . they will have used nine percent of the economic life of the dust shroud. Now, you can argue I'd make an adjustment because we estimate 150-day construction work-year use of it, for full-time use. This would suggest, though, that after one year, you will have used one-sixth of the life of that dust shroud and an employer is not going to throw it out. It's still functional. He'll use it for the next five years. He'll use it for six years. Any views on that?

    * * *

    MR. SESSIONS: Yes. That's a good point, and I hadn't thought about that.

    MR. STONE: Okay, thank you. A related point is actually the same issue. It would be operating in maintenance costs. You're--it's going to be one-sixth of our original estimate, but I don't think you've made that adjustment.

    MR. SESSIONS: Correct. (Document ID 3580, Tr. 1501-1502).

    After the hearing discussion, CISC revised its methodology, noting:

    After additional thought and discussion about this issue with several construction tradespeople, we . . . concluded that useful life is a function of both how often the tool and controls are used, but also how long they sit in the construction worker's truck and get bounced around going from job site to job site (even when they are not used), and how often they are taken out of the truck and returned to the truck (even when they are only set up then taken down at the job site but not actually used). Thus useful life will increase if a tool sits idle for some percentage of the time when it is available, but useful life will not increase to the same proportional extent as the decrease in usage. We assumed in the example in workbook Tab # X2B that using the tool and equipment 1/4 as often will double its useful life (Document ID 4217, p 89).

    OSHA agrees with this updated methodology and has adopted CISC's approach--essentially assuming one-half of the usage life over which to amortize the purchased control equipment--for jobs that typically involve intermittent short-term exposure. The jobs for which the Agency assumed a half-life of the control equipment were: (1) Hole drillers using hand-held or stand-mounted drills--for electricians, plumbers, carpenters, and their helpers, and for sheet metal workers; and (2) handheld power saws for carpenters and their helpers. Note that OSHA's adoption of this updated approach resolves CISC's criticism that OSHA had not accounted for productivity decreases from controls not being available when the worker needs to use them for short-term or intermittent silica jobs.

    For all other construction jobs (i.e., those not itemized above involving intermittent short-term exposure), OSHA did not adopt CISC's approach but instead (as in the PEA) used the market-derived rental rate for control equipment without either doubling the rental rate to take into account ``down-time'' or requiring purchase of the control equipment. There are several reasons OSHA retained its PEA approach for these jobs in the final rule:

    In most cases, an employer's own/rent decision for control equipment will be determined by the own/rent decision for the construction equipment (including construction tools) to which the control equipment will be applied. If the employer rents/owns the construction equipment, the employer will rent/own the control equipment. The major exception would be if a particular piece of control equipment could be applied to many types of construction equipment. An example might be a dust collector. In that situation, the employer might find it economic to rent the construction equipment and own the control equipment. But, in that case, the purchased control equipment will not be sitting idle.

    Construction equipment is sufficiently expensive that employers, as a general matter, will not find it economically efficient to have it sitting idle. That is why employers so frequently rent construction equipment. Of course, employers that do only one type of construction job all year (or those that are sufficiently large that they work on that particular type of construction job all year) will find it economic to own the construction equipment--as well as the control equipment--but then the control equipment will not be sitting idle.

    In light of permit requirements and other job-planning requirements, in almost all cases, the employer will have advance knowledge of the details of the construction job (as opposed to, sometimes, repair work in general industry). This knowledge would include the construction equipment--and controls--required to perform the job. In fact, employers will often schedule construction jobs precisely to avoid having construction equipment sitting idle. In other words, the typical employer--and certainly the competent employer--

    won't come to the job site unprepared, needing to leave the job site to obtain rental equipment or controls.

    The construction sector is a significant component of the U.S. economy. There is a large, competitive construction equipment/

    control rental market in place to serve it. In most places, employers should be able to obtain needed construction equipment/controls in a timely manner under terms similar to those estimated here.

    For the aforementioned reasons, OSHA believes that the ownership-

    versus-rental cost issue, except in the case of construction jobs that involve intermittent short-term exposure, is somewhat of a red herring. The difference in amortized cost should be negligible, given that employers will choose to own or rent based on whichever is the lower-

    cost alternative. In fact, because rental costs are typically somewhat higher than amortized ownership costs, OSHA may have overestimated compliance costs for those employers who purchase control equipment.

    Self-Employed Persons

    CISC, and its contractor Environomics, claimed in their comments that OSHA had omitted the costs of compliance by sole proprietors (typically self-employed persons) (Document ID 4217, p. 80). The inclusion of such costs and the circumstances under which they would arise are discussed in Chapter III of the FEA. In the FEA OSHA has accounted for costs associated with controlling employee exposures from sole proprietor activities. The actual self-employment data and the estimated effect on employer costs are presented at the end of this section on engineering control costs in construction.

    Full Cost vs. Incremental Cost

    Prior to the PEA, a participant in the SBREFA process noted that while OSHA established the total incremental cost for each silica control method (summarized for the final rule in Table V-35 of the FEA), the cost estimates were based on the application of a single control method. The commenter argued that there may be cases where two or more control methods would have to be applied concurrently to meet the exposure limits (Document ID 0968, p. 14). In response, OSHA noted in the PEA that for each task, specified control options correspond to the control methods described in the technological feasibility analysis in Chapter IV (of the PEA). These methods reflected the choices laid out in Table 1 of the proposed rule; they were also presented in Table V-25 in the PEA along with OSHA's calculation of the weighted average proportion of project costs attributable to labor and the incremental

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    control costs as a percentage of baseline project cost.

    Throughout the comment period, CISC reiterated its pre-PEA objections to OSHA's methodology of estimating incremental costs instead of the ``full'' compliance costs, which CISC defined as including the costs for employers to meet their existing duty to comply with OSHA's old PEL (CISC claims employers of ``nearly 60,000 workers'' were not in compliance with OSHA's preceding standard and would have OSHA attribute the costs of compliance with the preceding standard to the costs of this rule) (Document ID 4217, p. 33):

    In our view, OSHA has made two errors in the approach it has taken:

    First, the ``full'' compliance costs for reducing worker exposures from their current levels to below the proposed new PEL are the conceptually correct costs to estimate when assessing economic feasibility, not the ``incremental'' costs for reducing exposures to below the proposed new PEL from a starting point assuming compliance with the current PEL. In practice, employers will face the full costs, not the lesser incremental costs, and the economic feasibility assessment should consider whether employers can afford these full costs, not the hypothetical and lower incremental costs.

    Second, OSHA has made a conceptual error in the Agency's methodology for estimating compliance costs * * * Insofar as OSHA omits all costs for employees with exposures >250 microg/m\3\--failing to estimate the costs to reduce their exposures all the way down below 50 microg/m\3\ instead of only to below 250 microg/m\3\--OSHA estimates costs that fall short of the incremental costs of the Proposed Standard that the Agency aims to estimate. (Document ID 4217, pp. 96-97)

    Both arguments are now largely moot because in the FEA almost all of the construction engineering control costs are based on compliance with Table 1 and encompass all employees engaged in the Table 1 tasks, regardless of their current level of exposure. OSHA has included the full incremental--and full total--costs for all employers in construction who have workers who are performing tasks listed on Table 1, even those workers with exposures currently above 250 microg/m\3\.

    CISC's arguments for the construction sector are now only relevant to the very few tasks not covered by Table 1, such as tunnel boring. OSHA therefore addresses CISC's arguments in the context of those few tasks.

    The first argument is that employers who are not in compliance with the preceding PEL of 250 microg/m\3\ will have to incur costs to achieve that PEL in addition to the costs they will incur to reach the new PEL of 50 microg/m\3\. As laid out in the PEA, OSHA rejects this position, as this is inappropriate for estimating economic feasibility among firms making a good faith effort to comply with the existing silica rule. Employers who had a legal obligation to comply with OSHA's preceding PEL but failed to do so are not excused from their previous obligation by the new rule; nor can the fulfillment of a pre-existing duty be fairly re-characterized as a new duty resulting from a new rule. But this issue is not limited to construction, and a more complete discussion is presented in the general industry engineering control cost section in the FEA.

    The second argument can be dismissed on similar grounds. CISC's argument appears to assume that employers will incur different costs for different controls necessary to reduce exposures from above 250 microg/m\3\ down to 250 microg/m\3\, and from 250 microg/m\3\ down to 50 microg/m\3\. In many cases, however, the same controls needed to bring exposures below 250 microg/m\3\ will also bring exposures to 50 microg/m\3\ or below, so there would be no cost associated with the new rule. To the extent that separate controls are required to reduce exposures down from 250 microg/m\3\ to 50 microg/m\3\, OSHA does account for the costs for those controls.

    General Comments on Cost Methodology

    James Hardie Building Products commissioned Peter Soyka of Soyka & Company LLC to perform an evaluation of the PEA. While Mr. Soyka's comments cover many aspects of the analysis and overlap with those of other commenters, some were relatively unique.

    In one place, Mr. Soyka questions the entire method of analyzing jobs from the level of workers and their tasks. He expressed concern about both what he termed the failure to capture the cost to the establishment, as well as the need for workers to have controls available (Document ID 2322, Attachment G, p. 165). OSHA did not, however, ignore other costs for establishments. Elements of these costs are dealt with at the establishment level for some ancillary provisions of the standard, and are discussed later in this chapter. The second element, regarding the availability of controls for certain occupations, mirrors concerns raised by Environomics and CISC, and has been dealt with above.

    Elsewhere in his comments, Mr. Soyka states that ``OSHA should develop revised unit costs that consider the full array of elements that affect what a business charges its customers for a unit of time expended.'' Such unit costs,'' he submitted, ``would include direct labor, fringe benefits, overhead, SG&A, and a reasonable allowance for profit (e.g., the typical cost of capital found in a specific industry or overall)'' (Document ID 2322, Attachment G, p. 182). The approach put forward in the PEA and in the FEA incorporates fringe labor costs. OSHA has provided a sensitivity analysis of the effects of including other cost elements in the sensitivity analysis section of the FEA. As noted elsewhere, for the FEA the Agency recognizes that the labor productivity effect of adopting certain controls is accompanied by a loss of productivity in equipment under certain circumstances; that additional cost has been incorporated in the FEA. The National Association of Home Builders (NAHB) faulted the costing of engineering controls in the PEA on several grounds, including several very similar to those raised by Mr. Soyka and addressed earlier. NAHB also stated that OSHA has not considered the ``unique nature of construction, in that sites are not fixed in nature, and that equipment may need to be moved between several sites in a single day'' or the ``compliance costs for cleanup of the jobsites'' (Document ID 2296, p. 38). Both are addressed in the FEA as opportunity costs or housekeeping costs.

    Other Aspects of Unit Costs

    Following publication of the NPRM, a representative of petrochemical employers, the American Fuel and Petrochemical Manufacturers, raised concerns about retrofitting and clean-up costs that it claimed were improperly omitted from OSHA's analysis of engineering controls in construction:

    OSHA claims ``the estimated costs for the proposed silica standard rule include the additional costs necessary for employers to achieve full compliance.'' Yet it fails to consider the additional costs of retrofitting existing equipment to comply with Table 1 in Section 1926.1053 (Table 1). In addition to acquiring new engineering controls not previously implemented, many employers will have to modify pre-existing equipment to come into compliance (e.g., outfitting the cab of a heavy equipment bulldozer with air conditioning and positive pressure). Table V-3, found in OSHA's complete PEA, begins to address these costs by enumerating the capital and operating costs for the engineering controls required by Table 1. But it does not account for the ancillary costs of

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    retrofitting those controls, including the cost of retrofitting the equipment itself as well as the lost time the facility may absorb in doing so.

    OSHA also fails to account for the clean-up costs associated with the natural by-products from Table 1's required engineering controls. For example, many of the engineering controls require the use of wet methods or water delivery systems. Employers will incur costs from removing (from the clean-up process itself and lost time) excess water to prevent ice or mold from developing. Yet these costs go unaccounted for in the PEA (Document ID 2350, pp. 6-7).

    In the FEA, the Agency does not include any specific cost for retrofitting equipment. The record indicates that almost universally employers either already have equipment with the required controls available for use (e.g., wet method for saw), or the equipment allows for the easy addition of a control (e.g., shroud for HVAC). Furthermore, most equipment is portable and/or handheld and is relatively inexpensive with a useful life of two years or less. As a result, it would simply not make economic sense to retrofit the equipment when it would be less expensive to replace it. In addition, most other types of relevant construction equipment--heavier and drivable--generally have a useful life of ten years or less; control-

    ready equipment of this type has been on the market for years and is typically already in use. Thus, OSHA did not estimate any retrofitting costs. While some employers might still retain pieces of earth-moving equipment that do not have a cab that complies with Table 1, equipment with a cab is the industry standard for both purchase and rental. As discussed in this chapter in the context of productivity, the implication is that the market has shifted to heavy equipment with cabs even in the absence of a silica standard. In addition, in final Table 1 OSHA has reduced the number of tasks that require equipment with enclosed cabs to just a single task: Heavy equipment and utility vehicles used to abrade or fracture silica-containing materials or used during demolition activities involving silica-containing materials. For the odd piece of old, cab-less heavy equipment which does not conform to the requirements of Table 1, individual employers have the choice of renting the required equipment to perform that single task, or simply using the cab-less equipment only on non-silica tasks (thereby ceding the one silica-abrading construction task to employers that have more up-to-date equipment). In short, the requirement to use a cab when performing Table 1 tasks is not a requirement to retrofit all existing equipment that might conceivably be used for a Table 1 task.

    Regarding the question of clean-up costs, the commenter treats the issue as if there were no clean-up costs associated with generating silica currently. As discussed in the Environmental Impact Analysis (Section XIV of this preamble) and in the discussion of productivity impacts later in this section, there was substantial comment to the record indicating that in many, if not most, situations, the controls associated with reducing silica exposure will lead to a net decrease in the amount of time required for cleanup after a job. While OSHA is not attempting to quantify any potential cost savings, the record likewise does not support attributing additional costs to cleanup.

    Specific Industry/Equipment Category Cost Comments

    Crushing Machines

    William Turley, executive director of the Construction & Demolition Recycling Association (CDRA), broadly described the impacts he anticipated for his industry.

    Recyclers who crush materials for reentry into the economic mainstream as aggregate products would appear to have to do all of the following:

    Purchase and install climate-controlled enclosures or cabs for all crusher operators;

    Install crusher baghouses for particulate emission reduction;

    Enclose conveyor belts--a measure unprecedented in our industry;

    Install effectively designed and maintained water spraying equipment;

    Impose full-shift use of respirators for all quality control hand pickers working on processing lines;

    Establish and implement emission testing protocols and procedures to ensure compliance with the PEL;

    Implement medical surveillance programs for all employees engaged in material crushing activities; and

    Achieve a ``no visible emissions'' standard, which frankly is both unattainable and utterly unreasonable.

    To the best of our knowledge, no recycler in the United States has a system even resembling the above. The cost of such systems will unquestionably threaten the economic viability of construction & demolition debris recyclers across the Country. It must also be pointed out that the industry has an exceptionally diverse composition of larger operators with higher economic margins and small operations with limited capabilities to capitalize the type of equipment called for in this rulemaking (Document ID 2220, pp. 2-3).

    The final silica rule does not require all the above steps. OSHA expects that crushing machines will be used for construction/demolition activities, as discussed in detail in the Summary and Explanation of the standard. As such, OSHA anticipates that employers engaged in the recycling operation would follow Table 1 and would not need to conduct exposure monitoring.

    For crushing machines, OSHA removed the ``no visible emissions'' requirement and the requirement for enclosed cabs, both of which had been in the proposed Table 1. Employers are now required to use a spray system and comply with manufacturer instructions. Also, there is no requirement to enclose conveyor belts or install crusher baghouses. Instead, employees must use a remote control station or ventilated booth that provides fresh, climate-controlled air to the operator. For the FEA, OSHA added the cost of a ventilated booth for the use of crushing machines in construction/demolition activities. Most crushing machines are already equipped with movable controls that will allow operation of the machine from inside the booth, so no additional equipment modifications will be required for most machines. Crushers available for purchase or rental are also typically equipped with a water spray system, so OSHA has not assessed any incremental cost for sprayers.

    Homebuilding--Roofing

    The National Roofing Contractors Association (NRCA) objected to OSHA's preliminary cost estimates for controls used to limit silica exposure in roofing operations, claiming that OSHA's preliminary estimate of an average of $550 per year for firms that employ 20 workers or fewer (covering the majority of roofing contractors) had significantly underestimated the cost of specialized saws that would be required for roofing equipment. In support of the argument that OSHA had underestimated costs, NRCA identified costs for retrofitting portable saws with integrated dust collection systems along with specialized vacuums equipped with HEPA filters (Document ID 2214 p. 4).

    The task of cutting most roofing materials would fall under ``Handheld power saws (any blade diameter)'' in Table 1, and the final version of Table 1 does not allow for the dust collection methods described, so the majority of costs quoted by NAHB are not relevant. Instead, the final version of Table 1 requires that the employer use wet methods. Second, the estimate of $550 a year in costs to very small employers was an estimated average across all affected establishments with fewer than 20 employees, not just roofing operations in homebuilding. Questions of small business impact or economic

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    feasibility for the roofing industry are dealt with Chapter VI of the FEA.

    The comments submitted by consultant Peter Soyka on behalf of James Hardie Building Products (``Hardie'') presented a table of typical devices with engineering controls involved in fiber cement cutting and an un-sourced range of costs for the retail prices of those types of devices and their controls (Document ID 2322, p. 13).

    Hardie's inclusion of a table of retail prices for the purchase of equipment with controls suggests there may have been a misunderstanding of the nature of OSHA's cost methodology--it is not based on purchasing entirely new pieces of equipment, but making sure the equipment has the controls necessary to comply with Table 1. To the extent commenters submitted estimates addressing the latter question, OSHA has taken them into consideration in its final estimates.

    Asphalt Milling

    Fann Contracting, Inc. acknowledged that the availability of equipment with built-in controls is rising. However, the commenter suggested that OSHA's preliminary assessment of the design specifications and costs for the engineering controls identified in Table 1 of the proposed rule had under-counted the amount of milling machines and other paving-related equipment that the commenter believed would still require additional retrofits to enclosed cabs (sealing cracks, adding air conditioning, upgrading to HEPA filters, etc.) to satisfy the requirements in Table 1 (Document ID 2116, pp. 6-7).

    Table 1 in the final rule does not require a cab for milling machines or any of the equipment identified by the commenter for paving purposes, so the commenter's concerns are not relevant. Table 1 only requires cabs for ``(xvii) Heavy equipment and utility vehicles used to abrade or fracture silica-containing materials (e.g., hoe-ramming, rock ripping) or used during demolition activities involving silica-

    containing materials,'' and specifies it as an option for ``(ix) Vehicle-mounted drilling rigs for rock and concrete.'' Table 1 requires employers to use wet methods to control dust emissions from milling machines. These costs have been accounted for in the cost analysis.

    Drywall Finishing

    A SBREFA commenter raised questions about the availability of silica-free joint compound for drywall finishing (Document ID 0004). In the PEA, OSHA relied on NIOSH studies showing that silica-free joint compounds had become readily available in recent years (see ERG, 2007a, Section 3.2) (Document ID 1709). The cost model for the PEA assumed that 20 percent of drywall finishing jobs would continue to use conventional joint compound. Based on additional information, OSHA has determined that all commercially available joint compounds have no, or very low amounts of, silica and do not pose a risk to workers from respirable crystalline silica (Document ID 2296, pp. 32, 36; 1335, p. iii) and has therefore not included drywall finishing in Table 1 or taken any costs for this task (see Section XV. Summary and Explanation of the Standards, Specified Exposure Control Methods for more information).

    Number of Days Controls Are Used Annually

    Whether equipment, and the relevant controls, are rented or purchased, the effective annual cost of the equipment is based on the assumed number of days per year that it would be used. In the PEA, OSHA had estimated rental of the equipment for 150 days during each 365-day period. Based on comments received from industry representatives during the 2003 SBAR Panel process (Docket ID 0968), this estimate had been reduced from an average of 250 days in the Preliminary Initial Regulatory Flexibility Analysis (PIRFA). This reduced workday estimate presumably reflected winter weather slowdown in many parts of the country, as well as general weather conditions (such as rain) that can interfere with many construction processes, and resulted in \2/3\ higher daily rental rates for control equipment.

    However, Environomics, in developing its own cost estimates, assumed that control equipment would be used for 250 days a year, without an articulated rationale for departing from the estimate provided during the SBAR Panel process (Document ID 4023, Attachment 2, X2B-Hole Drilling Unit Costs, Cell P:Q44). More importantly, Environomics selectively and inconsistently applied 250 days only to the frequency of usage but not to the daily rate (which OSHA had based on 150 days of usage). To see why it is a problem to apply a different number of days to the same daily rate, consider a piece of control equipment, with a one-year life, known to cost $1,500. Using a 150-day construction work-year, OSHA would estimate a daily rate for the control equipment of $10 ($1,500/150 days in the construction work-

    year). The annual cost for that control would be $1,500 ($10 multiplied by 150 days). Using the same example, Environomics would keep OSHA's daily rate of $10 (amortized over 150 days) but apply it to a 250-day calendar to arrive at an annual cost of $2,500--where the one-year cost of the equipment was known to be $1,500. In short, the selective 250-

    day methodology Environomics used results in an overestimation of costs by 67 percent.

    Accordingly, OSHA has decided to retain the 150-day construction work year based on the best available evidence, and the Agency has consistently applied that work-year throughout the cost analysis developed in the FEA for construction. (General industry and maritime work is typically less affected by weather, so a separate work-year number of days is used for those calculations).

    Unit Control Costs

    In developing the cost estimates in the FEA, OSHA defined silica dust control measures for each representative job (see ERG (2007a, Document ID 1709). Generally, these controls involve either a water-

    spray approach (wet method) or a dust collection system to capture and suppress the release of respirable silica dust. Wet-method controls require a water source (e.g., tank) and hoses. The size of the tank varies with the nature of the job and ranges from a portable water tank (unspecified capacity) costing $15.50 a day to a 10,000 gallon water tank with an engine-driven discharge, costing $168.38 a day.\39\ Depending on the type of tool being used, dust collection methods entail vacuum equipment, including a vacuum unit and hoses, and either a dust shroud or an extractor. The capacity of the vacuum depends on the type and size of tool being used. Some equipment, such as concrete floor grinders, comes equipped with a dust collection system and a port for a vacuum hose. The estimates of control costs for those jobs using dust collection methods also include the cost for HEPA filters.

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    \39\ See Chapter X in the FEA for a discussion on the environmental impacts resulting from the use of wet methods for controlling exposure to silica.

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    The unit costs for most control equipment are based on price information collected from manufacturers and vendors. In some cases, control equipment costs were based on data from RSMeans (2008) on equipment rental charges (Document ID 1331). Table V-32 of the FEA shows the general unit control equipment costs and the assumptions that OSHA used to estimate the costs for specific types of jobs.

    For each job identified as needing engineering controls, OSHA estimated

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    the annual cost of the appropriate controls and translated this cost to a daily charge, based on an assumed use of 150 days per year (30 weeks), as explained earlier. The only exceptions were engineering controls expected to be used for short-term, intermittent work. For these controls, consistent with the CISC methodology that OSHA adopted, carpenters and other occupational groups were estimated to purchase this control equipment, and for costing purposes, OSHA amortized the equipment over its ``half-life''--that is, over 75 days rather than 150 days (effectively doubling the daily capital costs of the equipment). Accordingly, Table V-32 of the FEA shows separate daily cost estimates, for regular and for infrequent use, for a dust extraction kit and for a 10-15 gallon vacuum with a HEPA filter.

    Incremental Labor Costs and Productivity Impacts in Construction

    In addition to incremental equipment costs, OSHA estimated in the PEA the incremental labor costs generated by implementing silica dust controls. These labor costs were generated by: (1) The extra time needed for workers to set up the control equipment; (2) potential reductions in productivity stemming from use of the controls; (3) additional time to service vacuum dust control equipment; and (4) additional housekeeping time associated with or generated by the need to reduce exposures. All additional labor costs related to the use of controls were subsumed into a single additional labor productivity impact estimate for each of the representative job categories. Except where otherwise noted, the productivity impact described is negative, meaning that the addition of the control is expected to reduce productivity. To develop estimates of the labor productivity impacts of the dust control equipment that would be required as a result of the proposed standard, ERG interviewed equipment dealers, construction contractors, industry safety personnel, and researchers working on construction health topics.

    In part, because most silica dust controls are not yet the norm in construction, knowledge about the impact of dust controls on productivity was uneven and quite limited. More precisely, few individuals that ERG interviewed were in any position to compare productivity with and without controls and the literature on this topic appears deficient in this regard. Overall, telephone contacts produced a variety of opinions on labor productivity effects, but very few quantitative estimates. Of all the sources contacted, equipment rental agencies and construction firms estimated the largest (negative) productivity impacts. Some equipment vendors suggested that there are positive productivity effects from control equipment due to improved worker comfort (from the reduction in dust levels). Others suggested that the use of dust collection equipment reduces or eliminates the need to clean up dust after job completion. Comments to the record, discussed below, closely mirrored this preliminary information.

    The estimation of labor productivity effects is also complicated by the job- and site-specific factors that influence silica dust exposures and requirements for silica dust control. Potential exposures vary widely with hard-to-predict characteristics of some specific work tasks (e.g., characteristics of materials being drilled), environmental factors (e.g., wet or dry conditions, soil conditions, wind conditions), work locations (e.g., varying dust control and dust cleanup requirements for inside or outside jobs), and other factors. Generalizations about productivity impacts, therefore, are hampered by the range of silica dust control requirements and work circumstances.

    After considering the existing evidence OSHA concluded that labor productivity impacts are often likely to occur and accounted for them in the PEA analysis. In the PEA, depending on the general likelihood of productivity impacts for each activity, OSHA used a productivity impact ranging from zero to negative five percent of output. After considering the many comments advocating for both increasing and decreasing the productivity impact estimates, OSHA has concluded that the estimates in the PEA were approximately correct and has retained the PEA estimates for the FEA. The comments and factors influencing each selection are described in the following discussion.

    SBREFA Panel Comments on Productivity Impacts

    In response to the SBREFA Panel, the Reform OSHA Coalition commented on the estimates of the impact of exposure control equipment on productivity during construction operations. This SBREFA commenter noted that the estimates of the productivity impact of using additional control measures were based on interviews with dealers, contractors, and researchers working on construction health topics and expressed its opinion that it was not clear how this ``purely qualitative analysis was translated into productivity impact rates . . . . '' (Document ID 0968, p. 14). The commenter indicated that engineering control compliance costs would be sensitive to the ultimate choice of productivity impact measures (Id.).

    OSHA responded to these comments in the PEA as part of the discussion of the basis for OSHA's productivity estimates. OSHA summarizes the responses to SBREFA comments here for the convenience of the reader. As described in the PEA, ERG's research revealed little substantive, quantitative evidence about the magnitude of the productivity impacts of the controls, and in some cases, the direction of the impacts (positive or negative) appeared to depend on the specific nature of the job. OSHA's estimates in the preliminary analysis reflected ERG's best professional judgment about the likely magnitude of these impacts. Some of the estimates may be conservative because under some scenarios for certain tasks the productivity impacts could be significantly smaller than those shown in Table V-23 of the PEA. In some scenarios the productivity impact may even be positive.

    The same commenter also expressed a concern that even though ``silica is not now considered a hazardous waste,'' OSHA had not analyzed the impact of the proposed rule on disposal of ``silica-

    contaminated'' wastes such as ``filters of dust control vacuums and contaminated water discharge'' (Document ID 0968, p. 28). The commenter asserted that disposal issues are ``acute on the construction site where a means to readily dispose of such material or water is not available'' (Id.). The comment was somewhat puzzling because the comment was premised on the fact that there is not currently any ``hazardous'' classification for such waste that would trigger special disposal duties, and the commenter did not explain why any additional costs would be incurred beyond normal disposal practices. OSHA did not identify any new areas of cost in its Environmental Impacts analysis presented in the FEA, and finds no evidence that employers will be required to incur additional environmental costs as a result of this rule, other than some potential permit-modification notification costs addressed in the discussion of engineering control costs for general industry in the FEA. The incremental disposal costs resulting from dust collected in vacuums, discarded filters, and other sources in construction are therefore likely to be de minimis. An analysis of wet methods for dust controls suggests that in most cases the amount of slurry discharge is not

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    sufficient to cause a runoff to storm drains or surface water.\40\

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    \40\ For a more detailed discussion of this issue, see Chapter X of the FEA.

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    Public Comment on Productivity Impacts in Construction

    OSHA invited comment on the productivity impacts--positive and negative--resulting from the introduction of controls to limit exposure to silica. In the discussion below, OSHA reviews comments supporting both negative productivity impacts and positive productivity impacts. The comments supporting negative productivity impacts include assertions that OSHA underestimated the negative productivity impact of complying with the silica rule, failed to include a productivity impact on equipment, and failed to include a fixed productivity impact. OSHA considered those comments before concluding that it will generally retain the approach it used in the PEA, with the exception of selectively adding additional costs for productivity impacts on equipment in response to a point raised by CISC. OSHA will also explain separately why it is not calculating any productivity impact for two specific activities: (1) Use of cabs for earthmoving equipment, and (2) drywall installation.

    Public Comments Suggesting That OSHA Underestimated the Productivity Impacts Associated With Engineering Controls

    The Interlocking Concrete Pavement Institute reported that ``converting from in-place paver cutting to wet cutting and/or vacuum systems could induce a 50 percent productivity penalty,'' but did not otherwise substantiate that claim beyond noting that it was a survey response from one of its members (Document ID 2246, Attachment 1, p. 3).

    Mr. Soyka, in the comments prepared for Hardie, critiqued OSHA's estimates of the productivity impact on construction operations as ``far too small'' and urged OSHA to adjust productivity-loss estimates based on empirical data ``if available'' (Document ID 2322, Appendix G, pp. 14-15 and 21-22). However, the commenter did not clearly identify any such empirical data in the comments. The only labor-based engineering control cost alternative offered by the commenter that resembled ``empirical data'' is the addition of a seven-hour penalty per job that was ``based on a JHI time-motion study'' apparently conducted exclusively in a single industry (new home construction) and comprised of data from just the JHI study (Document ID 2322, Appendix G, Attachment A, p. A-8). OSHA could not determine whether it would actually supply new ``empirical evidence'' that would warrant a change from the preliminary estimate because the study was not submitted into the record. The commenter cites ``James Hardie Building Products, Inc., undated, pg. 15,'' which appears to align with an entry in the list of references to an undated ``James Hardie Labor Efficiency Manual,'' but that manual was not submitted into the record.

    Mr. Soyka recommended that OSHA use time-motion studies to derive the estimated productivity impacts.

    . . . Few of the productivity penalties estimated by OSHA are supported by actual data (e.g., time-motion studies). OSHA should apply a more conservative approach that considers how work flow and task completion are likely to be affected by newly required changes to existing practices as well as entirely new activities (Document ID 2322, Appendix G).

    In addition, Mr. Soyka developed an alternative cost model that included additional productivity impacts that OSHA did not include. In this model Mr. Soyka ``assumed that wherever possible, company owners in the residential construction industry will outsource their compliance obligations to specific subcontractors . . . providing the products and services that might generate significant amounts of silica dust'' (Document ID 2322, Appendix G, p. 26). In this scenario, Mr. Soyka determined that the employer would require ``the subcontractor to relocate its work location outside the house(s) being constructed to a distance sufficient to ensure that silica dust concentrations remained minimal inside and around the house(s)'' and that ``relocating the materials and work giving rise to silica dust generation . . . would add substantially to the time required to complete the associated tasks'' (Document ID 2322, Appendix G, p. 30). He accounted for this additional time by increasing the productivity impact on the specialty subcontractors to seven hours per job, ``based upon time-motion studies conducted by James Hardie (James Hardie Building Products, Inc., undated, pg. 15)'' (Document ID 2322, Appendix G, p. 31).

    Mr. Soyka's model also included a productivity impact for ``wearing respirators to account for fatigue and adverse impacts on employee-to-

    employee communication'' (Document ID 2322, Appendix G, p. 32).

    OSHA fundamentally disagrees with the Mr. Soyka's assumptions. Mr. Soyka's assumption that all silica-generating tasks need to be removed from the homebuilding site results from a misunderstanding of OSHA's statement that ``in response to the proposed rule, many employers are likely to assign work so that fewer construction workers perform tasks involving silica exposure; correspondingly, construction work involving silica exposure will tend to become a full-time job for some construction workers'' (FR, 2013, at 56357) (Document ID 2322, Appendix G, p. 25). OSHA did not mean that silica-generating tasks will be subcontracted out and that subcontractors will be forced to perform these tasks off-site. Rather, the Agency was acknowledging that construction employers would likely consolidate the responsibilities for performing silica-generating tasks to as few workers as possible in order to limit exposures to peripheral workers.

    As mentioned previously, the ``time-motion studies'' performed by James Hardie, compiled in an unpublished reference, were not provided for public inspection. Moreover, the description of how those data were used in developing the model suggests that Mr. Soyka's relevant assumptions are not based on time-motion studies of how long it actually takes to perform specific tasks with controls added. Rather, it appears that Mr. Soyka assumed inflated times to perform the tasks, based on a misunderstanding of what the proposed rule required; in any case, it is not descriptive of the requirements for the final rule. Mr. Soyka's suggested approach contrasts with the estimates provided by CISC/Environomics, which accepted the limitations of the analytical exercise and agreed with most of the estimates in the PEA regarding the ``variable'' productivity effect.

    Moreover, it should be noted that aside from weighing the possible competing forces on productivity in the course of a shift (e.g., more time for set up vs. less time required for clean-up), there is also a short-run/long-run phenomenon over a longer period as the standard comes into use. There may be a short learning curve until workers determine the most efficient way to perform a job when controls are introduced (Document ID 3581, p. 1700); in some cases the effect may be relatively larger until the method of performing a job is reconceptualized. Mr. Sokya criticizes OSHA for not recognizing ``the dynamic nature of construction'' (Document ID 2322, Appendix G, p. 19), but one obvious aspect of the dynamic nature of construction is that employers will be constantly adapting to changing circumstances and trying to find ways to

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    perform the job in the most cost-effective manner. In short, the Agency believes that a time-motion study of a particular task is neither necessary to determine approximately what the effect will be in the short-run, nor would it allow OSHA to determine what the long-run cost of integrating the controls will be.

    CISC and its consultant Environomics, as well as some other commenters, questioned OSHA's productivity-loss estimates associated with the required controls. CISC/Environomics claimed that overall OSHA ``underestimated productivity losses associated with performing tasks using the prescribed controls by an amount roughly equal to the average equipment intensity of about 42 percent'' (Document ID 2320, p. 29). CISC/Environomics reported that this underestimation came largely from OSHA failing to account for what they termed ``fixed productivity impacts'' and for productivity impacts to equipment. Both of these concerns are discussed below.

    In its post-hearing brief, CISC/Environomics presented the results from a questionnaire and interviews conducted with employers and knowledgeable tradespeople; the results included a finding that ``the variable penalty percentages . . . were the same as or slightly larger than those that OSHA had estimated'' (Document ID 4217, p. 92). CISC/Environomics did not submit the questionnaire or the answers received, nor the details of the interviews, to the record so OSHA could not fully evaluate the findings or compare them to its own findings. Based on the available summary information it appears that, while CISC and OSHA's estimates for variable productivity costs were nearly identical, it is not clear that CISC's estimates took current compliance into account. CISC stated that its members felt that ``something greater than zero variable productivity penalty should be estimated for masons using portable saws controlled with wet methods . . . and for heavy equipment operations using enclosed cabs and HEPA filters'' (Document ID 4217, pp. 92-93). OSHA acknowledges that there would be a productivity impact to comply with the requirements of the silica rule relative to using no controls for those activities. However, as shown in Chapter III of the FEA, Industry Profile, OSHA has found high levels of baseline compliance with the provisions of the rule for those activities. As is standard in OSHA's costing methodology, only costs above and beyond those incurred under current standards are attributable to the final rule.

    In addition, CISC argued that OSHA should take higher productivity impacts because ``in some fraction of these instances (where controls would be required), the controls are hellaciously difficult to use'' (Document ID 3580, Tr. 1321). The testimony goes on to give examples of such difficulties such as when ``building houses where the utilities are not yet in and the water is not yet in,'' when working in places where power is not readily available such as in parking garages or on scaffolding, and when doing work that requires wet methods outdoors in extremely cold temperatures (Document ID 3580, Tr. 1321-1322). A different commenter, the National Utility Contractors Association, similarly criticized OSHA's estimates for excluding additional water-

    transportation costs: ``there is not always a water supply available which would require trucking large volumes of water to the job site which adds additional costs.'' (Document ID 3729, p.3)

    Given the fact that the majority of the silica-generating equipment requiring controls under this standard--such as tuckpointing grinders and concrete drilling equipment--require electricity, OSHA does not find merit in applying any productivity impact simply because the controls for those tools may also need electricity. If the employer can find a way to power the equipment, it can also power the controls when necessary. Similarly, employers must commonly transport water to worksites without it for cleanup and sanitation purposes, and OSHA's technological feasibility analysis explains why the amount of water required to generate the spray mist is not typically very significant. Although it seems plausible that wet methods would occasionally be used outdoors by some employers in weather cold enough to freeze the water mist used to control the silica dust, this is far from a common construction occurrence. Moreover, it is not entirely clear from the record that freezing mist would decrease productivity. OSHA's estimates of productivity impacts is intended to represent an average across all situations, and the tiny fraction of time wet methods will need to be used outdoors in extremely cold weather should not skew the average productivity impact.

    CISC/Environomics stated that there should also be a productivity impact on equipment rental or use as well as for the additional labor to operate that equipment longer. Environomics reported that a complete cost estimate of productivity loss would include not only the additional labor time required, but also the cost of having to rent equipment for a longer period of time.

    . . . Simply put, a productivity penalty for labor will translate to a productivity penalty for equipment. For example, if due to a labor productivity loss, the labor time required to complete a job increases from eight hours to eight hours and 15 minutes, the equipment time required for job completion will also increase to eight hours and 15 minutes. Additional equipment rental costs will be incurred for the additional 15 minutes, or equipment owned by the employer will be delayed for use on another job by 15 minutes (Document ID 2320, p. 29).

    This concern was reiterated both in its hearing testimony (Document ID 3580, Tr.1323) and in its post-hearing brief where Environomics stated that ``OSHA's analysis should add an equipment component to the costs associated with whatever productivity penalty is incurred in performing a construction task using the Table 1 controls'' (Document ID 4217, p. 91). OSHA agrees, in part, and recognizes that there can be a productivity impact for equipment (as well as for labor) for many tasks when there is a cost created by having to extend the rental time of the equipment.

    In the PEA, OSHA had estimated the labor productivity impacts associated with engineering controls to reduce silica exposure. For the FEA, the Agency has added a parallel cost for the equipment portion of the cost for a number of equipment categories. These are itemized in Table V-34 of the FEA. For example, for Task 15 (Demolition of concrete slabs, mesh-reinforcing, up to 3''deep), there is estimated to be a 2 percent labor increase related to maintaining wet methods for dust suppression. In the original Means estimates, it was estimated that approximately 70 percent of the costs of the task were labor-related, divided between an operator and a laborer. This 2 percent additional cost is estimated to amount to $9.39 in added labor cost for an equipment operator and $7.84 for a laborer, or a total labor productivity cost per job of $17.23. For the FEA, OSHA is adding an additional cost item of $7.58 to reflect an opportunity cost, in the form of a prospective extended equipment rental cost, raising the total incremental estimated cost to $24.81 per task. As with the other construction engineering control costs, this additional cost item is task-specific.

    While OSHA judged that equipment productivity can be impacted negatively by the new rule for many tasks, there are two general categories for which the Agency determined that there would be

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    no impact on equipment productivity. The first broad category is short-

    term, intermittent work in which the equipment and control are often idle. An example would be a plumber drilling holes in concrete. The equipment and control are sufficiently inexpensive (relatively speaking) that the construction employer or trade contractor (or possibly even the tradesperson) would typically own rather than rent the equipment and control. As discussed elsewhere in the FEA, OSHA determined that certain tradespersons, such as plumbers, electricians, and their helpers, are more likely to purchase their equipment, rather than renting it. OSHA estimated the cost of purchasing control equipment at twice the rental cost.

    The second category of tasks for which the Agency did not assess any equipment productivity impact is the group of tasks in which there is not a fixed ratio of labor to capital (capital in this case including rental costs). For example, as explained in the following unit cost discussion, Task 10 (as detailed in Table V-34 of the FEA) involves performing earthmoving as a heavy equipment operation task. In this case, while extra time by a laborer would be required to tend to the application of wet methods, such application would be done simultaneously with actually performing the earth-moving task. Thus, while wet methods for Task 10 would require an added labor cost (itemized as a ``productivity'' cost), it would not actually slow down the operation so as to require the longer period of use of the equipment that would impose an equipment impact.

    CISC/Environomics also argued that part of the productivity effect was fixed and would therefore need to be accounted for separately. This fixed component, CISC/Environomics reported, would be ``typically involving activities such as initial set-up and final take-down and clean-up of the control equipment, which often occur at the beginning and end of a job or work shift'' (Document ID 4217, p. 90, see also 2320, p. 28; 3580, Tr. 1320). This would mean that shorter jobs would have a relatively larger percentage loss in productivity.

    Other commenters did not agree that there would be costs related to set up. During the hearings, Deven Johnson, of the Operative Plasterers' and Cement Masons' International Association, testified that the concrete grinding ``tools that are on the market today come integral with the capture device. . . The hose is attached to the grinder already. The electrical cord is attached to the motor already. . . . You simply plug it in and start using it . . . there's no setup time'' and that for ``a walk-behind concrete diamond-bladed saw for cutting slabs, the setup time is, make sure there's gas in it and . . . hook a water hose up to it and turn the water on'' (Document ID 3581, Tr. p. 1699). During the hearing, Manafort Brothers described a wheel-based machine used to suppress dust during demolition operations, which was simply wheeled onto the worksite and hooked up to a water supply and electrical source (Document ID 3583, Tr. 2430), and the Building Trades Construction Department (BCTD) of the AFL-CIO submitted an extensive list of available tools that included the controls required by the rule that would require little or no set up (Document ID 4073, Attachment 4a).

    Based on the evidence in the record, OSHA determined that any time needed to set up the engineering controls required by this rule is adequately accounted for in the productivity impacts the Agency has included, particularly in light of the fact that OSHA is not making any adjustment to account for productivity improvements that are likely to result from this rule (see the discussion of comments identifying productivity improvements later in this section). Environomics' inclusion of both a ``fixed'' productivity impact as well as a ``variable'' productivity impact, without recognizing offsetting productivity benefits identified by other commenters', results ins a significant overestimate of the productivity impact.

    Public Comments Suggesting That OSHA had Overestimated the Productivity Impacts Associated With Engineering Controls

    BCTD strongly disagreed with CISC's estimates about productivity decreases resulting from the rule, stating in their post-hearing brief:

    all that CISC offered to support these significant increases in the productivity impact is an explanation of how its approach to calculating productivity differs from OSHA's and a few examples, such as:

    So in the case of the carpenters with the dust extraction equipment on the drill and the HEPA vacuum, the carpenter takes a little bit longer to do his hole-drilling task because he's got to attach the equipment to the drill. He's got to attach the hose to the HEPA vacuum. He's got to walk over before he drills and he's got to turn on the HEPA vacuum. Then after he drills, he's got to turn off the HEPA vacuum. He's got to periodically empty the HEPA vacuum. He's got to worry about the vacuum hose from the drill to the vacuum getting kinked and all that sort of thing. So the job takes a little bit longer. Tr:1317-18.

    CISC offered no evidence that its analytical approach is more accurate than OSHA's. Moreover, this description of how its hypothetical carpenter would deploy control technology assumes the employer would select the most cumbersome and inefficient technique available, rather than taking advantage of the range of more suitable and less costly tools that are readily available on the market. See, e.g., Ex. 4073, Att.7a (ROI: hand-held drill with integrated dust collection) (Document ID 4223, pp. 55-56).

    BCTD also took exception to the fact that ``CISC acknowledged that `there may be a productivity net gain in terms of cleanup from using a control,' Tr:1319 (Sessions), but did not appear to have taken potential gains into consideration when estimating its lost productivity cost'' (Document ID 4223 pp. 55).

    Dr. Ruth Ruttenberg highlighted the various areas where the PEA may have overestimated the negative productivity effect of engineering controls in construction. She stated that the assumption of a negative impact on productivity

    . . . is yet another example of OSHA erring on the side of being conservative in cost estimates. Despite the fact that some who were interviewed suggested there could be a positive impact on productivity, OSHA's PEA assessed anywhere from 0 percent to a 5 percent penalty in productivity loss as a result of OSHA compliance with the proposed silica rule. (PEA, p. V-123-124) The impact of an assumption of lost productivity can be profound, and OSHA acknowledges this: ``. . . the magnitude of the productivity impacts can substantially change the estimate of the overall cost increase associated with controls'' (PEA, p. V-131).

    Despite the fact that OSHA leaves likely productivity increases out of its calculations, it does point to opportunities to increase productivity with dust control. . . .

    Limiting dust increases visibility for workers. (PEA, p. V-126) Vacuum systems speed up drilling because continuous removal of drill cuttings from the hole, reduce the need for workers to periodically stop and clean. (PEA, p. V-128) And the list goes on. OSHA's cost estimates are conservative, and high, when it comes to productivity impact (Document ID 2256-A4, p. 7).

    Productivity Improvements

    In addition to comment that the productivity loss due to this rule would be minimal, OSHA also received considerable comment to the record that the controls would improve productivity in a number of ways the Agency had not factored in--for example by reducing clean-up time by capturing dust at the source, improving worker comfort and morale, and encouraging inn