[Federal Register Volume 81, Number 58 (Friday, March 25, 2016)]
[Rules and Regulations]
[Pages 16285-16890]
[FR Doc No: 2016-04800]

Vol. 81

Friday,

No. 58

March 25, 2016

Part II

Book 2 of 3 Books

Pages 16285-16890

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

Federal Register / Vol. 81 , No. 58 / Friday, March 25, 2016 / Rules
and Regulations

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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 [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.

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<PHONE_NUMBER>; email
<EMAIL_ADDRESS>    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<PHONE_NUMBER>.

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 [mu]g/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.

    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 [mu]g/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 [mu]g/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
[mu]g/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 [mu]g/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 [mu]g/
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

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.

[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, ``[w]hen 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

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 ``[i]t 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

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, ``[t]he 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

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.

    [W]ithin 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 ``[f]easibility 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

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

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,
``[w]henever 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 [mu]g/m3 for
general industry and 250 [mu]g/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.
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

    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 [mu]g/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

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 [mu]g/m3)
(Document ID 1503, p. 15). ACGIH subsequently lowered the TLV for
crystalline silica to 0.025 mg/m3 (25 [mu]g/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 [mu]g/m3) for quartz and 0.05 mg/m3 (50
[mu]g/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

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.
[GRAPHIC] [TIFF OMITTED] TR25MR16.001

    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.

[GRAPHIC] [TIFF OMITTED] TR25MR16.002

    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

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 [mu]g/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 [deg]C, 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.

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 [deg]C). 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
[deg]C) 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
[deg]C, and at 1723 [deg]C 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 [deg]C 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

A. 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

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.

B. 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 [mu]g/m\3\ for general industry and between 250 and
500 [mu]g/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 [mu]g/m\3\
respirable crystalline silica, these estimated risks are substantially
reduced. Thus, OSHA concludes that the new PEL of 50 [mu]g/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 [mu]g/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 [mu]g/m\3\ and has since further lowered its
TLV for respirable crystalline silica to 25 [mu]g/m\3\. OSHA is setting
its revised PEL at 50 [mu]g/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
[mu]g/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,

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).
---------------------------------------------------------------------------

    \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).
---------------------------------------------------------------------------

    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, ``[o]ccupational 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

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 ``[w]hile
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 [micro]g/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

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 [micro]g/m\3\
respirable crystalline silica, and 5 to 23 deaths per 1,000 workers at
the revised PEL of 50 [micro]g/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 [micro]g/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\
---------------------------------------------------------------------------

    \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).
---------------------------------------------------------------------------

    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
[micro]g/m\3\ respirable crystalline silica, and 32 deaths per 1,000
workers exposed at the revised PEL of 50 [micro]g/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).

    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 [micro]g/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 [micro]g/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 [mu]g/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 [mu]g/m\3\ respirable crystalline silica.

C. 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 [mu]g/m\3\ respirable crystalline silica, OSHA estimated that these
risks would be substantially reduced. Cumulative risk estimates for