 United States Court of Appeals
         FOR THE DISTRICT OF COLUMBIA CIRCUIT



Argued September 26, 2017        Decided December 22, 2017

                        No. 16-1105

       NORTH AMERICA’S BUILDING TRADES UNIONS,
                     PETITIONER
                         v.

    OCCUPATIONAL SAFETY & HEALTH ADMINISTRATION
      AND UNITED STATES DEPARTMENT OF LABOR,
                   RESPONDENTS

    CHAMBER OF COMMERCE OF THE UNITED STATES OF
                 AMERICA, ET AL.,
                  INTERVENORS


       Consolidated with 16-1113, 16-1125, 16-1126,
           16-1131, 16-1137, 16-1138, 16-1146



 On Petitions for Review of a Final Rule of the Occupational
               Safety & Health Administration



    William L. Wehrum and Bradford T. Hammock argued the
cause for the Industry Petitioners. Susan F. Wiltsie, David
Craig Landin, Tressi L. Cordaro, Michael B. Schon and Linda
E. Kelly were with them on brief. Elizabeth C. Chandler
Clements entered an appearance.
                              2
     J. Michael Connolly argued the cause for the Petitioners-
Intervenors Chamber of Commerce of the United States, et al.
William S. Consovoy, Steven P. Lehotsky and Sheldon B.
Gilbert were with him on brief.

    Jeremiah A. Collins and Victoria L. Bor argued the cause
for the Union Petitioners. Randy S. Rabinowitz, Lynn K.
Rhinehart, Richard J. Brean and Ava Barbour were with them
on brief. Stephen A. Yokich entered an appearance.

    Kristen M. Lindberg and Lauren S. Goodman, Senior
Attorneys, and Louise McGauley Betts, Attorney, United States
Department of Labor, argued the cause for the Respondents.
On brief were Nicholas C. Geale, Acting Solicitor of Labor,
Heather R. Phillips, Counsel for Appellate Litigation,
Nathaniel I. Spiller, Counsel for Health Standards, and Anne R.
Godoy and Allison G. Kramer, Senior Attorneys.

     Victoria L. Bor argued the cause for the Respondents-
Intervenors. Jeremiah A. Collins, Randy S. Rabinowitz, Lynn
K. Rhinehart, Richard J. Brean and Ava Barbour were with her
on brief.

    William L. Wehrum, Susan F. Wiltsie, David Craig
Landin, Bradford T. Hammock, Tressi L. Cordaro and Linda
E. Kelly were on brief for the Industry Respondent-Intervenors.

   Lisa W. Jordan was on brief for the amici curiae The
American Thoracic Society, et al. in support of the respondent.
Adam Babich entered an appearance.

   Before: GARLAND, Chief Judge, and HENDERSON and
TATEL, Circuit Judges.
                                 3
    PER CURIAM: Respirable crystalline forms of silica, 1 a
compound made of silicon and oxygen, are commonly found
in workplaces with rock, sand, gravel, concrete, and brick.
Exposure to silica is one of the oldest known occupational
hazards. And the health effects of exposure to silica—most
commonly silicosis, a progressive and irreversible lung disease
caused by the inflammatory effects of silica—are not a thing of
the past. “Currently, silicosis is the most prevalent chronic
occupational disease in the world.” ROBBINS & COTRAN,
PATHOLOGIC BASIS OF DISEASE 690 (9th ed. 2015).

     In the United States, more than two million workers are
currently exposed to some level of silica. In 2016, the
Occupational Safety and Health Administration (OSHA), an
agency within the United States Department of Labor,
published a final rule regulating workplace exposure to silica.
Occupational Exposure to Respirable Crystalline Silica, 81
Fed. Reg. 16,285 (Mar. 25, 2016) (codified at 29 C.F.R. Pts.
1910, 1915, and 1926) (Silica Rule or Rule). Petitions to
review the Rule came from both sides; a collection of industry
petitioners (Industry) believes OSHA impermissibly made the
Rule too stringent and several union petitioners (Unions)
believe OSHA improperly failed to make the Rule stringent
enough.

    Industry petitioned for review of five issues: (1) whether
substantial evidence supports OSHA’s finding that limiting
workers’ silica exposure to the level set by the Rule reduces a
significant risk of material health impairment; (2) whether
substantial evidence supports OSHA’s finding that the Rule is
technologically feasible for the foundry, hydraulic fracturing,

    1
        The OSHA rule at issue regulates only respirable crystalline
forms of silica. See 29 C.F.R. § 1910.1053(a)(1). For ease of
reference, we use “silica” as a shorthand for respirable crystalline
silica.
                               4
and construction industries; (3) whether substantial evidence
supports OSHA’s finding that the Rule is economically feasible
for the foundry, hydraulic fracturing, and construction
industries; (4) whether OSHA violated the Administrative
Procedure Act (APA) in promulgating the Rule; and (5)
whether substantial evidence supports two ancillary provisions
of the Rule—one that allows workers who undergo medical
examinations to keep the results confidential from their
employers and one that prohibits employers from using dry
cleaning methods unless doing so is infeasible. We reject all of
Industry’s challenges.

     The Unions petitioned for review of two parts of the Rule:
(1) the requirement that medical surveillance for construction
workers be provided only if the employee has to wear a
respirator for 30 days for one employer in a one-year period;
and (2) the absence of medical removal protections. We reject
the Unions’ challenge to the construction standard’s 30-day
trigger for medical surveillance. We conclude that OSHA
failed to adequately explain its decision to omit medical
removal protections from the Rule and remand for further
consideration of the issue.

                    I.   BACKGROUND

     The Occupational Safety and Health Act (OSH Act)
authorizes the Secretary of Labor (Secretary) to “promulgate,
modify, or revoke any occupational safety or health standard,”
29 U.S.C. § 655(b), by requiring conditions or the adoption of
practices, means, or methods “reasonably necessary or
appropriate to provide safe or healthful employment and places
of employment,” id. § 652(8). If the standard applies to toxic
materials or harmful physical agents, the Secretary “shall set
the standard which most adequately assures, to the extent
feasible, on the basis of the best available evidence, that no
                                  5
employee will suffer material impairment of health or
functional capacity even if such employee has regular exposure
to the hazard” regulated by the standard “for the period of his
working life.” Id. § 655(b)(5). The Secretary has delegated
his authority to OSHA. See 72 Fed. Reg. 31,160 (June 5,
2007).

     In 1971, OSHA adopted a standard regulating exposure to
a variety of substances, including silica. Occupational Safety
and Health Standards; National Consensus Standards and
Established Federal Standards, 36 Fed. Reg. 10,466 (May 29,
1971). The 1971 rule established a permissible exposure limit
(PEL)—a time-weighted average of a worker’s exposure
during a workday—of 100 micrograms per cubic meter
(µg/m3) in general industry 2 and 250 µg/m3 in the construction
industry. See 81 Fed. Reg. at 16,294. In the 1990s, OSHA
studied the efficacy of the 1971 rule regarding silica-related
health effects in the workplace and concluded a new rule was
needed. See id. at 16,295.

      In 2016, OSHA promulgated its final Silica Rule. 81 Fed.
Reg. 16,285. The Rule lowers the PEL to 50 µg/m3 for all
covered industries, including as particularly relevant here, the
foundry, hydraulic fracturing, brick, and construction
industries. See 29 C.F.R. §§ 1910.1053(c), 1926.1153(d)(1).
Employers must assess silica exposure levels in the workplace
(or, for certain construction industry tasks, adopt specific “safe-
harbor” practices) and, if necessary, must implement

     2
        OSHA uses the phrase “general industry” to refer to the
standard set in 29 C.F.R. § 1910.1053, which “applies to all
occupational exposures to respirable crystalline silica, except”
construction work, agricultural operations, and sorptive-clay
processing. Id. § 1910.1053(a)(1)(i)–(iii). As relevant to the
petitions, general industry includes the foundry, hydraulic fracturing,
and brick industries.
                              6
engineering and work practice controls to keep exposures
below the PEL. Id. §§ 1910.1053(f)(1), 1926.1153(c)(1),
1926.1153(d)(3)(i). If engineering and work practice controls
cannot reduce exposures to the PEL, the employer must use
controls to the extent feasible and provide supplementary
respirator protections. Id.

     The Silica Rule also establishes various ancillary
provisions including, again, as relevant here, housekeeping
requirements and medical surveillance requirements. Under
the challenged housekeeping provision, employers are
prohibited from using dry sweeping methods to clean worksites
if doing so could contribute to employee exposure to silica
unless wet cleaning methods are infeasible.                 Id.
§§ 1910.1053(h)(1), 1926.1153(f)(1). Under the challenged
medical surveillance provisions, employers must provide
medical screening to silica-exposed workers if certain
conditions are met. Most of the information from the medical
examinations,       including      medical       professionals’
recommendations limiting the employee’s exposure to silica,
are confidential and cannot be released to the employer unless
the employee authorizes disclosure. Id. §§ 1910.1053(i)(6),
1926.1153(h)(6). Finally, the Rule provides no medical
removal protections to workers whose doctors recommend
either permanent or temporary removal from silica exposure on
the job.

    Different compliance dates were established for each
industry: June 23, 2017 for the construction industry, id.
§ 1926.1153(k); June 23, 2018 for the foundry industry, id.
§ 1910.1053(l); and June 23, 2021 for the hydraulic fracturing
industry, id.
                               7
                       II. ANALYSIS

     We first decide Industry’s challenges. In order, we
address OSHA’s significant risk findings, its technological
feasibility findings, its economic feasibility findings, the
procedural regularity of the Rule, and the challenged ancillary
provisions. The substantive issues are governed by the
“substantial evidence” standard, 29 U.S.C. § 655(f), under
which we require OSHA to “identify relevant factual evidence,
to explain the logic and the policies underlying any legislative
choice, to state candidly any assumptions on which it relies,
and to present its reasons for rejecting significant contrary
evidence and argument,” United Steelworkers of America v.
Marshall (Lead I), 647 F.2d 1189, 1207 (D.C. Cir. 1980). The
APA governs the procedural challenge to ensure the Rule is not
promulgated “without observance of procedure required by
law.” 5 U.S.C. § 706(2)(D).

    We then turn to the Unions’ challenges and address the 30-
day medical surveillance trigger in the construction standard
and the lack of medical removal protections in the general
industry standard. Where the Unions have failed to identify
evidence that their proposals would be feasible and generate
more than a de minimis benefit to worker health, we reject
them. See Building & Construction Trades Department, AFL-
CIO v. Brock (Asbestos), 838 F.2d 1258, 1271 (D.C. Cir. 1988).
Where the Unions have met this initial burden, we ask whether
OSHA has supported its decision with substantial evidence and
otherwise engaged in reasoned decisionmaking.

                    A. SIGNIFICANT RISK

    Before OSHA promulgates any permanent health or safety
standard, it must make a “threshold finding” that “it is at least
more likely than not that long-term exposure” to the regulated
substance at current exposure levels “presents a significant risk
                                  8
of material impairment” that “can be eliminated or lessened by
a change in practices.” Industrial Union Department, AFL-
CIO v. American Petroleum Institute (Benzene), 448 U.S. 607,
642, 653 (1980) (plurality). 3 The Supreme Court has provided
the guidepost that OSHA follows: a one-in-a-thousand risk that
exposure to the regulated substance will be fatal can reasonably
be considered significant but a one-in-a-billion risk is likely not
significant. Id. at 655–56.

     OSHA must support its significant risk finding with
substantial evidence. Id. at 653. Although it must rely on a
“body of reputable scientific thought” when assessing risk, id.
at 656, OSHA does not have to “calculate the exact probability
of harm” or support its finding “with anything approaching
scientific certainty,” id. at 655–56. OSHA is entitled to “some
leeway” when its “findings must be made on the frontiers of
scientific knowledge.” Id. at 656. We “do not reweigh the
evidence and come to our own conclusion[s]; rather, we assess
the reasonableness of OSHA’s conclusion.” Public Citizen
Health Research Group v. Tyson (Ethylene Oxide), 796 F.2d
1479, 1495 (D.C. Cir. 1986).

     In promulgating the Silica Rule, OSHA conducted a
Quantitative Risk Assessment in which it reviewed
toxicological, epidemiological, and experimental studies about
the adverse health effects of silica exposure. 81 Fed. Reg. at
16,380. OSHA quantified the excess risk 4 of silica-related

     3
        Although Benzene commanded only a plurality of the Court,
a majority of the Court endorsed the significant risk requirement in
a later case. See National Maritime Safety Association v. OSHA,
649 F.3d 743, 750 n.8 (D.C. Cir. 2011) (citing American Textile
Manufacturers Institute, Inc. v. Donovan, 452 U.S. 490, 506 (1981)).
     4
        Excess risk identifies the risk “solely attributable” to silica
exposure, 81 Fed. Reg. at 16,372, by “factoring in the probability of
surviving to a particular age assuming no exposure to [silica] and
                                9
health effects assuming exposure over a working life (45 years)
to various levels of silica, including the original general
industry PEL of 100 µg/m3, the original construction PEL of
250 µg/m3, and the new PEL of 50 µg/m3. Id. at 16,300.
OSHA concluded that silica exposure significantly “increases
the risk of” four adverse health effects: silicosis and other non-
malignant respiratory disease (NMRD) mortality, lung cancer
mortality, silicosis morbidity, and renal disease mortality. Id.
at 16,300, 16,386–87. OSHA also concluded that the risks at
50 µg/m3—the new PEL—are lower than the risks at the
original PELs of 100 µg/m3 and 250 µg/m3. Id. at 16,300. In
total, OSHA estimated that the Silica Rule will prevent 642
deaths and 918 cases of silica-related disease each year. Id. at
16,399. 5

     Industry challenges OSHA’s significant risk findings in
three ways. First, Industry attacks two parts of OSHA’s risk-
assessment methodology. Second, it challenges OSHA’s
findings on each of the four individual health risks. Finally,
Industry challenges OSHA’s decision to include the brick
industry within the scope of the Rule. We reject each
challenge.

                  1.   OSHA’s Methodology

     Industry challenges two components of OSHA’s risk-
assessment methodology: its no-threshold assumption and its
failure to account for a dose-rate effect. We uphold OSHA’s
decisions on both.


given the background probability of dying from any cause at or
before that age,” id. at 16,385.
     5
        The number of deaths and cases of silica-related disease
resulting from each of the individual adverse health effects is
discussed infra.
                               10
     First, Industry challenges OSHA’s use of no-threshold
exposure-response models in its risk assessments for silicosis
and lung cancer. 81 Fed. Reg. at 16,351. The no-threshold
concept means there is no exposure level below which workers
would not be expected to develop adverse health effects. Id.
OSHA did not definitively find that no threshold exists.
Instead, it found that if a threshold exists it does so below the
PEL, which justified its use of a no-threshold model. OSHA
supported its selection of the PEL with studies showing that
risks of lung cancer exist at 36 µg/m3 and 10 µg/m3, levels
lower than the PEL. Id. at 16,351, 16,356. To OSHA, the
studies showing risks below the PEL support its conclusion that
any threshold, if it exists, does so below the PEL. See id. at
16,351 (“As 36 µg/m3 is well below the previous industry PEL
of 100 µg/m3 and below the final PEL of 50 µg/m3, the . . .
study showed no evidence of an exposure-response threshold
high enough to impact OSHA’s choice of PEL.”). Industry, in
contrast, points to studies it claims not only show a threshold
exists but also show a threshold exists above the PEL. OSHA
rejected Industry’s argument because the contrary studies used
non-reactive and poorly soluble particles—which silica is
not—and therefore the “findings regarding” the particles
“[cannot] be extrapolated to crystalline silica.” Id. at 16,349.
OSHA acknowledged “there is considerable uncertainty” about
whether a threshold exists but found that “the weight of
evidence supports the view that, if there is a threshold,” it is
“likely lower than the” PEL. Id. at 16,351.

     OSHA’s no-threshold assumption is supported by
substantial evidence. Although Industry claims OSHA’s
position is inconsistent with common sense and “mounting
judicial skepticism” of no-threshold models, citing to several
district court and state court cases disapproving a no-threshold
approach, Industry Br. at 28–29, OSHA’s position is in line
with our precedent. In Ethylene Oxide, we upheld a no-
                              11
threshold model based on OSHA’s having found evidence of
adverse health effects at levels of exposure to ethylene oxide
below the established PEL, then extrapolating that evidence to
assume no threshold of ethylene oxide exposure existed below
which risks did not exist and rejecting two contrary comments
that purportedly showed a threshold did exist. 796 F.2d at
1500. As in Ethylene Oxide, Industry presents, and urges us
to adopt, “one side of the debate.” Id. But OSHA has
explained why it rejected Industry’s side of the debate,
presented the other side of the debate, and supported it with
evidence from which a reasonable conclusion could be made,
as OSHA did here, that no threshold of safe exposure to silica
exists. We cannot “choose a particular side as the ‘right’ one”
in a scientific dispute. Id. Accordingly, OSHA’s no-
threshold assumption satisfies our substantial evidence test.

     Second, Industry challenges OSHA’s decision not to
include a dose-rate effect in the model, which means OSHA
assessed health risks based on the cumulative amount of silica
exposure without accounting for the intensity of exposures.
81 Fed. Reg. at 16,375. OSHA took its position “because each
of the key . . . studies” OSHA relied on used cumulative
exposure as the only metric. Id. at 16,374–75. Multiple
commenters supported the notion that “cumulative exposure is
a reasonable and practical choice” and that cumulative
exposure “is often the best predictor of chronic disease.” Id.
at 16,375. Competing commenters argued that OSHA’s risk
assessment should account for the intensity of exposures. Id.
Industry relied on studies showing that not accounting for a
dose-rate effect “could overestimate risk at lower
concentrations.” Id. The studies supporting Industry’s
position, however, largely observed an intensity-based effect at
500 µg/m3 and 2,000 µg/m3, exposure levels so “far above the
previous PEL,” id. at 16,395, that OSHA determined the
                               12
studies were of little use to the “exposure range of interest”—
25 to 500 µg/m3, id. at 16,376.

     In Ethylene Oxide, we upheld OSHA’s decision not to
include a dose-rate effect in its model when faced with
“competing technical opinions” about whether the amount or
the intensity of ethylene oxide exposure mattered more.
Ethylene Oxide, 796 F.2d at 1504. OSHA did the same in its
Silica Rule: it took competing evidence, favored one side, and
explained the reasons for its decision. We “cannot expect
OSHA to [locate and use] absolutely conclusive studies on
these difficult medical issues” and we must uphold OSHA’s
choice, even in the face of “controverted” evidence, if it falls
within a “zone of reasonableness.” Lead I, 647 F.2d at 1253
(quoting Hercules, Inc. v. EPA, 598 F.2d 91, 107 (D.C. Cir.
1978)). We believe OSHA’s conclusions on handling the
purported dose-rate effect are reasonable. “[C]ourts cannot
interfere with reasonable interpretations of equivocal
evidence,” Ethylene Oxide, 796 F.2d at 1505, and therefore we
do not interfere here.

                 2.   Adverse Health Effects

     As noted earlier, OSHA concluded that long-term silica
exposure above the PEL presents a significant risk of four
discrete adverse health effects: (1) silicosis and NMRD
mortality; (2) lung cancer mortality; (3) silicosis morbidity; and
(4) renal disease mortality. 81 Fed. Reg. at 16,300, 16,386–
87. Industry challenges OSHA’s findings as to all four.
Industry acknowledged at oral argument that, to prevail, it
would have to show none of the discrete findings is supported
by substantial evidence. We address each in turn. We
conclude OSHA’s significant risk findings as to the first three
adverse health effects are supported by substantial evidence,
which supports OSHA’s overall finding of a significant risk.
                               13
We do not reach OSHA’s finding with respect to renal disease
mortality.

    i.   Silicosis or Non-Malignant Respiratory Disease
                          Mortality

     Silicosis is a progressive, irreversible lung disease caused
by the inflammatory effects of silica in the lungs. OSHA
found that silica exposure at the original PEL of 100 µg/m3
created an excess risk of silicosis mortality for 11 in 1,000
workers that would be reduced to 7 in 1,000 workers at the
Rule’s PEL of 50 µg/m3. 81 Fed. Reg. at 16,303, 16,312.
Other NMRD caused by silica exposure include emphysema,
chronic obstructive pulmonary disease, and chronic bronchitis.
Id. at 16,304. OSHA found that silica exposure at the 100
µg/m3 PEL created an excess risk of NMRD mortality
(including silicosis mortality) for 85 in 1,000 workers that
would be reduced to 44 in 1,000 workers at the Rule’s PEL of
50 µg/m3. Id. at 16,303. Both Industry and the Chambers
Intervenors 6 challenge OSHA’s findings on silicosis and
NMRD mortality.

    To support its findings on silicosis and NMRD mortality,
OSHA relied on two studies: the Mannetje study, which
showed a statistically significant association between silicosis
mortality and cumulative exposure to silica, and the Park study,
which quantified the relationship between silica exposure and
NMRD mortality. Id. at 16,317. Industry’s objections to
OSHA’s conclusions primarily attack the reliability of the Park
study. Industry claims the Park study (1) focused on workers
with cumulative exposure levels far above what workers

    6
       The Chamber of Commerce of the United States, the State
Chamber of Oklahoma, and the Greater North Dakota Chamber of
Commerce (collectively, Chambers) intervened on behalf of
Industry.
                                 14
typically faced under the original PEL and (2) produced results
that were likely skewed by smoking because the study had
smoking data for only one-half of the studied workers.

     In its rulemaking, OSHA addressed both criticisms. On
the first point, OSHA acknowledged “some uncertainty in
using models heavily influenced by exposures above the
previous PEL” but noted that the average cumulative exposure
of the studied workers was “lower than what the final rule
would permit over 45 years of exposure.” Id. at 16,318.
Accordingly, OSHA “[dis]agree[d] that the Park study should
be discounted” and instead concluded that the study was both
relevant and appropriate to rely on. Id. On the second point,
OSHA acknowledged that “comprehensive smoking data
would be ideal” but assessed the Park study’s mechanics in
detail and concluded that the risk estimates were “not likely to
be exaggerated due to [studied workers’] smoking habits.” Id.

     Under our substantial evidence standard, OSHA has a duty
to “present its reasons for rejecting significant contrary
evidence and argument.” Lead I, 647 F.2d at 1207. OSHA
acknowledged and adequately responded to Industry’s
criticisms of the Park study. Even if the Park study was
“flawed in some way,” OSHA is not precluded from relying on
imperfect evidence so long as it “recognize[s] and account[s]
for the methodological weaknesses” of the evidence. Ethylene
Oxide, 796 F.2d at 1487; see id. at 1495 (“While some of
OSHA’s evidence suffers from shortcomings, such incomplete
proof is inevitable when the Agency regulates on the frontiers
of scientific knowledge.”). OSHA did recognize and account
for the weaknesses of the two studies it relied on here. 7



     7
         Industry did not specifically challenge the Mannetje study in
its brief so we do not analyze OSHA’s reliance on it.
                                15
     The Chambers, meanwhile, present a record of death
certificates and their listed cause of death that shows silicosis-
attributed deaths dropped from 1,065 in 1968 (three years
before the 1971 PEL was implemented) to 123 in 2007. The
decline, according to the Chambers, shows that the current
risks are due not to exposure levels at the 1971 PEL but instead
are due to pre-1971 exposures or exposures occurring in
violation of the 1971 PEL. Thus, the Chambers argue, the
1971 rule is working and there is no need for a new one.

     But here again, OSHA adequately explained why it
rejected this evidence. First, OSHA concluded that the death
certificate data underreported risks after one commenter found
that silicosis was listed as the cause of death for only 14 percent
of people with confirmed silicosis. 81 Fed. Reg. at 16,328.
Second, the death certificate data “d[id] not include
information about exposure[]” levels for those who died as a
result of silicosis, which made the data “inadequate and
inappropriate for” setting a standard regulating silica at
particular exposure levels. Id. at 16,326. Indeed, the agency
that compiled and analyzed the death certificate data testified
that relying on the death certificates to show no significant risk
exists would be a “misuse” of the data. Id.

     Moreover, OSHA responded directly to the Chambers’
arguments that the death certificate data showed the risks of
silica exposure are no longer significant.                    OSHA
acknowledged that silicosis-related deaths have dropped since
1968 but pointed to evidence showing that the decline leveled
off at approximately 90 to 180 deaths per year since 2000. Id.
at 16,324. This evidence “suggest[s] that the number of
silicosis deaths . . . may be stabilizing,” id., which also suggests
that the significant risk of silicosis mortality would not
disappear if OSHA simply let the 1971 PEL run its course, as
Industry argued, id. at 16,325. OSHA also pointed to
                               16
evidence showing that the decline in silicosis-related deaths
tracks the decline in high-exposure jobs as much as it tracks
improved working conditions, further suggesting that OSHA
“still h[as] work to do” to make silica exposure safe. Id. at
16,325–26. Thus, although OSHA agreed that the death
certificate data was “useful for providing context and an
illustration of a significant general trend in the reduction of
deaths associated with silicosis over the past four to five
decades,” the “limited and incomplete” data made reliance on
the death certificates “inappropriate.” Id. at 16,330. OSHA
“described in some detail [its] reasons for choosing between
competing alternatives.”       Asbestos, 838 F.2d at 1266.
Accordingly, OSHA has met its burden to identify the evidence
it relied on and explain why it rejected contrary evidence.

                 ii. Lung Cancer Mortality

     OSHA found that silica exposure at the 100 µg/m3 PEL
created an excess risk of lung cancer mortality equal to 11 to
54 deaths per 1,000 workers that would be reduced to an excess
risk of 5 to 23 deaths per 1,000 workers at the 50 µg/m3 PEL.
81 Fed. Reg. at 16,338. Industry argues the conclusion hinges
on OSHA’s unsupported assumption that silica exposure
directly increases the risk of lung cancer in the absence of
silicosis. That is, if the risk of lung cancer depends on pre-
existing silicosis, then silica exposure alone does not create an
independent risk of lung cancer.

     Industry points to evidence that asserts the association
between silicosis and lung cancer is “more compelling” than
the association between silica exposure and lung cancer. Joint
Appendix (J.A.) 3027. But the mere suggestion in some
evidence that silicosis is a necessary precursor of lung cancer
does not bind the agency. See Ethylene Oxide, 796 F.2d at
1504 (noting that suggestive statements “do not amount to a
                               17
scientific certainty binding on the agency”). Meanwhile,
OSHA also cites to numerous studies that show silica exposure
can lead directly to lung cancer. 81 Fed. Reg. at 16,309
(recapping and summarizing findings). As one commenter
put it, the literature OSHA relied on shows “silica has been
established as a cause of lung cancer.” J.A. 7815. We lack
the technical expertise to second-guess OSHA’s judgment
when it “review[ed] all sides of the issue and reasonably
resolve[d] the matter.” Ethylene Oxide, 796 F.2d at 1500.
We do not second-guess OSHA’s conclusions here.

      Industry specifically challenges OSHA’s decision to give
weight to a 2004 Attfield and Costello study, which showed
there is an association between silica exposure and lung cancer,
instead of a 2011 Vacek study showing there is no such
association. 81 Fed. Reg. at 16,338. Industry provides a
laundry list of reasons why it believes the Vacek study is better:
it is more recent, covered more workers, covered more years,
and used more detailed information. But OSHA explained its
reasons for rejecting the Vacek study. Among them: the
Vacek study found an unexplained significant excess risk of
lung cancer that called into question all of its results and had a
low risk estimate for a particular type of worker (channel bar
operators) that OSHA concluded had major consequences for
the entire exposure analysis. Id. at 16,335–37. Moreover,
OSHA provided affirmative reasons for choosing the Attfield
and Costello study. Most importantly, OSHA reasoned, that
study accounted for a healthy worker survivor effect—the
tendency of healthy workers to remain in the workforce longer
than ill workers and therefore face more exposure than ill
workers, which “may” make the “risk of disease at higher
exposures” improperly “appear to be constant or decrease”—
but the Vacek study did not assess the healthy worker survivor
effect. Id. at 16,336. “We have then, at worst, the ordinary
situation of controverted evidence, in which we must defer to
                                18
the reasonable and conscientious interpretations of the
agency.” Lead I, 647 F.2d at 1258.

                    iii. Silicosis Morbidity

     To support its finding of a significant risk of silicosis
morbidity, OSHA relied on five studies that showed an excess
risk between 60 and 773 cases of silicosis morbidity per 1,000
workers at a level of 100 µg/m3 that would be reduced to an
excess risk between 20 and 170 cases of silicosis morbidity per
1,000 workers at a level of 50 µg/m3. 81 Fed. Reg. at 16,317.
The variance among studies, according to Industry, “suggests
that none of [the studies] is a reliable guide to a correct
quantification” of exposures and therefore none of the studies
can support a finding of a significant risk of silicosis morbidity.
J.A. 3368. OSHA concluded the results of the five studies did
not “differ remarkably,” 81 Fed. Reg. at 16,321, which Industry
asserts is “arbitrary and capricious reasoning,” Industry Br. at
39.

     In the rulemaking OSHA responded to critiques against
the individual studies upon which OSHA relied. See 81 Fed.
Reg. at 16,320–22. OSHA also responded to critiques of the
variance among the studies, albeit in less detailed fashion, and
concluded that the risk estimates among the studies “are in
reasonable agreement.”          Id. at 16,322.           OSHA’s
reconciliation of the data’s variance is not airtight. A more
important question, however, is whether the studies constitute
substantial evidence supporting OSHA’s finding of a
significant risk of silicosis morbidity at the initial PEL that is
reduced at the Rule’s PEL. They do.

     The variance in results may show uncertainty as to the
precise amount of the risk of silicosis morbidity. Maybe it
falls closer to 60 cases per 1,000 workers at 100 µg/m3; maybe
it falls closer to 773 per 1,000. Maybe it falls closer to 20
                                19
cases per 1,000 workers at 50 µg/m3; maybe it falls closer to
170. “While each study individually may not be a model of
textbook scientific inquiry,” we assess, again, the “cumulative
evidence” OSHA relied on. Ethylene Oxide, 796 F.2d at 1489.
Even assuming the actual amount of risk is closer to the low
end, a “reasonable person could draw from this evidence the
conclusion that exposure to” silica presents a significant risk of
silicosis morbidity. Id. “Even if a reasonable person could
also draw the opposite conclusion, we must uphold the
agency’s findings.” Id. We conclude, then, that OSHA’s
conclusion that exposure to silica presents a significant risk of
silicosis morbidity is supported by substantial evidence.

                 iv. Renal Disease Mortality

     OSHA concluded that the excess risk of renal disease
mortality would drop from 39 deaths per 1,000 workers at the
100 µg/m3 PEL to 32 deaths per 1,000 workers at the 50 µg/m3
PEL. 81 Fed. Reg. at 16,342. OSHA relied on a single
pooled study that provided “considerably less data” compared
to the studies of the other disease endpoints. Id. at 16,345.
OSHA rejected numerous other studies that showed no risk of
renal disease. Id. at 16,344–45. Industry argues that OSHA
lacked substantial evidence to support a finding of a significant
risk of renal disease mortality and failed to explain its
resolution of conflicting evidence.

     OSHA acknowledged in the rulemaking that the evidence
supporting its finding regarding renal disease mortality was
“less robust” than the evidence supporting its findings for other
silica-related health effects. Id. at 16,345. OSHA defended
its position with a single footnote in its brief. We note
OSHA’s concession that the evidence is weak; if OSHA had
relied solely on the risk of renal disease mortality to support the
                               20
Silica Rule, its decision may well have been unsupported by
substantial evidence.

     But we need not and do not decide whether OSHA
supported its renal disease findings with substantial evidence
because OSHA’s findings with respect to silicosis and NMRD
mortality, lung cancer mortality, and silicosis morbidity are
sufficient to uphold the requisite threshold finding of a
significant risk of material health impairment at the 100 µg/m3
PEL that will be reduced at the new PEL. See National
Maritime Safety Association v. OSHA, 649 F.3d 743, 752 n.11
(D.C. Cir. 2011) (upholding OSHA’s significant risk finding
where OSHA relied on four contributors to the risk but one was
flawed; if OSHA “relied on [the flawed] factor alone, its
significant risk determination might well have been arbitrary
and capricious” but the presence of the other substantiated
factors sufficiently supported OSHA’s significant risk finding).
And Industry does not show that any weakness with respect to
OSHA’s renal disease findings infected OSHA’s findings
regarding the other adverse health effects such that the entire
significant risk conclusion is undermined. Accordingly, we
do not decide the renal disease issue because OSHA, through
its supported findings on the other three adverse health effects,
has met its burden to show that the Silica Rule regulates a
significant risk of material harm.

                     3.   Brick Industry

     Industry argues OSHA should have excluded the brick
industry from the scope of the Silica Rule because OSHA did
not have substantial evidence to find a significant risk of
material harm in the brick industry. OSHA pins its findings
on one study (the Love study) that surveyed brick plant
workers. 81 Fed. Reg. at 16,378. The Love study reported
that 1.4 percent—a rate below OSHA’s risk estimates in other
                               21
industries but exceeding Benzene’s general 0.1 percent
benchmark—of brick workers had small abnormalities in x-
rays, which the authors said were “most likely” silicosis. Id.
Industry makes three arguments to contest the findings based
on the Love study.

     First, Industry argues that OSHA used the Love study
when it wanted to and did not use the Love study when it did
not want to. Specifically, OSHA found the Love study
showed a significant risk of silicosis but declined to include the
Love study in the group of studies that formed the basis of
OSHA’s silicosis morbidity quantitative risk assessment. See
id. at 16,377–78. If OSHA exhibits “apparently inconsistent
handling of the evidence available to it,” OSHA cannot be said
to have relied on the best available evidence. See American
Iron & Steel Institute v. OSHA (Lead II), 939 F.2d 975, 1009
(D.C. Cir. 1991) (per curiam) (rejecting OSHA’s conclusions
when it criticized one industry study yet relied on another study
with the same flaws).

     But OSHA explained its rationale. The Love study
excluded retired workers and had little follow-up data on the
workers it included. 81 Fed. Reg. at 16,378. These two data
pieces are “extremely important” to fully quantify risks of
silicosis morbidity because “silicosis typically develops slowly
and becomes detectable [decades after] a worker’s first
exposure.” Id. at 16,377–78. Without the two data pieces,
the Love study did not meet OSHA’s “rigorous standards used
in the studies on which OSHA’s [silicosis morbidity] risk
assessment relies” and therefore could not be included. Id. at
16,377. But the lack of the two data points did not render the
Love study meaningless—if anything, OSHA reasoned, the
failure to study workers at later stages of their career, when the
latent effects of silica exposure are more likely to manifest,
meant the Love study “underestimated” the risk of silicosis to
                               22
brick industry workers. Id. at 16,378. Moreover, the Love
study was the only study specific to the brick industry that used
exposure-response information, making it the “highest-
quality” study for ascertaining risks. Id. As one commenter
testified, the Love study was the “only sensible study to be used
for setting an exposure limit . . . in brick manufacturing.” Id.
OSHA, then, explained its reasoning and supported it with
substantial evidence.

     Second, Industry argues that even if the Love study is a
credible source, OSHA’s risk estimates in other industries and
for other disease endpoints (between 2 and 17 percent) at the
PEL are greater than the risk estimates for the brick industry
(1.4 percent), and therefore OSHA should have let the brick
industry’s risks remain unaltered.              But Industry
misunderstands the legal standard. The mere fact that the
brick industry faces a lower risk than other industries does not
mean the brick industry’s risks are not significant. And the
1.4 percent risk quantified by the Love study surpasses the
Supreme Court’s 0.1 percent benchmark. Benzene, 448 U.S.
at 655–56.

     Industry finally argues that OSHA’s different treatment of
the brick industry and the sorptive minerals industry is arbitrary
and capricious. According to Industry, the substances in both
industries have chemical properties that reduce the toxicity of
silica (which would reduce the health risks of exposure to
silica) yet the Rule includes the brick industry but not the
sorptive minerals industry. OSHA explained its decision in
the preamble to the rule. The evidence for the sorptive
minerals industry was unclear and thus insufficient to conclude
a significant risk exists. 81 Fed. Reg. at 16,379–80. In
contrast, the evidence in the brick industry—the Love study,
primarily—showed there is a significant risk. Id. at 16,377–
78. Even if brick clay and sorptive minerals have similar
                              23
chemical properties that reduce the toxicity of silica within
those compounds, OSHA found the evidence as it existed in the
record was not similar enough to treat them similarly. Id.
OSHA’s position is supported by substantial evidence and a
reasonable explanation, and therefore we uphold the inclusion
of the brick industry in the Silica Rule.

             B. TECHNOLOGICAL FEASIBILITY

     This court has interpreted the OSH Act’s requirement that
OSHA health standards protect workers “to the extent
feasible,” 29 U.S.C. § 655(b)(5), to include “two types of
feasibility,” namely, “technological and economic.” Lead I,
647 F.2d at 1264. Our standard of review narrowly cabins our
consideration of OSHA’s finding of technological feasibility.
Specifically, we must ensure only that OSHA found its
standard feasible and supported that finding with substantial
evidence.

     “To establish technological feasibility, OSHA, after
consulting the ‘best available evidence,’ 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 [standard] in most of its operations.’” Lead II,
939 F.2d at 980 (quoting Lead I, 647 F.2d at 1272). OSHA
need not show with certainty that all firms will be able to meet
the new standard in all operations. If “‘only the most
technologically advanced plants in an industry have been able
to achieve [the standard]—even if only in some of their
operations some of the time,’ then the standard is considered
feasible for the entire industry.” Id. (alteration in original)
(quoting Lead I, 647 F.2d at 1264).

    As with its finding of significant risk, OSHA must support
its finding of technological feasibility with substantial
evidence. Substantial evidence does not require absolute
                               24
“certainty.” Id. Where OSHA regulates on the frontiers of
scientific knowledge, it is bound to confront inconsistency and
uncertainty. But the mere “possibility of drawing two
inconsistent conclusions from the evidence does not prevent
[the] agency’s finding from being supported by substantial
evidence.” American Textile Manufacturers Institute, Inc. v.
Donovan (Cotton Dust), 452 U.S. 490, 523 (1981) (quoting
Consolo v. FMC, 383 U.S. 607, 620 (1966)). So long as
“OSHA makes reasonable predictions based on ‘credible
sources of information’ (e.g., data from existing plants and
expert testimony), then the court should defer to OSHA’s
feasibility determinations.” Lead II, 939 F.2d at 980.

     Where OSHA has demonstrated technological feasibility
for the typical firm in most operations and has supported that
finding with substantial evidence, it has satisfied its burden and
we must defer to its conclusions. To mount a successful attack
on OSHA’s feasibility finding, then, challengers must do more
than suggest that compliance will be infeasible for some firms
or in “a few isolated operations.” Id.

     In the robust process leading up to the promulgation of the
silica rule, OSHA found that the rule would be technologically
feasible based on a thorough consideration of available sources
of information. For general industry and construction, OSHA
identified job categories that involve silica exposure and
developed profiles showing current exposure levels. OSHA
then identified the individual jobs for which additional controls
are required to comply with the new PEL, and identified
available controls that would reduce exposure below the new
PEL. 81 Fed. Reg. at 16,433–34.

    OSHA concluded that achieving the new PEL is
technologically feasible for 87 out of 90 job categories
considered in general industry—including 36 categories in the
                               25
foundry industry, all of which were deemed feasible—and 19
of 23 tasks considered in construction. Id. at 16,454–55,
16,459. On this basis, OSHA found that there was a
reasonable possibility that the new standard could be achieved
by the typical employer in most operations and was thus
technologically feasible.

     In performing its analysis, OSHA relied on data from a
variety of sources, including reports from OSHA inspections,
National Institute for Occupational Safety and Health (NIOSH)
reports, site visits conducted by a contractor, data from external
stakeholders, and a variety of studies looking at the
effectiveness of various controls. OSHA also considered and
responded to testimony and comments submitted to the
rulemaking record.

     With our highly deferential standard of review and
OSHA’s process in mind, we now turn to Industry’s objections.
Industry challenges OSHA’s feasibility findings in only three
industries: foundries, hydraulic fracturing, and construction.
While Industry identifies sundry examples of infeasibility for
certain firms or in certain operations, their objections do not
collectively undermine OSHA’s overall finding of feasibility
for the typical firm in most operations nor do they meaningfully
call into question the evidence on which OSHA relied.

                         1. Foundries

     Industry disputes OSHA’s finding of technological
feasibility on two grounds: that variability in exposure levels
makes compliance infeasible; and that OSHA did not rely on
the best available evidence.

    On the issue of exposure variability, Industry contends that
because of the dynamic and unpredictable nature of silica
exposure, firms must strive to attain an exposure level well
                               26
below the new PEL to ensure compliance with certainty. This
argument runs headlong into our standard of review:
“Feasibility of compliance turns on whether exposure levels
. . . can be met in most operations most of the time; therefore,
it is the routine exposure levels that determine feasibility, and
atypical outliers cannot invalidate a feasibility finding.” Lead
II, 939 F.2d at 990.

     Industry’s focus on whether all foundries can always meet
the new standard with certainty is thus beside the point. The
relevant question is whether OSHA has shown that the typical
firm can meet the standard in most operations. OSHA has
done just that. It pointed to data—including over 1,000
samples from nearly 100 foundries—supporting its feasibility
finding. Indeed, a study by the American Foundry Society,
which Industry itself relies on, shows that the new PEL is
already being met in most foundry job categories. OSHA
further recognized that variability can be smoothed through
consistent use of engineering controls. And OSHA expressly
contemplates flexible enforcement to accommodate
unexpected swings in exposure levels, an approach this court
has approved in prior feasibility determinations. 81 Fed. Reg.
at 16,459; see Lead II, 939 F.2d at 991.

     Industry may well be right that exposure levels vary
uncontrollably and unpredictably across the foundry industry
and within individual firms. That, however, is exactly why
our standard of review does not require compliance from all
firms in all operations all of the time; it is designed to permit
OSHA to regulate in the face of variability and uncertainty.
And Industry has failed to show that variability in the foundry
industry undermines OSHA’s finding of feasibility for the
typical firm in most operations most of the time.
                                27
     Industry also challenges the foundry-industry evidence on
which OSHA relied. The data OSHA considered came from
a variety of sources including its own visits to worksites,
enforcement data, and other inspection reports, as well as
NIOSH reports, state program reports, industrial hygiene
literature, and survey data from the American Foundry Society,
all of which supported OSHA’s feasibility finding. Industry,
insisting that “no two foundries are alike,” contends that OSHA
ignored the best available evidence, namely, the experiences of
foundries attempting and failing to comply with the prior
standard. In particular, Industry singles out sand system
operators and finishers as two job categories in which
compliance is infeasible. Industry Br. at 63–65. But
Industry’s evidence suggests, at most, that compliance will be
infeasible for some foundries or in some operations. And
OSHA identifies controls that might be able to achieve
compliance in the specific foundries and operations that
Industry identifies. Even assuming that Industry is correct
that compliance is unachievable in the foundries and operations
it identifies, such isolated examples of infeasibility are, under
our standard of review, insufficient to defeat OSHA’s finding
of feasibility for “the typical” foundry in “most . . . operations.”
Lead I, 647 F.2d at 1272.

                   2. Hydraulic Fracturing

     Because OSHA only recently recognized the risk of silica
exposure in the hydraulic fracturing industry, available data is
limited and what data is available shows, unsurprisingly, that
the vast majority of firms are not yet in compliance with the
new standard. According to Industry, this evidence shows that
the new standard is unattainable as there is no evidence of any
controls reducing exposure below the new PEL.
                               28
     But even if sufficient controls do not yet exist, Industry’s
challenge to OSHA’s feasibility finding nonetheless fails. In
considering which controls can feasibly be implemented,
OSHA “is not bound to the technological status quo.” Lead I,
647 F.2d at 1264. “Because the OSH Act is a ‘technology-
forcing’ statute, OSHA can also ‘force industry to develop and
diffuse new technology’” to meet its standard. Lead II, 939
F.2d at 980 (quoting Lead I, 647 F.2d at 1264). So long as
OSHA “gives industry a reasonable time to develop new
technology” and “presents substantial evidence that companies
acting vigorously and in good faith can develop the
technology,” it can “require industry to meet PELs never
attained anywhere.” Lead I, 647 F.2d at 1264–65.

     Given the nascent state of silica-control technology in the
hydraulic fracturing industry, OSHA gave firms five years to
comply with the new standard. Acknowledging that controls
have yet to be widely implemented in the industry, OSHA
identified controls, some currently available and others under
development, that promise to sufficiently reduce exposure,
citing to comments from several vendors. 81 Fed. Reg. at
16,455. In support of the five-year grace period, OSHA relied
on an industry expert who described significant progress made
over the prior five years and an inventor of one silica-control
technology who explained that the technology took only three
years to develop. Id. at 16,457. Though Industry disagrees
with OSHA’s forecast of future silica-control developments in
hydraulic fracturing, the agency’s evidence is more than
sufficient “to show that modern technology has at least
conceived some industrial strategies or devices which are likely
to be capable of meeting the PEL and which the industries are
generally capable of adopting” in the extended time horizon
OSHA provided. Lead II, 939 F.2d at 1006 (quoting Lead I,
647 F.2d at 1266).
                               29
                       3. Construction

     In assessing the technological feasibility of its rule in the
construction industry, OSHA relied on the Table 1 safe harbor.
Under the new rule, if a construction employer implements the
controls listed on Table 1—applicable to nineteen of twenty-
three construction tasks—it is freed from its obligation to
achieve the new PEL. OSHA determined not only that most
employers would follow Table 1 for most tasks, but also that it
would be technologically feasible for them to do so given the
ready availability of Table 1 controls. OSHA also found the
rule to be technologically feasible for tasks not appearing on
Table 1. 81 Fed. Reg. at 16,458.

     Industry’s primary challenge to OSHA’s feasibility
finding is that the Table 1 controls cannot always be
implemented and sometimes require respiratory protection.
But even were we to accept Industry’s arguments, these
isolated exceptions hardly undermine OSHA’s finding of
feasibility for the typical firm in most operations.

     As to situations where Table 1 controls cannot be
implemented, Industry focuses on six tasks for which wet
methods are prescribed, arguing that it is sometimes infeasible
to introduce water to the work environment, such as for some
indoor work or in cold-weather environments. Industry Br. at
98–99. But OSHA adduced evidence showing that employers
can overcome many of the barriers identified by Industry, for
example, by using heated water in cold-weather environments.
81 Fed. Reg. at 16,460. Moreover, even where wet methods
cannot be implemented, Table 1 functions as just one of two
paths to compliance: where an employer cannot or elects not to
follow Table 1, it is free to take the traditional path to
compliance by implementing controls of its choice to reduce
exposures below the new PEL. OSHA acknowledged in the
                               30
rulemaking record that such situations may arise and
contemplated alternative controls that might be implemented.
Id. at 16,460–61. Even accepting Industry’s arguments that
compliance for some tasks is infeasible under certain work
conditions does not overcome OSHA’s finding of feasibility
for the typical employer in most operations. Because Industry
argues neither that the typical employer cannot implement wet
methods nor that such methods are required in most operations,
it has failed to carry its burden of showing that the use of wet
methods renders the rule infeasible.

    On the issue of respiratory protection, OSHA assesses
technological feasibility based on whether firms can “develop
and install engineering and work practice controls” to meet the
standard “without relying on respirators.” Lead I, 647 F.2d at
1272. The fact that “respirators will be necessary in a few . . .
operations, will not undermine th[e] general presumption in
favor of feasibility.” Id. Thus the question for our review
remains whether the need for respirators is so widespread as to
undermine OSHA’s finding of feasibility for the typical firm in
most operations.

     OSHA, however, contemplates only limited respirator use.
Industry argues that “one-third of [Table 1 tasks] require some
form of respiratory protection when the task is performed for
just over four hours,” which is “significant and . . . completely
undercuts OSHA’s claim of technological feasibility.”
Industry Br. at 95–96. Table 1, however, includes nineteen
construction tasks, thirteen of which require no respiratory
protection at all. OSHA Br. at 92 n.56 (explaining that though
only eighteen tasks are listed, a nineteenth task, performed by
ground crew assisting equipment operators, is covered by
Table 1). Certain others, the one-third of tasks to which
Industry refers, require respirators under only certain
circumstances, such as when the task is performed indoors or
                               31
for over four hours. See 29 C.F.R. § 1926.1153(c)(3). And
OSHA credibly found that most tasks would be performed for
four hours or less and/or outdoors. 81 Fed. Reg. at 16,724.
Again, the fact that respiratory protection will be required in
some operations some of the time fails to satisfy Industry’s
burden to rebut OSHA’s feasibility finding for the typical firm
in most operations.

     Industry points to OSHA’s finding that it expects 13% of
all workers to need some amount of respiratory protection as
an indication that the rule is infeasible. Specifically, Industry
argues that in litigation related to OSHA’s Hexavalent
Chromium rule, the agency rejected respirator use by 9.5% of
employees as unacceptably high. Industry Reply Br. at 51–52.
The very language Industry relies on, however, defeats its
claim. In the Hexavalent Chromium litigation, OSHA stated:
“While the agency estimated that a total of 9.5% of all
employees in all application groups would need respirators . . .
that overall figure did not factor into OSHA’s technological
feasibility findings . . . .” Public Citizen Health Research
Group v. OSHA, Nos. 06-1818 and 06-2604, Final Brief for
Respondents, at 45 (3d Cir. Dec. 14, 2007). There, OSHA
noted that “respirator use was more than ‘isolated’ where
almost one third or more of the exposed employees in the
affected groups would have to use respirators.” Id. Here,
OSHA’s conclusion that 13% of workers using respirators
amounts to only “isolated” respirator use neither overwhelms
its finding of technological feasibility nor conflicts with its
position in the Hexavalent Chromium litigation. As we have
explained, OSHA must show only that compliance is feasible
for the typical firm in most operations—that some respirator
use may sometimes be needed is not enough to defeat OSHA’s
finding.
                               32
     Even combining the effects of these two issues—the
sometimes need for respiratory protection and the occasional
situations where wet methods are infeasible—Industry has
failed to show that it is infeasible for the typical employer to
meet the standard in most operations. Some employers may
be unable to implement the Table 1 controls in all operations—
though OSHA reasonably explains why there are fewer such
situations than Industry suggests. And some may have to
resort to respiratory protection for certain tasks, though, as
OSHA points out, only for a minority of tasks and only under
certain circumstances.       But Industry’s identification of
atypical circumstances in a minority of operations where
compliance with Table 1 is infeasible falls far short of rebutting
OSHA’s well-supported finding of feasibility for the typical
firm in most operations.

    Industry mounts a handful of additional challenges. None
has merit.

     First, Industry again raises the issue of exposure
variability. But this argument fails in construction just as it
failed for the foundry industry: OSHA provided evidence
suggesting that variability is controllable and, in any event, our
standard of review is designed to accommodate just such
variability. Moreover, exposure variability—to the extent it
presents a problem—is further mitigated in construction, where
Table 1 provides a path to compliance without any need for
exposure testing.

     Next, Industry criticizes the evidence upon which OSHA
relied in determining how the PEL could feasibly be met.
Specifically, Industry takes issue with OSHA’s reliance on
short-duration exposure samples and its calculation of an eight-
hour average assuming no additional exposure during the un-
sampled portion of the eight-hour period. Industry Br. at 90–
                               33
94. Although few of OSHA’s exposure samples were eight
hours long, the vast majority (70%) were four hours or longer
and nearly half (43%) were more than six hours long. 81 Fed.
Reg. at 16,435. And OSHA considered Industry’s objection
and adequately justified the no-further-exposure assumption by
adducing evidence of the intermittent and short-duration nature
of silica exposure in construction tasks. Id. Moreover,
OSHA’s assumption aligns with its enforcement practice.
When OSHA compliance officers collect partial-shift samples
during an inspection, they calculate eight-hour time-weighted
average exposures using the same assumption of no further
exposure during the un-sampled period. The alignment
between OSHA’s evidence and its enforcement practice
confirms that any harm to Industry from this assumption is
more semantic than substantive.

     Finally, Industry disputes OSHA’s finding of feasibility
for four particular tasks: hole drillers using handheld or stand-
mounted drills, jackhammering and using other powered
handheld chipping tools, masonry cutters using stationary
saws, and mobile crushing machine operators and tenders.
Industry Br. at 99–105. We have no need to address
Industry’s arguments as to these tasks, for even were we to
accept them, Industry would still have failed to rebut OSHA’s
finding of feasibility in “most operations.” Lead II, 939 F.2d
at 990. In any event, OSHA cited evidence that employers
could reduce exposure levels for each task using available
controls. In response, Industry recites a number of by-now
familiar arguments: that OSHA’s data was inadequate, that the
tasks are sometimes performed for longer than OSHA assumes,
and that particular controls (again, wet methods) sometimes
cannot be implemented.           But OSHA considered and
responded to each of these objections, making “reasonable
predictions based on ‘credible sources of information.’” Lead
II, 939 F.2d at 980 (quoting Lead I, 647 F.2d at 1266). Once
                               34
again, Industry’s insistence that compliance is infeasible for
some firms in some operations some of the time cannot upend
our deference to OSHA’s well-supported finding that
compliance is feasible for the typical firm in most operations.

                 C. ECONOMIC FEASIBILITY

     The OSH Act’s requirement that OSHA health standards
protect workers “to the extent feasible,” 29 U.S.C. § 655(b)(5),
also requires OSHA to show that its rule is economically
feasible, Lead I, 647 F.2d at 1264. As with technological
feasibility, the scope of our review of OSHA’s economic
feasibility finding is narrowly circumscribed.

     A rule is economically feasible in a particular industry so
long as it does not “threaten massive dislocation to, or imperil
the existence of, the industry.” Id. at 1265. Thus, “[a]
standard is not infeasible simply because it is financially
burdensome or even because it threatens the survival of some
companies within an industry.”           Id. (citation omitted).
“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 980–81. OSHA must also provide “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.
“Courts, [moreover], ‘cannot expect hard and precise estimates
of costs.’” Lead II, 939 F.2d at 1006 (quoting Lead I, 647 F.2d
at 1266). As before, the mere “possibility of drawing two
inconsistent conclusions from the evidence” or deriving two
divergent cost models from the data “does not prevent [the]
agency’s finding from being supported by substantial
                               35
evidence.” Cotton Dust, 452 U.S. at 523 (quoting Consolo,
383 U.S. at 620).

     Industry does not challenge OSHA’s overall methodology
for assessing economic feasibility. Instead, it questions the
evidence on which OSHA relied in the foundry, hydraulic
fracturing, and construction industries. Industry also gestures
towards a challenge to OSHA’s findings on the brick industry,
claiming only that OSHA “cannot adopt a standard that
imposes very large costs on an industry without producing any
quantifiable health benefit.” Industry Br. at 130. But
because OSHA found significant risk in the brick industry, as
we explained above, and Industry does not otherwise claim
economic infeasibility, this argument is foreclosed.

     Industry’s economic feasibility arguments, like its
technological feasibility arguments, raise a host of claims about
OSHA’s sources that do not collectively undermine the
evidence OSHA relied on and the conclusions it reached,
especially in light of our standard of review and the narrow
scope of Industry’s challenge. In its economic feasibility
analysis, OSHA developed estimates of the annualized cost of
compliance for each affected industry—and for small and very
small employers within each industry—and compared those
costs against industry revenues and profits. See 81 Fed. Reg.
at 16,462–582 (describing OSHA’s economic feasibility
methodology). OSHA explained that “while there is no hard
and fast rule,” it “generally considers a standard to be
economically feasible” for an industry where annualized costs
of compliance are less than one percent of revenue or ten
percent of profit. Id. at 16,533. OSHA considers this
benchmark to be “fairly modest,” so costs exceeding the
threshold do not imply per se infeasibility, but rather serve as a
trigger for further analysis. Id.
                              36
     For each of the industries at issue here—foundries,
hydraulic fracturing, and construction—OSHA determined
that costs as a percentage of revenues and profits were below
the one percent and ten percent thresholds. Id. at 16,536,
16,538, 16,573. For foundries and construction, these costs
were well below these benchmarks for all industry subgroups
considered: even doubling OSHA’s cost estimates in foundries
and tripling them in construction would only barely trigger the
thresholds for further inquiry. Id. at 16,538 (showing, among
subgroups within the foundry industry, costs as a percentage of
profits of 5.62% at the greatest); id. at 16,573 (showing, among
subgroups in construction, costs as a percentage of profits of
3.66% at the greatest). For hydraulic fracturing, compliance
costs were somewhat nearer OSHA’s thresholds, though still
below, with costs as a percentage of revenues of 0.56% and
costs as a percentage of profits of 7.94%. Id. at 16,536
(assessing hydraulic fracturing as part of the “Support
Activities for Oil and Gas Operations” industry). OSHA thus
provided “a reasonable estimate of compliance costs and
demonstrate[d] a reasonable likelihood that these costs will not
threaten the existence or competitive structure of an industry.”
Lead I, 647 F.2d at 1272.

     Industry points out that compliance costs exceed OSHA’s
threshold for small and very small employers in the hydraulic
fracturing industry and for very small employers in the foundry
industry, arguing that this alone renders the rule economically
infeasible. Industry Br. at 71; see 81 Fed. Reg. at 16,553,
16,562, 16,564. As explained above, however, exceeding this
threshold does not in and of itself demonstrate infeasibility;
instead, it triggers further analysis by OSHA. 81 Fed. Reg. at
16,533–34.       And the standard for economic feasibility
contemplates that compliance may be infeasible for a subset of
firms within an industry, like the small and very small firms at
issue here. See Lead I, 647 F.2d at 1272 (allowing a finding
                              37
of economic feasibility even where a rule “portend[s] disaster
for some marginal firms”). Indeed, consistent with its
understanding of these thresholds as merely triggers for
additional analysis, OSHA engaged in further inquiry into the
impact on these firms and reasonably concluded that the Rule
did not threaten “massive industry dislocation.” See Lead II,
939 F.2d at 980.

                        1. Foundries

     Industry makes a handful of arguments against OSHA’s
sources and assumptions, relying primarily on analysis by URS
Corporation and Environomics showing compliance costs
much higher than OSHA’s estimates. Industry Br. at 72.
But, as explained above, our standard of review does not permit
us to compare competing analyses and decide which we
prefer—it leaves that responsibility to OSHA. So long as
OSHA supports its position with substantial evidence, we have
no need to consider alternatives it might otherwise have
adopted. We turn, then, to Industry’s challenges to the
evidence upon which OSHA did rely.

     First, Industry disputes OSHA’s assumption of an even
apportionment of costs between those required for compliance
with the prior PEL—which are not attributable to the new
rule—and those required to further reduce exposure from the
prior PEL to the new PEL—which are. Industry Br. at 76–77.
But OSHA specifically addressed Industry’s objection and
supported its decision to rely on this assumption with
substantial evidence. 81 Fed. Reg. at 16,473–74. OSHA
cited data in the record showing that the average worker
exposed above the prior PEL was exposed at levels
significantly higher than the prior PEL. Such high exposures
can be addressed only with certain substantial controls, like
local exhaust ventilation systems, which in turn account for the
                              38
bulk of the costs associated with exposure reduction. Id.
Accordingly, OSHA reasoned, since the bulk of the expense
will come from reducing uncontrolled environments to the
prior PEL, less cost will result from controls implemented to
reach the new PEL. Id. Moreover, the reduction from the
average uncontrolled level (300 µg/m3) to the old PEL (100
µg/m3) represents a larger reduction—both relatively and
absolutely—than the reduction from the old PEL (100 µg/m3)
to the new PEL (50 µg/m3), which mitigates Industry’s claim
that costs increase disproportionately as facilities reach lower
exposure levels. OSHA’s assumption here was just that, an
assumption, which the agency adequately supported on the
basis of the best available evidence. And given that OSHA’s
cost estimates were well below its threshold for concern, any
error resulting from this assumption would be harmless.
National Cottonseed Products Association v. Brock, 825 F.2d
482, 488 (D.C. Cir. 1987) (finding OSHA’s failure to include
certain costs in an economic feasibility analysis to be harmless
error).

     Industry next faults OSHA for engaging in a per-worker
assessment of costs—calculating compliance cost based on the
number of exposed workers—rather than looking at costs on a
per-facility basis. Industry Br. at 73–76. OSHA, however,
adequately defended its choice on a perfectly reasonable basis.
See 81 Fed. Reg. at 16,469–70. OSHA rejected the URS
study’s facility-based approach because it failed to take into
account situations where only some but not all workers are
exposed and where there are existing controls in place;
according to OSHA, record evidence showed that where one or
both of these conditions exists, firms can reduce exposure by
means other than a full set of controls. Id. Though OSHA’s
approach may understate costs in some situations where fixed
investment is out of proportion to the number of workers
impacted, the per-facility approach is vulnerable to the same
                              39
problem in the opposite direction. Between these imperfect
options, OSHA supported its decision to rely on the per-worker
approach with substantial evidence—all our standard of review
requires.

     Industry also criticizes OSHA’s exclusion of the cost of
certain controls mentioned in its technological feasibility
analysis. Industry Br. at 77–80. But given that the new rule
mandates no particular set of controls, OSHA considered the
lowest-cost combination of controls that would allow the
typical foundry to meet the new PEL. 81 Fed. Reg. at 16,482.
This court, moreover, has endorsed this “typical employer”
approach to economic feasibility. Lead II, 939 F.2d at 1005.
OSHA directly addressed Industry’s objection in the preamble
to the rule: “Just because a control is mentioned in the
technological feasibility analysis does not mean that OSHA has
determined that its use is required—only that it represents a
technologically feasible method for controlling exposures.”
81 Fed. Reg. at 16,482. Notwithstanding its decision to
exclude certain controls from its cost analysis, OSHA has
discharged its duty to provide “a reasonable assessment of the
likely range of costs of [the] standard.” Lead II, 939 F.2d at
1006 (alteration in original) (emphasis added) (quoting Lead I,
647 F.2d at 1266).

     Finally, Industry argues that OSHA’s cost estimates do not
reflect the best available evidence. They contend that the best
available evidence is “the actual experience of employers that
have installed the control” as provided by the American
Foundry Society. Industry Br. at 81 (emphasis omitted).
They point to two examples—ventilation and housekeeping
vacuum systems—where the Society’s cost estimates were
significantly higher than OSHA’s. Id. at 80–83. OSHA,
however, adequately defended its cost estimates for both of
these controls. For ventilation systems, OSHA based its cost
                              40
estimate on analysis by its contractor, Eastern Research Group,
finding the estimates to be reasonable, while acknowledging
“that there can be a wide range of both capital and operating
costs associated with” ventilation. 81 Fed. Reg. at 16,480.
For housekeeping, OSHA based its estimate on its calculation
of average production floor space from NIOSH field studies
and cost evidence from a firm specializing in the industrial
cleaning of foundries. Id. at 16,481. OSHA considered and
rejected Industry’s higher estimates of housekeeping costs,
which were based on a single quote and “communicat[ions]
with industry representatives.” Id. at 16,481–82. OSHA’s
well-supported estimates and considered rejection of
alternative evidence are sufficient to justify its findings of
economic feasibility.

                 2. Hydraulic Fracturing

     Industry alleges that OSHA relied upon “industry revenues
and profits, which . . . do not reflect the real world” because
they fail to capture a “significant drop in revenue” resulting
from declining oil prices. Industry Br. at 84. In its final
analysis, OSHA incorporated the most recent data available
and performed additional analysis to ensure that the new rule
would not imperil the hydraulic fracturing industry. 81 Fed.
Reg. at 16,549. OSHA expressly acknowledged that the
“recent drop in oil prices has caused a series of bankruptcies
and closures across the oil industry,” but cited a forecast of
increased oil prices in the coming years. Id. at 16,549–50.
Recognizing the uncertainty inherent in such predictions,
OSHA observed that the cost of complying with the rule is a
“small fraction” of the cost to the industry of fluctuation in
energy prices. Id. at 16,550. And OSHA’s delayed
implementation timeline in hydraulic fracturing gives the
industry further opportunity to develop new, cost-efficient
technologies. See Lead I, 647 F.2d at 1265 (“Granting
                              41
companies reasonable time to comply with new PELs might
. . . enhance economic feasibility generally . . . .”).

       OSHA concluded that “even in a lower price environment,
hydraulic fracturing entrepreneurs will be able to implement
the controls required by th[e] final rule without imposing
significant costs, causing massive economic dislocations to the
. . . industry, or imperiling the industry’s existence.” 81 Fed.
Reg. at 16,550. Given the inherent uncertainty in forecasting
future economic conditions, OSHA’s thorough consideration
of Industry’s concerns, and the delayed implementation
timeline, OSHA’s finding that the rule is economically feasible
in hydraulic fracturing finds ample support in the record.
Though Industry’s arguments raise concerns about the
fundamental health of the hydraulic fracturing industry, they
never claim that OSHA’s rule will seal the industry’s fate.

     As a final matter, Industry again argues that OSHA
underestimated compliance costs by including the cost of only
some of the controls discussed in the technological feasibility
analysis. Industry Br. at 83–85. But this argument fails here
just as it did for foundries: OSHA estimated only the typical
cost of compliance and need not consider every single control
discussed. See Lead II, 939 F.2d at 1005.

                      3. Construction

    Industry first contends that OSHA’s final cost estimates
“make no sense in the real world of construction,” pointing to
several industry subgroups where OSHA’s estimated
annualized cost per affected establishment is under $1,000.
Industry Br. at 106. But just because the amounts seem low
does not imply that they are unsupported. And OSHA
explained that many firms have only a handful of affected
employees, 81 Fed. Reg. at 16,408, and that recommended
controls are often inexpensive systems integrated into hand
                              42
tools, id. at 16,436. In light of OSHA’s explanation of the
reason for the apparently low costs in certain construction
industry groups, Industry’s bare argument that the costs are too
low carries little weight.

     Next, Industry critiques OSHA’s assumption of a 150-day
working year, which Industry argues is too short and thus
understates costs. Industry Br. at 107–08. But OSHA points
to sufficient record evidence supporting this assumption:
equipment cannot be used with perfect efficiency, especially in
light of weather conditions that interfere with construction.
Although OSHA does not explain how it arrived at 150 days,
any error would be harmless. 81 Fed. Reg. at 16,494.
Moreover, OSHA explains that this assumption does not
function the way Industry describes: the agency used the 150-
day assumption only as a divisor when calculating the per-day
cost of certain engineering controls. As a result, increasing
the days-per-year assumption would actually decrease the cost
per day. OSHA Br. at 141–42. Even were this assumption to
function in the way Industry imagines, costs in construction
would have had to triple before triggering OSHA’s threshold
for further inquiry, confirming that OSHA’s ultimate
conclusion was well supported. 81 Fed. Reg. at 16,573.

     Finally, Industry objects to OSHA’s calculation of
compliance costs based on an assumption that employers will
follow Table 1, arguing that this “ignores substantial evidence
in the record that employers will not be able to follow Table 1
in all of the operations all of the time.” Industry Br. at 108–
10. As before, however, OSHA need not look at the cost of
compliance for all employers in all operations all of the time;
rather, it is required to consider only the typical compliance
costs for the “typical” employer. Lead II, 939 F.2d at 1005.
OSHA did just that; indeed, the agency did more, calculating
alternative compliance costs for operations categorically
                               43
excluded from Table 1 (tunnel boring, for example), 81 Fed.
Reg. at 16,486, and estimating sampling and monitoring costs
for employers whose exposure levels are so low as to never
trigger the rule’s requirements and who would thus not follow
Table 1, id. at 16,514.

                          Conclusion

     OSHA’s cost estimates in each of these industries are
inevitably imperfect due to the limitations of available data and
the uncertainties inherent in predicting future costs. But this
is why “hard and precise estimates of costs” are not required.
Lead II, 939 F.2d at 1006 (quoting Lead I, 647 F.2d at 1266).
OSHA’s only obligation is to confirm, on the basis of
substantial evidence, that its rule does not “threaten massive
dislocation to, or imperil the existence of, the industry.” Id. at
980 (quoting Lead I, 647 F.2d at 1265). There can be little
doubt that OSHA has done so here.

               D. PROCEDURAL CHALLENGES

     Both the OSH Act and the APA, which govern the process
for promulgating occupational safety and health standards,
require the Secretary to publish proposed rules and provide an
opportunity for comment. 29 U.S.C. § 655(b)(2); 5 U.S.C.
§ 553. “[I]n order to allow for useful criticism, it is especially
important for the agency to identify and make available
technical studies and data that it has employed in reaching the
decisions to propose particular rules.” American Radio Relay
League, Inc. v. FCC, 524 F.3d 227, 236 (D.C. Cir. 2008)
(quoting Connecticut Light & Power Co. v. Nuclear Regulatory
Commission, 673 F.2d 525, 530 (D.C. Cir. 1982)). “An
agency commits serious procedural error when it fails to reveal
portions of the technical basis for a proposed rule in time to
allow for meaningful commentary.”              Owner-Operator
Independent Drivers Association v. Federal Motor Carrier
                               44
Safety Administration, 494 F.3d 188, 199 (D.C. Cir. 2007)
(quoting Solite Corp. v. EPA, 952 F.2d 473, 484 (D.C. Cir.
1991) (per curiam)).

   Industry points to two alleged procedural defects in
OSHA’s process.

     First, Industry faults OSHA for disclosing data from the
OSHA Information System (OIS) on the last day of the data-
submission period—June 3, 2014—thereby depriving Industry
of an opportunity to respond. Industry Br. at 117–18. But
OSHA’s reliance on the OIS data was unproblematic given that
it provided adequate opportunity for comment. After the data-
submission period, OSHA offered an additional two months—
until August 18—for parties to submit final briefs and
arguments, a deadline that OSHA twice extended. 81 Fed.
Reg. at 16,298. Though Industry argues that they had no
opportunity to submit additional data in response to the OIS
data, they never explain why the two-month response period
was insufficient to allow them opportunity for “meaningful
commentary.”         Owner-Operator Independent Drivers
Association, 494 F.3d at 199. Nor does Industry make any
effort to explain why they were prejudiced by OSHA’s actions.
Barring a total failure to engage in notice and comment, we
“will not set aside a rule absent a showing by the petitioners
‘that they suffered prejudice from the agency’s failure to
provide an opportunity for public comment.’” American
Radio Relay League, 524 F.3d at 237 (quoting Gerber v.
Norton, 294 F.3d 173, 182 (D.C. Cir. 2002)). OSHA’s actions
here were at worst harmless, and, more likely, not even in error.

     Second, Industry criticizes OSHA’s reliance on data and
estimates from its contractor Eastern Research Group (ERG),
arguing that OSHA failed to disclose the basis for ERG’s
assumptions. Industry Br. at 119–21. This court has
                               45
previously approved OSHA’s reliance on information from
external consultants in rulemaking, making clear that the key
question is whether the challenger can “buttress its general
allegation of excessive reliance with any specific proof that the
[agency] failed to confront personally the essential evidence
and arguments in setting the final standard.” See Lead I, 647
F.2d at 1217. Here, OSHA placed all available ERG evidence
in the record and made clear what information it relied upon in
reaching its conclusions. Though Industry criticizes OSHA
for relying on ERG’s “estimates” and interviews with
unidentified individuals, they fail to propose alternative data
sources or explain why ERG’s opinions are insufficient.
Industry has given us no grounds for questioning OSHA’s
conclusion that ERG provided the best available evidence.

                E. ANCILLARY CHALLENGES

     Although reducing the PEL to 50 µg/m3 represents the
Rule’s central innovation, OSHA determined that even the
reduced PEL poses substantial employee health risks. See 81
Fed. Reg. at 16,287 (“[OSHA] considers the level of risk
remaining at the new PEL to be significant.”). The Rule
therefore contains ancillary measures designed to “provid[e]
additional layers and types of protection” to exposed
employees. Id. at 16,294. Industry challenges two of these
measures. Finding that substantial evidence supports OSHA’s
choices, we reject both challenges. See International Union,
United Automobile, Aerospace & Agricultural Implement
Workers of America, UAW v. Pendergrass (Formaldehyde),
878 F.2d 389, 391–92 (D.C. Cir. 1989) (reviewing ancillary
provisions under substantial evidence standard).

                  1. Medical Surveillance

    Industry first targets the Rule’s medical surveillance
provisions. Under the Rule, employers must offer no-cost
                               46
medical surveillance to certain silica-exposed employees. See
29     C.F.R.    §§ 1910.1053(i)(1)(i);      1926.1153(h)(1)(i).
Participating employees receive periodic medical screening
and written reports that include, among other things, the
examining      physician’s      recommendations        regarding
“limitations on the employee’s exposure to respirable
crystalline    silica.”          Id.     §§ 1910.1053(i)(5)(iii);
1926.1153(h)(5)(iii). But absent the employee’s written
authorization,    the    employer       never    receives    the
recommendations.                Id.       §§ 1910.1053(i)(6)(ii);
1926.1153(h)(6)(ii).

     Industry challenges OSHA’s decision to let employees
decide whether to notify their employers of their doctors’
recommendations. Past standards, Industry argues, entitled
employers to such information regardless of employee consent.
And, Industry further contends, the Rule’s novel consent-based
approach unreasonably risks withholding from employers
information needed to ensure workplace safety.

      Industry correctly observes that prior OSHA standards
have unconditionally entitled employers to notice of their
employees’ medically indicated exposure limitations. See,
e.g.,      id.      §§ 1910.1026(k)(5)(i)(B)      (chromium);
1910.1028(i)(7)(i)(C)     (benzene);    1926.62(j)(3)(v)(A)(2)
(lead). Agencies, however, are “free to change their existing
policies as long as they provide a reasoned explanation for the
change.” Encino Motorcars, LLC v. Navarro, 136 S. Ct. 2117,
2125 (2016). Agencies undertaking such a change “need not
always provide a more detailed justification than what would
suffice for a new policy created on a blank slate,” so long as
they “display awareness that [they are] changing position” and
“show that there are good reasons for the new policy.” Id. at
2125–26 (quoting FCC v. Fox Television Stations, Inc., 556
U.S. 502, 515 (2009)); see also Formaldehyde, 878 F.2d at 400
                             47
(requiring “at the least some explanation” for an agency’s
“‘swerve’ from prior practice”).

     In the Rule’s preamble, OSHA openly acknowledged that
the Rule’s consent-based approach to reporting employees’
medical restrictions treads new ground. See 81 Fed. Reg. at
16,834 (“The requirements for the type of information
provided to the employer [under the Rule’s medical
surveillance provisions] are different from requirements of
other OSHA standards . . . .”). OSHA has also offered good
reasons for its new approach, explaining that disregarding
employees’ “reluctance to let employers know about their
health status” could compromise worker safety by deterring
employees fearful of the employment consequences of an
adverse diagnosis from participating in medical surveillance.
Id. at 16,832. And, more generally, “evolving notions about
where the balance between preventive health policy and patient
privacy is properly struck,” id. at 16,831, led OSHA to
conclude that “employees have the most at stake in terms of
their health and employability” and so should be entitled to
decide for themselves whether to relay potentially
compromising medical information, id. at 16,833.

     Industry challenges OSHA’s decision to allow employees
to withhold medical information from their employers, arguing
that knowing employees’ health status helps employers adopt
appropriate workplace health and safety measures. OSHA
considered and reasonably rejected this argument during the
rulemaking.     Silica-related illnesses have long latency
periods, and OSHA reasoned that an employee’s present
diagnosis with an illness likely contracted long ago “will not
provide useful information about” the efficacy of an
employer’s “current controls or exposure conditions.” Id.
(emphasis added). And although knowing which silica-
exposed employees are particularly vulnerable to adverse
                              48
health effects could prompt an employer to find safer
placements for those employees, OSHA preferred to leave
employees the freedom to decide for themselves whether to
seek such a placement. Because OSHA has “explain[ed] its
logic and the policies underlying its choices,” we have no basis
for second-guessing its reasonable judgments. National
Maritime Safety Association, 649 F.3d at 752.

     Industry also argues that the Rule’s medical surveillance
provisions exceed OSHA’s statutory authority to regulate.
Absent unconditional employer notification, Industry argues,
medical surveillance lacks the workplace nexus that is
prerequisite to OSH Act regulation. See Cotton Dust, 452
U.S. at 540 (“[T]he [OSH] Act in no way authorizes OSHA to
repair general unfairness to employees that is unrelated to
achievement of health and safety goals . . . .”). But the Rule’s
medical surveillance provisions obviously possess such a
nexus. After all, an employer assumes medical surveillance
obligations only by exposing its employees to workplace silica,
thereby creating the need to assess the exposure’s potential
health effects. Although Industry fleetingly argues that the
medical surveillance provisions violate the OSH Act’s
disclaimer of authority to “supersede or in any manner affect”
state worker’s compensation systems, 29 U.S.C. § 653(b)(4), it
entirely fails to explain how.

  2. Dry Sweeping, Dry Brushing, and Compressed Air

    Industry’s second challenge to the Rule’s ancillary
provisions targets measures that prohibit dry sweeping, dry
brushing, or (barring suitable ventilation) the use of
compressed air for certain purposes “where such activity could
contribute to employee [silica] exposure” and if alternative
methods are feasible. See 29 C.F.R. §§ 1910.1053(h);
1926.1153(f). The proposed rule would have limited these
                              49
housekeeping methods only where they could “contribute to
employee exposure to respirable crystalline silica that exceeds
the PEL.” 78 Fed. Reg. at 56,274, 56,499 (Sept. 12, 2013)
(emphasis added). The final rule, though, instead restricts
these methods whenever they could contribute to silica
exposure to any degree. Industry argues that this revision is
unsupported by substantial evidence because it essentially
imposes a wholesale prohibition on the covered methods.

     Industry’s challenge fails. OSHA found that silica
exposure, even at levels below the PEL, poses significant risks
to employee health, see 81 Fed. Reg. at 16,796, and that the
Rule’s restrictions on dry sweeping, dry brushing, and the use
of compressed air reduce exposure, see id. at 16,794. Except
insofar as Industry argues that OSHA lacked substantial
evidence to find significant employee health risks even at the
PEL—an argument that we have already rejected, see supra
Part II.A—Industry presents no meaningful challenge to these
findings. Industry briefly suggests that a study cited in the
Rule’s preamble as linking dry sweeping to increased silica
exposure was “insufficient to support OSHA’s prohibition on
all dry sweeping, dry brushing, or use of compressed air that
contributes to employee exposure to silica at any level.”
Industry Reply Br. at 63. The study, however, cited as an
“example,” was not the sole basis for OSHA’s conclusions.
See 81 Fed. Reg. at 16,794 (summarizing comments that
discuss other studies).

     Having failed to undermine OSHA’s supportable finding
that the Rule’s housekeeping provisions promote worker
safety, Industry next argues that OSHA inadequately addressed
concerns that alternatives to the restricted housekeeping
methods can be hazardous or impractical. But OSHA
explained in the preamble that the Rule resolves precisely these
concerns by allowing employers to use the restricted methods
                               50
where alternatives are infeasible. See id. at 16,796 (“[I]n
situations where [alternatives] would not be effective, would
cause damage, or would create a hazard in the workplace, the
employer is not required to use these [alternative] cleaning
methods.”). Industry quibbles that “[t]he Rule does not define
what is feasible in any particular situation” and that the
employer bears the burden of showing an alternative’s
infeasibility, Industry Br. at 115–16, though it offers nothing
beyond unsupported speculation to suggest that the
infeasibility exception will inadequately serve the very purpose
for which it was adopted.

                   F. UNION CHALLENGES

    We turn finally to the Unions’ challenges.

     As it has with many long-latency occupational diseases,
OSHA required employers to provide medical exams to help
combat the risks posed by silicosis and other silica-related
diseases. 29 C.F.R. §§ 1910.1053(i); 1926.1153(h). OSHA
concluded that such exams “will allow for identification of
respirable crystalline silica-related adverse health effects at an
early stage so that appropriate intervention measures can be
taken.” 81 Fed. Reg. at 16,625. Employer-provided medical
surveillance not only motivates employers to reduce exposures
to avoid surveillance costs, but also provides information to
employees so that they can “take action, such as changing jobs
or wearing a respirator for additional protection.” Id. at
16,626.

     The Unions’ challenges are to the temporal bookends to
these medical exams. The construction unions challenge (in
the construction standard only) the initial trigger for when an
employer must offer an exam. The general industry unions
challenge (in the general industry standard only) what happens
after an exam is completed.
                               51
              1. Medical Surveillance Trigger

     In the general industry standard, employers must offer
triennial exams to any employee “who will be occupationally
exposed . . . at or above the action level for 30 or more days per
year.” 29 C.F.R. §§ 1910.1053(i)(1)(i); 1910.1053(i)(3).
OSHA used the action level of 25 µg/m3 for this trigger because
it concluded that a significant risk persisted at the PEL of
50 µg/m3, and that employees exposed at lower levels still
faced a significant risk of developing silica-related diseases.
In the construction standard, however, OSHA determined that
it would be impractical for medical surveillance to be triggered
by any particular exposure limit because OSHA anticipated
that most construction employers would rely on Table 1 and
would not make exposure assessments. 81 Fed. Reg. at
16,815; see generally supra Part II.B.3. OSHA therefore
required construction employers to provide surveillance to
employees “who will be required . . . to use a respirator for 30
or more days per year” with that employer. 29 C.F.R.
§ 1926.1153(h)(1)(i); see 81 Fed. Reg. at 16,817. Because
respirator use in the construction industry (in Table 1) is
generally tied to exposure at or above the PEL of 50 µg/m3,
construction employees may be exposed to greater silica
concentrations before receiving medical surveillance than
general industry employees, for whom surveillance is tied to
exposure at the action level of 25 µg/m3.

    The Unions do not dispute that keying medical exams to
respirator use is sensible because using Table 1 eliminates the
need to measure actual exposure. Union Br. at 36; Union
Reply Br. at 14. The Unions are concerned, however, that
some employees might use a respirator for 30 days in a year—
and therefore endure exposures at or above the PEL for 30
days—but fall through the cracks of OSHA’s screening
mechanism because they split that use across multiple
                                52
employers. 8      This problem is especially acute in the
construction industry, the Unions argue, because
“[e]mployment in the construction industry is transitory and
intermittent.” Union Br. at 36. The solution to the problem,
they suggest, is for even a single day of respirator use to trigger
medical screening. 9

     In Asbestos, a union challenged OSHA’s decision to
trigger some employer duties at the action level and others at
the PEL. The union argued that it was “feasible to trigger
many of the latter duties at the action level rather than at the
PEL, and that the Secretary therefore erred in not so
providing.” 838 F.2d at 1274. OSHA had defended its
decision as reasonable priority-setting that “permit[ted]
employers to concentrate their resources on those employees
and workplace conditions with the potential for high asbestos
exposures.” Id. (quoting Occupational Exposure to Asbestos,
51 Fed. Reg. 22,612, 22,707 (June 20, 1986)). This court, like
the union, was “skeptical of the agency’s asserted justification”
because it did not explicitly relate to either feasibility or lack
of benefit. Id.

     Nonetheless, the court rejected the union’s challenge. As
we explained, “the force of the evidence and argument that
OSHA must offer to defend its choice will vary with the force
of the proponent’s evidence and argument.” Id. at 1271. And

    8
        The Unions also express concern that an employer might be
unable to predict an employee’s respirator use in the coming year.
Union Br. at 38. As OSHA explained in the preamble, however, the
trigger is met as soon as the employer knows respirator use will
exceed 30 days in the year, even if the employer did not initially
anticipate such use. 81 Fed. Reg. at 16,818.
     9
        Counsel conceded at oral argument that the Unions did not
advance before the agency the alternative approach of tracking
employees’ respirator use across employers. Oral Arg. at 1:57:25.
                               53
the burden is on the challenger to a rule to “demonstrat[e] that
the variations it advocates will be feasible to implement and
will provide more than a de minimis benefit for worker health.”
Id. Because in that case the union “failed to point to any
evidence” that using the stricter trigger “would result in a
greater than de minimis incremental benefit,” we concluded
that OSHA had not abused its discretion in rejecting the
suggested provision. Id. at 1274.

     Following this approach today, we reject the Unions’
challenge to the medical surveillance trigger in the construction
standard. OSHA’s stated reason for adopting the 30-day
trigger does leave something to be desired. OSHA noted that
commenters had suggested a range of possible triggers, and it
selected 30 days as “strik[ing] a reasonable balance between
the administrative burden of offering medical surveillance to
all employees, many of whom may not be further exposed or
only occasionally exposed, and the need for medical
surveillance for employees who are regularly exposed and
more likely to experience adverse health effects.” 81 Fed.
Reg. at 16,816. The Unions suggest that this statement
reflects the kind of balancing of “burdens and benefits” that is
impermissible for rulemaking under 29 U.S.C. § 655(b)(5).
Union Br. at 39; see Cotton Dust, 452 U.S. at 509; National
Cottonseed Products Association, 825 F.2d at 485 n.1.

     We do not, however, construe such a “casual” comment
“as amounting to an arguably improper cost-benefit test,
especially when OSHA has expressed its vigorous opposition
to such a test.” Lead I, 647 F.2d at 1309. OSHA did not
explicitly frame its rejection of the Unions’ proposal as
infeasible or as failing to protect against a material impairment
of health, the relevant considerations under § 655(b)(5). But
“[a]s long as the agency’s path may reasonably be discerned,
we will uphold the decision even if it is of less than ideal
                               54
clarity.” Casino Airlines, Inc. v. National Transportation
Safety Board, 439 F.3d 715, 717 (D.C. Cir. 2006) (internal
quotation marks omitted). OSHA’s explanation that many
employees would not be further exposed or only occasionally
exposed indicates that the agency saw little benefit in providing
medical surveillance to workers exposed at or above the PEL
for fewer than 30 days a year. And as in Asbestos, the Unions
have not pointed to any evidence that setting the trigger at one
day instead of 30 days would produce more than a de minimis
benefit to worker health. Indeed, they have not identified how
many—if any—employees would use a respirator more than 30
days in a year, but would not do so with any single employer.
Nor did OSHA act unreasonably in rejecting the Unions’
speculation that construction employers might deliberately
terminate employees nearing the 30-day trigger in an effort to
avoid the costs of medical surveillance, given that the costs of
hiring and training a new employee would likely exceed the
“modest” cost of providing triennial medical examinations for
an existing employee. 81 Fed. Reg. at 16,817. That being so,
we conclude that OSHA did not abuse the “almost unlimited
discretion the statute affords it to devise means to achieve the
congressionally mandated goal.” Asbestos, 838 F.2d at 1271
(internal quotation marks omitted).

              2. Medical Removal Protection

    Medical removal protection (MRP) provisions “typically
require the employer to temporarily remove an employee from
exposure when such an action is recommended in a written
medical opinion” and to “maintain the employee’s total normal
earnings, as well as all other employee rights and benefits,”
during the removal.        81 Fed. Reg. at 16,838; see
Formaldehyde, 878 F.2d at 399. 10 OSHA has included MRP
    10
         In this opinion, we use MRP to refer to transfer and wage
protections generally, and not to refer to any specific scheme.
                              55
provisions in some of its rules addressing worker health.
Indeed, it recently did so in the beryllium standard, 82 Fed.
Reg. 2,470, 2,720–21 (Jan. 9, 2017), which it promulgated after
the Silica Rule that is now before us. This court approved
such a provision in the lead standard, accepting OSHA’s
explanation that “removal was a preventive device” and that,
“unless workers were guaranteed all their wage and seniority
rights upon removal, they would resist cooperating with the
medical surveillance program that determined the need for
removal, since they reasonably might fear being fired or sent to
lower-paying jobs if they revealed dangerously high blood-lead
levels.” Lead I, 647 F.2d at 1237.

     OSHA has not always included MRP in its health
standards, however. See, e.g., Hexavalent Chromium Rule,
71 Fed. Reg. 10,100, 10,366 (Feb. 28, 2006); Ethylene Oxide
Rule, 49 Fed. Reg. 25,734, 25,788 (June 22, 1984). And when
it promulgated the Silica Rule, the agency had previously
included MRP in only six standards. See 81 Fed. Reg. at
16,838. It did not include MRP in the Rule’s general industry
standard, a decision the Unions now challenge.

     To start, we reject OSHA’s suggestion that we should deny
the Unions’ petition because they did not present sufficient
evidence of MRP’s economic feasibility. We can uphold a
rule only on grounds upon which the agency itself relied. See
NLRB v. CNN, 865 F.3d 740, 751 (D.C. Cir. 2017). And the
agency did not purport to reject MRP on that ground in the
silica rulemaking. See 81 Fed. Reg. at 16,838–40.

     According to the Unions, OSHA engaged in unreasoned
decisionmaking in failing to provide MRP for those employees:
(a) whose doctors recommend permanent removal; (b) whose
doctors recommend temporary removal to alleviate
exacerbated symptoms of chronic obstructive pulmonary
                             56
disease (COPD); (c) whose doctors recommend temporary
removal pending a determination by a specialist; and (d) who
are unable to wear a required respirator. The Unions contend
that OSHA’s stated reasons for rejecting MRP in each of these
four circumstances are inadequate.

     (a). We begin with OSHA’s rationale for denying any
period of MRP to employees whose doctors recommend
permanent removal.         OSHA acknowledged that “some
employees might benefit from removal from respirable
crystalline silica exposure to possibly prevent further
progression of disease.” 81 Fed. Reg. at 16,839; see Oral Arg.
at 2:07:07–:15.       But temporary removal would rarely
“improve employee health,” OSHA said, because silica-related
illnesses are irreversible. 81 Fed. Reg. at 16,839. To produce
a lasting health benefit, “removal[] would have to be
permanent,” and “[w]orkers’ compensation is the appropriate
remedy when permanent removal from exposure is required.”
Id.

     In some previous rules, however, OSHA has provided
MRP for employees whose doctors recommend permanent
removal. See, e.g., 29 C.F.R § 1910.1028(i)(8)(v) (benzene).
And we have held that the agency cannot rely “on an across-
the-board rule that appears inconsistent with past decisions.”
Formaldehyde, 878 F.2d at 401 (opinion on rehearing). One
reason OSHA has provided MRP is to ensure that employees
fully engage with medical surveillance by reporting their
symptoms.       Absent MRP, employees might conceal
symptoms rather than risk “being fired or sent to lower-paying
jobs if they revealed” those symptoms. Lead I, 647 F.2d at
1237; see Formaldehyde, 878 F.2d at 400. In the Silica Rule,
however, OSHA dismissed this rationale. Even without MRP,
it said, employees would readily cooperate with examining
physicians because the Rule’s enhanced medical privacy
                              57
protections would eliminate the risk of automatic wage loss.
81 Fed. Reg. at 16,389–40. Those protections withhold
doctors’ recommendations from employers absent employees’
written authorizations. See supra Part II.E.1.

     OSHA’s explanation misses a logical step. According to
OSHA, medical surveillance provides information so that
employees can “take action, such as changing jobs or wearing
a respirator for additional protection.” 81 Fed. Reg. at 16,626.
The medical privacy protections may well mitigate the concern
that employees will underreport symptoms to their doctors.
But without MRP, employees whose doctors recommend
removal may hide those recommendations from their
employers.

     OSHA has acknowledged that continued exposure can
worsen even an irreversible silica-related disease. See id. at
16,839; see Oral Arg. at 2:07:07–:15. And OSHA has not
explained why MRP—critical in some standards to protect
workers from having to decide between learning about their
health and avoiding economic loss—is not equally critical to
protect workers from having to choose between disclosing their
health issues (and thus preserving their health) and avoiding
economic loss. Because OSHA acknowledges the health
benefit of removal and has not given an adequate reason for
rejecting some period of MRP for employees whose doctors
recommend permanent removal, we remand to the agency for
reconsideration or further explanation.

     (b).    OSHA also concedes that, in some cases,
“employees might benefit from temporary removal . . . to
alleviate exacerbation of COPD.” 81 Fed. Reg. at 16,839; see
Oral Arg. at 2:09:41–:10:20. OSHA nonetheless rejected
medically recommended temporary removal because
symptoms likely would recur at some point after the removal
                              58
ended. But OSHA’s statutory mandate directs it to “set the
standard which most adequately assures . . . that no employee
will suffer material impairment of health . . . .” 29 U.S.C.
§ 655(b)(5). And, as OSHA explained in the preamble to this
rule, the agency considers “irritation of the skin, eyes, and
respiratory system . . . to be material impairments of health.”
81 Fed. Reg. at 16,290. OSHA may have valid reasons for
rejecting MRP for temporary removal to alleviate exacerbated
symptoms, but the fact that symptoms might recur when the
removal ends is not by itself a sufficient reason. Thus, a
remand to further address this circumstance is also warranted.

    (c). OSHA also rejected the Unions’ proposal that it
require MRP for those employees whose doctors recommend
temporary removal pending a determination by a specialist.
Although OSHA’s brief recognizes that the agency has
required such temporary removal under other standards, it
argues that removal would not benefit employees in this
rulemaking because “the available evidence suggests that,
given the slow progression of silica-related diseases, ‘there is
no urgent need for removal from . . . exposure while awaiting
a specialist determination.’” OSHA Br. at 157 (quoting 81
Fed. Reg. at 16,840).

     But that is not quite what OSHA said in the rulemaking.
Rather, it said that “in most cases, there is no urgent need for
removal from [silica] exposure while awaiting a specialist
determination.” 81 Fed. Reg. at 16,840 (emphasis added).
And it acknowledged that, although rare, one type of
silicosis—“acute silicosis”—is an exception to the generality
that silica-related diseases progress slowly. Id. Indeed,
OSHA said that “acute silicosis can occur within a few weeks
to months after inhalation exposure to extremely high levels”
of silica, leading to death “within months to a few years of
disease onset.” Id. at 16,381. In light of that, the agency has
                              59
not explained why temporary removal would not benefit those
workers whose physicians have found enough initial signs of
the disease to indicate referral to a specialist. We therefore
remand for the agency to better explain its decision not to
require MRP in this circumstance as well.

     (d). Although OSHA’s reasons for not requiring MRP in
the three circumstances just discussed are inadequate to sustain
those decisions, we reject the Unions’ contention that OSHA
failed to engage in reasoned decisionmaking by not including
MRP for employees who are unable to wear a respirator.
OSHA concluded that such a provision was unnecessary
because OSHA already requires employers to provide a
powered air-purifying respirator to employees who are unable
to wear a negative pressure respirator. 81 Fed. Reg. at 16,840;
see 29 C.F.R. § 1910.134(e)(6) (respiratory protection). The
Unions speculate that some employees might be unable to wear
either type of respirator, but they have not pointed to any
evidence indicating how many such employees there are likely
to be. We therefore reject this challenge because the Unions
have not met their burden to show that MRP would provide
more than a de minimis benefit in this circumstance. See
Asbestos, 838 F.2d at 1271.
                              60
                      III. CONCLUSION

     In sum, we reject all of the petitioners’ challenges to the
Silica Rule, with three exceptions. We hold that OSHA was
arbitrary and capricious in declining to require MRP for some
period when a medical professional recommends permanent
removal, when a medical professional recommends temporary
removal to alleviate COPD symptoms, and when a medical
professional recommends temporary removal pending a
specialist’s determination. We remand to the agency to
reconsider or further explain those aspects of the Rule.

                                                    So ordered.
