reduction associated with reducing the previous general industry PEL
and a 38-49 percent reduction associated with reducing the previous
construction/shipyard PEL.
    Thus, OSHA believes that the final PEL of 50 [mu]g/m\3\ respirable
crystalline silica will substantially reduce the risk of material
health impairments associated with exposure to silica. However, even at
this final PEL, as well as the action level of 25 [mu]g/m\3\, the risk
posed to workers with 45 years of

regular exposure to respirable crystalline silica is greater than 1 per
1,000 workers and is still clearly significant.
2. Silicosis Morbidity Risks
    OSHA's Final Quantitative Risk Assessment also characterizes the
risk of developing silicosis, defined as developing lung fibrosis
detected by chest x-ray. For 45 years of exposure at the previous
general industry PEL of 100 [mu]g/m\3\, OSHA estimates that the risk of
developing lung fibrosis consistent with an ILO category 1+ degree of
small opacity profusion ranges from 60 to 773 cases per 1,000. For
exposure at the previous construction and shipyard PELs, the risk
approaches 100 percent. The wide range of risk estimates derived from
the underlying studies relied on for the risk assessment may reflect
differences in the relative toxicity of quartz particles in different
workplaces; nevertheless, OSHA finds that each of these risk estimates
clearly represents a significant risk of developing fibrotic lesions in
the lung. Exposure to the final PEL of 50 [mu]g/m\3\ respirable
crystalline silica for 45 years yields an estimated risk of between 20
and 170 cases per 1,000 for developing fibrotic lesions consistent with
an ILO category of 1+. These risk estimates indicate that the final PEL
will result in a reduction in risk by about two-thirds or more, which
the Agency finds is a substantial reduction of the risk of developing
abnormal chest x-ray findings consistent with silicosis.
    One study of coal miners also permitted the agency to evaluate the
risk of developing lung fibrosis consistent with an ILO category 2+
degree of profusion of small opacities (Buchanan et al., 2003, Document
ID 0306). This level of profusion has been shown to be associated with
a higher prevalence of lung function decrement and an increased rate of
early mortality (Ng et al., 1987a, Document ID 1108; Begin et al.,
1988, 0296; Moore et al., 1988, 1099; Ng et al., 1992a, 0383; Infante-
Rivard, 1991, 1065). From this study, OSHA estimates that the risk
associated with 45 years of exposure to the previous general industry
100 [mu]g/m\3\ PEL is 301 cases per 1,000 workers, again a clearly
significant risk. Exposure to the final PEL of 50 [mu]g/m\3\ respirable
crystalline silica for 45 years yields an estimated risk of 55 cases
per 1,000 for developing lesions consistent with an ILO category 2+
degree of small opacity profusion. This represents a reduction in risk
of over 80 percent, again a clearly substantial reduction of the risk
of developing radiologic silicosis consistent with ILO category 2+.
3. Sources of Uncertainty and Variability in OSHA's Risk Assessment
    Throughout the development of OSHA's risk assessment for silica-
related health effects, sources of uncertainty and variability have
been identified by the Agency, peer reviewers, interagency reviewers,
stakeholders, scientific experts, and the general public. This
subsection reviews and summarizes several general areas of uncertainty
and variability in OSHA's risk assessment. As used in this section,
``uncertainty'' refers to lack of knowledge about factors affecting
exposure or risk, and ``variability'' refers to heterogeneity, for
example, across people, places, or time. For more detailed discussion
and evaluation of sources of uncertainty in the risk assessment and a
comprehensive review of comments received by OSHA on the risk
assessment, (see discussions provided throughout the previous section,
Section V, Health Effects).
    As shown in Table VI-1, OSHA's risk estimates for lung cancer are a
range derived from a pooled analysis of 10 cohort studies (Steenland et
al., 2001a, Document ID 0452; ToxaChemica, Inc., 2004, 0469), a study
of granite workers (Attfield and Costello, 2004, Document ID 0543), a
study of diatomaceous earth workers (Rice et al., 2001, Document ID
1118), a multi-cohort study of industrial sand workers (Hughes et al.,
2001, Document ID 1060), and a study of coal miners exposed to
respirable crystalline silica (Miller et al., 2007, Document ID 1305;
Miller and MacCalman, 2009, 1306). Similarly, a variety of studies in
several different working populations was used to derive risk estimates
of silicosis mortality, silicosis morbidity, and renal disease
mortality. The ranges of risks presented in Table VI-1 for silica
mortality and the other health endpoints thus reflect silica exposure-
response across a variety of industries and worker populations, which
may differ for reasons such as the processes in which silica exposure
occurs and the various kinds of minerals that co-exist with crystalline
silica in the dust particles (see discussion on variability in
toxicological potency of crystalline silica later in this section). The
ranges presented in Table VI-1 do not reflect statistical uncertainty
(e.g., 95% confidence intervals) or model uncertainty (e.g., the slope
of the exposure-response curve at exposures higher or lower than the
exposures of the study population) but do reflect variability in the
sources of data for the different studies.
    The risks presented in Table VI-1, however, do not reflect
variability in the consistency, duration or frequency of workers'
exposures. As discussed previously in this section, OSHA's final
estimates of health risks represent risk associated with exposure to an
8-hour time weighted average of 25, 50, 100, 250 and 500 [mu]g/m\3\
respirable crystalline silica. These levels represent the risks
associated with continuous occupational exposure over a working
lifetime of 45 years to the new action level, new PEL, previous general
industry PEL, and the range in exposure (250-500 [mu]g/m\3\) that
approximates the previous construction and shipyard PELs, respectively.
OSHA estimates risks assuming exposure over a working life so that it
can evaluate the significance of the risk associated with exposure at
the previous PELs in a manner consistent with Section 6(b)(5) of the
Act, which requires OSHA to set standards that substantially reduce
these risks to the extent feasible even if workers are exposed over a
full working lifetime. However, while the risk assessment is based on
the assumed working life of 45 years, OSHA recognizes that risks
associated with shorter-term or intermittent exposures at a given
airborne concentration of silica will be less than the risk associated
with continuous occupational exposure at the same concentration over a
working lifetime. OSHA thus also uses alternatives to the 45-year full-
time exposure metric in its projections of the benefits of the final
rule (Section VII of this preamble and the FEA) that reflect the
reduction in silica-related disease that the Agency expects will result
from implementation of the revised standard, using the various
estimates of workers' typical exposure levels and patterns.
    The remainder of this discussion reviews several general areas of
uncertainty and variability in OSHA's risk assessment that are not
quantitatively reflected in the risk estimates shown in Table VI-1, but
that provide important context for understanding these estimates,
including differences in the degree of uncertainty among the estimates.
These areas include exposure estimation error, dose-rate effects, model
form uncertainty, variability in toxicological potency of crystalline
silica, and additional sources of uncertainty specific to particular
endpoints, (e.g., the small number of cases in the renal disease
analysis), differing conclusions in the literature on silica as a
causative factor in renal disease and lung cancer, and reporting error
in silicosis mortality and morbidity. These different sources of
uncertainty have varying effects that can lead either to under- or
over-

estimation of risks. OSHA has taken these sources of uncertainty into
account in concluding that the body of scientific literature supports
the finding that there is significant risk at existing levels of
exposure. The Agency is not required to support the finding that a
``significant risk exists with anything approaching scientific
certainty'' (Benzene, 448 U.S. at 656).
a. Exposure Estimation Error
    As discussed in Section V, OSHA identified exposure estimation
error as a key source of uncertainty in most of the studies and thus
the Agency's risk assessment. OSHA's contractor, ToxaChemica, Inc.,
commissioned Drs. Kyle Steenland and Scott Bartell to perform an
uncertainty analysis to examine the effect of uncertainty due to
exposure estimation error in the pooled studies (Steenland et al.,
2001a, Document ID 0452; Mannetje 2002b, 1089) on the lung cancer and
silicosis mortality risk estimates (ToxaChemica, Inc., 2004, Document
ID 0469). Drs. Steenland and Bartell addressed two main sources of
error in the silica exposure estimates. The first arises from the
assignment of individual workers' exposures based either on exposure
measurements for a sample of workers in the same job or estimated
exposure levels for specific jobs in the past when no measurements were
available, via a job-exposure matrix (JEM) (Mannetje et al., 2002a,
Document ID 1090). The second arises from the conversion of
historically-available dust measurements, typically particle count
concentrations, to gravimetric respirable silica concentrations.
ToxaChemica, Inc. conducted an uncertainty analysis using the raw data
from the IARC multi-centric study to address these sources of error
(2004, Document ID 0469).
    To explore the potential effects of both kinds of uncertainty
described above, ToxaChemica, Inc. (2004, Document ID 0469) used the
distributions representing the error in job-specific exposure
assignment and the error in converting exposure metrics to generate 50
exposure simulations for each cohort. A study-specific coefficient and
a pooled coefficient were fit for each new simulation. The results
indicated that the only lung cancer cohort for which the mean of the
exposure coefficients derived from the simulations differed
substantially from the previously calculated exposure coefficient was
the South African gold cohort (simulation mean of 0.181 vs. original
coefficient of 0.582). This suggests that the results of exposure-
response analyses conducted using the South African cohort are
sensitive to error in exposure estimates; therefore, there is greater
uncertainty due to potential exposure estimation error in an exposure-
response model based on this cohort than is the case for the other nine
cohorts in Steenland et al's analysis (or, put another way, the
exposure estimation for the other nine cohorts was less sensitive to
the effects of exposure measurement uncertainty).
    For the pooled analysis, the mean coefficient estimate from the
simulations was 0.057, just slightly lower than the previous estimate
of 0.060. Based on these results, OSHA concluded that random error in
the underlying exposure estimates in the Steenland et al. (2001a,
Document ID 0452) pooled cohort study of lung cancer is not likely to
have substantially influenced the original findings.
    Following the same procedures described above for the lung cancer
analysis, ToxaChemica, Inc. (2004, Document ID 0469) combined both
sources of random measurement error in a Monte Carlo analysis of the
silicosis mortality data from Mannetje et al. (2002b, Document ID
1089). The silicosis mortality dataset appeared to be more sensitive to
possible error in exposure measurement than the lung cancer dataset,
for which the mean of the simulation coefficients was virtually
identical to the original. To reflect this exposure measurement
uncertainty, OSHA's final risk estimates derived from the pooled
analysis (Mannetje et al., 2002b, Document ID 1089), incorporated
ToxaChemica, Inc.'s simulated measurement error (2004, Document ID
0469).
b. Uncertainty Related to Dose-Rate Effects
    OSHA received comments citing uncertainty in its risk assessment
related to possible dose-rate effects in the silica exposure-response
relationships, particularly for silicosis. For example, the ACC
commented that extrapolating risks from the high mean exposure levels
in the Park et al. 2002 cohort (Document ID 0405) to the much lower
mean exposure levels relevant to OSHA's risk assessment contributes
uncertainty to the analysis (Document ID 4209, pp. 84-85), because of
the possibility that risk accrues differently at different exposure
concentrations. The ACC thus argued that the risk associated with any
particular level of cumulative exposure may be higher for exposure to a
high concentration of respirable crystalline silica over a short period
of time than for an equivalent cumulative exposure resulting from
exposure to a low concentration of respirable crystalline silica over a
long period of time (Document ID 4209, p. 58; 2307, Attachment A, pp.
93-94). These and similar comments on dose-rate effects questioned
OSHA's use of workers' cumulative exposure levels to estimate risk, as
the cumulative exposure metric does not capture dose-rate effects.
Thus, according to the ACC, if there are significant dose-rate effects
in the exposure-response relationship for a disease or other health
endpoint, use of the cumulative exposure metric could lead to error in
risk estimates.
    The rationale for OSHA's reliance on a cumulative exposure metric
to assess the risks of respirable crystalline silica is discussed in
Section V. With respect to this issue of uncertainty related to dose-
response effects, OSHA finds limited evidence in the record to either
support or refute the effects hypothesized by the ACC. As such, OSHA
acknowledges some uncertainty. Furthermore, use of an alternative
metric such as concentration would not provide assurance that
uncertainties would be mitigated or reduced.
    Two studies discussed in OSHA's Review of Health Effects Literature
and Preliminary QRA examined dose-rate effects on silicosis exposure-
response (Document ID 1711, pp. 342-344). Neither study found a dose-
rate effect relative to cumulative exposure at silica concentrations
near the previous OSHA PEL (Document ID 1711, pp. 342-344). However,
they did observe a dose-rate effect in instances where workers were
exposed to crystalline silica concentrations far above the previous PEL
(i.e., several-fold to orders of magnitude above 100 [mu]g/m\3\)
(Buchanan et al., 2003, Document ID 0306; Hughes et al., 1998, 1059).
The Hughes et al. (1998) study of diatomaceous earth workers found that
the relationship between cumulative silica exposure and risk of
silicosis was steeper for workers hired prior to 1950 and exposed to
average concentrations above 500 [micro]g/m\3\ compared to workers
hired after 1950 and exposed to lower average concentrations (Document
ID 1059). Hughes et al. reported that subdivisions for workers with
exposure to concentrations below 500 [mu]g/m\3\ were examined, but that
no differences were observed across these groups (Document ID 1059, p.
809). It is unclear whether sparse data at the low end of the
concentration range contributed to this finding, as the authors did not
provide detailed information on the distribution of exposures in the
study population.
    The Buchanan et al. (2003) study of Scottish coal miners adjusted
the cumulative exposure metric in the risk model to account for the
effects of exposures to high concentrations where

the investigators found that, at concentrations above 2000 [mu]g/m\3\,
the risk of silicosis was about three times higher than the risk
associated with exposure to lower concentrations but at the same
cumulative exposure (Document ID 0306, p. 162). Buchanan et al. noted
that only 16 percent of exposure hours among the workers in the study
occurred at levels below 10 [mu]g/m\3\ (Document ID 0306, p. 161), and
cautioned that insufficient data are available to predict effects at
very low concentrations where data are sparse (Document ID 0306, p.
163). However, 56 percent of hours occurred at levels between 10 and
100 [mu]g/m\3\. Detailed information on the hours worked at
concentrations within this range was not provided.
    Based on its review of these studies, OSHA concluded that there is
little evidence that a dose-rate effect exists at concentrations in the
range of the previous PEL (100 [mu]g/m\3\) (Document ID 1711, p. 344).
However, there remains some uncertainty related to dose-rate effects in
the Agency's silicosis risk assessment. Even if a dose-rate effect
exists only at concentrations far higher than the previous PEL, it is
possible for the dose-rate effect to impact model form if not properly
accounted for in study populations with high-concentration exposures.
This is one reason that OSHA presents a range of risk estimates based
on a variety of study populations exposed under different working
conditions. For example, as OSHA noted in its Review of Health Effects
Literature and Preliminary QRA (Document ID 1711, pp. 355-356), the
Park et al. study is complemented by the Mannetje et al. multi-cohort
silicosis mortality pooled study. Mannetje et al.'s study included
several cohorts that had exposure concentrations in the range of
interest for this rulemaking and also showed clear evidence of
significant risk of silicosis mortality at the previous general
industry and construction PELs (2002b, Document ID 1089). In addition,
OSHA used the model from the Buchanan et al. study in its silicosis
morbidity risk assessment to account for possible dose-rate effects at
high average concentrations (Document ID 1711, pp. 335-342). OSHA notes
that the risk estimates in the exposure range of interest (25-500
[mu]g/m\3\) derived from the Buchanan et al. (2003) study were not
appreciably different from those derived from the other studies of
silicosis morbidity (see Table VI-1).
c. Model Form Uncertainty
    Another source of uncertainty in OSHA's risk analysis is
uncertainty with respect to the form of the statistical models used to
characterize the relationship between exposure level and risk of
adverse health outcomes. As discussed in Section V, some commenters
expressed concern that studies relied on by OSHA may not have
considered all potential exposure-response relationships and might be
unable to discern differences between monotonic and non-monotonic
characteristics (e.g., Document ID 2307, Attachment A, p. 113-114).
    OSHA acknowledges that the possibility of error in selection of
exposure-response model forms is a source of uncertainty in the silica
risk assessment. To address this uncertainty, the Agency included
studies in the risk assessment that explored a variety of model forms.
For example, as discussed in Section V, the ToxaChemica reanalyses of
the Mannetje et al. silicosis mortality dataset and the Steenland et
al. lung cancer mortality data set examined several model forms
including a five-knot restricted spline analysis, which is a highly
flexible model form able to capture a variety of exposure-response
shapes (Document ID 0469, p. 50). The ToxaChemica reanalysis addresses
the issue of model form uncertainty by finding similar exposure-
response relationships regardless of the type of model used.
d. Uncertainty Related to Silica Exposure as a Risk Factor for Lung
Cancer
    As discussed in Section V, OSHA has reviewed the best available
evidence on the relationship between silica exposure and lung cancer
mortality, and has concluded that the weight of evidence supports the
finding that exposure to silica at the preceding and new PELs increases
the risk of lung cancer. However, OSHA acknowledges that not every
study in the literature on silica-related lung cancer reached the same
conclusions. This variability is to be expected in epidemiology, as
there are different cohorts, measurements, study designs, and
analytical methods, among other factors. OSHA further acknowledges that
there is uncertainty with respect to the magnitude of the risk of lung
cancer from silica exposure. In the case of silica, the exposure-
response relationship with lung cancer may be easily obscured, as
crystalline silica is a comparably weaker carcinogen (i.e., the
increase in risk per unit exposure is smaller) than other well-studied,
more potent carcinogens such as hexavalent chromium (Steenland et al.,
2001, Document ID 0452, p. 781) and tobacco smoke, a common co-exposure
in silica-exposed populations.
    A study by Vacek et al. (2011) illustrates the uncertainties
involved in evaluating risk of lung cancer from silica exposure. This
study found no significant association between respirable silica
exposure and lung cancer mortality in a cohort of Vermont granite
workers (Document ID 1486, pp. 75-81). Some commenters criticized
OSHA's preliminary risk assessment for rejecting the Vacek et al.
(2011) study and instead relying upon the Attfield and Costello (2004,
Document ID 0284) study of Vermont granite workers (Document ID 2307,
Attachment A, pp. 36-47; 4209, pp. 34-36). As discussed in detail in
Section V, OSHA reviewed the Vacek et al. study and all comments
received by the Agency on this issue, and has decided not to reject the
Attfield and Costello (2004) study in favor of the Vacek et al. (2011)
study as a basis for risk assessment. OSHA acknowledges that
comprehensive studies, such as those of Attfield and Costello (2004)
and Vacek et al. (2011), in the Vermont granite industry have shown
conflicting results with respect to lung cancer mortality (Document ID
0284; 1486). Although OSHA believes that the Attfield and Costello
(2004) study is the most appropriate Vermont granite study to use in
its QRA, it also relied upon other studies, and that the risk estimates
for lung cancer mortality based on those studies (i.e., Document ID
0543, 1060, 1118, 1306) still provide substantial evidence that
respirable crystalline silica poses a significant risk of lung cancer
to exposed workers.
e. Uncertainty Related to Renal Disease
    As discussed in Section V, OSHA acknowledges that there are
considerably less data for renal disease mortality than those for
silicosis, lung cancer, and non-malignant respiratory disease (NMRD)
mortality. Although the Agency believes the renal disease risk findings
are based on credible data, the risk findings based on them are less
robust than the findings for silicosis, lung cancer, and NMRD.
    Based upon its overall analysis of the literature, including the
negative studies, OSHA has concluded that there is substantial evidence
suggesting an association between exposure to crystalline silica and
increased risks of renal disease. This conclusion is supported by a
number of case reports and epidemiological studies that found
statistically significant associations between occupational exposure to
silica dust and chronic renal disease (Calvert et al., 1997, Document
ID 0976), subclinical renal changes (Ng et al., 1992c, Document ID
0386), end-stage renal disease morbidity (Steenland et

al., 1990, Document ID 1125), end-stage renal disease incidence
(Steenland et al., 2001b, Document ID 0456), chronic renal disease
mortality (Steenland et al., 2002a, 0448), and granulomatosis with
polyangitis (Nuyts et al., 1995, Document ID 0397). However, as
discussed in the Review of Health Effects Literature and Preliminary
QRA, the studies reviewed by OSHA included a number of studies that did
not show an association between crystalline silica and renal disease
(Document ID 1711, pp. 211-229). Additional negative studies by Birk et
al. (2009, Document ID 1468), and Mundt et al. (2011, Document ID 1478)
were reviewed in the Supplemental Literature Review of the Review of
Health Effects Literature and Preliminary QRA, which noted the short
follow-up period as a limitation, which reduces the likelihood that an
increased incidence of renal mortality would have been detected
(Document ID 1711, Supplement, pp. 6-12). Comments submitted to OSHA by
the ACC additionally cited several studies that did not show a
statistically significant association between exposure to crystalline
silica and renal disease mortality, including McDonald et al. (2005,
Document ID 1092), Vacek et al. (2011, Document ID 2340), Davis et al.
(1983, Document ID 0999), Koskela et al. (1987, Document ID 0363),
Cherry et al. (2012, article included in Document ID 2340), Steenland
et al. (2002b, Document ID 0454), Rosenman et al. (2000, Document ID
1120), and Calvert et al. (2003, Document ID 0309) (Document ID 2307,
Attachment A, pp. 140-145).
    As discussed in detail in Section V, OSHA concludes that the
evidence supporting causality regarding renal risk outweighs the
evidence casting doubt on that conclusion, but acknowledges this
divergence in the renal disease literature as a source of uncertainty.
    OSHA estimated quantitative risks for renal disease mortality
(Document ID 1711, pp. 314-316) using data from a pooled analysis of
renal disease, conducted by Steenland et al. (2002a, Document ID 0448).
The data set included 51 deaths from renal disease as an underlying
cause, which the authors of the pooled study, Drs. Kyle Steenland and
Scott Bartell, acknowledged to be insufficient to provide robust
estimates of risk (Document ID 2307, Attachment A, p. 139, citing 0469,
p. 27). OSHA agrees with Dr. Steenland and acknowledges, as it did in
its Review of Health Effects Literature and Preliminary QRA (Document
ID 1711, p. 357), that its quantitative risk estimates for renal
disease mortality are less robust than those for the other health
effects examined (i.e., lung cancer mortality, silicosis and NMRD
mortality, and silicosis morbidity).
f. Uncertainty in Reporting and Diagnosis of Silicosis Mortality and
Silicosis Morbidity
    OSHA's final quantitative risk assessment includes risk estimates
for silicosis mortality and morbidity. Silicosis mortality is
ascertained by analysis of death certificates for cause of death, and
morbidity is ascertained by the presence of chest radiographic
abnormalities consistent with silicosis among silica-exposed workers.
Each of these kinds of studies are associated with uncertainties in
case ascertainment and use of chest roentgenograms to detect lung
scarring due to silicosis.
    For silicosis mortality, OSHA's analysis includes a pooled analysis
of six epidemiological studies first published by Mannetje et al.
(2002b, Document ID 1089) and re-analyzed by OSHA's contractor
ToxaChemica (2004, Document ID 0469). OSHA finds that the estimates
from Mannetje et al. and ToxaChemica's analyses are likely to
understate the actual risk because silicosis is under-reported as a
cause of death, as discussed in Sections VC.2.iv and V.E in the context
of silicosis disease surveillance systems. To help address this
uncertainty, OSHA's risk analysis also included an exposure-response
analysis of diatomaceous earth (DE) workers (Park et al., 2002,
Document ID 0405), which better captures the totality of silica-related
respiratory disease than do the datasets analyzed by Mannetje et al.
and ToxaChemica. Park et al.. quantified the relationship between
cristobalite exposure and mortality caused by NMRD, which includes
silicosis, pneumoconiosis, emphysema, and chronic bronchitis. Because
NMRD captures much of the silicosis misclassification that results in
underestimation of the disease and includes risks from other lung
diseases associated with crystalline silica exposures, OSHA finds the
risk estimates derived from the Park et al. study are important to
include as part of OSHA's range of estimates of the risk of death from
silica-related respiratory diseases, including silicosis. (Document ID
1711, pp. 297-298). OSHA concludes that the range of silicosis and NMRD
risks presented in the final risk assessment, based on both the
ToxaChemica reanalysis of Mannetje et al.'s silicosis mortality data
and Park et al.'s study of NMRD mortality, provide a credible range of
estimates of mortality risk from silicosis and NMRD across a range of
industrial workplaces. The upper end of this range, based on the Park
et al. study, is less likely to underestimate risk as a result of
under-reporting of silicosis mortality, but cannot be directly compared
to risk estimates from studies that focused on cohorts of workers from
different industries.
    OSHA's estimates of silicosis morbidity risks are based on studies
of active and retired workers for which exposure histories could be
constructed and chest x-ray films could be evaluated for signs of
silicosis. There is evidence in the record that chest x-ray films are
relatively insensitive to detecting lung fibrosis. Hnizdo et al. (1993,
Document ID 1050) found chest x-ray films to have low sensitivity for
detecting lung fibrosis related to silicosis, compared to pathological
examination at autopsy. To address the low sensitivity of chest x-rays
for detecting silicosis, Hnizdo et al. (1993, Document ID 1050)
recommended that radiographs consistent with an ILO category of 0/1 or
greater be considered indicative of silicosis among workers exposed to
a high concentration of silica-containing dust. In like manner, to
maintain high specificity, chest x-rays classified as category 1/0 or
1/1 should be considered as a positive diagnosis of silicosis. Studies
relied on in OSHA's risk assessment typically used an ILO category of
1/0 or greater to identify cases of silicosis. According to Hnizdo et
al., they are unlikely to include many false positives (diagnoses of
silicosis where there is none), but may include false negatives
(failure to identify cases of silicosis). Thus, the use of chest
roentgenograms to ascertain silicosis cases in the morbidity studies
relied on by OSHA in its risk assessment could lead to an
underestimation of risk given the low sensitivity of chest
roentgenograms for detecting silicosis.
g. Variability in Toxicological Potency of Crystalline Silica
    As discussed in Section V, the toxicological potency of crystalline
silica is influenced by a number of physical and chemical factors that
affect the biological activity of inhaled silica particles. The
toxicological potency of crystalline silica is largely influenced by
the presence of oxygen free radicals on the surfaces of respirable
particles. These chemically-reactive oxygen species interact with
cellular components in the lung to promote and sustain the inflammatory
reaction responsible for the lung damage associated with exposure to
crystalline silica. The reactivity of particle surfaces is greatest
when crystalline silica has been freshly fractured by high-energy

work processes such as abrasive blasting, rock drilling, or sawing
concrete materials. As particles age in the air, the surface reactivity
decreases and exhibits lower toxicologic potency (Porter et al., 2002,
Document ID 1114; Shoemaker et al., 1995, 0437; Vallyathan et al.,
1995, 1128). In addition, surface impurities have been shown to alter
silica toxicity. For example, aluminum and aluminosilicate clay on
silica particles has been shown to decrease toxicity (Castranova et
al., 1997, Document ID 0978; Donaldson and Borm, 1998, 1004; Fubini,
1998, 1016; Donaldson and Borm, 1998, Document ID 1004; Fubini, 1998,
1016).
    In the preamble to the proposed standard, OSHA preliminarily
concluded that although there is evidence that several environmental
influences can modify surface activity to either enhance or diminish
the toxicity of silica, the available information was insufficient to
determine to what extent these influences may affect risk to workers in
any particular workplace setting (Document 1711, p. 350). OSHA
acknowledges that health risks are probably in the low end of the range
for workers in the brick manufacturing industry, although the evidence
still indicates that there is a significant risk at the previous
general industry PEL for those workers. OSHA also acknowledges that
there was a lack of evidence for a significant risk in the sorbent
minerals industry due to the nature of crystalline silica present in
those operations; as a result, it decided to exclude sorptive clay
processing from this rule. Furthermore, Dudley and Morriss (2015) raise
concerns about the whether the exposures reflected in the historical
cohorts used in the risk assessment are sufficiently reflective of
rapidly changing working conditions over the last 45 years.\11\
However, the risk estimates presented in Table VI-1 are based on
studies from a variety of industries, such that the risk ranges
presented are likely to include estimates appropriate to most working
populations. Thus, in OSHA's view, its significant risk finding is well
supported by the weight of best available evidence, notwithstanding
uncertainties that may be present to varying degrees in the numerous
studies relied upon and the even greater number of studies that the
Agency considered.
---------------------------------------------------------------------------

    \11\ Dudley, S. E. and Morriss, A. P. (2015), Will the
Occupational Safety and Health Administration's Proposed Standards
for Occupational Exposure to Respirable Crystalline Silica Reduce
Workplace Risk?. Rish Analysis, 35: 1191-1196. doi:10.1111/
risa.12341
---------------------------------------------------------------------------

4. OSHA's Response to Comments on Significant Risk of Material
Impairment
    OSHA received several comments pertaining to the Agency's
determination of a significant risk of material impairment of health
posed to workers exposed for a working life to the previous PELs.
Although many of these comments were supportive of OSHA's conclusions
regarding the significance of risk, others were critical or suggested
that OSHA has an obligation to further reduce the risk below that
estimated to remain at the revised PEL.
    Referring to the previous PELs for respirable crystalline silica,
the AFL-CIO commented that ``[w]orkers face a significant risk of harm
from silica exposure at the current permissible exposure limits,'' and
that ``[t]here is overwhelming evidence in the record that exposure to
respirable crystalline silica poses a significant health risk to
workers'' (Document ID 4204, pp. 10-11). The AFL-CIO noted that OSHA's
mortality risk estimates well exceeded the benchmark of 1/1,000 excess
risk over a working lifetime of exposure to the previous PELs, and also
highlighted the risks of silicosis morbidity (Document ID 4204, p. 13).
The AFL-CIO further pointed out that there is no cure for silicosis,
and quoted oral testimony from workers at the informal public hearings
demonstrating that ``[s]ilica-related diseases are still destroying
workers' lives and livelihoods'' (Document ID 4204, p. 19).
    Both the UAW and the Building and Construction Trades Department
(BCTD) concurred with the AFL-CIO that the previous PEL needs to be
lowered to adequately protect workers. Referring to the previous PEL,
the BCTD stated that ``[t]he record supports OSHA's determination that
exposures at the current PEL present a significant risk'' (Document ID
4223, p. 6). Although supportive of OSHA's proposed standard, the UAW
also suggested the adoption of a PEL of 25 [micro]g/m\3\ or lower where
feasible (Document ID 2282, Attachment 3, p.1), noting that a PEL set
at this level ``will significantly reduce workers' exposure to deadly
silica dust and prevent thousands of illnesses and deaths every year''
(Document ID 2282, Attachment 3, p. 25). Similarly, Charles Gordon, a
retired occupational safety and health attorney, commented that the
revised PEL ``leaves a remaining risk of 97 deaths per 1,000 workers
from silicosis, lung cancer, and renal disease combined'' (Document ID
4236, p. 2). Again, it should be noted that these risk estimates are
not additive because some individuals may suffer from multiple diseases
caused by exposure to silica. Instead, OSHA presents risk estimates for
each health endpoint.
    As discussed above, OSHA acknowledges that there remains a
significant risk of material impairment of health at the revised PEL; a
further reduction in the PEL, however, is not currently technologically
feasible (see Section VII, Summary of the Final Economic Analysis and
Final Regulatory Flexibility Analysis, in which OSHA summarizes its
assessment of the technological feasibility of the revised PEL).
Despite this, the final PEL will provide a very substantial reduction
in the risk of material impairment of health to silica-exposed workers,
as described in the Benzene decision (Benzene, 448 U.S. at 642).
    In contrast to the foregoing comments from labor groups contending
that OSHA would be setting the PEL too high if it made a final
determination to lower the preceding PELs to 50 [micro]g/m\3\, critical
comments came from industry groups including the American Chemistry
Council (ACC), which disagreed with OSHA's determination of a
significant risk of material impairment of health at the previous PELs.
The ACC stated, ``OSHA's assessment of these risks is flawed, and its
conclusions that the risks are significant at a PEL of 100 [micro]g/
m\3\ and would be substantially reduced by lowering the PEL to 50
[micro]g/m\3\ are unsupported'' (Document ID 4209, p. 12). The ACC then
asserted several ``fundamental shortcomings'' in OSHA's QRA on which
OSHA based its significant risk determination (Document ID 4209, pp.
16-17), including a variety of purported biases in the key studies on
which OSHA relied. OSHA addresses the ACC's concerns in detail in
Section V of this preamble dealing with the key studies relied upon by
the Agency for each health endpoint, as well as separate sections
addressing the issues of biases, causation, thresholds, the uncertainty
analysis, and the life table and exposure assumptions used in the QRA.
As more fully discussed in those sections, OSHA finds these concerns to
be unpersuasive. As discussed in Section V, the scientific community
and regulators in other advanced industrial societies agree on the need
for a PEL of at most 50 [micro]g/m\3\ based on demonstrated health
risks, and OSHA has used the best available evidence in the scientific
literature to estimate quantitative risks of silica-related illnesses
and thereby reach the same conclusion. OSHA's preliminary review of the
health effects literature and OSHA's preliminary QRA were, further,
examined by an independent, external peer review panel of

accomplished scientists, which lent credibility to the Agency's methods
and findings and led to some adjustments in the analysis that
strengthened OSHA's final risk assessment. There is, additionally,
widespread support for the Agency's methods and conclusions in the
rulemaking record. As such, OSHA is confident in its conclusion that
there is a significant risk of material impairment of health to workers
exposed to respirable crystalline silica at the levels of exposure
permitted under the previous PELs and under this final standard, and
finds no merit in broad assertions purporting to debunk this
conclusion.
    In summary, as discussed throughout Section V and this final rule,
OSHA concludes, based on the best available evidence in the scientific
literature, that workers' exposure to respirable crystalline silica at
the previous PELs results in a clearly significant risk of material
impairment of health. The serious, and potentially fatal, health
effects suffered by exposed workers include silicosis, lung cancer,
NMRD, renal disease, and autoimmune effects. OSHA finds that the risk
is substantially decreased, though still significant, at the new PEL of
50 [micro]g/m\3\ and below, including at the new action level of 25
[micro]g/m\3\. The Agency is constrained, however, from lowering the
PEL further by its finding that a lower PEL would be infeasible in many
operations across several industries. Given the significant risks faced
by workers exposed to respirable crystalline silica under the
previously-existing exposure limits, OSHA believes that it is
imperative that it issue this final standard pursuant to its statutory
mandate under the OSH Act.

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

A. Introduction

    OSHA's Final Economic Analysis and Final Regulatory Flexibility
Analysis (FEA) addresses issues related to the costs, benefits,
technological and economic feasibility, and the economic impacts
(including impacts on small entities) of this final respirable
crystalline silica rule and evaluates regulatory alternatives to the
final rule. Executive Orders 13563 and 12866 direct agencies to assess
all costs and benefits of available regulatory alternatives and, if
regulation is necessary, to select regulatory approaches that maximize
net benefits (including potential economic, environmental, and public
health and safety effects; distributive impacts; and equity). Executive
Order 13563 emphasized the importance of quantifying both costs and
benefits, of reducing costs, of harmonizing rules, and of promoting
flexibility. The full FEA has been placed in OSHA rulemaking docket
OSHA-2010-0034. This rule is an economically significant regulatory
action under Sec. 3(f)(1) of Executive Order 12866 and has been
reviewed by the Office of Information and Regulatory Affairs in the
Office of Management and Budget, as required by executive order.
    The purpose of the FEA is to:
     Identify the establishments and industries potentially
affected by the final rule;
     Estimate current exposures and the technologically
feasible methods of controlling these exposures;
     Estimate the benefits resulting from employers coming into
compliance with the final rule in terms of reductions in cases of
silicosis, lung cancer, other forms of chronic obstructive pulmonary
disease, and renal failure;
     Evaluate the costs and economic impacts that
establishments in the regulated community will incur to achieve
compliance with the final rule;
     Assess the economic feasibility of the final rule for
affected industries; and
     Assess the impact of the final rule on small entities
through a Final Regulatory Flexibility Analysis (FRFA), to include an
evaluation of significant regulatory alternatives to the final rule
that OSHA has considered.
Significant Changes to the FEA Between the Proposed Standards and the
Final Standards
    OSHA changed the FEA for several reasons:
     Changes to the rule, summarized in Section I of this
preamble and discussed in detail in the Summary and Explanation;
     Comments on the Preliminary Economic Analysis (PEA);
     Updates of economic data; and
     Recognition of errors in the PEA.
    OSHA revised its technological and economic analysis in response to
these changes and to comments received on the NPRM. The FEA contains
some costs that were not included in the PEA and updates data to use
more recent data sources and, in some cases, revised methodologies.
Detailed discussions of these changes are included in the relevant
sections throughout the FEA.
    The FEA contains the following chapters:

Chapter I. Introduction
Chapter II. Market Failure and the Need for Regulation
Chapter III. Profile of Affected Industries
Chapter IV. Technological Feasibility
Chapter V. Costs of Compliance
Chapter VI. Economic Feasibility Analysis and Regulatory Flexibility
Determination
Chapter VII. Benefits and Net Benefits
Chapter VIII. Regulatory Alternatives
Chapter IX. Final Regulatory Flexibility Analysis
Chapter X. Environmental Impacts

    Table VII-1 provides a summary of OSHA's best estimate of the costs
and estimated benefits of the final rule using a discount rate of 3
percent. As shown, the final rule is estimated to prevent 642
fatalities and 918 silica-related illnesses annually once it is fully
effective, and the estimated cost of the rule is $1,030 million
annually. Also as shown in Table VII-1, the discounted monetized
benefits of the final rule are estimated to be $8.7 billion annually,
and the final rule is estimated to generate net benefits of $7.7
billion annually. Table VII-1 also presents the estimated costs and
estimated benefits of the final rule using a discount rate of 7
percent.

[GRAPHIC] [TIFF OMITTED] TR25MR16.011

    The remainder of this section (Section VII) of the preamble is
organized as follows:

    B. Market Failure and the Need for Regulation
    C. Profile of Affected Industries
    D. Technological Feasibility
    E. Costs of Compliance
    F. Economic Feasibility Analysis and Regulatory Flexibility
Determination
    G. Benefits and Net Benefits
    H. Regulatory Alternatives
    I. Final Regulatory Flexibility Analysis.

B. Market Failure and the Need for Regulation

    Employees in work environments addressed by the final silica rule
are exposed to a variety of significant hazards that can and do cause
serious injury and death. As described in Chapter II of the FEA in
support of the final rule, OSHA concludes there is a failure of private
markets to protect workers from exposure to unnecessarily high levels
of respirable crystalline silica and that private markets, as well as
information dissemination programs, workers' compensation systems, and

tort liability options, each may fail to protect workers from silica
exposure, resulting in the need for a more protective OSHA silica rule.
    After carefully weighing the various potential advantages and
disadvantages of using a regulatory approach to improve upon the
current situation, OSHA concludes that, in the case of silica exposure,
the final mandatory standards represent the best choice for reducing
the risks to employees. In addition, rulemaking is necessary in this
case in order to replace older existing standards with updated, clear,
and consistent health standards.

C. Profile of Affected Industries

Introduction
    Chapter III of the FEA presents profile data for industries
potentially affected by the final silica rule. The discussion below
summarizes the findings in that chapter. As a first step, OSHA
identifies the North American Industrial Classification System (NAICS)
industries, both in general industry and maritime and in the
construction sector, with potential worker exposure to silica. Next,
OSHA provides summary statistics for the affected industries, including
the number of affected entities and establishments, the number of
workers whose exposure to silica could result in disease or death
(``at-risk workers''), and the average revenue for affected entities
and establishments.\12\ Finally, OSHA presents silica exposure profiles
for at-risk workers. These data are presented by sector and job
category. Summary data are also provided for the number of workers in
each affected industry who are currently exposed above the final silica
PEL of 50 [mu]g/m\3\, as well as above an alternative PEL of 100 [mu]g/
m\3\ for economic analysis purposes.
---------------------------------------------------------------------------

    \12\ The Census Bureau defines an establishment as a single
physical location at which business is conducted or services or
industrial operations are performed. The Census Bureau defines a
business firm or entity as a business organization consisting of one
or more domestic establishments in the same state and industry that
were specified under common ownership or control. The firm and the
establishment are the same for single-establishment firms. For each
multi-establishment firm, establishments in the same industry within
a state will be counted as one firm; the firm employment and annual
payroll are summed from the associated establishments. (US Census
Bureau, Statistics of US Businesses, Definitions. 2015, http://www.census.gov/econ/susb/definitions.html?cssp=SERP).
---------------------------------------------------------------------------

    The methodological basis for the industry and at-risk worker data
presented in this chapter comes from the PEA, the Eastern Research
Group (ERG) analysis supporting the PEA (2007a, 2007b, 2008a, and
2008b),\13\ and ERG's analytic support in preparing the FEA. The data
used in this chapter come from the rulemaking record (Docket OSHA-2010-
0034), the technological feasibility analyses presented in Chapter IV
of the FEA, and from OSHA (2016), which updated its earlier
spreadsheets to reflect the most recent industry data available. To do
so, ERG first matched the BLS Occupational Employment Statistics (OES)
survey occupational titles with the at-risk job categories, by NAICS
industry. ERG then calculated the percentages of production employment
represented by each at-risk job title within industry (see OSHA, 2016
for details on the calculation of employment percentages and the
mapping of at-risk job categorizations into OES occupations).\14\ ERG's
expertise for identifying the appropriate OES occupations and
calculating the employment percentages enabled OSHA to estimate the
number of employees in the at-risk job categories by NAICS industry
(Id.).
---------------------------------------------------------------------------

    \13\ Document ID, 1709, 1608, 1431, and 1365, respectively.
    \14\ Production employment includes workers in building and
grounds maintenance; forestry, fishing, and farming; installation
and maintenance; construction; production; and material handling
occupations.
---------------------------------------------------------------------------

    In the NPRM and PEA, OSHA invited the public to submit additional
information and data that might help improve the accuracy and
usefulness of the preliminary industry profile; the profile presented
here and in Chapter III of the FEA reflects public comment.
Selection of NAICS Industries for Analysis
    The technological feasibility analyses presented in Chapter IV of
the FEA identify the general industry and maritime sectors and the
construction activities potentially affected by the final silica
standard.
General Industry and Maritime
    Employees engaged in various activities in general industry and
maritime routinely encounter crystalline silica as a molding material,
as an inert mineral additive, as a component of fluids used to
stimulate well production of oil or natural gas, as a refractory
material, as a sandblasting abrasive, or as a natural component of the
base materials with which they work. Some industries use various forms
of silica for multiple purposes. As a result, employers are faced with
the challenge of limiting worker exposure to silica in dozens of job
categories throughout the general industry and maritime sectors.
    Job categories in general industry and maritime were selected for
analysis based on data from the technical industrial hygiene
literature, evidence from OSHA Special Emphasis Program (SEP) results,
and, in several cases, information from ERG site visit reports and
public comment submitted into the record. These data sources provided
evidence of silica exposures in numerous sectors. While the available
data are not entirely comprehensive, OSHA believes that silica
exposures in other sectors are quite limited.
    The industry subsectors in the overall general industry and
maritime application groups that OSHA identified as being potentially
affected by the final silica standard are as follows:

 Asphalt Paving Products
 Asphalt Roofing Materials
 Hydraulic Fracturing
 Industries with Captive Foundries
 Concrete Products
 Cut Stone
 Dental Equipment and Supplies
 Dental Laboratories
 Flat Glass
 Iron Foundries
 Jewelry
 Mineral Processing
 Mineral Wool
 Nonferrous Sand Casting Foundries
 Non-Sand Casting Foundries
 Other Ferrous Sand Casting Foundries
 Other Glass Products
 Paint and Coatings
 Porcelain Enameling
 Pottery
 Railroads
 Ready-Mix Concrete
 Refractories
 Refractory Repair
 Shipyards
 Structural Clay

    In some cases, affected industries presented in the technological
feasibility analysis have been disaggregated to facilitate the cost and
economic impact analysis. In particular, flat glass, mineral wool, and
other glass products are subsectors of the glass industry described in
Chapter IV, Section IV-9, of the FEA, and captive foundries,\15\ iron
foundries, nonferrous sand casting foundries, non-sand cast foundries,
and other ferrous sand casting foundries are subsectors of the

overall foundries industry presented in Chapter IV, Section IV-8, of
the FEA.
---------------------------------------------------------------------------

    \15\ Captive foundries include establishments in other
industries with foundry processes incidental to the primary products
manufactured. ERG (2008b, Document ID 1365) provides a discussion of
the methodological issues involved in estimating the number of
captive foundries and in identifying the industries in which they
are found. Since the 2008 ERG report, through comment in the public
record and the public hearings, OSHA has gained additional
information on the presence of captive foundries throughout general
industry.
---------------------------------------------------------------------------

    As described in ERG (2008b, Document ID 1365) and updated in OSHA
(2016), OSHA identified the six-digit NAICS codes for these subsectors
to develop a list of industries potentially affected by the final
silica standard. Table VII-2 presents the sectors listed above with
their corresponding six-digit NAICS industries. The NAICS codes and
associated industry definitions in the FEA are consistent with the 2012
NAICS edition.
BILLING CODE 4510-26-P
[GRAPHIC] [TIFF OMITTED] TR25MR16.012

[GRAPHIC] [TIFF OMITTED] TR25MR16.013

[GRAPHIC] [TIFF OMITTED] TR25MR16.014

[GRAPHIC] [TIFF OMITTED] TR25MR16.015

[GRAPHIC] [TIFF OMITTED] TR25MR16.016

BILLING CODE 4510-26-C
Construction
    The construction sector is an integral part of the nation's
economy, accounting for approximately 4.5 percent of total private
sector employment. Establishments in this industry are involved in a
wide variety of activities, including land development and subdivision,
homebuilding, construction of nonresidential buildings and other
structures, heavy construction work (including roadways and bridges),
and a myriad of special trades such as plumbing, roofing, electrical,
excavation, and demolition work.
    Construction activities were selected for analysis based on
historical data of recorded samples of construction worker exposures
from the OSHA Integrated Management Information System (IMIS) and the
National Institute for Occupational Safety and Health (NIOSH). In
addition, OSHA reviewed the industrial hygiene literature across the
full range of construction activities and focused on dusty operations
where silica sand was most likely to be fractured or abraded by work
operations. These physical processes have been found to cause the
silica exposures that pose the greatest risk of silicosis for workers.
    The construction activities, by equipment or task, that OSHA
identified as being potentially affected by the final silica standard
are as follows:
 Earth drilling
 Heavy Equipment Operators and Ground Crew Laborers--I
(Abrading or fracturing silica containing materials or demolishing
concrete or masonry structures)
 Heavy Equipment Operators and Ground Crew Laborers--II
(Grading and Excavating)
 Hole Drillers Using Handheld or Stand-Mounted Drills
 Jackhammers and Other Powered Handheld Chipping Tools
 Masonry and Concrete Cutters Using Portable Saws--I (Handheld
power saws)
 Masonry and Concrete Cutters Using Portable Saws--II (Handheld
power saws for cutting fiber-cement board)
 Masonry and Concrete Cutters Using Portable Saws--III (Walk-
behind saws)
 Masonry and Concrete Cutters Using Portable Saws--IV (Drivable
or ride-on concrete saws)
 Masonry and Concrete Cutters Using Portable Saws--V (Rig-
mounted core saws or drills)
 Masonry Cutters Using Stationary Saws
 Millers Using Portable or Mobile Machines--I (Walk-behind
milling machines and floor grinders)
 Millers Using Portable or Mobile Machines--II (Small drivable
milling machine (less than half-lane))
 Millers Using Portable or Mobile Machines--III (Milling
machines (half-lane and larger with cuts of any depth on asphalt only
and for cuts of four inches in depth or less on any other substrate))
 Rock and Concrete Drillers--I (Vehicle-mounted drilling rigs
for rock and concrete)
 Rock and Concrete Drillers--II (Dowel drilling rigs for
concrete)
 Mobile Crushing Machine Operators and Tenders
 Tuckpointers and Grinders--I (Handheld grinders for mortar
removal (e.g., tuckpointing))
 Tuckpointers and Grinders--II (Handheld grinders for uses
other than mortar removal)
    As shown in OSHA (2016) and in Chapter IV of the FEA, these
construction activities occur in the following industries and
governmental bodies, accompanied by their four-digit NAICS codes: \16\
\17\
---------------------------------------------------------------------------

    \16\ ERG and OSHA used the four-digit NAICS codes for the
construction sector both because the BLS's Occupational Employment
Statistics survey only provides data at this level of detail ad
because, unlike the case in general industry and maritime, job
categories in the construction sector are task-specific, not
industry-specific. Furthermore, as far as economic impacts are
concerned, IRS data on profitability are reported only at the four-
digit NAICS code level of detail.
    \17\ Some public employees in state and local governments are
exposed to elevated levels of respirable crystalline silica. These
exposures are included in the construction sector because they are
the result of construction activities.
---------------------------------------------------------------------------

 2361 Residential Building Construction
 2362 Nonresidential Building Construction

 2371 Utility System Construction
 2372 Land Subdivision
 2373 Highway, Street, and Bridge Construction
 2379 Other Heavy and Civil Engineering Construction
 2381 Foundation, Structure, and Building Exterior Contractors
 2382 Building Equipment Contractors
 2383 Building Finishing Contractors
 2389 Other Specialty Trade Contractors
 2211 Electric Utilities
 9992 State Government
 9993 Local Government
Characteristics of Affected Industries
    Table VII-3 provides an overview of the industries and estimated
number of workers affected by the final rule. Included in Table VII-3
are summary statistics for each of the affected industries, subtotals
for construction and for general industry and maritime, and grand
totals for all affected industries combined.
    The first five columns in Table VII-3 identify the NAICS code for
each industry in which workers are routinely exposed to respirable
crystalline silica and the name or title of the industry, followed by
the total number of entities, establishments, and employees for that
industry. Note that, while the industries are characterized by such
exposure, not every entity, establishment, and employee in these
affected industries engage in activities involving silica exposure.
    The next three columns in Table VII-3 show, for each affected
industry, the number of entities and establishments in which workers
are actually exposed to silica and the total number of workers exposed
to silica. The number of affected establishments was set equal to the
total number of establishments in an industry (based on Census data)
unless the number of affected establishments would exceed the number of
affected employees in the industry. In that case, the number of
affected establishments in the industry was set equal to the number of
affected employees, and the number of affected entities in the industry
was reduced so as to maintain the same ratio of entities to
establishments in the industry.\18\
---------------------------------------------------------------------------

    \18\ OSHA determined that removing this assumption would have a
negligible impact on total costs and would reduce the cost and
economic impact on the average affected establishment or entity.
---------------------------------------------------------------------------

BILLING CODE 4510-26-P

[GRAPHIC] [TIFF OMITTED] TR25MR16.017

[GRAPHIC] [TIFF OMITTED] TR25MR16.018

[GRAPHIC] [TIFF OMITTED] TR25MR16.019

[GRAPHIC] [TIFF OMITTED] TR25MR16.020

[GRAPHIC] [TIFF OMITTED] TR25MR16.021

[GRAPHIC] [TIFF OMITTED] TR25MR16.022

[GRAPHIC] [TIFF OMITTED] TR25MR16.023

[GRAPHIC] [TIFF OMITTED] TR25MR16.024

[GRAPHIC] [TIFF OMITTED] TR25MR16.025

[GRAPHIC] [TIFF OMITTED] TR25MR16.026

[GRAPHIC] [TIFF OMITTED] TR25MR16.027

BILLING CODE 4510-26-C
    As shown in Table VII-3, OSHA estimates that a total of 652,600
entities (586,800 in construction; 65,900 in general industry and
maritime), 675,800 establishments (600,700 in construction; 75,100 in
general industry and maritime), and 2.3 million workers (2.0 million in
construction; 0.3 million in general industry and maritime) would be
affected by the final silica rule. Note that only 67 percent of the
entities and establishments, and about 21 percent of the workers in
affected industries,

actually engage in activities involving silica exposure.\19\
---------------------------------------------------------------------------

    \19\ It should be emphasized that these percentages vary
significantly depending on the industry sector and, within an
industry sector, depending on the NAICS industry. For example, about
35 percent of the workers in construction, but only 6 percent of
workers in general industry, actually engage in activities involving
silica exposure. As an example within construction, about 35 percent
of workers in highway, street, and bridge construction, but only 3
percent of workers in state and local governments, actually engage
in activities involving silica exposure.
---------------------------------------------------------------------------

    The ninth column in Table VII-3, with data only for construction,
shows for each affected NAICS construction industry the number of full-
time-equivalent (FTE) affected workers that corresponds to the total
number of affected construction workers in the previous column.\20\
This distinction is necessary because affected construction workers may
spend large amounts of time working on tasks with no risk of silica
exposure. As shown in Table VII-3, the 2.0 million affected workers in
construction converts to approximately 387,700 FTE affected workers. In
contrast, OSHA based its analysis of the affected workers in general
industry and maritime on the assumption that they were engaged full
time in activities with some silica exposure.
---------------------------------------------------------------------------

    \20\ FTE affected workers becomes a relevant variable in the
estimation of control costs in the construction industry. The reason
is that, consistent with the costing methodology, control costs
depend only on how many worker-days there are in which exposures are
above the PEL. These are the worker-days in which controls are
required. For the derivation of FTEs, see Tables IV-8 and IV-22 and
the associated text in ERG (2007a, Document ID 1709).
---------------------------------------------------------------------------

    The last three columns in Table VII-3 show combined total revenues
for all entities (not just affected entities) in each affected
industry, and the average revenue per entity and per establishment in
each affected industry. Because OSHA did not have data to distinguish
revenues for affected entities and establishments in any industry,
average revenue per entity and average revenue per affected entity (as
well as average revenue per establishment and average revenue per
affected establishment) are estimated to be equal in value.
Silica Exposure Profile of At-Risk Workers
    The technological feasibility analyses presented in Chapter IV of
the FEA contain data and discussion of worker exposures to silica
throughout industry. Exposure profiles, by job category, were developed
from individual exposure measurements that were judged to be
substantive and to contain sufficient accompanying description to allow
interpretation of the circumstance of each measurement. The resulting
exposure profiles show the job categories with current overexposures to
silica and, thus, the workers for whom silica controls would be
implemented under the final rule.
    Chapter IV of the FEA includes a section with a detailed
description of the methods used to develop the exposure profile and to
assess the technological feasibility of the final standard. The final
exposure profiles take the exposure data that were used for the same
purpose in OSHA's PEA and build upon them, using new data in the
rulemaking record. The sampling data that were used to identify the
affected industries and to develop the exposure profiles presented in
the PEA were obtained from a comprehensive review of the following
sources of information: OSHA compliance inspections conducted before
2011, OSHA contractor (ERG) site visits performed for this rulemaking,
NIOSH site visits, NIOSH Health Hazard Evaluation reports (HHEs),
published literature, submissions by individual companies or
associations and, in a few cases, data from analogous operations
(Document ID 1720, pp. IV-2-IV-3). The exposure profiles presented in
the PEA were updated for the FEA using exposure measurements from the
OSHA Information System (OIS) that were taken during compliance
inspections conducted between 2011 and 2014 (Document ID 3958). In
addition, exposure data submitted to the record by rulemaking
participants were used to update the exposure profiles. The criteria
used for determining whether to include exposure data in the exposure
profiles are described in Section IV-2--Methodology in Chapter IV of
the FEA. As explained there, some of the original data are no longer
used in the exposure profiles based on those selection or screening
criteria. OSHA considers the exposure data relied upon for its analysis
to be the best available evidence of baseline silica exposure
conditions.
    Table VII-4 summarizes, from the exposure profiles, the total
number of workers at risk from silica exposure at any level, and the
distribution of 8-hour TWA respirable crystalline silica exposures by
job category for general industry and maritime sectors and for
construction activities. Exposures are grouped into the following
ranges: Less than 25 [mu]g/m\3\; >= 25 [mu]g/m\3\ and <= 50 [mu]g/m\3\;
> 50 [mu]g/m\3\ and <= 100 [mu]g/m\3\; > 100 [mu]g/m\3\ and <= 250
[mu]g/m\3\; and greater than 250 [mu]g/m\3\. These frequencies
represent the percentages of production employees in each job category
and sector currently exposed at levels within the indicated range.
    Table VII-5 presents data by NAICS code--for each affected general,
maritime, and construction industry--on the estimated number of workers
currently at risk from silica exposure, as well as the estimated number
of workers at risk of silica exposure at or above 25 [mu]g/m\3\, above
50 [mu]g/m\3\, and above 100 [mu]g/m\3\. As shown, an estimated
1,249,250 workers (1,097,000 in construction; 152,300 in general
industry and maritime) currently have silica exposures at or above the
new action level of 25 [mu]g/m\3\; an estimated 948,100 workers
(847,700 in construction; 100,400 in general industry and maritime)
currently have silica exposures above the new PEL of 50 [mu]g/m\3\; and
an estimated 578,000 workers (519,200 in construction; 58,800 in
general industry and maritime) currently have silica exposures above
100 [mu]g/m\3\--an alternative PEL investigated by OSHA for economic
analysis purposes.
BILLING CODE 4510-26-P

[GRAPHIC] [TIFF OMITTED] TR25MR16.028

[GRAPHIC] [TIFF OMITTED] TR25MR16.029

[GRAPHIC] [TIFF OMITTED] TR25MR16.030

[GRAPHIC] [TIFF OMITTED] TR25MR16.031

[GRAPHIC] [TIFF OMITTED] TR25MR16.032

[GRAPHIC] [TIFF OMITTED] TR25MR16.033

[GRAPHIC] [TIFF OMITTED] TR25MR16.034

[GRAPHIC] [TIFF OMITTED] TR25MR16.035

[GRAPHIC] [TIFF OMITTED] TR25MR16.036

[GRAPHIC] [TIFF OMITTED] TR25MR16.037

[GRAPHIC] [TIFF OMITTED] TR25MR16.038

[GRAPHIC] [TIFF OMITTED] TR25MR16.039

[GRAPHIC] [TIFF OMITTED] TR25MR16.040

BILLING CODE 4510-26-C

D. Technological Feasibility

    In Chapter IV of OSHA's FEA, OSHA assesses the technological
feasibility of the standard in all affected industry sectors and
application groups. The analysis presented in this chapter is organized
by industry sectors in general industry and maritime and by application
groups in the construction industry. Employee exposures were analyzed
at the operation, job category or task/activity level to the extent
that the necessary data were available.

OSHA collected exposure data to characterize current (baseline)
exposures and to identify the tasks, operations, and job categories for
which employers will need to either improve their process controls or
implement additional controls to reduce respirable crystalline silica
exposures to 50 [micro]g/m\3\ or below. In the few instances where
there were insufficient exposure data, OSHA used analogous operations
to characterize these operations.
    The technological feasibility analysis informed OSHA's selection of
the rule's permissible exposure limit (PEL) of 50 [micro]g/m\3\
respirable crystalline silica, consistent with the requirements of the
Occupational Safety and Health Act (``OSH Act''), 29 U.S.C. 651 et seq.
Section 6(b)(5) of the OSH Act requires that OSHA ``set the standard
which most adequately assures, to the extent feasible, on the basis of
the best available evidence, that no employee will suffer material
impairment of health or functional capacity'' (29 U.S.C. 655(b)(5)). In
fulfilling this statutory directive, OSHA is guided by the legal
standard expressed by the Court of Appeals for the D.C. Circuit for
demonstrating the technological feasibility of reducing occupational
exposure to a hazardous substance:

    OSHA must prove a reasonable possibility that the typical firm
will be able to develop and install engineering and work practice
controls that can meet the PEL in most of its operations. . . . The
effect of such proof is to establish a presumption that industry can
meet the PEL without relying on respirators. . . . Insufficient
proof of technological feasibility for a few isolated operations
within an industry, or even OSHA's concession that respirators will
be necessary in a few such operations, will not undermine this
general presumption in favor of feasibility. Rather, in such
operations firms will remain responsible for installing engineering
and work practice controls to the extent feasible, and for using
them to reduce . . . exposure as far as these controls can do so
(United Steelworkers of Am, AFL-CIO-CLC v. Marshall, 647 F.2d 1189,
1272 (D.C. Cir. 1980)).

    Additionally, the D.C. Circuit explained that ``[f]easibility of
compliance turns on whether exposure levels at or below [the PEL] can
be met in most operations most of the time . . . '' (Am. Iron & Steel
Inst. v. OSHA, 939 F.2d 975, 990 (D.C. Cir. 1991)); (see Section II,
Pertinent Legal Authority).
    Consistent with the legal standard described above, Chapter IV of
the FEA, which can be found at www.regulations.gov (docket OSHA-2010-
0034), describes OSHA's examination of the technological feasibility of
this rule on occupational exposure to respirable crystalline silica.
The chapter provides a description of the methodology and data used by
OSHA to analyze the technological feasibility of the standard, as well
as a discussion of the accuracy and reliability of current methods used
for the sampling and analysis of respirable crystalline silica. Chapter
IV contains OSHA's analyses, for 21 general industry sectors, 1
maritime sector, and 12 construction industry application groups, of
the technological feasibility of meeting the rule's requirements for
reducing exposures to silica. For each sector and application group,
OSHA addresses the extent to which the evidence in the record indicates
that engineering and work practice controls can reduce respirable
crystalline silica exposures to the PEL or below and maintain them at
that level. These individual technological feasibility analyses form
the basis for OSHA's overall finding that employees' exposures can be
reduced to the rule's PEL or below in most of the affected sectors'
operations. Throughout Chapter IV, OSHA describes and responds to
issues raised in the comments and testimony it received from interested
parties during the comment periods and public hearing OSHA held on the
proposed rule. The material below summarizes the detailed discussion
and presentation of OSHA's findings contained in Chapter IV of the FEA.
1. Methodology
    As noted above, OSHA's technological feasibility analysis for this
rule largely involved describing engineering and work practice controls
that OSHA concludes can be expected to control respirable crystalline
silica exposures to the PEL or below. For this portion of the analysis,
OSHA relied on information and exposure measurements from many
different sources, including OSHA's inspection database (OSHA
Information System (OIS)), OSHA inspection reports, National Institute
of Occupational Safety and Health (NIOSH) reports, site visits by NIOSH
and OSHA's contractor, Eastern Research Group, Inc. (ERG), and
materials from other federal agencies, state agencies, labor
organizations, industry associations, and other groups. In addition,
OSHA reviewed studies from the published literature that evaluated the
effectiveness of engineering controls and work practices in order to
estimate the reductions from current, baseline exposures to silica that
can be achieved through wider or improved implementation of such
controls. Finally, OSHA considered the extensive testimony and numerous
comments regarding the feasibility of implementing engineering and work
practice controls, including circumstances that preclude the use of
controls in certain situations. In total, OSHA's feasibility analysis
is based on hundreds of sources of information in the record,
constituting one of the largest databases of information OSHA has used
to evaluate the feasibility of a health standard.
    The technological feasibility chapter of the FEA describes the
industry sectors and application groups affected by the rule, and
identifies the sources of exposure to respirable crystalline silica for
each affected job category or task. The technological feasibility
analysis subdivides the general industry and maritime workplaces into
24 industry sectors.\21\ General industry sectors are identified
primarily based on the type of product manufactured (e.g., concrete
products, pottery, glass) or type of process used (e.g., foundries,
mineral processing, refractory repair). Where sufficiently detailed
information was available, the Agency further divided general industry
sectors into specific job categories on the basis of common factors
such as materials, work processes, equipment, and available exposure
control methods. OSHA notes that these job categories are intended to
represent job functions; actual job titles and responsibilities might
differ depending on the facility or industry practice.
---------------------------------------------------------------------------

    \21\ OSHA's technological feasibility analysis in the FEA is
divided into 22 sections, one for each of the general industry and
maritime sectors. However, separate technological feasibility
findings are made for three different foundry sectors (ferrous,
nonferrous, and non-sand casting foundries), making a total of 24
sectors for which separate analyses and findings are made (see Table
VII-8).
---------------------------------------------------------------------------

    For the construction industry, OSHA identified application groups
based on construction activities, tasks, or equipment that are commonly
recognized to create silica exposures; these tasks involve the use of
power tools (e.g., saws, drills, jackhammers) or larger equipment that
generates silica-containing dust (e.g., milling machines, rock and
concrete crushers, heavy equipment used in demolition or earthmoving).
The technological feasibility analysis for the construction industry
addresses 12 different application groups, defined by common
construction tasks or activities. OSHA organized construction workers
by application groups, rather than by industry sector or job titles,
because construction workers often perform multiple activities and job
titles do not always coincide with the sources of exposure; likewise,
the same equipment,

tool or task may be called by different names throughout construction
and its various subspecialties. By organizing construction activities
this way, OSHA was able to create exposure profiles for employees who
perform the same activities in any segment of the construction
industry.
    OSHA developed exposure profiles for each sector and application
group in order to characterize the baseline exposures and conditions
for each operation or task (see sections 4 and 5 of Chapter IV of the
FEA). The sample results included in the exposure profiles presented in
the Preliminary Economic Analysis (PEA) were obtained primarily from
OSHA compliance inspection reports and from NIOSH Health Hazard
Evaluation and control technology assessments. Samples were also
obtained from state plan case files, contractor site visits, published
literature and other sources. To ensure the exposure profiles were
based on the best available data, the exposure profiles were updated by
removing samples collected prior to 1990 (n = 290), leaving 2,512
samples from exposure profiles presented in the PEA from 1990 through
2007. More recent samples submitted by commenters during the rulemaking
(n = 153), primarily from 2009 through 2014, and samples obtained from
the OIS database (n = 699) from OSHA compliance inspections from 2011
to 2014 were added to exposure profiles, resulting in a total of 3,364
samples (2,483 for general industry and 881 for construction) in the
final exposure profiles. In total, these were obtained from 683 source
documents (see Table VII-6).
    The exposure profiles characterize what OSHA considers to be the
baseline, or current, exposures for each job category or application
group. Where sufficient information on control measures was available,
the exposure profiles were subdivided into sample results with and
without controls and the controls were discussed in the baseline
conditions section. OSHA also discusses the sampling results associated
with specific controls in the baseline conditions section. In these
cases, the exposure profiles include exposures associated with a range
of controlled and uncontrolled exposure scenarios.
[GRAPHIC] [TIFF OMITTED] TR25MR16.041

    The exposure profiles include silica exposure data only for
employees in the United States. Information on international exposure
levels is occasionally referenced for perspective or in discussions of
control options. The rule covers three major polymorphs of crystalline
silica (i.e., quartz, cristobalite, and tridymite). However, the vast
majority of crystalline silica encountered by employees in the United
States is in the quartz form, and the terms crystalline silica and
quartz are often used interchangeably. Unless specifically indicated
otherwise, all silica exposure data, samples, and results discussed in
the technological feasibility analysis refer to personal breathing zone
(PBZ) measurements of respirable crystalline silica.
---------------------------------------------------------------------------

    \22\ OSHA silica Special Emphasis Program (SEP) inspection
reports are from inspections conducted by OSHA compliance safety and
health officers (CSHOs) under the silica National Emphasis Program
between 1993 and 2000.
---------------------------------------------------------------------------

    In general industry and maritime, the exposure profiles in the
technological feasibility analysis consist mainly of full-shift
samples, collected over periods of 360 minutes or more (see

Table IV-02-G in the FEA). By using this criterion, OSHA ensured that
the samples included in the exposure profiles were collected for at
least three-quarters of a typical 8-hour shift and therefore captured
most activities involving exposure to silica at which the employee
spends a substantial amount of time (Document ID 0845, pp. 38-40; see
Table IV-02-G in the FEA). Due to the routine nature of most job
activities in general industry, OSHA assumed that, for the partial
shift samples of less than 480 minutes, the same level of exposure as
measured during the sampled portion of the shift continued during the
smaller, unsampled portion. OSHA considers the 6-hour (360-minute)
sampling duration to be a reasonable criterion for including a sample
because it limits the extent of uncertainty about general industry/
maritime employees' true exposures, as no more than 25 percent of an 8-
hour shift would be unsampled. The sample result is therefore assumed
to be representative of an 8-hour time-weighted average (TWA).
Moreover, by relying primarily on sampling results 360 minutes or
greater, OSHA minimized the number of results included in the profiles
reported as below the limit of detection (LOD). The LOD for an
analytical method refers to the smallest mass of silica that can be
detected on the filter used to collect the air sample. Many
laboratories currently report an LOD of 10 [mu]g or lower for quartz
samples (Document ID 0666). As discussed in the Methodology section of
Chapter IV of the FEA, relying primarily on samples with a duration of
360 minutes or greater allows OSHA to draw the conclusion that any
sample results reported as non-detect for silica are at most 16 [mu]g/
m\3\, and well below the action level of 25 [mu]g/m\3\.
    In the construction industry, approximately 43 percent of the
sampling data used in the exposure profiles also consisted of samples
collected over periods of 360 minutes or more. Most of the samples
(approximately 70%, or an additional 27%) in the construction industry
exposure profiles were collected over periods of 240 minutes or more
(see Table IV-02-G in the FEA). This allows OSHA to draw the conclusion
that any sample results reported as non-detect are below the action
level of 25 [mu]g/m\3\ (see Table IV-2-F in the FEA). Construction
workers typically spend their shifts working at multiple discrete tasks
and do not normally engage in any one task for the entire duration of a
shift; these varied tasks can include tasks that generate exposure to
respirable crystalline silica (Document ID 0677). Consequently, for
construction, OSHA assumed zero exposure during the unsampled portion
of the employee's shift unless there was evidence that silica exposures
continued for the entire shift. For example, if a sample measured an
average of 100 [mu]g/m\3\ over 240 minutes (4 hours), the result would
be recorded as 50 [mu]g/m\3\ TWA for a full 8-hour shift (480 minutes).
    The Construction Industry Safety Coalition (CISC), comprised of 25
trade associations, was critical of several aspects of OSHA's
feasibility analysis. CISC objected to the assumption of zero exposure
for the unsampled portion of the work shift when calculating 8-hour
TWAs for the construction exposure profiles. It claimed that assuming
zero exposure underestimated TWA exposure levels when compared with the
alternative assumption used for general industry that the exposure
level measured during the sampled time period remained at the same
level during the unsampled period (Document ID 2319, pp. 21-25). While
there would be some uncertainty whichever assumption OSHA used, OSHA
concludes that the no-exposure assumption for unsampled portions of a
shift produces a more accurate result than the assumption of continued
exposure at the same level because of the widely-recognized differences
in work patterns between general industry and construction operations.
In general industry, most operations are at a fixed location and
involve manufacturing processes that remain relatively constant over a
work shift. Also, most of the sample durations in general industry were
360 minutes or longer, and therefore were more likely to be
representative of 8-hour TWA exposures. In contrast, construction work
is much more variable with respect to the location of the work site,
the number of different tasks performed, and the duration of tasks
performed. As stated above, tasks that generate exposure to respirable
crystalline silica in construction are often performed on an
intermittent basis (e.g., Document ID 0677).
    OSHA's conclusion that the variability in sample durations for the
samples taken by OSHA in the construction industry more accurately
reflects the variability in exposure duration for these activities thus
comports with empirical experience. An assumption that exposure levels
during short-term tasks continued for the entire work shift would
substantially overestimate the actual 8-hour TWA exposures. The
Building and Construction Trades Department, AFL-CIO (BCTD) supported
OSHA's assumptions on work patterns, stating ``OSHA correctly treated
the unsampled time as having `zero exposure' in its technological
feasibility assessment'' (Document ID 4223, pp. 16-17). Its conclusion
was based on research performed by The Center to Protect Workers'
Rights, which developed a task-based exposure assessment model for the
construction industry that combines air sampling with task observations
and task durations in order to assess construction workers' exposure to
workplace hazards (Susi, et al., 2000, Document ID 4073, Attachment
8c). This model, when applied to masonry job sites, found that
employees spent much of their shifts performing non-silica-generating
tasks, both before and after the task involving silica exposure
(Document ID 4223, p. 16; 4073, Attachment 3a, pp. 1-2). BCTD indicated
that it was reasonable to assume these types of work patterns would be
similar for other construction tasks (Document ID 4223, pp. 16-17).
    CISC also commented that OSHA did not account for the varying
amounts of crystalline silica that could exist in materials being
disturbed by employees, and that OSHA did not account for differences
in exposure results ``due solely to what part of the country the
activity took place in'' (Document ID 2319, pp. 26-27). OSHA has
determined that the sampling data relied on to establish baseline
silica exposures are representative of the range of silica content in
materials worked on by construction workers. Information on the percent
silica content of the respirable dust sampled was available for 588 of
the 881 samples used in the exposure profiles for construction tasks.
The silica content in these samples ranged from less than 1 percent
(non-detect) to 50 percent, with an average silica content of 9.1
percent. Thus, the sample results in the exposure profiles reflect the
range in the silica content of the respirable dust sampled by OSHA at
construction work sites. Similarly, the exposure profiles contain
exposure results from many different construction tasks taken in a
variety of locations around the country under different weather
conditions. Therefore, OSHA concludes that the exposure data used in
the exposure profiles are the best available evidence of actual
exposures in construction representing nationwide weather patterns, and
that these data reflect the broad range of silica exposures experienced
by employees in the construction industry.
    Each section in the technical feasibility analysis presented in
Chapter

IV of the FEA begins with descriptions of the manufacturing or
industrial process or construction activity that has potential exposure
to respirable crystalline silica, each job category or construction
task with exposure, and the major activities and sources of exposure.
Exposure profiles based on the available sampling information are then
presented and used to characterize the baseline exposures and
conditions for each operation or task (including exposure controls
currently in use). Based on the profile of baseline exposures, each
section next includes a description of additional engineering and work
practice controls that can be implemented to reduce employee exposures
to at least the rule's PEL. In addition, comments and other evidence in
the record relating to the description of the industry sector or
application group, the exposure profile and baseline conditions, and
the need for additional controls are discussed in each section.
Finally, based on the exposure profile and assessment of available
controls and other pertinent evidence in the record, each section
includes a feasibility determination for each operation, task, or
activity, including an overall feasibility determination where more
than one operation, task, or activity is addressed in the section.
    In particular, OSHA evaluated information and testimony from the
record on the effectiveness of engineering and work practice controls
and either: (1) Identified controls that have been demonstrated to
reduce exposures to 50 [mu]g/m\3\ or below; or (2) evaluated the extent
to which baseline exposures would be reduced to 50 [mu]g/m\3\ or below
after applying the percent reduction in respirable silica or dust
exposure that has been demonstrated for a given control in the
operation or task under consideration or, in some cases, in analogous
circumstances. In some cases, the evidence demonstrates that most
exposures are already below the PEL. OSHA considers the evidence relied
on in making its feasibility determinations to be the best available
evidence on these issues.
    For general industry and maritime, the additional engineering
controls and work practices identified by OSHA consist of equipment and
approaches that are widely available and are already used in many
applications. In some cases, the same technology can be transferred or
adapted to similar operations in other industry sectors covered under
the scope of this rule. Such controls and work practices include
implementing and maintaining local exhaust ventilation (LEV) systems
with dust collection systems (such as integrated material transfer
stations); enclosing a conveyor of silica-containing material or other
containment systems; worker isolation; process modifications; dust
suppression, systems such as water sprays; and housekeeping. In many
cases, a combination of controls is necessary to control exposures to
silica. In general industry, enclosed and ventilated equipment is often
already in use. For example, most paint and coating production
operations have switched from manual transfer of raw materials
containing crystalline silica to integrated bag dumping stations
equipped with well-ventilated enclosures and bag compactors (e.g.,
Document ID 0199, pp. 9-10; 0943, p. 87; 1607 p. 10-19; 1720, p. IV-
237). Where the evidence shows that a type of control like the material
transfer system is already being used in a sector covered by the rule,
OSHA is able to conclude that it can be used more widely in that sector
as an additional control or can be adapted to other industry sectors
for use during similar operations (see sections IV-15 Paint and
Coatings, IV-16 Porcelain Enameling, IV-11 Glass, and IV-05 Concrete
Products, of the FEA for additional information).
    For construction, the exposure controls contained in Table 1 of the
rule consist primarily of water-based dust suppression systems, and LEV
systems that are integrated into hand tools and heavier equipment. As
shown in Chapter IV of the FEA, such systems are commercially available
from several vendors. In addition, equipment such as filtered,
ventilated booths or cabs and water-based systems for suppressing
fugitive dust generated by crushers and heavy equipment are available
to control exposures of construction workers to respirable crystalline
silica.
    OSHA received numerous comments that disputed OSHA's preliminary
conclusion in the Notice of Proposed Rulemaking (NPRM) that a PEL of 50
[mu]g/m\3\ TWA was technologically feasible. These comments addressed
two general areas of concern: (1) Whether sampling and analytical
methods are sufficiently accurate to reliably measure respirable
crystalline silica concentrations at levels around the PEL and action
level; and (2) whether engineering and work practice controls can
reduce exposures from current levels to the lower levels required to
comply with the new standards. These issues and OSHA's technological
feasibility findings are discussed in the sections that follow. Much
more detail can be found in Chapter IV of the FEA.
2. Feasibility Determination for Sampling and Analytical Methods
    As explained in Pertinent Legal Authority (Section II of this
preamble to the final rule), a finding that a standard is
technologically feasible requires that ``provisions such as exposure
measurement requirements must also be technologically feasible'' (see
Forging Indust. Ass'n v. Sec'y of Labor, 773 F.2d 1436, 1453 (4th Cir.
1985)). Thus, part of OSHA's technological feasibility assessment of a
new or revised health standard includes examining whether available
methods for measuring worker exposures have sufficient sensitivity and
precision to ensure that employers can evaluate compliance with the
standard and that workers have accurate information regarding their
exposure to hazardous substances. Consistent with the Supreme Court's
definition of ``feasibility'', OSHA finds that it is feasible to
measure worker exposures to a hazardous substance if achieving a
reasonable degree of sensitivity and precision with sampling and
analytical methods is ``capable of being done'' (Am. Textile Mfrs.
Inst., Inc. v. Donovan, 452 U.S. 490, 509-510 (1981)). OSHA also notes
that its analysis of the technological feasibility of the sampling and
analysis of respirable crystalline silica must be performed in
recognition of the fact that, as recognized by federal courts of
appeals, measurement error is inherent to sampling (Nat'l Min. Assoc.
v. Sec'y, U.S. Dep't of Labor, Nos. 14-11942, 14-12163, slip op. at 55
(11th Cir. Jan. 25, 2016); Am. Mining Cong. v. Marshall, 671 F.2d 1251,
1256 (10th Cir. 1982)). ``Since there is no perfect sampling method,
the Secretary has discretion to adopt any sampling method that
approximates exposure with reasonable accuracy.'' Am. Mining Cong. v.
Marshall, 671 F.2d at 1256.
    Since the late 1960s, exposures to respirable crystalline silica
(hereinafter referred to as ``silica'') have typically been measured
using personal respirable dust samplers coupled with laboratory
analysis of the crystalline silica content of the collected airborne
dust. The laboratory analysis is usually performed using X-ray
diffraction (XRD) or infrared spectroscopy (IR). A colorimetric method
of analysis that was used by a few laboratories has now been phased out
(Harper et al., 2014, Document ID 3998, Attachment 8, p. 1). OSHA has
successfully used XRD analysis since the early 1970s to enforce its
previous PELs for crystalline silica, which, for general industry, were
approximately equivalent to 100 micrograms per cubic meter ([mu]g/m\3\)
for quartz and 50 [mu]g/m\3\ for cristobalite and

tridymite (and within the range of about 250 [mu]g/m\3\ to 500 [mu]g/
m\3\ for quartz in construction). There are no other generally accepted
methods for measuring worker exposure to respirable crystalline silica.
    The ability of current sampling and analytical methods to
accurately measure worker exposures to respirable crystalline silica
was a subject of much comment in the rulemaking record. In particular,
the Chamber of Commerce (Chamber) and American Chemistry Council (ACC)
submitted comments and testimony maintaining that existing methods do
not measure respirable crystalline silica exposures with sufficient
accuracy to support OSHA's proposal in the Notice of Proposed
Rulemaking to reduce the PEL to 50 [mu]g/m\3\ and establish the 25
[mu]g/m\3\ action level (Document ID 2285; 2288, pp. 17-21; 2307,
Attachment A, pp. 198-227; 4209, pp. 129-155; 3436, p. 8; 3456, pp. 18-
19; 3460; 3461; 3462; 4194, pp. 17-21). Similar views were expressed by
several other rulemaking participants (e.g., Document ID 2056, p. 1;
2085, p. 3; 2174; 2185, pp. 5-6; 2195, Attachment 1, p. 37; 2276, pp.
4-5; 2317, p. 2; 2379, Comments, pp. 28-30; 4224, pp. 11-14; 4232,
Attachment 1, pp. 3-24). Specifically, these commenters argue that, due
to several asserted sources of error, current sampling and analytical
methods do not meet the NIOSH accuracy criterion of 25
percent (NIOSH Manual of Analytical Methods, http://www.cdc.gov/niosh/docs/95-117/). Their arguments include: (1) That there is sampling
error attributed to bias against the particle-size selection criteria
that defines the performance of the samplers and variation in
performance between sampling devices; (2) that the accuracy and
precision of the analytical method at the low levels of silica that
would be collected at the revised PEL and action level is less than
that in the range of the previous PELs for silica, particularly in the
presence of interfering substances; and (3) variation between
laboratories analyzing comparable samples adds an unacceptable degree
of uncertainty. After considering all of the testimony and evidence in
the record, OSHA rejects these arguments and, as discussed below,
concludes that it is feasible to obtain measurements of respirable
crystalline silica at the final rule's PEL and action level with
reasonable accuracy.
    OSHA is basing its conclusions on the following findings, which are
described in detail in this section. First, although there is variation
in the performance of respirable dust samplers, studies have
demonstrated that, for the majority of work settings, samplers will
perform with an acceptable level of bias (as defined by international
standards) as measured against internationally recognized particle-size
selection criteria that define respirable dust samplers. This means
that the respirable dust mass collected by the sampler will be
reasonably close to the mass that would be collected by an ideal
sampler that exactly matches the particle-size selection criteria. In
addition, OSHA finds that the measure of precision of the analytical
methods for samples collected at crystalline silica concentrations
equal to the revised PEL and action level is only somewhat higher
(i.e., somewhat less precise) than that for samples collected at
concentrations equal to the previous, higher PELs. Further, the
analytical methods can account for interferences such that, with few
exceptions, the sensitivity and precision of the method are not
significantly compromised. Studies of measurement variability between
laboratories, as determined by proficiency testing, have demonstrated a
significant decline in inter-laboratory variability in recent years.
Improvements in inter-laboratory variability have been attributed to
changes in proficiency test procedures as well as greater
standardization of analytical procedures among laboratories. Finally,
although measurement variability increases at low sample loads compared
to sample loads in the range of the former PELs, OSHA finds, based on
these studies, that the magnitude of this increase has also declined in
recent years.
    Several rulemaking participants commented that OSHA's analysis of
the feasibility of sampling and analytical methods for crystalline
silica was well supported and sound (Document ID 2080, pp. 3-4; 2244,
p. 3; 2371, Attachment 1, p. 5; 3578, Tr. 941; 3586, Tr. 3284; 3577,
Tr. 851-852; 4214, pp. 12-13; 4223, pp. 30-33). Gregory Siwinski, CIH,
and Dr. Michael Lax, Medical Director of Upstate Medical University, an
occupational health clinical center, commented that current laboratory
methods can measure respirable crystalline silica at the 50 [mu]g/m\3\
PEL and 25 [mu]g/m\3\ action level, and that they have measured
exposures below the action level (Document ID 2244, p. 3). Dr. Celeste
Montforton of the George Washington School of Public Health testified
that ``[i]ndustrial hygienists, company safety personnel, consultants,
and government inspectors have been conducting for decades workplace
sampling for respirable silica . . .'' and that some governments, such
as Manitoba and British Columbia, are successfully collecting and
analyzing samples to determine compliance with their occupational
exposure limits of 25 [mu]g/m\3\ (Document ID 3577, Tr. 851-852). Dr.
Frank Mirer of the CUNY School of Public Health, formerly with the UAW
and on behalf of the AFL-CIO, stated that ``[a]ir sampling is feasible
at 25 [mu]g/m\3\ and below for [a] full shift and even for part shift.
It was dealt with adequately in the OSHA proposal'' (Document ID 3578,
Tr. 941).
    The ACC, Chamber, and others base their argument that sampling and
analytical methods for respirable crystalline silica are insufficiently
precise on strict adherence to NIOSH's accuracy criterion of 25 percent at a 95-percent confidence level for chemical sampling
and analysis methods (http://www.cdc.gov/niosh/docs/95-117/). The ACC
pointed out that ``OSHA standards typically reflect the NIOSH Accuracy
Criterion by requiring employers to use a method of monitoring and
analysis that has an accuracy of plus or minus 25 percent . . . ,'' and
cited a number of OSHA standards where the Agency has included such
requirements (benzene, 29 CFR 1910.1028; lead (which requires a method
accuracy of 20%), 29 CFR 1910.1025; cadmium, 29 CFR
1910.1027; chromium (VI), 29 CFR 1910.1026) (Document ID 4209, p. 129).
However, the NIOSH accuracy criterion is not a hard, bright-line rule
in the sense that a sampling and analytical method must be rejected if
it fails to meet this level of accuracy, but is rather a goal or target
to be used in methods development. Where evidence has shown that a
method does not meet the accuracy criterion at the PEL or action level,
OSHA has stipulated a less rigorous level of accuracy to be achieved.
For example, OSHA's acrylonitrile standard requires use of a method
that is accurate to 35 percent at the PEL and 50 percent at the action level (29 CFR 1910.1045), and several
OSHA standards require that 35 percent accuracy be obtained
at the action level (arsenic, 29 CFR 1910.1018; ethylene oxide, 29 CFR
1910.1047; formaldehyde, 29 CFR 1910.1048; 1,3-butadiene, 29 CFR
1910.1051; methylene chloride, 29 CFR 1910.1052). As discussed below,
the precision of the sampling and analytical method for crystalline
silica, as currently implemented using OSHA Method ID-142 for X-ray
diffraction, is about 21 percent for quartz and
cristobalite.
    In the remainder of this section, OSHA first describes available
respirable dust sampling methods and

addresses comments and testimony related to the performance and
accuracy of respirable dust samplers. Following that discussion, OSHA
summarizes available analytical methods for measuring crystalline
silica in respirable dust samples and addresses comments and evidence
regarding analytical method precision, the presence of interfering
materials, and reported variability between laboratories analyzing
comparable samples.
a. Respirable Dust Sampling Devices
    Respirable dust comprises particles small enough that, when
inhaled, they are capable of reaching the pulmonary region of the lung
where gas exchange takes place. Measurement of respirable dusts
requires the separation of particles by size to assess exposures to the
respirable fraction of airborne dusts. A variety of different
industrial hygiene sampling devices, such as cyclones and elutriators,
have been developed to separate the respirable fraction of airborne
dust from the non-respirable fraction. Cyclones are the most commonly
used size-selective sampling devices, or ``samplers,'' for assessing
personal exposures to respirable dusts such as crystalline silica. The
current OSHA (ID-142, revised December 1996, Document ID 0946) and
NIOSH (Method 7500, Document ID 0901; Method 7602, 0903; Method 7603,
http://www.cdc.gov/niosh/docs/2003-154/pdfs/7603.pdf) methods for
sampling and analysis of crystalline silica specify the use of
cyclones.
    Although respirable dust commonly refers to dust particles having
an aerodynamic diameter of 10 [mu]m (micrometer) or less, it is more
precisely defined by the collection efficiency of the respiratory
system as described by a particle collection efficiency model. These
models are often depicted by particle collection efficiency curves that
describe, for each particle size range, the mass fraction of particles
deposited in various parts of the respiratory system. These curves
serve as the ``yardsticks'' against which the performance of cyclone
samplers should be compared (Vincent, 2007, Document ID 1456). Figure
VII-1 below shows particle collection efficiency curves for two
particle size selection criteria: The criteria specified in the 1968
American Conference of Governmental Industrial Hygienists (ACGIH)
Threshold Limit Value (TLV) for respirable dust, which was the basis
for the prior OSHA general industry silica PEL, and an international
specification by the International Organization for Standardization
(ISO) and the Comit[eacute] Europ[eacute]en de Normalisation (CEN)
known as the ISO/CEN convention, which was adopted by ACGIH in 1994 and
is the basis for the definition of respirable crystalline silica in the
final rule. In addition to the curves, which cover the full range of
particle sizes that comprise respirable dust, particle size collection
criteria are also often described by their 50-percent respirable ``cut
size'' or ``cut point.'' This is the aerodynamic diameter at which 50
percent of the particle mass is collected, i.e., the particle size that
the sampler can collect with 50-percent efficiency. Particles with a
diameter smaller than the 50-percent cut point are collected with an
efficiency greater than 50 percent, while larger-diameter particles are
collected with an efficiency less than 50 percent. The cut point for
the 1968 ACGIH specification is 3.5 [mu]m and for the ISO/CEN
convention is 4.0 [mu]m (Lippman, 2001, Document ID 1446, pp. 107,
113).
[GRAPHIC] [TIFF OMITTED] TR25MR16.042

    For most workplace conditions, the change in the criteria for
respirable dust in the final rule would theoretically increase the mass
of respirable dust collected over that measured under the previous
criteria by an amount that depends on the size distribution of airborne
particles in the workplace. Soderholm (1991, Document ID 1661) examined
these differences based on 31 aerosol size distributions measured in
various industrial workplaces (e.g., coal mine, lead smelter, brass
foundry, bakery, shielded metal arc [SMA] welding, spray painting,
pistol range) and determined the percentage increase in the mass of
respirable dust that would be collected under the ISO/CEN convention
over that which would be collected under the 1968 ACGIH criteria.
Soderholm concluded that, for all but three of the 31 size
distributions that were evaluated, the increased respirable dust mass
that would be collected using the ISO/CEN convention for respirable
dust instead of the 1968 ACGIH criteria would be less than 30 percent,
with most size distributions (25 out of the 31 examined, or 80 percent)
resulting in a difference of between 0 and 20 percent (Document ID
1661, pp. 248-249, Figure 1). In the PEA, OSHA stated its belief that
the magnitude of this effect does not outweigh the advantages of
adopting the ISO/CEN convention. In particular, most respirable dust
samplers on the market today are designed and calibrated to perform in
a manner that closely conforms to the international ISO/CEN convention.
    Incorporating the ISO/CEN convention in the definition of
respirable crystalline silica will permit employers to use any sampling
device that conforms to the ISO/CEN convention. There are a variety of
these cyclone samplers on the market, such as the Dorr-Oliver, Higgins-
Dewell (HD), GK2.69, SIMPEDS, and SKC aluminum. In the PEA, OSHA
reviewed several studies demonstrating that these samplers collect
respirable particles with efficiencies that closely match the ISO/CEN
convention (Document ID 1720, pp. IV-21--IV-24). In addition to cyclone
samplers, there are also personal impactors available for use at flow
rates from 2 to 8 L/min that have been shown to conform closely with
the ISO/CEN convention (Document ID 1834, Attachment 1). Cyclones and
impactors both separate particles by size based on inertia. When an
airstream containing particles changes direction, smaller particles
remain suspended in the airstream and larger ones impact a surface and
are removed from the airstream. Cyclones employ a vortex to separate
particles centrifugally, while impactors use a laminar airflow around a
flat surface such that particles in the desired size range impact onto
the surface.
    The current OSHA sampling method for crystalline silica, ID-142, is
the method used by OSHA to enforce the silica PELs and is used by some
employers as well. It specifies that a respirable sample be collected
by drawing air at 1.7  0.2 liters/minute (L/min) through a
Dorr-Oliver 10 millimeter (mm) nylon cyclone attached to a cassette
containing a 5-[mu]m pore-size, 37-mm diameter polyvinyl chloride (PVC)
filter (Document ID 0946). NIOSH sampling and analysis methods for
crystalline silica (Method 7500, Method 7602, Method 7603) have also
adopted the ISO/CEN convention with flow rate specifications of 1.7 L/
min for the Dorr-Oliver 10-mm nylon cyclone and 2.2 L/min for the HD
cyclone (Document ID 0901; 0903). Method 7500 also allows for the use
of an aluminum cyclone at 2.5 L/min. NIOSH is revising its respirable
dust method to include any sampler designed to meet the ISO/CEN
criteria (Document ID 3579, Tr. 218).
    The devices discussed above, when used at the appropriate flow
rates, are capable of collecting a quantity of respirable crystalline
silica that exceeds the quantitative detection limit for quartz (the
principle form of crystalline silica) of 10 [mu]g for OSHA's XRD method
(Document ID 0946). For several scenarios based on using various
devices and sampling times (8-hour, 4-hour, and 1-hour samples), OSHA
calculated the amount of respirable quartz that would be collected at
quartz concentrations equal to the existing general industry PEL, the
proposed (and now final) rule's PEL, and the proposed (and now final)
rule's action level. As seen in Table IV.3-A, computations show that
the 10-mm nylon Dorr-Oliver operated at an optimized flow rate of 1.7
L/min, the aluminum cyclone operated at 2.5 L/min, the HD cyclone
operated at 2.2 L/min, and the GK2.69 operated at 4.2 L/min will all
collect enough quartz during an 8-hour or 4-hour sampling period to
meet or exceed the 10 [micro]g quartz limit of quantification for OSHA
Method ID-142. Therefore, each of the commercially available cyclones
is capable of collecting a sufficient quantity of quartz to exceed the
limit of quantification when airborne concentrations are at or below
the action level, provided that at least 4-hour air samples are taken.
Table VII-7 also shows that the samplers can collect enough silica to
meet the limit of quantification when the airborne respirable silica
concentration is below the action level of 25 [mu]g/m\3\, in one case
as low as 5 [mu]g/m\3\.

[GRAPHIC] [TIFF OMITTED] TR25MR16.043

    A comment from the National Rural Electric Cooperative Association
(NRECA) stated that the current OSHA and NIOSH analytical methods
require sampling to collect a minimum of 400 liters of air, and that at
the flow rates specified for current samplers, sampling would have to
be performed for approximately 2.5 to 4 hours; however, this is
considerably longer than most construction tasks performed in
electrical transmission and distribution work, which tend to last 2
hours or less (Document ID 2365, pp. 2, 6-7). OSHA does not view this
discrepancy to be a problem. The minimum sampling times indicated in
the OSHA and NIOSH methods contemplate that exposure occurs over most
of the work shift. Construction operations frequently involve shorter-
term tasks after which there is no further exposure to respirable
crystalline silica. In those situations, OSHA often does not itself
continue sampling during inspections and does not expect employers to
continue sampling when there is no exposure to silica, and considers
the sampling result that is obtained from shorter-term task sampling to
be sufficient to represent a worker's 8-hour time-weighted-average
(TWA) exposure, which can be calculated assuming no exposure for the
period of the shift that is not sampled. If the airborne concentration
of silica for the task is low, the sampling result would likely be
below the limit of quantification. In that case, it would be safe for
the employer to assume that the exposure is below the action level.
Transition to ISO-CEN Criteria for Samplers
    In the final rule, OSHA is adopting the ISO/CEN particle size-
selective criteria for respirable dust samplers used to measure
exposures to respirable crystalline silica. Under the ISO/CEN
convention, samplers should collect 50 percent of the mass of particles
that are 4 [mu]m in diameter (referred to as the cut point), with
smaller particles being collected at higher efficiency and larger
particles being collected at lower efficiency. Particles greater than
10 [mu]m in diameter, which are not considered to be respirable, are to
be excluded from the sample based on the ISO/CEN convention (Document
ID 1446, pp. 112-113).
    Several rulemaking participants supported OSHA's proposed adoption
of the ISO/CEN criteria for respirable dust samplers (Document ID 1730;
1969; 3576, Tr. 290; 3579, Tr. 218-219; 4233, p. 4). For example, a
representative of SKC, Inc., which manufactures samplers used to
collect respirable crystalline silica, stated that:

    Adoption of the ISO/CEN performance standard for respirable dust
samplers by OSHA will bring the U.S. regulatory standards in line
with standards/guidelines established by other occupational health
and safety agencies, regulatory bodies, and scientific consensus
organizations around the world. It will also align OSHA performance
criteria for respirable dust samplers to that of NIOSH (Document ID
1730, pp. 1-2).

    As discussed above, OSHA's previous (and currently enforceable)
general industry PEL for crystalline silica was based on a 1968 ACGIH
definition, which specified a model with a cut point of 3.5 [mu]m.
Based on available studies conducted over 40 years ago, the Dorr-Oliver
10-mm cyclone was thought to perform closely to this specification. As
such, it is the sampling device specified in OSHA's respirable dust
sampling and analytical methods, including Method ID-142 for respirable
crystalline silica (Document ID 0946). For most sizes of respirable
particles, the ISO/CEN convention specifies a greater efficiency in
particle collection than does the 1968 ACGIH model; consequently,
samplers designed to meet the ISO/CEN convention will capture somewhat
greater mass of airborne particle than would a sampler designed to the
1968 ACGIH model, with the magnitude of the increased mass dependent on
the distribution of particle sizes in the air. For most particle size
distributions encountered in workplaces, the increase in dust mass
theoretically collected under the ISO/CEN convention compared to the
ACGIH model would be 25 percent or less (Soderholm, 1991, Document ID
1661).
    Several rulemaking participants commented that moving from the 1968
ACGIH model to the ISO/CEN convention effectively decreased the PEL and
action level below the levels intended, since more dust would be
collected by samplers that conform to

the ISO/CEN convention than by those that conform to the 1968 ACGIH
model (Document ID 2174; 2195, p. 30; 2285, pp. 3-4; 2307, Attachments
10, p. 19, and 12, p. 3; 2317, p. 2; 3456, p. 10; 4194, pp. 15-16). For
example, the Chamber commented that adopting the ISO/CEN specification
``can result in citations for over exposure to quartz dust where none
would have been issued prior to the adoption of this convention''
(Document ID 2288, p. 16). OSHA disagrees with this assessment because,
based on more recent evaluations (Bartley et al., 1994, Document ID
1438, Attachment 2; Lee et al., 2010, 3616; 2012, 3615), the Dorr-
Oliver 10-mm cyclone that has been used by the Agency for enforcement
of respirable dust standards for decades has been found to perform
reasonably closely (i.e., with an acceptable level of bias) to the ISO/
CEN specification when operated at the 1.7 L/min flow rate specified by
OSHA's existing method. Consequently, OSHA and employers can continue
to use the Dorr-Oliver cyclone to evaluate compliance against the final
PEL of 50 [mu]g/m\3\ without having to change equipment or procedures,
and thus would not be collecting a greater quantity of dust than
before. Furthermore, OSHA notes that other ISO/CEN-compliant samplers,
such as the SKC 10-mm aluminum cyclone and the HD cyclone specified in
the NIOSH Method 7500, are already widely used by investigators and
employers to evaluate exposures to respirable crystalline silica
against benchmark standards. Therefore, the change from the ACGIH
convention to the ISO/CEN convention is more a continuation of the
status quo than a drastic change from prior practice.
    Other rulemaking participants argued that moving to the ISO/CEN
convention effectively invalidates OSHA's risk and feasibility analyses
since the exposure data that underlie these analyses were obtained
using devices conforming to the 1968 ACGIH specification. For example,
Thomas Hall, testifying for the Chamber, stated that moving to the ISO/
CEN convention ``would produce a difference in [current] exposure
results from . . . historical measurements that have been used in the
risk assessments'' (Document ID 3576, Tr. 435). Similarly, in its pre-
hearing comments, the ACC argued that:

    When OSHA conducted technological feasibility studies for
attaining the proposed 50 [mu]g/m\3\ PEL, the Agency based its
decisions on samples collected using the current ACGIH method, not
the proposed ISO/CEN method. Thus, the switch to the ISO/CEN
definition will have two impacts on feasibility. First, it will add
uncertainty regarding OSHA's technological feasibility determination
because greater reductions in exposure will be required to achieve a
50 [mu]g/m\3\ PEL measured by the ISO/CEN definition than by the
ACGIH definition that OSHA applied. Second, OSHA's use of the ACGIH
definition to estimate compliance costs causes the Agency to
underestimate the costs of achieving the 50 [mu]g/m\3\ PEL because
OSHA did not account for the additional workers whose exposures
would exceed the proposed PEL under the ISO/CEN definition but who
would be exposed below the proposed PEL if measured under the ACGIH
definition (Document ID 2307, Attachment 8, p. 9).

    OSHA rejects these arguments for the following reasons. First, with
respect to the risk information relied on by the Agency, exposure data
used in the various studies were collected from employer records
reflecting use of several different methods. Some studies estimated
worker exposures to silica from particle counts, for which the sampling
method using impingers does not strictly conform to either the ACGIH or
ISO/CEN conventions (e.g., Rice et al., Document ID 1118; Park et al.,
Document ID 0405; Attfield and Costello, Document ID 0285; Hughes et
al., Document ID 1060). Other studies used measurements taken using
cyclone samplers and modern gravimetric methods of silica analysis
(e.g., Rice et al. and Park et al., data obtained from cyclone pre-
separator up through 1988, Document ID 1118, 0405; Hughes et al., data
from 10-mm nylon cyclone through 1998, Document ID 1060). OSHA believes
it likely that exposure data collected using cyclones in these studies
likely conformed to the ISO/CEN specification since flow rates
recommended in the OSHA and NIOSH methods were most likely used. The
studies by Miller and MacCalman (Document ID 1097) and by Buchanan et
al. (Document ID 0306) used exposure measurements made with the MRE
113A dust sampler, which does conform reasonably well with the ISO/CEN
specification (Gorner et al., Document ID 1457, p. 47). The studies by
Chen et al. (2001, Document ID 0332; 2005, Document ID 0985) estimated
worker exposures to silica from total dust measurements that were
converted to respirable silica measurements from side-by-side
comparisons of the total dust sampling method with samples taken using
a Dorr-Oliver cyclone operated at 1.7 L/min, which is consistent with
the ISO/CEN convention (see Section V, Health Effects, of this preamble
and OSHA's Preliminary Review of Health Effects Literature and
Preliminary Quantitative Risk Assessment, Document ID 1711). Thus, it
is simply not the case that the exposure assessments conducted for
these studies necessarily reflect results from dust samples collected
with a device conforming to the 1968 ACGIH particle size-selective
criteria, and OSHA finds that no adjustment of OSHA's risk estimates to
reflect exposure measurements consistent with the ISO/CEN convention is
warranted.
    Second, with respect to the feasibility analysis, OSHA relied on
exposure data and constructed exposure profiles based principally on
measurements made by compliance officers using the Dorr-Oliver cyclone
operated at 1.7 L/min, as the Agency has done since Method ID-142 was
developed in 1981, well before the 1990 cut-off date for data used to
construct the exposure profiles. As explained earlier in the section,
recent research shows that the Dorr-Oliver cyclone operated at this
flow rate performs in a manner consistent with the ISO/CEN
specification. Other data relied on by OSHA comes from investigations
and studies conducted by NIOSH and others who used various cyclones
that conform to the ISO/CEN specification. Thus, OSHA finds that the
exposure profiles being relied on to evaluate feasibility and costs of
compliance do not reflect sample results obtained using the 1968 ACGIH
model. Instead, the vast majority of sample results relied upon were
collected in a manner consistent with the requirements of the final
rule. NIOSH supported this assessment, stating that, given the Dorr-
Oliver sampler operated at a flow rate of 1.7 L/min conforms closely to
the ISO/CEN convention, ``there is continuation with historic exposure
data'' (Document ID 4233, p. 4). For these reasons, OSHA finds that it
is appropriate to rely on the feasibility and cost analyses and
underlying exposure data without adjustment to account for the final
rule's adoption of the ISO/CEN specification for respirable dust
samplers.
Sampling Error
    Several commenters raised issues concerning the accuracy of
respirable dust samplers in relation to the ISO/CEN criteria, asserting
that sampling respirable dust is uncertain and inaccurate, and that
there are numerous sources of error. Chief among these were Dr. Thomas
Hall of Industrial Hygiene Specialty Resources, LLC, testifying for the
Chamber, and Paul K. Scott of ChemRisk, testifying for the ACC.
    The Chamber's witnesses and others referenced studies showing that
all samplers were biased against the ISO/CEN particle-size selection
convention. This means that the sampler would collect more or less mass
of respirable particulate than would an ideal sampler

that exactly conforms to the ISO/CEN convention. OSHA discussed this
issue in the PEA, noting that most samplers tend to over-sample smaller
particles and under-sample larger particles, compared to the ISO/CEN
convention, at their optimized flow rates. This means that, for
particle size distributions dominated by smaller particles, the sampler
will collect more mass than would be predicted from an ideal sampler
that exactly conforms to the ISO/CEN convention. For particle size
distributions dominated by larger particles in the respirable range,
less mass would be collected than predicted. In the PEA, OSHA evaluated
several studies that showed that several cyclone samplers exhibited a
bias of 10 percent or less for most particle size distributions
encountered in the workplace. Some of these studies found biases as
high as 20 percent but only for particle size distributions
having a large mass median aerodynamic diameter (MMAD) (i.e., 20
[micro]m or larger) and narrow distribution of particle sizes (i.e., a
geometric standard deviation (GSD) of 2 or less) (Document ID 1720, pp.
IV-21--IV-24). Such particle size distributions are infrequently seen
in the workplace; for well-controlled environments, Frank Hearl of
NIOSH testified that the GSD for typical particle size distributions
would be about 2 (Document ID 3579, Tr. 187). Dr. Hall (Document ID
3576, Tr. 502) testified, similarly, that it would be around 1.8 to 3
for well-controlled environments and higher for uncontrolled
environments (see also Liden and Kenny, 1993, Document ID 1450, p. 390,
Figure 5; Soderholm, 1991,1661, p. 249, Figure 1). Furthermore, a
particle size distribution with a large MMAD and small GSD would
contain only a very small percentage (< 10%) of respirable dust that
would be collected by a sampler optimized to the ISO/CEN criteria
(Soderholm, 1991, Document ID 1661, p. 249, Figure 2). According to
Liden and Kenny (1993), ``samplers will perform reasonably well
providing the absolute bias in sampling is kept to within 10 percent .
. . this aim can be achieved . . . over the majority of size
distributions likely to be found in field sampling'' (Document ID 1450,
p. 390).