obligation to designate a competent person is clearly specified in
paragraph (g)(4) and the definition clearly states that the competent
person has authority to promptly apply corrective measures.
    The competent person concept has been broadly used in OSHA
construction standards (e.g., 29 CFR 1926.32(f) and 1926.20(b)(2)),
particularly in safety standards. This standard does not affect the
competent person provisions in these other standards.
    ``Employee exposure'' means the exposure to airborne respirable
crystalline silica that would occur if the employee were not using a
respirator. This definition clarifies the requirement that employee
exposure must be measured as if no respiratory protection is being
worn. The definition, which is consistent with OSHA's previous use of
the term in other standards, did not generate any comment and is
unchanged from the proposal.
    ``High-efficiency particulate air (HEPA) filter'' means a filter
that is at least 99.97 percent efficient in removing mono-dispersed
particles of 0.3 micrometers in diameter. The definition is unchanged
from the proposal. HEPA filters are more efficient than membrane
filters because they are designed to target much smaller particles. In
the housekeeping requirements of paragraph (h)(1) of the standard for
general industry and maritime (paragraph (f)(1) of the standard for
construction), OSHA refers to HEPA-filtered vacuuming as an example of
an appropriate cleaning method, and the Table 1 entry for handheld and
stand-mounted drills requires use of a HEPA-filtered vacuum (if a
commercially available hole-cleaning kit connected to a dust collector
is not being used). OSHA had also proposed HEPA-filtered dust
collectors as controls for some tasks listed on Table 1 of the proposed
standard for construction.
    The Agency received one comment related to HEPA filters from the
Occupational and Environmental Health Consulting Services (OEHCS).
First, OEHCS recommended that the definition be expanded to indicate
that HEPA filters are effective at removing particles in the 0.3-
micrometer size range, as measured by a laser particle counter. Second,
it requested addition of the term ``Portable High Efficiency Air
Filtration (PHEAF)'' device, defined as a portable device equipped with
a certified HEPA filter that, when tested as a complete unit, is 99.97
percent effective in removing particles in the 0.3-micrometer size
range, as measured by a laser particle counter (Document ID 1953, pp.
4-6). OEHCS advocated for a requirement that portable filtration
devices (e.g., HEPA vacuums, dust collectors used on tools, and filter
systems for enclosed cabs) meet the definition of PHEAF. It argued that
HEPA vacuums or other portable filtration devices might not perform
effectively in the field due to inadequate, damaged, or deteriorating
sealing surfaces; replacement filters that do not fit correctly; filter
cabinets that are damaged; or filters that are punctured. Claiming that
damaged filters might not build up enough pressure differential to
signal that they should be changed, OEHCS recommended a requirement for
field testing the devices using a laser particle counter to ensure that
HEPA filters function as intended (Document ID 1953, Attachment 1, pp.
2-4).
    OSHA encourages employers to ensure that HEPA filters function in
the field according to the specifications of this definition. However,
the Agency concludes that it is not appropriate to include requirements
for PHEAF devices, as defined by OEHCS, or laser particle counting
testing, in the rule due to the lack of documented effectiveness or
consistency with the definition and because of the lack of support in
the record. As a result, OSHA is retaining its proposed definition for
HEPA filter and is not adding PHEAF to the definitions section.
    ``Objective data'' means information, such as air monitoring data
from industry-wide surveys or calculations based on the composition of
a substance, demonstrating employee exposure to respirable crystalline
silica associated with a particular product or material or a specific
process, task, or activity. The data must reflect workplace conditions
closely resembling or with a higher exposure potential than the
processes, types of material, control methods, work practices, and
environmental conditions in the employer's current operations.
    The proposed definition of ``objective data'' also included
``calculations based on the . . . chemical and physical properties of a
substance'' as an example of a type of objective data that might
demonstrate employee exposure to respirable crystalline silica. BCTD
objected to this example's inclusion in the definition (Document ID
2371, Attachment 1, pp. 11-12). Although BCTD agreed that the chemical
and physical properties of a substance are among the factors that may
be relevant in determining whether data from one set of circumstances
can be used to characterize the exposures in other circumstances, BCTD
stated that the proposed definition suggested that the chemical and
physical properties of the material could be determinative in every
instance. It also maintained that on construction sites the work
processes themselves are more consistently a significant predictor of
ambient silica exposures than percentage of silica in the material
itself. Finally, BCTD argued that it is very important to focus not
only on the overall operation, but also the specific silica dust-
generating task.
    In including this item in the definition, OSHA did not intend to
imply that it would be relevant in all circumstances. Nonetheless, OSHA
has removed the phrase ``chemical and physical properties'' from the
final definition of ``objective data'' because it has concluded that a
substance's

chemical and physical properties are not typically relevant for
demonstrating exposures to respirable crystalline silica. However, in
those instances where a substance's physical and chemical properties
demonstrate employee exposure to respirable crystalline silica
associated with a particular product or material or a specific process,
task, or activity, an employer may use that information as objective
data under this rule.
    The proposed rule also stated that objective data is information
demonstrating employee exposure to respirable crystalline silica
associated with a particular product or material or a specific process,
operation, or activity. Throughout this rule, OSHA has often replaced
the word ``operation'' with the word ``task'' (see summary and
explanation of Specified Exposure Control Methods for further
discussion). OSHA has made the change to ``task'' (instead of
``operation'') in this definition to remain consistent with that
change. This is also consistent with NIOSH's recommendation to add
specificity to the definition by including the term ``task'' (Document
ID 2177, Attachment B, p. 12).
    In addition, the proposal indicated that ``objective data'' needed
to reflect workplace conditions closely resembling the processes, types
of material, control methods, work practices, and environmental
conditions in the employer's current operations. Dow Chemical Company
stated that this requirement is generally appropriate, but argued that
when data pertain to a more challenging work environment with higher
potential for exposure, those data should be considered objective data
(Document ID 2270, p. 2). It explained:

    If data from a more challenging environment demonstrate
compliance with the Permissible Exposure Limit, then one may infer
with confidence that workers in a less challenging environment
(i.e., with less potential for exposure) are also not exposed above
the PEL. Even if the two work environments are not ``closely
resembling,'' the data are still an objective, valid method of
screening workplaces that have a clearly lower risk of exposure
(Document ID 2270, p. 2).

    OSHA agrees with Dow that data pertaining to an environment with
higher exposure potential can be used as objective data for other
environments with less potential for exposure. Therefore, OSHA added
``or with a higher exposure potential'' to the definition.
    Edison Electric Institute (EEI) requested that OSHA harmonize the
definition of ``objective data'' throughout its regulations (Document
ID 2357, p. 22). OSHA recognizes that the term has evolved over time
based on the Agency's experience implementing those standards.
``Objective data'', as defined in this standard, is based on the record
in this rulemaking and reflects an appropriate definition in the
context of exposures to respirable crystalline silica. Additionally,
OSHA has established a process, the Standards Improvement Project, to
improve and streamline OSHA standards, including the revision of
individual requirements within rules that are inconsistent. OSHA will
consider reviewing the consistency of this definition in the next
iteration of this ongoing effort.
    Many commenters suggested that OSHA add specificity with regards to
what is considered objective data and establish criteria for objective
data in the definition (e.g., Document ID 2177, Attachment B, p. 11;
2181, p. 5; 2253, p. 4; 2256, Attachment 2, p. 10; 2339, p. 7; 2371,
Attachment 1, p. 12; 2379, Appendix 1, pp. 54-55; 2380, Attachment 2,
p. 26; 4223, p. 70). As discussed in the summary and explanation of
Exposure Assessment, OSHA intends for the performance option to give
employers flexibility to accurately characterize exposures using
whatever processes or data are most appropriate for their
circumstances. The Agency concludes it would be inconsistent to include
specifications or criteria in the definition of objective data and thus
has not done so here.
    Commenters also provided examples of alternative exposure
measurement and characterization strategies that could generate
objective data, such as: area sampling (Document ID 2195, pp. 36-37);
area exposure profile mapping (Document ID 2379, Appendix 1, pp. 48-
49); real-time monitoring (Document ID 2256, Attachment 3, p. 12; 2357,
pp. 37-38; 2379, Appendix 1, pp. 48-49, 55-56; 3578, Tr. 941-942; 3579,
Tr. 161-162; 3588, Tr. 3798-3800; 4204, p. 56); and geotechnical
profiling with testing for crystalline silica content (Document ID
2262, p. 13). Trolex LTD pointed to emerging methods and technologies,
such as new optical methods for particle counting and identification,
which might provide enhanced measurements of real-time employee
exposure to respirable crystalline silica in the future (Document ID
1969, p. 2).
    In addition, commenters provided specific examples of types of
information and information sources that they felt should be considered
objective data. For example, the American Foundry Society (AFS)
commented that objective data should include data that permits reliable
estimation of exposure, such as: data from real-time monitors and area
exposure mapping; data from less than full-shift samples where
professional judgment can be used to determine exposure levels; and
exposure data where the percent of silica is calculated using a
historical average for the area or operation involved (Document ID
2379, Appendix 1, pp. 54-55). The National Association of Manufacturers
suggested the following as reliable sources of objective data:
published scientific reports in the open scientific literature; NIOSH
Health Hazard Evaluations; insurance carriers' loss prevention reports;
and information that the silica in a process cannot be released because
it is bound in a matrix preventing formation of respirable particles
(Document ID 2380, Attachment 2, p. 26). ASSE identified industry-wide
data, safety data sheets from product manufacturers, prior historical
sampling data under comparable conditions, and aggregated company-wide
sampling information as reliable sources of objective data (Document ID
3578, Tr. 1036). Commenters also pointed to data collected by a trade
association from its members (e.g., Document ID 2181, pp. 5-6, 7; 2371,
Attachment 1, Appendix A; 3544, pp. 12-13; 3583, Tr. 2394; 3585, Tr.
2905-2906; 3588, Tr. 3936-3938; 4197, pp. 1-6; 4198, pp. 1-181; 4223,
pp. 68-70).
    The Agency, while including specific examples in the definition
(i.e., air monitoring data from industry-wide surveys and calculations
based on the composition of a substance), does not intend to limit the
information that can be considered objective data to the information
from those sources. OSHA agrees that data developed with alternative
exposure measurement and characterization strategies, both those
currently available and those that become available in the future, and
the types of information and information sources suggested by
commenters can be used as objective data where the conditions of the
definition are satisfied. Monitoring data obtained prior to the
effective date of the rule can also be considered objective data if it
demonstrates employee exposure to respirable crystalline silica
associated with a particular product or material or a specific process,
task, or activity and reflects workplace conditions closely resembling
or with a higher exposure potential than the processes, types of
material, control methods, work practices, and environmental conditions
in the employer's current operation.
    Objective data is further discussed in the summary and explanation
of Scope

and Application (paragraph (a)(2) for general industry and maritime)
and Exposure Assessment (paragraph (d) for general industry and
maritime standard and paragraph (d)(2) for the construction standard).
    ``Physician or other licensed health care professional [PLHCP]''
means an individual whose legally permitted scope of practice (i.e.,
license, registration, or certification) allows him or her to
independently provide or be delegated the responsibility to provide
some or all of the particular health care services required by
paragraph (i) of this section (paragraph (h) of the standard for
construction). This definition is unchanged from the proposal, and is
included because the standard requires that all medical examinations
and procedures be performed by or under the supervision of a PLHCP.
    OSHA received two comments on the definition of PHLCP, both of
which addressed the scope of the PHLCP's qualifications, from APHA and
ATS (Document ID 2175, p. 5; 2178, Attachment 1, p. 5). ATS agreed with
OSHA's determination of who is qualified to be a PLHCP (Document ID
2175, p. 5). APHA advocated that the PLHCP:

. . . should be licensed for independent practice . . . and have
training and experience in clinical and in population/preventive
health, in managing and interpreting group surveillance information,
and in the care and management of respiratory illness (Document ID
2178, Attachment 1, p. 5).

APHA commented that:

. . . different members of the health team may provide different
required services through referral or other arrangements, but the
designated PLHCP should have responsibility for program oversight
and coordination (Document ID 2178, Attachment 1, p. 5).

    As discussed further in the summary and explanation of Medical
Surveillance, OSHA agrees that different tasks may be performed by
various PLHCPs, according to their licenses, but has determined that
requiring a license for independent practice and the extra training and
responsibilities advocated by APHA are neither necessary nor
appropriate for the PLHCP in OSHA standards. Any PLHCP may perform the
medical examinations and procedures required under the standard when he
or she is licensed, registered, or certified by state law to do so. Who
qualifies to be a PLHCP is determined on a state-by-state basis by
state licensing bodies. OSHA's broad definition for PLHCP gives the
employer the flexibility to retain the services of a variety of
qualified licensed health care professionals. Moreover, since the term
PHLCP includes more than just physicians, it addresses concerns about
the limited availability of medical providers in rural areas (e.g.,
Document ID 2116, Attachment 1, p. 43; 2365, p. 10).
    OSHA has included the same definition for PLHCP in other standards
and continues to find that it is appropriate to allow any individual to
perform medical examinations and procedures that must be made available
under the standard when he or she is appropriately licensed by state
law to do so and is therefore operating under his or her legal scope of
practice. PLHCP, as defined and used in this standard, is consistent
with other recent OSHA standards, such as chromium (VI) (29 CFR
1910.1026), methylene chloride (29 CFR 1910.1052), and respiratory
protection (29 CFR 1910.134). OSHA's experience with PLHCPs in these
other standards supports the Agency's determination.
    ``Regulated Area'' means an area, demarcated by the employer, where
an employee's exposure to airborne concentrations of respirable
crystalline silica exceeds, or can reasonably be expected to exceed,
the PEL. The definition is unchanged from the proposed standard. This
definition is consistent with the use of the term in other OSHA
standards, including those for chromium (VI) (29 CFR 1910.1026), 1,3-
butadiene (29 CFR 1910.1051), and methylene chloride (29 CFR
1910.1052).
    OSHA proposed the inclusion of regulated areas in the standards for
both construction and general industry/maritime, but has not included
this provision, or the associated definition, in the final standard for
construction. Construction industry stakeholders should instead refer
to paragraph (g)(1)(iv) for written exposure control plan requirements
to describe procedures for restricting access.
    Several stakeholders, including the Construction Industry Safety
Coalition (CISC) and National Association of Home Builders, requested
that OSHA clarify what ``reasonably expected'' means (e.g., Document ID
2296, p. 25; 2319, p. 89). CISC argued that ``[s]uch subjective
language is not enforceable and . . . will be fraught with compliance
problems . . .'' (Document ID 2296, p. 25; 2319, p. 89).
    As noted above, the language in the regulated areas definition has
been included in a number of previous OSHA standards. Based on OSHA's
experience with these standards, OSHA expects that employers will have
little difficulty understanding the meaning of the phrase ``reasonably
be expected to exceed.'' One reason OSHA chooses to utilize language
that has been used in previous standards, where possible, is to avoid
the sort of confusion CISC describes. In addition, the basis for
establishing regulated areas in general industry and maritime and the
reason for omitting this requirement in the construction standard are
discussed in further detail in the summary and explanation of Regulated
Areas.
    ``Respirable crystalline silica'' means quartz, cristobalite, and/
or tridymite contained in airborne particles that are determined to be
respirable by a sampling device designed to meet the characteristics
for respirable-particle-size-selective samplers specified in the
International Organization for Standardization (ISO) 7708:1995: Air
Quality--Particle Size Fraction Definitions for Health-Related
Sampling. The definition in the rule is very similar to the proposed
definition with one modification. OSHA changed the wording from ``means
airborne particles that contain quartz, cristobalite, and/or tridymite
and whose measurement is determined by a sampling device . . .'' to
``means quartz, cristobalite, and/or tridymite contained in airborne
particles that are determined to be respirable by a sampling device . .
.'' to make it clear that only that portion of the particles that is
composed of quartz, cristobalite, and/or tridymite is considered to be
respirable crystalline silica.
    The definition for respirable crystalline silica encompasses the
forms of silica (i.e., quartz, cristobalite, and tridymite) covered
under current OSHA standards and harmonizes the Agency's practice with
current aerosol science and the international consensus that the ISO
convention represents. The American Conference of Governmental
Industrial Hygienists (ACGIH) and the European Committee for
Standardization (CEN) have adopted the ISO criteria for respirable
particulate collection efficiency, and the criteria are sometimes
referred to as the ISO/CEN definition. NIOSH has also adopted the ISO
definition in its Manual of Sampling and Analytical Methods (Document
ID 0903, p. 2). Adoption of this definition by OSHA allows for
workplace sampling for respirable crystalline silica exposures to be
conducted using any particulate sampling device that conforms to the
ISO criteria (i.e., a device that collects dust according to the
particle collection efficiency curve specified in the ISO standard).
The relationship between the ISO criteria for respirable particulate
collection efficiency and the ACGIH criteria is discussed in greater
detail in

the Sampling and Analysis discussion in Chapter IV of the FEA.
    The U.S. Chamber of Commerce (the Chamber), Halliburton, and the
National Rural Electric Cooperative Association (NRECA) asserted that
OSHA's proposed definition of respirable crystalline silica would
encompass non-respirable particles (Document ID 2288, p. 15; 2302, p.
7; 2365, p. 12). NRECA stated:

. . . the proposed definition would include anything that gets
collected onto the sampling media from respirable-particle size-
selective samplers. Unfortunately, these samplers are not fool-proof
and often much larger sized particles do make their way into the
sampling media; that is, they collect total crystalline silica dusts
rather than just the respirable portions. This definition will
include all total dusts that make their way through the cyclone and
into the sampling media, thus suggesting a much larger exposure than
is otherwise the case . . . (Document ID 2365, p. 12).

    As indicated in the discussion of the feasibility of measuring
respirable crystalline silica exposures in Chapter IV of the FEA, there
is currently no sampling device that precisely matches the ISO criteria
in capturing respirable dust. However, available research indicates
that many existing devices can achieve good agreement with the ISO
criteria. When operated correctly, the sampling devices do not collect
total dusts; they collect only the respirable fraction.
    The Chamber and NRECA also argued that OSHA's proposed definition
of respirable crystalline silica would include substances other than
crystalline silica (Document ID 2288, p. 15; 2365, p. 12; 3578, Tr.
1138). NRECA stated:

    An additional concern with the definition is that it states
``any particles that contain quartz, cristobalite, and/or tridymite
. . .'' It is possible to interpret this portion of the definition
to mean that any other mineral/impurities that were able to be
collected into the sampling media will be counted/weighed as opposed
to just the silica portions . . . (Document ID 2365, p. 12).

In addition, American Industrial Hygiene Association (AIHA) indicated
that the proposed definition would include the entirety of a sample of
dust containing any miniscule but detectable quantity of quartz,
cristobalite or tridymite, and recommended revising the definition
(Document ID 2169, pp. 2-3).
    OSHA recognizes that the proposed definition could have been
misunderstood to encompass components of respirable dust particles
other than quartz, cristobalite, and tridymite. This was not the
Agency's intent, and, in response to these comments, OSHA has revised
the definition to clarify that only the portion of the particles
composed of quartz, cristobalite, or tridymite is considered to be
included in the definition of respirable crystalline silica.
    Ameren Corporation supported OSHA's inclusion of quartz and
cristobalite and allowing the use of a sampling device designed to meet
the characteristics for respirable particle size-selective samplers
specified in ISO 7708:1995 in the definition, but indicated that the
definition should be limited to a ``percentage of 1% or greater''
(Document ID 2315, p. 3). However, it did not provide a rationale for
why OSHA should include this in the definition. Including such a
limitation in the definition of respirable crystalline silica would
have the effect of limiting coverage of the rule to situations where
crystalline silica concentrations in a mixture exceed the 1 percent
threshold. As discussed in the summary and explanation of Scope and
Application, OSHA concludes that it is not appropriate to limit
coverage of the rule to situations where concentrations of crystalline
silica in a mixture exceed a 1 percent threshold.
    The Society for Protective Coatings (SSPC) and the National
Automobile Dealers Association recommended that OSHA distinguish
between amorphous silica and crystalline silica in the definition
(Document ID 2120, p. 2; 2358, p. 5). SSPC also provided a link to a
Web page (http://www.crystallinesilica.eu/content/what-respirable-crystalline-silica-rcs) to guide the Agency on revising the definition.
OSHA finds that the term ``crystalline'' is sufficiently descriptive
and does not merit further explanation in the definition. However, the
Agency affirms here that fused quartz and other forms of amorphous
silica are not considered crystalline silica under the rule.
    The SEFA Group (formerly the Southeastern Fly Ash Company)
suggested adding a definition for ``free respirable crystalline
silica'' to describe crystalline silica as an independent structure
with varying surface chemistry, as distinguished from crystalline
silica that is incorporated into a larger matrix of the parent mineral
(Document ID 2123, p. 2). OSHA has revised the definition to clarify
that respirable crystalline silica includes only the crystalline silica
contained in airborne particles, i.e., the component in dust that is
crystalline silica and not some other mineral. The Agency does not
agree that defining the term ``free respirable crystalline silica''
will alter the meaning or enhance the clarity of the rule, and has not
added this term.
    ``Specialist'' means an American Board Certified Specialist in
Pulmonary Disease or an American Board Certified Specialist in
Occupational Medicine. The term is used in paragraph (i) of the
standard for general industry and maritime, (paragraph (h) of the
standard for construction), which sets forth requirements for medical
surveillance. For example, paragraph (i)(7)(i) of the standard for
general industry and maritime, (paragraph (h)(7)(i) of the standard for
construction) requires that the employer make available a medical
examination when specialist referral is indicated in the PLHCP's
written medical opinion for the employer.
    The proposed rule did not include this term in the Definitions
paragraph because it only allowed referral to an American Board
Certified Specialist in Pulmonary disease, which was clearly addressed
in the Medical Surveillance paragraph of the rule. However, several
commenters recommended that OSHA expand the types of specialists to
whom employees could be referred. For example, Dow Chemical requested
that OSHA not require the pulmonary specialist to be board certified to
expand availability of specialists and noted that several OSHA
standards, such as benzene and 1,3-butadiene, do not require the
specialist to be board certified (Document ID 2270, pp. 5-8). The Glass
Association of America, Asphalt Roofing Manufacturers Association,
North American Insulation Manufacturers Association, ATS, and BCTD
requested that OSHA also allow referral to an occupational medicine
specialist, with many of them specifying a board certified occupational
medicine specialist (Document ID 2215, p. 9; 2291, p. 26; 2348,
Attachment 1, p. 40; 3577, Tr. 778; 4223, p. 129).
    OSHA is retaining the requirement for board certification to ensure
a high level of competency. However, OSHA is persuaded by comments and
testimony that individuals who are either American Board Certified in
Occupational Medicine or American Board Certified in Pulmonary Disease
are recognized specialists qualified to examine patients referred for
possible respirable crystalline silica-related diseases. OSHA concludes
that both pulmonary disease and occupational medicine specialists are
qualified to counsel employees regarding work practices and personal
habits that could affect their respiratory health, consistent with
recommendations in Section 4.7.2 in ASTM standards E 1132-06, Standard
Practice for Health Requirements Relating to Occupational

Exposure to Respirable Crystalline Silica and E 2626-09, Standard
Practice for Health Requirements Relating to Occupational Exposure to
Respirable Crystalline Silica for Construction and Demolition
Activities (Document ID 1466, p. 5; 1504, p. 5). OSHA therefore added
the definition to allow referrals to providers who are American Board
certified in pulmonary disease or occupational medicine. The addition
of the term to definitions also allows OSHA to simply refer to
``specialist'' when referring to American Board certified pulmonary
disease and occupational medicine specialists in the medical
surveillance paragraph of the rule.
    ``Assistant Secretary,'' ``Director,'' and ``This section'' are
also defined terms. The definitions are consistent with OSHA's previous
use of these terms in other health standards and have not changed since
the proposal, which elicited no comments.
    Finally, stakeholders suggested that OSHA define a number of new
terms, including: ``affected employee'' (American Iron and Steel
Institute (AISI) (Document ID 2261, p. 4)), ``aged silica'' (the
Sorptive Minerals Institute (Document ID 3587, Tr. 3698-3699)),
``asphalt milling'' (IUOE (Document ID 2262, pp. 23-24)), ``chest
radiograph'' (NIOSH (Document ID 2177, Comment B, pp. 40-41)),
``controlling employer'' (BAC and BCTD (Document ID 2329, p. 7; 2371,
pp. 38-40)), ``each employee'' or ``each affected employee'' (AISI
(Document ID 3492, p. 3)), ``earth moving'' (IUOE (Document ID 2262,
pp. 6-9, 15)), ``earth moving equipment'' (IUOE (Document ID 3583, Tr.
2356-2360; 2262, pp. 6-9, 15)), ``estimating respirable dust,
excessive'' (Industrial Hygiene Specialty Resources (Document ID 2285,
p. 7)), ``gross contamination'' or ``grossly contaminated'' (ORCHSE,
AFS, and NAHB (Document ID 2277, p. 4; 3584, Tr. 2669-2671; 3487, pp.
21-22; 2296, p. 29; 2379, Attachment B, p. 32)), ``grossly'' (Tile
Council of North America (Document ID 2363, p. 6)), ``intermittent
work'' (EEI (Document ID 2357, p. 14)), ``respirable dust'' (AFS
(Document ID 2379, Attachment B, pp. 16, 28)), ``safety and health
professional technician'' (Dr. Bird of the Chamber (Document ID 3578,
Tr. 1176-1177)), ``short duration'' (EEI (Document ID 2357, p. 14)),
and ``silica exposure'' (AIHA (Document ID 2169, p. 5)).
    OSHA has concluded that these terms do not need to be defined in
the rule. Many of the terms were part of the proposal or were included
in stakeholder's comments on the proposal, but do not appear in the
rule. For example, the proposed rule contained a provision related to
protective work clothing in regulated areas that would have been
triggered where there is potential for employees' work clothing to
become grossly contaminated with finely divided material containing
crystalline silica. As discussed in summary and explanation of
Regulated Areas, OSHA has not included a requirement for employers to
provide protective work clothing or other means of removing silica dust
from clothing in the rule, and the rule does not otherwise use the
terms ``grossly,'' ``gross contamination,'' or ``grossly
contaminated.'' Therefore, there is no reason to define these terms.
    OSHA concludes that many of the other terms that stakeholders asked
the Agency to define are sufficiently explained in the preamble or
their meanings are clear. For example, OSHA explains the term
``affected employee'' in the summary and explanation of Exposure
Assessment. Because the term only appears in paragraphs (d)(6) and (7)
of the standard for general industry and maritime (paragraphs
(d)(2)(vi) and (vii) for construction) and is thoroughly explained in
the summary and explanation, OSHA concludes that it need not be defined
in this section.
    Specified Exposure Control Methods. OSHA's standard requires
employers engaged in construction to control their employees' exposure
to respirable crystalline silica. Paragraph (c) of the standard for
construction describes the specified exposure control methods approach.
This approach includes ``Table 1: Specified Exposure Control Methods
When Working With Materials Containing Crystalline Silica,'' a table
identifying common construction tasks known to generate high exposures
to respirable crystalline silica and specifying appropriate and
effective engineering controls, work practices, and respiratory
protection for each identified task. For each employee engaged in a
task identified on Table 1, the employer is required to fully and
properly implement the engineering controls, work practices, and
respiratory protection specified for the task on Table 1, unless the
employer assesses and limits the exposure of the employee to respirable
crystalline silica in accordance with paragraph (d) of the standard for
construction. If the employer fully and properly implements the
engineering controls, work practices, and respiratory protection
specified for each employee engaged in a task identified on Table 1,
the employer is not required to conduct exposure assessments or
otherwise comply with a PEL for those employees. If the employer does
not follow Table 1 for employees engaged in identified tasks or if the
respirable crystalline silica-generating task is not identified on
Table 1, the employer must assess and limit the exposure of employees
in accordance with paragraph (d) of the standard for construction.
Paragraph (d) of the standard for construction imposes requirements
similar to OSHA's traditional approach of requiring employers to
demonstrate compliance with a PEL through required exposure assessments
and controlling employee exposures through the use of feasible
engineering controls and work practices (i.e., the hierarchy of
controls) (see the summary and explanation of Alternative Exposure
Control Methods for further discussion of this approach).
    The concept for the specified exposure control methods approach was
included in the proposed rule. OSHA also included a version of Table 1
in the proposed rule for construction employers, identifying specific
engineering controls, work practices, and respiratory protection for
common construction tasks that employers could use to meet the
requirement to implement engineering and work practice controls.
Employers fully implementing the engineering controls, work practices,
and respiratory protection on Table 1 would not have been required to
conduct exposure assessments for employees performing a listed task,
but would have been required to comply with the 50 [micro]g/m\3\ PEL
for those employees. For tasks where respirator use was to be required,
employees were presumed to be exposed above the PEL, and thus the
proposed standard would have required the employer to comply with all
provisions that would be triggered by exposure above the PEL (e.g.,
regulated areas, medical surveillance), except for exposure monitoring.
    Prior to the NPRM, OSHA included this alternative compliance
approach in the Preliminary Initial Regulatory Flexibility Analysis
(PIRFA) provided to small business representatives during the Small
Business Regulatory Enforcement Fairness Act (SBREFA) process (Document
ID 0938, pp. 16-17). Participants in the SBREFA process generally
supported the approach and their comments further informed the Agency
in developing the proposed rule (Document ID 0937, pp. 37-39). An
alternative compliance approach similar to that developed by OSHA for
the SBREFA process was also included in ASTM E 2625-09, Standard
Practice for Controlling Occupational Exposure to Respirable
Crystalline Silica for Construction and Demolition Activities, a
consensus standard issued in May

2009 developed by a committee consisting of both labor and industry
representatives for crystalline silica exposures in construction
(Document ID 1504). Following this, on December 10, 2009, the Advisory
Committee on Construction Safety and Health (ACCSH) recommended that
OSHA include the specified exposure control methods approach in its
proposed rule (Document ID 1500, p. 13).
    The approach of specifying a list of tasks with a corresponding
list of controls to simplify compliance in the construction industry
received wide support from representatives in government, including the
National Institute for Occupational Safety and Health (NIOSH);
professional organizations, including the American Industrial Hygiene
Association (AIHA) and the American Society of Safety Engineers (ASSE);
labor, including the International Union of Operating Engineers (IUOE),
the Building and Construction Trades Department of the AFL-CIO (BCTD),
the Laborers' Health and Safety Fund of North America (LHSFNA), and the
International Union of Bricklayers and Allied Craftworkers (BAC); and
industry groups, including the Associated General Contractors of New
York State, the Edison Electric Institute (EEI), and the National
Asphalt Pavement Association (NAPA) (e.g., Document ID 2177, Attachment
B, p. 23; 3578, Tr. 1028; 2339, p. 8; 3583, Tr. 2337-2338; 2371,
Attachment 1, p. 22-23; 3589, Tr. 4192-4193; 2329, pp. 5-6; 2145, pp.
4-5; 3583, Tr. 2171; 2357, p. 26). Walter Jones, an industrial
hygienist representing LHSFNA, testified that the approach ``not only
makes compliance . . . easier to determine, enforce, and teach, it also
assures acceptable levels of healthfulness'' (Document ID 3589, Tr.
4193).
    Industry trade associations, such as the Construction Industry
Safety Coalition (CISC), Leading Builders of America (LBA), the
Mechanical Contractors Association of America, and individual
construction employers, including Atlantic Concrete Cutting, Inc. and
Holes Incorporated, generally supported the overall approach while
being critical of the specifics of Table 1 (e.g., Document ID 4217, p.
20; 2367, p. 2; 2338, p. 3; 2269, pp. 21-22; 2143, pp. 2-3). CISC
stated that its group of employers ``continues to be appreciative of
OSHA's efforts to try to make a simple compliance option . . . for
construction employers'' (Document ID 4217, p. 20).
    One commenter, Francisco Trujillo, safety director for Miller and
Long, Inc., suggested that the specified exposure control methods
approach to compliance in the construction industry is not a substitute
for safety professionals and industrial hygienists conducting exposure
assessments and selecting the appropriate engineering controls, work
practices, and respiratory protection for each task based on the
results. He commented that ``[t]he implication that if Table 1 is
followed everything will be fine is unrealistic . . .'' and recommended
that Table 1 be at most non-mandatory guidance (Document ID 2345, p.
4).
    OSHA agrees that safety professionals and industrial hygienists
play a key role in ensuring the safety of employees exposed to silica
during certain activities, including those not listed on Table 1, and
can also help ensure that the engineering controls, work practices, and
respiratory protection specified on Table 1 are fully and properly
implemented. However, as discussed below, the Agency is not persuaded
that construction employees will always be better protected by the
traditional performance approach of establishing a PEL and requiring
periodic exposure assessments, particularly when the tasks and tools
that cause high exposures to respirable crystalline silica, and the
dust control technologies available to address such exposures, can be
readily identified.
    Although there was general agreement among commenters that an
alternative approach was needed to simplify compliance for the
construction industry, commenters provided various opinions on how such
an alternative compliance approach should be structured to ensure that
it was workable in practice. Several commenters, including BCTD,
LHSFNA, EEI, LBA, Fann Contracting, Inc., CISC, ASSE, the National
Association of Home Builders (NAHB), the Associated Builders and
Contractors (ABC), and Holes Incorporated, urged OSHA to exempt
employers complying with Table 1 from also complying with the PEL
(e.g., Document ID 2371, Attachment 1, p. 26; 4223, p. 92-94; 4207, p.
3; 2357, p. 26; 2269, pp. 21-22; 2116, Attachment 1, p. 29; 2319, pp.
123-124; 2339, pp. 8-9; 2296, p. 41; 2289, p. 7; 3580, Tr. 1364). Holes
Incorporated and ABC suggested that employers would not use an approach
that required compliance with both the PEL and specified engineering
controls (Document ID 3580, Tr. 1364; 2289, p. 7). The National Utility
Contractors Association (NUCA) argued that not linking the actions on
Table 1 directly to compliance with the regulation was confusing and
would make it difficult for contactors to be certain they are in
compliance (Document ID 2171, p. 2). ASSE suggested that Table 1 should
constitute compliance with the PEL because the listed controls ``can be
viewed as akin to implementing all technologically feasible controls''
(Document ID 2339, pp. 8-9). BCTD commented that the focus of OSHA's
enforcement efforts should be on ensuring that employers have fully and
properly implemented the controls listed on Table 1 (Document ID 2371,
Attachment 1, p. 26).
    Similarly, commenters from both industry and labor, including the
American Federation of State, County, and Municipal Employees,
Mechanical Contractors Association of America, the American Federation
of Labor and Congress of Industrial Organizations, BAC, BCTD, and
LHSFNA, also argued that exposure assessments should not be required
where employers implement control measures specified on Table 1 for
construction tasks (e.g., Document ID 2106, p. 3; 2143, pp. 2-3; 2256,
Attachment 2, p. 10; 2329, pp. 5-6; 2371, Attachment 1, pp. 6-7; 4207,
p. 2). LHSFNA stated that:

. . . air monitoring is less practical in construction, where the
jobsite and work is constantly changing, than in general industry
where work exposures are more stable. In construction, air
monitoring results often come back from the lab after the task has
ended and thus are of little value . . . (Document ID 2253, p. 2).

    On the other hand, other commenters, including NIOSH, argued that
fully implementing the controls described on Table 1 would not
automatically provide a sufficient level of confidence that exposures
are adequately controlled; employers would also need to ensure that the
exposures of employees performing Table 1 tasks would not exceed the
revised PEL (e.g., Document ID 2177, Attachment B, p. 17). Mr.
Trujillo's comment emphasizing the role of safety professionals and
recommending that Table 1 be at most non-mandatory guidance was to the
same effect (Document ID 2345, p. 4).
    Several commenters, including Fann Contracting, IUOE, LBA, CISC,
Charles Gordon, a retired occupational safety and health attorney, Arch
Masonry, Inc., and NUCA argued that as proposed, the alternative
compliance option would not necessarily simplify compliance for some
employers, as they would still need to do exposure assessments for a
variety of reasons, such as monitoring employees working in the
vicinity of Table 1 tasks, complying with the PEL, providing monitoring
data to controlling employers on multi-employer worksites, and
complying with the rule for tasks

that are not listed on Table 1 (Document ID 2116, Attachment 1, p. 3;
2262, pp. 44-45; 2269, pp. 21-22; 2319, p. 6; 3538, p. 16; 3580, Tr.
1473-1474; 3587, Tr. 3677-3679; 3583, Tr. 2243).
    Other commenters supported the inclusion of exposure assessment
requirements for employees performing tasks on Table 1 even where
employers implement the specified engineering controls, work practices,
and respiratory protection to best protect employees in the
construction industry. The Center for Progressive Reform commented
that:

[t]he same principles that weigh in favor of a requirement to
monitor silica exposure in other industries holds for the
construction industry--monitoring gives workers, employers, OSHA,
and researchers valuable information that can be used to reduce
workplace hazards (Document ID 2351, p. 11).

    The International Safety Equipment Association (ISEA) opined that
the most protective approach for employees is for employers to take air
samples of respirable crystalline silica (Document ID 2212, p. 1). AIHA
argued that there remained a need for exposure monitoring to verify
that the controls in place for Table 1 tasks actually reduce exposures
(Document ID 2169, p. 3). NIOSH recommended periodic exposure
monitoring requirements for these tasks to provide a sufficient level
of confidence that exposures are adequately controlled and that the
employers' selection of equipment, maintenance practices, and employee
training were effective (Document ID 2177, Attachment B, pp. 17, 26).
Charles Gordon proposed that when performing a Table 1 task, employers
should be required to semi-annually monitor each task and keep records
of that monitoring to ensure that workers are not exposed to high
levels of respirable crystalline silica (Document ID 3539; 3588, Tr.
3801).
    After reviewing the comments on this issue, OSHA concludes that the
best approach for protecting employees exposed to respirable
crystalline silica in the construction industry is to provide a set of
effective, easy to understand, and readily implemented controls for the
common equipment and tasks that are the predominant sources of exposure
to respirable crystalline silica. OSHA is persuaded by comments and
data in the record that requiring specific engineering controls, work
practices, and respiratory protection for construction tasks, in lieu
of a performance-oriented approach involving a PEL and exposure
assessment, is justified for several reasons so long as employers fully
and properly implement the engineering controls, work practices, and
respiratory protection specified on Table 1.
    First, the controls listed on Table 1 represent the feasible
controls identified in the record for each listed task, and there is
substantial evidence that demonstrates that, for most of the Table 1
tasks, exposure to respirable crystalline silica can be consistently
controlled below 50 [micro]g/m\3\ using those controls (see Chapter IV
of the Final Economic and Regulatory Flexibility Analysis (FEA)). As
such, Table 1 provides a less burdensome means of achieving protection
at least equivalent to that provided by the alternative exposure
control methods that include the 50 [micro]g/m\3\ PEL, which OSHA has
determined to be the lowest feasible exposure level that could be
achieved most of the time for most of the tasks listed on Table 1. For
example, as discussed in Section 5.7 of Chapter IV of the FEA, exposure
data demonstrates that the engineering controls and work practices
specified on Table 1 for stationary masonry saws (wet cutting)
significantly reduce employees' exposures to respirable crystalline
silica from a mean of 329 [micro]g/m\3\, when cutting masonry dry, to a
mean of 41 [micro]g/m\3\. Additionally, the record developed during the
rulemaking process has contributed greatly to the Agency's
understanding of the effectiveness of the prescribed controls. Based on
the record, OSHA is confident that exposures will be adequately
controlled using the specified methods supplemented with appropriate
respiratory protection for those few tasks that are very difficult to
control using engineering controls and work practices alone.
    Second, this approach recognizes and avoids the challenges of
characterizing employee exposures to crystalline silica accurately in
many construction tasks while also ensuring that employees are
protected. In manufacturing settings and other more stable environments
subject to the general industry standard, exposure assessment can
provide an accurate depiction of the silica exposure that could be
typically expected for employees in normal operating conditions. In
general, such assessments need not be repeated frequently, costs are
therefore minimized, and the results will be timely even if there is a
delay for lab processing. In contrast, the frequent changes in
workplace conditions that are common in construction work (e.g.,
environment, location), along with potential time-lags in the exposure
assessment process, provide a compelling argument for the specified
exposure control methods approach that emphasizes clear and timely
guidance capable of protecting the employees during their shifts
instead of relying on a minimum exposure assessment requirement to
characterize employee exposures.
    Third, requiring employers to implement specified dust controls
absent an additional PEL requirement simplifies compliance for
employers who fully and properly implement the engineering controls,
work practices, and respiratory protection listed on Table 1.
Simplifying compliance will also encourage employers performing tasks
listed on Table 1 to use this approach, rather than the alternative of
performing exposure assessments and implementing dust controls, as
required by paragraph (d) of the standard for construction, and thus,
will also reduce regulatory burden on construction employers of all
sizes. For this reason, OSHA expects that the vast majority of
construction employers will choose to follow Table 1 for all Table 1
tasks.
    Fourth, this approach will also create greater awareness of
appropriate controls, which may in turn facilitate better
implementation and compliance, by making it far easier for employees to
understand what controls are effective for a given task and what
controls the employer must provide. Employees can locate the task they
are performing on Table 1 and immediately see what controls are
required, along with any specifications for those controls. It will,
further, be clear if an employer is not providing the correct controls
or ensuring that they are being used appropriately.
    ``Fully and properly'' implementing the specified exposure control
methods. In order for employers to comply with paragraph (c) of the
standard for construction, they must ``fully and properly'' implement
the engineering controls, work practices, and respiratory protection
for each employee engaged in a task identified on Table 1. While
several commenters, including BAC and BCTD, supported this requirement
(e.g., Document ID 2329, p. 6; 2371, Attachment 1, p. 24), BCTD also
urged OSHA to clarify the meaning of ``fully and properly''
implementing the specified engineering controls and work practices on
Table 1 to ensure that employers know what is required of them and how
the standard will be enforced (Document ID 4223, p. 92; 2371,
Attachment 1, p. 27-29).
    Other commenters provided suggestions for what they believed should
be considered ``fully and properly implementing'' the controls
specified on Table 1. NIOSH recommended that OSHA provide checklists
and require a daily evaluation

of engineering controls to determine if the controls are performing as
designed and to ensure that employees using the controls are trained
and have the appropriate materials to operate the controls properly
(Document ID 2177, Attachment B, pp. 21-22). IUOE recommended that
regular inspections of engineering controls in enclosed cabs should be
required (Document ID 2262, p. 29). Anthony Bodway, Special Projects
Manager at Payne & Dolan, Inc., representing NAPA, testified that his
paving company uses a daily maintenance checklist to ensure that the
controls are functioning properly and meeting the standards set by the
equipment manufacturers (Document ID 3583, Tr. 2194-2197). AIHA
suggested that OSHA require employers to follow the manufacturer's user
instructions for installation, use, and maintenance of engineering
controls, unless there is a written variance from the manufacturer
(Document ID 2169, p. 5). Charles Gordon argued that OSHA should
require a competent person to evaluate the use of the controls
specified on Table 1 initially and periodically in order to ensure that
they are fully and properly implemented (Document ID 4236, p. 4). In
general disagreement with these comments, the National Stone, Sand, and
Gravel Association (NSSGA) argued that, while employers should conduct
routine maintenance of the controls, OSHA should not require an
employer to complete an evaluation or inspection checklist of controls
or work practices at a certain frequency (Document ID 2327, Attachment
1, p. 21).
    Although the specified exposure control methods approach affords
compliance flexibility for the employer, OSHA sees value in reminding
employers and employees that this option will only be protective if
they take steps to ensure that the engineering controls, work
practices, and respiratory protection are as effective as possible.
Thus, the Agency is requiring employers to fully and properly implement
the specified engineering controls, work practices, and respiratory
protection for each employee performing a task described on Table 1 in
order to be in compliance with paragraph (c)(1) of the standard for
construction. To do otherwise would undermine the entire basis for this
compliance approach.
    Merely having the specified controls present is not sufficient to
constitute ``fully and properly'' implementing those controls.
Employees will not be protected from exposure to respirable crystalline
silica if the specified engineering controls, work practices, and
respiratory protection are not also implemented effectively. In order
to be in compliance with paragraph (c)(1) of the standard for
construction, employers are required to ensure that the controls are
present and maintained and that employees understand the proper use of
those controls and use them accordingly.
    While OSHA has decided not to further define ``fully and properly''
by providing specific checklists for employers or requiring employers
to conduct inspections at set intervals, there are several readily
identifiable indicators that dust controls are or are not being fully
and properly implemented, many of which are discussed with regard to
specific equipment and tasks in Chapter IV of the FEA and in the
discussions of specific controls that appear further below in the
section. For example, for dust collection systems, the shroud or
cowling must be intact and installed in accordance with the
manufacturer's instructions; the hose connecting the tool to the vacuum
must be intact and without kinks or tight bends that would prevent the
vacuum from providing the air flow recommended by the tool
manufacturer; the filter(s) on the vacuum must be cleaned or changed as
frequently as necessary in order to ensure they remain effective (it
may be necessary to activate a back-pulse filter cleaning mechanism
several times during the course of a shift); and dust collection bags
must be emptied as frequently as necessary to avoid overfilling, which
would inhibit the vacuum system from operating effectively. For water-
based dust suppression systems, an adequate supply of water for dust
suppression must be available on site. For worksites without access to
a water main, a portable water tank or water truck having enough water
for the task must be provided. The spray nozzles must be working
properly to produce a spray pattern that applies water at the point of
dust generation and inspected at regular intervals to ensure they are
not clogged or damaged. All hoses and connections must be inspected as
necessary for leaks that could signal that an inadequate flow rate is
being delivered.
    Manufacturer's instructions can also provide information about how
to fully and properly implement and maintain controls. For example, the
operator's instruction manual for EDCO concrete/asphalt saws provides a
pre-start checklist that includes information about the proper
functioning of wet-cutting equipment (Document ID 1676, p. 5). In some
cases, industry associations and employers, in collaboration with
equipment manufacturers, have also developed best practices with regard
to the full and proper implementation of engineering controls, work
practices, and respiratory protection for their particular industry or
operation. For example, NAPA and the Association of Equipment
Manufacturers (AEM) provided operational guidance for water systems
during milling operations that includes pre-operation inspection
activities, preparations for safe operation, and other operation
considerations (Document ID 2181, p. 52).
    In addition, paragraph (g) of the standard for construction
requires employers to establish and implement a written exposure
control plan, which includes provisions for a competent person to make
frequent and regular inspection of job sites, materials, and equipment
in order to implement the plan (see the summary and explanation of
Written Exposure Control Plan for discussion about this requirement).
Thus, the requirement for a written exposure control plan and the
competent person, which was added to the final standard for
construction, provides additional safeguards for ensuring that
employers fully and properly implement Table 1.
    OSHA expects that in most instances it will be straightforward for
a designated competent person to identify whether the controls have
been fully and properly implemented. For example, a significant amount
of visible dust being frequently or continuously emitted from the
material being worked on can serve as an indication that controls are
not fully and properly implemented. A small amount of dust can be
expected even with new equipment that is operating as intended by the
manufacturer. The amount of visible dust associated with the new dust
controls should be noted when equipment is put into service and checked
periodically. A noticeable increase in dust emissions would indicate
that the dust control system is not operating as intended.
    Employees engaged in Table 1 tasks. Commenters expressed concerns
about the lack of requirements in the proposed rule to protect
employees assisting with Table 1 tasks or working in the vicinity of
others engaged in Table 1 tasks (e.g., Document ID 2116, Attachment 1,
pp. 2-3). In response, OSHA has clarified the language in paragraph
(c)(1) of the standard for construction to encompass all employees
``engaged in a task identified on Table 1.'' This phrasing is intended
to include not only the equipment operator, but also laborers and other
employees who are assisting with the task or have some

responsibility for the completion of the task, even if they are not
directly operating the equipment. For example, where an employee is
assisting another employee operating a walk-behind saw indoors by
guiding the saw and making sure that the cutting is precise, that
employee would be considered to be engaged in the task and would need
to wear a respirator. Similarly, employees assisting a jackhammer task
would be considered to be engaged in the task and would also be
required to wear a respirator if they engaged in the task outdoors for
more than four hours in a work shift.
    It is not OSHA's intent, however, for all employees who are in the
vicinity of a listed task to be considered ``engaged in the task.'' To
protect the other employees in the vicinity of a listed task, the
employer must account for the potential exposures of these employees to
respirable crystalline silica as part of its written exposure control
plan. As discussed in the summary and explanation of Written Exposure
Control Plan, paragraph (g)(1)(iv) of the standard for construction
requires a description of the procedures used to restrict access to
work areas, when necessary, to limit the number of employees exposed
and their exposure levels. Employers must develop procedures to
restrict or limit access when employees in the vicinity of silica-
generating tasks are exposed to excessive respirable crystalline silica
levels. Such a situation might occur in a variety of circumstances,
including when an employee who is not engaged in the task, but is
working in the vicinity of another employee performing a Table 1 task
requiring respiratory protection, is exposed to clearly visible dust
emissions (e.g., an employee directing traffic around another employee
jackhammering for more than four hours in a shift). In that case, the
competent person, as required under paragraph (g)(4) of the standard
for construction, would assess the situation in accordance with the
employer's procedures to determine if it presents a recognized hazard,
and if it does, take immediate and effective steps to protect employees
by implementing the procedures described in the written exposure
control plan. For the above example, this could include positioning the
employee directing traffic at a safe distance upwind from the dust-
generating activity.
    Table 1. As discussed above, paragraph (c)(1) of the standard for
construction includes ``Table 1: Specified Exposure Control Methods
When Working With Materials Containing Crystalline Silica,'' which
identifies 18 common construction equipment/tasks known to generate
high exposures to respirable crystalline silica. For each equipment/
task identified, Table 1 specifies appropriate and effective
engineering and work practice control methods. Some entries contain
multiple engineering controls and work practices. In those instances,
OSHA has determined that the specified combination of engineering
controls and work practices is necessary for reducing exposures and
requires employers to implement all of the listed engineering controls
and work practices in order to be in compliance. Some entries contain
multiple compliance options denoted with an ``OR'' (e.g., (c)(1)(ix),
(c)(1)(x), (c)(1)(xii), (c)(1)(xiii), (c)(1)(xv), and (c)(1)(xviii) of
the standard for construction). For those entries, OSHA has determined
that more than one control strategy could effectively reduce exposures
and permits the employer to decide which option could be best
implemented on the worksite. Table 1 also specifies respiratory
protection for those entries where OSHA has determined from its
analysis of technological feasibility it is needed to ensure employees
are protected from exposures to respirable crystalline silica. These
respirator requirements are divided by task duration (i.e., ``less than
or equal to four-hours-per-shift'' and ``greater than four-hours-per-
shift'').
    Table 1 in the final standard differs from Table 1 in the proposed
standard in a number of respects. As proposed, ``Table 1--Exposure
Control Methods for Selected Construction Operations,'' listed 13
construction operations that expose employees to respirable crystalline
silica, as well as control strategies and respiratory protection that
reduce those exposures. In developing Table 1 for the proposed
standard, OSHA reviewed the industrial hygiene literature across the
full range of construction activities and focused on tasks where
silica-containing materials were most likely to be fractured or abraded
and where control measures existed to offer protection against a
variety of working conditions. OSHA also included additional
specifications on proposed Table 1 to ensure that the strategies listed
were properly implemented and remained effective.
    Table 1 was the subject of many comments in the rulemaking record.
Commenters, such as BCTD, urged OSHA to reconsider its use of the
proposed term ``operation'' to describe the activities listed on Table
1 (Document ID 2371, Attachment 1, p. 23). Kellie Vazquez, on behalf of
Holes Incorporated and CISC, suggested that it would be helpful to
include more specifically-defined tasks, rather than broader operations
(Document ID 2320, pp. 8-9). In the same vein, BCTD suggested that OSHA
``revise [Table 1] to make clear that its focus is on particular silica
dust-generating tasks, not more broadly-defined operations'' as ``there
is an important distinction between specific tasks that may generate
silica dust and the employer's overall operation, which may include
different silica dust-generating tasks, requiring different controls''
(Document ID 2371, Attachment 1, p. 23). BCTD also recommended that, to
avoid confusion, Table 1 should specify that each task is being
performed on or with a material that contains silica (Document ID 2371,
Attachment 1, p. 24). Responding to both suggestions, OSHA has changed
the terminology used in Table 1 from ``Operation'' to ``Equipment/
Task'' to clarify that the controls apply to silica-generating
activities done by employees and silica exposure generated by
equipment, and has revised the title of Table 1 accordingly to
``Specified Exposure Control Methods When Working with Materials
Containing Crystalline Silica.''
    Other commenters requested that OSHA include additional activities
on Table 1. The Sheet Metal Air Conditioning Contractors National
Association (SMACNA) commented that using powder-actuated tools should
be added (Document ID 2226, p. 2), and the Interlocking Concrete
Pavement Institute (ICPI) suggested that OSHA include compacting
pavers, sweeping sand into paver joints, and compacting the aggregate
base (Document ID 2246, pp. 2, 11). NAHB noted that Table 1 failed to
cover hand-mixing concrete (Document ID 2334, p. 4). OSHA did not
receive data showing that employees engaged in many of these additional
minor tasks (pulling concrete forms, mixing concrete for post holes,
etc.) experience significant routine exposure to respirable crystalline
silica above the action level that would require their employers to
comply with provisions of this rule. Because OSHA does not currently
have data indicating that additional controls for these tasks would be
needed on a regular basis or would be effective, it has determined not
to include them on Table 1.
    OSHA recognizes the possibility that employers may later discover
that there are tasks that are not covered by Table 1 where they may
have difficulty meeting the PEL. If such cases arise, OSHA can address
them in several ways, including: considering technological or economic
infeasibility defenses, and applying its variance process--either
temporary or permanent, pursuant to which an

employer can apply to exclude an industry or process from enforcement
of the standard based principally on a showing that it is providing
equivalent protection for its workers.
    Several commenters requested that OSHA add tasks or activities and
equipment to Table 1 that are associated with general industry
operations such as asphalt plant operations, shale gas fracturing, and
artificial stone and granite countertop work (Document ID 2212, p. 2;
2116, Attachment 1, p. 28; 2244, p. 4). OSHA is not including these in
the construction standard for the reasons discussed in the summary and
explanation of Scope.
    NUCA requested that OSHA add underground construction, specifically
excavation, onto Table 1, stating:

    The nature of excavation underground construction is
continuously mobile. Exposure assessments take time to evaluate by a
lab, and in that time, the jobsite conditions will change or crews
will move to other sites. Test results simply could not be available
in enough time to be relevant to a particular jobsite. This not only
makes costly lab assessments irrelevant to particular sites, it also
does nothing to protect the workers on those sites (Document ID
2171, p. 2).

    OSHA's technological feasibility analysis for underground
operations (Section 5.12 of Chapter IV of the FEA) indicates that
employees performing activities not specific to tunneling, such as
grinding, hole drilling, or chipping, receive similar exposures from
their equipment as employees performing those same activities
aboveground in enclosed environments (e.g., indoors). As a result,
employers can comply with the dust control requirements of the standard
by fully and properly implementing the dust controls specified on Table
1 of the final standard for construction for those tasks. However, as
explained in the technological feasibility analysis cited above, OSHA
determined that it was not possible to develop a clear control
specification that would prove effective for most situations where
tunnel boring machines, road headers, and similar kinds of equipment
are used. Effective dust control for operations that use these kinds of
equipment consists of a combination of water sprays at the tunnel face
and along the conveyors that remove material from the face, general
dilution ventilation through the tunnel, local exhaust ventilation for
excavating equipment and conveyor transfer points, and enclosed cabs
for the operators. Dust control may also require enclosures for
conveyors and belt cleaning mechanisms. Designing effective and
efficient dust control systems must take into account specific factors
of the tunnel project and equipment being used, and are analogous to
dust control strategies used in underground mines, as described in
NIOSH's Handbook for Dust Control in Mining (Document ID 0887). Given
the degree of complexity and project-specific considerations that
should be taken into account, OSHA determined that it was not possible
to devise an effective specification applicable to all tunnel projects
and thus has not added an entry for tunnel boring in underground
construction to Table 1.
    Likewise, although abrasive blasting is a common source of silica
exposure in construction, OSHA does not include an entry for abrasive
blasting on Table 1 for reasons explained more fully below. As
described in the Introduction to Chapter IV of the FEA, the tasks
included on Table 1 of the final rule are those that have been widely
recognized as high-exposure tasks in construction, and for which there
has been considerable research performed on the effectiveness of dust
control strategies. The record indicates that the tasks reflected in
Table 1, with few exceptions such as underground construction and
abrasive blasting, are the tasks that employers will most frequently
need to address to ensure employee protection from crystalline silica
hazards. For tasks not included on Table 1 that foreseeably generate
silica exposures above the action level, construction employers will,
in accordance with paragraph (d) of the standard for construction, need
to conduct an exposure assessment and maintain exposures at or below
the PEL through use of the traditional hierarchy of controls.
    Commenters also weighed in on OSHA's general approach to selecting
the engineering controls and work practices for each task. LBA argued
that there was a disconnect between the feasibility evidence and the
controls and work practices included on Table 1 (Document ID 2269, p.
17). NAHB urged OSHA to ensure that the protection methods included on
Table 1 are based on verifiable studies that show effective solutions
(Document ID 2296, p. 28). BCTD also opined that only ``control
measures supported by good quality evidence should be listed on Table
1'' (Document ID 2371, Attachment 1, p. 24).
    OSHA agrees that the engineering controls, work practices, and
respiratory protection specified on Table 1 need to be consistent with
the evidence presented in its technological feasibility analyses (see
Chapter IV of the FEA). To that end, OSHA has based the specifications
on Table 1 on extensive exposure data collected from a variety of
sources including NIOSH reports, data submitted to the record, OSHA's
compliance case files, and published literature.
    Requirements for water delivery systems and dust collection
systems. OSHA is requiring the use of an integrated water delivery
system supplied by the equipment manufacturer for several types of
equipment listed on Table 1: Stationary masonry saws; handheld power
saws (any blade diameter); walk-behind saws; drivable saws; rig-mounted
core saws or drills; handheld grinders for uses other than mortar
removal; and walk-behind milling machines and floor grinders. OSHA is
requiring the use of systems that are developed in conjunction with the
tool because they are more likely to control dust emissions effectively
by applying water at the appropriate dust emission points based on tool
configuration and not interfere with other tool components or safety
devices.
    CISC commented that the requirement for an integrated water system
limited options for employers and may reduce the use of the table,
stating ``. . . if a construction employer finds a way to effectively
deliver water through another mechanism, in the CISC's view that should
be encouraged'' (Document ID 2319, p. 103; 2320, p. 16). OSHA expects
that most employers will use integrated water systems, as provided by
manufacturers, and will follow Table 1 but its intent is not to
prohibit the use of other dust suppression methods during cutting.
Employers may implement other controls or wet method configurations if
they determine that the alternative control is more appropriate for
their intended use. However, employers who choose to use controls not
listed on Table 1 will be required to conduct exposure assessments and
comply with the PEL in accordance with paragraph (d) of the standard
for construction.
    CISC also questioned the appropriateness of requiring an integrated
water delivery system when most integrated systems are intended to keep
the blade cool and are not designed for dust suppression (Document ID
2319, p. 103; 2320, p. 16). In written testimony, Rashod Johnson of the
Mason Contractors Association of America stated that

the vast majority of masonry saws provide water on the blade itself.
This is solely for the purpose of keeping the blade cool during
cutting. A side effect, just happens to be dust suppression. Now,
manufacturers of these saws are starting to explicitly state that
the water used is for cooling the blade only and

should not be used to suppress dust (Document ID 2286, p. 2).

    However, product literature from five major saw manufacturers
(Andreas Stihl, Husqvarna, Hilti, Makita USA, and Wacker Group)
highlights the use of water application equipment to suppress dust in
addition to blade cooling (Document ID 3998, Attachment 12a, pp. 9, 15-
16; 3998, Attachment 12e, p. 3; 3998, Attachment 12f; 3998, Attachment
12g, p. 5; 3998, Attachment 12h, p. 8). For example, Stihl's manual for
the model 410 and 420 cut-off machines (handheld masonry saws)
specifically recommends a water flow rate for dust suppression
(Document ID 3998, Attachment 12a, pp. 9, 15-16). Furthermore, Stihl is
not the only cut-off saw manufacturer to state that water used with its
product is intended to suppress dust emissions. Husqvarna's product
literature for the K 3000 Wet describes the product as a power cutter
for wet applications that is equipped with a dust extinguisher system
(Document ID 3998, Attachment 12f, p. 1). Hilti also recognizes that
water suppresses dust and recommends the use of wet cutting to reduce
dust in its instruction manual for the Hilti DSH 700/DSH 900 model
handheld masonry saws (Document ID 3998, Attachment 12e, p. 3).
    CISC asked that OSHA clarify whether there needs to be a separate
integrated water delivery system in addition to the system provided by
the manufacturer to keep the blade cool (Document ID 2319, p. 104).
Beamer et al. (2005) conducted experiments to observe the differences
in the various wet cutting methods available and found that the
greatest improvement in dust reduction occurred with freely flowing
water applied at a rate of 48 gallons per hour (0.8 gallons per
minute), resulting in dust reduction of about 93 percent and confirming
the benefits of water flowing over the stationary saw cutting blade
compared with other misting systems (Document ID 1555, p. 509). That,
in addition to the manufacturer information submitted to the record,
indicates that the existing water systems for blade cooling are
effective at respirable dust capture and will satisfy the requirements
under paragraphs (c)(1)(i) through (c)(1)(xviii) of the standard for
construction where integrated water systems are required. Therefore,
OSHA has determined that, where water-based dust suppression can be
used with tools and equipment, those that are equipped with an
integrated water delivery system are effective and the best available
technology for controlling respirable crystalline silica. A separate
integrated water delivery system in addition to the system provided by
the manufacturer to keep the blade cool is not required.
    OSHA is requiring the use of a commercially available dust
collection system (i.e., local exhaust ventilation (LEV)) for several
types of equipment listed on Table 1, including: handheld power saws
for fiber cement board (with a blade diameter of 8 inches or less),
handheld and stand-mounted drills (including impact and rotary hammer
drills), jackhammers and handheld power chipping tools (as an
alternative to a water delivery system), handheld grinders for mortar
removal, and handheld grinders for uses other than mortar removal (as
an alternative to a water delivery system). OSHA's intent is to ensure
that employers use equipment that is appropriately designed for the
tool being used and that will be effective in capturing dust generated
from using the tool.
    CISC opposed OSHA's requirement for commercially available systems,
stating ``[t]his specification eliminates specialty manufactured
products that may be equally effective'' (Document ID 2320, p. 11).
However, CISC did not provide examples or describe what is meant by
``specialty manufactured products.'' It is not OSHA's intent to prevent
employers from using products that are custom made by aftermarket
manufacturers (i.e., made by someone other than the original tool
manufacturer) which are intended to fit the make and model of the tool
and designed to meet the particular needs and specifications of the
employer purchasing the product. These systems are designed to work
effectively with the equipment and not introduce new hazards such as
obstructing or interfering with safety mechanisms. The ``commercially
available'' limitation is meant only to eliminate do-it-yourself on-
site improvisations by the employer. An employer is free to improvise
and use controls that are not commercially available. However, those
systems would not meet the requirements of Table 1 and the employer
will be required to conduct exposure assessments and comply with the
PEL in accordance with paragraph (d) of the standard for construction.
    In Table 1 of the proposed rule, OSHA would have required dust
collection systems be equipped with High-Efficiency Particulate Air
(HEPA) filters, which are 99.97 percent efficient in capturing
particles having an aerodynamic diameter of 0.3 [mu]m or larger. In the
final standard, OSHA is not requiring the use of HEPA filters and
instead is requiring the use of filters with a capture efficiency of 99
percent or greater for respirable particulate. Although OSHA received
comments and testimony in support of using HEPA filters to capture
silica dust (Document ID 1953, pp. 3-4; 1973, pp. 2-3), extensive
comments were submitted to the record expressing concern regarding this
requirement.
    Occupational and Environmental Health Consulting Services, Inc.
(OEHCS) noted the numerous deficiencies found with HEPA filtration from
ineffective seals, deterioration of the filter, and inadequate testing
prior to use, which often results in employee exposure to potentially-
hazardous particles and possible recontamination of the work
environment (Document ID 1953, Attachment 1). The Precast/Prestressed
Concrete Institute (PCI), NUCA, and LBA noted that HEPA filters do not
work well in the construction environment because filters will clog up
quickly and must be changed often (Document ID 2276, p. 10; 3729, p. 3;
2269, p. 23). CISC noted that HEPA filters will typically not last an
entire shift, stating that they clog up quickly and need to be
monitored and changed frequently (Document ID 2320, p. 114).
Consequently, CISC asserted, HEPA filters are not effective at
filtering respirable dust or at reducing exposures to respirable silica
(Document ID 2319, p. 95).
    OSHA reached the same conclusion in its technological feasibility
finding for mortar and concrete grinding as well (see Section 5.11 of
Chapter IV of the FEA). Finding that best practices may counsel toward
the use of HEPA-rated filters in the case of grinding, and particularly
mortar grinding, OSHA nonetheless determined that under field
conditions HEPA filters may rapidly clog, leading to an increase in
static pressure drop and loss of the airflow needed for LEV to
effectively capture silica dust at the point of generation (Document ID
0731, pp. 375, 384).
    OSHA is persuaded that it should not require that dust collection
systems be equipped with HEPA filters because HEPA filters in some
applications will result in loss of airflow and concomitant degradation
of dust-capture efficiency. In examining manufacturers' specifications
for many commercially-available dust collectors, OSHA finds that most
offer, in addition to HEPA filters, other filters with a 99 percent
efficiency or better in the respirable-particle-size range. Many
examples of products equipped with filters that do not meet HEPA
specifications but nevertheless meet the requirement for 99 percent
efficiency in the respirable-particle-size range were submitted to the

record and include the EDCO Vortex 2000 (captures 99 percent of 0.5
[micro]m or larger particles) (Document ID 4073, Attachment 4a, Row
55), the iQ 360x stationary saw (99.5 percent, particle size
unspecified) (Document ID 4073, Attachment 4a, Row 58), a Porter-Cable
vacuum (99.85 percent, particle size unspecified) (Document ID 3998,
Attachment 13p), the Bosch 3931A (99.93 percent of 3 [micro]m
particles) (Document ID 3998, Attachment 10, p. 29), the CS Unitec
(99.93 percent of 0.3 [micro]m particles) (Document ID 4073, Attachment
4a, Row 99), and the Dustless 16-gallon collector (``almost HEPA,''
filters to 0.5 [micro]m particles) (Document ID 4073, Attachment 4a,
Row 211). A filter efficiency of at least 99 percent allows for longer
tool usage, compared to one with a HEPA filter, before significant
drops in airflow of the dust collection system. Furthermore, as
explained above, requiring that dust collectors be equipped with HEPA
filters can cause rapid airflow drop, reducing dust capture efficiency
at the shroud or hood and exposing employees to high respirable dust
and silica concentrations. Therefore, OSHA has decided not to require
HEPA filters on Table 1 for dust collection systems and instead
requires that dust collectors have a filter with 99 percent or greater
particle capture efficiency. Employers should consult with their
suppliers to determine the dust collection equipment that will best
suit their needs for a given application.
    OSHA also received many specific comments about particular changes
to the notes and additional specifications, associated with the entries
on Table 1, and on the specified engineering and work practice control
methods identified for each entry, which are further discussed later in
this section.
    Notes and additional specifications on Table 1. Several commenters
responded to the appropriateness of including the notes and additional
specifications in the individual entries on Table 1. OSHA included
these in the proposed rule to ensure that the strategies listed were
properly implemented and remained effective.
    Some commenters stated that the notes were too detailed, while
others argued that the notes were not detailed enough (Document ID
2319, p. 6; 2262, p. 29; 3581, Tr. 1631-1632; 3585, Tr. 2924-2925,
3052-3053; 4223, pp. 95-97). Several commenters expressed concern that
certain notes were unrealistic or too confusing for an employer to
comply with. CISC stated that the inclusion of the notes left Table 1
``unworkable'' for most employers in the construction industry
(Document 2319, p. 6). Others questioned whether these additional
specifications were a mandatory component of Table 1 or simply
suggested guidelines to help determine the efficacy of the control
(Document ID 2296, p. 28; 3441, pp. 4-5). On the other hand, some
commenters asserted that the additional specifications were needed on
Table 1 to ensure that controls are properly operated and effective
(Document ID 3589, Tr. 4286-4287; 3581, Tr. 1631-1632; 4223, pp. 95-
97).
    To balance the need to clarify how the specifications apply to make
Table 1 workable with the need to provide more specific information
about the controls in order to ensure that they are effective, OSHA has
removed most of the notes and additional specifications from the
individual entries on Table 1 and has instead included revised
specifications for the controls in paragraph (c)(2) of the standard for
construction. This approach has the added benefit of making Table 1
more readable because specifications that apply to multiple rows can
now be addressed in a single subparagraph.
    Paragraph (c)(2)(i) of the standard for construction requires
employers to provide a means of exhaust as needed to minimize the
accumulation of visible airborne dust for tasks performed indoors or in
enclosed areas. When tasks are performed indoors or in enclosed areas,
the dispersal of dust can be impeded such that concentrations can build
up without the aid of forced ventilation. Flanagan et al. (2006)
concluded that the degree to which a work area is enclosed is an
important determinant of employee exposure based on data demonstrating
increased exposures to respirable crystalline silica for enclosed
environments (those with two to four walls, as well as those having
walls, a roof, and windows), as compared to outdoor environments
(Document ID 0677, pp. 148-149). Increased exposures to respirable
crystalline silica were also demonstrated for tasks listed on Table 1
in enclosed areas, such as jackhammering inside a large pool area
(Document ID 3958, Rows 1064, 1065, 1066) and handheld sawing in a
large garage building open in front and closed on three sides (Document
ID 3777, p. 65).
    Sufficient air circulation in enclosed or indoor environments is
important to ensure the effectiveness of the control strategies
included on Table 1 and to prevent the accumulation of airborne dust.
The ``means of exhaust'' necessary to minimize the accumulation of
visible airborne dust could include dilution ventilation through the
use of portable fans that increase air movement and assist in the
removal and dispersion of airborne dust, which would otherwise remain
in the enclosure and contribute to elevated exposures. To be effective,
the ventilation must be implemented so that movements of employees, or
the opening of doors and windows, will not adversely affect the
airflow.
    Paragraph (c)(2)(ii) of the standard for construction requires
employers, for tasks performed using wet methods, to apply water at
flow rates sufficient to minimize release of visible dust generated by
the task. BCTD and LHSFNA encouraged OSHA to specify minimum flow rates
for water where there are data or studies to support such a
recommendation (Document ID 3581, Tr. 1632; 3589, Tr. 4286-4287). NIOSH
recommended a flow rate of 0.5 L/min for handheld power saws based on
experimental data and recommended that OSHA specify a minimum water
flow rate of 300 mL/minute for jackhammers based on a field study of
control equipment fabricated specifically for the study (Document ID
2177, Attachment B, pp. 19, 33; 0867, p. 6). Water has been proven an
efficient engineering control method to reduce exposures to airborne
crystalline silica-containing dust. Adequate dust capture is dependent
on a variety of factors such as dust particle size, velocity, spray
nozzle size and location, use of surfactants or other binders, and
environmental factors (water hardness, humidity, weather, etc.) that
must be considered when implementing wet methods. Water flow rates
suggested by various studies, while perhaps instructive, may not be
applicable to all of the different types of equipment that could be
used or the conditions that may be encountered by employers following
Table 1. Because the appropriate water flow rates for controlling
silica dust emissions can vary, OSHA is not establishing a required
flow rate for wet suppression systems or specifying a flow rate for
individual Table 1 entries.
    Paragraphs (c)(2)(iii)(A)-(F) of the standard for construction
require employers implementing measures that include an enclosed cab or
booth to ensure that the enclosed cab or booth is maintained as free as
practicable from settled dust, has door seals and closing mechanisms
that work properly, has gaskets and seals that are in good condition
and work properly, is under positive pressure maintained through
continuous delivery of fresh air, has intake air that is filtered
through a pre-filter that is 95 percent efficient in the 0.3-10.0
[micro]m range (e.g., MERV-16 or

better), and has heating and cooling capabilities.
    Dust can be unintentionally carried into enclosed cabs or booths
through a number of routes, including on employees' boots, during the
opening of doors when accessing or exiting the cab, through leaks in
the system, or when employees roll down windows. IUOE, recommending
that OSHA add specificity to the cab requirements (e.g., heating and
air conditioning, housekeeping), argued that without greater
specificity ``there is a grave danger that intended safeguards become
counterproductive as dust is re-circulated within the enclosures''
(Document ID 2262, pp. 29-33).
    Direct-reading instruments show that fine particle (0.3 micron
([mu]m) in size) concentrations inside operator cabs can be reduced by
an average of 93 percent when cabs are clean, sealed, and have a
functionally adequate filtration and pressurization system (Document ID
1563, p. 1). Cecala et al. (2005) studied modifications designed to
lower respirable dust levels in an enclosed cab on a 20-year-old
surface drill at a silica sand operation. The study found that
effective filtration and cab integrity (e.g., new gaskets, sealed
cracks to maintain a positive-pressure environment) are the two key
components necessary for dust control in an enclosed cab (Document ID
1563, p. 1).
    OSHA determined that the requirements specified in paragraphs
(c)(2)(iii)(A)-(F) of the standard for construction reduce the
likelihood of respirable crystalline silica exposure in enclosed cabs
or booths when employees are present by lowering the potential for dust
to be re-suspended inside the enclosure, promoting the ability of the
enclosed cab or booth to keep dust from entering through cracks or
openings (e.g., seals, gaskets, and closing mechanisms are present, in
good condition, and work properly), ensuring that the working
conditions in the cab are comfortable so that employees are less likely
to open the window of the cab, and ensuring that the fresh air provided
to the employee does not contain silica particles.
    IUOE also suggested that OSHA require employers to provide boot
brushes or mudflingers to minimize the dust brought into the cab, to
equip cabs with dust-resistant materials, and to affix warning labels
to the interior of the cab (Document ID 2262, p. 30; 4025, p. 17). The
Agency has not included these additional requirements since it expects
that the specifications in paragraphs (c)(2)(iii)(A)-(F) of the
standard for construction combined with frequent inspections by the
competent person will be sufficient to protect employees against the
potential respirable crystalline silica exposures within the enclosure.
    OSHA has not included more specific requirements in paragraphs
(c)(2)(i)-(c)(2)(iii) of the standard for construction (e.g.,
establishing a minimum face velocity, volumetric flow rate for air
movement, or a required number of air changes; flow rate for wet
suppression systems; or a frequency for the cleaning of cabs or
booths). However, as discussed in the summary and explanation of
Written Exposure Control Plan, paragraph (g)(1)(ii) of the standard for
construction requires the employer to establish and implement a written
exposure control plan that describes the engineering controls and work
practices used to limit employee exposure to respirable crystalline
silica. This description should include details such as the appropriate
means of exhaust needed to minimize the accumulation of visible
airborne dust for a particular task, the appropriate flow rate and
droplet size needed for wet suppression systems to minimize release of
visible dust, and the procedures for maintaining and cleaning an
enclosed cab or booth. Paragraph (g)(4) of the standard for
construction also requires a competent person to make frequent and
regular inspections of the jobsite, materials, and equipment (including
engineering controls) to implement the written exposure control plan.
    OSHA did not include specifications on visible dust and wet slurry,
included as notes in individual entries on proposed Table 1, in the
standard. The Agency has determined that these issues are best
addressed by other provisions of the standard, rather than as a note or
additional specification included in each relevant Table 1 entry.
Further discussion about these specifications is also included below.
    Many commenters expressed concern with the note, contained in
proposed Table 1 for all but two entries, requiring employers to
operate equipment such that no visible dust is emitted from the
process. Industry commenters, including the Power Tool Institute (PTI),
Western Construction Group, SMACNA, the Independent Electrical
Contractors, the Distribution Contractors Association, CISC, the
Utility and Transportation Contractors Association of New Jersey,
Atlantic Concrete Cutting, ABC, LBA, Holes Incorporated, and N.S. Giles
Foundations objected to this note, stating that it was an unrealistic
requirement which made Table 1 unworkable (e.g., Document ID 1973, pp.
2-9; 2183, p. 3; 2226, p. 2; 2250, p. 2; 2309, p. 4; 2319, pp. 97-98;
4217, p. 6; 2356, p. 2; 2367, p. 2; 2289, p. 7; 2269, p. 21; 3441, p.
5; 3598, pp. 1-2).
    Some industry commenters asserted that it is impossible to perform
tasks, such as sawing, grinding, and drilling, without generating any
visible dust (Document ID 2357, pp. 27-28; 3441, p. 6; 4073, Attachment
9e, p. 1). Holes Incorporated noted that when grinding or using other
hand-held pieces of equipment, the work cannot be performed with the
tool flush against the impacted surface, and at times, there will be a
gap and visible dust will be emitted even when local exhaust
ventilation or wet methods are utilized (Document ID 3441, p. 6).
    Other commenters expressed concern that there is no true dustless
system, clarifying that even those tools marketed as ``dustless''
produce some level of airborne dust (Document ID 2345, p. 4; 3585, Tr.
2960; 4216, pp. 2-3). Francisco Trujillo, safety director for Miller
and Long, stated that:

    Every ``dustless'' system I have ever witnessed has produced
some level of airborne dust. This fact alone should show that Table
1 sets criteria that are impossible to achieve . . . (Document ID
2345, p. 4).

    On the other hand, commenters, including NAPA and BAC, noted that
in their experience there is no visible dust generated when certain
equipment, such as asphalt machines for milling or stationary masonry
saws, is used with available dust controls (Document ID 3583, Tr. 2216;
3585, Tr. 3072). They did not, however, provide any indication that the
same results could be achieved with all of the other equipment listed
on Table 1.
    Several commenters provided a different rationale for their
objections to this note. AIHA opined that the requirement to operate
equipment such that no visible dust is emitted from the process is a
subjective determination and recommended it be removed from Table 1
entries (Document ID 3578, Tr. 1029-1030; 2169, p. 5). The Masonry and
Concrete Saw Manufacturers Institute (SMI) noted that ``[a]dding
requirements for . . . avoiding visible dust have not been researched
specific to respirable silica dust and may have no beneficial impact''
(Document ID 2316, p. 2). NAHB and Holes Incorporated expressed concern
that the requirement was a general dust rule, rather than regulating
crystalline silica since Table 1 doesn't specify whether ``no visible
dust'' refers to visible silica dust or just dust in general (Document
ID 2296, p. 29; 3580, Tr. 1355-1356).

    Not all industry commenters objected to the note on visible dust
contained in the proposed Table 1. ICPI supported a version of Table 1
that included the no-visible-dust requirement for nearly all of the
operations listed (Document ID 2352, pp. 4-8).
    Commenters from both industry and labor suggested revisions to
clarify the note and make it workable. LHSFNA believed the note was
needed to ensure the effective use of controls and was not too vague,
but acknowledged that the language could be clarified to say something
like ``visible dust should be minimized'' (Document ID 4207, p. 2).
BCTD also provided significantly revised language for the no-visible-
dust requirement. For those operations that involve cutting and
grinding on silica-containing substrate, BCTD suggested that, for wet
systems, Table 1 of the standard should require that water flow be
``sufficient to control the dust generated so that no visible dust . .
. is emitted from the process once the blade has entered the substrate
being cut'' and that the relevant note on Table 1 be revised to read:

    A small amount of visible dust may be present when the blade or
tool initially enters the substrate and when it is being removed at
the end of a task. However, if visible dust is present after the
blade or tool has entered the work surface/substrate, this is a sign
that the control is not working properly. The operation should be
stopped and the equipment and/or workers' cutting technique checked
and fixed (Document ID 4223, Appendix 1, p. 14).

    PTI's suggested revisions to Table 1 include a note for many of the
entries specifying that ``during operation, if excessive visible dust
is emitted from the process, immediately stop work and verify that the
dust control system is functioning properly'' (Document ID 1973, pp. 2-
9).
    While opinions varied widely on the utility of a no-visible-dust
requirement, no commenters suggested that excessive visible dust
generated from tasks abrading silica-containing materials (sawing,
grinding, etc.) does not present a risk of significant employee
exposure to silica. As noted above, BCTD confirmed that the presence of
visible dust after the blade or tool has entered the work surface/
substrate is a sign that the control method is not working properly
(Document ID 4223, Appendix 1, p. 14). PTI recommended that, when
excessive visible dust was present, work stop immediately until the
employer could verify the proper functioning of the control (Document
ID 1973, pp. 2-9).
    OSHA agrees that excessive visible dust is an indication that a
control's effectiveness may be compromised, but, after reviewing the
entire record on this point, has decided not to include a no-visible-
dust requirement for the Table 1 entries. Instead, it has concluded
that the purpose of such a requirement is best achieved by bolstering
other requirements in the rule, as it applies to construction. First,
OSHA considers the written exposure control plan to be centrally
important and expects employers to address signs that controls may not
be working effectively (e.g., dust is visible) as part of their written
exposure control plans required under paragraph (g) of the standard for
construction (see summary and explanation of Written Exposure Control
Plan for further discussion). Second, during the designated competent
person's frequent and regular inspections of job sites, materials, and
equipment to implement the written exposure control plan, as required
under paragraph (g)(4) of the standard for construction, OSHA expects
that person to make routine observations of dust generated from tasks
being conducted. Where increases in visible dust occur, the competent
person's assigned role is to take prompt corrective action (e.g., make
corrections or adjustments as needed).
    OSHA finds that the difference between the small amount of dust
generated when control measures are operated effectively and the large
amount of dust generated during tasks when control measures are not
used or not operated effectively can readily be observed. Several
videos presented in the record support this conclusion (e.g., Document
ID 4073, Attachment 4b). These videos demonstrate that when a task is
uncontrolled or inadequately controlled, a large dust plume can be
seen. When controls such as water or vacuum-based ventilation are used,
little dust is observable. These significant differences in the
observable dust generated during controlled and inadequately-controlled
tasks provide an opportunity for employers to readily detect poorly-
performing equipment and address these problems quickly. The principle
concern, however, is with a lot of visible dust, rather than any
visible dust, which is a concern for which the appropriate corrective
action is difficult to quantify or state in objective terms. Instead,
the presence of significant visible dust lends itself to a more
process-oriented control approach, as exemplified by the written
exposure control plan and competent person requirements. OSHA thus
concludes that the issue of visible dust is best addressed by the
requirement to fully and properly implement the controls specified on
Table 1, and the written exposure control plan and competent person
requirements, rather than as a note or additional specification
included in each Table 1 entry.
    Commenters also objected to the specification to prevent wet slurry
from accumulating and drying when implementing wet methods, as proposed
for several Table 1 entries. Both Holes Incorporated and NAHB objected
to the ambiguity of the requirement and presented concerns about how
employers on a construction site would comply with such a requirement
(Document ID 3441, p. 9; 2296, p. 28).
    Other commenters expressed concern regarding the disposal of silica
slurry (Document ID 2246, pp. 9-10; 3585, Tr. 2886; 2319, p. 94). ICPI
noted that employers have to expend extra effort to locate a place to
dispose of dust-filled slurry, which is not possible in some conditions
or locations (Document ID 2246, pp. 9-10). CISC described how slurry
created using wet-cutting methods outside can flow into storm drains,
potentially violating environmental regulations (Document ID 2319, p.
94). The Mason Contractors Association of America explained that in
California, silica slurry produced from wet cutting is classified as a
hazardous material, requiring contractors working in the state to
follow hazmat procedures for its disposal (Document ID 3585, Tr. 2886).
    However, NIOSH argued that since the vast majority of masonry saws
provide water on the blade itself to cool and lubricate the blade and
suppress dust, employers already have to deal with slurry when cutting
masonry and concrete (Document ID 4233, Attachment 1, p. 6). OSHA
agrees that the standard does not pose any new requirements regarding
the disposal of slurry on employers who already use wet methods for
sawing masonry products.
    OSHA concludes that any measures necessary to manage slurry in
order limit employee exposure to respirable crystalline silica (i.e.,
exposure that results from slurry drying and dust particles becoming
airborne) are best addressed through the employer's written exposure
control plan and competent person requirements, rather than as a note
or additional specification included in each Table 1 entry. These
requirements are discussed above and in the summary and explanation of
Written Exposure Control Plan.
    In several Table 1 entries, OSHA has included a requirement to
operate and maintain tools in accordance with

manufacturer's instructions to minimize dust emissions. This
requirement is intended to ensure that the controls are implemented
effectively to reduce exposures to respirable crystalline silica.
Manufacturer's instructions that influence the effectiveness of the
tool and controls with regard to minimizing dust emissions may include,
but are not limited to, additional specifications for water flow rates,
air flow rates, vacuum equipment, rotation of the blade, maintaining
and changing blades, and frequencies for changing water.
    Respiratory protection specified on Table 1. Industry associations,
including the American Subcontractors Association (ASA), the Institute
of Makers of Explosives (IME), the General Contractors Association of
New York (GCANY), and CISC, commented on the appropriateness of the
respirators that OSHA proposed for Table 1 (e.g., Document ID 2213, p.
2; 2187, p. 3; 2314, p. 2; 2319, p. 102). For example, ASA stated:

    OSHA's proposed Table 1 for construction would seem to suggest
that the Agency believes a construction employer can achieve the PEL
with engineering and work practice controls. Yet the Agency then
requires respiratory protection for 60 percent of the operations
listed in Table 1. This failure is even more perplexing since OSHA
failed to identify, obtain and/or cite sufficient data for its
conclusions with respect to the 13 operations addressed in Table 1
(Document ID 2187, p. 3).

GCANY explained in their comments that ``[c]urrent respiratory
protective equipment is cumbersome to wear and to work in and would
expose the worker to other hazards on a job site'' (Document ID 2314,
p. 2). CISC urged OSHA to ``eliminate the heavy use of respiratory
protection,'' arguing that:

    OSHA's reliance on respiratory protection is analytically
inconsistent with its position that it is technologically feasible
to reach the proposed PEL in most construction operations most of
the time, and particularly when the control measures specified in
Table 1 are used. Requiring such heavy use of respirators . . . will
serve as a significant barrier to effective use of [Table 1]
(Document ID 2319, p. 102).

    Respirator requirements on Table 1 of the final rule are based on a
review of all the evidence pertaining to exposure profiles and
available controls in the rulemaking record, including an evaluation of
the updated exposure profiles and evidence on available controls
submitted to the rulemaking record, as described in Chapter IV of the
FEA. A primary purpose of such evaluation was for OSHA to better
identify those situations where exposures above the PEL are likely to
persist despite full and proper implementation of the specified
engineering and work practice controls and supplemental respiratory
protection will therefore be necessary to ensure employees are
protected from silica-related health risks. As documented in its
analyses of technological feasibility for each Table 1 task, OSHA finds
that most of the time employees are performing tasks on Table 1,
respiratory protection will not be required. For most of the tasks or
equipment on Table 1, OSHA expects that work will be performed for four
hours or less and/or outdoors (see Chapter IV of the FEA). For certain
tasks listed on Table 1, OSHA was able to distinguish indoor
environments, where exposures are typically above 50 [micro]g/m\3\ even
with the use of engineering controls and work practices, from outdoor
environments, where engineering controls can typically maintain
exposures below 50 [micro]g/m\3\, in order to eliminate requirements
for respiratory protection where tasks are performed outdoors (e.g.,
using handheld grinders for uses other than mortar removal
(c)(1)(xii)). Elsewhere, OSHA was able to further refine the equipment
or tasks listed on Table 1 (e.g., handheld power saws (c)(1)(ii)-(iii);
walk-behind and drivable masonry saws (c)(iv)-(v); milling machines
(c)(1)(xiii)-(xv)) in order to eliminate previously proposed
requirements for respiratory protection. In other cases, OSHA found
engineering controls and work practices specified on Table 1 sufficient
to maintain employee exposures at or below 50 [micro]g/m\3\ when fully
and properly implemented (e.g., (c)(1)(i), (c)(1)(ix), (c)(1)(xiv)),
and thus determined that a respiratory protection requirement was not
necessary. Specific changes to the respiratory protection requirements
for each task listed on Table 1 are discussed in more detail below.
    Consequently, required respiratory protection under Table 1 is
limited to situations in which OSHA has determined that exposures over
50 [micro]g/m\3\ will often occur. For example, OSHA is not requiring
the use of respiratory protection when handheld power saws (any blade
diameter) are used outdoors, for less than four hours, with water-based
dust suppression systems because OSHA's exposure profile indicates that
exposures will be below 50 [micro]g/m\3\ TWA most of the time that saws
are used, given typical work patterns (e.g., outdoors for less than
four hours per shift) (see Section 5.6 of Chapter IV of the FEA). Data
submitted to the record by the Concrete Sawing and Drilling Association
(CSDA) (Document ID 3497) also show that wet sawing produces exposures
below 50 [micro]g/m\3\ TWA with typical use patterns during the work
shift. In contrast, indoor use of handheld wet power saws generates
frequent exposures in excess of 50 [micro]g/m\3\ TWA with typical use
patterns during the work shift; from OSHA's exposure profile, half of
the exposure samples associated with using handheld power saws indoors
exceed 50 [micro]g/m\3\ TWA, and two indoor samples included in the
data submitted by CSDA were above a TWA of 50 [micro]g/m\3\ (Document
ID 3497, p. 5). As a result, Table 1 requires supplemental respirator
use when handheld power saws are used indoors or in an enclosed area
with water-based dust suppression systems.
    OSHA has also used the terms ``indoors or in an enclosed area''
rather than ``indoors or within a partially sheltered area'' in order
to clarify that any requirement to use respiratory protection when the
task is performed under these conditions is limited to those areas
where the dispersal of dust can be impeded such that concentrations can
build up without the aid of forced ventilation. For example, a work
area with only a roof that does not impede the dispersal of dust would
not be considered ``enclosed,'' while it may have been considered by
some to be a ``partially sheltered area.''
    As a result of these modifications, OSHA expects that many fewer
employees will need to use respiratory protection than was the case for
the proposed rule, and respiratory protection will not be necessary for
the most commonly encountered work situations and environments
specified on Table 1.
    ISEA suggested that OSHA make the respirator requirements on Table
1 more user-friendly and performance-oriented by listing only an APF
and recommending that users consult the APF table found in the
respiratory protection standard, rather than listing generic respirator
types (Document ID 2212, p. 2). In response to this comment, OSHA has
maintained certain requirements for respiratory protection, but has
eliminated specific requirements for the type of respirator that must
be used (e.g., half-mask respirator, powered air-purifying respirator
(PAPR) with loose-fitting helmet or negative pressure full facepiece).
Instead, OSHA includes on Table 1 only the minimum Assigned Protection
Factor (APF) required. This change from the proposal provides the
employer with the option of determining which respirator offers the
best protection for its employees in the multitude of construction
environments

that may be encountered. However, this is only the minimum protection
factor required for the respirator, and employers have the flexibility
to provide a more protective respirator to those employees who request
one or require a more protective respirator based on the employer's
evaluation of the worksite. As discussed in the summary and explanation
of Respiratory Protection, paragraph (d)(3)(i)(A) of the respiratory
protection standard (29 CFR 1910.134), which includes a table that can
be used to determine the type or class of respirator that is expected
to provide employees with a particular APF, can help employers
determine the type of respirator that would meet the required minimum
APF specified by Table 1. In order to reflect this change to the
respirator requirements, the Agency has modified the heading on Table 1
to ``Required Respiratory Protection and Minimum Assigned Protection
Factor (APF).''
    The respirator requirements on Table 1 are divided by task
duration: ``less than or equal to four hours/shift'' and ``greater than
four hours/shift.'' AIHA recommended that OSHA clarify what time is
included when determining less than or greater than four hours
(Document ID 2169, p. 6). OSHA has determined that time starts when the
operator begins using the tool, and continues to be counted until he or
she completes the task. This time includes intermittent breaks in tool
usage and clean-up. For example, an employee cuts and places bricks,
one at a time, for three hours consecutively. The employee then spends
30 minutes cleaning up the saw and empting slurry or dust collectors.
All three hours spent cutting and laying bricks along with the 30
minutes for clean-up count. Tasks that are performed multiple times per
day, during distinct time periods, should be counted as separate tasks,
and times should be combined. For example, an employee cuts multiple
bricks for 15 minutes, lays bricks for two hours and returns to cut
more bricks for another 30 minutes. The two hours spent laying bricks
do not count towards the total time for compliance with Table 1.
    The duration of a task that generates respirable crystalline silica
influences the extent of employee exposure and, in some cases,
requirements for use of respirators. Some commenters suggested that
OSHA modify the time breakdown for activities and respirator usage,
such as BCTD's suggestion to divide tasks on Table 1 into two hours,
four hours, and eight hours. Other commenters such as CISC, Holes
Incorporated, and the Mason Contractors Association of America,
suggested that OSHA exclude short duration tasks (e.g., 90 minutes or
less) from Table 1, and NUCA suggested that the four hour cutoff is
arbitrary and had no data to support it (Document ID 4073, Attachment
14f, p. 2; 2319, pp. 100-102; 3580, Tr. 1453; 3585, Tr. 2882; 3729, p.
3).
    After reviewing these comments, OSHA has decided to maintain this
division in the standard. OSHA selected four hours as an appropriate
division point for respirator usage because it finds that employers and
employees can anticipate whether a task will take less than half of a
shift or more than half of a shift (as opposed to smaller time
intervals), and so can plan accordingly on the need for respirator use
on a given job. In addition, OSHA selected only a single durational
division for respirator tasks in all of the relevant Table 1 tasks to
avoid the confusion that could result from triggering mandatory
respirator use at different times for different tasks. OSHA also
determined that excluding short duration tasks from Table 1, although
included in the ASTM E 2625-09 consensus standard, was inappropriate,
given that employees engaged in a task listed on Table 1 are best
protected using the available engineering controls, work practices, and
respiratory protection specified for the task and are only exempt from
complying with the standard where employee exposure will remain below
25 [micro]g/m\3\ as a time-weighted average under any foreseeable
conditions (see summary and explanation of Scope for further discussion
of this exclusion).
    Table 1 of the proposed rule used the phrase ``4 hours per day'' to
indicate when respirators were required, but Table 1 of the final
standard uses ``4 hours per shift.'' OSHA's exposure data is largely
drawn from samples of employee exposure averaged over an 8-hour period,
which is a typical time for a shift. The proposed rule referred to a
time period of four hours ``per day'' for the purpose of limiting
employee's exposure during the normal 8-hour shift that most employees
work during a single day. OSHA recognizes, however, that some common
tasks such as jackhammering during nighttime highway construction may
occur during an 8-hour period that spans two calendar days (e.g., 8
p.m. until 4 a.m.). OSHA did not intend to allow employees to be
exposed to respirable crystalline silica without respiratory protection
for longer than four hours in that scenario, so OSHA has specified four
hours ``per shift'' in the final rule.
    OSHA also recognizes that the form and length of a shift may vary
such that an employee may have a break between work periods (e.g., four
hours on, two hours off, four hours on), work shifts may be longer than
eight hours, or employees may work double shifts within a single day.
The work periods in each of those examples constitutes a ``shift'' for
purposes of determining the maximum amount of time that an employee may
spend on one of the applicable Table 1 tasks without respiratory
protection. OSHA's exposure data is not sufficient to support the
conclusion that a longer duration of exposure without respiratory
protection would be safe just because that exposure is spread out over
a period that is longer than the normal 8-hour shift. Thus, an employee
who works a 12-hour shift from 8 p.m. to 10 a.m. with a 2-hour rest
break in the middle would have to wear a respirator if engaged in an
applicable Table 1 task such as jackhammering outdoors if the employee
will be jackhammering from 8 p.m. to 11 p.m., taking a break from 11
p.m. until 2 a.m., and then jackhammering again from 2 a.m. until 4
a.m. for a total of five hours of jackhammering. However, assuming no
other silica exposure, the employee would not require respiratory
protection if the jackhammering is limited to 8 p.m. until 11 p.m. and
2 a.m. until 3 a.m. for a total of four hours, even if the employee
repeats the same shift and jackhammering times every day of the week.
Accordingly, the change from ``per day'' to ``per shift'' clarifies
OSHA's original intention regarding when respirator use is required for
Table 1 tasks.
    The requirement to provide respirators for Table 1 tasks is based
on the anticipated duration of the task. Some commenters, such as EEI,
expressed confusion about how this requirement would apply to non-
continuous work (e.g., Document ID 2357, p. 27). EEI opined that:

    The nature of non-continuous work can also make it hard to
anticipate when a certain task may exceed four hours per day.
Suppose, for example, a job task using a stationary masonry saw is
not anticipated to last beyond four hours, so all controls listed in
Table 1 are followed, and the employee does not wear a respirator.
Then, due to unforeseen complications, the job lasts beyond four
hours. Simply following the regulations as proposed, it is unclear
whether the employee would be allowed to put on a half-mask after
four hours, or if OSHA will not allow the employer to use the Table
1 option because the employee was not in a half-mask for the first
four hours (Document ID 2357, p. 27).

In contrast, other commenters suggested that, despite the variable
nature of the work, employers and employees generally know how long it
will take to complete a particular task (e.g.,

Document ID 3581, Tr. 1684, 1686). OSHA recognizes, based on the
comments above and the nature of construction work in general, that
application of this requirement warrants some flexibility. For several
Table 1 tasks, respiratory protection with the appropriate APF is
required if the duration of a task is anticipated to exceed four hours,
but is not required if the duration of a task is less than or equal to
four hours (e.g., (c)(1)(ii), (c)(1)(x), (c)(1)(xii)). For these tasks,
the Agency does not expect employers to know exactly how long it will
take to perform a task. Rather, OSHA expects employers to make a good-
faith judgment of the task's anticipated duration over the work shift
based on previous experience and all other available information. If
the employer anticipates that an employee will be engaged in a task for
more than four hours, the employer must provide respirators (if
required by Table 1) to the employee at the beginning of the shift. For
example, in the case of an employee grinding concrete walls indoors,
the employer should know, in advance, the area of surface that is to be
worked on in the course of a shift. If, based on the employer's
experience, the time needed to grind that area is typically less than
four hours, the employer would not be required to provide respirators
to the employee. If, however, using the same example, the employer
experiences unforeseen difficulties that extend the task duration
beyond four hours, the employer would be required under Table 1 to
provide the listed respiratory protection as soon as it becomes evident
that the duration of the grinding task may exceed the 4-hour limit,
measured from the beginning of the task rather than the point when the
need for extra time becomes evident.
    Commenters, including BCTD, Fann Contracting, and IUOE, expressed
confusion about whether an employee must wear a respirator for the
entire duration of a task when that task is expected to last more than
four hours, or rather wear the respirator for only the portion of the
task that exceeds four hours (e.g., Document ID 3581, Tr. 1681; 2116,
Attachment 1, p. 28; 2262, p. 27). OSHA hereby clarifies that the
intent is to require respirator use throughout the duration of the
task.
    The objective of the silica standard is to limit an employee's
average exposure over a work shift. In each of OSHA's health standards,
this is accomplished by establishing a PEL expressed as an 8-hour TWA.
Because a PEL is a time-weighted average, the Agency has traditionally
required employees to use respirators throughout a shift when employees
work on a task or in an area where exposure to a hazardous substance
contributes significantly to an employee's exposure in excess of the
PEL at any point during that shift. This same reasoning applies to
wearing a respirator from the beginning of a shift where respirators
are required on Table 1. Thus, OSHA is continuing the same approach to
respirator use for tasks listed on Table 1 of the standard for
construction as it has for other OSHA health standards. Under Table 1
of the final standard for construction, when a respirator is required
only when a task is performed for more than four hours per shift and
when the employer estimates that the duration of the task will exceed
four hours, the employer must provide and ensure that a respirator is
used the entire time that task is performed over the shift, not just
during the time beyond the first four hours that the task is performed.
For example, if an employer anticipates that an employee will operate a
jackhammer outdoors for more than four hours, the employer must provide
respiratory protection with an APF of 10 and require that it be used
for the entire duration of the task. For tasks that are typically
intermittent, employers are required to estimate at the outset the
total time during the shift that the task itself will be performed and
provide respirators required by Table 1 based on that estimate. If an
employer knows from experience that an employee will perform a single
task listed on Table 1 for four hours or less during a single shift,
then the employer must ensure that the employee uses whichever
respirator is specified in the ``<= 4 hr/shift'' column on Table 1 (or
need not provide a respirator if no respirator is required on Table 1
for that duration). As another example, if a contractor needs to cut
four concrete walls using a handheld power saw (outdoors), and cutting
each wall typically takes 45 minutes to complete, for a total time of 3
hours, the employer would not be required by Table 1 to provide a
respirator. But if cutting each wall typically takes in excess of 60
minutes, the employer should expect that the total duration of the task
will exceed four hours and provide respirators as required under Table
1. The employer is required to provide respirators as soon as it
becomes evident that the duration of the task will exceed four hours.
Thus, in most situations an employee will be protected by a respirator
for all or the majority of a task that exceeds four hours because the
rate of progress on the task will become apparent to the employer early
on. An employee cannot be allowed to work more than four hours without
a respirator when one is required under Table 1 because the employer
will have certainty at that point that the task is exceeding four
hours.
    The above examples assume that employees are engaged in only one
task covered by Table 1 each shift. Paragraph (c)(3) of the standard
for construction requires that, where employees perform more than one
task on Table 1 during the course of a shift for a combined total of
more than four hours, employers must provide, for the entire duration
of each task performed, respiratory protection that is consistent with
that specified in the ``> 4 hr/shift'' column of Table 1, even if the
individual duration of each task is less than four hours. If no
respirator is specified for a task in the ``> 4 hr/shift'' column of
Table 1, then respirator use would not be required for that part of the
employee's shift. For example, if an employer plans to have his