Makita, DeWalt, Bosch, and Ostec all make grinding dust collection
systems (see Chapter IV of the FEA).
    The LEV-based exposure controls for surface grinding function
similarly to the LEV-based controls for mortar removal described in
paragraph (c)(1)(xi) of the standard for construction, as mortar
removal (tuckpointing) is simply a specialized form of grinding that
uses the same grinding tools. The factors that influence vacuum flow
rate for mortar removal (tuckpointing) are equally important to LEV
dust controls for all types of surface grinding, and for other hand-
operated power tools as well. Collingwood and Heitbrink note that
``vacuum cleaners will probably continue to be an important control
option for respirable dust exposures in construction for dust exposure
sources such as mortar removal, concrete grinding, hole drilling, and
brick cutting where water application is impractical'' (Document ID
0600, p. 884). Older studies of LEV effectiveness have found exposure
reductions of 86-99 percent (Document ID 0611, p. 463; 0247, pp. 6, 8).
A more recent study by Akbar-Khanzadeh et al. found silica dust
exposure reduced by 98-99 percent, depending on the vacuum type used
(Document ID 3609, p. 707). Akbar-Khanzadeh and Brillhart and Echt and
Sieber both reported reduced silica exposures when workers used LEV
shrouds with vacuum attachments during surface grinding, although the
silica exposure results were variable and some exceeded 50 [micro]g/
m\3\ even with use of the controls (Document ID 0521, pp. 344-345;
0632, pp. 459-460).
    OSHA received a number of comments about the proposed entry on
Table 1 for handheld (or hand-operated) grinders using LEV. The
proposed entry specified use of a grinder with a commercially available
shroud and dust control system. Several commenters questioned why
shrouds needed to be commercially available and whether appropriate
shrouds are, in fact, commercially available (e.g., Document ID 2319,
p. 105; 2316, p. 2; 2171, p. 9). Francisco Trujillo from Miller and
Long stated ``dust collection systems used on hand grinders received
very disappointing results. In fact, no hand grinder equipped with a
dust collection system was capable of bringing exposure levels below
the current [i.e., the preceding] PEL'' (Document ID 3585, Tr. 2963).
He further explained that this was due to the limited capabilities of
the dust collection systems maintaining complete surface contact during
the frequent grinding of columns and walls (Document ID 3585, Tr. 2963-
2964). However, he found that a vacuum system designed for use with
ceiling grinders ``greatly reduced the amount of dust expelled from the
process but did not completely eliminate it. It was a very, very dusty
activity, and now it's moderately so'' (Document ID 3585, Tr. 2962). He
reported that although all sampling results were below the preceding
PEL, three out of five samples were still above 50 [micro]g/m\3\. He
also reported that none of the hand grinders with dust controls that
Miller and Long evaluated were effective with columns and wall corners
and that even with these LEV systems, the same number of workers were
in Miller and Long's respiratory protection program (Document ID 3585,
Tr. 2962-2964, 3012).
    In Section 5.11 of Chapter IV of the FEA, OSHA's exposure profile
shows that 60 percent of ceiling grinders who perform overhead grinding
using LEV, and 50 percent of outdoor grinders using LEV or water have
achieved exposures below 50 [micro]g/m\3\, while 25 percent of other
grinders working indoors with LEV have achieved exposures below 50
[micro]g/m\3\. These results demonstrate that exposures of 50 [micro]g/
m\3\ or below are achievable with technology available at the time of
sampling. Much of the data in the exposure profile reflects samples
collected over ten years ago, before many of the engineering studies
described in the FEA were conducted. OSHA expects that capture
technology will continue to improve in response to market demand.
    In addition, Gerry Scarano, representing BAC, stated that since
2009, ``the availability and effectiveness of control options have
improved, adding force to OSHA's conclusion that it is feasible to
reduce the dust in most cases down to the proposed PEL'' (Document ID
3581, Tr. 1562). Thus, the effectiveness of controls available today is
likely higher than those that were used when the exposure samples
included in the exposure profile were obtained.
    SMI commented that there are no commercially available dust shrouds
that currently meet American National Standards Institute (ANSI) B7.1
(and OSHA) guard design requirements (Document ID 2316, p. 2). SMI
stated that available dust shrouds are plastic and are used in place of
the original equipment's steel guards but do not meet the requirements
of ANSI B7.1, which is a safety design specification standard for
grinding wheels (Document ID 2316, p. 2). However, NIOSH reported that
several major tool manufacturers sell grinders with integrated dust
shrouds designed to meet applicable safety standards, and the tools are
labeled accordingly. For example, the Underwriter's Laboratory

(UL) mark carried by the products of several manufacturers signifies
that their tools meet the requirements of ANSI/UL/CSA 60745-2-3, which
incorporates ANSI B7.1 by reference (Document ID 4233, Attachment 1, p.
8). Catalogs of tool manufacturers submitted to the docket by NIOSH
include grinders that meet this standard and other tools that bear the
SA approval mark of the Canadian Standards Association, an OSHA
Nationally Recognized Testing Lab (NRTL, described under 29 CFR 1910.7)
(Document ID 3998, Attachment 10, pp. 7-9, 15, 45). OSHA anticipates
that, once there is a market demand, additional tool manufacturers will
offer shrouds meeting these machine guarding requirements. OSHA finds
that compliant shrouds are already commercially available, and will not
create a greater hazard.
    In the proposed standard, OSHA specified that the dust collection
system must have an air flow of at least 25 cfm per inch of wheel
diameter. OSHA has maintained this requirement in the final standard.
CISC commented that for larger blades, it may be difficult to design
and operate a system that pulls air flow at 25 cfm per inch of blade
diameter (Document ID 2319, p. 105). NAHB also expressed concern that a
dust collector with a HEPA vacuum would need to be at least 112.5 cfm
for a small, 4.5-inch grinder (Document ID 2296, Attachment 1, p. 29).
PTI recommended revising the Table 1 entry for grinders to require use
of vacuums equipped with a HEPA filter that operates at 80 cubic feet
per minute or greater, noting that commercial dust collection systems
are typically rated at approximately 130 cfm (Document ID 1973, pp. 2-
3). BCTD, on the other hand, recommended that OSHA specify airflow
rates for grinder LEV based on blade diameter (Document ID 2371, p.
32). As explained above in the discussion of grinders used for mortar
removal, OSHA has determined that 25 cfm per inch of blade diameter is
more protective and consistent with established engineering principles
as reflected in the ACGIH Industrial Ventilation Manual, 28th Edition,
which generally expresses minimum cfm requirements for a variety of
(stationary) grinders in relation to the wheel diameter (Document ID
3883, pp. 13-147--13-152).
    To adequately capture debris during the grinding, OSHA is requiring
that dust collection systems used with grinders have a filter with 99-
percent or greater efficiency, along with either a cyclonic pre-
separator to collect large debris before the air reaches the filters or
a filter-cleaning mechanism. Because the same factors that cause air
flow to decline during tuckpointing affect air flow during other tasks
such as surface grinding, the measures discussed in the section on
grinders used for mortar removal also need to be used when surface
grinding to minimize filter clogging.
    Echt and Sieber reported respirable quartz concentrations ranging
from 44 [micro]g/m\3\ to 260 [micro]g/m\3\ during two to three hour
surface grinding tasks with LEV at a construction site. Each day, one
or two 18-pound bags of debris were collected in a vacuum cleaner. The
investigators measured actual air flow rates three times over the
course of five sampling days, reporting an air flow range from 86 to
106 cfm (Document ID 0632, pp. 459-460). As noted in the discussion of
LEV controls required for handheld grinders for mortar removal
(tuckpointing), Heitbrink and Santalla-El[iacute]as also reported that
air flow is affected by filter loading (Document ID 0731, p. 383).
Using more extensive measurements (continuous data logging every 8
seconds), Collingwood and Heitbrink evaluated the same vacuum model
used by Echt and Sieber and found that average initial air flow was 71
cfm, which declined to 48 cfm over the task-based work sessions, even
with knocking the dust from filters using the manufacturer's
recommended method as deemed necessary (Document ID 0600, p. 884). As
previously discussed, the accumulation of material and debris on the
filter (filter caking) during work causes pressure losses that
eventually limit air flows in even the most powerful vacuums. As debris
accumulates, the filter becomes caked with collected dust and air flow
decreases. Unless the filter is properly cleaned according to the
manufacturer's instructions, the air flows declines rapidly.
    OSHA included three additional specifications in the proposed
standard; two of these, preventing wet slurry from accumulating and
drying, and ensuring that visible dust was not emitted from the
process, were completely removed as described above. OSHA is retaining
the third specification, which requires employers to minimize the
accumulation of visible airborne dust when working indoors or in
enclosed areas by providing sufficient ventilation when needed; this
requirement is now located in paragraph (c)(2)(i) of the standard for
construction.
    In the proposed standard, OSHA required the use of a half-mask
respirator with an APF of 10 during wet grinding for more than four
hours. No respiratory protection was required when wet grinding for
four hours or less. When using a grinder equipped with a commercially
available dust collection system, OSHA required the use of a half-mask
respirator with an APF of 10 regardless of task duration. In the final
standard, OSHA has decided it is appropriate to distinguish between
respiratory protection needed when grinding outdoors and grinding
indoors or in enclosed areas. This division has allowed OSHA to more
appropriately apply the use of respirators, limiting the number of
tasks that requires their usage. Based on data in the record, OSHA
concludes that most employees using hand-operated grinders without
controls currently experience exposures above 50 [micro]g/m\3\ TWA.
However, when grinders are operated with dust collection or wet systems
outdoors, exposures will be reduced to or below 50 [micro]g/m\3\ most
of the time. The exposure profile in Table IV.5.11-B in Section 5.11 of
Chapter IV of the FEA shows that 50 percent of grinders working
outdoors using water or LEV are exposed below 50 [mu]g/m\3\. These
results demonstrate that silica exposures at or below 50 [mu]g/m\3\
have already been achieved for half of exposed workers with technology
available at the time of sampling. Much of the data in the exposure
profile reflects samples collected over ten years ago, before many of
the engineering studies described in the FEA were conducted. OSHA
expects that dust capture technology will continue to improve in
response to market demand. When fully and properly implemented, OSHA
expects that exposures to silica will be at or below 50 [mu]g/m\3\ most
of the time when water-based dust suppression or LEV systems are used
for outdoor grinding and that respiratory protection will not need to
be relied on to protect employees.
    The available data presented in Table IV.5.11-B in Section 5.11 of
Chapter IV of the FEA suggest that the mean indoor grinding exposure
level with dust collection systems is about twice that for grinding
outdoors, with 50 percent of exposures between 100 and 250 [micro]g/
m\3\. Exposures measured within a test chamber during grinding
operations confirm that high exposures result from grinding concrete
indoors, even with good dust collection equipment (Document ID 3609),
with mean task-based sample results generally falling between 100 and
200 [micro]g/m\3\. Based on the available data for indoor grinding,
OSHA concludes that, when grinding with a commercially available shroud
and dust collection system for four hours or less per shift, resulting

exposures should generally be no higher than grinding outdoors for a
full shift and thus should not necessitate the use of respiratory
protection. However, for indoor grinding tasks performed more than four
hours per shift, the Agency concludes that exposures will consistently
exceed 50 [micro]g/m\3\. Therefore, Table 1 requires respiratory
protection with an APF of at least 10 when grinding with dust
collection systems for more than four hours per shift indoors or in an
enclosed area.
    OSHA finds that there is inadequate evidence in the record to
demonstrate that wet grinding indoors or in an enclosed area is as
effective as using LEV. Accordingly, OSHA is permitting the use of
water-based dust control for grinding tasks outdoors only and is not
requiring the use of respiratory protection regardless of the duration
of the task. OSHA notes from its exposure profile that the vast
majority of exposure samples taken during indoor grinding where dust
controls were used made use of LEV systems rather than water-based dust
control systems (21 out of 23 samples) (see Section 5.11 of Chapter IV
of the FEA). If an employer decides to use a wet method for indoor
grinding, it will be operating outside of Table 1 and will have to
comply with the paragraph (d) alternative method of compliance.
    Walk-behind milling machines and floor grinders. Paragraph
(c)(1)(xiii) of the standard for construction requires walk-behind
milling machines and floor grinders used to grate or grind solid
surfaces (such as concrete, asphalt, masonry walls and sidewalks, see
Section 5.8 of Chapter IV of the FEA) to be equipped with an integrated
water delivery system that continuously feeds water to the cutting
surface, or with a dust collection system recommended by the
manufacturer of the milling machine or floor grinder, a filter with 99
percent or greater efficiency, and a filter-cleaning mechanism. When
using an LEV dust collector system indoors or in enclosed areas, Table
1 also requires that loose dust be cleaned with a HEPA-filtered vacuum
in between passes of the milling machine or floor grinder. Both options
require that the tool be operated in accordance with the manufacturer's
instructions to minimize dust emissions. No respiratory protection is
required by Table 1, regardless of task duration or work location.
    Paragraph (c)(1)(xiii) of the standard for construction covers
wheeled machines, equipped with a cutting tool, that are guided by hand
with the worker positioned more than an arm's length away from the
grinding action of the tool (e.g., milling machines, scarifiers, floor
grinders). Laborers or construction workers operate these machines
during specialty tasks such as resurfacing floors, repairing pavement,
or creating grooves for electrical cables (Document ID 0036, p. 15;
3958; 3959, p. 39). In the proposed standard, walk-behind milling
machines were included under the entry for ``Milling'' as ``walk-behind
milling tools.'' In response to commenters' recommendations, and
recognizing that suitable dust control measures differ among different
milling machines, OSHA has decided it is more appropriate to divide
milling activities into three subgroups: Walk-behind machines and floor
grinders, small drivable milling machines (less than half-lane), and
large drivable milling machines (half-lane and larger) (Document ID
3583, Tr. 2171, 2212-2213; 2181, pp. 4, 7, 9).
    Walk-behind milling machines and floor grinders are currently
available with water systems (e.g., Document ID 0524; 0642), and with
dust collection systems (e.g., Document ID 1276; 0636; 0642; 4073,
Attachment 4a, Rows 131-133, 150-152). Additionally, some scarifiers,
particularly those intended for indoor use, are available with both a
vacuum port (for connecting to a portable industrial vacuum system) and
a water mist system as standard equipment (Document ID 0642).
    In specifying the option for a machine equipped with an integrated
water delivery system that continuously feeds water to the cutting
surface, OSHA is not specifying a minimum flow rate for water used with
the integrated delivery system, but rather anticipates that the water
flow rates specified by the manufacturer will optimize dust reduction.
Evidence in the record demonstrates the effectiveness of wet methods to
control exposures when using walk-behind milling machines and floor
grinders. ERG (2000) measured exposure levels below the LOD (12
[micro]g/m\3\) for workers using wet methods while milling a newly
installed terrazzo floor indoors (Document ID 0200, p. 11). Echt et al.
(2002) tested a custom-built water-fed system that provided a copious
amount of water (15 gallons per minute) to the concrete work surface
(not the cutting teeth) milled by a scabbler with an 8-inch cutting
width. The investigators compared results from alternating 5-minute
periods of milling with and without the water-feed activated. The water
reduced average respirable dust levels by at least 80 percent. A
separate NIOSH study on drivable milling machines reports that under
common road milling conditions, water spray provided to the cutting
drum area at 12 gallons per minute is capable of suppressing dust
generated by a 7-foot wide (84 inches) drivable milling machine cutting
drum (an application rate of just 0.14 gallons per minute per inch of
cutting width) (Document ID 1251, pp. 7-9, 14). Based on this evidence,
OSHA concludes that, with careful adjustment, water spray methods using
a fraction of the water used in the Echt et al. (2002) scabbler study
should prove at least as effective in reducing silica dust exposures
generated by walk-behind milling machines and floor grinders.
    Blute et al. (1999) evaluated silica exposures among workers using
wet dust control methods for scabbling and large-scale grinding tasks
at an underground construction site. In this case, rather than being
walk-behind equipment, the scabblers and grinders were attached to the
articulated arm of front-end loaders (Document ID 0562, p. 633).
Although these workers used drivable machines (removing more material
than the typical walk-behind milling machine), their work (scabbling
and grinding excess concrete from tunnel walls) demonstrates the value
of wet methods when these activities are performed in enclosed spaces.
This is particularly relevant to walk-behind milling machines that are
frequently used indoors to mill concrete surfaces. In the underground
work environment, all three workers experienced task-based silica
concentrations below the preceding PEL with only one of the results (79
[micro]g/m\3\) exceeding 50 [micro]g/m\3\ (Document ID 0562, p. 637).
OSHA has determined that the information discussed above and in the FEA
is the best available evidence and supports the use of wet methods to
control silica dust while using walk-behind milling machines.
    Alternatively, employers following Table 1 may use a machine
equipped with a dust collection system recommended by the manufacturer.
The similarity between vehicular and walk-behind milling machines
supports the use of vacuum dust collection (exhaust suction) methods
for the smaller, walk-behind form of milling equipment. A study by TNO
Bouw (2002) found that when exhaust suction methods were applied to the
milling drum area of drivable milling machines, exposure levels for
operators obtained over a five-day period ranged from less than 4
[micro]g/m\3\ to 28 [micro]g/m\3\. The study also found similar
exposure results for machine tenders, who walked next to the machines;
results ranged from less than 3 [micro]g/m\3\ to 29 [micro]g/m\3\
(Document ID 1184, p. 25). OSHA inspection data from a construction
site using a scarifier and

a floor grinder, both equipped with LEV, to mill a concrete floor found
no silica exposure for either of the workers (Document ID 3958, Rows
209-211, 214-215). OSHA's exposure profile, contained in Section 5.8 of
Chapter IV of the FEA, contains these and four other exposure results
for workers using walk-behind equipment at two indoor construction
sites using LEV, where only one detectable result exceeded 50 [micro]g/
m\3\.
    Based on the evidence in the record, OSHA has determined that
employees' exposure when using walk-behind milling machines can be
further reduced by cleaning up debris when work is performed indoors or
in enclosed areas. During a study on exposures while operating a
scabbler in a parking garage, researchers noted that the worker
generated the most airborne dust when passing the machine over a
previously milled area (Document ID 0633, pp. 812-813). OSHA's OIS data
also contains a non-detectable silica exposure result for a helper who
vacuumed behind the operator of a floor grinder and scarifier preparing
an indoor concrete floor for painting where LEV was used as the dust
control (Document ID 3958, Row 211). Under paragraph (c)(1)(xiii) of
the standard for construction, when using a walk-behind milling machine
or floor grinder indoors or in an enclosed area, milling debris in the
form of loose dust must be removed with a HEPA-filtered vacuum prior to
making a second pass over an area. This prevents the debris from
interfering with the seal between machine and floor and minimizes the
gap. Additionally, it prevents debris from being re-suspended and
acting as another source of exposure. Accordingly, OSHA is requiring
the use of a vacuum with a HEPA filter to clean up any loose dust prior
to making additional passes over the area when work is conducted
indoors or in enclosed spaces with LEV (Document ID 0633, pp. 812-813;
1391, pp. 28, 40).
    In addition, the effectiveness of vacuum suction also depends on
minimizing the gap between the bottom of the machine and the surface
being milled, as discussed by Hallin (1983), who found that exposures
to respirable dust increased when the housing around the base of the
tool was removed (Document ID 1391, p. 25). To achieve acceptable dust
control and ensure that the LEV system is fully and properly
implemented, milling must proceed in a manner that limits the gap
between the bottom of the walk-behind milling machine and the surface
being milled.
    Based on the data described above, OSHA concludes that most
employees operating walk-behind milling machines will experience
exposure levels of 50 [micro]g/m\3\ or below most of the time when
employers implement the controls outlined in Table 1 under paragraph
(c)(1)(xiii) of the standard for construction. OSHA finds that controls
effective for driven milling machines are adaptable to the smaller
walk-behind milling machines. Even in indoor environments, low
exposures can be achieved for most walk-behind milling machine
operators through the proper use of controls, including the use of
HEPA-filtered vacuum systems intended to clear debris in between
milling passes when dry grinding and the use of ventilation as required
under paragraph (c)(2)(i) of the standard for construction. Therefore,
OSHA concludes that exposure will remain below 50 [micro]g/m\3\ most of
the time, even when working indoors for more than four hours, and is
not requiring the use of respiratory protection, regardless of task
duration or work location.
    Small Drivable Milling Machines (less than half-lane). Employees
engaged in this task use small drivable milling equipment to grate or
grind solid surfaces, such as concrete floors, sidewalks, and asphalt
roads. The smaller drivable machines mill a narrower strip of pavement
than large milling machines (median of 20 inches compared to a minimum
of 79 inches for large machines), and typically are capable of milling
less depth (median 8 inches) than a large machine (median 13 inches)
(Document ID 1229; 3958). Milling machinery, both large and small,
often uses a rapidly rotating drum or a bit covered with nibs to abrade
surfaces, although other mechanisms (including systems based on impact,
shot-blast, or rotating abrasive cups) are common.
    The proposed standard contained a single entry for ``Milling'' and
treated all drivable milling machines alike, requiring them to use a
water-fed system that continuously applied water at the cut point. In
the final standard, OSHA has separated smaller milling machines (less
than a half-lane wide) from larger ones based on comment and testimony
in the record. In response to commenters, OSHA has decided it is more
appropriate to divide drivable milling activities into separate entries
for large milling machines (half-lane and larger) and small milling
machines (less than half-lane) (Document ID, 3583, Tr. 2171, 2212-2213;
2181, pp. 4, 7, 9). IUOE and a road milling machine manufacturer
categorized drivable milling machines as either small or large (half-
lane or larger, with cutting drum about 79 inches or wider) (Document
ID 3583, Tr. 2441; 1229). NAPA commented that large milling machines
should be identified separately on Table 1 of the construction
standard. Based on these comments and evidence showing that the dust
control systems are different between the two classes of drivable
milling machine (Document ID 3583, Tr. 2171, 2212-2213), Table 1 in the
final standard treats them as two separate tasks.
    Under paragraph (c)(1)(xiv) of the standard for construction, small
drivable milling machines (less than a half-lane in width) must be used
with supplemental water sprays designed to suppress dust. The water
used must be combined with a surfactant. Manufacturers of smaller
drivable milling machines currently make such systems (Document ID
1229; 4073, Attachment 4a). Unlike for larger milling machines, Table 1
does not specify as an option a water spray and exhaust ventilation
combination system for small milling machines because it appears that
such systems are not currently available.
    Including a surfactant additive in the water is a practical way to
reduce employee exposures to the lowest level achievable with this wet
method (Document ID 1216, p. 3; 1217, Slides 4 and 8; 3583, Tr. 2187-
2188). This is because it offers particle binding properties that are
ideal for dust suppression (Document ID 1216, p. 3).
    Small drivable milling machines generally produce less dust than
large drivable machines, since small machines are used intermittently
and have smaller cutting tools (Document ID 1229, pp. 1-3; 3583, Tr.
2213). As discussed in the technological feasibility section on millers
using portable or mobile machines (see Section 5.8 of Chapter IV of the
FEA), OSHA concluded that, rather than relying on the very limited
(two) existing data points for workers using small drivable milling
machines, the exposure profile for this group is better represented by
a surrogate data set comprising the more comprehensive and wide ranging
profile for the entire group of workers using drivable milling machines
(including operators and tenders/helpers of both large and small
drivable milling machines). Thus, the exposure profile for small
drivable milling machines (n = 31) shows a median exposure of 21
[micro]g/m\3\ and a mean exposure of 48 [micro]g/m\3\, with overall
exposures ranging from 5 [micro]g/m\3\ to 340 [micro]g/m\3\. Therefore,
considering the ample evidence on the effectiveness of water-based dust
control systems for large as well as small drivable milling machines,
OSHA finds that this control is

applicable to small drivable milling machines.
    Water applied to the cutting drum helps reduce respirable silica
exposures among milling machine operators and helpers. In a study
conducted in the Netherlands, a water spray dust emission suppression
system using additives reduced the PBZ respirable quartz exposures of
asphalt milling machine drivers to a mean of 20 [micro]g/m\3\, with a
range of 9 [micro]g/m\3\ to 30 [micro]g/m\3\ (Document ID 1216, p. 4).
Milling machine tenders benefitted equally from the system, having a
mean PBZ respirable quartz exposure of 8 [micro]g/m\3\ with a range of
4 [micro]g/m\3\ to 12 [micro]g/m\3\. In his comments, Anthony Bodway,
representing NAPA, stated his belief that employee exposures from
asphalt road milling machines will be reduced to levels below 50
[micro]g/m\3\ when milling machines are fitted with effectively
designed water spray systems paired with surfactants and routine
inspections to ensure the system components are working properly
(Document ID 2181, p. 10). He noted that all six major road milling
machine manufacturers have recently begun, or will soon be, offering
dust control optimized water spray systems as standard equipment or
retrofit kits (Document ID 2181, pp. 21-29). One water spray design for
asphalt pavement milling evaluated by NIOSH showed more promise than
others, reducing dust release by 38 to 46 percent (Document ID 4141, p.
26). Although his comment was related to large drivable milling
machines, wet dust control technology is available for small drivable
milling machines (Document ID 1229; 4073, Attachment 4a).
    Based on information presented here and in the technological
feasibility analysis (see Section 5.8 of Chapter IV of the FEA), OSHA
concludes that employers using the controls required by paragraph
(c)(1)(xiv) of the standard for construction can reduce exposure levels
to 50 [micro]g/m\3\ or below for most employees operating or helping
with small drivable milling machines most of the time. The similarities
to large drivable milling machines are sufficient to indicate that the
wet dust suppression control technology is transferable to the smaller
drivable machines. Even if these smaller machines do not achieve the
extent of dust suppression demonstrated for larger machines because
they perform specialty milling operations and not flat removal of
asphalt typically performed by large drivable machines prior to laying
of new asphalt, the intermittent nature of operations for which small
drivable milling machines are used will help to maintain 8-hour TWA
exposure levels substantially lower than they would be for continuous
operation (Document ID 3583, Tr. 2213-2215). Therefore, OSHA is not
requiring the use of respiratory protection regardless of task duration
when using small drivable milling machines (less than half-lane)
equipped with supplemental water sprays combined with a surfactant.
    Large drivable milling machines (half-lane or larger). Paragraph
(c)(1)(xv) of the standard for construction has three control options
for employers operating large (one-half lane or wider) milling
machines. When making cuts of four inches in depth or less on any
substrate, the control options are either to use a machine equipped
with exhaust ventilation on the drum enclosure and supplemental water
sprays designed to suppress dust or a machine equipped with
supplemental water spray designed to suppress dust combined with a
surfactant. When milling only on asphalt, Table 1 allows cuts of any
depth to be made when machines are equipped with exhaust ventilation on
the drum enclosure and supplemental water sprays designed to suppress
dust.
    These controls are currently available (Document ID 2181, pp. 11,
21-29). All of the manufacturers of large milling machines currently
provide dust-suppressing water spray systems on new equipment and as
retrofit kits for older machines. In addition, as discussed in the
Section 5.8.4 of Chapter IV of the FEA, new machines will be equipped
with both dust-suppressing water spray systems and dust collection
systems by 2017 at the latest, when industry members are committed
under the Silica/Asphalt Milling Machine Partnership, which includes
representatives from the road construction contractors industry and
major road milling machine manufacturers, NAPA, AEM, IUOE, LHSFNA, and
NIOSH, to equip new machines with both dust-suppressing water spray
systems and LEV (Document ID 2181, pp. 11, 21-29).
    The controls included on Table 1 for large drivable milling
machines are based on research on dust control technologies conducted
by the Silica/Asphalt Milling Machine Partnership, which has been
studying dust controls for milling machines since 2003 (Document ID
2181, pp. 1-2; 3583, Tr. 2152, 2160; 4149) with the goal to develop
innovative engineering controls ``that all but eliminate dust and
potential silica exposure,'' and methods ``to retrofit existing milling
machines to ensure a safe workplace'' (Document ID 3583, Tr. 2153).
Much of the data contained in the record on the effectiveness of
control strategies for large drivable milling machines come from the
Partnerhip's efforts and are contained in NIOSH publications (see Table
IV.5.8-B in Section 5.8 of Chapter IV of the FEA).
    Based on the data in the record, exposures among large drivable
milling machine operators can be reduced to 50 [micro]g/m\3\ or less
most of the time. The exposure profile in Section 5.8 of Chapter IV of
the FEA shows that 79 percent of all large drivable milling machine
operators already experience silica levels below 50 [micro]g/m\3\ as a
result of using water spray intended to cool the cutting drum.
Similarly, exposure levels for 67 percent of tenders working alongside
large milling machines are below 50 [micro]g/m\3\. Based on the
Agency's review of studies in the record, which show that low silica
exposures can be achieved for both operators and tenders across varying
water spray flow rates, OSHA concludes that improvements to cooling
water spray systems can help to further reduce exposures of employees
currently experiencing exposures above 50 [micro]g/m\3\ (see Tables
IV.5.8-D and IV.5.8-E in Section 5.8 of Chapter IV of the FEA).
However, information is insufficient to confirm that the use of water
alone in existing systems will reliably control all employees'
exposures. Based on the Agency's review of evidence in the rulemaking
record, OSHA has determined that supplementing water with a dust
suppressant additive or with an exhaust ventilation on the drum
enclosure (controls that were not included on proposed Table 1), will
achieve levels below 50 [micro]g/m\3\ for all or almost all operators
and helpers most of the time when making cuts of four inches in depth
or less on any substrate (see Table IV.5.8-E in Section 5.8 of Chapter
IV of the FEA) (Document ID 1216, p. 4; 4147, pp. v, 13; 4149, pp. v,
13). Additionally, OSHA has determined that when milling asphalt only,
the addition of exhaust ventilation on the drum enclosure will achieve
levels below 50 [micro]g/m\3\ for workers making cuts of any depth
(Document ID 4149).
    NIOSH recommended LEV plus water-spray dust suppression controls be
included on Table 1 for drivable milling machines (Document ID 2177,
Attachment B, p. 20). As discussed in Section 5.8.4 of Chapter IV of
the FEA, a dust suppression system with a foam additive kept exposures
below 30 [micro]g/m\3\, and the use of water sprays combined with LEV
systems kept exposures under 25 [micro]g/m\3\ (Document ID 1184, pp. 5,
25; 1217, p. 4). These methods, combined with water spray

systems purposefully designed to control dust at the cutting drum,
transfer points, and conveyors, will control silica exposures among
vehicular milling machine operators and tenders to 50 [micro]g/m\3\ or
below during typical removal operations under the typical range of
conditions. Manufacturers of large milling machines are committed under
the Silica/Asphalt Milling Machine Partnership to equip new machines
with both dust-suppressing water spray systems and LEV by 2017
(Document ID 2181, pp. 11, 21-29). Until such time that new machines
equipped with LEV and water dust suppression systems are available, all
six major road milling machine manufacturers have recently begun, or
will soon be, offering dust control optimized water spray systems as
standard equipment and/or retrofit kits, which are expected to meet the
requirements for Table 1 for cuts of four inches in depth or less on
any substrate (Document ID 2181, pp. 21-29).
    Proposed Table 1 specified the use of a respirator (half-mask APF
10) for drivable milling machines with a water-fed system used more
than four hours a day irrespective of the material milled. NAPA
recommended removing the proposed requirements for use of respirators
when milling asphalt (Document ID 2181, pp. 11-12, 16). Upon review of
the evidence in the record, OSHA agrees that this is appropriate for
all asphalt and concrete milling operations. As explained in Section
5.8 of Chapter IV of the FEA, the controls contained in Table 1 in the
final standard will keep exposures below 50 [micro]g/m\3\ for most
operators and tenders of large drivable milling machines most of the
time. Evidence submitted to the record by NAPA and NIOSH shows both
water-based dust suppression systems and combination LEV/water-based
systems during asphalt milling results in employee exposures lower than
50 [mu]g/m\3\ (Document ID 2177 Attachment B, p. 20; 1184, pp. 5, 25;
1217, p. 4). Accordingly, respiratory protection is not required under
Table 1 of the final standard for operating large drivable milling
machines to mill asphalt. Although there is some qualitative evidence
indicating that exposures when milling concrete for more than four
hours may be somewhat higher, and could exceed 50 [mu]g/m\3\ some of
the time, there is no hard data permitting OSHA to treat asphalt and
concrete milling differently with respect to imposing a respirator
requirement or to conclude that most concrete milling for that duration
will be above 50 [mu]g/m\3\ most of the time. Therefore, OSHA is not
including a respirator requirement in the final standard for either
asphalt or concrete milling, regardless of task duration.
    IUOE recommended separate treatment of operators and tenders of
large milling machines since the exposures of operators are lower than
the exposures of tenders. IUOE further stated that operators are
located farther from the silica source than tenders, and appropriate
protection varies depending upon the location of the worker from the
silica source (Document ID 2262, p. 24). Evidence summarized above
shows that most tenders and operators will not experience silica
exposures in excess of 50 [mu]g/m\3\ when either of the control options
required by Table 1 is implemented. The exposure profile in Table
IV.5.8-C in Section 5.8 of Chapter IV of the FEA shows that the mean of
respirable crystalline silica exposures for operators of large milling
machines is 39 [micro]g/m\3\ (median 17 [micro]g/m\3\) and the slightly
higher mean for tenders is 57 [micro]g/m\3\ (median 27 [micro]g/m\3\).
Sample results presented in the exposure profile indicate that 79
percent of all large drivable milling machine operators already
experience silica levels below 50 [micro]g/m\3\ as a result of using
water spray intended to cool the cutting drum. Similarly, exposure
levels for most tenders (67 percent) working alongside large milling
machines are already below 50 [micro]g/m\3\ (see Tables IV.5.8-D and
IV.5.8-E in Section 5.8 of Chapter IV of the FEA). Therefore, OSHA
concludes that separate control measures do not need to be specified
for operators and tenders.
    Proposed Table 1 contained dust control specifications for all
drivable milling machines, including when milling concrete. OSHA
received comments from IUOE, BCTD, and NAPA recommending that Table 1
be modified to separate asphalt milling and concrete milling and
require appropriate controls based on the respective exposure levels
(Document ID 2262, pp. 3, 17; 2371, Attachment 1, p. 26; 2181, p. 9).
Concrete milling is performed less frequently than asphalt milling
(Document ID 1231; 3583, Tr. 2213-2214), but silica exposures could be
higher than when milling asphalt. This difference is likely due to the
potential for the silica content to be higher in some concrete compared
with some asphalts (Document ID 1699), and also the softness and
``stickiness'' of asphalt milled warm, which likely helps reduce
separation of the pavement components and perhaps limits dust release
in hot weather (Document ID 1251, p. 14; 1231). In addition, cutting
drums for concrete have smaller teeth, which can produce more fine dust
than is the case with asphalt (Document ID 1699). Anthony Bodway,
representing NAPA, also noted that silica exposures are higher for
concrete milling than for asphalt milling (Document ID 2181, p. 15). In
the FEA, OSHA concludes that water dust suppression and LEV systems
should be equally effective for concrete and asphalt in terms of
percent reduction in dust emissions when making cuts of four inches in
depth or less on any substrate (see Section 5.8 of Chapter IV of the
FEA). However, to the extent that milling concrete is dustier (i.e., a
larger amount of respirable dust is liberated), exposures to silica
during concrete milling may be somewhat higher than is the case for
asphalt milling even with the use of dust controls. As previously
explained, however, OSHA lacks quantitative data supporting these
comments to allow it to impose more stringent requirements,
specifically a requirement to use respirators, on concrete milling and
not on asphalt milling or to conclude that exposures will be over the
PEL for most operators most of the time doing either task.
    The Silica/Asphalt Milling Machine Partnership conducted field
trials for large road milling machine LEV systems making cuts up to 11
inches deep (Document ID 4147; 4149). NIOSH evaluated exposures among
workers at four road construction sites (Document ID 4147, pp. v, 5-7,
13, Table 1; 4149, pp. v, 5-7, 13, Table 1). All the samples obtained
during the studies for operators and tenders combined showed that
exposure levels never exceeded 25 [mu]g/m\3\ when workers used machines
fitted with the LEV system, even when making cuts up to 11 inches deep
in asphalt (Document ID 4147, pp. v, 6-7, 13, Table 1; 4149, pp. v, 5-
7, 13, Table 1). In fact, the highest sample result (24 [mu]g/m\3\ for
a ``groundsman'' walking beside a milling machine removing 11 inches of
pavement on each pass) was the only sample result to exceed 13 [mu]g/
m\3\ during the two sampling dates (Document ID 4147, pp. v, 5-7, 13,
Table 1; 4149, pp. v, 5-7, 13, Table 1). Therefore OSHA is confident
that when removing asphalt only, workers can make cuts of any depth
without elevated exposures to silica.
    However, other evidence contained in the record indicates that
cutting depths of more than four inches, in one pass, reduces the
effectiveness of controls (Document ID 3798, pp. 2, 14; 0555, p. 1).
Therefore OSHA has determined that if an employer is using a large
drivable milling machine to mill concrete, or road surface material
that contains both concrete and asphalt, deeper than four

inches, it is not covered by 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.
    IUOE also recommended excluding road demolition and asphalt
reclamation from asphalt milling in Table 1. Road demolition involves
removal of the road substructure in addition to the road surface
material and asphalt reclamation involves deeper cuts than typical
``mill and fill'' cuts of four inches in depth or less. IUOE asserted
that this change should eliminate the need for respirator use by
operators during typical asphalt ``mill and fill'' operations when
engineering controls are properly implemented (Document ID 2262, p.
23).
    Paragraph (c)(1)(xv) of the standard for construction excludes road
demolition and asphalt reclamation operations by limiting milling
activities on materials other than asphalt to cuts of four inches in
depth or less. The NIOSH studies of LEV for drivable milling machines
were conducted using large asphalt road milling machines (half-lane or
wider) and provide strong evidence that exposure levels below 50 [mu]g/
m\3\ (and even below 25 [mu]g/m\3\) can be achieved for employees
operating this type of equipment during typical shallow ``mill and
fill'' type road milling (i.e., cuts of four inches in depth or less)
(see Table IV.5.8-E in Section 5.8 of Chapter IV of the FEA). In one
NIOSH study, the removal of excess pavement during milling machine
demolition-type work (12 inches of pavement all at once), created a
large gap between the road and the milling machine drum enclosure,
allowing more dust to escape than during typical milling conditions
(Document ID 0555, p. 1). Also, a NIOSH trial, using only drum cooling
water and alternate spray nozzles, showed elevated silica exposure
levels when the road milling machine intermittently ground through the
asphalt layer into an aggregate and concrete underlayment (Document ID
3798, pp. 2, 14). Milling operators will rarely encounter these ``worst
case'' conditions (Document ID 0555, p. 1).
    As previously stated, when milling only on asphalt, OSHA is
allowing cuts of any depth to be made when machines are equipped with
exhaust ventilation on the drum enclosure and supplemental water sprays
designed to suppress dust. When milling all other material to a depth
of more than four inches Table 1 does not apply and employers will be
required to conduct exposure assessments and comply with the PEL in
accordance with paragraph (d) of the standard for construction.
Additionally, road demolition, such as cutting the roadway into
manageable size pieces or squares that involves equipment other than
milling machines, such as saws, dowel drills, and various kinds of
heavy equipment, is not covered under this entry on Table 1 (see
Sections 5.3, 5.6, and 5.9 of Chapter IV of the FEA). In those
instances employers will need to follow the appropriate entries on
Table 1 for the equipment used or conduct exposure assessments and
comply with the PEL in accordance with paragraph (d) of the standard
for construction.
    Crushing machines. Crushing machines are used to reduce large
rocks, concrete, or construction rubble down to sizes suitable for
various construction uses (see Section 5.10 of Chapter IV of the FEA).
When using crushers, paragraph (c)(1)(xvi) of the standard for
construction requires the use of equipment designed to deliver water
spray or mist for dust suppression at crusher and other points where
dust is generated (e.g., at hoppers, conveyors, sieves/sizing or
vibrating components, and discharge points), and a remote control
station or ventilated booth that provides fresh, climate-controlled air
to the operator. In the proposed standard, OSHA listed this entry as
``Rock Crushing.'' For the final standard OSHA has revised the title of
this entry to clarify that it includes concrete crushing, which is
often performed at demolition projects (Document ID 4073, Attachment
9a; 4073, Attachment 10a; 4073, Attachment 10b; 4234, Attachment 1, pp.
15-16). Proposed Table 1 would have required the use of wet methods or
dust suppressants or LEV systems at feed hoppers and along conveyor
belts. Information contained in the record indicates that LEV alone is
not effective in reducing exposures to 50 [mu]g/m\3\ or below, and that
it is necessary to require both a water spray system and either a
remote control station or filtered control booth to protect the
operator and employees engaged in crushing operations (see Section 5.10
of Chapter IV of the FEA).
    Wet spray methods can greatly reduce the exposure levels of
operators and laborers who work near crushers tending the equipment,
removing jammed material from hoppers, picking debris out of the
material stream, and performing other tasks (Document ID 0203, pp. 3-6,
9; 1152; 1360; 1431, pp. 3-93-3-94; 3472, pp. 61-76; 4073, Attachment
9a; 4073, Attachment 15g, p. 1). These systems are currently available
and all crushers and associated machinery (conveyors, sizing screens,
discharge points) can be retrofitted with water spray or foam systems
(Document ID 1360; 0769; 0770; 0830; 0831; 0832). Spray systems can be
installed for remote control activation (Document ID 0203, pp. 11, 12,
14; 0830). The design and application of water spray systems will vary
depending on application. For airborne dust suppression, spray nozzles
should be located far enough from the target area to provide coverage
but not so far so as to be carried away by wind. In addition, nozzles
should be positioned to maximize the time that water droplets interact
with airborne dust. Droplet size should be between 10 and 150 [mu]m
(Document ID 1540, pp. 62-63). Alternatively, to prevent airborne dust
from being generated, nozzles should be located upstream of dust
generation points and positioned to thoroughly wet the material, and
the volume and size of droplets increased to ensure that the material
is sufficiently wetted (Document ID 1540, pp. 62-63). Information from
IUOE, BCTD, and the U.K. Health and Safety Executive shows that water
application can be expected to reduce exposure levels from 78 to 90
percent (Document ID 1330, p. 94; 4025, Attachment 2; 4073, Attachment
9a, pp. 1-4; 4073, Attachment 15g, p. 2).
    The record did not contain information on exposures of tenders or
other employees working near a crusher operation without dust controls.
However, OSHA concludes that employees assisting with crusher
operations can be exposed to elevated levels of respirable crystalline
silica if water sprays are not used to control dust emissions. This
conclusion is based on evidence gathered by OSHA's contractor, ERG,
which visited a concrete crusher site. At the site, ERG observed a
crusher operator who spent time outside of a control booth shoveling
dried material from under a conveyor. The operator was exposed to 54
[mu]g/m\3\ TWA despite the time he spent in the booth where the silica
concentration was non-detectable (Document ID 0203, p. 9). Thus, this
operator's TWA exposure to silica can be entirely attributed to his
work around the crusher, much as a tender would have been doing.
Without the benefit of spending some time in the booth, and the fact
that the material being crushed was wet from rain and a freeze the
night before, the operator's exposure could have been even higher
(Document ID 0203). This indicates that tenders assisting with crusher
operations, who do not have the benefit of a booth for protection from
exposure, can be exposed to excessive levels of crystalline silica-
containing dust when

water is not applied to areas where dust emissions occur. The potential
exposure of tenders and other employees who are in the vicinity of
crusher operations underscores the importance of using water spray
systems to reduce dust emissions. Such systems will reduce dust
exposures generally, thereby reducing exposures for tenders and other
employees in the vicinity of the crusher. Moreover, as discussed below,
OSHA is not specifying the use of LEV systems for crushing operations
on Table 1 of the final standard because LEV has not been proven to be
an effective or widely available alternative.
    CISC argued that OSHA's preliminary finding that it was feasible to
achieve exposures of 50 [mu]g/m\3\ for tenders was unfounded and based
on no data on exposures of crushing machine tenders (Document ID 2319,
pp. 62-63). However, there are data in the record that inform the
Agency with respect to exposure of crushing machine tenders and the
effectiveness of dust controls in reducing their exposures to silica.
As described above, a crusher operator performing tasks along the
conveyor belt was exposed much as a tender would be. OSHA identified
one exposure measurement from an enforcement case for a laborer working
near a mobile crusher at an asphalt plant; the laborer's exposure was
43 [mu]g/m\3\ (8-hour TWA) based on a half-day of sampling (Document ID
0186, pp. 60-61). In addition to assisting with the crusher operation,
he also mixed a blend of sand, crushed concrete, asphalt, and soil,
which likely contributed to his exposure. He was working about 50 feet
from the crusher hopper where it was evident from the inspection report
that his exposure was much lower than that of the operator (Document ID
0186, p. 37). Bello and Woskie found exposures of demolition workers,
including those near a crushing operation, were below 50 [mu]g/m\3\
when water was used as dust controls for the demolition project
(Document ID 4073, Attachment 9a, pp. 3-4). OSHA thus rejects CISC's
contention that the absence of direct evidence of exposures to tenders
means that OSHA cannot regulate them or draw reasonable inferences
about the technological feasibility of controlling their exposures
(Document ID 2319, pp. 62-63).
    Crushers are currently available with remote controls as standard
equipment (Document ID 0770; 0769, p. 2). The remote operation permits
the operator to stand back from the crusher or move upwind of dust
emissions. IUOE provided exposure data from large highway
reconstruction projects (Document ID 4025, Attachment 2, p. 9). Four
samples were collected where the operator platform was next to the
crushing operation and the operator was directly exposed to the crusher
emissions, resulting in a mean respirable crystalline silica exposure
of 410 [mu]g/m\3\ (Document ID 4025, Attachment 2, p. 9). Water use was
observed but no details were provided on the extent of use or the
systems in place. There was an approximately 66 percent reduction in
exposure to respirable crystalline silica of the crusher operator
working from a remote location (the remote location mean exposure was
140 [mu]g/m\3\) (Document ID 4025, Attachment 2, p. 9). IUOE addressed
the utility of remote controls in its comments on the proposed
standard, and requested that OSHA evaluate remote control technologies
as an exposure control method and include this type of control in Table
1 (Document ID 2262, p. 45; 3583, Tr. 2341).
    An isolated and ventilated operator control booth can significantly
reduce the respirable silica exposures of employees associated with
crushing. At a visit to a crusher facility, ERG found non-detectable
levels of respirable crystalline silica inside the operator's control
booth, compared to a concentration of 103 [mu]g/m\3\ outside, despite
the booth having poor door seals, using recirculated rather than fresh
air, and having foam filters (as opposed to the MERV-16 or better
filters required by paragraph (c)(2)(iii)(E) of the standard for
construction) (Document ID 0203, pp. 12-13).
    Other studies of operator cabs also reported silica or dust
exposure reductions ranging from 80 percent to greater than 90 percent
(Document ID 0589, p. 3; 0590, p. 54; 1431, p. 3-95). In the PEA, OSHA
recognized that control booths for crushers are commercially available,
although they are not commonly used on construction sites (Document ID
1720, p. IV-494). However, Kyle Zimmer, director of health and safety
for IUOE Local 478, stated during the hearing that ``contractors report
that they are using portable crusher control booths with air
conditioning to operate the plant remotely'' (Document ID 3583, Tr.
2341).
    Evidence indicates that operators experience high exposure levels
when they must operate the crusher from above the feed hopper where
dust emissions are highest (Document ID 0030; 4073, Attachment 10a). In
light of this evidence, OSHA concludes that removing or isolating the
operator from this high-exposure location will be effective in lowering
the exposure of the operator. It is not clear that a control booth
alone will be sufficient to protect the operator from exposure to
silica, since operators periodically leave the booth to perform work
around the crusher, and the booth does not offer any protection for
other employees outside the booth such as tenders. A study of crushers
used in the South Australian extraction industry found operator
exposures ranged from 20 to 400 [mu]g/m\3\ (with a median of 65 [mu]g/
m\3\) while crushing dry material and using control booths or cabs
(Document ID 0647). Four of the eight sample results were at or below
50 [mu]g/m\3\, and at least two of the sampled workers occasionally
exited the cabins to free machinery blockages (Document ID 0647).
    Because providing a filtered booth for the operator will not
protect other employees assisting with the operation or working nearby,
OSHA finds that a water-based dust suppression system is necessary to
prevent excessive exposure to silica among tenders and other employees
nearby. Therefore, OSHA has determined that the combination of water
use and either a remote control station or a ventilated booth for the
mobile crusher operator will be effective in minimizing exposure of the
operators and tenders. Summary data submitted by IUOE show that, with
water use, the addition of remote control stations further reduced
operator exposures by a factor of 3 (Document ID 4025, Attachment 2, p.
9). At the crusher operation visited by ERG, the operator's TWA
exposure was 54 [mu]g/m\3\ while working in a booth, and his exposure
would have been lower had water been applied to dried material he was
shoveling from under the conveyor.
    In the proposed standard, OSHA required the use of a half-mask
respirator with an APF of 10 for all employees outside of the cab,
regardless of task duration or whether water sprays or LEV were
implemented. No respiratory protection was required for those employees
who operated the crusher from within the cab. OSHA proposed to require
respirator use because the data available at the time suggested that
neither water spray nor LEV systems would consistently reduce exposures
to 50 [mu]g/m\3\ or less, and that high exposures (even in excess of
the preceding PEL) could still occur. The crushing machine entry for
Table 1 in the final standard does not require respiratory protection
for tenders or mobile crusher operators because the evidence described
above indicates that the use of water systems, combined with a remote
control station or ventilated

booth, will reduce most employees' exposures to respirable silica to 50
[mu]g/m\3\ or less most of the time.
    Information from IUOE, BCTD and the U.K. Health and Safety
Executive show that water application can be expected to reduce
exposure levels by 78 to 90 percent (Document ID 1330; 4025, Attachment
2, pp. 7-23; 4073, Attachment 9a, pp. 1-4; 4073, Attachment 15g, p. 2).
Using the mid-point of this exposure control range (84 percent) and
applying it to the highest value in the exposure profile (300 [mu]g/
m\3\), would yield an exposure of slightly less than 50 [mu]g/m\3\ TWA
for an eight-hour work day. However, other evidence suggests that wet
spray methods may not consistently achieve exposures below 50 [mu]g/
m\3\ (Document ID 0030; 4025, Attachment 2, pp. 7-23), although little
detail was available on how water was applied. The evidence is clear
that the highest exposures occur at the hopper where material is fed by
front-end loaders or another conveyor, an area that is most likely to
be tended by the operator (Document ID 0030; 4073, Attachment 10a;
0203). Therefore, OSHA finds that it is also necessary to use a remote
control station or filtered booth to ensure the protection of crusher
operators.
    The use of LEV systems was discussed in the NPRM, but evidence in
the record indicates that it has yet to be proven practicable for
mobile construction crushing equipment and is not currently used
extensively. William Turley of the Construction and Demolition
Recycling Association stated, ``While there are crushing operations
that have used baghouses on the crusher, none use . . . ventilation
equipment for conveyors'' (Document ID 2220, p. 2). Phillip Rice of
Fann Contracting contended that large crushing systems with multiple
conveyor belts would make it very difficult to use LEV cost effectively
(Document ID 2116, Attachment 1, p. 31). In contrast, Kyle Zimmer of
IUOE testified that employers are using dust collectors with baghouses
at some crushing operations (Document ID 3583, Tr. 2341). Nevertheless,
the record does not contain substantial and convincing evidence that
LEV alone can be applied when using mobile crushing machines to reduce
exposure levels to the same extent as water-based dust suppression
systems combined with the use of remote control stations or filtered
control booths. Therefore, OSHA is not specifying the use of LEV
systems for crushing operations on Table 1 of the final standard.
    Heavy equipment and utility vehicles used to abrade or fracture
silica containing materials (e.g., hoe-ramming, rock ripping) or used
during demolition activities involving silica-containing materials.
Employees engaged in this task operate a variety of wheeled or tracked
vehicles ranging in size from large heavy construction equipment, such
as bulldozers, scrapers, loaders, cranes and road graders, to smaller
and medium sized utility vehicles, such as tractors, bobcats and
backhoes, with attached tools that are used to move, fracture, or
abrade rock, soil, and demolition debris (see Section 5.3 of Chapter IV
of the FEA). For example, equipment operators typically perform
activities such as the demolition of concrete or masonry structures,
hoe-ramming, rock ripping, and the loading, dumping, and removal of
demolition debris, which may include the loading and dumping of rock,
and other demolition activities (see Table IV.5.3-A in Section 5.3 of
Chapter IV of the FEA).
    Paragraph (c)(1)(xvii) of the standard for construction requires
the operator to be in an enclosed cab, regardless of whether other
employees are in the area and the cab must meet the requirements of
paragraph (c)(2)(iii) of the standard for construction. When other
employees are engaged in the task, water, dust suppressants, or both
combined must also be applied as necessary to minimize dust emissions.
Paragraph (c)(2)(iii) of the standard for construction requires
enclosed cabs to be kept as free as practicable from settled dust, to
have door seals and closing mechanisms that work properly, to be under
positive pressure maintained through continuous delivery of fresh air,
to have gaskets and seals that are in good condition and work properly,
to have intake air that is filtered through a filter that is 95 percent
efficient in the 0.3-10.0 [mu]m range, and to have heating and cooling
capabilities.
    In the proposed Table 1, OSHA included one entry for heavy
equipment and required that an enclosed cab be used. Although OSHA
analyzed all types of work with heavy equipment, including demolition,
in its preliminary feasibility analysis for heavy equipment, the
proposed Table 1 entry described the activity as ``use of heavy
equipment during earthmoving activities.''
    Several commenters requested clarification on what uses of heavy
equipment OSHA intended to cover in the entry on proposed Table 1. IUOE
requested that OSHA include a definition of the range of ``activities
encompassed within earthmoving,'' and specifically acknowledge whether
or not demolition activities are intended to be encompassed within this
definition of earthmoving on Table 1 (Document ID 2262, p. 7). IUOE
further explained that while earthmoving activities are ``dust-filled''
and likely to result in some exposure to respirable silica, it was
inappropriate to combine earthmoving and demolition into one entry for
heavy equipment operators on Table 1 because earthmoving ``does not
fracture or abrade silica-containing materials, and thus, does not
expose any heavy equipment operators to [a] high concentration of
respirable silica.'' IUOE opined that treating the two tasks separately
in the final rule would allow for better control of the hazards
(Document ID 2262, pp. 3, 6, 9, 14). LHSFNA supported the IUOE position
on demolition versus earthmoving and how it should be addressed in
Table 1 (Document ID 4207, p. 3). BCTD requested that Table 1 specify
that the Table 1 controls only apply when the listed task is performed
on or with silica-containing materials, noting that some operations,
such as earthmoving equipment, do not generate silica dust unless the
material contains silica (Document ID 2371, p. 24).
    OSHA agrees with these recommendations and has separated heavy
equipment into two entries on Table 1: Paragraph (c)(1)(xvii) of the
standard for construction covers heavy equipment and utility vehicles
used to abrade or fracture silica-containing materials or during
demolition activities; paragraph (c)(1)(xviii) of the standard for
construction covers heavy equipment and utility vehicles used for tasks
such as grading and excavating (but not including demolishing,
abrading, or fracturing silica-containing materials). As explained
below, only heavy equipment and utility vehicles used to abrade or
fracture silica-containing materials or during demolition activities
require an enclosed cab at all times, whereas the employer has a choice
between an enclosed cab or applying water and/or dust suppressant when
these vehicles are used for tasks such as grading and excavating,
provided there are no other employees engaged in the task beside the
heavy equipment operator.
    In the proposed standard, the only control option for heavy
equipment was to operate from within enclosed cabs. Several commenters
noted that enclosed cabs do not protect other employees, such as
laborers, who perform tasks in the area but remain outside the cab
(e.g., Document ID 2262, p. 24). Fann Contracting explained that not
including laborers on Table 1 would ``render the table pointless
because employers would have to conduct

frequent exposure assessments of those employees'' (Document ID 2116,
Attachment 1, p. 3). Because of the reasonable concerns raised by these
commenters, OSHA has included controls (water and/or dust suppressants)
on Table 1 to protect employees, other than the operator, who are
engaged in the tasks. The other employees included under this entry for
Table 1 are typically laborers who work nearby supporting the heavy
equipment operator (i.e., applying dust suppressant, spotting, and
clearing debris). When these materials contain crystalline silica, dust
generated during these activities is a primary source of exposure for
the equipment operators and the laborers.
    NUCA expressed concern that operating from within a fully enclosed
cab may reduce visibility of the work zone and impair verbal
communication. and thereby pose potential safety risks (Document ID
2171, pp. 2, 4, 22). However, modern heavy equipment already come
equipped with enclosed, filtered cabs that are designed with visibility
in mind to allow the operator to perform the work required.
Furthermore, radios or cell phones can be used for communication if
necessary. Therefore, OSHA concludes that filtered, fully enclosed cabs
have been and can continue to be used without compromising worker
safety or the effectiveness of the cab.
    The exposure profile in Table IV.5.3-B in Section 5.3 of Chapter IV
of the FEA shows that approximately 8 percent (1 out of 13 samples) of
heavy equipment operators performing demolition, abrading, or
fracturing activities have exposures above 50 [mu]g/m\3\. OSHA also
found a mean TWA exposure of 25 [mu]g/m\3\ for the six samples in the
record for laborers who assisted heavy equipment operators by providing
water for dust control during demolition projects. Table IV.5.3-C in
Section 5.3 of Chapter IV of the FEA compares silica exposures among
heavy equipment operators with the silica exposures of laborers engaged
in the same task. These data are a subset of the exposure profile
(Table IV.5.3-B in Section 5.3 of Chapter IV of the FEA) and provide
evidence of the effectiveness of applying dust suppressants for dust
control during demolition activities. The results for the six samples
for laborers were less than 50 [mu]g/m\3\ and were lower than the heavy
equipment operators not in an enclosed cab.
    The information presented in OSHA's technological feasibility
analysis for heavy equipment operators and ground crew laborers
(Section 5.3 of Chapter IV of the FEA) and summarized above provides
evidence that the use of enclosed cabs and water and/or dust
suppressants will reduce exposures to 50 [mu]g/m\3\ or less for
operators and laborers when these controls are fully and properly
implemented. Therefore, OSHA is not requiring the use of respiratory
protection for heavy equipment operators and laborers who assist heavy
equipment operators during demolition activities involving silica-
containing materials or activities where silica-containing materials
are abraded or fractured, regardless of the duration of the task. Fann
Contracting questioned whether operators who use enclosed cabs would be
required to wear respiratory protection when exiting the equipment cab
(Document ID 2116, Attachment 1, p. 23). Since the specified control
method on Table 1 for this task requires the use of an enclosed cab,
the task is not being performed once the operator exits the enclosed
cab and the resulting exposure will have ceased, and no respiratory
protection is required in that circumstance. However, if other
abrading, fracturing, or demolition work is continuing while an
operator is outside the cab, that operator is considered to be an
employee ``engaged in the task'' and must be protected by the
application of water and/or dust suppressants.
    Heavy equipment and utility vehicles used for tasks such as grading
and excavating but not including demolishing, abrading, or fracturing
silica-containing materials. When operating heavy equipment and smaller
sized utility vehicles for tasks such as grading and excavating that do
not involve demolition or the fracturing or abrading of silica,
paragraph (c)(1)(xviii) of the standard for construction requires that
the employee who will be operating the equipment operate from within an
enclosed cab or that the employer applies water and/or dust
suppressants as necessary to minimize dust emissions. If other
employees (e.g., laborer) are engaged in the task, water and/or dust
suppressants must be applied as necessary to minimize dust emissions
even where the operator of the equipment is working inside an enclosed
cab. However, the employer need not provide an enclosed, filtered cab
for the operator of the equipment.
    Employees engaged in this task operate a variety of wheeled or
tracked vehicles ranging in size from large heavy construction
equipment, such as bulldozers, scrapers, loaders, and road graders, to
smaller and medium sized utility vehicles, such as tractors, bobcats
and backhoes, with attached tools that are used to excavate and move
soil, rock, and other silica-containing materials (see Section 5.3 of
Chapter IV of the FEA). Typically tasks conducted with this equipment
include earthmoving, grading, excavating, and other activities such as
moving, loading, and dumping soil and rock (see Table IV.5.3-B in
Section 5.3 of Chapter IV of the FEA). In addition, the railroad
industry uses such heavy equipment to dump and grade silica-containing
ballast in track work to support the ties and rails. Such track work is
generally subject to OSHA's construction standards, and the use of
heavy railroad equipment for this purpose is therefore covered under
this task in Table 1 of the final standard.
    As discussed under the explanation of (c)(1)(xvii) of the standard
for construction, OSHA included one entry for heavy equipment operators
performing earthmoving activities in the proposed standard, but has
divided this entry to distinguish between the controls needed when
using heavy equipment for abrading, fracturing, or demolishing silica-
containing material, on the one hand, and for grading and excavating
silica-containing materials, on the other hand.
    OSHA's exposure profile for earthmoving (i.e., excavation)
operations shows that a large majority of exposures (87.5 percent) are
below 25 [mu]g/m\3\ (see Section 5.3 of Chapter IV of the FEA). IUOE
commented that earthmoving should not be the focus of the rule, stating
that earthmoving activity ``does not fracture or abrade silica-
containing materials, and thus, does not expose heavy equipment
operators to high concentrations of respirable silica'' (Document ID
2262, p. 6). Martin Turek, assistant coordinator and safety
administrator for IUOE Local 150, stated that ``it is unlikely that
moving soil or clay will generate respirable silica in concentrations .
. . above the [proposed] PEL'' (Document ID 3583, Tr. 2358).
    Under both entries, however, the specified controls to protect
laborers are the same. Thus, as when engaged in abrading, fracturing,
or demolition tasks near or alongside heavy equipment or utility
vehicles, OSHA has included a requirement that water and/or dust
suppressants be applied as necessary to minimize dust emissions so that
employees, including such laborers, who are engaged in such tasks as
grading and excavating silica-containing materials in conjunction with
operators of heavy equipment or utility vehicles are protected from
excessive exposure to respirable crystalline silica.
    Enclosed cabs are not mandated for this task. They may be used if
the equipment operator is the only

employee engaged in the task, as an alternative to water and/or dust
suppressants. However, where enclosed cabs are used, they must meet the
requirements outlined in paragraph (c)(2)(iii) of the standard for
construction. Those requirements specify that enclosed cabs must be
kept as free as practicable from settled dust, must have door seals and
closing mechanisms that work properly, must have gaskets and seals that
are in good condition and work properly, must be under positive
pressure maintained through continuous delivery of fresh air, must have
intake air that is filtered through a filter that is 95 percent
efficient in the 0.3-10.0 [mu]m range, and must have heating and
cooling capabilities. If employees other than the equipment operator
are engaged in the task, Table 1 requires the application of water and/
or dust suppressants as necessary to minimize dust emissions, which
protects the operator as well as the laborers from silica exposures
above the PEL. As demonstrated by OSHA's exposure profile and the other
evidence in OSHA's technological feasibility for heavy equipment
operators and ground crew laborers (Section 5.3 of Chapter IV of the
FEA), wet dust suppression methods (e.g., water or calcium chloride)
are already a common and effective means for reducing exposures among
heavy equipment operators and laborers to 50 [mu]g/m\3\ or below.
    Other commenters were concerned about the availability of enclosed
cabs on heavy equipment used for these types of earthmoving activities.
NUCA, NAHB, and CISC expressed concern regarding the cab requirements;
NUCA stated that the majority of earthmoving equipment is ``equipped
with open canopies or unpressurized cabs'' (Document ID 2171, p. 3;
2296, p. 32; 2319, p. 114). OSHA understands that some equipment
currently in use may not be equipped with enclosed, pressurized cabs as
required by Table 1 when enclosed cabs are used. Where an employer
chooses not to retrofit existing equipment for grading and excavating,
it must apply water and/or dust suppressants as necessary to minimize
dust emissions in order to comply with Table 1. Employers that neither
choose to retrofit equipment nor suppress dust using water or other
dust suppressants must comply with the requirements of paragraph (d) of
the standard for construction.
    Evidence in the record indicates that exposures of employees during
common excavation and grading operations are likely to remain below 25
[mu]g/m\3\ most of the time. OSHA has therefore determined that
respiratory protection is not needed when the employer fully and
properly implements the controls on Table 1. Fann Contracting
questioned whether operators who use enclosed cabs would be required to
wear respiratory protection when exiting the equipment cab (Document ID
2116, Attachment 1, p. 23). As explained above, there is no requirement
for respiratory protection when the employee is entering or exiting the
cab since the task is not being performed at that time. However, if
other grading or excavation work is continuing while an operator is
outside the cab, that operator is considered to be an employee
``engaged in the task'' and must be protected by the application of
water and/or dust suppressants.
    Drywall finishers. Table 1 of the final rule does not specify
controls for drywall finishing. In the proposed standard, ``drywall
finishing (with silica-containing material)'' was an entry on Table 1.
The control options on proposed Table 1 were to use a pole sander or
hand sander equipped with a dust collection system or to use wet
methods to smooth or sand the drywall seam. However, information in the
rulemaking record indicates that drywall compound currently in use does
not usually contain silica (Document ID 2296, pp. 32, 36). NAHB
commented that much of the drywall joint compound currently used in
residential construction has no or very low silica content and members
can resolve any concerns regarding silica exposure by making sure to
use low silica containing product (Document ID 2296, pp. 32, 36). While
CISC agreed that contractors ``can utilize `silica-free' joint compound
and perform drywall installation in a manner that creates exposures
below the proposed PEL,'' it expressed concern that ``silica-free''
joint compound may contain more than trace amounts of silica, which
could result in exposures to silica (Document ID 2319, pp. 38, 43).
    NIOSH tested bulk samples of a commercially available joint
compound and found up to 6 percent quartz, although silica was not
listed on the safety data sheet for the product (Document ID 0213, p.
5). However, in a more recent study, NIOSH determined that three of six
drywall compounds purchased at a retail store contained only trace
amounts of silica (less than 0.5 percent) (Document ID 1335, p. iii).
The researchers concluded that for the most part the results of each
sample analysis agreed with the composition stated in the
manufacturers' material safety data sheets (Document ID 1335, pp. 3-4,
7, 10). OSHA finds that joint compound is more accurately labeled than
it was in the past, and that manufacturers' labeling and SDSs are the
best source for determining whether employees may be exposed to silica
that could become respirable.
    Additionally, the exposure profile includes 15 full-shift, personal
breathing zone samples of respirable crystalline silica. The median
exposure is 12 [mu]g/m\3\, the mean is 17 [mu]g/m\3\, and the range is
8 [mu]g/m\3\ (limit of detection (LOD)) to 72 [mu]g/m\3\, which was the
only result above 50 [mu]g/m\3\. The 72 [mu]g/m\3\ sample was obtained
for a worker performing overhead sanding directly above his breathing
zone (Document ID 1335, p. 13). One other sample exceeded 25 [mu]g/m\3\
(Document ID 1335, p. 14). Therefore, because no additional controls
are needed for most drywall finishers, OSHA has not included an entry
for drywall finishers in Table 1 in the final standard.
    In the event that the use of silica-free joint compound is not
possible, or during renovation work where silica-containing joint
compound might be present, OSHA has determined that there are
engineering controls, as discussed in Section 5.2 of Chapter IV of the
FEA, that reduce exposure to respirable crystalline silica to 50 [mu]g/
m\3\ or below. In that situation employers will have to comply with
paragraph (d) of the standard for construction. Johnston Construction
Company commented that a requirement for air purifying respirators
should be included in the rule for one of the dustiest tasks performed
(Document ID 1951). OSHA agrees that sanding silica-free joint compound
can potentially generate high levels of respirable nuisance dust that
does not contain silica and for which respiratory protection may be
needed in some situations. While high exposures to nuisance dusts may
result from sanding joint compound, available evidence shows exposures
to respirable crystalline silica will be low.
    Abrasive blasting. Table 1 of the final standard does not specify
controls for abrasive blasting; this is unchanged from the proposed
rule.
    The Society for Protective Coatings (SSPC) requested that abrasive
blasting be included in Table 1 (Document ID 2120, p. 3). SSPC
recommended the inclusion of an abrasive blasting entry which
``simplifies compliance and eliminates the need for measuring workers'
exposure to silica, while still ensuring adequate protection for
workers'' (Document ID 2120, p. 3). However, OSHA has determined that
it is not appropriate to add abrasive blasting to Table 1.
    There are a variety of options available to employers to control

exposure to respirable crystalline silica during blasting operations.
As discussed in the technological feasibility analysis (Section 5.1 of
Chapter IV of the FEA), these include (1) use of abrasive media other
than silica sand to reduce crystalline silica dust emissions, (2) use
of wet blasting techniques, (3) use of dust suppressors, (4) use of
dust collection systems, and (5) use of hydro-blasting technologies
that avoid having to use abrasive media.
    OSHA has decided that employees will be best protected when
employers, following the traditional approach set forth in paragraph
(d) in the standard for construction, choose among these dust control
strategies to select the controls that best fit the needs of each job.
OSHA's conclusion is based on the following additional considerations:
(1) Abrasive blasting operators must, separate from this rule, be
provided with and wear the respiratory protection required by 29 CFR
1926.57(f), and (2) employees helping with the operation, or who
otherwise must be in the vicinity of the operation, must also be
adequately protected by a combination of engineering controls, work
practices, and respirators. OSHA thus concluded that the Table 1
approach did not lend itself to specifying one or more controls that
would be suitable for all such operations. Furthermore, based on its
technological feasibility analysis for abrasive blasting (see Section
5.1 of Chapter IV of the FEA), respirators will be needed whatever
engineering or work practice control the employer uses under the
hierarchy of controls to lower silica exposure to the lowest level
feasible. Accordingly, based on the reasons discussed above, the Agency
is not mandating a particular dust control approach or approaches for
abrasive blasting and has therefore not included it as an entry in
Table 1 of the final standard.

Alternative Exposure Control Methods

    Paragraph (d) of the standard for construction describes the
requirements for the alternative exposure control methods approach,
which applies for tasks not listed in Table 1 or where the employer
chooses not to follow Table 1 or does not fully and properly implement
the engineering controls, work practices, and respiratory protection
described in Table 1. The alternative exposure control methods approach
is similar to OSHA's traditional approach of demonstrating compliance
with a permissible exposure limit (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). With the exception of the option to comply with either
paragraph (c) or paragraph (d), construction employers are required to
comply with all other paragraphs of the standard for construction.
    Paragraph (d)(1) specifies that construction employers who must or
choose to follow paragraph (d) shall limit employee exposures to
respirable crystalline silica at or below the PEL of 50 [mu]g/m\3\ as
an 8-hour time weighted average. The PEL is fully discussed in the
summary and explanation of Permissible Exposure Limit.
    Paragraph (d)(2) specifies the requirements for exposure
assessments, such as the types of assessments that are required under
the standard (i.e., performance or scheduled monitoring options), when
or how often those assessments must be conducted, methods of sample
analysis, employee notification of results, and the opportunity for
employees or their representatives to observe monitoring. These
requirements are fully discussed in the summary and explanation of
Exposure Assessment.
    Paragraph (d)(3) specifies the methods of compliance, which include
a requirement to reduce exposure through feasible engineering and work
practice controls before using respiratory protection, and cross-
references standards for abrasive blasting. These requirements are
fully discussed in the summary and explanation of Methods of
Compliance.

Permissible Exposure Limit (PEL)

    Paragraph (c) of the standard for general industry and maritime
(paragraph (d)(1) in the construction standard) establishes an 8-hour
time-weighted average (TWA) exposure limit of 50 micrograms of
respirable crystalline silica per cubic meter of air (50 [mu]g/m\3\).
This limit means that over the course of any 8-hour work shift,
exposures can fluctuate but the average exposure to respirable
crystalline silica cannot exceed 50 [mu]g/m\3\. The PEL is the same for
both general industry/maritime and construction. The PEL of 50 [mu]g/
m\3\ applies in the construction standard for tasks not listed on Table
1 or where the employer is not fully and properly implementing the
specified exposure control methods in paragraph (c) of the standard.
The PEL of 50 [mu]g/m\3\ does not apply directly to tasks listed on
Table 1, but the ability to achieve that PEL was the metric by which
OSHA decided on the specified exposure control(s) listed and whether
supplementary respiratory protection is required in some or all
circumstances for a particular task.
    OSHA proposed a PEL of 50 [mu]g/m\3\ because the Agency
preliminarily determined that occupational exposure to respirable
crystalline silica at the previous PELs, which were approximately
equivalent to 100 [mu]g/m\3\ for general industry and 250 [mu]g/m\3\
for construction and shipyards, resulted in a significant risk of
material health impairment to exposed workers, and that compliance with
the proposed PEL would substantially reduce that risk. OSHA also
preliminarily found the level of risk remaining at the proposed PEL to
be significant, but considered a PEL of 50 [mu]g/m\3\ to be the lowest
level that was technologically feasible overall.
    The PEL was a focus of comment in the rulemaking process, revealing
sharply divided opinion on the justification for and attainability of a
PEL of 50 [mu]g/m\3\. Many commenters representing labor unions, public
health associations, academic institutions, occupational health
professionals, and others expressed support for the proposed PEL (e.g.,
Document ID 1785, p. 2; 1878, p. 1; 2080, p. 1; 2106, p. 3; 2145, p. 3;
2166, p. 1; 2173, p. 2; 2178, Attachment 1, p. 2; 2318, p. 10; 2339, p.
7; 2341, p. 2; 3399, p. 4; 3403, p. 2; 3478, p. 1; 3601, Attachment 2,
p. 5; 3588, Tr. 3769; 4204, p. 50; 4207, p. 1). Other commenters
representing a wide range of industries, including construction,
foundries, concrete, brick and tile manufacturing, mineral excavation,
utility providers, and others, did not believe the proposed PEL was
appropriate. Stakeholders also offered opinions on the proposed
alternative PELs of 25 [mu]g/m\3\ and 100 [mu]g/m\3\.
    Some commenters contended that OSHA's proposed PEL was too low,
arguing that the proposed limit was infeasible or not justified by the
health and risk evidence (e.g., Document ID 1964; 1992, pp. 1, 8-10;
2024, pp. 1-2; 2067, p. 3; 2075, pp. 1-2; 2104, p. 1; 2119, Attachment
1; 2143, pp. 1-2; 2171, p. 1; 2185, pp. 2-4; 2191, p. 3; 2210,
Attachment 1, p. 6; 2268; 2269, pp. 2-3; 2279, pp. 2, 9; 2284, p. 2;
2289, p. 3; 2296; p. 39; 2301, Attachment 1, pp. 7-9; 2305, pp. 4-5,
15; 2312, p. 2; 2348, Attachment 1, pp. 32-33; 2349, p. 3; 2350, pp.
10-11; 2384, pp. 2, 9; 2182, pp. 3-4; 2102, pp. 1, 3; 2211, pp. 3-4;
2283, p. 2; 2250, p. 2; 2288, p. 8; 2300, p. 2; 2338, p. 2; 2356, p. 2;
2376; 2379, Appendix 1, p. 53; 3275, pp. 1-2). Many of these commenters
supported the adoption of the proposed alternative PEL of 100 [mu]g/
m\3\.
    Other commenters, including the United Automobile, Aerospace, and
Agricultural Implement Workers of America and the American Public
Health Association, contended that the

remaining risk at 50 [mu]g/m\3\ is excessive and argued that OSHA
should adopt a PEL of 25 [mu]g/m\3\ or even lower (e.g., Document ID
2163, Attachment 1, pp. 3, 13; 2176, pp. 1-2; 3577, Tr. 851-852; 3582,
Tr. 1853-1854; 3589, Tr. 4165; 4236, pp. 5-6). The American Federation
of Labor and Congress of Industrial Organizations (AFL-CIO) urged OSHA
to fully evaluate the evidence and set a lower PEL if deemed to be
feasible (Document ID 3578, Tr. 923-924).
    After considering the evidence in the rulemaking record, OSHA is
establishing a PEL of 50 [mu]g/m\3\. OSHA's examination of health
effects evidence, discussed in Section V, Health Effects, and Section
VI, Final Quantitative Risk Assessment and Significance of Risk,
confirms the Agency's preliminary conclusion that exposure to
respirable crystalline silica at the previous PELs results in a
significant risk of material health impairment to exposed workers, and
that compliance with the revised PEL will substantially reduce that
risk. OSHA's Quantitative Risk Assessment indicates that a 45-year
exposure to respirable crystalline silica at the preceding general
industry PEL would lead to between 11 and 54 excess deaths from lung
cancer, 11 deaths from silicosis, 85 deaths from all forms of non-
malignant respiratory disease (including silicosis as well as other
diseases such as chronic bronchitis and emphysema), and 39 deaths from
renal disease per 1000 workers. Exposures at the preceding construction
and shipyard PEL would result in even higher levels of risk. As
discussed in Section VII of this preamble, Summary of the Final
Economic Analysis and Final Regulatory Flexibility Analysis, these
results clearly represent a risk of material impairment of health that
is significant within the context of the ``Benzene'' decision (Indus.
Union Dep't, AFL-CIO v. Am. Petroleum Inst., 448 U.S. 607 (1980)). OSHA
has determined that lowering the PEL to 50 [mu]g/m\3\ will reduce the
lifetime excess risk of death per 1000 workers to between 5 and 23
deaths from lung cancer, 7 deaths from silicosis, 44 deaths from non-
malignant respiratory disease, and 32 deaths from renal disease.
    The Agency considers the level of risk remaining at the revised PEL
to be significant. However, based on the evidence evaluated during the
rulemaking process, OSHA has determined a PEL of 50 [mu]g/m\3\ is
appropriate because it is the lowest level feasible. As discussed in
Chapters IV and VI of Final Economic Analysis and Final Regulatory
Flexibility Analysis (FEA) and summarized in Section VII of this
preamble, the PEL is technologically and economically feasible for all
industry sectors, although it will be a technological challenge for
several affected sectors and will require the use of respirators for
certain job categories and tasks. As guided by the 1988 ``Asbestos''
decision (Bldg & Constr. Trades Dep't v. Brock, 838 F.2d 1258, 1266
(D.C. Cir. 1988)), OSHA is including additional requirements in the
rule to further reduce the remaining risk. OSHA anticipates that the
ancillary provisions in the rule will further reduce the risk beyond
the reduction that will be achieved by the PEL alone.
    OSHA has also determined that the proposed alternative PELs, 100
[mu]g/m\3\ and 25 [mu]g/m\3\, are inappropriate. As noted above,
significant risk to employees' health exists at the previous PELs, and
at and below the PEL of 50 [mu]g/m\3\. Because OSHA has determined that
a PEL of 50 [mu]g/m\3\ is technologically and economically feasible,
the Agency concludes that setting the PEL at 100 [mu]g/m\3\--a level
the Agency knows would continue to expose workers to significant risk
of material impairment to their health greater than is the case at 50
[mu]g/m\3\--would be contrary to the mandate in the OSH Act, which
requires the Secretary to promulgate a standard

. . . which most adequately assures, to the extent feasible, on the
basis of the best available evidence, that no employee will suffer
material impairment of health or functional capacity even if such
employee has regular exposure to the hazard dealt with by such
standard for the period of his working life (29 U.S.C. 655(b)).

Thus, the Agency has rejected the proposed alternative PEL of 100
[mu]g/m\3\.
    Even though OSHA's risk assessment indicates that a significant
risk also exists at the revised action level of 25 [mu]g/m\3\, the
Agency is not adopting the alternative PEL of 25 [mu]g/m\3\ because a
PEL of 50 [mu]g/m\3\ is the lowest exposure limit that can be found to
be technologically feasible for many of the industries covered by the
rule. Specifically, OSHA has determined that the information in the
rulemaking record either demonstrates that the proposed alternative PEL
of 25 [mu]g/m\3\ would not be achievable for most of the affected
industry sectors and application groups or the information is
insufficient to conclude that engineering and work practice controls
can consistently reduce exposures to or below 25 [mu]g/m\3\. Therefore,
OSHA cannot find that the proposed alternative PEL of 25 [mu]g/m\3\ is
achievable for most operations in the affected industries (see Section
VII of this preamble and Chapter IV of the FEA). Moreover, OSHA also
concludes that it would hugely complicate both compliance with and
enforcement of the rule if it were to set a PEL of 25 [mu]g/m\3\ for a
minority of industries or operations where it would be technologically
feasible and a PEL of 50 [mu]g/m\3\ for the remaining industries and
operations where technological feasibility at the lower PEL is
demonstrably unattainable, doubtful or unknown.
    Instead, OSHA has concluded that a PEL of 50 [mu]g/m\3\ is
economically and technologically feasible for all of the affected
industries and has decided to exercise its discretion to issue this
uniform PEL to avoid the enormous compliance and enforcement
complications that would ensue if it were to bifurcate the PEL (see
Section II, Pertinent Legal Authority, discussing the chromium (VI)
decision). Other issues related to OSHA's adoption of a PEL of 50
[mu]g/m\3\ are discussed below. The discussion is organized around the
following topics: Coverage of quartz, cristobalite, and tridymite; the
PEL as a gravimetric measurement of respirable dust; industry-specific
PELs; enhanced enforcement; environmental sources of crystalline silica
exposure; collection efficiency; coal dust; and CFR entries.
    Coverage of quartz, cristobalite, and tridymite. As discussed in
the summary and explanation of Definitions, the PEL applies to the
three forms of crystalline silica (i.e., quartz, cristobalite, and
tridymite) covered under previous OSHA PELs. Specifically, paragraph
(b) of the rule defines the term ``respirable crystalline silica'' to
mean

. . . quartz, cristobalite, and tridymite contained in airborne
particles whose measurement is determined by a sampling device
designed to meet the characteristics for particle-size-selective
samplers specified in International Organization for Standardization
(ISO) 7708:1995: Air Quality--Particle Size Fraction Definitions for
Health-Related Sampling.

    The proposed definition of respirable crystalline silica also would
have established a single PEL that would have encompassed the three
forms of silica covered under the previous OSHA silica PELs. While
commenters generally supported a single PEL for respirable crystalline
silica, they did not all agree on whether a single PEL should include
quartz, cristobalite, and tridymite (e.g., Document ID 1731, p. 2;
2315, p. 9). Some commenters argued that the PEL should include all
three forms; some suggested that the single PEL should be for only
quartz and cristobalite (e.g., Document ID 2177, Attachment B, p. 10;
2196, Attachment

1, p. 5; 3403, p. 4; 4212, p. 3) or only quartz (e.g., Document ID
2185, p. 6). NIOSH noted that ``tridymite is extremely rare in
workplaces, so a separate PEL probably cannot be supported by
epidemiologic evidence and may not be warranted for this material
(Document ID 2177, Attachment B, p. 10). Southern Company argued that

. . . the inclusion of tridymite and cristobalite are not supported
by the data and, due to their rare nature, serve to unnecessarily
create upward bias of the exposure evaluations due to the laboratory
detection limitations (Document ID 2185, p. 2).

    Halliburton Energy Services said that, given that OSHA has
acknowledged that the risk to workers exposed to a given level of
respirable crystalline silica may not be equivalent in different work
environments, OSHA's ``one size fits all'' silica PEL for different
forms of crystalline silica with varied physicochemical properties was
unwarranted (Document ID 2302, p. 5).
    As discussed in Section V, Health Effects, OSHA has concluded,
based on the available scientific evidence, that quartz, cristobalite,
and tridymite have similar toxicity and carcinogenic potency. The
Agency therefore concludes that a single PEL is appropriate for quartz,
cristobalite, and tridymite.
    The PEL as a gravimetric measurement of respirable dust. The
revised PEL, like OSHA's proposed PEL, is expressed as a gravimetric
measurement of respirable crystalline silica. The preceding PELs were
formulas that were inconsistent between industries and forms of
crystalline silica. For general industry (see 29 CFR 1910.1000, Table
Z-3), the PEL for crystalline silica in the form of respirable quartz
was based on two alternative formulas: (1) A particle-count formula
(PELmppcf = 250/(% quartz + 5) as respirable dust); and (2)
a mass formula proposed by the American Conference of Governmental
Industrial Hygienists (ACGIH) in 1968 (PEL = (10 mg/m\3\)/(% quartz +
2) as respirable dust). The general industry PELs for crystalline
silica in the form of cristobalite and tridymite were one-half of the
value calculated from either of the above two formulas for quartz. For
construction (29 CFR 1926.55, Appendix A) and shipyards (29 CFR
1915.1000, Table Z), the formula for the PEL for crystalline silica in
the form of quartz (PELmppcf = 250/(% quartz + 5) as
respirable dust), which requires particle counting, was derived from
the 1970 ACGIH threshold limit value (TLV). Based on the formulas, the
PELs for quartz, expressed as time-weighted averages (TWAs), were
approximately equivalent to 100 [mu]g/m\3\ for general industry and 250
[mu]g/m\3\ for construction and shipyards. As detailed in the
discussion of sampling and analysis in Chapter IV of the FEA, OSHA
finds that the formula based on particle-counting technology used in
the preceding general industry, construction, and shipyard PELs has
been rendered obsolete by respirable mass (gravimetric) sampling.
    A number of commenters supported the proposed switch from these
formulas to a PEL expressed as a gravimetric measurement of respirable
crystalline silica. For example, several stakeholders, including the
American Foundry Society (AFS), the American Petroleum Institute, the
Fertilizer Institute, and the North American Insulation Manufacturers
Association, agreed that OSHA should revise the previous formulaic PELs
into straightforward concentration/gravimetric-based thresholds (e.g.,
Document ID 2101, p. 4; 2145, p. 3; 2278, p. 2; 2301, Attachment 1, p.
4; 4213, p. 8; 4229, p. 27). Others suggested the previous formulaic
PELs are confusing, complicated (e.g., Document ID 2175, p. 5; 2185, p.
2), and outdated (e.g., Document ID 2163, Attachment 1, p. 2; 2204;
3588, Tr. 3769). Ameren Corporation also expressed support for the
elimination of the PELs calculated based on the percent silica in the
sample (Document ID 2315, p. 8).
    After considering the record on this issue, OSHA has decided to
adopt a PEL which is expressed as a gravimetric measurement of
respirable crystalline silica. OSHA expects that the revised PEL will
improve compliance because the PEL is simple and relatively easy to
understand, and is consistent with modern sampling and analytical
methods. In addition, OSHA finds that a uniform PEL will provide
consistent levels of protection for workers in all sectors covered by
the rule.
    Industry-specific PELs. Some commenters urged OSHA to take an
industry-specific approach to regulating respirable crystalline silica
exposures. Southern Company urged OSHA to consider a vertical standard
that addresses industries with known negative health impacts from
silica-containing materials (Document ID 2185, p. 2). Battery Council
International asked OSHA to set the PEL based on relevant particle size
and the size distribution data and recommended that OSHA adjust the PEL
for different industry segments consistent with these data (Document ID
2361, pp. 1-2). Other commenters suggested that the PEL should be lower
for certain industries, such as hydraulic fracturing and dental
equipment manufacturing (Document ID 2282, Attachment 3, p. 12; 2374,
Attachment 1, p. 5).
    OSHA considers the level of risk remaining at the new PEL of 50
[mu]g/m\3\ to be significant. Although OSHA expects the ancillary
provisions of the standard to reduce this risk below what engineering
and work practice controls alone can achieve, the Agency realizes that
lower PELs might be achievable in some industries and operations, which
would reduce this risk even further. However, as explained below, OSHA
concludes that the significant costs, including opportunity costs, of
devoting the resources necessary to attempting to establish and apply
multiple PELs for the diverse group of industries and operations
covered by the standard would undermine the value of this reduction
(see Building & Constr. Trades Dep't v. U.S. Dep't of Labor, 838 F.2d
1258, 1273 (D.C. Cir. 1988) (administrative difficulties, if
appropriately spelled out, could justify a decision to select a uniform
PEL)).
    Requiring OSHA to set multiple PELs--taking into account the
feasibility considerations unique to each industry or operation or
group of them--would impose an enormous evidentiary burden on OSHA to
ascertain and establish the specific situations, if any, in which a
lower PEL could be reached. Such an onerous obligation would inevitably
delay, if not preclude, the adoption of important health standards. In
addition, the demanding burden of setting multiple PELs would be
complicated by the difficulties inherent in precisely defining and
clearly distinguishing between affected industries and operations where
the classification determines legal obligations. The definitional and
line-drawing problem is far less significant when OSHA merely uses a
unit of industries and operations for analytical purposes, and when it
sets a PEL in the aggregate, i.e., when its analysis is limited to
determining whether a particular PEL is the lowest feasible level for
affected industries as a whole. If OSHA had to set multiple PELs, and
assign industries or operations to those PELs, the problem would become
much more pronounced as the consequences of imprecise classifications
would become much more significant.
    OSHA also finds that a uniform PEL will ultimately make the
standard more effective by making it easier for affected employers to
understand and comply with the standard's requirements. Moreover, a
uniform PEL makes it

possible for OSHA to provide clearer guidance to the regulated
community and to identify non-compliant conditions. For these reasons,
OSHA has always interpreted Section 6(b)(5) of the Act to accord the
Agency substantial discretion to set the PEL at the lowest level that
is feasible for industries and operations as a whole. In adopting the
arsenic standard, for example, OSHA expressly declined to set different
PELs, finding that ``[s]uch an approach would be extremely difficult to
implement'' (43 FR 19584, 19601 (5/5/1978)). In that instance, OSHA
explained:

    The approach OSHA believes appropriate and has chosen for this
and other standards is the lowest level achievable through
engineering controls and work practices in the majority of
locations. This approach is intended to provide maximum protection
without excessively heavy respirator use. Id.
    OSHA has also rejected such an approach in rulemakings on
benzene and chromium (VI).

(see 43 FR 5918, 5947 (2/10/1978); 71 FR 10100, 10337-10338 (2/28/
2006)).

    In the case of cotton dust, where OSHA did set different PELs for
certain discrete groups, the groups involved exposures to different
kinds of cotton dust and different degrees of risk. Even so, OSHA did
not adopt a unique PEL for every single affected sector (see 43 FR
27350, 37360-37361 (6/23/1978)); OSHA set one PEL for textile
industries and a separate PEL for non-textile industries, but expressly
rejected the option of adopting different exposure limits for each non-
textile industry). OSHA recognizes that the exception from the scope of
this rule for exposures that result from the processing of sorptive
clays results in a different PEL being enforced in that sector.
However, the processing of sorptive clays is a very small industry
sector, and OSHA finds that this sector can be readily segregated from
other industry sectors covered by the rule.
    Enhanced enforcement. Several commenters suggested retaining the
preceding PELs and focusing OSHA efforts on enhanced enforcement rather
than on a new rule (e.g., Document ID 1741, Attachment 1; 2067, p. 4;
2183, p. 4; 2185, p. 2; 2210, Attachment 1, pp. 3, 7; 2261, pp. 2-3;
2283, p. 2; 2292, p. 2; 2344, p. 2; 2349, p. 3; 2363, p. 10; 3486, p.
1; 3496, p. 3). Some of these commenters, such as the Small Business
Administration's Office of Advocacy, indicated that OSHA data show
widespread noncompliance with the previous PELs and suggested that
silica-related illnesses could be linked to noncompliance (e.g.,
Document ID 2349, p. 3). Others, such as Arch Masonry, urged OSHA to
consider information and testimony about noncompliant work environments
as evidence of an enforcement problem rather than evidence to support a
new rule (e.g., Document ID 3587, Tr. 3651-3652). The Mercatus Center
asked OSHA to explain how improved enforcement of the existing rule is
not superior to a more stringent PEL (Document ID 1819, p. 9).
    As discussed in Section V, Health Effects, OSHA does not find these
arguments persuasive. First, many of the commenters used OSHA's
enforcement data to make this point. These data were obtained during
inspections where non-compliance was suspected and thus were skewed in
the direction of exceeding the preceding PELs. As the Building and
Construction Trades Department, AFL-CIO (BCTD) explained, OSHA data
showing noncompliance with the preceding PEL is not representative of
typical exposure levels, since sampling for compliance purposes targets
worst-case exposure scenarios (Document ID 3581, Tr. 1634-1636).
    Moreover, not all commenters agreed that overexposures were
``widespread.'' A few other commenters (e.g., AFS) thought that OSHA
substantially overstated the number of workers occupationally exposed
above 100 [mu]g/m\3\ in its PEA (Document ID 2379, Attachment B, p.
25). In either case, OSHA's analysis evaluated risks at various
exposure levels, as is required by the OSH Act. As noted above, the
available data indicate that exposure to respirable crystalline silica
at the preceding PELs results in a significant risk of material health
impairment among exposed employees. Simply enforcing the preceding PELs
will not substantially reduce or eliminate this significant risk.
    Exposure Variability. Commenters, including the Asphalt Roofing
Manufacturers Association (ARMA), argued that because OSHA PELs are
never-to-be-exceeded limits, employers must maintain average exposures
well below the PEL to have confidence that exposures are rigorously
maintained at or below the PEL every day, for every worker (e.g.,
Document ID 2291, pp. 5-7). The Construction Industry Safety Coalition
(CISC) made a similar argument regarding the need to control exposure
levels to well below the PEL due to the variability of silica exposures
on construction worksites in order to assure compliance (Document ID
4217, p. 12).
    OSHA recognizes that differences in exposure can occur due to
workplace variables such as fluctuations in environmental conditions or
air movement. However, many of the major sources of day-to-day
variability can be moderated by the consistent use of engineering
controls and appropriate work practices (Document ID 3578, Tr. 971;
3589, Tr. 4251-4252; 4234, Attachment 2, pp. 31-38).
    OSHA has acknowledged and discussed exposure variability in past
rulemakings where the same issue was raised (e.g., benzene, 52 FR
34534; asbestos, 53 FR 35609; lead in construction, 58 FR 26590;
formaldehyde, 57 FR 22290; cadmium, 57 FR 42102; and chromium (VI), 71
FR 10099). In its asbestos rulemaking, for example, OSHA found that
industry's argument about uncontrollable fluctuations was exaggerated
because such fluctuations could be minimized through proper inspection
and maintenance of engineering controls and through proper training and
supervision of employees whose work practices affected exposure levels
(59 FR 40964, 40967 (8/10/94)). The Agency also noted that its
enforcement policy gives employers the opportunity to show that a
compliance officer's measurement over the PEL is unrepresentatively
high and does not justify a citation, thus alleviating the concern
employers might have that they will be cited on the basis of a single
measurement that results from uncontrollable fluctuations (59 FR at
40967).
    Reviewing courts have held that OSHA's obligation to show that a
PEL can be achieved in most operations most of the time has been met
despite the presence of random exposure variability. These courts have
noted, in particular, OSHA's flexible enforcement policies, which allow
the Agency to take such exposure variability into account before
issuing a citation (e.g., Building & Constr. Trades Dept. v. Brock, 838
F.2d 1258 (D.C. Cir. 1988) (``Asbestos II'')). In the Asbestos II case,
the D.C. Circuit cited with approval OSHA's policy of allowing for a
possible re-inspection if OSHA measured an asbestos exposure above the
PEL during an inspection. If the employer appeared to be using, to the
extent feasible, appropriate work practices and engineering controls,
OSHA could agree not to issue a citation at that time based on that
inspection and to re-inspect at a later time. Such a re-inspection
would help determine if that over-exposure was typical or simply a
random, uncontrollable fluctuation; OSHA could then determine whether
or not to issue a citation accordingly (Asbestos II at 1268; 51 FR
22653 (6/20/1986)). Thus OSHA has, in the past, adopted fair and
flexible enforcement policies to deal with the issue of exposure
variability

and will do the same for enforcement of the new silica standards.
    Such an enforcement policy recognizes the possibility that OSHA may
measure silica exposures on a day when exposures are above the PEL due
to unforeseeable, random exposure variations. In such a case, when the
employer has previously monitored the work area, OSHA inspectors would
review the employer's long-term body of data demonstrating the exposure
pattern for tasks/operations that are representative of those under
OSHA's evaluation. After comparing the employer's exposure data with
OSHA's sampling results, OSHA's determination whether to resample would
be governed by the inspector's judgment of whether the OSHA sampling
results are representative.
    Where an employer can show, based on a series of measurements made
pursuant to the sampling and analytical protocols set out in these
standards or other relevant data, that the OSHA one-day measurement may
be unrepresentatively high, OSHA may re-inspect the workplace and
measure exposures again. If, after such a reinspection, OSHA has reason
to believe that there are circumstances that account for the high
exposure measurement, OSHA may decide not to issue a citation.
    For OSHA to consider a reinspection rather than citation, an
employer must demonstrate that the inspector's one-day sample is
unrepresentative of normal exposure levels. In most cases, this
demonstration would consist of a series of full shift measurements
representative of the exposure of the employee under consideration.
These measurements should consist of all valid measurements related to
the employee under consideration taken within the last year and should
show that only on rare occasions could random fluctuations result in
TWA concentrations above the PEL.
    Environmental sources of crystalline silica exposure. Some
stakeholders raised concerns about the extent to which crystalline
silica dust from naturally-occurring environmental sources (e.g., in
southwestern regions of the United States) might contribute to employee
exposures to respirable crystalline silica and artificially inflate
sampling measurements (e.g., Document ID 1785, p. 4; 2116, Attachment
1, pp. 19-20; 3230, p. 1; 3533, p. 22). SMI cited an EPA study
published in 1996 (Document ID 3637), and indicated that mean
concentrations of ambient atmospheric respirable crystalline silica
across 22 cities in the United States range from 0.9 to 8 [mu]g/m\3\
(Document ID 3533, p. 20). OSHA recognizes that there can be occasions
when environmental sources of silica may affect occupational sampling
results. However, OSHA notes that the data utilized in the 1996 study
were originally published in an earlier (1984) journal article by Davis
et al. (Document ID 3852), and the EPA report included important
caveats about the environmental data that were available at the time
(Document ID 3637, pp. 3-29, 3-31--3-34). For example, the section of
the EPA report on ``Limitations of Current Data'' states:

    The lack of current, direct measures of ambient quartz
concentrations is a major limitation of the data available for use
in estimating U.S. ambient silica concentrations (Document ID 3637,
pp. 3-31).

    The report also indicated that ``. . . another limitation of the
available data is the fact that neither current nor dated quartz
measurements were taken using PM10 samplers'' (Document ID
3637, pp. 3-33).
    In addition, OSHA notes that the sampling methodology used in the
Davis study does not measure respirable crystalline silica, as defined
in OSHA's silica rule. Rather, the Davis study presents data from
dichotomous samplers that are equipped with particle size selection
inlets. These samplers allow for measurement of two particle size
fractions: A fine fraction with particle sizes having aerodynamic
diameter less than 2.5 microns (PM2.5) and a coarse fraction
designed to eliminate particles greater than about 15 microns in
aerodynamic diameter (PM15). By contrast, OSHA's definition
for respirable crystalline silica is tied to an International
Organization for Standardization (ISO) sampling methodology that has
different size-specific mass collection efficiencies. Of particular
importance, the dichotomous samplers from the Davis study collect
particles with aerodynamic diameters between 10 and 15 microns that are
generally excluded from the ISO sampling methodology; and the
dichotomous samplers likely collect a considerably higher portion of
particles with aerodynamic diameters between 5 and 10 microns.
    OSHA concludes that the sampling results presented in the Davis
study are not comparable to respirable crystalline silica measurements,
as defined in OSHA's rule. It is clear that the sampling methodology
considered in the Davis study would overstate respirable crystalline
silica levels measured using the ISO sampling methodology. Moreover,
OSHA has demonstrated that compliance with the PEL is technologically
feasible. OSHA's evaluation of the technological feasibility of the PEL
involved evaluation of thousands of respirable crystalline silica
samples collected in a variety of occupational settings that include
contributions from environmental sources in different geographic areas.
Because the exposure data considered by OSHA in its evaluation of the
technological feasibility of the PEL includes contributions from
environmental sources, these contributions are already taken into
account in determining the feasibility of the PEL. Therefore, OSHA
finds that environmental sources of respirable crystalline silica
exposure, to the extent they contribute to workplace exposures, are
already considered in the Agency's conclusion that the revised PEL is
feasible.
    Collection efficiency. In the rule, OSHA is adopting the ISO/CEN
particle size-selective criteria for respirable dust samplers used to
measure exposures to respirable crystalline silica. Several commenters,
including U.S. Aggregates, the National Industrial Sand Association,
and the U.S. Chamber of Commerce, argued that moving from the current
criteria to the ISO/CEN convention effectively decreases the PEL and
action level below the levels intended, since more dust would be
collected by samplers that conform to the ISO/CEN convention than by
those that conform to the current criteria (Document ID 2174; 2195, p.
30; 2285, pp. 3-4; 2317, p. 2; 3456, p. 10; 4194, pp. 15-16). However,
as discussed in Chapter IV of the FEA, the Dorr-Oliver 10-mm cyclone
used by OSHA for enforcement of respirable dust standards conforms to
the ISO/CEN specification with acceptable bias and accuracy when
operated in accordance with OSHA's existing method (i.e., measurements
taken using the Dorr-Oliver 10-mm cyclone following OSHA's existing
method provide results that are consistent with the ISO/CEN convention,
and therefore are acceptable for measuring respirable crystalline
silica exposures under the rule). The change from the previous criteria
to the ISO/CEN convention is therefore effectively a continuation of
current practice.
    Coal dust. Southern Company, the American Iron and Steel Institute,
and Ameren Corporation indicated that revising the respirable
crystalline silica PEL creates uncertainty with regard to the PEL for
coal dust, which continues to use the previous criteria for calculation
of respirable crystalline silica (Document ID 2185, p. 2; 2261, pp. 2,
5; 2315, p. 8). They urged the Agency to address how the existing coal

dust PEL will interact with the new PEL and calculation for exposure to
respirable crystalline silica. For example, Southern Company stated:

. . . it is unclear to us what the expectation would be in
evaluating and managing exposures to either of these substances when
the effective source of these exposures is the same. If both PELs
apply, this would mean duplicate or dual sampling (Document ID 2185,
p. 2).

Ameren also questioned whether employers would be required to sample
for both respirable crystalline silica and respirable coal dust on
workers who are potentially exposed to both substances. Ameren
suggested that OSHA should consider changing the PELs for amorphous
silica and coal dust so that they are consistent with the revised PEL
for respirable crystalline silica (Document ID 2315, pp. 2, 8).
    OSHA clarifies that the respirable crystalline silica rule does not
change the existing PEL for coal dust. However, as indicated
previously, the Dorr-Oliver 10-mm cyclone used by OSHA for enforcement
of respirable dust standards exhibits acceptable bias against the ISO/
CEN specification when operated in accordance with OSHA's existing
method. Employers can continue to use the Dorr-Oliver cyclone to
evaluate compliance with the new respirable crystalline silica PEL, as
well as with the PEL for coal dust; duplicate sampling is not
necessary. Employers can also use other ISO/CEN-compliant samplers to
evaluate compliance with either or both PELs.
    CFR entries. The rule revises entries for crystalline silica in 29
CFR 1910.1000 Table Z-1 to cross-reference the new standard, 1910.1053.
A comparable revision to 29 CFR 1915.1000 Table Z cross-references
1915.1053, which in turn cross-references 1910.1053. The entries for
crystalline silica in 29 CFR 1926.55 Appendix A are revised to cross-
reference 1926.1153. General industry standards are located in Part
1910; maritime standards are located in Part 1915; and construction
standards are located in Part 1926.
    The preceding PELs for respirable crystalline silica are retained
in 29 CFR 1910.1000 Table Z-3, 29 CFR 1915.1000 Table Z, and 29 CFR
1926.55 Appendix A. Footnotes are added to make clear that these PELs
apply to any sectors or operations where the new PEL of 50 [mu]g/m\3\
is not in effect, such as the processing of sorptive clays. These PELs
are also applicable during the time between publication of the silica
rule and the dates established for compliance with the rule, as well as
in the event of regulatory delay, a stay, or partial or full
invalidation by the Court.
    While the preceding PELs for respirable crystalline silica in 29
CFR 1910.1000 Table Z-3 are being retained, the PELs for total
crystalline silica dust are being deleted. OSHA proposed to delete the
previous general industry PELs for exposure to total crystalline silica
dust because development of crystalline silica-related disease is
related to the respirable fraction of, rather than total, dust exposure
(see Section V, Health Effects). This view is consistent with that of
ACGIH, which no longer has a Threshold Limit Value for total
crystalline silica dust. NIOSH does not have a Recommended Exposure
Level for total crystalline silica exposure, and neither the National
Toxicology Program nor the International Agency for Research on Cancer
has linked exposure to total crystalline silica dust exposure to
cancer, as they have with respirable crystalline silica exposure.

Exposure Assessment

    Paragraph (d) of the standard for general industry and maritime
(paragraph (d)(2) of the standard for construction) sets forth
requirements for assessing employee exposures to respirable crystalline
silica. The requirements are issued pursuant to section 6(b)(7) of the
OSH Act, which mandates that any standard promulgated under section
6(b) shall, where appropriate, ``provide for monitoring or measuring
employee exposure at such locations and intervals, and in such manner
as may be necessary for the protection of employees'' (29 U.S.C.
655(b)(7)).
    Assessing employee exposure to toxic substances is a well-
recognized and accepted risk management tool. The purposes of requiring
an assessment of employee exposures to respirable crystalline silica
include: Determination of the extent and degree of exposure at the
worksite; identification and prevention of employee overexposure;
identification of the sources of exposure; collection of exposure data
so that the employer can select the proper control methods to be used;
and evaluation of the effectiveness of those selected methods.
Assessment enables employers to meet their legal obligation to ensure
that their employees are not exposed in excess of the permissible
exposure limit (PEL) and to ensure employees have access to accurate
information about their exposure levels, as required by section 8(c)(3)
of the Act (29 U.S.C. 657(c)(3)). In addition, exposure data enable the
physicians or other licensed health care professionals (PLHCP)
performing medical examinations to be informed of the extent of
occupational exposures.
    In the proposed standard for general industry and maritime, OSHA
included a requirement for employers to assess the exposure of
employees who are reasonably expected to be exposed to respirable
crystalline silica at or above the action level of 25 [micro]g/m\3\.
This obligation consisted of: An initial exposure assessment, unless
monitoring had been performed in the previous 12 months, or the
employer had objective data to demonstrate that exposures would be
below the action level under any expected conditions; periodic exposure
assessments, following either a scheduled monitoring option (with the
frequency of monitoring determined by the results of the initial and
subsequent monitoring) or a performance option (i.e., use of any
combination of air monitoring data or objective data sufficient to
accurately characterize employee exposures); and additional exposure
assessments when changes in the workplace resulted in new or additional
exposures to respirable crystalline silica at or above the action
level. The proposed standard also included provisions for the method of
sample analysis, employee notification of assessment results, and
observation of monitoring.
    The proposed standard for construction included the same
requirements for exposure assessment as the proposed standard for
general industry and maritime; however, employers were not required to
assess the exposure of employees performing tasks on Table 1 where the
employer fully implemented the engineering controls, work practices,
and respiratory protection specified in Table 1. This exception to the
general requirement for exposure assessment was intended to relieve the
construction employer of the burden of performing an exposure
assessment in these situations, because appropriate control measures
are already identified.