and at all times. Employers who comply with Table 1 need not assess
employee exposures as otherwise required under paragraph (f), and
workers in these circumstances will not have the benefit of
conventional exposure data to characterize their exposures. Because, in
the absence of an exposure assessment, employers will not be able to
confirm that exposures are below the PEL, or identify circumstances in
which exposures may exceed the PEL, the Agency is proposing to require
respiratory protection in situations where overexposures may occur even
with the implementation of engineering and work practice controls. The
Agency is requesting comments regarding the appropriateness of the use
and selection of respirators in several operations.
    If an employer anticipates that a worker will perform a single
operation listed in Table 1 for four hours or less during a single
shift, then the employer must ensure that the worker uses whichever
respirator is specified in the ``<=4 hr/day'' column in the table. For
example, if an employer anticipates that a worker will operate a
stationary masonry saw for four hours or less, and the worker does not
perform any other operation listed in Table 1, the worker would not be
required to use respiratory protection because there is no respirator
requirement for that entry in the table.
    If an employer anticipates that a worker will perform a single
operation listed in Table 1 for more than four hours, then the employer
must ensure that the worker uses the respirator specified in the ``>4
hr/day'' column in Table 1 for the entire duration of the operation.
For example, if an employer anticipates that a worker will operate a
stationary masonry saw for more than four hours, and the worker does
not perform any other operation listed in Table 1, the worker would be
required to wear a half-mask respirator for the entire duration of the
operation (refer to Table 1).
    Additionally, for workers who engage in two or more discrete
operations from Table 1 for a total of more than four hours during a
single work shift, employers that rely on Table 1 must provide, for the
entire duration of each operation performed, the respirator specified
in the ``>4 hr/day'' column for that operation, even if the duration of
that operation is less than four hours. If no respirator is specified
for an operation in the ``>4 hr/day'' column, then respirator use would
not be required for that part of a worker's shift.
    For example, if a worker is using a stationary masonry saw for
three hours and engages in tuckpointing for two hours in the same the
shift, the employer would be required to ensure that the worker uses a
half-mask respirator for the three hours engaged in sawing, and a
tight-fitting, full-face PAPR for the two hours engaged in tuckpointing
work. In other words, if a worker uses a stationary saw and engages in
a tuckpointing operation for a total of more than four hours in a
single work shift, the worker would be required to use a half-mask
respirator for the entire time he or she operates the stationary saw
and a tight-fitting, full-face PAPR for the tuckpointing work,
regardless of how long each task is performed.
    The following paragraphs describe the engineering controls, work
practices and respirators selected for each of the operations listed in
Table 1. In addition, the Agency describes the information that it has
relied upon to develop the control strategies.
    For most control strategies in the table, OSHA is proposing to
require additional specifications to ensure that the strategies are
effective. The most frequently required additional specifications are:
     Changing water frequently when using water delivery
systems, to avoid silt build-up in the water and prevent wet slurry
from accumulating and drying. This prevents silica from becoming
airborne when the water becomes aerosolized by the rotation of
equipment or when the water dries and leaves residual respirable
silica-containing dust.
     Operating equipment such that no visible dust is emitted
from the process. Visible dust may be an indication that the controls
are not operating effectively. The absence of visible dust does not
necessarily indicate that workers are protected, but visible dust is a
clear indication of a potential problem.
     Providing sufficient ventilation to prevent build-up of
visible airborne dust when working indoors or in enclosed spaces.
Stagnant air in an enclosed

environment may increase worker exposures.
     Ensuring that saw blades and abrasive discs are not
excessively worn. Excessive wear tends to increase respirable silica
emissions and worker exposures.
     Using dust collectors according to manufacturers'
specifications. Manufacturer specifications are often based on
operation-specific designs.
    Use of stationary masonry saws. For workers operating stationary
masonry saws, OSHA is proposing to require that the saws be equipped
with an integrated water delivery system that is operated and
maintained to minimize dust emissions. The exposure profile created for
this operation shows that cutting with wet methods offers a clear
reduction to exposures, as opposed to dry cutting with no controls or
with a mix of administrative or other engineering controls. The Agency
obtained 12 samples for workers dry cutting with no engineering
controls, 9 samples for workers dry cutting with a mix of controls, and
7 samples for workers operating the saws with water at the point of
operation. The mean, median, and range values were all lower for
workers using wet methods:
     Median of 33 [mu]g/m\3\ (a 34-percent reduction from dry
cutting and 63-percent reduction from dry cutting with some controls).
     Mean of 42 [mu]g/m\3\ (an 88-percent reduction from dry
cutting and 80-percent reduction from dry cutting with some controls).
     A maximum value of 93 [mu]g/m\3\, as opposed to a maximum
value of 2,005 [mu]g/m\3\ for dry cutting, and 824 [mu]g/m\3\ for dry
cutting with some controls.

The Agency concludes, based on this information and the analysis
discussed in the exposure profile for this operation (PEA, Chapter 4),
that the water delivery system specified in Table 1 consistently
reduces worker exposures to or below the proposed PEL when the saws are
used for four hours or less. As a result, respiratory protection is not
included in the control strategy for these operations. OSHA believes
that, even when workers operate stationary masonry saws for eight
hours, wet methods will reduce 8-hour exposures to or below the
proposed PEL most of time, as described in Chapter 4 of the PEA.
However, the maximum TWA value measured for a stationary masonry saw
operator is 93 [mu]g/m\3\, equivalent to a 4-hr exposure of 47 [mu]g/
m\3\ (see Chapter 4 of the PEA). Thus, when workers perform this
operation for more than four hours, silica exposures may occasionally
exceed the PEL. Because, in the absence of an exposure assessment,
employers will not be able to confirm that exposures are below the PEL,
or identify circumstances in which exposures may exceed the PEL, the
proposed rule requires that employers provide half-mask respirators to
workers who use stationary masonry saws for more than four hours.
    Use of hand-operated grinders. The table provides employers with
two different control strategies.
    Option 1: Use water-fed grinders that continuously feed water to
the cutting surface, operated and maintained to minimize dust
emissions. For operations lasting less than four hours, OSHA is
proposing that respirators will not be required. For operations lasting
four hours or more, OSHA is proposing the use of half-mask respirators
to ensure workers are protected.
    For its technological feasibility analysis, OSHA did not obtain any
sample results where wet grinding occurred. Information available to
the Agency suggests that overexposures still occur when using wet
methods and that there are additional challenges such as limited
applications. OSHA has decided to include this control strategy based
on the use of water systems on similar tools used in the cut stone and
stone products manufacturing industry that have shown a reduction of
exposures to well below 100 [micro]g/m\3\ (OSHA 3362-05). The Agency
believes that similar reductions can be achieved for grinding
operations because the amount of respirable dust produced in these
operations is comparable. Based on this inference, OSHA believes that
wet methods alone will provide sufficient protection for shifts lasting
four hours or less, and is proposing to require the use of half-mask
respirators with an APF of 10 for shifts lasting more than four hours.
    The Agency requests comments and additional information regarding
wet grinding and the adequacy of this control strategy.
    Option 2: Use hand-operated grinders with commercially available
shrouds and dust collection systems operated and maintained to minimize
dust emission. The dust collector must be equipped with a HEPA filter
and must operate at 25 cubic feet per minute (cfm) or greater airflow
per inch of blade diameter. OSHA is proposing to require the use of
half-mask respirators at all times, for outdoor and indoor operations
alike, to ensure workers are protected.
    OSHA's exposure profile for this operation contains 13 samples
associated with the use of LEV. Two of these samples are associated
with outdoor activities (40 [micro]g/m\3\ and 53 [micro]g/m\3\), and 11
samples are associated with indoor work (a range of 12 [micro]g/m\3\ to
208 [micro]g/m\3\). Overall, exposure samples show that outdoor
exposures are lower than indoor exposures. The mean, median, and range
values for these operations are:
     Median of 47 [mu]g/m\3\ for outdoor operations with LEV,
and 107 [mu]g/m\3\ for indoor operations with LEV.
     Mean of 46 [mu]g/m\3\ for outdoor operations with LEV, and
96 [mu]g/m\3\ for indoor operations with LEV.
     A maximum value of 53 [mu]g/m\3\ for outdoor operations
with LEV, and 208 [mu]g/m\3\ for indoor operations with LEV.
    These values suggest that workers would sometimes achieve levels
below the proposed PEL with LEV. However, the Agency recognizes that
elevated exposures occur even with the use of LEV in these operations
based on the fact that 8 out of 13 samples collected exceed the
proposed PEL, with 6 samples ranging from 100 [mu]g/m\3\ to 250 [mu]g/
m\3\. Based on this information, OSHA is proposing that employers apply
the engineering control specified and equip workers with half-mask
respirators at all times. It is important to note that OSHA has
preliminarily concluded that the LEV control outlined in the table will
not reduce and maintain exposures to the proposed PEL for all workers.
However, these controls will reduce exposures within the APF of 10
offered by half-mask respirators. The Agency seeks additional
information to confirm that the control strategy (including the use of
half-mask respirators) listed in the table will reduce workers'
exposure to or below the PEL.
    Tuckpointing. OSHA is proposing to require employers to equip
grinding tools with commercially available shrouds and dust collection
systems, operated and maintained to minimize dust emissions. The
grinder must be operated flush against the working surface, with
grinding operations performed against the natural rotation of the blade
(i.e., mortar debris must be directed into the exhaust). Employers
would be required to use vacuums that provide at least 80 cubic feet
per minute (cfm) to 85 cfm airflow through the shroud and include
filters that are at least 99 percent efficient.
    Recent dust control efforts for tuckpointing have focused on using
a dust collection hood, or shroud, which encloses most of the grinding
blade. It is used with a vacuum cleaner system that exhausts air from
these hood systems and collects dust and debris. These shroud and
vacuum combinations capture substantial amounts of debris, but air
monitoring results summarized in OSHA's exposure profile for this

operation show that even with this control in place, silica exposures
often continue to exceed 100 [mu]g/m\3\, with many of the results
exceeding 250 [mu]g/m\3\.
    The highest exposure obtained for outdoor work with LEV (6,196
[micro]g/m\3\), and many other exposures, suggest that there are
circumstances in which the protection factor offered by a PAPR will be
needed to reduce worker exposure to below 50 [micro]g/m\3\. OSHA is
aware that some exposures may be effectively controlled with the LEV
system and a respirator with an APF of 10, but is proposing to require
the use of the LEV system with respirators that provide an APF of 50 to
ensure that the control strategy protects those workers with extremely
elevated exposures. Based on this information, OSHA estimates that a
substantial percentage of the worker population will need respiratory
protection in the form of a powered air-purifying respirator (PAPR)
with a loose-fitting helmet or a negative-pressure full-facepiece
respirator regardless of task duration.
    Furthermore, OSHA is stressing the importance of sufficient air
circulation in enclosed or indoor environments to maximize the effect
of the control strategy outlined. Elevated results are reported for
tuckpointers in operations performed in areas with limited air
circulation (including indoors). As such, the Agency is proposing to
require employers to provide for ventilation to prevent the
accumulation of airborne dust during operations performed in enclosed
spaces, in addition to requiring equipment to be operated so that no
visible dust is emitted from the process.
    Use of jackhammers and other impact drillers. The table provides
employers with two different control strategies.
    Option 1: Apply a continuous stream or spray of water at the point
of operation.
    Results in OSHA's exposure profile show that the wet methods
attempted in the five samples obtained were not effective at all in
reducing exposures; in fact, the statistical values are higher than
those under baseline conditions. Based on the best available
information, OSHA believes that no single wet method was applied
effectively and consistently throughout these operations, and the data
obtained for wet methods is reflective of that inconsistency (ERG-C,
2008; PEA, Chapter 4). The three highest results for the samples
corresponding to wet methods show respirable dust levels higher than
the mean respirable dust value for comparable uncontrolled operations,
indicating that the wet method control was not applied effectively, as
it was not reducing total respirable dust levels.
    Conversely, however, OSHA has obtained information from individual
employers, NIOSH, and an informal consortium of New Jersey
organizations interested in controlling silica during road construction
activities that have all tested wet dust suppression methods with
chipping and breaking equipment. The results of these tests indicate
that wet dust suppression is effective in reducing respirable
crystalline silica exposures.
    The Agency obtained a reading for a jackhammer operator breaking
concrete outdoors, where a continuous stream of water was directed at
the breaking point. When compared with the median value in the exposure
profile for outdoor and uncontrolled operations, the result represents
a 77-percent exposure reduction in respirable quartz (OSHA SEP
Inspection Report 106719750).
    NIOSH provided similar findings when it completed several studies
evaluating water spray devices to suppress dust created while workers
used chipping and breaking equipment. Compared with concentrations
during uncontrolled pavement breaking, respirable dust results were
between 72 and 90 percent lower when the water spray was used (NIOSH
EPHB-282-11a, 2003). A follow-up NIOSH study reported a similar 77-
percent reduction in silica concentration during 60-minute trials with
a solid cone nozzle producing water mist (NIOSH EPHB-282-11c-2, 2004).
    Two other findings also show that water spray systems are effective
in reducing respirable dust concentrations. Williams and Sam (1999)
evaluated a shop-built water spray system attached to a hand-held
pneumatic chipper used by a worker removing hardened concrete from
inside a mixing truck drum. Although this task is not typically
performed by construction workers, it represents a worst-case
environment (in a confined space or indoors) for construction concrete
chipping and breaking jobs. Water spray decreased respirable dust by
about 70 percent in the worker's breathing zone, again showing that a
water spray system offers substantial reduction in silica-containing
dust generated.
    Additionally, the New Jersey Laborers Health and Safety Fund,
NIOSH, and the New Jersey Department of Health and Senior Services have
collaborated in publishing simple instructions for developing spray
equipment for jackhammers. A design tested in New Jersey involving a
double water spray--one on each side of the breaker blade--reduced peak
dust concentrations by approximately 90 percent compared with the peak
concentration measured for uncontrolled breaking (Hoffer, 2007; NIOSH
2008-127, 2008; NJDHSS, no date).
    OSHA believes that, even when workers perform impact drilling for
eight hours, wet methods will reduce TWA exposures to or below the
proposed PEL most of time, as described in Chapter 4 of the PEA.
However, when workers perform this operation for more than four hours,
silica exposures may occasionally exceed the PEL. Because, in the
absence of an exposure assessment, employers will not be able to
confirm that exposures are below the PEL, or identify circumstances in
which exposures may exceed the PEL, the proposed rule requires that
employers provide respiratory protection to workers who perform impact
drilling for more than four hours.
    OSHA notes that applying the lowest exposure reduction of the
values reported in the studies would reduce the highest range of
exposures to within an APF of 10 provided by a half-mask respirator
and, thus, consistently and adequately protect workers for a full
shift. Additionally, for impact drilling operations lasting four hours
or less, OSHA is proposing to allow workers to use water delivery
systems without the use of respiratory protection, as the Agency
believes that this dust suppression method alone will provide
consistent, sufficient protection. OSHA is requesting comments and
additional information that address the appropriateness of this control
strategy.
    It is important to mention that the highest exposures in the
profile were obtained during indoor work, with a maximum value of 3,059
[mu]g/m\3\. OSHA believes that these elevated results are in part due
to poor air circulation in enclosed environments. The Agency believes
that it is particularly important to ensure adequate air circulation
during indoor work, so that airborne dust does not accumulate and
contribute to higher exposures. As such, the proposed Table 1 includes
a specification that directs employers to provide adequate ventilation
during indoor work so as to prevent build-up of visible airborne dust.
    Option 2: Use tool-mounted shroud and HEPA-filtered dust collection
system, operated and maintained to minimize dust emissions.
    Based on available information, LEV systems are also able to
effectively reduce respirable airborne silica dust. NIOSH tested two
tool-mounted LEV shrouds during work with chipping hammers intended for
chipping vertical concrete surfaces. Comparing multiple

short-term samples, NIOSH found that the shrouds reduced respirable
dust by 48 to 60 percent (Echt et al., 2003; NIOSH EPHB 282-11a, 2003).
In a separate evaluation, NIOSH showed that this type of LEV system
controls dust equally well for smaller chipping equipment. Mean silica
levels decreased 69 percent when the workers used a tool-mounted LEV
shroud in enclosed spaces (NIOSH EPHB 247-19, 2001). In this study, a
combination of LEV and general exhaust ventilation provided additional
dust control, resulting in a 78 percent decrease in silica readings.
This finding further supports OSHA's proposal to ensure that additional
ventilation is provided during indoor work to prevent the accumulation
of airborne dust.
    OSHA believes that, even when workers perform impact drilling for
eight hours, these controls will reduce TWA exposures to or below the
proposed PEL most of time, as described in Chapter 4 of the PEA.
However, when workers perform this operation for more than four hours,
silica exposures may occasionally exceed the PEL. Because, in the
absence of an exposure assessment, employers will not be able to
confirm that exposures are below the PEL, or identify circumstances in
which exposures may exceed the PEL, the proposed rule requires that
employers provide respiratory protection to workers who perform impact
drilling for more than four hours. OSHA believes that that LEV systems
will reduce the highest range of airborne respirable silica
concentrations (in the exposure profile) to within an APF provided by a
half-mask respirator for operations lasting a full shift. For
operations lasting four hours or less, OSHA is proposing to allow
workers to use the shroud and HEPA vacuum system without respirators,
as the Agency believes that this control alone will provide consistent,
sufficient protection. The highest exposure values were obtained during
indoor work, and the Agency is proposing that employers provide
appropriate air circulation in order to maximize the effectiveness of
the proposed control strategy.
    Use of rotary hammers or drills (except overhead use). Table 1
requires that drills be equipped with a hood or cowl and a HEPA-
filtered dust collector, operated and maintained to minimize dust
emissions. The proposed control strategy also directs employers to
eliminate blowing or dry sweeping drilling debris from working
surfaces.
    Of the 14 respirable quartz readings summarized in the exposure
profile for this operation, seven represent hole drilling indoors under
uncontrolled conditions. The highest reading obtained for workers in
this job category, 286 [mu]g/m\3\, was recorded for a worker drilling
holes with a \3/4\-inch bit in the floor of a concrete parking garage
where air circulation was poor (Lofgren, 1993). The other seven
results, most of which were collected during outdoor drilling of brick
and rock, are also spread over a wide range but tend to be lower than
(less than half) the indoor values, with a maximum of 130 [mu]g/m\3\
(NIOSH HETA-2003-0275-2926).
    Shepherd et al. (2009) found that compared with uncontrolled
drilling, using dust collection cowls connected to portable vacuums
reduced silica exposures by 91 to 98 percent. The researchers tested
four commercially available combinations of two cowls and two vacuums
indoors. Although investigators note that results might vary for
different drill types and drill bit sizes, OSHA estimates that the
proposed control strategy will consistently maintain exposures below
the proposed PEL even during periods of intense drilling. OSHA is
proposing that employers ensure that dust collectors are used according
to manufacturer's specifications in order to maximize dust reduction,
and that the vacuums used are appropriate for the nature of the task to
provide the adequate suction rate.
    Based on the percent reductions documented in the Shepherd study,
using a drill equipped with a hood or cowl and a HEPA-filtered dust
collector reduces the highest exposure reading in the profile to levels
below the proposed PEL. As such, OSHA anticipates that this control
strategy alone will reduce or maintain exposures below 50 [mu]g/m\3\
for workers using rotary hammers or drills for durations up to 8 hours
(excluding overhead work).
    Hallin (1983) indicates a greater potential for overexposure during
overhead drilling. A test run reported that drilling for 120 minutes
into a concrete ceiling with a percussion drill and a hammer drill gave
respirable quartz concentrations of 1,740 [mu]g/m\3\ and 720 [mu]g/
m\3\, respectively. The percussion drill was later fitted with a dust
collector, and a 180-minute test run produced a value of 80 [mu]g/m\3\.
This type of drilling was not addressed in the Shepherd report;
therefore, OSHA cannot confirm that using the cowl and dust collector
would sufficiently protect workers. The Agency has no additional
information that would indicate that exposures resulting from overhead
work might be consistently reduced below the proposed PEL. Based on
these factors, OSHA is proposing to exclude this particular task from
Table 1. Furthermore, the Agency concurs with the recommendation made
by Hallin (1983) that overhead drilling is ergonomically stressful and
should not be performed consistently for a full shift.
    Use of vehicle-mounted earth-drilling rigs for rock and concrete.
Although the equipment used for each type of drilling varies, OSHA has
addressed workers using drilling rigs of all types for rock, earth, and
concrete together in the same section of the technological feasibility
analysis. This is because the worker activities have much in common and
the general methods of silica control are also similar. Specifically,
these workers control the vehicle-mounted or rig-based drills from more
than an arm's length from the drill bit(s). They also perform certain
intermittent tasks near the drilling point, such as fine-tuning the bit
position, moving debris away from the drill hole, and working directly
or indirectly with compressed air to blow debris from deep within the
holes.
    When drilling rock, workers typically use rigs that are vertically
oriented and equipped to produce a deep hole through the addition of
bit extensions. This operation generally involves the drilling of one
hole for an extended period of time, with minimal interruption. In
contrast, when drilling concrete, workers often use rigs that consist
of an array of one or many drills fixed to the maneuverable arm of a
construction vehicle or purpose-built mobile machine, which permits the
operator to produce a series of precisely spaced mid-size holes. This
process requires operators to frequently start and stop the drilling
process.
    Based on these differences, OSHA is proposing to require separate
additional specifications for rock drilling and concrete drilling, with
both types of drilling using LEV at the point of operation and water to
suppress dust from the dust collector exhaust. The Agency estimates
that these control strategies will protect workers from overexposures,
as consistent use of dust extraction shrouds or hoods reduces worker
exposures at both rock and concrete drilling sites. The control
strategies for rock drilling and concrete drilling are discussed below.
    OHSA recognizes that enclosed cabs are available for concrete and
rock drilling rigs, and operators who work in enclosed cabs will
experience exposure reductions (ERG-C, 2008). OSHA is proposing that
respirators will not be required for these operators, regardless of
length of shift. Although cabs benefit operators while in the cab, they
do not affect workers' exposure during positioning or hole-tending
activities. To effectively control exposures of all

workers involved in the operation, employers must apply the engineering
controls outlined in Table 1 to manage exposure sources.
    In order for the cabs to work optimally, OSHA is proposing that
cabs have the following characteristics: (1) Air conditioning and
positive pressure is maintained at all times, (2) incoming air is
filtered through a pre-filter and a HEPA filter, (3) the cab interior
is maintained as free as practicable from settled dust, and (4) door
seals and closing mechanisms are working properly. Cecala et al. (2005)
studied modifications designed to lower respirable dust levels in an
enclosed cab on a 20-year-old surface drill at a silica sand operation.
The study found that effective filtration and cab integrity (e.g., new
gaskets, sealed cracks to maintain a positive-pressure environment) are
the two key components necessary for dust control in an enclosed cab.
OSHA believes that the cab specifications outlined will promote proper
air filtration and cab integrity. Rock drilling. The control strategy
for this operation specifies the use of a dust collection system around
the drill bits as well as a water spray to wet the exhaust, operated
and maintained to minimize dust emissions. Respiratory protection will
not be required unless work is being performed under the shroud at the
point of operation.
    Modern shroud designs, which are commercially available, have been
shown to consistently achieve respirable dust reductions (Reed et al.,
2008; Drilling Rig Manufacturer A, 2009). Moreover, NIOSH has
quantified reductions in dust emissions associated with LEV used with a
dowel drilling machine. For these concrete drilling rigs, NIOSH found
that close-capture dust collection hoods reduced respirable dust
concentrations by 89 percent compared with drilling without the hoods.
OSHA believes that similar reductions are achievable on rock drilling
machines equipped with dust collection systems, as the quantity of
airborne dust generated is comparable for both types of drilling.
    Additionally, OSHA believes it is important for employers to use
dust collectors in accordance with manufacturer specifications. NIOSH
has shown that dust collector efficiency is improved when workers use
an appropriate suction rate, maintain the shroud in good condition, and
keep the shroud positioned to fully enclose the bit as it enters the
hole. The Agency is also proposing to include a visible dust
specification, which employers can use as a tool to identify potential
problems with controls.
    Due to the nature of rock drilling, workers often have to work
under the shroud to clear tailings and dust from in or around the hole.
When this work is performed, workers do not receive the same amount of
protection from the control system, and they have to work closer to the
point of dust generation. As such, OSHA believes that workers will
experience higher exposures. In order to ensure that workers are
adequately protected, OSHA is proposing that employers ensure that
workers use half-mask respirators when working under shrouds at the
point of operation. The Agency is seeking comments and additional
information that address the appropriateness of this specification.
    The Agency is also proposing to require employers to use a water
delivery system to suppress dust emanating from the dust collector
exhaust. Research shows that in the vicinity of a rock-drilling rig,
dust collector dumping operations are the largest single contributor of
airborne respirable particulates. Maksimovic and Page has shown that in
rock-drilling rigs, this source contributed 38 percent of the
respirable dust emissions, while the deck shroud contributed 24 percent
(reported in Reed et al., 2008). NIOSH reports that modifications
(involving water delivery systems) to dust collector discharge areas
have reduced exposures from this source by 63 to 89 percent, which
means that overall airborne particles can be reduced by at least 24
percent.
    For example, a result of 54 [micro]g/m\3\ was obtained for a worker
who operated a rig equipped with a vacuum dust collection system. This
overexposure resulted from the lack of dust suppression while dust was
being dumped from the second filter of the collector--not from the
actual drilling operation. Information from the inspection shows that
the collector had two filters, and water was used to suppress dust from
dumping operations from the first filter only (OSHA SEP Inspection
Report 300340908). OSHA believes that adding a water delivery system to
suppress dust from the discharge at the second filter would have
resulted in a lower exposure. This result indicates that the control
strategy outlined, when applied effectively, will adequately protect
workers during a full work shift without requiring respirators.
    Concrete drilling. The control strategy for this operation
specifies the use of a dust collection system around the drill bits as
well as a low-flow water spray to wet the exhaust, operated and
maintained to minimize dust emissions.
    NIOSH has recommended several modifications to typical concrete
drilling rig dust collection equipment (NIOSH EPHB 334-11a, 2008). OSHA
anticipates that these upgrades will help ensure that optimal dust
collection efficiency is maintained over time. As such, the Agency is
proposing to require these additional specifications:

 Using smooth ducts and maintaining a duct transport velocity
of 4,000 feet per minute to prevent duct clogging
 Providing duct clean-out points to aid in duct maintenance and
prevent clogging, and
 Installing pressure gauges across dust collection filters so
the operator can clean or change the filter at an appropriate time

    Furthermore, Minnich 2009 demonstrated that a dust plume originated
from the point of operation after a worker activated a drill and LEV
system simultaneously. OSHA believes that the overall collection
efficiency would be improved by activating the exhaust suction prior to
initiating drilling and deactivating it after the drill bit stops
rotating, and is proposing to require that employers operate their LEV
systems in this manner.
    Similar to rock drilling, OSHA believes it is important for
employers to use dust collectors in accordance with manufacturer
specifications based on the NIOSH findings described in the rock
drilling section. The Agency is also proposing to include a visible
dust specification for concrete drilling, as it will help employers
identify potential problems with controls.
    While the available data do not specifically characterize the
effects of controls for concrete drilling rigs in all circumstances,
the Agency has substantial data on the effectiveness of controls in
rock drilling, and based on the similarities of these operations (refer
to PEA, Chapter 4). OSHA estimates that these controls provide similar
protection in concrete drilling and are able to reduce and maintain
exposures to the proposed PEL most of the time. Implementing the
additional specifications listed in Table 1 will also provide
protection. However, OSHA cannot rule out the possibility that silica
exposures will occasionally exceed the PEL, when workers perform this
operation outside of an enclosed cab for more than four hours. Because,
in the absence of an exposure assessment, employers will not be able to
confirm that exposures are below the PEL, or identify circumstances in
which exposures may exceed the PEL, the proposed rule requires that
employers provide half-mask respirators to workers who perform concrete
drilling outside of

an enclosed cab for more than four hours.
    OSHA seeks additional data to describe the efficacy of the controls
described above in reducing exposures for workers who operate concrete
drilling rigs. Additionally, the Agency is requesting comments and
additional information regarding the adequacy of the control strategy
described in Table 1.
    Use of drivable milling machines. Table 1 proposes that employers
use water-fed systems that deliver water continuously at the cut point
to suppress dust, operated and maintained to minimize dust emissions.
The table also includes a visible dust provision, which helps employers
identify potential problems with the control strategy. The Agency is
proposing that no respiratory protection will be required for shifts
lasting four hours or less, and that half-mask respirators be used for
operations lasting more than four hours.
    Some machines are equipped with water delivery systems that are
specifically designed to suppress dust. However, water is more
generally applied to the cutting drum of milling machines to prevent
mechanical overheating. OSHA believes that improved water delivery
systems will help reduce exposures for the worker population that
remains overexposed. For example, a study conducted in the Netherlands
with a novel dust emission suppression system shows the potential
impact of a water-delivery system (combined with an additive) as a
control strategy. Compared with a standard milling machine that uses
cooling water only on the blade, the use of an aerosolized water and
foam dust suppression system reduced the mean exposure for drivers and
tenders by about 95 and 98 percent, respectively (Van Rooij and
Klaasse, 2007). The same study also reported results for the use of
aerosolized water without the additive. Aerosolized water alone
provided a substantial benefit, reducing the mean exposure for drivers
and tenders by about 88 and 84 percent, respectively.
    Based on the exposure profile, OSHA anticipates that the vast
majority of workers already experience exposure levels below the
proposed PEL for operations lasting four hours or less. With water
delivery systems designed specifically to suppress dust, the Agency
expects that workers will be consistently protected against respirable
crystalline silica exposures. With this control strategy in place, OSHA
believes that respirators will not be necessary for operations lasting
four hours or less.
    OSHA believes that, even when workers operate drivable milling
machines for eight hours, water delivery systems will reduce TWA
exposures to or below the proposed PEL most of time, as described in
Chapter 4 of the PEA. However, OSHA cannot rule out the possibility
that silica exposures will occasionally exceed the PEL under certain
circumstances, when workers operate these machines for more than four
hours. Because, in the absence of an exposure assessment, employers
will not be able to confirm that exposures are below the PEL, or
identify circumstances in which exposures may exceed the PEL, the
proposed rule requires that employers provide respiratory protection to
workers who operate drivable milling machines for more than four hours.
    Based on the range of exposures in the exposure profile (see
Chapter 4 of the PEA), OSHA anticipates that properly designed water
delivery systems to suppress dust and half-mask respirators will
provide sufficient protection (the highest exposure measured for any
worker is 340 [mu]g/m\3\, with no dust suppression controls in place).
As such, the Agency believes that using wet methods and half-mask
respirators is a control strategy that consistently protects workers
for operations lasting more than four hours.
    Walking behind milling machines. For walk-behind milling machines,
Table 1 provides workers with two options for controlling exposures to
crystalline silica.
    The first option directs employers to use water-fed equipment that
continuously feeds water to the cutting surface to suppress dust,
operated and maintained to minimize dust emissions.
    The exposure profile for this operation contains six samples, with
the highest exposure being the only one above the proposed PEL. The two
lowest exposures in the profile (both are 12 [mu]g/m\3\) were obtained
for workers that used water-fed machines (ERG-C, 2008), indicating that
the wet method effectively controls silica exposure.
    If the highest exposure in the profile is weighted for four hours,
the adjusted exposure is less than the proposed PEL. Thus, OSHA
anticipates that for operations lasting four hours or less, workers
will be consistently protected by wet methods.
    OSHA believes that, even when workers operate walk-behind milling
machines for eight hours, water delivery systems will reduce TWA
exposures to or below the proposed PEL most of time, as described in
Chapter 4 of the PEA. However, when workers operate these machines for
more than four hours, silica exposures may occasionally exceed the PEL
under certain circumstances. Because, in the absence of an exposure
assessment, employers will not be able to confirm that exposures are
below the PEL, or identify circumstances in which exposures may exceed
the PEL, the proposed rule requires that employers provide respiratory
protection to workers who operate walk-behind milling machines for more
than four hours. The Agency believes the use of a half-mask respirator
will ensure consistent worker protection.
    The second option is to use tools equipped with commercially
available shrouds and dust collection systems, which are operated and
maintained to minimize dust emissions. The dust collector must be
equipped with a HEPA filter and must operate at an adequate airflow to
minimize airborne visible dust. Additionally, the dust collector must
be used in accordance with manufacturer specifications including the
airflow rate.
    To date OSHA has not been able to quantify the effectiveness of
currently available LEV in controlling respirable quartz levels
associated with walk-behind milling operations; however, OSHA believes
that evidence from similar construction tasks supports its value for
workers performing milling. OSHA believes that the LEV dust control
option will work at least as effectively for milling machines as for
tuckpointing grinders. Although the tuckpointers using LEV still
experienced a geometric mean result of 60 [mu]g/m\3\, walk-behind
milling machine operators have the advantages of lower uncontrolled
exposure levels, greater distance between the tool and their breathing
zone, and equipment that is self-supporting (the milling drum enclosure
more easily kept sealed against the floor), rather than hand-held.
Therefore, an LEV system with an appropriately sized vacuum will
similarly reduce most walk-behind milling machine operator exposures.
    Based on the exposure samples analyzed, OSHA estimates that most
workers already have exposures under the proposed PEL for operations
lasting four hours or less, and is not proposing to require respirator
use.
    For operations lasting more than four hours, the Agency believes
that at most the workers will be protected by using LEV alone, as
described Chapter 4 of the PEA. However, the Agency cannot rule out the
possibility that workers who operate these machines for more than four
hours will occasionally receive exposures that exceed the PEL, under
certain circumstances. Because, in the

absence of an exposure assessment, employers will not be able to
confirm that exposures are below the PEL, or identify circumstances in
which exposures may exceed the PEL, the proposed rule requires that
employers provide half-mask respirators to workers who operate drivable
milling machines for more than four hours.
    Use of hand-held masonry saws. Table 1 provides employers with two
different control strategies. Along with the engineering controls
listed in Table 1, OSHA is proposing the additional specifications that
will aid employers in using the engineering controls optimally.
     Prevent wet slurry from accumulating and drying. The
accumulation and drying of wet slurry can lead to settled dust that is
easily resuspended and can contribute to worker exposures.
     Ensure that the equipment is operated such that no visible
dust is emitted from the process. When controls are functioning
properly, visible dust should not be observed. This specification will
help employers identify potential problems with the control strategy.
     When working indoors, provide sufficient ventilation to
prevent build-up of visible airborne dust. Proper airflow prevents air
from becoming stagnant and dilutes the levels of respirable crystalline
silica.
     Use dust collectors in accordance with manufacturer
specifications. Selecting the correct system and flow rates will
consistently reduce exposure.
    Option 1: Employers use a water-fed system that delivers water
continuously at the cut point, operated and maintained to minimize dust
emissions.
    The exposure profile for outdoor cutting with wet methods shows
that for shift lasting four hours or less, workers consistently
experience exposure below the proposed PEL. The Agency believes that
wet methods alone will provide protection and is proposing to require
that employers apply the wet method control without the use of
respiratory protection.
    OSHA believes that, even when workers operate hand-held masonry
saws outdoors for eight hours, wet methods will reduce TWA exposures to
or below the proposed PEL most of time, as described in Chapter 4 of
the PEA. However, on the basis of the two highest sample results in the
exposure profile (see Chapter 4 of the PEA), the Agency believes that
silica exposures may occasionally exceed the PEL under certain
circumstances, when workers perform these operations outdoors for more
than four hours. Because, in the absence of an exposure assessment,
employers will not be able to confirm that exposures are below the PEL,
or identify circumstances in which exposures may exceed the PEL, the
proposed rule requires that employers provide half-mask respirators to
workers who operate hand-held masonry saws outdoors for more than four
hours.
    Similarly, the highest readings in the exposure profile for
operations using wet methods indoors suggest that silica exposures may
sometimes exceed the PEL even for workers who perform these activities
for less than four hours. Therefore, the Agency is proposing to require
the use of a half-mask respirator with an APF of 10 for workers who
operate hand-held masonry saws indoors or within a partially sheltered
area, regardless of task duration.
    Option 2: Use a saw equipped with a local exhaust dust collection
system, operated and maintained to minimize dust emissions.
    While the exposure profile does not contain any samples for work
involving hand-held masonry saws conducted with LEV in place, several
studies have shown the general effectiveness of LEV to reduce silica
concentrations. Meeker et al. (2009) shows that LEV can reduce
respirable silica exposures to levels near 100 [mu]g/m\3\ during short-
term periods of active cutting outdoors. Since most workers cut
intermittently even during times of active cutting (e.g., 10 or 20
seconds using the saw followed by a longer period--up to several
minutes--of measuring and moving materials or equipment), 8-hour TWA
values are likely to be considerably lower (Flanagan et al., 2001).
However, OSHA has not been able to confirm that LEV methods offer the
same degree of exposure reduction to workers currently experiencing
more modest, but still elevated, exposures.
    Thus, the Agency cannot rule out the possibility that silica
exposures will sometimes exceed the PEL, even when workers perform
these operations for less than four hours. Because, in the absence of
an exposure assessment, employers will not be able to confirm that
exposures are below the PEL, or identify circumstances in which
exposures may exceed the PEL, the proposed rule requires that employers
provide half-mask respirators to workers who use LEV to control
exposures while operating hand-held masonry saws outdoors.
    While OSHA does not have exposure data to specifically describe
indoor operations using LEV controls, Thorpe et al. (1999) and Meeker
et al. (2009) reported exposure reductions by 88 to 93 percent for
outdoor operation. OSHA believes that these exposure reductions would
be similar in indoor operations because there is no added general
ventilation in these environments such as natural air circulation
outdoors and airborne dust tends to become more stagnant indoors. Given
the very high uncontrolled exposures documented in the Chapter 4 of the
PEA, even the projected exposure reduction from LEV does not rule out
the possibility that exposures above 500 [mu]g/m\3\ will occasionally
occur under certain circumstances. Because, in the absence of an
exposure assessment, employers will not be able to confirm that
exposures are below the PEL, or identify circumstances in which
exposures may exceed the PEL, the proposed rule requires that employers
provide full face-piece respirators to workers who operate hand-held
masonry saws indoors or in partially enclosed areas, regardless of task
duration.
    Use of portable walk-behind or drivable masonry saws. Table 1
directs employers to use a water-fed system that delivers water
continuously at the cut point, operated and maintained to minimize dust
emissions with the following specifications:
     Prevent wet slurry from accumulating and drying. The
accumulation and drying of wet slurry can lead to settled dust that is
easily resuspended and can contribute to worker exposures.
     Ensure that the equipment is operated such that no visible
dust is emitted from the process. When controls are functioning
properly, visible dust should not be observed. This specification will
help employers identify potential problems with the control strategy.
     When working indoors, provide sufficient ventilation to
prevent build-up of visible airborne dust. Proper airflow prevents air
from becoming stagnant and dilutes the levels of respirable crystalline
silica.
    The exposure profile for this operation shows that of the 12
respirable silica results associated with wet-cutting concrete outdoors
using walk-behind saws, only 1 measurement exceeded the proposed PEL,
while 8 were less than the LOD. These results suggest that for outdoor
operations, water-fed walk-behind saws provide adequate protection for
workers.
    Based on this information, OSHA believes that by using the wet
method controls as specified, workers will be provided with consistent,
adequate protection and is proposing to not require the use of a
respirator when working outdoors.

    Flanagan et al. (2001) reported higher 8-hour TWA respirable silica
levels for operators and their assistants who used water-fed walk-
behind saws indoors for most of their shift (the worst-case conditions
resulted in four 8-hour TWA values between 130 [mu]g/m\3\ and 710
[mu]g/m\3\). The author noted that factors such as inadequate
ventilation or poor wet vacuum capture efficiency contributed to the
higher indoor respirable silica levels.
    By applying the additional specifications and engineering controls
outlined in Table 1, OSHA believes that indoor exposures will be
reduced to levels where respiratory protection with an APF of 10 will
provide adequate protection. OSHA is proposing to require the use of a
half-mask respirator for tasks of all duration when working indoors or
in partially shielded areas.
    Rock crushing. Table 1 provides employers with two control
strategies to protect employees not working in enclosed cabs. Both
options (described below) require the use of half-mask respirators
regardless of task duration.
    For equipment operators working within an enclosed cab, OSHA is
proposing that cabs have the following characteristics: (1) air
conditioning and positive pressure is maintained at all times, (2)
incoming air is filtered through a pre-filter and a HEPA filter, (3)
the cab is maintained as free as practicable from settled dust, and (4)
door seals and closing mechanisms are working properly. Cecala et al.
(2005) studied modifications designed to lower respirable dust levels
in an enclosed cab on a 20-year-old surface drill at a silica sand
operation. The study found that effective filtration and cab integrity
(e.g., new gaskets, sealed cracks to maintain a positive-pressure
environment) are the two key components necessary for dust control in
an enclosed cab. OSHA believes that the cab specifications outlined
will promote proper air filtration and cab integrity. OSHA is proposing
that operators who work in enclosed cabs meeting these specifications
will not be required to wear respirators.
    OSHA is also proposing an additional specification, which requires
that dust control equipment be operated such that no visible dust is
emitted from the process. When controls are functioning properly
visible dust should not be observed, and this specification will help
employers identify potential problems with the control strategy.
    Option 1: Use wet methods or dust suppressants.
    Based on available information, OSHA believes that water or other
dust suppression is used during rock crushing activities but that the
application may be either inconsistent or inefficient (ERG-C, 2008).
However, the Agency has obtained other information that shows that dust
suppression systems have been effective in reducing exposures. For
example, a silica result of 54 [mu]g/m\3\ was obtained for the operator
of a stationary crusher at a concrete recycling facility using fine
mist water spray (ERG-concr-crush-A, 2001). It is important to note
that this machine operator spent much of the shift in a poorly sealed
booth directly over the crusher, but left the booth frequently to tend
to other activities. Due to the lack of information regarding the
workshift, OSHA cannot asses the full extent of the impact that water
dust control had on the worker exposure.
    Gottesfeld et al. (2008) summarized a study conducted in India at
several rock crushing facilities. The study demonstrates that after
water spray installation, 70 percent of the breathing zone and area
results were less than 50 [mu]g/m\3\, and just one result exceeded 250
[mu]g/m\3\. In contrast, before the water mist system was added, all
results exceeded 50 [mu]g/m\3\, and 60 percent were greater than 250
[mu]g/m\3\, a condition similar to those in OSHA's exposure profile for
workers associated with rock crushing machines. OSHA acknowledges that
worksites may different in the United States, but believes that similar
exposure reductions can be achieved with rock crushers in the U.S.
    Wet dust suppression options that can offer a substantial benefit
include water expanded into foam, steam, compressed water fog, and
wetting agents (surfactants added to water to reduce surface tension)
(ERG-C, 2008). OSHA believes that when used properly and consistently,
these dust suppressants could reduce silica concentrations at least as
effectively as and more consistently than directional water mist spray
alone, achieving exposure reductions of 70- to 90-percent.
    OSHA acknowledges that available data is inadequate to indicate
whether water mist or other dust suppressants alone are sufficient to
reduce these workers' silica exposures below 50 [mu]g/m\3\. However,
based on the best available information, OSHA estimates that by
consistently using properly directed water mist spray (or other dust
suppression methods), the vast majority of rock crushers can achieve
consistent results in a range that is compatible with use of a half-
mask respirator with an APF of 10.
    Option 2: Use local exhaust ventilation systems at feed hoppers and
along conveyor belts, operated and maintained to minimize dust
emissions.
    Information available to OSHA indicates that LEV is capable of
reducing silica concentrations. For example, Ellis Drewitt (1997)
reported a reading of 300 [mu]g/m\3\ for a worker in Australia using a
dust extraction system (when compared to the uncontrolled mean of 798
[mu]g/m\3\ in the exposure profile).
    Another international report from Iran describes a site where
workers used rock crushers with LEV (Bahrami et al., 2008). The report
demonstrated that LEV systems were associated with a marked decrease in
respirable dust. Among 20 personal silica samples for process workers
and hopper-filling workers associated with rock crushers after LEV was
installed, the mean PBZ respirable quartz results were 190 [mu]g/m\3\
to 400 [mu]g/m\3\, respectively. It is important to note that the bulk
samples of this rock contained 85 to 97 percent quartz. The Agency
believes that these levels would likely have been lower if the rock had
not been nearly pure silica. If the respirable dust sample had
contained the more typical 12 percent silica on the filter, OSHA
estimates that the corresponding airborne silica concentrations would
have been 92 [mu]g/m\3\ to 178 [mu]g/m\3\. The Agency recognizes that
exposures may be higher than this estimate, but does not possess
additional information that more clearly characterizes worker exposures
with the implementation of LEV controls.
    As such, OSHA believes that a fully functioning LEV system can
control exposures for most workers to within the protection factor
offered by a half-mask respirator. OSHA is aware of the difficulties
present in applying LEV to rock crushing operations, and is requesting
additional information addressing the appropriateness and
practicability of this control strategy.
    Drywall finishing (with silica-containing material). The main
source of exposure for drywall finishing operations occurs when dust is
generated while sanding dried, silica-containing joint compound (ERG-C,
2008). Fourteen of the 15 samples collected for the exposure profile
for this operation show exposures below the proposed PEL, with 7
samples below the LOD. The one overexposure, 72 [mu]g/m\3\, was
obtained for a worker performing overhead sanding (NIOSH HETA 94-0078-
2660, 1997). Table 1 provides employers with two control strategies;
neither option requires the use of respirators.
    Option 1: Use pole sander or hand sander equipped with a dust
collection system, operated and maintained to minimize dust emissions.
Use dust

collectors according to manufacturer specifications.
    NIOSH tested the effectiveness of five off-the-shelf ventilated
sanding systems during drywall finishing: three designed to control
dust during pole sanding, and two to control dust during hand sanding.
Total dust area sample results revealed that all five systems were
effective for reducing total airborne dust by at least 80 percent,
ranging up to 97 percent (NIOSH ECTB-208-11a, 1995). This effectiveness
was confirmed in a study by Young-Corbett and Nussbaum (2009a), which
found that using a ventilated sander during drywall sanding reduced
respirable dust in the PBZ by 88 percent compared with a block sander
(no controls).
    Silica exposures were not measured explicitly in these studies, but
OSHA estimates that based on the reported total dust reductions, even
the highest exposure in the profile can be reduced to levels below the
proposed PEL. The Agency reasonably estimates that this control
strategy will adequately protect workers without the need for
respirators.
    Although ventilated sanders are the most effective exposure control
option for silica-containing joint compound, and they offer indirect
benefits to workers and managers (NIOSH Appl. Occup. Environ. Hyg. 15,
2000), there are many perceived barriers to their adoption in the
workplace (NIOSH ECTB-208-11a, 1995; Young-Corbett and Nussbaum,
2009b). Hence, Option 2 is provided to employers as a way to comply
with paragraph (f)(1) of the proposed rule.
    Option 2: Use wet methods to smooth or sand the drywall seam.
    Young-Corbett and Nussbaum (2009a) found that a wet sponge sander
reduces respirable dust in the PBZ by 60 percent compared with a block
sander (no controls). Other wet methods include wiping a clean, damp
sponge over the still-damp joint compound to smooth the seam and
rinsing the sponge in a bucket of water as it becomes loaded with
compound, or wetting dried joint compound with a spray bottle and
sanding with sandpaper (NIOSH ECTB-208-11a, 1995).
    Again, silica exposures were not explicitly measured in the Young-
Corbett and Nussbaum study. Based on the reported respirable dust
reduction, however, OSHA estimates that even the highest exposure in
the profile can be reduced and maintained below the proposed PEL. As
such, the Agency believes that using wet methods will offer adequate
protection without requiring respirators.
    Use of heavy equipment during earthmoving. The exposure profile for
this operation ranges from 11 [micro]g/m\3\ to 170 [micro]g/m\3\, with
about 13 percent of the values exceeding the proposed PEL. Table 1
provides for the option of operating equipment from enclosed cabs to
control exposures. It specifies that workers operate equipment from
within enclosed cabs that have the following characteristics:
     Air conditioning with positive pressure maintained at all
times;
     Incoming air filtered through a pre-filter and a HEPA
filter;
     Having the cab be as free as practicable from settled
dust; and
     Door seals and closing mechanisms that are working
properly.
    Based on published research, ERG-C (2008) found that effective
enclosed cabs generally have these four characteristics, and extensive
literature suggests that the exposure reductions can range from 80 to
more than 90 percent in this industry (Rappaport et al., 2003; Pannel
and Grogin, 2000; Cecala et al., 2005; NIOSH 528, 2007).
    The exposure profile shows that of the 19 results for which the
status of the cab was established, 17 were for unenclosed cabs. Both of
the operations involving enclosed cabs had exposures of about 12
[micro]g/m\3\, while operations involving several of the unenclosed
cabs were associated with worker exposures greater than 50 [micro]g/
m\3\ and up to 87 [micro]g/m\3\. This information allows OSHA to
determine that operators using enclosed cabs as proposed by this option
will effectively protect workers. Respiratory protection will not be
needed.
    Concerning abrasive blasting operations, paragraph (f)(2) of the
general industry/maritime proposed rule and paragraph (f)(3) of the
construction proposed rule direct employers to comply with the
requirements of 29 CFR 1910.94 (Ventilation), and for shipyard
employment 29 CFR 1915.34 (Mechanical Paint Removers) and 29 CFR part
1915, subpart I (Personal protective equipment). These standards apply
to abrasive blasting operations that involve crystalline silica-
containing blasting agents or substrates. Employers should consult
these other standards to ensure that they comply with personal
protective equipment, ventilation, and other operation-specific safety
requirements.
    OSHA is aware of current and past efforts of domestic and
international entities to ban silica sand as an abrasive blasting
agent. Given the best available information to date, the Agency does
not believe that banning silica sand is the most appropriate course of
action, as OSHA has concerns about potential harmful exposures to other
substances that the alternatives might introduce in a workplace.
Further toxicity data are necessary before the Agency can reach any
conclusions about the hazards of these substitutes relative to the
hazards of silica. The following paragraphs provide further information
regarding abrasive blasting agents.
    The annual use of silica sand for abrasive blasting operations has
decreased from about 1.5 million tons in 1996 to 0.5 million tons in
2007, which roughly represents a 67-percent reduction (Greskevitch and
Symlal, 2009)). This reduction might reflect the use of alternative
blasting media, the increased use of high-pressure water-jetting
techniques, and the use of cleaning techniques that do not require open
sand blasting. Several substitutes for silica sand are available for
abrasive blasting operations, and current data indicate that the
abrasive products with the highest U.S consumptions are: coal slag,
copper slag, nickel slag, garnet, staurolite, olivine, steel grit, and
crushed glass.
    A NIOSH study compared the short-term pulmonary toxicity of several
abrasive blasting agents (NIOSH, Blasting Abrasives: Health Hazard
Comparison, 2001). This study reported that specular hematite and steel
grit presented less short-term in vivo toxicity and respirable dust
exposure in comparison to blast sand. Overall, crushed glass, nickel
glass, staurolite, garnet, and copper slag were similar to blast sand
in both categories. Coal slag and olivine showed more short-term in
vivo toxicity than blast sand and were reported as similar to blast
sand regarding respirable dust exposure. This study did not examine
long-term hazards or non-lung effects.
    Hubbs et al. (2005) mention that of the nine alternatives to silica
sand, NIOSH has identified five of them-coal slag, steel grit, specular
hematite, garnet, and crushed glass-for further testing to determine
the relative potential of these agents to induce lung fibrosis in rats
exposed to whole-body inhalation. These abrasive materials were
selected for study based on high production, number of workers exposed,
short-term intratracheal instillation \39\ relative toxicity studies,
and inadequacy of available current data (Hubbs et al., 2005). The
National Toxicology Program is performing long-term (39 weeks), in

vivo, toxicity studies of these abrasive blasting agents.
---------------------------------------------------------------------------

    \39\ Intratracheal instillation is an alternative to inhalation
exposure studies. Test material is delivered in a bolus aqueous
solution to the lung through a syringe and ball-tipped needle into
the tracheal (Phalen, 1984).
---------------------------------------------------------------------------

    Additionally, another NIOSH study (KTA-Tator, 1998) monitored
exposures to several OSHA-regulated toxic substances that were created
by the use of silica sand and substitute abrasive blasting materials.
The study showed that several substitutes create exposures or potential
exposures to various OSHA-regulated substances. The study showed
exposures or potential exposures to: (1) Arsenic, when using steel
grit, nickel slag, copper slag and coal slag; (2) beryllium, when using
garnet, copper slag, and coal slag; (3) cadmium, when using nickel slag
and copper slag; (4) chromium, when using steel grit, nickel slag, and
copper slag; and (5) lead, when using copper slag.
    Since these studies were performed, the Agency has learned that
specular hematite is not being manufactured in the United States due to
patent-owner specification. In addition, the elevated cost of steel has
a substantial impact on the availability to some employers to use
substitutes like steel grit and steel shot.
    Elevated silica exposures have been found during the use of low-
silica abrasives as well, even when blasting on non-silica substrates.
For example, the use of the blasting media Starblast XL (staurolite),
which contains less than 1 percent quartz according to its
manufacturer, resulted in a respirable quartz level of 1,580 [micro]g/
m\3\. The area sample (369-minute) was taken inside a containment
structure erected around two steel tanks. The elevated exposure
occurred because the high levels of abrasive generated during blasting
in containment overwhelmed the ventilation system (NIOSH, 1993b). This
example emphasizes the impact of control methods in specific working
environments. In order to reduce elevated exposures closer to the PEL
in situations like these, employers should examine the full spectrum of
available controls, and how these controls perform in specific working
conditions. Employers may find, for example, that they would have to
provide supplementary respiratory protection to adequately protect
workers that perform abrasive blasting in areas where the accumulation
of dust remains stagnant (e.g. confined spaces) in a worker's personal
breathing zone and overwhelms exhaust ventilation systems. Other
engineering controls the same employer may consider would be wet and/or
automated blasting.
    Paragraph (f)(4) of the construction proposed rule, and Paragraph
(f)(3) of the general industry/maritime proposed rule specify that
accumulations of crystalline silica in the work place are to be cleaned
by HEPA-filter vacuums or wet methods. This section also prohibits the
use of compressed air, dry sweeping, and dry brushing to clean clothing
or surfaces contaminated with crystalline silica. These requirements
are being proposed to help regulate the amount of crystalline silica
that becomes airborne, thus providing effective control of worker
exposure. The requirements of paragraph (f)(4) are consistent with
general industry standards for hazardous substances, such as cadmium
and asbestos, which specify that work surfaces be cleaned wherever
possible by vacuuming with a HEPA-filtered vacuum. Much documentation
shows that moving from compressed air blowing and dry sweeping to HEPA-
filtered vacuums and the application of wet methods effectively reduces
worker exposures during cleaning activities (PEA, Chapter 4).
    A study of Finnish construction workers compared the respirable
crystalline silica levels during dry sweeping or when using alternative
cleaning methods. Compared with dry sweeping, estimated worker
exposures were about three times lower when workers used wet sweeping
and five times lower when they used vacuums. In the asphalt roofing
industry, NIOSH and OSHA both recommended vacuuming with HEPA-filtered
vacuums as a method to minimize exposure. In five Health Hazard
Evaluations at asphalt roofing manufacturing facilities, NIOSH
recommended vacuuming as opposed to compressed air for cleaning dust
out of equipment (ERG-GI, 2008).
    OSHA's technological feasibility analysis points to numerous other
instances where cleaning methods are of particular importance in
reducing worker exposures. In the rock and concrete drilling industry,
OSHA recommends that workers use HEPA-filtered vacuums instead of
compressed air to clean holes in order to reduce-or even eliminate-
substantial exposure during hole-tending activities. In the porcelain
enameling industry, a facility has used a vacuum fitted with a HEPA
filter for all cleaning. To minimize generating airborne dust, workers
avoid dry sweeping and only shovel or scrape materials that are damp
(Porcelain Industries, 2004a; 2004b).
    For millers using portable or mobile equipment, Echt et al. (2002)
reported that cleanup is critical for engineering controls to work most
effectively for walk-behind milling machines. The study reported that
airborne dust increased when a scabbler passed over previously milled
areas. It was recommended that debris be cleaned using a HEPA-filtered
vacuum prior to making a second pass over an area. This step enhanced
LEV capability and prevented debris from being re-suspended.
    Several facilities have adopted the recommended cleaning methods as
part as an overall effort to reduce exposures. For example, in the
jewelry and dental laboratories industries, additional controls to
reduce exposures below the proposed PEL include LEV, wet methods,
substitution, isolation, work practices, and improved housekeeping such
as the use of a HEPA-filtered vacuum for cleaning operations. These
examples again also show the value of applying a combination of
controls to reduce exposures below the PEL.
    Paragraph (f)(5) of the construction proposed rule, and Paragraph
(f)(4) of the general industry/maritime proposed rule specify that the
employer must not rotate workers to different jobs to achieve
compliance with the PEL. OSHA proposes this prohibition because silica
is a carcinogen, and the Agency assumes that any level of exposure to a
carcinogen places a worker at risk. With worker rotation, the
population of exposed workers increases.
    This provision is not a general prohibition of worker rotation
wherever workers are exposed to crystalline silica. It is only intended
to restrict its use as a compliance method for the proposed PEL; worker
rotation may be used as deemed appropriate by the employer in
activities such as to provide cross-training and to allow workers to
alternate physically demanding operations with less arduous ones. This
same provision was used for the asbestos (29 CFR 1910.1001 and 29 CFR
1926.1101), hexavalent chromium (29 CR 1910.1026), butadiene (29 CFR
1910.1051), methylene chloride (29 CFR 1910.1052), cadmium (29 CFR
1910.1027 and 29 CFR 1926.1127), and methylenedianiline (29 CFR
1926.60) OSHA standards.

(g) Respiratory Protection

    During situations where employee exposure to respirable crystalline
silica is expected to be above the PEL, paragraph (g) requires the
employer to protect employees' health through the use of respirators.
Specifically, in areas where exposures exceed the PEL, respirators are
required during the installation and implementation of engineering and
work practice controls; during work operations where engineering and
work practice controls are not feasible; when all feasible engineering
and work practice controls have been implemented but are not

sufficient to reduce exposure to or below the PEL; and during periods
when any employee is in a regulated area or an area for which an access
control plan indicates that use of respirators is necessary.
    These limitations on the required use of respirators are generally
consistent with other OSHA health standards, such as methylene chloride
(29 CFR 1910.1052) and chromium (VI) (29 CFR 1910.1026). They reflect
the Agency's determination, discussed above in section (f) (Methods of
compliance), that respirators are inherently less reliable than
engineering and work practice controls in reducing employee exposure to
respirable crystalline silica. OSHA has therefore proposed to allow
reliance on respirators only in certain designated situations.
    Proposed paragraph (g)(1)(i) requires the use of respirators in
areas where exposures exceed the PEL during periods when engineering
and/or work practice controls are being installed or implemented. OSHA
recognizes that respirators may be essential to achieve the PEL under
these circumstances. During these times, employees would have to use
respirators for temporary protection until the hierarchy of controls
has been implemented.
    OSHA anticipates that engineering controls will be in place by the
start-up date specified in paragraph (k)(2)(ii) of the construction and
the general industry/maritime proposed standards. The Agency realizes
that in some cases employers may commence operations, install new or
modified equipment, or make other workplace changes that result in new
or additional exposures to crystalline silica after the effective date
as defined by paragraph (k)(1). In these cases, a reasonable amount of
time may be needed before appropriate engineering controls can be
installed and proper work practices implemented. When employee
exposures exceed the PEL in these situations, employers must provide
their employees with respiratory protection and require its use.
    Proposed paragraph (g)(1)(ii) requires respiratory protection in
areas where exposures exceed the PEL during work operations in which
engineering and work practice controls are not feasible. OSHA
anticipates that there will be few situations where no feasible
engineering or work practice controls are available to limit employee
exposure to respirable crystalline silica. In situations where
respirators are used as the sole form of protection to achieve
compliance with the PEL, the employer will be required to demonstrate
that engineering and work practice controls are not feasible.
    Proposed paragraph (g)(1)(iii) requires the use of respirators for
supplemental protection in circumstances where feasible engineering and
work practice controls alone cannot reduce exposure levels to or below
the PEL. Examples include some tuckpointing, jackhammering, and
abrasive blasting operations. The employer must always install and
implement engineering and work practice controls whenever they are
feasible, even if these controls alone cannot reduce employee exposures
to or below the PEL. Whenever respirators are used as supplemental
protection to achieve compliance with the PEL, the burden is on the
employer to demonstrate that engineering and work practice controls
alone are insufficient to achieve the PEL.
    Under proposed paragraph (g)(1)(iv), employers have to provide
respiratory protection during periods when any employee is in a
regulated area. Proposed paragraph (e) in the general industry/maritime
standard and proposed paragraph (e)(2) in the construction standard
would require employers to establish a regulated area wherever an
unprotected employee's exposure to airborne concentrations of
respirable crystalline silica is, or can reasonably be expected to be,
in excess of the PEL. OSHA has included the provision requiring
respirator use in regulated areas in the proposed rule to make it clear
that each employee is required to wear a respirator when present in a
regulated area, regardless of the duration of time spent in the area.
Because of the potentially serious results of exposure, OSHA believes
that this provision is necessary and appropriate because it would have
the effect of limiting unnecessary exposures to employees who enter
regulated areas, even if they are only in a regulated area for a short
period of time.
    Proposed paragraph (e)(3) gives the employer the option of
developing an access control plan as a means of minimizing exposures to
employees not directly involved in operations that generate respirable
crystalline silica. This written access control plan would serve as an
alternative to setting up regulated areas under paragraph (e)(2). An
access control plan must include procedures for providing and requiring
the use of respiratory protection in areas where exposures can
reasonably be expected to exceed the PEL. Proposed paragraph (g)(1)(v)
of the construction standard requires the use of respiratory protection
when specified by the access control plan.
    Proposed paragraph (g)(2) requires the employer to implement a
comprehensive respiratory protection program in accordance with the
Agency's respiratory protection standard (29 CFR 1910.134) whenever
respirators are used to comply with the requirements of the respirable
crystalline silica standard. The respiratory protection program is
designed to ensure that respirators are properly used in the workplace
and are effective in protecting workers. The program must include:
procedures for selecting respirators for use in the workplace; medical
evaluation of employees required to use respirators; fit-testing
procedures for tight-fitting respirators; procedures for proper use of
respirators in routine and reasonably foreseeable emergency situations;
procedures and schedules for maintaining respirators; procedures to
ensure adequate quality, quantity, and flow of breathing air for
atmosphere-supplying respirators; training of employees in respiratory
hazards to which they might be exposed and the proper use of
respirators; and procedures for evaluating the effectiveness of the
program.
    In 2006, OSHA revised the respiratory protection standard (29 CFR
1910.134) to include assigned protection factors (71 FR 50122, Aug. 24,
2006). Assigned protection factor means the workplace level of
respiratory protection that a respirator or class of respirators is
expected to provide to employees when the employer implements a
respiratory protection program under 29 CFR 1910.134. The revised
standard includes a table (Table 1--Assigned Protection Factors) that
employers must use to select sufficiently protective respirators for
employees who may be exposed to respirable crystalline silica.
    Proposed paragraph (g)(3) for the construction standard indicates
that, for the operations listed in Table 1 in paragraph (f) of the
construction standard, if the employer fully implements the engineering
controls, work practices, and respiratory protection described in Table
1, the employer shall be considered to be in compliance with the
requirements for selection of respirators in 29 CFR 1910.134 paragraph
(d). Paragraph (d) of 29 CFR 1910.134 requires the employer to evaluate
respiratory hazards in the workplace, identify relevant workplace and
user factors, and base respirator selection on these factors. There is
no need for the employer to complete this process when following Table
1, because Table 1 specifies the type of respirator required for a
particular operation.

(h) Medical Surveillance

    In paragraph (h)(1)(i), OSHA proposes to require that each employer
covered by this rule make medical surveillance available at no cost,
and at a reasonable time and place, for all employees who are
occupationally exposed to respirable crystalline silica above the PEL
for 30 or more days per year.
    There is a general consensus that medical surveillance is necessary
for employees exposed to respirable crystalline silica. Medical
surveillance for workers exposed to respirable crystalline silica is
included in standards developed by ASTM International (ASTM, 2006;
2009) as well as in guidance or recommendations developed by the
American College of Occupational and Environmental Medicine (ACOEM,
2006), the Building and Construction Trades Department, AFL-CIO (BCTD,
2001), the Industrial Minerals Association/Mine Safety and Health
Administration (IMA/MSHA, 2008), National Industrial Sand Association
(NISA, 2010), and the World Health Organization (WHO, 1996). Although
the specific recommendations made by these organizations differ in
certain respects, they are consistent in indicating that regular
medical examinations are appropriate for workers with substantial
exposures to respirable crystalline silica.
    The purposes of medical surveillance for respirable crystalline
silica include the following: to determine, where reasonably possible,
if an individual can be exposed to respirable crystalline silica in his
or her workplace without experiencing adverse health effects; to
identify respirable crystalline silica-related adverse health effects
so that appropriate intervention measures can be taken; and to
determine the employee's fitness to use personal protective equipment
such as respirators. The proposal is consistent with Section 6(b)(7) of
the OSH Act (29 U.S.C. 655(b)(7)) which requires that, where
appropriate, medical surveillance programs be included in OSHA
standards to determine whether the health of workers is adversely
affected by exposure to the hazard addressed by the standard. Other
OSHA health standards, such as chromium (VI) (29 CFR 1910.1026),
methylene chloride (29 CFR 1910.1052), and cadmium (29 CFR 1910.1027),
also include medical surveillance requirements.
    The proposed standard is intended to encourage participation by
requiring that medical examinations be made available by the employer
without cost to employees (also required by Section 6(b)(7) of the
Act), and at a reasonable time and place. If participation requires
travel away from the worksite, the employer is required to bear the
cost. Employees must be paid for time spent taking medical
examinations, including travel time.
    OSHA is proposing that medical surveillance be made available to
employees exposed to respirable crystalline silica above the PEL for 30
or more days a year. In contrast, the ASTM standards (Section 4.6.1)
require medical surveillance for workers with actual or anticipated
exposures to respirable crystalline silica at concentrations that
exceed the occupational exposure limit for 120 or more days a year
(ASTM, 2006; 2009). The OSHA proposal for medical surveillance of
employees exposed to respirable crystalline silica above the PEL for 30
or more days per year is more comprehensive than the ASTM
recommendation. Both the OSHA proposal and the ASTM standard use
exposure above the occupational exposure limit as the trigger for
medical surveillance. However, the OSHA proposal is more protective
than the ASTM standard because it calls for medical surveillance of
workers exposed for a shorter duration of time.
    OSHA believes that the proposed cutoffs, based both on exposure
level and on the number of days per year that an employee is exposed to
respirable crystalline silica, are a reasonable and administratively
convenient basis for providing medical surveillance benefits to
respirable crystalline silica-exposed workers. With the exception of
the asbestos standard (29 CFR 1910.1001), which doesn't specify an
action level, medical surveillance in OSHA standards such as chromium
(VI) (29 CFR 1910.1026), methylene chloride (29 CFR 1910.1052), and
cadmium (29 CFR 1910.1027) is triggered by exposure at or above action
level. However, OSHA notes that employees exposed at or below the PEL,
or exposed above the PEL for only a few days in a year, will be at
lower risk of developing respirable crystalline silica-related disease
than employees who are exposed above the PEL for 30 or more days per
year. Medical surveillance triggered by exposures above the PEL covers
employees who face the highest risk of developing disease related to
respirable crystalline silica exposure. OSHA estimates that
approximately 351,000 employees would be exposed above the proposed PEL
for more than 30 days per year, and therefore require medical
surveillance under the proposed standard. For comparison, OSHA
estimates approximately 1,026,000 employees would be exposed above the
proposed action level of 25 ug/[micro]\3\ but at or below the proposed
PEL, a difference of 675,000 employees. The total number of medical
exams required, which takes into account turnover in the work force,
would be similarly affected. For example, in the first year following
promulgation, approximately 454,000 exams would be required under the
proposed standard. If medical surveillance was triggered at the action
level rather than the PEL, over 1,280,000 exams would be required.
Under the proposed standard, periodic medical exams would be required
on a triennial basis, increasing over time the total number of medical
exams. Thus, requiring medical surveillance only for employees exposed
above the proposed PEL reduces the burden on employers and focuses
resources on the employees at highest risk. OSHA solicits comments on
the approporate trigger for medical surveillance in the issues section
of the NPRM.
    Paragraph (h)(1)(ii) of the proposal requires that the medical
examinations made available under the rule be performed by a physician
or other licensed health care professional (PLHCP). The term ``PLHCP,''
as discussed further in section (b) (Definitions), above, refers to
individuals whose legal scope of practice allows them to provide, or be
delegated responsibility to provide, some or all of the health care
services required by the medical surveillance provisions. The
determination of who qualifies as a PLHCP is thus determined on a
state-by-state basis. OSHA considers it appropriate to allow any
professional to perform medical examinations and procedures made
available under the standard when they are licensed by state law to do
so. This provision provides flexibility to the employer, and reduces
cost and compliance burdens. The proposed requirement is consistent
with the approach of other recent OSHA standards, such as chromium (VI)
(29 CFR 1910.1026), methylene chloride (29 CFR 1910.1052), and
respiratory protection (29 CFR 1910.134).
    The proposed standard also specifies how frequently medical
examinations are to be offered to those employees covered by the
medical surveillance program. Under paragraph (h)(2), employers are
required to make available to covered employees an initial (baseline)
examination within 30 days after initial assignment unless the employee
has received a medical examination provided in accordance with the
standard within the past three years. The proposed requirement that a

medical examination be offered at the time of initial assignment is
intended to determine if an individual will be able to work in the job
involving respirable crystalline silica exposure without adverse
effects. It also serves the useful function of establishing a health
baseline for future reference. Where an examination that complies with
the requirements of the standard has been provided in the past three
years, that previous examination would serve these purposes, and an
additional examination would not be needed. For example, some employees
may work short-term jobs associated with construction projects and
other activities of limited duration. In these circumstances, an
employee may work for several different employers over the course of a
three-year period. In such cases, each employer who hires the employee
within three years of the employee's last medical examination would not
have to make available an initial medical examination, but could rely
on a written medical opinion from an examination provided in the past
three years, if the examination complied with the requirements of the
standard.
    Proposed paragraphs (h)(2)(i)-(vi) specify that the baseline
medical examination provided by the PLHCP must consist of: medical and
work history; physical examination with special emphasis on the
respiratory system; chest X-ray or equivalent diagnostic study;
pulmonary function test; latent tuberculosis test; and other tests
deemed appropriate by the PLHCP. Special emphasis is placed on the
portions of the medical and work history focusing on exposure to
respirable-crystalline silica or other agents affecting the respiratory
system, history of respiratory system dysfunction (including signs and
symptoms such as shortness of breath, coughing, and wheezing), history
of tuberculosis, and smoking.
    Medical and work histories are required because they are an
efficient and inexpensive means for collecting information that can aid
in identifying individuals who are at risk because of hazardous
exposures (ACOEM, 2006; WHO, 1996). Information on present and past
work exposures, medical illnesses, and symptoms can lead to the
detection of diseases at early stages when preventive measures can be
taken. Recording of symptoms is important because, in some cases,
symptoms indicating onset of disease can occur in the absence of
abnormal laboratory test findings.
    The physical exam focuses on the respiratory system, which is known
to be susceptible to respirable crystalline silica toxicity. Aspects of
the physical exam, such as visual inspection, palpation, tapping, and
listening with a stethoscope, would allow the PLHCP to detect
abnormalities in chest shape or lung sounds that are associated with
compromised lung function (WHO, 1996; IMA/MSHA, 2008; NISA, 2010;
ACOEM, 2006). The ASTM standards do not specifically address a physical
exam as part of medical surveillance, but physical exams are included
in other recommendations (IMA/MSHA, 2008; NISA, 2010; ACOEM, 2006;
BCTD, 2001). OSHA's proposal for a physical exam provides for a more
comprehensive medical evaluation than that required by the ASTM
standards.
    OSHA proposes that an X-ray or an equivalent diagnostic study be
made available at the first medical examination. An initial chest X-
ray, although not useful for preventing silicosis, can be useful for
diagnosing silicosis, for detecting mycobacterial disease, and for
detecting large opacities associated with cancer (IMA/MSHA 2008). It
also provides baseline data upon which to assess any subsequent
changes. X-rays are the standard medical test to diagnose respirable
crystalline silica-related lung diseases. However, the proposal allows
for an equivalent diagnostic study in place of the chest X-ray. This is
intended to allow for use of technologically advanced imaging
techniques in place of conventional X-rays.
    An example of a diagnostic study that is equivalent to an X-ray is
a digital chest radiograph. Medical imaging is currently in the process
of transitioning from conventional film-based radiography to digital
radiography systems. Digital imaging systems offer a number of
advantages over conventional film-based X-rays, including more
consistent image quality, faster results, increased ability to share
images with multiple readers, simplified storage of images, and reduced
risk for technicians and the environment due to the elimination of
chemicals for developing film (Attfield and Weissman, 2009).
    The proposed standard calls for an X-ray size of no less than 14 x
17 inches and no more than 16 x17 inches at full inspiration, which is
consistent with the X-ray film size required in NIOSH specifications
for medical examination of underground coal miners (42 CFR part 37).
The proposed standard also specifies interpretation and classification
of X-rays according to the International Labour Organization (ILO)
International Classification of Radiographs of Pneumoconioses by a
NIOSH-certified ``B'' reader. The ILO recently made standard digital
radiographic images available and has published guidelines on the
interpretation and classification of digital radiographic images (ILO
2011). Therefore, digital radiographic images can now be evaluated
according to the same ILO guidelines as X-ray films and are considered
equivalent diagnostic tests. The ILO guidelines require that digital
images be displayed on a medical-grade flat-panel monitor designed for
diagnostic radiology. ILO specifications for those monitors include a
minimal diagonal display of 21 inches per image, a maximum to minimum
luminance ratio of at least 50, a maximum luminance of no less than 250
candelas per square meter, a pixel pitch not to exceed 210 [micro]m,
and a resolution no less than 2.5 line-pairs per millimeter. NIOSH
(2011) has published guidelines for conducting digital radiography and
displaying digital radiographic images in a manner that will allow for
classification according to ILO guidelines. Hard copies printed from
digital images are not recommended for classification because they give
the appearance of more opacities compared to films or digital images
(Franzblau et al., 2009).
    The ILO system was designed to assess X-ray and digital
radiographic image quality and to describe radiographic findings of
pneumoconiosis in a simple and reproducible way (NISA, 2010; WHO, 1996;
IMA/MSHA, 2008). The procedure involves scoring opacities according to
shape, size, location, and profusion. Opacities are first classified as
either small or large, with small opacities representing simple
silicosis and large opacities representing complicated silicosis. The
best indicator of silicosis severity is profusion, which is the B
reader's assessment of the amount of small opacities seen in the lung
fields (NISA, 2010; IMA/MSHA, 2008). Using a standard set of ILO X-ray
films or digital radiographic images, the B reader compares the
workers' X-rays or digital radiographic images with the ILO films or
digital radiographic images and rates the profusion of small opacities.
The numbers 0, 1, 2, or 3 are used to indicate increasing amounts of
small opacities. A 12-point profusion scale is employed, in which the B
reader gives a first choice and then a second choice profusion rating.
    A NIOSH-certified B reader is a physician who has demonstrated
competency in the ILO classification system by passing proficiency and
periodic recertification examinations (NIOSH, 2011a). The NIOSH
certification procedures were designed to improve the proficiency of X-
ray and

digital radiographic image readers and minimize variability of
readings. Standardized procedures for the evaluation of X-ray films and
digital images by certified, qualified individuals is warranted by the
prevalence and seriousness of silicosis. As of February 12, 2013, there
were 242 certified B readers in the United States.
    Other radiological test methods that may be useful are computed
tomography (CT) or high resolution computed tomography (HRCT) scans.
Two older studies reported that CT or HRCT scans were not more
sensitive than X-rays for detecting silicosis but were more sensitive
than X-rays at distinguishing between early and advanced stages of
silicosis (B[eacute]gin et al., 1987a; Talini et al., 1995). More
recent studies and reviews reported that CT or HRCT may be superior to
chest X-ray in the early detection of silicosis and the identification
of progressive massive fibrosis (PMF) (Sun et al., 2008; Lopes et al.,
2008; Blum et al., 2008). However, the value of CT or HRCT scans should
be balanced with risks and disadvantages of those methods, which
include higher radiation doses (WHO, 1996).
    CT or HRCT scans could be considered ``equivalent diagnostic
studies'' under paragraph (h)(2)(iii) of the proposed standard.
However, standardized methods for interpreting and reporting the
results of CT or HRCT scans are not currently available. The Agency
seeks comment on whether CT and HRCT scans should be considered
``equivalent diagnostic studies'' under the standard, and has included
this topic in the ``Issues'' section of this preamble.
    Paragraph (h)(2)(iv) of the proposed OSHA standard calls for
spirometry testing (forced vital capacity [FVC], forced expiratory
volume at one second [FEV1], and FEV1/FVC ratio)
by a spirometry technician with current certification from a NIOSH-
approved spirometry course as part of the baseline medical examination.
Pulmonary function tests, such as spirometry, are optional under the
ASTM standards (ASTM, 2006; 2009). ASTM (2006, 2009) and others point
to a lack of evidence that routine spirometry testing is useful for
detecting early stages of respirable crystalline silica-related
disease. They indicate that most abnormalities detected by spirometry
screening are not related to respirable crystalline silica-related
diseases but rather to factors such as smoking and non-occupationally
related diseases. There are also a number of obstacles to widespread
use of spirometry including inadequate training of medical personnel,
technical problems with some spirometers, and lack of standardization
for testing methodologies and procedures (ACOEM, 2011; IMA/MSHA, 2008;
ATS/ERS, 2005; NISA, 2010). However, ACOEM, (2011), IMA/MSHA (2008),
American Thoracic Society/European Respiratory Society (ATS/ERS, 2005),
and NISA (2010) go on to note that properly conducted spirometry is
considered a useful part of respiratory medical surveillance programs.
    Because quality lung function tests are useful for obtaining
information about the employee's lung capacity and respiratory flow
rate, OSHA proposes to require spirometry as part of the baseline
medical examination. Information provided by spirometry is useful for
determining baseline lung function status upon which to assess any
subsequent lung function changes and for evaluating any loss of lung
function. This information may also be useful in assessing the health
of employees who wear respirators. The proposed requirement is
consistent with the approach of other OSHA standards, such as those for
asbestos (29 CFR 1910.1001) and cadmium (29 CFR 1910.1027).
    Because it is imperative that spirometry be conducted according to
strict standards for quality control and for results to be consistently
interpreted, OSHA proposes that spirometry be administered by a
spirometry technician with current certification from a NIOSH-approved
spirometry course. The NIOSH-approved spirometry training is based upon
procedures and interpretation standards developed by the ATS/ERS and
European Respiratory Society and addresses topics such as instrument
calibration, testing performance, data quality, and interpretation of
results (NIOSH, 2011b). Requiring spirometry technicians to have
current certification from a NIOSH-approved spirometry course will
improve their proficiency in generating quality results that are
consistently interpreted. Similar recommendations are included in the
ASTM standards (Section <IP_ADDRESS>) (ASTM 2006; 2009).
    In paragraph (h)(2)(v), OSHA proposes testing for latent
tuberculosis infection at the baseline medical examination. In
contrast, the ASTM standards (Section <IP_ADDRESS>) recommend tuberculosis
testing only when an X-ray shows evidence of silicosis (ASTM, 2006;
2009). NISA (2010) recommends baseline tuberculosis testing and
periodic testing in workers who have chest X-ray readings of 1/0 or
higher or more than 25 years of exposure to respirable crystalline
silica. OSHA believes that a general requirement for testing during the
initial medical examination will serve to protect workers exposed to
respirable crystalline silica by identifying latent tuberculosis
infection so it can be treated before active (infectious) tuberculosis
develops.
    In 2008, there were almost 13,000 new cases of active tuberculosis
in the U.S. Although incidence of tuberculosis continues to decrease in
the U.S., the ultimate goal of tuberculosis control and prevention in
the U.S. is the elimination of tuberculosis (CDC, 2009). Active
tuberculosis cases are prevented by identifying and treating those with
latent tuberculosis disease.
    As described in OSHA's Health Effects analysis and summarized in
Section V of this preamble, the risk of developing active tuberculosis
infection is higher in individuals with silicosis than those without
silicosis (Balmes, 1990; Cowie, 1994; Hnizdo and Murray, 1998;
Kleinschmidt and Churchyard, 1997; Murray et al., 1996). Moreover,
there is evidence that exposure to silica increases the risk for
pulmonary tuberculosis, independent of the presence of silicosis
(Cowie, 1994; Hnizdo and Murray, 1998; teWaterNaude et al., 2006). OSHA
therefore preliminarily concludes that it is in the best interest of
both the employer and the affected worker to identify latent
tuberculosis prior to silica exposure. The increased risk of developing
active pulmonary tuberculosis places not only the worker, but also his
or her co-workers and family members at increased risk of acquiring
this potentially fatal infectious disease. Early treatment of latent
disease would eliminate this risk. Testing for latent tuberculosis
infection will identify cases of this disease and alert affected
workers, so that the necessary treatment can be obtained from their
local public health department or other health care provider. OSHA's
proposed requirement is consistent with the recommendations of ACOEM
(2006), which recommends tuberculosis screening for all silica-exposed
workers. The Centers for Disease Control and Prevention recommends that
tuberculosis testing target populations who are at the highest risk of
developing the disease, including those with silicosis (CDC, 2000). The
Agency seeks comment on its preliminary determination that all workers
receiving an initial medical exam should receive testing for latent
tuberculosis infection, and has included this topic in the ``Issues''
section of this preamble.

    Paragraph (h)(2)(vi) of the proposal gives the examining PLHCP the
flexibility to determine additional tests deemed to be appropriate.
While the tests conducted under this section are for screening
purposes, diagnostic tests may be necessary to address a specific
medical complaint or finding (IMA/MSHA, 2008). For example, the PLHCP
may decide that additional tests are needed to address abnormal
findings in a pulmonary function test. OSHA believes that the PLHCP is
in the best position to decide if any additional medical tests are
necessary for each individual examined. Where additional tests are
deemed appropriate by the PLHCP, the proposed standard would require
that they be made available.
    In paragraph (h)(3)(i), OSHA proposes periodic examinations
including medical and work history, physical examination emphasizing
the respiratory system, chest X-rays and pulmonary function tests, and
other tests deemed to be appropriate by the PLHCP. The examinations
would be required every three years under paragraph (h)(3) of this
proposal, unless the PLHCP recommends that they be made available more
frequently. The specific requirements for the examinations and the
value of the examinations for screening workers exposed to respirable
crystalline silica were addressed above. The proposed requirement for
examinations every three years is consistent with the ASTM standards
(Section 4.6.5), which recommend that medical surveillance be conducted
no less than every three years (ASTM, 2006; 2009). Other standards
recommend periodic evaluations at intervals ranging from two to five
years, depending on duration of exposure (IMA/MSHA, 2008; NISA, 2010;
ACOEM, 2006; BCTD, 2001).
    The main goal of periodic medical surveillance for workers is to
detect adverse health effects at an early and potentially reversible
stage. Based on the Agency's experience, OSHA believes that
surveillance every three years would strike a reasonable balance
between the need to diagnose health effects at an early stage and the
limited number of cases likely to be identified through surveillance.
    The proposed requirement that employers offer a chest X-ray or an
equivalent diagnostic test as part of the periodic medical examination
conducted every three years is an important aspect of early disease
detection. As indicated above, X-rays are appropriate tools for
detecting and monitoring the progression of silicosis, possible
complications such as mycobacterial disease, and large opacities
related to cancer (IMA/MSHA 2008). Detection of simple silicosis by
periodic X-ray could allow for implementation of exposure reduction
methods that are likely to decrease the risk of disease progression
(ACOEM, 2006). X-rays would also allow the detection of treatable
conditions, such as mycobacterial infections (ACOEM, 2006).
    X-rays conducted every three years as part of the triennial medical
examinations are appropriate considering the long latency period of
most respirable crystalline silica-related diseases. The proposed
three-year frequency for chest X-rays represents a simplified approach
that balances a reasonable time frame for detecting disease and
administrative convenience. Under paragraph (h)(3)(ii) of the proposed
standard, the PLHCP can request X-rays more frequently. The proposed
frequency is consistent with the ASTM standards, as well as ACOEM
recommendations (ASTM, 2006; 2009; ACOEM, 2006). Other groups recommend
X-rays at intervals ranging from every two to five years, depending on
exposure duration (IMA/MSHA, 2008; NISA, 2010; WHO, 1996). OSHA is
interested in comments on the proposed X-ray frequency and has raised
this topic in the ``Issues'' section of this preamble.
    Proposed paragraph (h)(3) also requires that spirometry (FVC,
FEV1, and FEV1/FVC ratio) be offered by a
spirometry technician with current certification from a NIOSH-approved
spirometry course, as part of the medical examination conducted every
three years. As noted above, spirometry is optional in the ASTM
standards (ASTM, 2006; 2009). However, OSHA believes that periodic
spirometry is a potentially valuable tool for detecting respirable
crystalline silica-related disease and monitoring the health of exposed
workers.
    Periodic spirometry that adheres to strict quality standards is
useful for monitoring progressive lung function changes to identify
individual workers or groups of workers with abnormal lung function
changes. Quality longitudinal spirometry testing that compares workers'
lung function to their baseline levels is useful for detecting
excessive declines in lung function that could lead to severe
impairment over time. For example, recent studies have shown that
excessive decline in lung function can be an early warning sign for
risk of COPD development (Wang et al., 2009). Identifying workers who
are at risk of developing severe decrements in lung function would
allow for interventions to prevent further progression of disease. OSHA
is proposing a medical examination including a lung function test every
three years because exposure to respirable crystalline silica does not
usually cause severe declines in lung function over short time periods.
The proposed frequency is consistent with ACOEM (2006) and BCTD (2001),
which recommend lung function testing every two to three years. WHO
(1996) and NISA (2010) recommend annual pulmonary function testing, but
WHO (1996) states that if this is not feasible, it can be conducted at
the same frequency as chest X-rays (every two to five years). Paragraph
(h)(3) of the proposed standard gives the PLHCP the authority to
request lung function testing more frequently. The PLHCP might
recommend such a test because of age, tenure, exposure level, or
abnormal results. The Agency seeks comment on the proposed frequency of
pulmonary function testing and has raised this topic in the ``Issues''
section of this preamble.
    Paragraph (h)(4) of the proposed standard would require the
employer to ensure the examining PLHCP has a copy of the standard, and
to provide the following information to the PLHCP: a description of the
affected employee's former, current, and anticipated duties as they
relate to respirable crystalline silica exposure; the employee's
former, current, and anticipated exposure level; a description of any
personal protective equipment used or to be used by the employee,
including when and for how long the employee has used that equipment;
and information from records of employment-related medical examinations
previously provided to the affected employee and currently within the
control of the employer. Making this information available to the PLHCP
will aid in the evaluation of the employee's health in relation to
assigned duties and fitness to use personal protective equipment, when
necessary. The results of exposure monitoring are part of the
information that would be supplied to the PLHCP responsible for medical
surveillance. These results contribute valuable information to assist
the PLHCP in determining if an employee is likely to be at risk of
harmful effects from respirable crystalline silica exposure. A well-
documented exposure history also assists the PLHCP in determining if a
condition (e.g., compromised pulmonary function) may be related to
respirable crystalline silica exposure. Where the employer does not
have information directly indicating an employee's exposure (e.g.,
where the employer uses Table 1 in the proposed

construction standard and does not perform exposure monitoring), an
indication of the presumed exposure associated with the operation
(i.e., at or above the action level, above the PEL) would fulfill this
requirement.
    Proposed paragraph (h)(5)(i) requires that the employer obtain a
written medical opinion from the PLHCP within 30 days of each medical
examination. The purpose of this requirement is to provide the employer
with a medical basis to aid in the determination of placement of
employees and to assess the employee's ability to use protective
clothing and equipment. OSHA believes the 30-day period will provide
the PLHCP sufficient time to receive and consider the results of any
tests included in the examination, and allow the employer to take any
necessary protective measures in a timely manner. The proposed
requirement that the opinion be in written form is intended to ensure
that employers and employees receive the benefit of this information.
    Paragraphs (h)(5)(i)(A)-(D) of the proposal specify what must be
included in the PLHCP's opinion. The standard first proposes that the
PLHCP's written medical opinion describe the employee's health
condition as it relates to exposure to respirable crystalline silica,
including any conditions that would put the employee at increased risk
of material impairment of health from further exposure to respirable
crystalline silica. The standard also proposes that the PLHCP's written
medical opinion include recommended limitations for the employee's
exposure to respirable crystalline silica or use of personal protective
equipment such as respirators. These proposed requirements are
consistent with the overall goals of medical surveillance: to determine
if an individual can be exposed to respirable crystalline silica
present in his or her workplace without experiencing adverse health
effects, to identify respirable crystalline silica-related adverse
health effects so that appropriate intervention measures can be taken,
and to determine the employee's fitness to use personal protective
equipment such as respirators.
    Paragraph (h)(5)(i)(C) proposes that the PLHCP must include in the
written medical opinion a statement that the employee should be
examined by a pulmonary specialist if the X-ray is classified as 1/0 or
higher by the ``B'' reader, or if referral to a pulmonary specialist is
otherwise deemed appropriate by the PLHCP. As described above,
paragraph (h)(2)(iii) of the proposed standard requires that X-rays be
interpreted according to the ILO Classification of Radiographs of
Pneumoconioses. The ASTM standards recommend that workers with
profusion opacities greater than 1/1 (profusion similar to that shown
on a standard category 1 radiograph) be evaluated at a frequency
determined by a physician qualified in pulmonary disease (Section
4.7.1) and receive annual counseling by a physician or other person
knowledgeable in occupational safety and health (Section 4.7.2) (ASTM,
2006; 2009). The proposed OSHA standard addresses pneumoconiosis at an
earlier stage than the ASTM standards, thus allowing for intervention
at an earlier indication of possibly abnormal findings.
    Paragraph (h)(5)(i)(D) of the proposal would require that the PLHCP
include in the written medical opinion a statement that the PLHCP has
explained to the employee the medical examination results, including
conditions related to respirable crystalline silica exposure that
require further evaluation or treatment and any recommendations related
to use of protective clothing or equipment. Under this provision, OSHA
anticipates that the employee will be informed directly by the PLHCP of
all results of his or her medical examination, including conditions of
nonoccupational origin. Direct consultation between the PLHCP and
employee ensures that the employee will receive all information about
health status, including non-occupationally related conditions, that
are not communicated to the employer.
    Under proposed paragraph (h)(5)(ii), the employer must ensure that
the PLHCP does not include findings unrelated to crystalline silica
exposure in the written opinion provided to the employer or otherwise
reveal such findings to the employer. OSHA has proposed this provision
to ensure confidentiality of medical information and to reassure
employees participating in medical surveillance that they will not be
penalized or embarrassed as a result of the employer obtaining
information about them not directly pertinent to occupational exposure
to respirable crystalline silica. Paragraph (h)(5)(iii) of the proposed
standard requires the employer to provide a copy of the PLHCP's written
opinion to the employee within two weeks after the employer receives
it, to ensure that the employee has been informed of the results of the
examination in a timely manner.
    OSHA is aware of concerns that the written medical opinion may
divulge confidential information regarding an employee's medical
condition, or may otherwise divulge information that may adversely
affect an individual's employment status. The Building and Construction
Trades Department, AFL-CIO has expressed the view that, except in
limited circumstances, any decision to disclose medical information to
an employer should be left to the employee (BCTD, 2009). OSHA respects
concerns for medical privacy and is aware of how disclosure of medical
information could potentially impact workers. The proposed requirements
are intended to balance employee privacy with employers' need for
information to assess possible health effects or risks related to
respirable crystalline silica exposure by employees. OSHA seeks comment
on the proposed requirement for the employer to obtain a written
medical opinion, and has raised this topic in the ``Issues'' section of
this preamble.
    Proposed paragraph (h)(6)(i) requires that an examination by a
pulmonary specialist be offered when indicated in the PLHCP's written
opinion. This requirement is intended to ensure that individuals with
abnormal findings are seen by a professional with expertise in
respiratory disease who can provide not only expert medical judgment,
but also counseling regarding work practices and personal habits that
could affect these individuals' respiratory health. In this respect the
proposed provision is conceptually consistent with the provision in the
ASTM standards (4.7.2) for counseling by a physician or other person
qualified in occupational safety and health. Data presented by the
American Board of Internal Medicine (ABIM) indicate that as of February
5, 2013, 13,138 physicians in the United States had valid certificates
in pulmonary disease (ABIM, 2013). ABIM does not report how many of
these physicians are currently practicing. However, ABIM does report
that 4,378 new certificates in pulmonary disease were issued in the
period from 2001-20010 (ABIM, 2012). Because physicians are likely to
practice in the field for some time after receiving their
certification, this figure indicates that a substantial number of
pulmonary specialists are available to perform examinations required
under the proposed standard.
    Paragraph (h)(6)(i) further proposes that these additional
examinations by pulmonary specialists must be made available within 30
days following receipt of the PLHCP's recommendation that examination
by such a specialist is indicated. OSHA proposes, under paragraph
(h)(6)(ii), that the employer provide the pulmonary specialist with the
same information that is provided to the original PLHCP (i.e., a copy
of the

standard; a description of the affected employee's former, current, and
anticipated duties as they relate to respirable crystalline silica
exposure; the employee's former, current, and anticipated exposure
level; a description of any personal protective equipment used or to be
used by the employee, including when and for how long the employee has
used that equipment; and information from records of employment-related
medical examinations previously provided to the affected employee,
currently within the control of the employer). The reasons why the
pulmonary specialist should receive this information are the same as
those for the PLHCP and were addressed above.
    Proposed paragraph (h)(6)(iii) requires the employer to obtain a
written medical opinion from the pulmonary specialist comparable to the
written opinion obtained from the original PLHCP, including a
description of the employee's health condition as it relates to
respirable crystalline silica exposure, the pulmonary specialist's
opinion as to whether the employee would be placed at increased risk of
material health impairment as a result of exposure to respirable
crystalline silica, and any recommended limitations on the employee's
exposure to respirable crystalline silica or use of personal protective
equipment. The pulmonary specialist would also need to state in the
written opinion that these findings were explained to the employee. The
reasons why the pulmonary specialist should provide this information to
the employer are the same as those for the PLHCP and were addressed
above.
    Some OSHA health standards contain a provision for medical removal
protection (MRP). MRP typically requires that the employer temporarily
remove an employee from exposure when such an action is recommended in
a written medical opinion. During the time of removal, the employer is
required to maintain the total normal earnings, as well as all other
employee rights and benefits, of the removed employee. However, MRP is
not intended to serve as a workers' compensation system. The primary
reason MRP was included in previous standards was to encourage employee
participation in medical surveillance. By protecting employees who are
removed on a temporary basis from economic loss, this potential
disincentive to participating in medical surveillance is alleviated.
Previous standards also included MRP requirements to prevent the onset
of disease and to detect and minimize the extent of existing disease.
For example, OSHA's cadmium standard (29 CFR 1910.1026) provides for
MRP based on criteria such as biological monitoring results and
evidence of cadmium-related disease. Removal from exposure can allow
for biological monitoring results to return to acceptable levels, or
for improvement in the employee's health condition.
    OSHA has made a preliminary determination that MRP is not
reasonably necessary or appropriate for respirable crystalline silica-
related health effects. Thus, the proposed rule does not include a
provision for MRP. The Agency believes that respirable crystalline
silica-related health effects (e.g., silicosis) are generally chronic
conditions that are not remedied by temporary removal from exposure.
Since situations where temporary removal would be appropriate are not
anticipated to occur, OSHA does not believe that MRP is necessary. The
Agency seeks comment on this preliminary determination, and has
included this topic in the ``Issues'' section of this preamble.

(i) Communication of Respirable Crystalline Silica Hazards to Employees

    The proposed standard includes requirements intended to ensure that
the dangers of respirable crystalline silica exposure are communicated
to employees by means of labels, safety data sheets, and employee
information and training. OSHA believes that it is necessary to inform
employees of the hazards to which they are exposed, along with
associated protective measures, so that employees understand how they
can minimize potential health hazards. As part of an overall hazard
communication program, training serves to explain and reinforce the
information presented on labels and in safety data sheets. These
written forms of communication will be effective and relevant only when
employees understand the information presented and are aware of the
actions to be taken to avoid or minimize exposures, thereby reducing
the possibility of experiencing adverse health effects.
    OSHA has proposed to revise its existing hazard communication
standard (HCS) (29 CFR 1910.1200) to conform with the United Nations'
Globally Harmonized System of Classification and Labelling of Chemicals
(GHS), Revision 3. (See 74 FR 50280, Sept. 30, 2009.) The hazard
communication requirements of the proposed crystalline silica rule are
designed to be consistent with the revised HCS, while including
additional specific requirements needed to protect employees exposed to
respirable crystalline silica. OSHA intends for the requirements of the
respirable crystalline silica rule to conform with the final hazard
communication standard. The proposed requirements are also consistent
with the worker training and education provisions of ASTM
International's standards addressing control of occupational exposure
to respirable crystalline silica (Section 4.8 in both E 1132-06 and E
2625-09) (ASTM, 2006; 2009).
    In the HCS rulemaking, OSHA proposed to revise substance-specific
health standards by referencing the HCS requirements for labels, safety
data sheets, and training and by identifying the hazards that need to
be addressed in the employer's written hazard communication program.
Accordingly, proposed paragraph (i)(1) of the silica rule requires
compliance with the HCS requirements and lists cancer, lung effects,
immune system effects, and kidney effects as hazards that need to be
addressed in the employer's hazard communication program. These are the
health effects that OSHA has preliminarily determined to be associated
with respirable crystalline silica exposure.
    Proposed paragraph (i)(2)(i) requires the employer to ensure that
each affected employee can demonstrate knowledge of the specified
training elements (discussed below). When using the term ``affected
employee'' in this context, OSHA is referring to any employee who may
be exposed to respirable crystalline silica under normal conditions of
use or in a foreseeable emergency. Employee knowledge of the specified
training elements could be determined through methods such as
discussion of the required training subjects, written tests, or oral
quizzes. In order to ensure that employees comprehend the material
presented during training, it is critical that trainees have the
opportunity to ask questions and receive answers if they do not fully
understand the material that is presented to them. When videotape
presentations or computer-based programs are used, this requirement may
be met by having a qualified trainer available to address questions
after the presentation, or providing a telephone hotline so that
trainees will have direct access to a qualified trainer.
    Proposed paragraphs (i)(2)(i)(A) and (B), which require training on
specific operations in the workplace that could result in respirable
crystalline silica exposure and specific procedures the employer has
implemented to protect employees from exposure to respirable
crystalline silica, closely parallel the HCS. OSHA has included these

elements in the proposed respirable crystalline silica rule to ensure
that both employers and employees understand the sources of potential
silica exposure and control measures used to reduce exposure. Workers
have a particularly important role in controlling silica exposures
because work practices often play a crucial role in controlling
exposures, and engineering controls frequently require action on the
part of workers to function effectively. For example, stationary
masonry saws using wet methods to control dust may require adjustment
of the nozzle and the water flow rate to ensure that an adequate volume
of water reaches the cutting area. Water filters may need to be rinsed
or replaced at regular intervals, and basin water may need to be
replaced on a regular basis to prevent clogging of the nozzles.
Similarly, the effectiveness of local exhaust ventilation systems,
another common method used to control exposures to respirable
crystalline silica, is often enhanced by the use of proper work
practices. When tuckpointing, for instance, workers should ensure that
the shroud surrounding the grinding wheel remains flush against the
working surface to minimize the amount of dust that escapes from the
collection system. Operating the grinder in one direction (counter to
the direction of blade rotation) is effective in directing mortar
debris into the exhaust system, and backing the blade off before