Diesel Particulate Matter Exposure of Underground Coal Miners

Note: EPA no longer updates this information, but it may be useful as a reference or resource.

[Federal Register: January 19, 2001 (Volume 66, Number 13)]
[Rules and Regulations]
[Page 5525-5574]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr19ja01-11]

[[Page 5525]]

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Part II

Department of Labor

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Mine Safety and Health Administration

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30 CFR Part 72

Diesel Particulate Matter Exposure of Underground Coal Miners; Final
Rule

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30 CFR Part 57

Diesel Particulate Matter Exposure of Undergound Metal and Nonmetal
Miners; Final R

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ule

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DEPARTMENT OF LABOR

Mine Safety and Health Administration

30 CFR Part 72

RIN 1219-AA74

Diesel Particulate Matter Exposure of Underground Coal Miners

AGENCY: Mine Safety and Health Administration (MSHA), Labor.

ACTION: Final rule.

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SUMMARY: This rule establishes new health standards for underground
coal mines that use equipment powered by diesel engines.
This rule is designed to reduce the risks to underground coal
miners of serious health hazards that are associated with exposure to
high concentrations of diesel particulate matter (dpm). DPM is a very
small particle in diesel exhaust. Underground miners are exposed to far
higher concentrations of this fine particulate than any other group of
workers. The best available evidence indicates that such high exposures
put these miners at excess risk of a variety of adverse health effects,
including lung cancer.
The final rule for underground coal mines would require that the
dpm emissions from certain pieces of equipment be restricted to
prescribed levels. Underground coal mine operators would also be
required to train miners about the hazards of dpm exposure.
By separate notice, MSHA will publish a rule to reduce dpm
exposures in underground coal mines.

DATES: The provisions of the final rule are effective March 20, 2001.
However, Sec. 72.500(b) will not apply until July 19, 2002;
Sec. 72.501(b) will not apply until July 21, 2003; and, Sec. 72.501(c)
will not apply until January 19, 2005.

FOR FURTHER INFORMATION CONTACT: David L. Meyer, Director, Office of
Standards, Regulations, and Variances, MSHA, 4015 Wilson Boulevard,
Arlington, VA 22203-1984. Mr. Meyer can be reached at dmeyer@msha.gov
(Internet E-mail), 703-235-1910 (voice), or 703-235-5551 (fax). You may
obtain copies of the final rule in alternative formats by calling this
number. The alternative formats available are either a large print
version of the final rule or the final rule in an electronic file on
computer disk. The final rule also is available on the Internet at
http://www.msha.gov/REGSINFO.HTM.

SUPPLEMENTARY INFORMATION:

I. Key Features of MSHA's Final Rule Limiting the Concentration of
Diesel Particulate Matter (DPM) in Underground Coal Mines

(1) What are the requirements for permissible equipment?

Permissible equipment must not emit more than 2.5 grams per hour of
dpm, as measured in a laboratory test. Any permissible equipment that
is added to a mine's inventory underground more than 60 days after the
date this rule is published will have to meet this standard upon
introduction. This includes newly purchased equipment, used equipment,
or a piece of equipment receiving a replacement engine with a different
serial number than the engine it is replacing, including engines or
equipment coming from one mine into another. It does not include a
piece of equipment whose engine was previously part of the mine's
inventory and rebuilt.
Within 18 months from the date the rule is issued, the entire
permissible fleet must meet this standard.
The rule leaves the choice of controls used to achieve the
emissions limit to operators. Operators may use any combination of
controls (e.g., cleaner engine, OCC, filter) to meet the emissions
standard specified in this section.
As a practical matter, MSHA expects that to comply with this
standard, most permissible equipment will be equipped with a paper
filter. As explained in Part IV of this preamble, MSHA has verified
that there are commercially available paper filters which will allow
99% of the existing 541 units in the permissible fleet to meet this
requirement--including permissible units powered by the Deutz MWM 916,
the Caterpillar 3304 and the Caterpillar 3306. Commercially available
paper filters capable of bringing the emissions of these units into
compliance include a model which can be installed directly on the
exhaust coming from a water scrubber or on the exhaust coming from a
heat exchanger, as well as the integrated DST system. Other
filters which use paper with the same performance characteristics will
also be acceptable. Control devices whose dpm removal efficiency has
not been demonstrated by laboratory testing on a diesel engine can be
evaluated following the procedures in 30 CFR 72.503 of this part added
by this rulemaking. Moreover, the rule provides that MSHA may rely upon
the test results of other organizations who perform equivalent tests.
MSHA will publish on its web site a list of tested control devices
and their performance. Compliance will be determined by reference to
this data--there will be no in-mine testing.
The only engine which might not be able to meet these requirements
for dpm emissions from permissible equipment with a paper filter is the
Isuzu QD-100. MSHA's inventory indicates there are currently only two
units of permissible equipment using this engine; however, these two
units can comply at a derated power setting.
The engines currently approved for permissible use are generally
high in particulate emissions. MSHA is committed to taking actions
which will facilitate the approval for permissible use of the lower-
emission engines which have become available in recent years. These
actions could include waiving test fees, contracting for the
performance of such tests, or on an interim basis permitting the use of
an engine approved for nonpermissible use in a permissible package.
MSHA will solicit input from the mining community, through a Federal
Register notice as it considers how to proceed in this regard.

(2) What are the requirements for heavy-duty non-permissible equipment?

Non-permissible heavy duty equipment will ultimately not be
permitted under the final rule to emit more than 2.5 grams per hour of
dpm. For reasons of feasibility, this requirement will be implemented
in phases.
Any heavy duty equipment added to a mine's inventory more than 60
days after the date of publication of this rule will have to comply
with an interim emissions limit for that machine of 5.0 gr/hr. This
includes newly purchased equipment, used equipment, or a piece of
equipment receiving a replacement engine with a different serial number
than the engine it is replacing, including engines or equipment coming
from one mine into another. It does not include a piece of equipment
whose engine was previously part of the mine's inventory and rebuilt.
All heavy duty equipment in the fleet must meet the interim
standard of 5.0 grams per hour of dpm in 30 months.
Finally, another 18 months later (4 years in all), all
nonpermissible heavy duty equipment in the fleet will have to meet the
final standard of 2.5 grams per hour of dpm.
As with permissible equipment, the rule leaves the choice of
controls used to achieve the emissions limit to operators. Any
combination of controls (e.g., cleaner engine, OCC, filter) can be used
as long as compliance with the standard specified in this section is
met.

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As a practical matter, MSHA believes that most existing heavy duty
equipment will utilize commercially available hot gas filters (e.g.,
ceramic cell, wound fiber, sintered metal, etc.) to comply with the
final limit. All the existing fleet can reach the interim limit with
such a filter; some will not need one. MSHA determined that all but a
few can reach the final limit with such a filter.
The rule provides that MSHA may rely upon the test results of
organizations who perform filtration efficiency tests. In this regard,
MSHA will accept the results of filter tests performed by VERT. VERT is
an acronym for Verminderung der Emissionen von Realmaschinen in
Tunnelbau, a consortium of several European agencies conducting diesel
emission research in connection with major planned tunneling projects
in Austria, Switzerland and Germany. VERT was established to advance
hot gas filter technology due to concerns in Europe about dpm levels.
This gave VERT the opportunity to acquire the necessary filter
evaluation expertise. A wide range of commercially available hot gas
filters have been tested by VERT and the filtration efficiency
determined. The Secretary may also accept filter efficiency test
results from other testing organizations that can demonstrate a high
level of expertise in filter evaluation (see Sec. 72.503(c) of the
final rule).
Operators using the DST'' system with the catalytic convertor on
heavy duty equipment, or the Jeffrey dry exhaust system, will also be
deemed in compliance with the final rule, since test results conducted
in the same manner as the requirement in the final rule demonstrate
that those systems can reduce the emissions from all existing heavy
duty engines to below the limit. Filtration devices whose filter
efficiency has not been demonstrated by testing on a diesel engine can
be evaluated following the procedures in 30 CFR 72.503 of this part
added by this rulemaking.
MSHA will publish on its web site a list of tested control devices
and their performance. Compliance will be determined by reference to
this data--there will be no in-mine testing.
The standard may also be met through the use of newer, cleaner
engines in some heavy duty equipment with low horsepower engines. There
are already many engines approved for non-permissible use in
underground coal mines that will enable heavy duty equipment to limit
emissions, thus allowing the use of lower efficiency filters. MSHA is
also considering approaches that would expedite the approval of
additional engines based on evidence that such engines meet EPA
standards which ensure the engines are at least as clean as required
under MSHA approval standards.

(3) What are the requirements for generators and compressors?

The final rule provides that generators and compressors meet the
same dpm emissions standards as heavy duty equipment. Thus, generators
and compressors will ultimately not be permitted to emit more than 2.5
grams per hour of dpm. Generators and compressors introduced into the
fleet of an underground coal mine more than 60 days after the final
rule is published will have to meet an interim emissions limit of 5.0
g/hr. Generators and compressors in the existing fleet will have 30
months to meet the interim standard of 5.0 grams per hour of dpm. After
an additional 18 months (4 years in all), all generators and
compressors underground will have to meet the final standard of 2.5
grams per hour of dpm.
Although the proposed rule would not have covered generators and
compressors, MSHA explicitly asked the mining community if there were
types of light duty equipment that should, because of operating
characteristics, be treated like heavy duty equipment. Generators and
compressors generate more dpm emissions than other light-duty equipment
based on their known duty cycle and type of work for which they are
designed; indeed, they use engines whose horsepower often exceeds that
in permissible equipment. Accordingly, MSHA has determined they should
be covered by this rulemaking.
MSHA's inventory indicates that the 34 generators and 29
compressors constitute less than 3% of the underground light duty
diesel fleet. The existing compressors are using engines which should
meet the standard's interim and final requirements with a commercially
available hot gas filter.
Generators and compressors will be able to utilize the same
technologies as heavy duty machines to comply with this standard. This
will include hot gas filters or paper filters, as appropriate. Smaller
generators and compressors may utilize the clean engine technologies.

(4) What are the requirements for other nonpermissible equipment?

The final rule provides that any piece of nonpermissible light-duty
equipment introduced into an underground coal mine more than 60 days
after the date of publication of the rule must not emit more than 5.0
grams per hour of dpm. This includes newly purchased equipment, used
equipment, or a piece of equipment receiving a replacement engine with
a different serial number than the engine it is replacing, including
engines or equipment coming from one mine into another, but it does not
include a piece of equipment whose engine was previously part of the
mine's inventory and rebuilt.
The final rule does not impose any new requirements on the existing
nonpermissible light-duty fleet (except for generators and compressors
as noted above).
While new light duty equipment would not have been covered by the
proposed rule, MSHA explicitly asked the mining community if it would
be feasible to cover such new light duty equipment, even if it were not
feasible to set limits for all light duty equipment. MSHA has
determined that it is feasible to require that newly introduced light
duty equipment meet the same 5 gr/hr standard as new heavy duty
equipment.
To facilitate compliance with this standard, light duty equipment
which uses an engine meeting certain EPA standards listed in the MSHA
rule will be deemed to automatically meet the MSHA dpm standard for
newly introduced light-duty equipment. For example, any ``heavy duty
highway engine'' produced after 1994 will be deemed to meet this dpm
standard. The agency has determined that there are already MSHA
approved engines available in a full range of horsepower sizes that can
meet the EPA standards listed in this final rule.
In practice, what this rule does is simply ensure that very old
engines with few, if any, emission controls are not added to a mine's
current light duty fleet, thus accelerating the turnover to a newer
generation of technology.

(5) Is there a summary of the applicable requirements and effective
dates?

All of the emissions standards established by MSHA's final rule are
summarized in Table I-1.

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(6) What other requirements are contained in the final rule for
underground coal mines?

Miners have to be trained annually in the risks of dpm exposure and
in control methods being used at the mine. Also, certain information
about diesel engines and aftertreatment devices has to be added to the
mine ventilation plan. The paperwork requirements added by this rule
are small--on average, less than 7 hours in the first year and 4 hours
per year thereafter for a mine operator that uses diesel powered
equipment. Furthermore, manufacturers of diesel powered equipment will
incur burden hours only during the first year that the rule is in
effect in order to amend existing MSHA approvals. During the first year
that the rule is in effect the average manufacturer will incur 70
paperwork burden hours.

(7) Will the final rule eliminate any health risks to miners resulting
from the use of diesel powered equipment underground?

Although the Agency expects that health risks will be substantially
reduced by this rule, the best available evidence indicates that a
significant risk of adverse health effects due to dpm exposures will
remain after the rule is fully implemented.
MSHA considered establishing stricter standards for certain types
of equipment, and covering more light duty equipment, but concluded
that such actions would either be technologically or economically
infeasible for the coal mining industry as a whole at this time. As
MSHA takes actions to facilitate the introduction of newer and cleaner
engines underground, and as control technologies continue to develop,
additional reductions in dpm levels may become feasible for the
industry as a whole. MSHA will continue to monitor developments in this
area.

(8) What are the costs and benefits of the final rule?

Costs
Table I-2 summarizes the compliance costs to mine operators that
use diesel powered equipment for each section of the rule; total
compliance costs are about $7 million a year. Table I-3 summarizes the
compliance costs to mine operators that use diesel powered equipment by
mine size (i.e., mines employing fewer than 20 workers, mines employing
between 20 and 500 workers, and mines employing more than 500 workers).
In addition, there is a total annualized cost to diesel equipment
manufacturers of $30,030.
MSHA's full Regulatory Economic Analysis, (REA) from which Tables
I-2 and I-3 are derived, provides considerable detail on the
assumptions MSHA used in developing these cost estimates, and on the
costs associated with the controls required for particular engines in
the current fleet. For example, MSHA is estimating that for a
Caterpillar 3304 PCNA in a heavy duty piece of equipment, an operator
will have to spend about $4,500 a year to achieve compliance with the
limits for that equipment (hot gas filter, cost annualized, plus annual
costs of regeneration). Copies of MSHA's full (REA) analysis are in the
record and are available to the mining community upon request.

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Benefits
Benefits of the rule include reductions in lung cancer. In the long
run, as the mining population turns over, MSHA estimates that a minimum
of 1.8 lung cancer deaths will be avoided per year.\1\
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\1\ This lower bound figure could significantly underestimate
the magnitude of the health benefits. For example, the estimate
based on the mean value of all the studies examined is 13 lung
cancer deaths avoided per year.
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Benefits of the rule will also include reductions in the risk of
death from cardiovascular, cardiopulmonary, or respiratory causes and
in sensory irritation and respiratory symptoms. MSHA does not believe
that the available data can support reliable or precise quantitative
estimates of these benefits. Nevertheless, the expected reductions in
the risk of death from cardiovascular, cardiopulmonary, or respiratory
causes appear to be significant, and the expected reductions in sensory
irritation and respiratory symptoms appear to be rather large.

(9) What actions has MSHA taken, and what additional actions does it
plan to take, to facilitate compliance with this rule?

This rule is a continuation of efforts by MSHA to help the mining
community deal with the use of diesel engines in mining. The diesel
equipment rule, now in effect, has itself contributed to the reduction
of diesel exhaust emissions through the use of low sulfur diesel fuel,
the requirement that all engines underground be approved, and improved
maintenance. In one case, testimony was presented by a mine operator
that timely engine maintenance, triggered by the weekly undiluted
exhaust emissions test required by the new regulation, has greatly
reduced carbon monoxide emissions from diesel equipment. These properly
tuned engines will generate less particulate. MSHA has devoted
workshops specifically to dpm control, issued a Toolbox of control
methods to assist the mining community in this regard, and developed a
computerized Estimator to help individual mines evaluate the impact of
alternative approaches of controlling dpm emissions. The agency has
verified the efficiency of the current generation of paper filters, and
has sponsored work on the measurement of dpm in ambient mine
atmospheres.
This final rule includes certain provisions to facilitate
compliance--e.g., authorizing MSHA to rely on the testing requirements
of organizations like VERT, and permitting compliance with certain EPA
requirements to be deemed as compliance with the requirements in this
rule for newly introduced light duty equipment. The agency is, as
described above, planning to take action in consultation with the
mining community to facilitate the approval, and in particular the
approval for permissible use, of a newer, cleaner generation of diesel
engines. The agency will be preparing a compliance guide for this rule,
and posting a variety of useful information on its web site. If
necessary, additional workshops may be scheduled. In addition, MSHA is
ready to provide special technical assistance to those who are planning
to bring new engines or equipment underground in the next few months.

(10) Are surface mines addressed in this rule?

Surface areas of underground mines, and surface mines, are not
covered by this rule. In certain situations the concentrations of dpm
at surface mines may be a cause for concern: e.g., production areas
where miners work in the open air in close proximity to loader-haulers
and trucks powered by older, out-of-tune diesel engines, shops, or
other confined spaces where diesel engines are running. The Agency
believes, however, that these problems are currently limited and
readily controlled through education and technical assistance. The
Agency would like to emphasize, however, that surface miners are
entitled to the same level of protection as other miners; and the
Agency's risk assessment indicates that even short-term exposures to
concentrations of dpm like those observed may result in serious health
problems. Accordingly, in addition to providing education and technical
assistance to surface mines, the Agency will also continue to evaluate
the hazards of diesel particulate exposure at surface mines and will
take any necessary action, including regulatory action if warranted, to
help the mining community minimize any hazards.

II. Background Information

This part provides the context for this preamble. The nine topics
covered are:
(1) The role of diesel-powered equipment in underground coal mining
in the United States;
(2) The composition of diesel exhaust and diesel particulate matter
(dpm);
(3) The difficulties in measuring ambient dpm in underground coal
mines;
(4) Limiting the public's exposure to diesel and other fine
particulates--ambient air quality standards;
(5) The impact on emissions of MSHA approval standards and
environmental tailpipe standards;
(6) Methods for controlling dpm emissions in underground coal
mines;
(7) Existing standards for underground coal mines that limit miner
exposure to diesel emissions;
(8) Information on how certain states are restricting occupational
exposure to diesel particulate matter; and
(9) A history of this rulemaking.
Material on these subjects which was available to MSHA at the time
of the proposed rulemaking was included in Part II of the preamble that
accompanied the proposed rule (63 FR 17501 et seq.). This version has
been updated to reflect the record, to discuss certain issues relevant
to underground coal mines in more detail, and reorganized as
appropriate.

(1) The Role of Diesel-Powered Equipment in Underground Coal Mining in
the United States

Diesel engines, first developed about a century ago, now power a
full range of mining equipment. However at this time, less than 20% of
underground coal mines (fewer than 150 underground coal mines) utilize
this technology. Equipment powered by other sources (electrical power
delivered by cable or trolley, and battery power) continues to
predominate in this mining sector. Moreover, unlike in other mining
sectors, most of the current diesel fleet in underground coal mines
consists of light-duty support vehicles, and only limited numbers of
the equipment used in digging or hauling coal is powered by diesel
engines.
Many in the mining industry believe that diesel-powered equipment
has productivity and safety advantages over equipment powered by other
sources. Others cite evidence to the contrary, and several key
underground coal mining states continue to ban or significantly
restrict the use of diesel-powered equipment in underground coal mines.
The use of diesel engines to power equipment in underground coal mining
is increasing and appears likely to continue to do so absent
significant improvement in other power technologies.
Historical Overview of Diesel Power Use in Mining. As discussed in
the notice of proposed rulemaking, the diesel engine was developed in
1892 by the German engineer Rudolph Diesel. It was originally intended
to burn coal dust with high thermodynamic efficiency. Later, the diesel
engine was modified to burn middle distillate petroleum (diesel fuel).
In diesel engines, liquid fuel droplets are injected

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into a prechamber or directly into the cylinder of the engine. Due to
compression of air in the cylinder the temperature rises high enough in
the cylinder to ignite the fuel.
The first diesel engines were not suited for many tasks because
they were too large and heavy (weighing 450 lbs. per horsepower). It
was not until the 1920's that an efficient lightweight diesel power
unit was developed. Since diesel engines were built ruggedly and had
few operational failures, they were used in the military, railway,
farm, construction, trucking, and busing industries. The U.S. mining
industry was slow to begin using these engines. Thus, when in 1935 the
former U.S. Bureau of Mines published a comprehensive overview on metal
mine ventilation (McElroy, 1935), it did not mention ventilation
requirements for diesel-powered equipment. By contrast, the European
mining community began using these engines in significant numbers, and
various reports on the subject were published during the 1930's.
According to a 1936 summary of these reports (Rice, 1936), the diesel
engine had been introduced into German mines by 1927. By 1936, diesel
engines were used extensively in coal mines in Germany, France, Belgium
and Great Britain. Diesel engines were also used in potash, iron and
other mines in Europe. Their primary use was in locomotives for hauling
material.
It was not until 1939 that the first diesel engine was used in the
United States mining industry, when a diesel haulage truck was used in
a limestone mine in Pennsylvania, and not until 1946 was a diesel
engine used in coal mines. Today, however, diesel engines are used to
power a wide variety of equipment in all sectors of U.S. mining.
Production equipment includes vehicles such as haultrucks and shuttle
cars, load-haul-dump units, face drills, and explosives trucks. Diesel
engines are also used in support equipment including generators and air
compressors, ambulances, crane trucks, ditch diggers, foam machines,
forklifts, graders, locomotives, longwall component carriers, lube
units, mine sealant machines, personnel carriers, hydraulic power
units, rock dusting machines, roof drills, tractors, utility trucks,
water spray units, and welders.
Current Patterns of Diesel Power Use in Underground Coal Mining.
The underground coal mining sector is not as reliant upon diesel power
as are other mining sectors. While nearly all underground metal and
nonmetal mines, and nearly all surface mines, use diesel-powered
equipment, less than 20% of underground coal mines use it. Table II-1
provides further information on the current inventory.

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The great majority of the diesel engines used in underground coal
mines are used to power support equipment, rather than production
equipment. This is in sharp contrast to other sectors. For example, in
underground metal and nonmetal mines, of the approximate 4,100 pieces
of diesel equipment normally in use at the time of MSHA's proposal,
nearly half of the units were estimated to be used for loading and
hauling. By contrast, of the approximately 3,000 pieces of diesel
equipment in use in underground coal mines, MSHA estimates that fewer
than 10% are used for coal loading and haulage. Moreover, because of
space constraints and other operating conditions in underground coal
mines, virtually all coal loading and hauling equipment has engines
less than 200 horsepower; by contrast, virtually all such equipment in
metal and nonmetal mines has engines greater than 200 horsepower and
ranging to more than 750 horsepower or greater. As a result, the
average horsepower of diesel engines powering equipment in underground
coal mines is much less than the average engine in underground metal
and nonmetal mines and all surface mines. This is significant because,
other things being equal, lower horsepower engines are going to produce
less dpm emissions by mass than higher horsepower engines.
The engines in underground coal mines can be divided into three
categories recognized under existing MSHA regulations: ``permissible'',
``heavy-duty nonpermissible'', and ``light-duty nonpermissible.'' In
this final dpm rule, MSHA is establishing different requirements for
each of these categories. Accordingly, some background on this
categorization is needed.
Use of Diesel Engines in Permissible Equipment. Under existing
regulations, equipment, whether powered by diesel engines or
electricity, that is used in areas of the mine where methane gas is
likely to be present in dangerous concentrations must be MSHA-approved
``permissible'' equipment.

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Permissible diesel powered equipment for use in coal mines is provided
with special equipment to prevent the ignition of methane. This special
equipment includes flame arresters and special treatment of flanges and
joints. Since diesel engines normally have very hot surface
temperatures and hot exhaust gas that can constitute an ignition
source, permissible diesels must be provided with a means to maintain
the temperatures of surfaces and the exhaust gas below 302 deg.F.
MSHA regulations are very specific in defining those areas of the
mine where permissible equipment is required. Generally, permissible
equipment is required where the coal mining is actually being
performed, because the mining process typically liberates methane.
These areas are commonly referred to as ``inby'' areas. In some cases,
however, permissible equipment is required to be used in other areas of
the mine. For example, only permissible diesel-powered equipment may be
used in return aircourses. The permissible equipment provides an
additional level of fire protection because of the strict temperature
controls on the equipment surface and exhaust. This increased
protection is required because of the potential for the accumulation of
dangerous levels of methane in these aircourses.
MSHA's January 2000 inventory indicates that of the 3,121 diesel
powered pieces of equipment in underground coal mines, 528 units are
permissible pieces. The emissions generated by permissible equipment
make a significant contribution to dpm concentrations in the mines
where they are functioning. This is because the equipment has large
engines, works hard and continuously in locations generally far from
ventilation sources, and in close quarters with miners.
Moreover, the engines which have to date been approved for
permissible use are among those which emit the highest levels of dpm
(in grams/hour): the Caterpillar 3304, Caterpillar 3306 (available in
two horsepower sizes), the Deutz D916-6, and the Isuzu QD-100. The
Deutz D916-6 is still used in underground coal mines, however, it is no
longer in production. MSHA recently approved the Caterpillar 3306PCTA
permissible, the first approved turbocharged engine.
Diesel engines in the horsepower ratings required to power
permissible equipment are now available in new low emissions technology
engines. However, none of them has been approved for use on permissible
equipment because no applications for MSHA approval have been received.
This situation may reflect a lack of adequate incentives for engine and
equipment manufacturers to incur the development costs to meet MSHA
permissibility requirements or to pay the fees required for approval.
MSHA is developing programs that would facilitate the availability
of engines that utilize the latest technologies to reduce gaseous and
particulate emissions for use in permissible equipment. Current engine
designs that utilize low emissions technologies are currently approved
by MSHA in nonpermissible form.
One of the programs that MSHA is considering would follow the
precedent established in the recently published diesel equipment rule.
To facilitate compliance with this dpm rule, MSHA is considering
funding the additional emissions testing needed to gain permissibility
approval, previously approved, non-permissible engines that utilize low
emissions technology engines, or waiving the normal fees that the
Agency charges for the administrative and technical evaluation portion
of the approval process.
Alternatively, MSHA may relax, as an interim measure, the
requirement that engine approvals be issued only to engine
manufacturers. Under this program an equipment manufacturer could
utilize an engine, approved by MSHA as nonpermissible, in a permissible
power package. MSHA would ensure that the additional emissions tests
required for permissible engines are conducted as part of the power
package approval process. Provisions of the two programs could be
combined.
While the availability of cleaner engines would help reduce the dpm
emissions from the permissible fleet, there are aftertreatment filters
available for such equipment that are both highly efficient and
relatively low cost. As discussed in more detail in section 6 of this
part, because the exhaust temperature of these permissible pieces of
equipment must be cooled for safety reasons, aftertreatment devices
whose filtration media consists of paper can be directly installed on
this equipment. Paper filters exposed to uncooled exhaust pose a fire
and ignition hazard.
Use of Diesel Engines in Nonpermissible Equipment. In those areas
of an underground coal mine where methane concentrations can be limited
through the control of ventilation air, permissible equipment is not
required. Generally, this is the case in areas away from the face,
often referred to as ``outby'' areas. Most equipment operating in
underground coal mines is ``nonpermissible'' equipment.
Nonpermissible equipment is divided into several categories for
purposes of the diesel equipment rules that currently apply in
underground coal mines (30 CFR part 75). In pertinent part, those rules
provide:

Sec. 75.1908 Nonpermissible diesel-powered equipment; categories

(a) Heavy-duty diesel-powered equipment includes--
(1) Equipment that cuts or moves rock or coal;
(2) Equipment that performs drilling or bolting functions;
(3) Equipment that moves longwall components;
(4) Self-propelled diesel fuel transportation units and self-
propelled lube units; or
(5) Machines used to transport portable diesel fuel
transportation units or portable lube units.
(b) Light-duty diesel-powered equipment is any diesel-powered
equipment that does not meet the criteria of paragraph (a) * * *
(c) * * *.
(d) Diesel-powered ambulances and fire fighting equipment are a
special category of equipment that may be used underground only in
accordance with the mine fire fighting and evacuation plan * * *.

MSHA's inventory indicates that of the 3,121 diesel powered pieces
of equipment, 497 are heavy duty nonpermissible pieces, 66 are
generators and air compressors, and 2,030--that is, about two-thirds of
the total underground coal diesel fleet at present--are other light
duty nonpermissible pieces.
The rationale for the division of nonpermissible dieselized
equipment into these classes requires some background here because in
this rulemaking on dpm, MSHA proposed making a significant distinction
between the requirements applicable to each class.
The division resulted from MSHA's 1996 regulation establishing
safety rules for the use of dieselized equipment in underground coal
mines (the general history and purpose of which are summarized in
section 9 of this Part). As discussed in the preamble to the final
diesel safety rule (61 FR 55459-61), the purpose of the categorization
was to take the diversity of nonpermissible equipment into account in
establishing regulatory requirements relevant to safety. The final
categorization scheme for nonpermissible equipment developed over the
course of time in response to public comments to the proposed rule.
Equipment falling within the heavy duty category is typically used
for extended periods during a shift on a continuous, rather than an
intermittent,

[[Page 5534]]

basis. Heavy duty equipment also moves heavy loads or performs
considerable work. Accordingly, to ensure such equipment could operate
in a safe manner, the safety rule required that each piece of heavy
duty equipment:

* * * has to be equipped with an automatic fire suppression system
addressing the additional fire risks resulting from the way this
equipment is used. Heavy-duty equipment also produces greater levels
of gaseous contaminants, and under the final rule is therefore
subject to weekly undiluted exhaust emissions tests * * * and is
included in the air quantity calculation of ventilation of diesel-
powered equipment * * *. (61 FR 55461)

It is important to note that there are other types of underground
coal mining equipment which, although they have operating
characteristics much like heavy duty equipment, were not designated as
such under the diesel equipment rule. That is because such equipment
(e.g., generators and compressors) is considered as portable equipment
and special requirements were established in that rule to address the
hazards presented by that equipment.
Ambulances and fire-fighting equipment which use diesel engines
have operating characteristics like light-duty equipment, but under the
diesel equipment rule are considered a special category of equipment
that does not have to meet the requirements of that rule. The equipment
in this category must only be used in emergencies or fire drills and in
compliance with fire fighting and evaluation plan requirements.
Consequently, such equipment is not required to have an approved engine
or power package or comply with the design and performance requirements
of Secs. 75.1909 and 75.1910 (61 FR 55461).
Under the diesel equipment rule, heavy-duty equipment may be used
to perform light-duty work; but equipment that is classified as light-
duty may not be used, even intermittently, to perform the functions
listed in paragraphs (a)(1) through (a)(5) of 30 CFR 75.1908 because it
is not required to have the automatic fire suppression system that MSHA
determined was necessary for such kinds of work. (Id.) As noted in the
preamble, two machines of the same model could fall into different
equipment categories depending on how they are used. Although of the
same design, they do not present the same risk of fire because of the
way in which they are used, nor do they produce the same quantities of
exhaust contaminants:

``* * * machines that are operated for extended periods of time
under heavy load generate more contaminants than machines that are
not.'' (Id.)

It was for this reason--the rate of contaminant generation--that in
proposing a rule to limit the concentration of dpm in underground coal
mines, MSHA proposed making a distinction between heavy-duty equipment
and light-duty equipment. MSHA proposed requiring heavy-duty
nonpermissible equipment and permissible equipment to be equipped with
filters capable of removing 95% of the dpm emitted by the engines in
those pieces of equipment. The proposal did not include any controls
for the dpm emitted from light-duty equipment nor for ambulances and
fire-fighting equipment. As noted in section 9 of this part, the Agency
asked the mining community to comment on the Agency's assumptions and
consider some options in this regard. The record on this matter and
MSHA's final decision are discussed in Part IV.
Whether categorized as heavy-duty or light-duty, the engine exhaust
from nonpermissible equipment is not required to be cooled for safety
reasons like exhaust from permissible equipment. Accordingly, this
means that paper-type filters cannot be added directly to
nonpermissible equipment without first adding a water scrubber or heat
exchanger; otherwise, the paper would burn. As a result, control
devices that are designed to filter hot exhaust gases (e.g., ceramic
filters) provide a cost effective alternative for dpm control with
nonpermissible equipment.
Does Diesel Power Have Advantages Over Alternative Sources of Power
for Equipment Used in Underground Coal Mines? As pointed out by a
commenter, a number of power sources for mining equipment have been
tried in the mining industry only to be rejected for various reasons
(e.g., gasoline engines, cables, and compressed air). Today, this
commenter continued, there are three general ways of powering mining
equipment: electric power (delivered by electric trailing cables or by
trolley wires), on-board battery power, and diesel. Table II-2
reproduces a list provided by this commenter as to his view of some of
the ``advantages and challenges'' of these power sources; MSHA is
reproducing this list as a convenient summary, but does not necessarily
agree or disagree with each specific entry.

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[[Page 5536]]

Some in the mining industry strongly favor the use of diesel
engines to power equipment in underground coal mines. A representative
of a company with four underground coal mines testified that it has 200
pieces operated by diesel power, and is continuing to add more. Another
commenter stated that diesel is the power source of choice for moving
personnel and supplies in large underground mines where coal is moved
by conveyor belt.
A number of commenters asserted that diesel-powered equipment has
productivity and safety advantages over electrically-powered and
battery-powered equipment.
One commenter argued that diesel reduces the risks associated with
the use of electrical equipment by eliminating the need for trolley
wires, trolley poles and trailing cables that cause injuries, accidents
and fatalities--shocks, electrocutions, burns, fires, tripping or being
struck by trolley poles, and also reduce the number of material
handling injuries. This commenter also argued that unlike electrical
power, diesel use does not restrict mining plans or the mining cycle
because operations are not hampered by cable length or time consuming
power moves, provide greater flexibility in underground travel routes,
and make equipment moves from one area of a mine to another more
efficient. This commenter further claimed that compared to battery-
powered mining equipment (which arguably provides the same
flexibility), diesels can haul coal more efficiently over longer
distance, provide more power, and eliminate time-consuming battery
change-out time.
Another commenter noted the increased potential for fatalities and
injuries in underground coal mines when trolley wires are present, and
further that trolley wires restrict ventilation in one entry.
Another commenter noted the difficulties of evacuating miners in
the event of emergencies over the large distances in some underground
mines using sources of power that were more prone to failure than
diesel.
Another commenter asserted that all of the 18 employees who had
died since 1972 as a result of exposed overhead direct current trolley
lines could have lived if diesel power had been in use, and pointed to
examples of fires initiated by trolley wires with associated loss of
productivity. This commenter also noted that battery powered equipment
has been known to cause injuries, and explosions both from its
production of hydrogen gas and from sparks igniting methane in the mine
atmosphere.
Commenters also note that many asserted safety risks associated
with the use of diesel powered equipment in underground coal mines have
now been addressed as a result of MSHA's safety rules.
Other commenters, however, pointed out that there are a number of
the nation's most productive underground coal mines (including both
those using longwall and those using room and pillar mining techniques)
which do not use this technology. These commenters challenged industry
claims that diesel power is necessary for business to survive. Some
also noted that miners are trained to protect themselves better from
safety hazards that accompany the use of electrical power, like
tripping on cables and electrical hazards, but are not able to protect
themselves from health hazards they cannot see. In this regard, the
hearing transcripts are replete with reminders by underground coal
miners of their concern about what they are breathing in light of the
tragic experience with black lung disease.
As indicated by MSHA in the preamble to the proposed rule (63 FR
17503), not many studies done recently address the contentions that
diesel power provides safety and/or productivity advantages, and the
studies which have been reviewed by MSHA do not clearly support this
hypothesis.

Outlook for Use of Diesel Engines To Power Equipment in Underground
Coal Mines

The use of diesel engines to power equipment in underground coal
mining is increasing. In fact, since this rulemaking was proposed,
MSHA's inventory has recorded an increase of about 5% in the number of
diesel-powered pieces of equipment at the roughly 145 coal mines using
diesel power underground. This trend appears likely to continue, absent
significant improvement in other power technologies.
Several key underground coal mining states--Ohio, Pennsylvania and
West Virginia--continue to ban or significantly restrict the use of
diesel-powered equipment in underground coal mines (as discussed in
section 8 of this Part). There are 339 underground coal mines in these
states. If the current restrictions in these States were relaxed, in
accordance with the expressed interest of industry groups toward this
end, many of these underground coal mines are likely to begin using
diesel to power some equipment.
Full implementation of MSHA's recent rules for the safe use of
diesel-powered equipment in underground coal mines (discussed in
section 7 of this part), is also likely to lead to increased diesel use
because they resolve certain safety concerns that discouraged the
mining community from using such equipment more widely. Another factor
suggesting that the use of diesel power will expand is that both miners
and mine operators are concerned about the future of their industry.
On the other hand, operators as well as miners have acknowledged
that potential health hazards associated with the use of diesel power
must be addressed if its use is to become widespread. Although the
Agency expects that health risks will be substantially reduced by this
rule, the best available evidence indicates that a significant risk of
adverse health effects due to dpm exposures will remain after the rule
is fully implemented. As explained in Part V of this preamble, however,
MSHA has concluded that the underground coal mining sector as a whole
cannot feasibly reduce dpm concentrations further at this time.
Nevertheless, the efforts by US and overseas environmental regulators
to restrict dpm and other diesel emissions into the environment,
discussed in sections 4, 5 and 6 of this Part, are leading to
technological improvements in engines, fuel and filters that will help
reduce this risk.
Currently, diesel power faces only a limited number of competitive
power sources. It is unclear how quickly new ways to generate energy to
run mobile vehicles will be available for use in underground mining
activities. New hybrid electric automobiles have been introduced this
year by two manufacturers (Honda and Toyota); these vehicles combine
traditional internal combustion power sources (in this case gasoline)
with electric storage and generating devices that can take over during
part of the operating period. By reducing the time the vehicle is
directly powered by combustion, such vehicles reduce emissions. Further
developments in electric storage devices (batteries), and chemical
systems that generate electricity (fuel cells) are being encouraged by
government-private sector partnerships. For further information on
recent developments, see the Department of Energy alternative fuels web
site at http://www.afdc.doe.gov/altfuels.html., and ``The Future of
Fuel Cells'' in the July 1999 issue of Scientific American. Until such
new technologies mature, and are reviewed for safe use underground,
MSHA assumes that the mining community's interest in the use
underground of diesel-power as an

[[Page 5537]]

alternative to direct electric power is likely to continue.

(2) The Composition of Diesel Exhaust and Diesel Particulate Matter
(DPM)

The emissions from diesel engines are actually a complex mixture of
compounds, containing gaseous and particulate fractions. The specific
composition of the diesel exhaust in a mine will vary with the type of
engines used and how they are used. Factors such as type of fuel, load
cycle, engine maintenance, tuning, and exhaust treatment will affect
the composition of both the gaseous and particulate fractions of the
exhaust. This complexity is compounded by the multitude of
environmental settings in which diesel-powered equipment is operated.
Nevertheless, there are a few basic facts about diesel emissions that
are of general applicability.
The gaseous constituents of diesel exhaust include oxides of
carbon, nitrogen and sulfur, alkanes and alkenes (e.g., butadiene),
aldehydes (e.g., formaldehyde), monocyclic aromatics (e.g., benzene,
toluene), and polycyclic aromatic hydrocarbons (e.g., phenanthrene,
fluoranthene). The oxides of nitrogen (NOX) merit particular
mention because in the atmosphere they can precipitate onto particulate
matter. Thus, reducing the emissions of NOX is a way that
engine manufacturers can control particulate production indirectly.
(See section 5 of this part).
The particulate components of the diesel exhaust gas include the
so-called diesel soot and solid aerosols such as ash particulates,
metallic abrasion particles, sulfates and silicates. Most of these
particulates are in the invisible sub-micron range of 100nm.
The main particulate fraction of diesel exhaust is made up of very
small individual particles. These particles have a solid core
consisting mainly of elemental carbon. They also have a very surface-
rich morphology. This extensive surface absorbs many other toxic
substances, that are transported with the particulates, and can
penetrate deep into the lungs. More than 1,800 different organic
compounds have been identified as absorbed onto the elemental carbon
core. A portion of this hydrocarbon material results from incomplete
combustion of fuel; however, most is derived from engine lubrication.
In addition, the diesel particles contain a fraction of non-organic
adsorbed materials. Figure II-1 illustrates the composition of dpm.

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Diesel particles released to the atmosphere can be in the form of
individual particles or chain aggregates (Vuk, Jones, and Johnson,
1976). In underground coal mines, more than 90% of these particles and
chain aggregates are submicrometer in size--i.e., less than 1
micrometer (1 micron) in diameter. Dust generated by mining and
crushing of material--e.g., silica dust, coal dust, rock dust--is
generally not submicrometer in size. Figure II-2 shows a typical size
distribution of the particles found in the environment of a mine using
equipment powered by diesel engines (Cantrell and Rubow, 1992). The
vertical axis represents relative dpm concentration, and the horizontal
axis the particle diameter.
As can be seen, the distribution is bimodal, with dpm generally
less than 1 m in size, and dust generated by the mining
process greater than 1 m.

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[[Page 5538]]

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As shown on Figure II-3 diesel particulates have a bimodal size
distribution which includes small nuclei mode particles and larger
accumulation mode particles. As further shown, most of diesel particle
mass is contained in the accumulation mode but most of the particle
number can be found in the nuclei mode.

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[[Page 5539]]

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BILLING CODE 4510-43-C

The particles in the nuclei mode, also know as nanoparticles, are
being investigated for their health hazard relevance. Interest in these
particles has been sparked by the finding that newer ``low polluting''
engines emit higher numbers of small particles than the old engine
technology engines. Although the exact composition of diesel
nanoparticles is not known, it is thought that they may be composed of
condensates (hydrocarbons, water, sulfuric acid). The amount of these
condensates and the number of nanoparticles depends very significantly
on the particulate sampling conditions, such as dilution ratios, which
were applied during the measurement.
Both the maximum particle concentration and the position of the
nuclei and accumulation mode peaks, however, depend on which
representation is chosen. In mass distributions, the majority of the
particulates (i.e., the particulate mass) is found in the accumulation
mode. The nuclei mode, depending on the engine technology and particle
sampling technique, may be as low as a few percent, sometimes even less
than 1%. A different picture is presented when the number distribution
representation is used. Generally, the number of particles in the
nuclei mode contributes to more than 50% of the total particle count.
However, sometimes the nuclei mode particles represent as much as 99%
of the total particulate number. The topic of dpm, with particular
reference to very tiny particles known as nanoparticles, is discussed
further in section 5 of this Part.

(3) The Difficulties of Measuring Ambient DPM in Underground Coal
Mines.

As it indicated in its notice of proposed rulemaking to limit the
concentrations of dpm in underground coal mines (63 FR 17498, 17500),
MSHA decided not to propose a rule to require the measurement of
ambient dpm levels in underground coal mines in order to determine
compliance. The Agency observed that while there are a number of
methods which can measure ambient dpm at high concentrations in
underground coal mines with reasonable accuracy. When the purpose is
exposure assessment, MSHA does not believe any of these methods provide
the accuracy that would be required to measure ambient dpm levels in
underground coal mines at lower concentrations.
In particular, MSHA expressed concern about potential difficulties
in using the available methods to distinguish between dpm and submicron
coal mine dust (63 FR 17506-17507). While the use of an available
impactor device can prevent larger particles from entering the sampler
(e.g., carbonates), albeit at the expense of eliminating the larger
fraction of dpm as well, there are limits on the extent to which it can
help MSHA distinguish how much of the fine particulate reaching the
sampler is coal dust and how much is dpm. To make the distinction
analytically, NIOSH method 5040 would have to be adjusted so that only
the elemental carbon is determined. However, as MSHA noted, there are
no established relationships between the concentration of elemental
carbon and total dpm under various operating conditions. The organic
carbon component of dpm can vary with engine type and duty cycle;
hence, the amount of whole dpm present for a measured amount of
elemental carbon may vary. Accordingly, MSHA concluded that it was
``not confident that there is a measurement method for dpm that will
provide accurate, consistent and verifiable results at lower
concentration levels in underground coal mines'' (63 FR 17500).
Since there has been no disagreement with MSHA's initial conclusion
about the current availability of an accurate, consistent and
verifiable method of measuring dpm concentration levels in underground
coal mines, the final rule is not dependent on ambient air
measurements. MSHA has proposed using such a method for underground
metal and nonmetal mines, and the validity of the measurement was the
subject of much comment; accordingly, a more complete discussion of
this topic will be found in the preamble of the final rule for
underground metal and nonmetal mines.

[[Page 5540]]

(4) Limiting the Public's Exposure to Diesel and Other Fine
Particulates--Ambient Air Quality Standards

Pursuant to the Clean Air Act, the Federal Environmental Protection
Agency (EPA) is responsible for setting air pollution standards to
protect the public from toxic air contaminants. These include standards
to limit exposure to particulate matter. The pressures to comply with
these limits have an impact upon the mining industry, which emits
various types of particulate matter into the environment during mining
operations, and a special impact on the coal mining industry whose
product is used extensively in emission-generating power facilities.
But those standards hold interest for the mining community in other
ways as well, for underlying some of them is a large body of evidence
on the harmful effects of airborne particulate matter on human health.
Increasingly, that evidence has pointed toward the risks of the
smallest particulates--including the particles generated by diesel
engines.
This section provides an overview of EPA's rulemaking efforts to
limit the ambient air concentration of particulate matter, including
its recent particular focus on diesel and other fine particulates.
Additional and up-to-date information about the most current rulemaking
in this regard is available on an EPA's Web site, http://www.epa.gov/
ttn/oarpg/naaqsfin/.
EPA is also engaged in other work of interest to the mining
community. Together with some state environmental agencies, EPA has
actually established limits on the amount of particulate matter that
can be emitted by diesel engines. This topic is discussed in the next
section of this Part (section 5). Environmental regulations also
establish the maximum sulfur content permitted in diesel fuel used in
highway vehicles, and such sulfur content can be an important factor in
dpm generation. This topic is discussed in section 6 of this Part. In
addition, EPA and some state environmental agencies have also been
exploring whether diesel particulate matter is a carcinogen or a toxic
material at the concentrations in which it appears in the ambient
atmosphere; discussion of these studies can be found in Part III of
this preamble.
Background. Air quality standards involve a two-step process:
Standard setting by EPA, and implementation by each State.
Under the law, EPA is specifically responsible for reviewing the
scientific literature concerning air pollutants, and establishing and
revising National Ambient Air Quality Standards (NAAQS) to minimize the
risks to health and the environment associated with such pollutants.
This review is to be conducted every five years. Feasibility of
compliance by pollution sources is not supposed to be a factor in
establishing NAAQS. Rather, EPA is required to set the level that
provides ``an adequate margin of safety'' in protecting the health of
the public.
Implementation of each national standard is the responsibility of
the states. Each must develop a state implementation plan that ensures
air quality in the state consistent with the ambient air quality
standard. Thus, each state has a great deal of flexibility in targeting
particular modes of emission (e.g., mobile or stationary, specific
industry or all, public sources of emissions vs. private-sector
sources), and in what requirements to impose on polluters. However, EPA
must approve the state plans pursuant to criteria it establishes, and
then take measurements of pollution to determine whether all counties
within the state are meeting each ambient air quality standard. An area
not meeting an NAAQS is known as a ``nonattainment area''.
Total Suspended Particulates (TSP). Particulate matter originates
from all types of stationary, mobile and natural sources, and can also
be created from the transformation of a variety of gaseous emissions
from such sources. In the context of a global atmosphere, all these
particles mix together, and both people and the environment are exposed
to a ``particulate soup,'' the chemical and physical properties of
which vary greatly with time, region, meteorology, and source category.
The first ambient air quality standards dealing with particulate
matter did not distinguish among these particles. Rather, the EPA
established a single NAAQS for ``total suspended particulates'', known
as ``TSP.'' Under this approach, the states could come into compliance
with the ambient air requirement by controlling any type or size of
TSP. As long as the total TSP was under the NAAQS--which was
established based on the science available in the 1970s--the state met
the requirement.
Particulates Less than 10 Microns in Diameter (PM10).
When the EPA completed a new review of the scientific evidence in the
mid-eighties, its conclusions led it to revise the particulate NAAQS to
focus more narrowly on those particulates less than 10 microns in
diameter, or PM10. The standard issued in 1987 contained two
components: an annual average PM10 limit of 50 g/
m3, and a 24-hour PM10 limit of 150 g/
m3. This new standard required the states to reevaluate
their situations and, if they had areas that exceeded the new
PM10 limit, to refocus their compliance plans on reducing
the levels of particulates smaller than 10 microns in size. Sources of
PM10 include power plants, iron and steel production,
chemical and wood products manufacturing, wind-blown and roadway
fugitive dust, secondary aerosols and many natural sources.
Some state implementation plans required surface mines to take
actions to help the state meet the PM10 standard. In
particular, some surface mines in Western states were required to
control the coarser particles--e.g., by spraying water on roadways to
limit dust. The mining industry has objected to such controls, arguing
that the coarser particles do not adversely impact health, and has
sought to have them excluded from the EPA ambient air standards (Shea,
1995; comments of Newmont Gold Company, March 11, 1997, EPA docket
number A-95-54, IV-D-2346).
Particulate Less than 2.5 Microns in Diameter (PM2.5).
The next EPA scientific review was completed in 1996. A proposed rule
was published in November of 1996, and, after public hearings and
review by the Office of Management and Budget, a final rule was
promulgated on July 18, 1997 (62 FR 38651).
The new rule further modifies the standard for particulate matter.
Under the new rule, the existing national ambient air quality standard
for PM10 remains basically the same--an annual average limit
of 50 g/m3 (with some adjustment as to how this is
measured for compliance purposes), and a 24-hour ceiling of 150
g/m3. In addition, however, the new rule would
establish a NAAQS for ``fine particulate matter'' that is less than 2.5
microns in size. The PM2.5 annual limit was set at 15
g/m3, with a 24-hour ceiling of 65 g/
m3.
The basis for the PM2.5 NAAQS was a large body of
scientific data indicating that particles in this size range are
responsible for the most serious health effects associated with
particulate matter. The evidence was thoroughly reviewed by a number of
scientific panels through an extended process. The proposed rule
resulted in considerable public attention, and hearings by Congress, in
which the scientific evidence was further discussed. Moreover,
challenges to the EPA's determination that this size category warranted
rulemaking were rejected by a three-judge panel of the DC Circuit
Court. (ATA v. EPA, 175 F.3d 1027, D.C. Circuit 1999).

[[Page 5541]]

A majority of the DC Circuit Court, however, agreed with challenges
to the EPA's determination to keep the existing requirements on
PM10 as a surrogate for the coarser particulates in this
category (those particulates between 2.5 and 10 microns in diameter);
instead, the Court ordered EPA to develop a new standard for this size
category.
Implications for the Mining Community. As noted earlier in this
part, diesel particulate matter is mostly less than 1.0 micron in size.
It is, therefore, a fine particulate; in some regions of the country,
diesel particulate generated by highway and off-road vehicles
constitutes a significant portion of the ambient fine particulate (June
16, 1997, PM-2.5 Composition and Sources, Office of Air Quality
Planning and Standards, EPA). As noted in Part III of this preamble,
some of the scientific studies of health risk from fine particulates
used to support the EPA rulemaking were conducted in areas where the
major fine particulate was from diesel emissions. Accordingly, MSHA has
concluded that it must consider the body of evidence of human health
risk from environmental exposure to fine particulates in assessing the
risk of harm to miners of occupational exposure to diesel particulate,
and did so in its risk assessment (see part III of this preamble).
Comments on the appropriateness of this conclusion by MSHA, are
reviewed in Part III.
(5) The impact on emissions of MSHA approval standards and
environmental tailpipe standards.
MSHA requires that the gaseous emissions from all diesel engines
used in underground coal mines meet certain minimum standards of
cleanliness; only engines which meet those standards are ``approved''
for use in underground coal mines. The 1996 diesel equipment safety
rule required that all engines in the underground mining fleet be
approved engines. Thus, these rules set a ceiling for various types of
diesel gas emissions. But diesel engines do not have to meet a dpm
emissions standard to be ``approved'' for underground use.
Engine emissions of dpm are however, restricted by Federal
environmental regulations, supplemented in some cases by State
restrictions. Over time, these regulations have required, and are
continuing to require, that new diesel engines meet tighter and tighter
standards on dpm emissions. As these cleaner engines replace or
supplement older engines in underground coal mines, they can lead to a
significant reduction in the amount of dpm emitted by the underground
fleet.
This section reviews developments in this area. Although this
subject was discussed in the preamble of the proposed dpm rule (63 FR
17507), this review here updates the relevant information.
MSHA Approval Requirements for Engines Used in Underground Coal
Mines. MSHA requires that all diesel engines used in underground coal
mines be ``approved'' by MSHA for such use, and be maintained by
operators in approved condition. Among other things, approval of an
engine by MSHA ensures that engines exceeding certain pollutant
standards are not used in underground coal mines. MSHA sets the
standards for such approval, establishes the testing criteria for the
approval process, and administers the tests. The costs to obtain
approval of an engine are usually borne by the engine manufacturer or
equipment manufacturer.
MSHA's 1996 diesel equipment rule (discussed in more detail in
section 7 of this Part) made significant changes to diesel engine
requirements for underground coal mines. The new rule required the
entire underground coal fleet to convert to approved engines no later
than November 1999. Accordingly, by the time this rule to limiting dpm
exposure goes into effect, all diesel engines in underground coal mines
are expected to be approved engines.
The new rule also required that during the approval process the
agency determine the particulate index (PI) for the engine. The
particulate index (or PI), calculated under the provisions of 30 CFR
7.89, indicates the air quantity necessary to dilute the diesel
particulate in the engine exhaust to 1 milligram of diesel particulate
matter per cubic meter of air.
Unlike the ventilation rate set for each engine, the PI does not
appear on the engine's approval plate (61 FR 55421). Furthermore, the
particulate index of an engine is not, under the diesel equipment rule,
used to determine whether or not the engine can be used in an
underground coal mine.
At the time the diesel equipment rule was issued, MSHA explicitly
deferred the question of whether to require engines used in mining
environments to meet a specific PI (61 FR 55420-21, 55437). While the
matter was discussed during the diesel equipment rulemaking, the
approach taken in the final rule was to adopt the multi-level aproach
recommended by the Diesel Advisory Committee. This multi-level approach
included the requirement to use clean fuel, low emission engines,
equipment design, maintenance, and ventilation, all of which are
included in the final rule. The requirement for determining the
particulate index was included in the diesel equipment rule in order to
provide information to the mining community in purchasing equipment--so
that mine operators can compare the particulate levels generated by
different engines. Mine operators and equipment manufacturers, can use
the information along with consideration of the type of machine the
engines would power and the area of the mine in which it would be used
to make decisions concerning the engine's contribution of diesel
particulate to the mine's total respirable dust. Equipment
manufacturers can use the particulate index to design and install
exhaust after-treatments (61 FR 55421). So that the PI for any engine
is known to the mining community, MSHA reports the index in the
approval letter, posts the PI and ventilating air requirement for all
approved engines on its website, and publishes the index containing its
lists of approved engines.
In the proposed dpm rule, MSHA indicated that given that the
equipment rule was recently promulgated, it did not yet have enough
information to determine the feasibility of a requirement that certain
engines meet a specific PI in order to be used underground (63 FR
17564). MSHA received comments on this subject during the hearings and
thereafter; the Agency's response to these comments is included in Part
IV of this preamble.
Authority for Environmental Engine Emission Standards. The Clean
Air Act authorizes the federal Environmental Protection Agency (EPA) to
establish nationwide standards for mobile sources of air pollution,
including those powered by diesel engines (often referred to in
environmental regulations as ``compression ignition'' or ``CI''
engines). These standards are designed to reduce the amount of certain
harmful atmospheric pollutants emanating from mobile sources: the mass
of particulate matter, nitrogen oxides (which as previously noted, can
result in the generation of particulates in the atmosphere),
hydrocarbons and carbon monoxide.
California has its own engine emission standards. New engines
destined for use in California must meet these standards. The standards
are issued and administered by the California Air Resources Board
(CARB). In many cases, the California standards are the same as the
national standards; as noted herein, the EPA and CARB have worked on
certain agreements with the industry toward that end. In other

[[Page 5542]]

situations, the California standards may be more stringent than federal
standards.
Regulatory responsibility for implementation of the Clean Air Act
is vested in the Office of Transportation and Air Quality (formerly the
Office of Mobile Sources), part of the Office of Air and Radiation of
the EPA. Some of the discussion which follows was derived from
materials which can be accessed from the agency's home page on the
World Wide Web at (http://www.epa.gov/omswww/omshome.htm). Information
about the California standards may be found at the CARB home page at
(http://www.arb.ca.gov/homepage.htm).
Diesel engines are generally divided into three broad categories
for purposes of engine emissions standards, in accordance with the
primary use for which the type of engine is designed: (1) Light duty
vehicles and light duty trucks (i.e., trucks under 8500 lbs GVWR, which
include pick-up trucks and SUVs. EPA has also established a class of
``medium duty passenger vehicles'' which include passenger vehicles
over 8500 lbs. These vehicles, mostly large SUVs, are treated like
light-duty trucks for the purposes of emission standards; (2) heavy
duty highway engines (i.e., those designed primarily to power trucks)
greater than 8500 lbs GVWR) which range from the largest pick-up trucks
to over the road trucks); and (3) nonroad vehicles (i.e., those engines
designed primarily to power small equipment, construction equipment,
locomotives, farm equipment and other non-highway uses).
The terms ``heavy duty'' and ``light duty'' are used differently by
EPA and MSHA. The category of an engine for purposes of environmental
regulations is not the same as the category of mining equipment in
which it is used. The engine categories used by EPA have been
established with reference to normal transportation uses. But as
explained in section 1 of this Part, MSHA has established a
classification system for underground coal mining equipment based on
how that equipment is used in mining. This system includes
``permissible'' equipment (required where explosive methane gas may be
present in significant quantities) and two categories of
``nonpermissible'' equipment known as ``heavy duty nonpermissible'' and
``light duty nonpermissible''. Accordingly, ``heavy duty'' engines
might be used in ``light duty'' nonpermissible equipment.
The exact emission standards which a new diesel engine must meet
varies with engine category and the date of manufacture. Through a
series of regulatory actions, EPA has developed a detailed
implementation schedule for each of the three engine categories. The
schedule generally forces technology while taking into account certain
technological realities.
Detailed information about each of the three engine categories is
provided below; a summary table of particulate matter emission limits
is included at the end of the discussion.
EPA Emission Standards for Light-Duty Vehicles and Light Duty
Trucks. Although vehicle engines in these categories are not currently
approved for use in underground coal mines, it might be sought in the
future. Accordingly, some information about the applicable
environmental regulations is provided here.\2\
---------------------------------------------------------------------------

\2\ The discussion focuses on the particulate matter
requirements for light duty trucks, although the current pm
requirement for all light duty vehicles is the same. The EPA
regulations for these categories apply to the unit, rather than just
to the engine itself; for heavy-duty highway engines and nonroad
engines, the regulations attach to the engines.
---------------------------------------------------------------------------

Current light-duty vehicles generally comply with the Tier 1 and
National LEV emission standards. Particulate-matter emission limits are
found in 40 CFR part 86. In 1999, EPA issued new Tier 2 standards that
will be applicable to light-duty cars and trucks beginning in 2004.
With respect to pm, the new rules phase in tighter emissions limits to
parts of production runs for various subcategories of these engines
over several years; by 2009, all light duty trucks must limit pm
emissions to a maximum of 0.02 g/mi (40 CFR 86.1811-04(c)). Engine
manufacturers may, of course, produce complying engines before the
various dates required.
EPA Emissions Standards for Heavy-Duty Highway Engines. In 1988, a
standard limiting particulate matter emitted from the heavy duty
highway diesel engines went into effect, limiting dpm emissions to 0.6
g/bhp-hr. The Clean Air Act Amendments of 1990 and associated
regulations provided for phasing in even tighter controls on
NOX and particulate matter through 1998. Thus, engines had
to meet ever tighter standards for NOX in model years 1990,
1991 and 1998; and tighter standards for PM in 1991 (0.25 g/bhp-hr) and
1994 (0.10 g/bhp-hr). The latter remains the standard for PM from these
engines for current production runs (40 CFR 86.094-11(a)(1)(iv)(B)).
Since any heavy duty highway engine manufactured since 1994 must meet
this standard, there is a supply of engines available today which meet
this standard. These engines are used in commercial mining pickup
trucks.
New standards for this category of engines are gradually being put
into place. On October 21, 1997, EPA issued a new rule for certain
gaseous emissions from heavy duty highway engines that will take effect
for engine model years starting in 2004 (62 FR 54693). The rule
establishes a combined requirement for NOX and Non-methane
Hydrocarbon (NMHC). The combined standard is set at 2.5 g/bhp-hr, which
includes a cap of 0.5g/bhp-hr for NMHC. EPA promulgated a rulemaking on
December 22, 2000 (65 FR 80776) to adopt the next phase of new
standards for these engines. EPA is taking an integrated approach to:
(a) Reduce the content of sulfur in diesel fuel; and thereafter, (b)
require heavy-duty highway engines to meet tighter emission standards,
including standards for PM. The purpose of the diesel fuel component of
the rulemaking is to make it technologically feasible for engine
manufacturers and emissions control device makers to produce engines in
which dpm emissions are limited to desired levels in this and other
engine categories. The EPA's rule will reduce pm emissions from new
heavy-duty engines to 0.01 g/bhp-hr, a reduction from the current 0.1
g/bhp-hr. MSHA assumes it will be some time before there is a
significant supply of engines that can meet this standard, and the fuel
supply to make that possible.
EPA Emissions Standards for Nonroad Engines. Nonroad engines are
those designed primarily to power small portable equipment such as
compressors and generators, large construction equipment such as haul
trucks, loaders and graders, locomotives and other miscellaneous
equipment with non-highway uses. Engines of this type are used most
frequently in the underground coal mines to power equipment.
Nonroad diesel engines were not subjected to emission controls as
early as other diesel engines. The 1990 Clean Air Act Amendments
specifically directed EPA to study the contribution of nonroad engines
to air pollution, and regulate them if warranted (Section 213 of the
Clean Air Act). In 1991, EPA released a study that documented higher
than expected emission levels across a broad spectrum of nonroad
engines and equipment (EPA Fact Sheet, EPA420-F-96-009, 1996). In
response, EPA initiated several regulatory programs. One of these set
Tier 1 emission standards for larger land-based nonroad engines (other
than for rail use). Limits were established for engine emissions of

[[Page 5543]]

hydrocarbons, carbon monoxide, NOX, and dpm. The limits were
phased in over model years from 1996 to 2000. With respect to
particulate matter, the rules required that starting in model year
1996, nonroad engines from 175 to 750 hp meet a limit on pm emissions
of 0.4 g/bhp-hr, and that starting in model year 2000, nonroad engines
over 750 hp meet the same limit.
Particulate matter standards for locomotive engines were set
subsequently (63 FR 18978, April, 1998). The standards are different
for line-haul duty-cycle engine and switch duty-cycle engines. For
model years from 2000 to 2004, the standards limit pm emissions to 0.45
g/bhp-hr and 0.54 g/bhp-hr respectively; after model year 2005, the
limits drop to 0.20 g/bhp-hr and 0.24 g/bhp-hr respectively.
In October 1998, EPA established additional standards for nonroad
engines (63 FR 56968). Among these are gaseous and particulate matter
limits adopted for the first time (Tier 1 limits) for nonroad engines
under 50 hp. Tier 2 emissions standards for engines between 50 and 175
hp include pm standards for the first time. Further, they establish
Tier II particulate matter limits for all other land-based nonroad
engines (other than locomotives which previously had Tier II
standards). Some of the non-particulate emissions limits set by the
1998 rule are subject to a technology review in 2001 to ensure that the
required levels are feasible; EPA has indicated that in the context of
that review, it intends to consider further limits for particulate
matter. Because of the phase-in of these Tier II pm standards, and the
fact that some manufacturers will produce engines meeting the standard
before the requirements go into effect, there are or soon will be some
Tier II pm engines in some sizes available, but it is likely to be a
few years before a full size range of Tier II pm nonroad engines is
available.
Table II-3 provides a full list of the EPA required particulate
matter limitations on nonroad diesel engines for tier 1 and 2. For
example, a nonroad engine of 175 hp produced in 2001 must meet a
standard of 0.4 g/hp-hr; a similar engine produced in 2003 or
thereafter must meet a standard of 0.15 g/hp-hr.

Table II-3.--EPA Nonroad Engine PM Requirements
----------------------------------------------------------------------------------------------------------------
Year first PM limit (g/
kW range Tier applicable kW-hr)
----------------------------------------------------------------------------------------------------------------
kW8............................................................. 1 2000 1.00
2 2005 0.80
8kW19................................................ 1 2000 0.80
19kW37............................................... 1 1999 0.80
2 2004 0.60
37kW75............................................... 1 1998 ..............
2 2004 0.40
75kW130.............................................. 1 1997 ..............
2 2003 0.30
130kW225............................................. 1 1996 0.54
2 2003 0.20
225kW450............................................. 1 1996 0.54
2 2001 0.20
450kW560............................................. 1 1996 0.54
2 2002 0.20
kW>560.......................................................... 1 2000 0.54
2 2006 0.20
----------------------------------------------------------------------------------------------------------------

The Impact of MSHA and EPA Engine Emission Standards on the
Underground Coal Mining Fleet. In the mining industry, engines and
equipment are often purchased in used condition, and frequently
rebuilt. Thus, many of the diesel engines in an underground coal mine's
fleet today may only meet older environmental emission standards, or no
environmental standards at all. Although the environmental tailpipe
requirements on dpm are already bringing about a reduction in the
overall contribution of dpm to the general atmosphere, the beneficial
effects of the EPA regulations on mining atmospheres will be slower
absent incentive or regulatory actions that accelerate the turnover of
mining fleets to engines that emit less dpm. Moreover, while the
requirement that all underground coal mine engines be ``MSHA approved''
is leading to a less polluting fleet than would otherwise be the case,
there are many approved engines that do emit significant levels of
pollution, and in particular dpm. As noted in the discussion of MSHA's
approval requirements, the Agency is taking internal actions to ensure
that these requirements do not inadvertently slow the introduction of
cleaner engine technology.
It should be noted that in theory, underground mines can still
purchase certain types of new engines that do not have to meet EPA
standards. For example, the current rules on nonroad diesel engines
state that they do not apply to engines intended to be used in
underground coal and metal and nonmetal mines (40 CFR 89.1(b)).
Moreover, it is not uncommon for engine manufacturers to take a model
submitted for EPA testing and adjust the horsepower or other features
for use in a mining application. In recent years, however, engine
manufacturers have significantly cut back on such adjustments because
the mining community is not a major market. Accordingly, MSHA believes
that most of the diesel engines that will be available for underground
mines in the future will meet the applicable EPA standard. In addition,
many of the recently approved engines by MSHA currently meet the tier
II nonroad pm standards.
The Question of Nanoparticles. Comments received from several
commenters on the proposed rule for diesel particulate matter exposure
of underground coal miners raised questions relative to
``nanoparticles;'' i.e., particles found in the exhaust of diesel
engines that are less than 50 nanometers (nm) in diameter.
One commenter was concerned about recent indications that
nanoparticles may pose more of a health risk than the larger particles
that are emitted from a diesel engine. This commenter submitted
information demonstrating

[[Page 5544]]

that nanoparticles emitted from the engine could be removed effectively
from the exhaust using aftertreatment devices such as ceramic traps.
Another commenter was concerned that MSHA's proposed rule for
underground coal mines is based on removing 95% of the particulate by
mass. He believed that this reduction in mass was attributed to those
particles greater than 0.1m but less than 1m and did
not address the recent scientific hypothesis that it may be the very
small nanopaticles that are responsible for adverse health effects.
Based on the recent scientific information on the potential health
effects resulting from exposure to nanoparticles, this commenter did
not believe that potential the risk of cancer would be reduced if
exposure levels to nanoparticles increased. He indicated that studies
suggest that the increase in nanoparticles will exceed 6 times their
current levels.
Current environmental emission standards established by EPA and
CARB, and the particulate index calculated by MSHA, focus on the total
mass of diesel particulate matter emitted by an engine--for example,
the number of grams per some unit of measure (i.e. grams/brake-
horsepower). Thus, the technology under development by the engine
industry to meet the standards accordingly focuses on reducing the mass
of dpm emitted from the engine. There is some evidence, however, that
some aspects of this new technology, particularly fuel injection, is
resulting in an increase in the number of nanoparticles emitted from
the engine.
Figure II-3, repeated here from section 2 of this Part, illustrates
this situation (Majewski, W. Addy, Diesel Progress, June, 1998).

BILLING 4510-43-P

[GRAPHIC] [TIFF OMITTED] TR19JA01.007

BILLING CODE 4510-43-C
The formation of particulates starts with particle nucleation
followed by subsequent agglomeration of the nuclei particles into an
accumulation mode. Thus, as illustrated in Figure II-3, the majority of
the mass of dpm is found in the accumulation mode, where the particles
are generally between 0.1 and 1 micron in diameter. However, when
considering the number of particles emitted from the engine, more than
half and sometimes almost all of the particles (by number) are in the
nuclei mode.
A number of studies have demonstrated that the size of the
particles emitted from the newer low emission diesel engines, has
shifted toward the generation of nuclei mode particles. One study
(cited by Majewski) compared a 1991 engine to its 1988 counterpart. The
total PM mass in the newer engine was reduced by about 80%; but the new
engine generated thousands of times more particles than the older
engine (3000 times as much at 75 percent load and about 14,000 times as
much at 25 percent load). One hypothesis offered for this phenomenon is
that the cleaner engines produce less soot particles on which
particulates can condense and accumulate, and hence they remain in
nuclei mode. The accumulation particles act as a ``sponge'' for the
condensation and/or adsorption of volatile materials. In the absence of
that sponge, gas species which are to become liquid or solid will
nucleate to form large numbers of small particles (see diesel.net
technology guide). Mayer, while pointing out that nanoparticle
production was a problem with older engines as well, concurs that the
technology used to clean up pollution in newer engines is not having
any positive impact on nanoparticle production. While there is
scientific evidence that the newer engines, designed to reduce the mass
of pollutants emitted from the diesel engine, emit more particles in
the nuclei mode, quantifying the magnitude of these particles has been
difficult. This is because as dpm is released into the

[[Page 5545]]

atmosphere the diesel particulate undergoes very complex changes. In
addition, current sampling procedures produce artificial particulates,
which otherwise would not exist under atmospheric conditions.
Experimental work conducted at West Virginia University (Bukarski)
indicate that nanoparticles are not generated during the combustion
process, but rather during other physical and chemical processes which
the exhaust undergoes in aftertreatment systems.
While current medical research findings indicate that small
particulates, particularly those below 2m in diameter, may be
more harmful to human health than the larger ones, much more medical
research and diesel emission studies are needed to fully characterize
diesel nanoparticles emissions and their influence on human health. If
nanoparticles are found to have an adverse health impact by virtue of
size or number, it could require significant adjustments in
environmental engine emission regulation and technology. It could also
have implications for the type of controls utilized, with some
asserting that aftertreatment filters are the only effective way to
limit the emission of nanoparticles and others asserting that
aftertreatment filters can increase the number of nanoparticles.
As discussed in Part III, the available evidence on the risks for
dpm exposure do not currently include enough data to draw conclusions
about the risks of exposure to significant numbers of very small
particles. Research on nanoparticles and their health effects is
currently a topic of investigation. As there have been few measurements
of the number of particles emitted (as opposed to mass), it will be
very difficult for epidemiologists to extrapolate information in this
regard.
Based on the comments received and a review of the literature
currently available on the nanoparticle issue, MSHA believes that
promulgation of the final rules for underground coal and metal and
nonmetal mines is necessary to protect miners. The nanoparticle issues
discussed above will not be answered for some time because of the
extensive research required to address the questions raised. MSHA's
rules will require the application of exhaust aftertreatment devices on
nearly all of the most polluting engines. The application of these
measures will reduce the number of nanoparticles as well as the mass of
the larger particles to which a miner will be exposed--miners wanted
aftertreatment on all machines for this purpose.

(6) Other Methods for Controlling DPM in Underground Coal Mines

As discussed in the last section, the introduction of new engines
underground will play a significant role in reducing the concentration
of dpm in underground coal mines. There are, however, other approaches
to reducing dpm concentrations in underground coal mines. Among these
are: use of aftertreatment devices to eliminate particulates emitted by
an engine; altering fuel composition to minimize engine particulate
emission; use of maintenance practices and diagnostic systems to ensure
that fuel, engine and aftertreatment technologies work as intended to
minimize emissions; enhancing ventilation to reduce particulate
concentrations in a work area; enclosing workers in cabs or other
filtered areas to protect them from exposure; and use of work and fleet
practices that reduce miner exposures to emissions.
As noted in section 9 of this Part, information about these
approaches was solicited from the mining community in a series of
workshops in 1995, and highlights were published by MSHA as an appendix
to the proposed rule on dpm ``Practical Ways to Control Exposure to
Diesel Exhaust in Mining--a Toolbox.'' During the hearings and in
written comments on this rulemaking, these control methods were
discussed.
This section provides updated information on two methods for
controlling dpm emissions: aftertreatment devices and diesel fuel
content. There was considerable comment on aftertreatment devices
because MSHA's proposed rule would have required that certain equipment
be equipped with high-efficiency particulate filters; the efficiency of
such devices remains an important issue in determining the
technological and economic feasibility of the final rule. Moreover,
some commenters strongly favored the use of oxidation catalytic
converters, a type of aftertreatment device used to reduce gaseous
emission but which can also lessen dpm levels. Accordingly, information
about them is reviewed here. With respect to diesel fuel composition, a
recent rulemaking initiative by EPA, and actions taken by other
countries in this regard, are discussed here because of their
implications for the mining community.
Emissions aftertreatment devices. One of the most discussed
approaches to controlling dpm emissions involves the use of devices
placed on the end of the tailpipe to physically trap diesel particulate
emissions and thus limit their discharge into the mine atmosphere.
These aftertreatment devices are often referred to as ``particle
traps'' or ``soot traps,'' but the term filter is also used. The two
primary categories of particulate traps are those composed of ceramic
materials (and thus capable of handling uncooled exhaust), and those
composed of paper materials (which require the exhaust to first be
cooled). Typically, the latter are designed for conventional
permissible equipment which have water scrubbers installed which cool
the exhaust. However, another alternative that is now used in coal
mines is ``dry system technology'' which cools the diesel exhaust with
a heat exchanger and then uses a paper filter. In addition, ``oxidation
catalytic converters,'' devices used to limit the emission of diesel
gases, and ``water scrubbers,'' devices used to cool the emission of
diesel gases, are discussed here as well, because they also can have
effect on limiting particle emission.
Water Scrubbers. Water scrubbers are devices added to the exhaust
system of diesel equipment. Water scrubbers are essentially metal boxes
containing water through which the diesel exhaust gas passes. The
exhaust gas is cooled, generally to below 170 degrees F. A small
fraction of the unburned hydrocarbons is condensed and remains in the
water with some of the dpm. Tests conducted by the former Bureau of
Mines and others indicate that no more than 20 to 30 percent of the dpm
is removed. However, MSHA has no definitive evidence on the amount of
dpm reduction that can be achieved with a particular water scrubber.
The water scrubber does not remove the carbon monoxide, the oxides of
nitrogen, or other gaseous emission that remains a gas at room
temperature, so their effectiveness as aftertreatment devices is
limited.
The water scrubber serves as an effective spark and flame arrester
and as a means to cool the exhaust gas. Consequently, it is used in
most of the permissible diesel equipment in mining as part of the
safety components needed to gain MSHA approval.
The water scrubber has several operating characteristics which keep
it from being a candidate for an aftertreatment device on
nonpermissible equipment. The space required on the vehicle to store
sufficient water for an 8 hour shift is not available on some
equipment. Furthermore, the exhaust contains a great deal of water
vapor which condenses under some mining conditions creating a fog which
can adversely effect visibility. Also, operation of the equipment on
slopes can cause the water level in the scrubber

[[Page 5546]]

to change resulting in water blowing out the exhaust pipe. Control
devices can be placed within the scrubber to maintain the appropriate
water level. Because these devices are in contact with the water
through which the exhaust gas has passed, they need frequent
maintenance to insure that they are operating properly and have not
been corroded by the acidic water created by the exhaust gas. The water
scrubber must be flushed frequently to remove the acidic water and the
dpm and other exhaust residue which forms a sludge that adversely
effects the operation of the unit. These problems, coupled with the
relatively low dpm removal efficiency, have prevented widespread use of
water scrubbers as a primary dpm control device on nonpermissible
equipment.
Oxidation Catalytic Converters (OCCs). Oxidation catalytic
converters (OCCs) were among the first devices added to diesel engines
in mines to reduce the concentration of harmful gaseous emissions
discharged into the mine environment. OCCs began to be used in
underground mines in the 1960's to control carbon monoxide,
hydrocarbons and odor (Haney, Saseen, Waytulonis, 1997). Their use has
been widespread. It has been estimated that more than 10,000 OCCs have
been put into the mining industry over the last several years
(McKinnon, dpm Workshop, Beckley, WV, 1995).
Several of the harmful emissions in diesel exhaust are produced as
a result of incomplete combustion of the diesel fuel in the combustion
chamber of the engine. These include carbon monoxide and unburned
hydrocarbons including harmful aldehydes. Catalytic converters, when
operating properly, remove significant percentages of the carbon
monoxide and unburned hydrocarbons. Higher operating temperatures,
achieved by hotter exhaust gas, improve the conversion efficiency.
Oxidation catalytic converters operate, in effect, by continuing
the combustion process outside the combustion chamber. This is
accomplished by utilizing the oxygen in the exhaust gas to oxidize the
contaminants. A very small amount of material with catalytic
properties, usually platinum or a combination of the noble metals, is
deposited on the surfaces of the catalytic converter over which the
exhaust gas passes. This catalyst allows the chemical oxidation
reaction to occur at a lower temperature than would normally be
required.
For the catalytic converter to work effectively, the exhaust gas
temperature must be above 370 degrees Fahrenheit for carbon monoxide
and 500 degrees Fahrenheit for hydrocarbons. Most converters are
installed as close to the exhaust manifold as possible to minimize the
heat loss from the exhaust gas through the walls of the exhaust pipe.
Insulating the segment of the exhaust pipe between the exhaust manifold
and the catalytic converter extends the portion of the vehicle duty
cycle in which the converter works effectively.
The earliest catalytic converters for mining use consisted of
alumina pellets coated with the catalytic material and enclosed in a
container. The exhaust gas flowed through the pellet bed where the
exhaust gas came into contact with the catalyst. Designs have evolved,
and now the most common design is a metallic substrate, formed to
resemble a honeycomb, housed in a metal shell. The catalyst is
deposited on the surfaces of the honeycomb. The exhaust gas flows
through the honeycomb and comes into contact with the catalyst.
Soon after catalytic converters were introduced, it became apparent
that there was a problem due to the sulfur found in diesel fuels in use
at that time. Most diesel fuels in the United States contained anywhere
from 0.25 to 0.50 percent sulfur or more on a mass basis. In the
combustion chamber, this sulfur was converted to SO2,
SO3, or SO4 in various concentrations, depending
on the engine operating conditions. In general, most of the sulfur was
converted to gaseous SO2. When exhaust containing the
gaseous sulfur dioxide passed through the catalytic converter, a large
proportion of it was converted to solid sulphates which are in fact,
diesel particulate. Sulfates can ``poison'' the catalyst, severely
reducing its life.
Recently, as described elsewhere in this preamble, the EPA required
that diesel fuel used for over the road trucks contain no more than 500
ppm (0.05 percent) sulfur. This action made low sulfur fuel available
throughout the United States. MSHA, in its recently promulgated
regulations for the use of diesel powered equipment in underground coal
mines required that this low sulfur fuel be used. When the low sulfur
fuel is burned in an engine and passed through a converter with a
moderately active catalyst, only small amounts of SO2 and
additional sulfate based particulate are created. However, when a very
active catalyst is used, to lower the operating temperature of the
converter or to enhance the CO removal efficiency, even the low sulfur
fuel has sufficient sulfur present to create an SO2 and
sulfate based particulate problem. Consequently, as discussed later in
this section, the EPA has notified the public of its intentions to
promulgate regulations that would limit the sulfur content of future
diesel fuel to 15 ppm (0.0015 percent) for on-highway use in 2006.
The particulate removal capabilities of some OCCs are significant
in gravimetric terms. In 1995, the EPA implemented standards requiring
older buses in urban areas to reduce the dpm emissions from rebuilt bus
engines (40 CFR 85.1403). Aftertreatment manufacturers developed
catalytic converter systems capable of reducing dpm by 20%. Such
systems are available for larger diesel engines common in the
underground metal and nonmetal sector. However, as has been pointed out
by Mayer, the portion of particulate mass that seems to be impacted by
OCCs is the soluble component, and this is a smaller percentage of
particulate mass in utility vehicle engines than in automotive engines.
Moreover, some measurements indicate that more than 40% of NO is
converted to more toxic NO2, and that particulate mass
actually increases using an OCC at full load due to the formation of
sulfates. In summation, Mayer concluded that the OCCs do not reduce the
combustion particulates, produce sulfate particulates, or have
unfavorable gaseous phase reactions increasing toxicity, and that the
positive effects are irrelevant for construction site diesel engines.
He concludes that the negative effects outweigh the benefits (Mayer).
The Phase 1 interim data report of the Diesel Emission Control-
Sulfur Effects (DECSE) Program (a joint government-industry program
established to explore lower sulfur content that is discussed in more
detail later in this section) similarly indicates that testing of OCCs
under certain operating conditions can increase dpm emissions due to an
increase in the sulfate fraction. (DECSE Program Summary, Dec. 1999)
Another commenter also notes that oxidation catalytic activity can
increase sulfates under certain operating temperatures, and that
oxidation is a part of aftertreatment systems approaches like the
DST and some ceramic traps. But this commenter asserts that
the sulfate production occurs at an operating mode that is seldom seen
in real operation.
Other commenters during the rulemaking strongly supported the use
of OCCs to reduce particulate and other diesel emissions. They argue
that the OCCs result in significant reductions in dpm and in dpm
generating gases. One commenter noted that with a clean engine, an OCC
might well reduce particulates enough to meet any requirements
established by MSHA.

[[Page 5547]]

However, another commenter noted that OCCs and ceramic traps can
fail when used at higher altitude mines due to the lower oxygen content
in the exhaust system. Another commenter asserted that OCCs are not
effective at low temperature, although they are improving. Accordingly,
this commenter indicated that OCCs have an impact only on light duty
equipment when the equipment is working, not when it is idling, and are
virtually useless on permissible equipment because of the low exhaust
temperatures achieved through cooling. Despite a specific request from
MSHA at the rulemaking hearings, no data were provided by OCC advocates
to demonstrate that they can perform well at the lower temperatures
normally found in light duty equipment.
Hot gas particulate traps. Throughout this preamble, MSHA is
referring to the particulate traps (filters) that can be used in the
undiluted hot exhaust stream from the diesel engine as hot gas filter.
Hot gas filter refers to the current commercially available particulate
filters such as ceramic cell, woven fiber filter, sintered metal
filter, etc.
Following publication of EPA rules in 1985 limiting diesel
particulate emissions from heavy duty diesel engines, development of
aftertreatment devices capable of more significant reductions in
particulate levels began to be developed for Comerica applications.
The wall flow type ceramic honeycomb diesel particulate filter
system was initially the most promising approach (SAE, SP-735, 1988).
This consisted of a ceramic substrate encased in a shock-and vibration-
absorbing material covered with a protective metal shell. The ceramic
substrate is arranged in the shape of a honeycomb with the openings
parallel to the centerline. The ends of the openings of the honeycomb
cells are plugged alternately. When the exhaust gas flows through the
particulate trap, it is forced by the plugged end to flow through the
ceramic wall to the adjacent passage and then out into the mine
atmosphere. The ceramic material is engineered with pores in the
ceramic material sufficiently large to allow the gas to pass through
without placing excessive back pressure on the engine, but small enough
to trap the particulate on the wall of the ceramic material.
Consequently, these units are called wall flow traps.
Work with ceramic filters in the last few years has led to the
development of the ceramic fiber wound filter cartridge (SAE, SP-1073,
1995). The ceramic fiber has been reported by the manufacturer to have
dpm reduction efficiencies up to 80 percent. This system has been used
on vehicles to comply with German requirements that exhaust from all
diesel engines used in confined areas be filtered. Other manufacturers
have made the wall flow type ceramic honeycomb dpm filter system
commercially available to meet the German standard. One commenter noted
that a total exhaust, wall-flow, ceramic filter developed in Canada in
collaboration with a US firm has been successfully demonstrated
underground with a reduction of between 60% and 90% of particulate
matter.
The development of these devices has proceeded in response to
international and national efforts to regulate dpm emissions. However,
due to the extensive work performed by the engine manufacturers on new
technological designs of the diesel engine's combustion system, and the
use of low sulfur fuel, particulate traps were found to be unnecessary
for compliance with the EPA standards of the time for vehicle engines.
These devices proved to be quite effective in removing particulate,
achieving particulate removal efficiencies of greater than 90 percent.
It was quickly recognized that this technology, while not
immediately required for most vehicles, might be useful in mining
applications. The former Bureau of Mines investigated the use of
catalyzed diesel particulate filters in underground mines in the United
States (BOM, RI-9478, 1993). The study demonstrated that filters could
work, but that there were problems associated with their use on
individual unit installations, and the Bureau made recommendations for
installation of ceramic filters on mining vehicles.
Canadian mines also began to experiment with ceramic traps in the
1980's with similar results (BOM, IC 9324, 1992). Work in Canada today
continues under the auspices of the Diesel Emission Evaluation Program
(DEEP), established by the Canadian Centre for Mineral and Energy
Technology in 1996 (DEEP Plenary Proceedings, November 1996). The goals
of DEEP are to: (1) evaluate aerosol sampling and analytical methods
for dpm; and (2) evaluate the in-mine performance and costs of various
diesel exhaust control strategies.
Reservations regarding their usefulness and practicality remain.
One commenter stated at one of the MSHA workshops in 1995, ``while
ceramic filters give good results early in their life cycle, they have
a relatively short life, are very expensive and unreliable.'' Another
commenter reported unsuccessful experiments with ceramic filters in
1991 due to their inability to regenerate at low temperatures, lack of
reliability, high cost of purchase and installation, and short life.
Another reported that ceramics would not work at higher altitudes
because of lower oxygen content in the exhaust system. Another
commenter pointed out that elevated operating temperatures in certain
engine modes can result in sulfates adding as much as 50% to total
particulate mass, and asserted that ceramic traps alone were unable to
offset this effect on their own.
In response to the proposed rule, MSHA received information and
claims about the current efficiency of such technologies. One
commenter, representing those who manufacture emissions controls, and
referring to technologies other than low temperature paper filters--
such as higher temperature disposable paper filters, ceramic monolith
diesel particulate filters, wound ceramic fiber filters, and metal
fiber filters--asserted that there were technologies which could
achieve in excess of 95% filtration efficiency under ``many operating
conditions.'' Another commenter submitted copies of information
provided to that commenter by individual manufacturers of emission
control systems, many of which made similar claims. Another commenter,
however, questioned manufacturer claims, asserting big differences had
been observed between such claims an independent 8-mode tests.
It appears that two groups in particular have been doing some
research comparing the efficiency of recent ceramic models: the
University of West Virginia, as part of that State's efforts to develop
rules on the use of diesel-powered equipment underground; and VERT
(Verminderung der Emissionen von Realmaschinen in Tunnelbau), a
consortium of several European agencies conducting research in
connection with major planned tunneling projects in Austria,
Switzerland and Germany to protect occupational health and subsequent
legislation in each of the three countries restricting diesel emissions
in tunneling (in both cases, background on the regulatory efforts of
the jurisdictions involved is discussed in section 8 of this part).
The legislature of the State of West Virginia enacted the West
Virginia Diesel Act, which created the West Virginia Diesel Commission
and set forth an administrative vehicle to allow and regulate the use
of diesel equipment in underground coal mines in that state. West
Virginia University was appropriated funds to test diesel exhaust
controls, as well as an array of

[[Page 5548]]

diesel particulate filters. The University was asked to provide
technical support and data necessary for the Commission to make
decisions on standards for emission controls.
The University provided data on four different engines and an
assortment of configurations of available control devices, both hot gas
filters and the DST system (a system which, first cools the
exhaust, then runs it through a paper filter). The range of collection
efficiencies reported for the ceramic filters and oxidation catalysts
combined fell between 65% and 78%. The highest collection efficiency
obtained using the ISO 8 mode test cycle (test cycle described in rule)
was 81% on the DST system. The University reported problems
with this system that would account for the lower than expected
efficiency for a paper filter type system. A commenter who spoke for
the Commission at MSHA's public hearing expressed serious reservations
of the 95% collection efficiency of MSHA's proposed rule and believed
it was not achievable with technology based on the University's current
work. The WV Commission also provided MSHA a detailed proposal for
setting a laboratory diesel particulate standard of 0.5 milligram per
cubic meter. As discussed in part IV, this is similar to the
Pennsylvania standard, but without a strict filter efficiency value,
and as further discussed in part IV, MSHA's approach in this final rule
is similar.
VERT's studies of particulate traps are detailed in two articles
published in 1999 which have been widely disseminated to the diesel
community here through www.DieselNet.com (Mayer et al., March 1999, and
Mayer, April 1999). The March article focuses on the efficiency of the
traps; the April article compares the efficiency of other approaches
(OCCs, fuel reformulation, engine modifications to reduce ultra-fine
particulates) with that of the traps. Here we focus only on the
information about particulate traps.
The authors of the March article report that 29 particulate trap
systems were tested using various ceramic, metal and fiber filter media
and several regeneration systems. The authors of the March article
summarize their conclusions as follows:

The results of the 4-year investigations of construction site
engines on test rigs and in the field are clear: particulate trap
technology is the only acceptable choice among all available
measures. Traps proved to be an extremely efficient method to
curtail the finest particles. Several systems demonstrated a
filtration rate of more than 99% for ultra-fine particulates.
Specific development may further improve the filtration rate.
A two-year field test, with subsequent trap inspection,
confirmed the results pertaining to filtration characteristics of
ultra-fine particles. No curtailment of the ultra-fine particles is
obtained with any of the following: reformulated fuel, new
lubricants, oxidation catalytic converters, and optimization of the
engine combustion.
Particulate traps represent the best available technology (BAT).
Traps must therefore be employed to curtail the particulate
emissions that the law demands are minimized. This technology was
implemented in occupational health programs in Germany, Switzerland
and Austria.

On the bench tests, it appears that the traps reduce the overall
particulate matter by between 70 and 80%, with better results for solid
ultrafine particulates; under hot gas conditions, it appears the non-
solid components of particulate matter cannot be dependably retained by
these traps. Consistent with this finding, it was found that polycyclic
aromatic hydrocarbons (PAHs) decreased proportionately to the
gravimetric decrease of carbon mass. The tests also explored the impact
of additives on trap efficiency, and the impact of back pressure.
The field tests confirmed that the traps were easy to mount and
retained their reliability over time, although regeneration using an
external power source was required when low exhaust temperatures failed
to do this automatically. Electronic monitoring of back pressure was
recommended. In general, the tests confirmed that a whole series of
trap systems have a high filtration rate and stable long time
properties and are capable of performing under difficult construction
site conditions. Again, the field tests indicated a very high reduction
(97-99%) by particulate count, but a lower rate of reduction in terms
of mass.
Subsequently, VERT has evaluated additional commerically available
filter systems. A list of recently evaluated hot gas filters are shown
in Table II-4. The filtration efficiency, expressed on a gravimetric
basis is shown in the column headed ``PMAG--without additive''. The
filtration efficiencies determined by VERT for these 6 filter systems
range from 80.7% to 94.5%. The average efficiency of these filters is
87%. MSHA will be updating the list of VERT's evaluated systems as they
become available.

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Some commenters asserted that the VERT work was for relatively
small engines and not for large engines, i.e. 600-700 hp, and hence
could not be relied upon to demonstrate the availability of filters of
such high efficiencies for the larger equipment used in some
underground mines. MSHA believes this comment is misplaced. The
efficiency of a filter is attributable to the design of the filter and
not the size of the engine. VERT is documenting filter efficiencies of
commercially available filters. It is customary in the industry,
however, for the filter manufacturer to size the filter to fit the size
of the engine. The mine operator must work with the filter manufacturer
to verify that the filter needed will work for the intended machine.
MSHA believes that this is no different for other types of options
installed on machines for underground mining use.
More information about the results of the VERT tests on specific
filters, and how MSHA intends to use this information to aid the mining
industry in complying with the requirements of the standards for heavy
duty equipment, generators and compressors, are discussed in Part IV of
this preamble.
The accumulated dpm must be removed from particulate traps
periodically. This is usually done by burning off the accumulated
particulate in a controlled manner, called regeneration. If the diesel
equipment on which the trap is installed has a duty cycle which creates
an exhaust gas temperature greater than about 650 degrees Fahrenheit
for more than 25 percent of the operating time, the unit will be self
cleaning. That is, the hot exhaust gas will burn off the particulate as
it accumulates. Unfortunately, only hard working equipment, such as
load, haul, dump and haulage equipment usually satisfies the exhaust
gas temperature and duration requirements to self regenerate.
Techniques are available to lower the temperature needed to
initiate the regeneration. One technique under development is to use a
fuel additive. A comparatively small amount of a chemical is added to
the diesel fuel and burns along with the fuel in the combustion
chamber. The additive is reported to lower the required regeneration
temperature significantly. The additive combustion products are
retained as a residue in the particulate trap. The trap must be removed
from the equipment periodically to flush the residue. Another technique
used to lower the regeneration temperature is to apply a catalyst to
the surfaces of the trap material. The action of the catalyst is
similar to that of the fuel additive. The catalyst also lowers the
concentration of some gaseous emissions in the same manner as the
oxidation catalytic converter described earlier.
A very active catalyst applied to the particulate trap surfaces and
a very active catalyst in a catalytic converter installed upstream of
the trap can create a situation in which the trap performs less
efficiently than expected. Burning low sulfur diesel fuel, containing
less than 500 ppm sulfur, will result in the creation of significant
quantities of sulfates in the exhaust gas. These sulfates will still be
in the gaseous state when they reach the ceramic trap and will pass
through the trap. These sulfates will condense later forming diesel
particulate. Special care must be taken in the selection of the
catalyst formulation to ensure that sulfate formation is avoided. This
problem does not occur in systems designed with a catalytic converter
upstream of a water scrubber. The gaseous phase sulfates will condense
when contacting the water in the scrubber and will not be discharged
into the mine atmosphere. Thus far, no permissible diesel packages have
been approved which incorporate a catalytic converter upstream of the
water scrubber. One research project conducted by the former Bureau of
Mines which attempted this arrangement was unsuccessful. In attempting
to maintain a surface temperature less than the 300 degrees Fahrenheit
(required for permissibility purposes) the exhaust gas was be cooled to
the point that the catalytic converter did not reach the necessary
operating temperature. It would appear that a means to isolate the
catalytic converter from the exhaust gas water jacket is necessary for
the arrangement to function as intended.
If the machine on which the particulate trap is installed does not
work hard enough to regenerate the trap with the hot exhaust gas and
the option to use a fuel additive or catalyzed trap is not appropriate,
the trap can still be regenerated while installed on the machine.
Systems are available whereby air is heated by an externally applied
heat source and caused to flow through the particle trap when the
engine is stopped. The heat can be supplied by an electrical resistance
element installed in front of the trap. The heat can also be supplied
by a burner installed into the exhaust pipe in front of the trap. The
burner is fueled by an auxiliary fuel line. The fuel is ignited
creating large quantities of hot gas. With both systems, an air line is
also connected to the exhaust pipe to create a flow of hot gases
through the particulate trap. Both systems utilize operator panels to
control the regeneration process.
Equipment owners may choose to remove the particle trap from the
machine to perform the regeneration. Particle traps are available with
quick release devices. The trap is then placed on a specially designed
device that creates a controlled flow of heated air that is passed
through the filter burning off the accumulated particulate.
The selection of the most appropriate means to regenerate the trap
is dependent on the equipment type, the equipment duty cycle, and the
equipment utilization practices at the mine.
A program under the Canadian DEEP project is field testing dpm
filter systems in a New Brunswick Mine. Investigators are testing four
filter systems on trucks and scoops. The initial feedback from Canada
is very favorable concerning the performance of filters. Operators are
very positive and are requesting the vehicles equipped with the filters
because of the noticeable improvement in air quality and an absence of
smoke even under transient load conditions. One system undergoing
testing utilizes an electrical heating element installed in the filter
system to provide the heated air for regeneration of the filter. This
heating element requires connection of the filter to an external
electrical source at the end of the shift. Initial tests have been
successful.
VERT has also published information on the extent of dpm filter
usage in Europe as evidence that the filter technology has attained
wide spread acceptance. MSHA believes this information is relevant to
coal and metal/nonmetal mining because the tunneling equipment on which
these filters are installed is similar to metal/nonmetal equipment and
can be applied to heavy duty equipment in coal mining operations. VERT
stated that over 4,500 filter systems have been deployed in England,
Scandinavia, and Germany. Deutz Corporation has deployed 400 systems
(Deutz's design) with full flow burners for regeneration of filters
installed on engines between 50-600kw. The Oberland-Mangold company has
approximately 1,000 systems in the field. They have accumulated an
average of 8,400 operating hours in forklift trucks, 10,600 operating
hours in construction site engines, and 19,200 operating hours in
stationary equipment. The Unikat company has introduced in Switzerland
over 250 traps since 1989 and 3,000 worldwide with some operating more
than 20,000 hours. In German industry,

[[Page 5551]]

approximately 1,500 traps in forklifts are installed annually.
Paper filters. In 1990, the former Bureau of Mines conducted a
project to develop a means to reduce the amount of dpm emitted from
permissible diesel powered equipment using technologies that were
available commercially and that could be applied to existing equipment.
The project was conducted with the cooperation of an equipment
manufacturer, a mine operator, and MSHA. In light of the fact that all
permissible diesel powered equipment, at that time, utilized water
scrubbers to meet the MSHA approval requirements, the physical
characteristics of the exhaust from that type of equipment were the
basis for the selection of candidate technologies. The technology
selected for development was the pleated media filter or paper filter
as it came to be called. The filter selected was an intake air cleaner
normally used for over the road trucks. That filter was acceptable for
use with permissible diesel equipment because the temperature of the
exhaust gas from the water scrubber was less than 170 degrees F, well
below the ignition point of the filter material. Recognizing that under
some operating modes, water would be discharged along with the exhaust,
a water trap was installed in the exhaust stream before it passed
through the filter. After MSHA conducted a thorough permissibility
evaluation of the modified system, this filter was installed on a
permissible diesel coal haulage vehicle and a series of in-mine trials
were conducted. It was determined, by in mine ambient gravimetric
sampling, that the particulate filter reduced dpm emissions by 95
percent compared with the same machine without the filter. The test
results showed that the filters would last between one and two shifts,
depending on how hard the equipment worked. (BOM, IC 9324).
Following the successful completion of the former Bureau of Mines
mine trial, several equipment manufacturers applied for and received
MSHA approval to offer the paper filter kits as options on a number of
permissible diesel machines. These filter kits were installed on other
machines at the mine where the original tests were conducted, and
later, on machines at other mines.
Despite the initial reports on the high efficiency of paper
filters, during the hearings and in the comments on this rulemaking a
number of commenters questioned whether, in practice, paper filters
could achieve efficiencies on the order of 95% when used on existing
permissible equipment. In order to determine whether it could verify
those concerns, MSHA contracted with the Southwest Research Institute
to verify the ability of such a paper filter to reduce the dpm
generated by a typical engine used in permissible equipment. The
results of this verification investigation are reviewed in Part IV of
this preamble. They confirmed that commercially available paper filters
are capable of achieving very high efficiencies.
Another commenter noted that the volatile fraction of particulate
is not trapped by hot gas filters, but rather passes through the filter
in gaseous form. The volatile fraction consists of, among other
components, gaseous forms of sulfur compounds, lube oil and the high
boiling point fraction of unburned fuel. These components condense in
the mine atmosphere as diesel particulate. The commenter asserted that
the process of volatilization is reduced in the water cooled exhaust,
but it is present nevertheless.
MSHA recognizes that the volatile fraction of dpm passes through
hot gas filters. This volatile fraction later condenses in the mine
atmosphere and is collected on particulate samplers. This is not the
case with hot gas filters that utilize a catalytic converter. The
volatile fraction is oxidized in the catalytic converter and the gases
produced do not condense as particulate. Paper filters are typically
used with water scrubbers or heat exchangers, both of which condense
the volatile fraction into dpm before the exhaust gas reaches the paper
filter. This allows the paper filter to trap the condensed volatile
fraction.
Dry systems technology. The recently developed means of achieving
permissibility with diesel powered equipment in the United States is
the dry exhaust conditioning system or dry system. This system combines
several of the concepts described above as well as new, innovative
approaches. The system also solves some of the problems encountered
with older technologies.
The dry system in its most basic form consists of a heat exchanger
to cool the exhaust gas, a mechanical flame arrestor to prevent the
discharge of any flame from within the engine into the mine atmosphere,
and a spark arrestor to prevent sparks from being discharged. The
surfaces of these components and the piping connecting them are
maintained below the 300 degrees F required by MSHA approval
requirements. A filter, of the type normally used as an intake air
filter element, is installed in the exhaust system as the spark
arrestor. In terms of controlling dpm emissions, the most significant
feature of the system is the use of this air filter element as a
particulate filter. The filter media has an allowable operating
temperature rating greater than the 300 degree F exhaust gas
temperature allowed by MSHA approval regulations. These filters are
reported to last up to sixteen hours, depending on how hard the machine
operates.
The dry system can operate on any grade without the problems
encountered by water scrubbers. Furthermore, there is no problem with
fog created by operation of the water scrubber. Dry systems have been
installed and are operating successfully on diesel haulage equipment,
longwall component carriers, longwall component extraction equipment,
and in nonpermissible form, on locomotives. However, as pointed out by
commenters, requiring the use of a dry system on all mining equipment
would be expensive, cumbersome, and in many cases would require
considerable engineering measures that might render them infeasible.
Although the dry systems were originally designed for permissible
equipment applications, they can also be used directly on outby
equipment (whose emissions are not already cooled), or to replace water
scrubbers used to cool most permissible equipment with a system that
includes additional aftertreatment.
Two manufacturers have received approval for diesel power packages
that are configured as described above; Paas Technologies, (under
various corporate designations including Minecraft and a registered
trade name, Dry Systems Technology, or DST ) and Jeffrey
Mining Equipment Company (currently Long-Airdox-Jeffrey).
The design of the dry system manufactured by DST
includes a catalytic converter. However, with respect to the basic Paas
Technologies system, without a catalytic converter, the initial
reported laboratory reductions in dpm were dramatic: up to 98%.
During the hearings, however, there were many questions about the
applicability of the early results to MSHA's proposed requirement that
emissions of certain equipment be reduced 95% by mass. It was indicated
by a commenter that the original Paas Technology dry system tests with
a paper filter were performed at West Virginia University used high
sulfur fuel which is currently prohibited in underground coal mines.
The commenter stated that the University tested different fuels
containing varying sulfur contents and the results indicated a
fluctuation in overall dpm emission results. The commenter stated the

[[Page 5552]]

difference in dpm collection efficiency by the filter was on the order
of 12 to 15%. Another commenter stated the difference in dpm reduction
using a 0.37 percent fuel sulfur and a 0.04 percent fuel sulfur was
about 22 percent. This commenter further stated that other published
papers from Europe report the same dpm reductions with varying fuel
sulfur levels, approximately 15 to 20 percent reduction.
As was stated ealier, Paas Technologies has further developed its
system by the adding a catalytic converter in the exhaust before the
particulate paper filter. Paas Technologies have developed a technique
whereby the catalytic converter is mounted so that the exhaust gas
temperature remains high enough for the converter to operate
effectively while complying with the MSHA surface temperature
requirement. In addition to removing most of the carbon monoxide, the
catalytic converter removes most of the unburned hydrocarbons before
they are cooled and condensed. This feature extends the operating life
of the filter. Any sulfate formed in the catalytic converter or in the
engine combustion process condenses to a solid form as the exhaust gas
passes through the heat exchanger and is collected in the particulate
filter.
Paas Technologies submitted a detailed set of test results on a
94hp MWM D-916-6 test engine equipped with a Model M38 DST
Management System, which included the catalytic converter, for the
rulemaking record. These tests were conducted by Southwest Research
Institute using an 8-mode test, with ASTM No. 2-D diesel fuel. Both the
test cycle and test fuel (low sulfur) conformed with the test procedure
detailed in the proposed rule and in this final rule. In idle mode, the
dpm emissions were reduced about 90%; in mode 5, the dpm emissions were
down 99%; on average of the 8 modes, the dpm emissions were reduced by
97%.
The Jeffrey system, which does not utilize a catalytic converter,
was the subject of the MSHA verification initiative, noted in part IV.
The verification was conducted in such a way as to test filter
efficiency separately from whole system, with the low sulfur fuel
required for coal mine use and without a catalytic converter. The
verification confirmed that the paper filter has a dpm removal
efficiency greater than 95 percent.
This data submitted to the rulemaking record demonstrates that
paper filters used on dry systems can achieve a filtration efficiency
that allows equipment to meet the 2.5 gm/hr standard with low sulfur
diesel fuel both with and without a catalytic converter in the system.
Reformulated fuels. It has long been known that sulfur content can
have a big effect on dpm emissions. In the diesel equipment rule, MSHA
requires that fuel used in underground coal mines have less than 0.05%
(500 ppm) sulfur. EPA regulations requiring that such low-sulfur fuel
(less than 500 ppm) be used in highway engines, in order to limit air
pollution, have in practice ensured that this is the type of diesel
fuel available to mine operators, and they currently use this type of
fuel for all engines.
EPA has proposed a rule which would require further reductions in
the sulfur content of highway diesel fuel. Such an action was taken for
gasoline fuel on December 21, 1999.
On May 13, 1999 (64 FR 26142) EPA published an Advance Notice of
Proposed Rulemaking (ANPRM) relative to changes for diesel fuel. In
explaining why it was initiating this action, EPA noted that diesel
engines ``contribute greatly'' to a number of serious air pollution
problems, and that diesel emissions account for a large portion of the
country's particulate matter and nitrogen oxides-a key precursor to
ozone. EPA noted that while these emissions come mostly from heavy-duty
truck and nonroad engines, they expected the contribution to dpm
emissions from light-duty equipment to grow due to manufacturers' plans
to greatly increase the sale of light duty trucks. These vehicles are
now subject to Tier 2 emission standards, whether powered by gasoline
or diesel fuel. Such standards may be difficult to meet without
advanced catalyst technologies that in turn are likely to require
sulfur reductions in the fuel.
Moreover, planned Tier 3 standards for nonroad vehicles would
require similar action (64 FR 26143). (For more information on the EPA
planned engine standards, see section 5 of this Part). The EPA noted
that the European Union has adopted new specifications for diesel fuel
that would limit it to 50 ppm by 2005, (an interim limit of 350 ppm by
this year), that the entire diesel fuel supply in the United Kingdom
should soon be at 50 ppm, and that Japan and other nations were working
toward the same goal (64 FR 26148).
In the ANPRM, EPA specifically noted that while continuously
regenerating ceramic filters have shown considerable promise for
limiting dpm emissions even at fairly low exhaust temperatures, the
systems were fairly intolerant of fuel sulfur. Accordingly, the agency
hopes to gather information on whether or not low sulfur fuel was
needed for effective PM control (64 FR 26150). EPA's proposed rule was
published in May 2000 and EPA issued final regulations addressing
emissions standards (December 2000) for new model year 2007 heavy-duty
diesel engines and the low-sulfur fuel rule. The regulations require
ultra-low sulfur fuel be phased in during 2006-2009.
A joint government-industry partnership is also investigating the
relationship between varying levels of sulfur content and emissions
reduction performance on various control technologies, including
particulate filters and oxidation catalytic convertors. This program is
supported by the Department of Energy's Office of Heavy Vehicles
Technologies, two national laboratories, the Engine Manufacturers
Association, and the Manufacturers of Emission Controls Association. It
is known as the Diesel Emission Control-Sulfur Effects (DECSE) Program;
more information is available from its web site, http://
www.ott.doe.gov/decse.
MSHA expects that once such cleaner fuel is required for
transportation use, it will in practice become the fuel used in mining
as well--directly reducing engine particulate emissions, increasing the
efficiency of aftertreatment devices, and eventually through the
introduction of new generation of cleaner equipment. Mayer states that
reducing sulfur content, decreasing aromatic components and increasing
the Cetane index of diesel fuel can generally result in a 5% to 15%
reduction in total particulate emissions.
Several commenters in this rulemaking suggested other fuel
formulations which could have a beneficial effect on dpm emissions. One
commenter encouraged the use of FRF, Fire Resistant Fuel, which has
various safety features as well as lower NOX and PM, and
noted it is under study for use by the military.
Another commenter noted the development of a catalytic ignition
system that permits the engines to operate on alternative fuels which
greatly reduce harmful emissions. For example, using a water-methanol
mix, the commenter noted dramatic reductions in harmful emissions of
NOX, CO and HC over a gasoline, spark ignition engine. This
commenter also noted that the ignition system could operate on a diesel
engine, but provided no information about emissions reductions by its
use.
Meyer reports the results of a test by VERT of a special synthetic
fuel containing neither sulfur nor bound nitrogen nor aromatics, with a
very high

[[Page 5553]]

Cetane index. The fuel performed very well, but produced only abut 10%
fewer particulates than low sulfur diesel fuel, nor did it show any
improvement in diminishing nonparticulate emissions.
Cabs. Even though cabs are not the type of control device that is
attached to the exhaust of the diesel engine to reduce emissions, cabs
can protect miners from environmental exposures to dpm. Both cabs and
control booths are discussed in the context of reducing miners
exposures to dpm.
A cab is an enclosure around the operator installed on a piece of
mobile equipment. It can provide the same type of protection as a booth
at a crusher station as found in some surface operations. While cabs
are not available for all mining equipment, they are available for much
of the larger equipment that also has application in the construction
industry.
To be effective, a cab should be tightly sealed with windows and
doors closed. Rubber seals around doors and windows should be in good
condition. Door and window latches must operate properly. In addition
to being well sealed, the cab should have an air filtration and
pressurizing system. Air intake should be located away from engine
exhaust. The airflow should provide one air change per minute for the
cab and should pressurize the cab to 0.20 inches of water. While these
are not absolute requirements, they do provide a guideline of how a cab
should be designed. If a cab does not have an air filtration and
pressurizing system, the diesel particulate concentration inside the
cab will be similar to the diesel particulate concentration outside the
cab.
MSHA has evaluated the efficiency of cab filters for diesel
particulate reduction. Several different types of filter media have
been tested in underground mines. These include standard filter paper
and high efficiency filter paper. Filter papers can reduce diesel
particulate exposures by 60 percent to 90 percent. When changing filter
media, it is necessary to make sure that the airflow into the cab is
not reduced and that the airflow through an air conditioning system is
not reduced.
Although the installation of a cab does not relieve the mine
operator from the responsibility of complying with the equipment dpm
limits, cabs provide assistance in complying with noise and respirable
dust regulations. Cabs protect the equipment operator protection from
dpm, respirable dust and noise exposures.

(7) Existing Standards for Underground Coal Mines That Assist in
Limiting Miner Exposure to Diesel Emissions

MSHA already has in place various requirements that indirectly help
to control miner exposure to diesel emissions in underground mines--
including exposure to diesel particulate. The first such requirements
were developed in the 1940's; the most recent went into full effect
only in November, 1999. It is important to understand these
requirements because they form the base upon which this new rule is
overlaid.
Early developments. In 1944, part 31 established procedures for
limiting the gaseous emissions from diesel powered equipment and
establishing the recommended dilution air quantity for mine locomotives
that use diesel fuel. In 1949, part 32 established procedures for
testing of mobile diesel-powered equipment for non-coal mines. In 1961,
part 36 was added to provide requirements for the use of diesel
equipment in gassy noncoal mines, in which engines must be temperature
controlled to prevent explosive hazards. These rules were drafted in
response to research conducted by the former Bureau of Mines.
Continued research by the former Bureau of Mines in the 1950s and
1960s led to refinements of its ventilation recommendations,
particularly when multiple engines are in use. An airflow of 100 to 250
cfm/bhp for engines that have a properly adjusted fuel to air ratio was
recommended (Holtz, 1960). An additive ventilation requirement was
recommended for operation of multiple diesel units, which could be
relaxed based on the mine operating procedures. This approach was
subsequently refined to become a 100-75-50 percent guideline (MSHA
Policy Memorandum 81-19MM, 1981). Under this guideline, when multiple
pieces of diesel equipment are operated, the required airflow on a
split of air would be the sum of: (a) 100 percent of the approval plate
quantity for the vehicle with the highest approval plate air quantity
requirement; (b) 75 percent of the approval plate air quantity
requirement of the vehicle with the next highest approval plate air
quantity requirement; and (c) 50 percent of the approval plate airflow
for each additional piece of diesel equipment.
Limitations on Diesel Gasses. MSHA has limits on some of the gasses
produced in diesel exhaust. These are listed in Table II-5, for both
coal mines and metal/nonmetal mines, together with information about
the recommendations in this regard of other organizations. As indicated
in the table, MSHA requires mine operators to comply with gas specific
threshold limit values (TLVs) recommended by the American
Conference of Governmental Industrial Hygienists (ACGIH) in 1972 (for
coal mines) and in 1973 (for metal and nonmetal mines).

BILLING CODE 4510-43-P

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BILLING CODE 4510-43-C
To change an MSHA exposure limit, regulatory action is required
because the rule does not provide for their automatic updating. In
1989, MSHA proposed changing some of these gas limits in the context of
a proposed rule on air quality standards (54 FR 35760). Following
opportunity for comment and hearings, a portion of that proposed air
quality rule (concerning control of drill dust and blasting) was
promulgated. As a result of a recent legal action, MSHA's efforts to
revise the specific limits for those gases emitted by diesel engines
have been placed under the continued supervision of a federal court of
appeals. This action is discussed in more detail in section 9 of this
Part.
Diesel Equipment Rule for Underground Coal Mines. On October 25,
1996, MSHA promulgated standards for the ``Approval, Exhaust Gas
Monitoring, and Safety Requirements for the Use of Diesel-Powered
Equipment in Underground Coal Mines'' (61 FR 55412). The history of
this ``diesel equipment rule'' (sometimes referred to here as the
``diesel safety rule'' to help distinguish it from this rulemaking
which is oriented toward health) is set forth as part of the history of
this rulemaking (see section 9 of this part).
The diesel equipment rule focuses on the safe use of diesels in
underground coal mines. Integrated requirements are established for the
safe storage, handling, and transport of diesel fuel underground,
training of mine personnel, minimum ventilating air quantities for
diesel powered equipment, monitoring of gaseous diesel exhaust
emissions, maintenance requirements, incorporation of fire suppression
systems, and design features for nonpermissible machines.
Certain requirements were included in the diesel equipment rule
that are directly related to reducing diesel emissions. For example,
the diesel equipment rule requires that the emissions of permissible
and heavy duty equipment be tested weekly. The tests are conducted
using instrumentation and the tests are conducted with the engines
operated at a loaded condition which is representative of actual
operation. The results are monitored and recorded. Higher than normal
emissions readings indicate that the engines and equipment are not
being maintained in approved condition. Although some of these
requirements help reduce dpm emissions, they were not included in the
rule for that specific purpose.
Lower-emission engines. The diesel equipment rule requires that
virtually all diesel-powered engines used in underground coal mines be
approved by MSHA; see 30 CFR part 7, (approval requirements), part 36
(permissible machines defined), and part 75 (use of such equipment in
underground coal mines). The approval requirements, among other things,
require clean-burning engines in diesel-powered equipment (61 FR
55417). In promulgating the final rule, MSHA recognized that clean-
burning engines are ``critically important'' to reducing toxic gasses
to levels that can be controlled through ventilation. To achieve the
objective of clean-burning engines, the rule sets performance standards
which must be met by virtually all diesel-powered equipment in
underground coal mines.

[[Page 5555]]

As noted in section 5 of this part, the technical requirements for
approved diesel engines focus on limiting the amount of various gases
that an engine can emit, including undiluted exhaust limits for carbon
monoxide and oxides of nitrogen (61 FR 55419). The limits for these
gasses are derived from existing 30 CFR part 36.
The diesel equipment rule also provides that the particulate matter
emitted by approved engines be determined during the testing required
to gain approval. The particulate index (or PI), calculated under the
provisions of 30 CFR 7.89, indicates what air quantity is necessary to
dilute the diesel particulate in the engine exhaust to 1 milligram of
diesel particulate matter per cubic meter of air. The purpose of the PI
requirement is discussed in more detail in section 5 of this part.
Gas Monitoring. The diesel equipment rule also addresses the
monitoring and control of gaseous diesel exhaust emissions (30 CFR part
70; 61 FR 55413). In this regard, the rule requires that mine operators
take samples of carbon monoxide and nitrogen dioxide as part of
existing onshift workplace examinations (61 FR 55413, 55430-55431).
Samples exceeding an action level of 50 percent of the threshold limits
set forth in 30 CFR 75.322 trigger corrective action by the mine
operator (30 CFR part 70, 61 FR 55413).
Engine Maintenance. The diesel equipment rule requires that diesel-
powered equipment be maintained in safe and approved condition (30 CFR
75.1914; 61 FR 55414). As explained in the preamble, maintenance
requirements were included because of MSHA's recognition that
inadequate equipment maintenance can, among other things, result in
increased levels of harmful gaseous and particulate components from
diesel exhaust (61 FR 55413-55414).
The rule also requires the weekly examination of diesel-powered
equipment (30 CFR 75.1914(g)). To determine if more extensive
maintenance is required, the rule further requires a weekly check of
the gaseous CO emission levels on permissible and heavy duty outby
machines. The CO check requires that the engine be operated at a
repeatable loaded condition and the CO measured. The carbon monoxide
concentration in the exhaust provides a good indication of engine
condition. If the CO measurement increases to a higher concentration
than what was normally measured during the past weekly checks, then a
maintenance person would know that a problem has developed that
requires further investigation.
In addition, operators are required to establish programs to ensure
that those performing maintenance on diesel equipment are qualified (61
FR 55414).
Fuel. The diesel equipment rule also requires that underground coal
mine operators use diesel fuel with a sulfur content of 0.05% (500 ppm)
or less (30 CFR 75.1910(a); 61 FR 55413). Some types of exhaust
aftertreatment technology designed to lower hazardous diesel emissions
work more effectively when the sulfur content of the fuel is low. More
effective aftertreatment devices will result in reduced hydrocarbons,
carbon monoxide, and particulate levels. Low sulfur fuel also greatly
reduces the sulfate production from the catalytic converters currently
in use in underground coal mines thereby decreasing exhaust
particulate. To further reduce miners' exposure to diesel exhaust, the
final rule prohibits operators from unnecessarily idling diesel-powered
equipment (30 CFR 75.1916(d).
Ventilation. The diesel equipment rule requires that as part of the
approval process, ventilating air quantities necessary to maintain the
gaseous emissions of diesel engines within existing required ambient
limits be set. The ventilating air quantities are required to appear on
the engine's approval plate. The rule also requires generally that mine
operators maintain the approval plate quantity minimum airflow in areas
of underground coal mines where diesel-powered equipment is operated.
The engine's approval plate air quantity is also used to determine the
minimum air quantity in areas where multiple units of diesel powered
equipment are being operated. The minimum ventilating air quantity
where multiple units of diesel powered equipment are operated on
working sections and in areas where mechanized mining equipment is
being installed or removed, must be the sum of 100 percent of the
approval plate quantities of all of the equipment. As stated in the
preamble of the diesel equipment rule, MSHA believes that effective
mine ventilation is a key component in the control of miners' exposure
to gasses and particulate emissions generated by diesel equipment.
Impact of the diesel equipment rule on dpm. The diesel equipment
rule is helping the mining community use diesel-powered equipment more
safely in underground coal mines. Moreover, the diesel equipment rule
has many features which reduce the emission and concentration of
harmful diesel emissions in underground coal mines--including the
particulate component of these emissions.
During the public hearings on the equipment rule, miners complained
about the high concentrations of diesel emissions at the section
loading point and in the areas of the mine where longwall equipment is
being installed or removed. Accordingly, MSHA established, in that
rule, provisions which would address miners' concerns.
The equipment rule required that the approval plate ventilation
quantity be provided at the section loading point. The loading point is
also identified as a location where regular air quality samples are
required to be taken. Corrective action is required if the samples of
CO and NO2 exceeded more than one half the allowable
concentration limit of these gases.
Longwall equipment installations and removals are handled in a
similar manner. The diesel emissions from all of the equipment in the
area of the mine where the longwall move is being made are required to
be considered in establishing the amount of ventilation air to be
provided. A specific location where that quantity is to be measured is
established. Additionally, the same air quality sampling program
required for section loading points is required for areas of the mine
where the longwall move is to take place.
Permissible haulage vehicles contribute the largest quantities of
emissions at the section loading point. Longwall moves are typically
carried out by permissible and heavy duty equipment such as shield
carriers, mules, and locomotives which produce large quantities of
diesel emissions. Emissions from these vehicles are reduced by the use
of approved engines, low sulfur fuel, the loaded repeatable engine
condition testing, regular maintenance by trained personnel and the
ventilation and sampling provisions of the diesel equipment rule.
Because the effective dates for provisions of the diesel equipment
regulations are staggered, the full impact of the new rules was not
known at the time the dpm hearings were held. MSHA expects that the
concentrations of diesel emissions at the section loading point and
during longwall moves will be reduced as these provisions are fully
implemented.
In developing the diesel equipment rule, however, MSHA did not
explicitly consider the risks to miners of a working lifetime of dpm
exposure at very high levels, nor the actions that could be taken to
specifically reduce dpm exposure levels in underground coal mines. It
was understood that the agency would be taking a separate look

[[Page 5556]]

at the health risks of dpm exposure. (61 FR 55420).

(8) Information on How Certain States Are Restricting Occupational
Exposure to DPM

As noted earlier in this part, the Federal government has long been
involved in efforts to restrict diesel particulate emissions into the
environment--both through ambient air quality standards, and through
restrictions on diesel engine emissions. While MSHA's actions to limit
the concentration of dpm in underground mines are the first effort by
the Federal government to deal with the special risks faced by workers
exposed to diesel exhaust on the job, several states have already taken
actions in this regard with respect to underground coal mines.
This section reviews some of these actions, as they were the
subject of considerable discussion and comment during this rulemaking.
Pennsylvania. As indicated in section 1, Pennsylvania essentially
had a ban on the use of diesel-powered equipment in underground coal
mines for many years. As noted by one commenter, diesel engines were
permitted provided the request was approved by the Secretary of the
Department of Environmental Protection but no request was ever
approved.
In 1995, one company in the State submitted a plan for approval and
started negotiations with its local union representatives. This led to
statewide discussions and the adoption of a new law in the State that
permits the use of diesel-powered equipment in deep coal mines under
certain circumstances specified in the law (Act 182). As further noted
by this commenter, the drafters of the law completed their work before
the issuance of MSHA's new regulation on the safe use of diesel-powered
equipment in underground coal mines. The Pennsylvania law, unlike
MSHA's diesel equipment rule, specifically addresses diesel
particulate. The State did not set a limit on the exposure of miners to
dpm, nor did it establish a limit on the concentration of dpm in deep
coal mines. Rather, it approached the issue by imposing controls that
will limit dpm emissions at the source.
First, all diesel engines used in underground deep coal mines in
Pennsylvania must be MSHA-approved engines with an ``exhaust emissions
control and conditioning system'' that meets certain tests. (Article
II-A, Section 203-A, Exhaust Emission Controls). Among these are dpm
emissions from each engine no greater than ``an average concentration
of 0.12 mg/m 3 diluted by fifty percent of the MSHA approval
plate ventilation for that diesel engine.'' In addition, any exhaust
emissions control and conditioning system must include a ``Diesel
Particulate Matter (DPM) filter capable of an average of ninety-five
percent or greater reduction of dpm emissions.'' It also requires the
use of an oxidation catalytic converter. Thus, the Pennsylvania statute
requires the use of low-emitting engines, and then the use of
aftertreatment devices that significantly reduce the particulates
emitted from these engines.
The Pennsylvania law also has a number of other requirements for
the safe use of diesel-powered equipment in the particularly hazardous
environments of underground coal mines. Many of these parallel the
requirements in MSHA's diesel equipment rule. Like MSHA's requirements,
they too can result in reducing miner exposure to diesel particulate--
e.g., regular maintenance of diesel engines by qualified personnel and
equipment operator examinations. The requirements in the Pennsylvania
law take into account the need to maintain the aftertreatment devices
required to control diesel particulate.
While both mine operators and labor supported this approach, it
remains controversial. During the hearings on this rulemaking, one
commenter indicated that at the time the standards were established, it
would have taken a 95% filter to reduce dpm from certain equipment to
the 0.12 mg/m 3 emissions standard because 0.25 sulfur fuel
was being utilized. This test reported by the commenter was completed
prior to MSHA promulgating the diesel equipment rule that required the
use of .05% sulfur fuel. Another commenter pointed out that as
operators in the state began considering the use of newer, less
polluting engines, achieving an efficiency of 95% reduction of the
emissions from any such engines would become even more difficult. There
was some disagreement among the commenters as to whether existing
technology would permit operators to meet the 0.12 mg/m 3
emission standard in many situations.
One commenter described the difficulty in efforts to get a small
outby unit approved under the current Pennsylvania law. Accordingly,
the industry has indicated that it would seek additional changes in the
Pennsylvania diesel law. Commenters representing miners indicated that
they were also involved in these discussions.
West Virginia. Until 1997, West Virginia law banned the use of
diesel-powered equipment in underground coal mines. In that year, the
State created the joint labor-management West Virginia Diesel Equipment
Commission (Commission) and charged it with developing regulations to
permit and govern diesel engine use in underground coal mines. As
explained by several commenters, the Commission, in collaboration with
West Virginia University (WVU), developed a protocol for testing diesel
engine exhaust controls, and the legislature appropriated more than
$150,000 for WVU to test diesel exhaust controls and an array of diesel
particulate filters.
There were a number of comments received by MSHA on the test
protocols and results. These are discussed in appropriate parts in this
preamble. One commenter noted that various manufacturers of products
have been very interested in how their products compare to those of
other manufacturers tested by the WVU. Another asserted that mine
operators had been slowing the scheduling of tests by WVA.
Pursuant to the West Virginia law establishing the Commission, the
Commission was given only a limited time to determine the applicable
rules for the use of diesel engines underground, or the matter was
required to be referred to an arbitrator for resolution. One commenter
during the hearings noted that the Commission had not been able to
reach resolution and that indeed arbitration was the next step. Other
commenters described the proposal of the industry members of the
Commission--0.5mg/m3 for all equipment, as configured,
before approval is granted. In this regard, the industry members of the
West Virginia Commission said:

``We urge you to accelerate the finalization of * * * these
proposed rules. We believe that will aid our cause, as well as the
other states that currently don't use diesel.'' (Id.)

Virginia. According to one commenter, diesel engine use in
underground mining was legalized in Virginia in the mid-1980s. It was
originally used on some heavy production equipment, but the haze it
created was so thick it led to a drop in production. Thereafter, most
diesel equipment has been used outby (805 pieces). The current state
regulations consist of requiring that MSHA approved engines be used,
and that the ``most up-to-date, approved, available diesel engine
exhaust aftertreatment package'' be utilized. There are no distinctions
between types of equipment. The commenter noted that more hearings were
planned soon. Under a directive from the governor of Virginia, the
state is reviewing its

[[Page 5557]]

regulations and making recommendations for revisions to sections of its
law on diesels.
Ohio. The record of this rulemaking contains little specific
information on the restrictions on the underground use of diesel-
powered equipment in Ohio. MSHA understands, however, that in practice
it is not used. According to a communication with the Division of Mines
and Reclamation of the Ohio Division of Natural Resources, this outcome
stems from a law enacted on October 29, 1995, now codified as section
1567.35 of Ohio Revised Code Title 15, which imposes strict safety
restrictions on the use of various fuels underground.

(9) History of this Rulemaking

As discussed throughout this part, the Federal government has
worked closely with the mining community to ascertain whether and how
diesel-powered equipment might be used safety and healthfully in this
industry. As the evidence began to grow that exposure to diesel exhaust
might be harmful to miners, particularly in underground mines, formal
agency actions were initiated to investigate this possibility and to
determine what, if any, actions might be appropriate. These actions,
including a number of non-regulatory initiatives taken by MSHA, are
summarized here in chronological sequence.
Activities Prior to Proposed Rulemaking on DPM. In 1984, the
National Institute for Occupational Safety and Health (NIOSH)
established a standing Mine Health Research Advisory Committee to
advise it on matters involving or related to mine health research. In
turn, that standing body established the Mine Health Research Advisory
Committee Diesel Subgroup to determine if:

* * * there is a scientific basis for developing a recommendation on
the use of diesel equipment in underground mining operations and
defining the limits of current knowledge, and recommending areas of
research for NIOSH, if any, taking into account other investigators'
ongoing and planned research. (49 FR 37174).

In 1985, MSHA established an Interagency Task Group with NIOSH and
the former Bureau of Mines (BOM) to assess the health and safety
implications of the use of diesel-powered equipment in underground coal
mines.
In April 1986, in part as a result of the recommendation of the
Task Group, MSHA began drafting proposed regulations on the approval
and use of diesel-powered equipment in underground coal mines. Also in
1986, the Mine Health Research Advisory Committee Diesel Subgroup
(which, as noted above, was created by a standing NIOSH committee)
summarized the evidence available at that time as follows:

It is our opinion that although there are some data suggesting a
small excess risk of adverse health effects associated with exposure
to diesel exhaust, these data are not compelling enough to exclude
diesels from underground mines. In cases where diesel equipment is
used in mines, controls should be employed to minimize exposure to
diesel exhaust.

On October 6, 1987, pursuant to section 102(c) of the Mine Act, 30
U.S.C. 812(c), which authorizes MSHA to appoint such advisory
committees as it deems appropriate, the agency appointed an advisory
committee ``to provide advice on the complex issues concerning the use
of diesel-powered equipment in underground coal mines.'' (52 FR 37381).
MSHA appointed nine members to this committee, officially known as The
Mine Safety and Health Administration Advisory Committee on Standards
and Regulations for Diesel-Powered Equipment in Underground Coal Mines
(hereafter the MSHA Diesel Advisory Committee). As required by section
101(a)(1) of the Mine Act, MSHA provided the MSHA Diesel Advisory
Committee with draft regulations on the approval and use of diesel-
powered equipment in underground coal mines. The draft regulations did
not include standards setting specific limitations on diesel
particulate, nor had MSHA at that time determined that such standards
would be promulgated.
In July 1988, the MSHA Diesel Advisory Committee completed its work
with the issuance of a report entitled ``Report of the Mine Safety and
Health Administration Advisory Committee on Standards and Regulations
for Diesel-Powered Equipment in Underground Coal Mines.'' It also
recommended that MSHA promulgate standards governing the approval and
use of diesel-powered equipment in underground coal mines. The MSHA
Diesel Advisory Committee recommended that MSHA promulgate standards
limiting underground coal miners' exposure to diesel exhaust.
With respect to diesel particulate, the MSHA Diesel Advisory
Committee recommended that MSHA ``set in motion a mechanism whereby a
diesel particulate standard can be set.'' (MSHA, 1988). In this regard,
the MSHA Diesel Advisory Committee determined that because of
inadequacies in the data on the health effects of diesel particulate
matter and inadequacies in the technology for monitoring the amount of
diesel particulate matter at that time, it could not recommend that
MSHA promulgate a standard specifically limiting the level of diesel
particulate matter in underground coal mines (Id. 64-65). Instead, the
MSHA Diesel Advisory Committee recommended that MSHA ask NIOSH and the
former Bureau of Mines to prioritize research in the development of
sampling methods and devices for diesel particulate.
The MSHA Diesel Advisory Committee also recommended that MSHA
request a study on the chronic and acute effects of diesel emissions
(Id.). In addition, the MSHA Diesel Advisory Committee recommended that
the control of diesel particulate ``be accomplished through a
combination of measures including fuel requirements, equipment design,
and in-mine controls such as the ventilation system and equipment
maintenance in conjunction with undiluted exhaust measurements.'' The
MSHA Diesel Advisory Committee further recommended that particulate
emissions ``be evaluated in the equipment approval process and a
particulate emission index reported.'' (Id. at 9).
In addition, the MSHA Diesel Advisory Committee recommended that
``the total respirable particulate, including diesel particulate,
should not exceed the existing two milligrams per cubic meter
respirable dust standard.'' (Id. at 9.) It should be noted that section
202(b)(2) of the Mine Act requires that coal mine operators maintain
the average concentration of respirable dust at their mines at or below
two milligrams per cubic meter which effectively prohibits diesel
particulate matter in excess of two milligrams per cubic meter (30
U.S.C. 842(b)(2)).
As noted, the MSHA Diesel Advisory Committee issued its report in
1988. During that year, NIOSH issued a Current Intelligence Bulletin
recommending that whole diesel exhaust be regarded as a potential
carcinogen and controlled to the lowest feasible exposure level (NIOSH,
1988). In its bulletin, NIOSH concluded that although the excess risk
of cancer in diesel exhaust exposed workers had not been quantitatively
estimated, it is logical to assume that reductions in exposure to
diesel exhaust in the workplace would reduce the excess risk. NIOSH
stated that ``[g]iven what we currently know, there is an urgent need
for efforts to be made to reduce occupational exposures to DEP [dpm] in
mines.''
Consistent with the MSHA Diesel Advisory Committee's research
recommendations, MSHA, in September 1988, formally requested NIOSH to

[[Page 5558]]

perform a risk assessment for exposure to diesel particulate. (57 FR
500). MSHA also requested assistance from NIOSH and the former BOM in
developing sampling and analytical methodologies for assessing exposure
to diesel particulate in mining operations. (Id.). In part, as a result
of the MSHA Diesel Advisory Committee's recommendation, MSHA also
participated in studies on diesel particulate sampling methodologies
and determination of underground occupational exposure to diesel
particulate.
On October 4, 1989, MSHA published a Notice of Proposed Rulemaking
on approval requirements, exposure monitoring, and safety requirements
for the use of diesel-powered equipment in underground coal mines. (54
FR 40950). The proposed rule, among other things, addressed, and in
fact followed, the MSHA Diesel Advisory Committee's recommendation that
MSHA promulgate regulations requiring the approval of diesel engines
(54 FR 40951), limiting gaseous pollutants from diesel equipment,
(Id.), establishing ventilation requirements based on approval plate
dilution air quantities (54 FR 40990), requiring equipment maintenance
(54 FR 40958), requiring that trained personnel work on diesel-powered
equipment, (54 FR 40995), establishing fuel requirements, (Id.),
establishing gaseous contaminant monitoring (54 FR 40989), and
requiring that a particulate index indicating the quantity of air
needed to dilute particulate emissions from diesel engines be
established. (54 FR 40953).
On January 6, 1992, MSHA published an Advance Notice of Proposed
Rulemaking (ANPRM) indicating it was in the early stages of developing
a rule specifically addressing miners exposure to diesel particulate
(57 FR 500). In the ANPRM, MSHA, among other things, sought comment on
specific reports on diesel particulate prepared by NIOSH and the former
BOM. MSHA also sought comment on reports on diesel particulate which
were prepared by or in conjunction with MSHA (57 FR 501). The ANPRM
also sought comments on the health effects, technological and economic
feasibility, and provisions which should be considered for inclusion in
a diesel particulate rule (57 FR 501). The notice also identified five
specific areas where the agency was particularly interested in
comments, and about which it asked a number of detailed questions: (1)
Exposure limits, including the basis thereof; (2) the validity of the
NIOSH risk assessment model and the validity of various types of
studies; (3) information about non-cancer risks, non-lung routes of
entry, and the confounding effects of tobacco smoking; (4) the
availability, accuracy and proper use of sampling and monitoring
methods for diesel particulate; and (5) the technological and economic
feasibility of various types of controls, including ventilation, diesel
fuel, engine design, aftertreatment devices, and maintenance by
mechanics with specialized training. The notice also solicited specific
information from the mining community on ``the need for a medical
surveillance or screening program and on the use of respiratory
equipment.'' (57 FR 500). The comment period on the ANPRM closed on
July 10, 1992.
While MSHA was completing a ``comprehensive analysis of the
comments and any other information received'' in response to the ANPRM
(57 FR 501), it took also several actions to encourage the mining
community to begin to deal with the problems identified.
In 1995, MSHA sponsored three workshops ``to bring together in a
forum format the U.S. organizations who have a stake in limiting the
exposure of miners to diesel particulate (including) mine operators,
labor unions, trade organizations, engine manufacturers, fuel
producers, exhaust aftertreatment manufacturers, and academia.''
(McAteer, 1995). The sessions provided an overview of the literature
and of diesel particulate exposures in the mining industry, state-of-
the-art technologies available for reducing diesel particulate levels,
presentations on engineering technologies toward that end, and
identification of possible strategies whereby miners' exposure to
diesel particulate matter can be limited both practically and
effectively.
The first workshop was held in Beckley, West Virginia on September
12 and 13, and the other two were held on October 6, and October 12 and
13, 1995, in Mt Vernon, Illinois and Salt Lake City, Utah,
respectively. A transcript was made. During a speech early the next
year, the Deputy Assistant Secretary for MSHA characterized what took
place at these workshops:

The biggest debate at the workshops was whether or not diesel
exhaust causes lung cancer and whether MSHA should move to regulate
exposures. Despite this debate, what emerged at the workshops was a
general recognition and agreement that a health problem seems to
exist with the current high levels of diesel exhaust exposure in the
mines. One could observe that while all the debate about the studies
and the level of risk was going on, something else interesting was
happening at the workshops: one by one miners, mining companies, and
manufacturers began describing efforts already underway to reduce
exposures. Many are actively trying to solve what they clearly
recognize is a problem. Some mine operators had switched to low
sulfur fuel that reduces particulate levels. Some had increased mine
ventilation. One company had tried a soy-based fuel and found it
lowered particulate levels. Several were instituting better
maintenance techniques for equipment. Another had hired extra diesel
mechanics. Several companies had purchased electronically
controlled, cleaner, engines. Another was testing a prototype of a
new filter system. Yet another was using disposable diesel exhaust
filters. These were not all flawless attempts, nor were they all
inexpensive. But one presenter after another described examples of
serious efforts currently underway to reduce diesel emissions.
(Hricko, 1996).

In March of 1997, MSHA issued, in draft form, a publication
entitled ``Practical Ways to Control Exposure to Diesel Exhaust in
Mining--a Toolbox''. The draft publication was disseminated by MSHA to
all underground mines known to use diesel equipment and posted on
MSHA's Web site.
As explained in the publication, the Toolbox was designed to
disseminate to the mining community information gained through the
workshops about methods being used to reduce miner exposures to dpm.
MSHA's Toolbox provided specific information about nine types of
controls that can reduce dpm exposures: low emission engines; fuels;
aftertreatment devices; ventilation; enclosed cabs; engine maintenance;
work practices and training; fleet management; and respiratory
protective equipment. Some of these approaches reduce emissions from
diesel engines; others focus on reducing miner exposure to whatever
emissions are present. Quotations from workshop participants were used
to illustrate when and how such controls might be helpful.
As it clearly stated in its introductory section entitled ``How to
Use This Publication,'' the Toolbox was not designed as a guide to
existing or pending regulations. As MSHA noted in that regard:

While the (regulatory) requirements that will ultimately be
implemented, and the schedule of implementation, are of course
uncertain at this time, MSHA encourages the mining community not to
wait to protect miners' health. MSHA is confident that whatever the
final requirements may be, the mining community will find this
Toolbox information of significant value.

On October 25, 1996, MSHA published a final rule addressing
approval, exhaust monitoring, and safety requirements for the use of
diesel-powered equipment in underground coal mines (61 FR 55412). The
final rule addresses, and in large part is consistent

[[Page 5559]]

with, the specific recommendations made by the MSHA Diesel Advisory
Committee for limiting underground coal miners' exposure to diesel
exhaust. As noted in section 7 of this part, the diesel safety rule was
implemented in steps concluding in late 1999. Aspects of this diesel
safety rule had a significant impact on this rulemaking.
In the Fall of 1997, following comment, MSHA's Toolbox was
finalized and disseminated to the mining community. At the same time,
MSHA made available to the mining community a software modeling tool
developed by the Agency to facilitate dpm control. This model enables
an operator to evaluate the effect which various alternative
combinations of controls would have on the dpm concentration in a
particular mine--before making the investment. MSHA refers to this
model as ``the Estimator''. The Estimator is in the form of a template
that can be used on standard computer spreadsheet programs. As
information about a new combination of controls is entered, the results
are promptly displayed.
Proposed Rulemaking on Dpm. On April 9, 1998, MSHA published a
proposed rule to ``reduce the risks to underground coal miners of
serious health hazards that are associated with exposure to high
concentrations of diesel particulate matter'' (63 FR 17492).
MSHA went to some lengths to ensure the mining community would be
able to review and comment on the proposed rule. The agency made copies
of the proposal available for review by the mining community at each
district and field office location, at the National Mine Safety and
Health Academy, and at each technical support center. MSHA also
provided the opportunity for comments to be accepted from the mining
community at each of those locations, as well as through mail,
e-mail and fax to the national office. MSHA also distributed the
proposal to all underground mines, to mining associations and other
interested parties. A copy was also posted on MSHA's website.
In order to further facilitate participation by the mining
community, MSHA developed as an introduction to its preamble explaining
the proposed rule a ``plain language'' questions and answers section.
The notice of proposed rulemaking reviewed and discussed the
comments received in response to the ANPRM, including information on
such control approaches as fuel type, fuel additives, and maintenance
practices (63 FR 17512-17514). For the convenience of the mining
community, a copy of MSHA's Toolbox was also reprinted as an Appendix
at the end of the notice of proposed rulemaking (63 FR 17580 et seq.).
A complete description of the Estimator, and several examples, were
also presented in the preamble of the proposed dpm rule (63 FR 17565 et
seq.).
The proposed dpm rule was fairly simple. In addition to miner
training, the proposed rule would have required aftertreatment filters
on all permissible equipment and, subsequently, on all heavy duty
nonpermissible equipment.
Throughout the preamble, MSHA discussed a number of other approaches
that might have merit in limiting the concentration of dpm in
underground coal mines. MSHA made it very clear to the mining community
that the rule being proposed represented only one of the approaches
which might ultimately be required by the final rule and on which
comment was being solicited by the proposed rulemaking notice.
For example, the agency noted the following:

``MSHA recognizes that a specification standard does not allow
for the use of future alternative technologies that might provide
the same or enhanced protection at the same or lower cost. MSHA
welcomes comment as to whether and how the proposed rule can be
modified to enhance its flexibility in this regard * * *. (There
are) two alternative specification standards which would provide
somewhat more flexibility for coal mine operators. Alternative 1
would treat the filter and engine as a package that has to meet a
particular emission standard. Instead of requiring that all engines
be equipped with a high-efficiency filter, this approach would
provide some credit for the use of lower-polluting engines.
Alternative 2 would also provide credit for mine ventilation beyond
that required.'' (63 FR 17498)

These alternatives were further discussed in a separate Question and
Answer (#12). The agency was also clear it would welcome comment on
``whether there are some types of light-duty equipment whose dpm
emissions should, and could feasibly, be controlled'', and ``whether it
would be feasible for this sector to implement a requirement that any
new light-duty equipment added to a mine's fleet be filtered'' Question
and Answer (#6) (63 FR 17556).
MSHA also discussed and welcomed comment on a number of other
alternatives: e.g., restricting the exposure of underground coal mines
to all fine particulates regardless of source (63 FR 17495); and the
use of administrative controls (e.g., rotation of personnel) and
personal protective equipment (e.g., respirators) to reduce the dpm
exposure of miners. The Agency also sought comments on its risk
assessment, presented in full in the preamble to the proposed rule
(Part III). As noted therein, this was the first risk assessment ever
performed by the agency to be peer reviewed. Such a review is not
required under the agency's statute, but MSHA took the time to obtain
such a review in this instance due to significant disagreement within
the mining community about the health risks of exposure to dpm (63 FR
17521).
MSHA also asked for comment on its economic assumptions in the
preamble. Two of the Questions and Answers (#5 and #7) were
specifically devoted to cost impacts, including those on small mines.
MSHA also specifically requested all members of the mining community to
consider using the Estimator in developing comments on the proposed
rulemaking (63 FR 17565).
On July 14, 1998, in accordance with the National Environmental
Protection Act, MSHA published a notice in the Federal Register seeking
comment on its preliminary determination that the proposed rule would
not have a significant environmental impact (63 FR 37796).
The initial comment period was scheduled to last for 120 days until
August 7, 1998. In response to requests from the public, on August 5,
1998, MSHA extended the initial comment period on the proposed rule
(and the comment period on its preliminary determination of no
significant environmental impact) for an additional 60 days, until
October 9, 1998 (63 FR 41755). That notice also announced MSHA's intent
to hold public hearings on the proposal.
On October 19, 1998, MSHA announced in the Federal Register
locations of four public hearings on the proposed rule. The agency
further announced that the close of the post-hearing comment period and
rulemaking record would be on February 16, 1999 (63 FR 55811).
In November 1998, MSHA held hearings in Salt Lake City, Utah and
Beckley, West Virginia. In December 1998, hearings were held in Mt.
Vernon, Illinois, and Birmingham, Alabama.
These hearings were well attended. Testimony was presented by
individual miners, representatives of miners, individual coal
companies, mining industry associations, representatives of engine and
equipment manufacturers and one individual manufacturer. Members of the
mining community participating had an extensive opportunity to hear and
respond to alternative views; some participated in several hearings.
They also had an opportunity to engage in direct dialogue

[[Page 5560]]

with members of MSHA's rulemaking committee-responding to questions and
asking questions on their own. There was extensive comment not only
about the provisions of the proposed rule itself, but also about the
need for diesel powered equipment in this sector, the risks associated
with its use, the need for regulation in this sector, alternative
approaches (including but not limited to those on which MSHA
specifically sought comment), and the technological and economic
feasibility of various alternatives.
During the hearings, MSHA made a number of requests that
information provided at the hearing be supplemented by submission of
cited sources, additional data, and in particular for data to support
assertions made about various control technologies. MSHA again
solicited information concerning the agency's cost assumptions, for the
results of studies using MSHA's Estimator model, and also asked for any
data on a number of other points. For example, the agency requested
further information on the size distribution of particles from cleaner
engines, on the viability of a fine particulate standard in lieu of a
dpm standard, for a list of any studies concerning the risks of dpm or
lack thereof, and data on equipment upgrades.
On February 12, 1999, (64 FR 7144) MSHA published a notice in the
Federal Register announcing: (1) The availability of three additional
studies discussed in the preamble of the proposed rule but not
available at the time of publication; and (2) the extension of the
post-hearing comment period and close of record for 60 additional days,
until April 30, 1999.
On April 27, 1999, in response to requests from the public, MSHA
extended the post-hearing comment period and close of record for 90
additional days, until July 26, 1999 (64 FR 22592).
On July 8, 1999, MSHA published a notice in the Federal Register
correcting technical errors in the preamble discussion on the Diesel
Emission Control Estimator formula in the Appendix to Part V of the
proposed rulemaking notice, and correcting Figure V-5 of the preamble.
Comments on these changes were solicited by July 26, 1999, the close of
the rulemaking record (64 FR 36826). The Estimator model was
subsequently published in the literature.
The rulemaking record closed on July 26, 1999, fifteen months after
the date the proposed rule was published for public notice. The
comments, like the hearings, reflected extensive participation in this
effort by the full range of interests in the mining community and
covered a full range of ideas and alternatives.
On June 30, 2000, the rulemaking record was reopened for 30 days in
order to obtain public comment on certain additional documents which
the agency determined should be placed in the rulemaking record. Those
documents were MSHA's paper filter verification studies and the recent
information from VERT on the performance of hot gas filters mentioned
in section 6 of this Part. In addition, the notice provided an
opportunity for comment on additional documents being placed in the
rulemaking record for a related rulemaking for underground metal and
nonmetal mines, and an opportunity to comment on some additional
documents on risk being placed in both records. In this regard, the
notice reassured the mining community that any comments filed on risk
in either rulemaking proceeding would be placed in both records, since
the two rulemakings utilize the same risk assessment.
Other Related Activity. On September 3, 1999, the United States
Court of Appeals for the District of Columbia Circuit issued its
decision on writ of mandamus sought by the United Mine Workers to
compel MSHA to issue final regulations controlling gaseous emissions in
the exhaust of diesel engines used in underground coal mines. (190 F.3d
545.) The UMWA argued that such action should have been completed some
years before as part of MSHA's air quality rulemaking to update
emissions limits on hundreds of exposure limits. The Court found that
the Agency was in violation of the statute's requirement that the
Secretary must either promulgate final regulations, or explain her
decision not to promulgate them, within ninety days of the
certification of the record of a hearing if one is held or the close of
the public comment period if a hearing is not held 30 U.S.C. 811(a)(4).
However, the Court declined to immediately issue the mandamus order
sought in this case because, among other factors: (a) The UMWA agreed
that the diesel equipment rules alone may have the desired effect of
reducing exposure to these gases; (b) the UMWA further agreed that the
control of diesel particulate matter and respirable mine dust rank as
higher rulemaking priorities for MSHA; and (c) MSHA submitted a
tentative schedule for such rulemaking that the court found to be
reasonable. However, the court retained jurisdiction of the case to
ensure MSHA would move forward on this matter, and ordered several
reports by the agency on its progress on December 31, 1999, June 30,
2000, December 31, 2000, and December 31, 2001.

III. Risk Assessment

Introduction

1. Exposures of U.S. Miners
a. Underground Coal Mines
b. Underground Metal and Nonmetal Mines
c. Surface Mines
d. Miner Exposures Compared to Exposures of Other Groups
2. Health Effects Associated with Dpm Exposures
a. Relevancy Considerations
i. Animal Studies
ii. Reversible Health Effects
iii. Health Effects Associated with PM2.5 in Ambient
Air
b. Acute Health Effects
i. Symptoms Reported by Exposed Miners
ii. Studies Based on Exposures to Diesel Emissions
iii. Studies Based on Exposures to Particulate Matter in Ambient
Air
c. Chronic Health Effects
i. Studies Based on Exposures to Diesel Emissions
(1) Chronic Effects other than Cancer
(2) Cancer
(a) Lung Cancer
(i) Evaluation Criteria
(ii) Studies Involving Miners
(iii) Best Available Epidemiologic Evidence
(iv) Counter-Evidence
(v) Summation
(b) Bladder Cancer
ii. Studies Based on Exposures to PM2.5 in Ambient
Air
d. Mechanisms of Toxicity
i. Agent of Toxicity
ii. Deposition, Clearance, and Retention
iii. Effects other than Cancer
iv. Lung Cancer
(1) Genotoxicity Studies
(2) Animal Inhalation Studies
3. Characterization of Risk
a. Material Impairments to Miners' Health or Functional Capacity
i. Sensory Irritations and Respiratory Symptoms (including
allergenic responses)
ii. Premature Death from Cardiovascular, Cardiopulmonary, or
Respiratory Causes
iii. Lung Cancer
(1) Summary of Collective Epidemiologic Evidence
(a) Consistency of Epidemiologic Results
(b) Best Available Epidemiologic Evidence
(c) Studies with Quantitative or Semiquantitative Exposure
Assessments
(d) Studies Involving Miners
(2) Meta-Analyses
(3) Potential Systematic Biases
(4) Causality
(5) Other Interpretations of the Evidence
b. Significance of the Risk of Material Impairment to Miners
i. Meaning of Significant Risk
(1) Legal Requirements
(2) Standards and Guidelines for Risk Assessment
ii. Significance of Risk for Underground Miners Exposed to DPM

[[Page 5561]]

(1) Sensory Irritations and Respiratory Symptoms (including
allergenic responses)
(2) Premature Death from Cardiovascular, Cardiopulmonary, or
Respiratory Causes
(3) Lung Cancer
(a) Risk Assessment Based on Studies Involving Miners
(b) Risk Assessment Based on Miners' Cumulative Exposure
(i) Exposure-Response Relationships from Studies Outside Mining
(ii) Exposure-Response Relationships from Studies on Miners
(iii) Excess Risk at Specific DPM Exposure Levels
c. The Rule's Expected Impact on Risk
4. Conclusions

Introduction

MSHA has reviewed the scientific literature to evaluate the
potential health effects of occupational dpm exposures at levels
encountered in the mining industry. This part of the preamble presents
MSHA's review of the currently available information and MSHA's
assessment of health risks associated with those exposures. All
material submitted during the public comment periods was considered
before MSHA drew its final conclusions.
The risk assessment begins in Section III.1, with a discussion of
dpm exposure levels observed by MSHA in the mining industry. This is
followed by a review, in Section III.2, of information available to
MSHA on health effects that have been studied in association with dpm
exposure. Finally, in Section III.3 entitled ``Characterization of
Risk,'' the Agency considers three questions that must be addressed for
rulemaking under the Mine Act and relates the available information
about risks of dpm exposure at current levels to the regulatory
requirements.
A risk assessment must be technical enough to present the evidence
and describe the main controversies surrounding it. At the same time,
an overly technical presentation could cause stakeholders to lose sight
of the main points. MSHA is guided by the first principle the National
Research Council established for risk characterization, that the
approach be:

[a] decision driven activity, directed toward informing choices and
solving problems * * * Oversimplifying the science or skewing the
results through selectivity can lead to the inappropriate use of
scientific information in risk management decisions, but providing
full information, if it does not address key concerns of the
intended audience, can undermine that audience's trust in the risk
analysis.

Although the final rule covers only one sector, this portion of the
preamble was intended to enable MSHA and other interested parties to
assess risks throughout the coal and M/NM mining industries.
Accordingly, the risk assessment includes information pertaining to all
sectors of the mining industry. All public comments on the exposures of
miners and the health effects of dpm exposure--whether submitted
specifically for the coal rulemaking or for the metal/nonmetal
rulemaking--were incorporated into the record for each rulemaking and
have been considered for this assessment.
MSHA had an earlier version of this risk assessment independently
peer reviewed. The risk assessment as proposed incorporated revisions
made in accordance with the reviewers' recommendations, and the final
version presented here contains clarifications and other responses to
public comments. With regard to the risk assessment as published in the
proposed preamble, the reviewers stated that:

* * * principles for identifying evidence and characterizing risk
are thoughtfully set out. The scope of the document is carefully
described, addressing potential concerns about the scope of
coverage. Reference citations are adequate and up to date. The
document is written in a balanced fashion, addressing uncertainties
and asking for additional information and comments as appropriate.
(Samet and Burke, Nov. 1997).

Some commenters generally agreed with this opinion. Dr. James
Weeks, representing the UMWA, found the proposed risk assessment to be
``balanced, thorough, and systematic.'' Dr. Paul Schulte, representing
NIOSH, stated that ``MSHA has prepared a thorough review of the health
effects associated with exposure to high concentrations of dpm, and
NIOSH concurs with the published [proposed] characterization of risks
associated with these exposures.'' Dr. Michael Silverstein,
representing the Washington State Dept. of Labor and Industries, found
MSHA's ``regulatory logic * * * thoroughly persuasive.'' He commented
that ``the best available scientific evidence shows that diesel
particulate exposure is associated with serious material impairment of
health * * * the evidence * * * is particularly strong and certainly
provides a sufficient basis for regulatory action.''
Many commenters, however, vigorously criticized various aspects of
the proposed assessment and some of the scientific studies on which it
was based. MSHA's final assessment, published here, was modified to
respond to all of these criticisms. Also, in response to commenters'
suggestions, this assessment incorporates some research studies and
literature reviews not covered or inadequately discussed in the
previous version.
Some commenters expressed the opinion that the proposed risk
assessment should have been peer-reviewed by a group representing
government, labor, industry, and independent scientists. Since the
rulemaking process included a pre-hearing comment period, eight public
hearings (four for coal and four for M/NM), and two post-hearing
comment periods, these constituencies had ample opportunity to review
and comment upon MSHA's proposed risk assessment. The length of the
comment period for the Coal Dpm proposal was 15 months. The length of
the comment period for the Metal/Nonmetal Dpm proposal was nine months.

1. Exposures of U.S. Miners

Information about U.S. miner exposures comes from published studies
and from additional mine investigations conducted by MSHA since
1993.\3\ Previously published studies of exposures to dpm among U.S.
miners are: Watts (1989, 1992), Cantrell (1992, 1993), Haney (1992),
and Tomb and Haney (1995). MSHA has also conducted investigations
subsequent to the period covered in Tomb and Haney (1995), and the
previously unpublished data through mid-1998 are included here. Both
the published and unpublished studies were placed in the record with
the proposal, giving MSHA's stakeholders the opportunity to analyze and
comment on all of the exposure data considered.
---------------------------------------------------------------------------

\3\ MSHA has only limited information about miner exposures in
other countries. Based on 223 personal and area samples, average
exposures at 21 Canadian noncoal mines were reported to range from
170 to 1300 g/m 3 (respirable combustible dust),
with maximum measurements ranging from 1020 to 3100 g/m
3 (Gangel and Dainty, 1993). Among 622 full shift
measurements collected since 1989 in German underground noncoal
mines, 91 (15%) exceeded 400 g/m 3 (total
carbon) (Dahmann et al., 1996). As explained elsewhere in this
preamble, 400 g/m 3 (total carbon) corresponds
to approximately 500 g/m 3 dpm.
---------------------------------------------------------------------------

MSHA's field studies involved measuring dpm concentrations at a
total of 50 mines: 27 underground metal and nonmetal (M/NM) mines, 12
underground coal mines, and 11 surface mining operations (both coal and
M/NM). At all surface mines and all underground coal mines, dpm
measurements were made using the size-selective method, based on
gravimetric determination of the amount of submicrometer dust collected
with an impactor. With few exceptions, dpm measurements at underground
M/NM mines were made using the Respirable Combustible Dust (RCD) method
(with

[[Page 5562]]

no impactor). At two of the underground M/NM mines, measurements were
made using the total carbon (TC) method, and at one, RCD measurements
were made in one year and TC measurements in another. Measurements at
the two remaining underground M/NM mines were made using the size-
selective method, as in coal and surface mines.\4\ Weighing errors
inherent in the gravimetric analysis required for both size-selective
and RCD methods become statistically insignificant at the relatively
high dpm concentrations observed.
---------------------------------------------------------------------------

\4\ The various methods of measuring dpm are explained in
section 3 of Part II of the preamble to the proposed rule. This
explanation, along with additional information on these methods, is
also provided in section 3 of Part II of the preamble to the final
M/NM rule.
---------------------------------------------------------------------------

According to MSHA's experience, the dpm samples reflect exposures
typical of mines known to use diesel equipment for face haulage in the
U.S. However, they do not constitute a random sample of mines, and care
was taken in the proposed risk assessment not to characterize results
as necessarily representing conditions in all mines. Several commenters
objected to MSHA's use of these exposure measurements in making
comparisons to exposures reported in other industries and, for M/NM, in
estimating the proposed rule's impact. These objections are addressed
in Sections III.1.d and III.3.b.ii(3)(c) below. Comments related to the
measurement methods used in underground coal and M/NM mines are
addressed, respectively, in Sections III.1.b and III.1.c.
Each underground study typically included personal dpm exposure
measurements for approximately five production workers. Also, area
samples were collected in return airways of underground mines to
determine diesel particulate emission rates.\5\ Operational information
such as the amount and type of equipment, airflow rates, fuel, and
maintenance was also recorded. Mines were selected to obtain a wide
range of diesel equipment usage and mining methods. Mines with greater
than 175 horsepower and less than 175 horsepower production equipment
were sampled. Single and multiple level mines were sampled. Mine level
heights ranged from eight to one-hundred feet. In general, MSHA's
studies focused on face production areas of mines, where the highest
concentrations of dpm could be expected; but, since some miners do not
spend their time in face areas, samples were collected in other areas
as well, to get a more complete picture of miner exposure. Because of
potential interferences from tobacco smoke in underground M/NM mines,
samples were not collected on or near smokers.
---------------------------------------------------------------------------

\5\ Since area samples in return airways do not necessarily
represent locations where miners normally work or travel, they were
excluded from the present analysis. A number of area samples were
included, however, as described in Sections III.1.b and III.1.c. The
included area samples were all taken in production areas and
haulageways.
---------------------------------------------------------------------------

Table III-1 summarizes key results from MSHA's studies. The higher
concentrations in underground mines were typically found in the
haulageways and face areas where numerous pieces of equipment were
operating, or where airflow was low relative to the amount of equipment
operating. In production areas and haulageways of underground mines
where diesel powered equipment was used, the mean dpm concentration
observed was 644 g/m3 for coal and 808 g/
m3 for M/NM. In travelways of underground mines where diesel
powered equipment was used, the mean dpm concentration (based on 112
area samples not included in Table III-1) was 517 g/
m3 for M/NM and 103 g/m3 for coal. In
surface mines, the higher concentrations were generally associated with
truck drivers and front-end loader operators. The mean dpm
concentration observed was less than 200 g/m3 at
all eleven of the surface mines in which measurements were made. More
information about the dpm concentrations observed in each sector is
presented in the material that follows.

Table III-1.--Full-Shift Diesel Particulate Matter Concentrations Observed in Production Areas and Haulageways of 50 Dieselized U.S. Mines
--------------------------------------------------------------------------------------------------------------------------------------------------------
Standard error of
Mine type Number of mines Number of samples Mean exposure mean (g/ Exposure range
(g/m\3\) m\3\) (g/m\3\)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Surface.................................................. 11 45 88 11 9-380
Underground Coala........................................ 12 226 644 41 0-3.650
Underground Metal and Nonmetal........................... 27 355 808 39 10-5.570
--------------------------------------------------------------------------------------------------------------------------------------------------------
Note: Intake and return area samples are excluded.

a. Underground Coal Mines

Approximately 145 out of the 910 existing underground coal mines
currently utilize diesel powered equipment. Of these 145 mines, 32
mines currently use diesel equipment for face coal haulage. The
remaining mines use diesel equipment for transportation, materials
handling and other support operations. MSHA focused its efforts in
measuring dpm concentrations in coal mines on mines that use diesel
powered equipment for face coal haulage. Twelve mines using diesel-
powered face haulage were sampled. Mines with diesel powered face
haulage were selected because the face is an area with a high
concentration of vehicles operating at a heavy duty cycle at the
furthest end of the mine's ventilation system.
Diesel particulate levels in underground mines depend on: (1) The
amount, size, and workload of diesel equipment; (2) the rate of
ventilation; and, (3) the effectiveness of whatever diesel particulate
control technology may be in place. In the dieselized mines studied by
MSHA, the sections used either two or three diesel coal haulage
vehicles. In eastern mines, the haulage vehicles were equipped with a
nominal 100 horsepower engine. In western mines, the haulage vehicles
were equipped with a nominal 150 horsepower engine. Ventilation rates
ranged from the approval plate requirement, based on the 100-75-50
percent rule (Holtz, 1960), to ten times the approval plate
requirement. In most cases, the section airflow was approximately twice
the approval plate requirement. Other control technology included
aftertreatment filters and fuel. Two types of aftertreatment filters
were used. These filters included a disposable diesel emission filter
(DDEF) and a Wire Mesh Filter (WMF). The DDEF is a commercially
available product; the WMF was developed by and only used at one mine.
Both low sulfur and high sulfur fuels were used.
Figure III-1 displays the range of exposure measurements obtained
by MSHA in the field studies it conducted in underground coal mines. A
study

[[Page 5563]]

normally consisted of collecting samples on the continuous miner
operator and coal haulage vehicle operators for two to three shifts,
along with area samples in the haulageways. A total of 142 personal
samples and 84 area samples were collected, excluding any area samples
taken in intake or return airways.

BILLING CODE 4510-43-P
[GRAPHIC] [TIFF OMITTED] TR19JA01.010

BILLING CODE 4510-43-C
As stated in the proposed risk assessment, no statistically
significant difference was observed in mean dpm concentration between
the personal and area samples.\6\ A total of 19 individual measurements
exceeded 1500 g/m3, still excluding intake and
return area samples. Although the three highest of these were from area
samples, nine of the 19 measurements exceeding 1500 g/
m3 were from personal samples.
---------------------------------------------------------------------------

\6\ One commenter (IMC Global) noted that MSHA had provided no
data verifying this statement. For the 142 personal samples, the
mean dpm concentration measurement was 608 g/m3,
with a standard error of 42.5 g/m3. For the 84
area samples, the mean was 705 g/m3, with a
standard error of 82.1 g/m3. The significance
level (p-value) of a t-test comparing these means is 0.29 using a
separate-variance test or 0.25 using a pooled-variance test.
Therefore, a difference in population means cannot be inferred at
any confidence level greater than 75%. Here, and in other sections
of this risk assessment, MSHA has employed standard statistical
methods described in textbooks on elementary statistical inference.
---------------------------------------------------------------------------

In six mines, measurements were taken both with and without use of
disposable after-treatment filters, so that a total of eighteen
studies, carried out in twelve mines, are displayed. Without use of
after-treatment filters, average observed dpm concentrations exceeded
500 g/m3 in eight of the twelve mines and exceeded
1000 g/m3 in four.\7\ At five of the twelve mines,
all dpm measurements were 300 g/m3 or greater in
the absence of after-treatment filters.
---------------------------------------------------------------------------

\7\ In coal mine E, the average as expressed by the mean
exceeded 1000 g/m3, but the median did not.
---------------------------------------------------------------------------

The highest dpm concentrations observed at coal mines were
collected at Mine ``G.'' Eight of these samples were collected during
employment of WMFs, and eight were collected while filters were not
being employed. Without filters, the mean dpm concentration observed at
Mine ``G'' was 2052 g/m3 (median = 2100 g/
m3). With

[[Page 5564]]

employment of WMFs, the mean dropped to 1241 g/m3
(median = 1235 g/m3).
Filters were employed during three of the four studies showing
median dpm concentration at or below 200 g/m3.
After adjusting for outby sources of dpm, exposures were found to be
reduced by up to 95 percent in mines using the DDEF and by
approximately 50 percent in the mine using the WMF.
The higher dpm concentrations observed at the mine using the WMF
(Mine ``G*'') are attributable partly to the lower section airflow. The
only study without filters showing a median concentration at or below
200 g/m3 was conducted in a mine (Mine ``A'') which
had section airflow approximately ten times the nameplate requirement.
The section airflow at the mine using the WMF was approximately the
nameplate requirement.
Some commenters [e.g., WV Coal Assoc and Energy West] objected to
MSHA's presentation of underground coal mine exposures based on
measurements made using the size-selective method (gravimetric
determination of the amount of submicrometer dust collected with an
impactor). These commenters argued that the data were `` * * *
collected with emissions monitoring devices discredited by MSHA itself
in the preamble * * *'' and that these measurements do not reliably ``*
* * distinguish it [dpm] from other particles in coal mine dust, at the
critical upper end range of submicron particles.''
MSHA did not ``discredit'' use of the size-selective method for all
purposes. As discussed elsewhere in this preamble, the size-selective
method of measuring dpm was designed by the former BOM specifically for
use in coal mines, and the size distribution of coal mine dust was
taken into account in its development. Despite the recognized
interference from a small fraction of coal mine dust particles, MSHA
considers gravimetric size-selective measurements to be reasonably
accurate in measuring dpm concentrations greater than 200 g/
m3, based on a full-shift sample, when coal mine dust
concentrations are not excessive (i.e., not greater than 2.0 mg/
m3). Interference from submicrometer coal mine dust is
counter-balanced, to some extent, by the fraction of larger size,
uncaptured dpm. Coal mine dust concentrations were not excessive when
MSHA collected its size-selective samples. Therefore, even if as much
as 10 percent of the coal mine dust were submicrometer, this fraction
would not have contributed significantly to the high concentrations
observed at the sampled mines.
At lower concentrations, or shorter sampling times, random
variability in the gravimetric determination of weight gain becomes
significant, compared to the weight of dust accumulated on the filter.
For this reason, MSHA has rejected the use of the gravimetric size-
selective method for enforcement purposes.\8\ This does not mean,
however, that MSHA has ``discredited'' this method for other purposes,
including detection of very high dpm concentrations at coal mines
(i.e., greater than 500 g/m3) and estimation of
average dpm concentrations, based on multiple samples, when coal mine
dust concentrations are not excessive. On the contrary, MSHA regards
the gravimetric size-selective method as a useful tool for detecting
and monitoring very high dpm concentrations and for estimating average
exposures.
---------------------------------------------------------------------------

\8\ MSHA has concluded that random weighing variability would
make it impractical to use the size-selective method to enforce
compliance with any dpm concentration limit less than about 300
g/m3. MSHA believes that, at such levels,
single-sample noncompliance determinations based on the size-
selective method could not be made at a sufficiently high confidence
level.
---------------------------------------------------------------------------

b. Underground Metal and Nonmetal Mines

Currently there are approximately 265 underground M/NM mines in the
United States. Nearly all of these mines utilize diesel powered
equipment, and 27 of those doing so were sampled by MSHA for dpm.\9\
The M/NM studies typically included measurements of dpm exposure for
dieselized production equipment operators (such as truck drivers, roof
bolters, haulage vehicles) on two to three shifts. A number of area
samples were also collected. None of the M/NM mines studied were using
diesel particulate afterfilters.
---------------------------------------------------------------------------

\9\ The proposal discussed data from 25 underground M/NM mines.
Studies at two additional mines, carried out too late to be included
in the proposal, were placed into the public record along with the
earlier studies. During the proceedings, MSHA provided copies of all
of these studies to stakeholders requesting them.
---------------------------------------------------------------------------

Figure III-2 displays the range of dpm concentrations measured by
MSHA in the 27 underground M/NM mines studied. A total of 275 personal
samples and 80 area samples were collected, excluding intake and return
area samples. Personal exposures observed ranged from less than 100
g/m3 to more than 3500 g/m3.
Exposure measurements based on area samples ranged from less than 100
g/m3 to more than 3000 g/m3.
With the exception of Mine ``V'', personal exposures were for face
workers. Mine ``V'' did not use dieselized face equipment.

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As stated in the proposed risk assessment, no statistically
significant difference was observed in mean dpm concentration between
the personal and area samples.\10\ A total of 45 individual
measurements exceeded 1500 g/m\3\, still excluding intake and
return area samples. The three highest of these, all exceeding 3500
g/m\3\, were from personal samples. Of the 45 measurements
exceeding 1500 g/m\3\, 30 were from personal samples and 15
were from area samples.
---------------------------------------------------------------------------

\10\ One commenter (IMC Global) noted that MSHA had provided no
data verifying this statement. For the 275 personal samples, the
mean dpm concentration measurement was 770 g/m\3\, with a
standard error of 42.8 g/m\3\. For the 80 area samples, the
mean was 939 g/m\3\, with a standard error of 86.6
g/m\3\. The significance level (p-value) of a t-test
comparing these means is 0.08 using a separate-variance test or 0.07
using a pooled-variance test. Therefore, a difference in population
means cannot be inferred at a 95% confidence level.
---------------------------------------------------------------------------

Average observed dpm concentrations exceeded 500 g/m\3\ in
18 of the 27 underground M/NM mines and exceeded 1000 g/m\3\
in 12.\11\ At eight of the 27 mines, all dpm measurements exceeded 300
g/m\3\. The highest dpm concentrations observed at M/NM mines
were collected at Mine ``E''. Based on 16 samples, the mean dpm
concentration observed at Mine ``E'' was 2008 g/m\3\ (median =
1835 g/m\3\). Twenty-five percent of the dpm measurements at
this mine exceeded 2400 g/m\3\. All four of these were based
on personal samples.
---------------------------------------------------------------------------

\11\ At M/NM mines C, I, J, P, and Z the average as expressed by
the mean exceeded 1000 g/m\3\ but the median did not. At M/
NM mines H and S, the median exceeded 1000 g/m\3\ but the
mean did not. At M/NM mine K, the mean exceeded 500 g/m\3\,
but the median did not.
---------------------------------------------------------------------------

As with underground coal mines, dpm levels in underground M/NM
mines are related to the amount and size of equipment, to the
ventilation rate, and to the effectiveness of the diesel particulate
control technology employed. In the dieselized M/NM mines studied by
MSHA, front-end-loaders were used either to load ore onto trucks or to
haul and load ore onto belts. Additional pieces of diesel powered
support equipment, such as bolters and mantrips, were also used at the
mines. The typical piece of production equipment was rated at 150 to
350 horsepower. Ventilation rates in the M/NM mines studied mostly
ranged from 100 to 200 cfm per horsepower of equipment. In only a few
of the mines inventoried did ventilation exceed 200 cfm/hp. For single-
level mines, working areas were ventilated in series (i.e., the exhaust
air from one area became the intake for the next working area). For
multi-level mines, each level typically had a separate fresh air
supply. One or two working areas could be on a level. Control
technology used to reduce diesel particulate emissions in mines
inventoried included oxidation catalytic converters and engine
maintenance programs. Both low sulfur and high sulfur fuel were used;
some mines used aviation grade low sulfur fuel.
Some commenters argued that, because of the limited number of
underground M/NM mines sampled by MSHA, ``* * * results of MSHA's
admittedly non-random sample cannot be extrapolated to other mines.''
[MARG] More specifically, IMC Global claimed that since only 25 [now
27] of about 260 underground M/NM mines were sampled,\12\ then ``if the
* * * measurements are correct, this information shows at best
potential exposure problems to diesel particulate in only 10% of the
miners working in the metal-nonmetal mining sector and then only for
certain unlisted commodities.'' \13\ IMC Global went on to suggest that
MSHA should ``perform sufficient additional exposure monitoring * * *
to show that the diesel particulate exposures are representative of the
entire industry before promulgating regulations that will be applicable
to the entire industry.''
---------------------------------------------------------------------------

\12\ Three underground M/NM mine surveys, carried out too late
to be included in the discussion, were placed into the public record
and provided to interested stakeholders. These surveys contained
data from two additional underground M/NM mines (``Z'' and ``aa'')
and additional data for a mine (``d'') that had previously been
surveyed. The risk assessment has now been updated to include these
data, representing a total of 27 underground M/NM mines.
\13\ A breakdown by commodity is given at the end of this
subsection.
---------------------------------------------------------------------------

As mentioned earlier, MSHA acknowledges that the mines for which
dpm measurements are available do not comprise a statistically random
sample of all underground M/NM mines. MSHA also acknowledges that the
results obtained for these mines cannot be extrapolated in a
statistically rigorous way to the entire population of underground M/NM
mines. According to MSHA's experience, however, the selected mines (and
sampling locations within those mines) represent typical diesel
equipment use conditions at underground M/NM mines. MSHA believes that
results at these mines, as depicted in Figure III-2, in fact fairly
reflect the variety of diesel equipment used by the industry,
regardless of type of M/NM mine. Based on its extensive experience with
underground mines, MSHA believes that this body of data better
represents those diverse diesel equipment use conditions, with respect
to dpm exposures, than any other body of data currently available.
MSHA strongly disagrees with IMC Global's contention that, ``* * *
this information shows at best potential exposure problems to diesel
particulate in only 10% of the miners working in the metal-nonmetal
mining sector.'' IMC Global apparently drew this conclusion from the
fact that MSHA sampled approximately ten percent of all underground M/
NM mines. This line of argument, however, depends on an unwarranted and
highly unrealistic assumption: Namely, that all of the underground M/NM
mines not included in the sampled group of 25 experience essentially no
``potential [dpm] exposure problems.'' MSHA certainly did not go out
and, by chance or design, pick for sampling just exactly those mines
experiencing the highest dpm concentrations. IMC Global's argument
fails to recognize that the sampled mines could be fairly
representative without being randomly chosen.
MSHA also disagrees with the premise that 27 [or 25 as in the
proposal] is an inherently insufficient number of mines to sample for
the purpose of identifying an industry-wide dpm exposure problem that
would justify regulation. The between-mine standard deviation of the 27
mean concentrations observed within mines was 450 g/m\3\.
Therefore, the standard error of the estimated grand mean, based on the
variability observed between mines, was
[GRAPHIC] [TIFF OMITTED] TR19JA01.012

MSHA considers this degree of uncertainty to be acceptable, given that
the overall mean concentration observed exceeded 800 g/m\3\.
---------------------------------------------------------------------------

\14\ This quantity, 87 g/m\3\, differs from the
standard error of the mean of individual measurements for
underground M/NM mines, presented in Table III-1. The tabled value
is based on 355 measurements whose standard deviation is 727
g/m\3\. Therefore, the standard error of the mean of all
individual measurements is 727/355 =
39 g/m\3\, as shown in the table. Similarly, the mean of
all individual measurements (listed in Table III-1 as 808
g/m\3\) differs from the grand mean of individual mean
concentrations observed within mines, which is 838 g/m\3\.
---------------------------------------------------------------------------

Several commenters questioned MSHA's use of the RCD and size-
selective methods for measuring dpm exposures at underground M/NM
mines. IMC Global indicated that MSHA's RCD measurements might
systematically inflate the dpm concentrations presented in this
section, because ``* * * estimates for the non-diesel particulate
component of RCD actually vary between 10% to 50%, averaging 33%.''

[[Page 5567]]

MSHA considers the size-selective, gravimetric method capable of
providing reasonably accurate measurements when the dpm concentration
is greater than 200 g/m3, interferences are
adequately limited, and the measurement is based on a full-shift
sample. Relatively few M/NM measurements were made using this method,
and none at the mines showing the highest dpm concentrations. No
evidence was presented that the size distribution of coal mine dust
(for which the impactor was specifically developed) differs from that
of other mineral dusts in a way that significantly alters the
impactor's performance. Similarly, MSHA considers the RCD method, when
properly applied, to be capable of providing reasonably accurate dpm
measurements at concentrations greater than 200 g/
m3. As with the size selective method, however, random
weighing errors can significantly reduce the precision of even full-
shift RCD measurements at lower dpm concentrations. For this reason, in
order to maintain a sufficiently high confidence level for its
noncompliance determinations, MSHA will not use the RCD method for
enforcement purposes. This does not mean, however, that MSHA has
``discredited'' the RCD measurements for all other purposes, including
detection of very high dpm concentrations (i.e., greater than 300
g/m3) and estimation of average concentrations
based on multiple samples. On the contrary, MSHA considers the RCD
method to be a useful tool for detecting and monitoring very high dpm
concentrations in appropriate environments and for estimating average
exposures when those exposures are excessive.
MSHA did not employ an impactor in its RCD measurements, and it is
true that some of these measurements may have been subject to
interference from lubrication oil mists. However, MSHA believes that
the high estimates sometimes made of the non-dpm component of RCD
(cited by IMC Global) do not apply to the RCD measurements depicted in
Figure III-2. MSHA has three reasons for believing these RCD
measurements consisted almost entirely of dpm:
(1) MSHA took special care to sample only environments where
interferences would not be significant. No samples were taken near
pneumatic drills or smoking miners.
(2) There was no interference from carbonates. The RCD analysis was
performed at 500 deg. C, and carbonates are not released below
1000 deg. C. (Gangel and Dainty, 1993)
(3) Although high sulphur fuel was used in some mines, thereby
adding sulfates to the RCD measurement, these sulfates are considered
part of the dpm, as explained in section 2 of Part II of this preamble.
Sulfates should not be regarded as an interference in RCD measurements
of dpm.
Commenters presented no evidence that there were substantial
interferences in MSHA's RCD measurements, and, as stated above, MSHA
was careful to avoid them. Therefore, MSHA considers it reasonable, in
the context of this risk assessment, to assume that all of the RCD was
in fact dpm. Moreover, in the majority of underground M/NM mines
sampled, even if the RCD measurements were reduced by \1/3\, the mine's
average would still be excessive: it would still exceed the maximum
exposure level reported for non-mining occupations presented in Section
III.1.d.
The breakdown, as suggested by IMC Global, of sampled underground
M/NM mines by commodity is as follows:

------------------------------------------------------------------------
Number
Commodity of
mines
------------------------------------------------------------------------
Copper......................................................... 2
Gold........................................................... 1
Lead/Zinc...................................................... 6
Limestone...................................................... 6
Potash......................................................... 2
Salt........................................................... 6
Trona (soda ash)............................................... 2
Other Nonmetal................................................. 2
--------
Total...................................................... 27
------------------------------------------------------------------------

c. Surface Mines

Currently, there are approximately 12,620 surface mining operations
in the United States. The total consists of approximately 1,550 coal
mines and 11,070 M/NM mines. Virtually all of these mines utilize
diesel powered equipment.
MSHA conducted dpm studies at eleven surface mining operations:
eight coal mines and three M/NM mines. MSHA deliberately directed its
surface sampling efforts toward occupations likely to experience high
dpm concentrations. To help select such occupations, MSHA first made a
visual examination (based on blackness of the filter) of surface mine
respirable dust samples collected during a November 1994 study of
surface coal mines. This preliminary screening of samples indicated
that relatively high surface mine dpm concentrations are typically
associated with front-end-loader operators and haulage-truck operators;
accordingly, sampling focused on these operations. A total of 45
samples was collected.
Figure III-3 displays the range of dpm concentrations measured at
the eleven surface mines. The average dpm concentration observed was
less than 200 g/m3 at all mines sampled. The
maximum dpm concentration observed was less than or equal to 200
g/m3 in 8 of the 11 mines (73%). The surface mine
studies suggest that even when sampling is performed at the areas of
surface mines believed most likely to have high exposures, dpm
concentrations are generally likely to be less than 200 g/
m3.

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[[Page 5569]]

d. Miner Exposures Compared to Exposures of Other Groups

Occupational exposure to diesel particulate primarily originates
from industrial operations employing equipment powered with diesel
engines. Diesel engines are used to power ships, locomotives, heavy
duty trucks, heavy machinery, as well as a small number of light-duty
passenger cars and trucks. NIOSH has estimated that approximately 1.35
million workers are occupationally exposed to the combustion products
of diesel fuel in approximately 80,000 workplaces in the United States.
(NIOSH 1988) Workers who are likely to be exposed to diesel emissions
include: mine workers; bridge and tunnel workers; railroad workers;
loading dock workers; truck drivers; fork-lift drivers; farm workers;
and, auto, truck, and bus maintenance garage workers (NIOSH, 1988).
Besides miners, groups for which occupational exposures have been
reported and health effects have been studied include loading dock
workers, truck drivers, and railroad workers.
As estimated by the reported geometric mean,\15\ the median site-
specific occupational exposures for loading dock workers operating or
otherwise exposed to unfiltered diesel fork lift trucks ranged from 23
to 55 g/m3, as measured by submicrometer elemental
carbon (EC) (NIOSH, 1990). Reported geometric mean concentrations of
submicrometer EC ranged from 2.0 to 7.0 g/m3 for
truck drivers and from 4.8 to 28 g/m3 for truck
mechanics, depending on weather conditions (Zaebst et al., 1991).
---------------------------------------------------------------------------

\15\ Median concentrations were not reported. The geometric mean
provides a smoothed estimate of the median.
---------------------------------------------------------------------------

Because these exposure averages, unlike those for railroad workers
and miners, were reported in terms of EC, it is necessary, for purposes
of comparison, to convert them to estimates of total dpm. Watts (1995)
states that ``elemental carbon generally accounts for about 40% to 60%
of diesel particulate mass.'' Therefore, in earlier versions of this
risk assessment, a 2.0 conversion factor was assumed for dock workers,
truck drivers, and truck mechanics, based on the midpoint of the 40-60%
range proposed by Watts.
Some commenters objected to MSHA's use of this conversion factor.
IMC Global, for example, asserted that Watts' ``* * * 40 to 60%
relationship between elemental carbon and diesel particulate mass * * *
applies only to underground coal mines where diesel haulage equipment
is used.'' IMC Global, and other commenters, also objected to MSHA's
use of a single conversion factor for ``* * * different types of diesel
engines under different duty cycles with different fuels and different
types of emission control devices (if any) subjected to varying degrees
of maintenance.''
MSHA's quotation from Watts (1995) was taken from the ``Summary''
section of his paper. That paper covers a variety of occupational
environments, and the summary makes no mention of coal mines. The
sentence immediately preceding the quoted passage refers to the
``occupational environment'' in general, and there is no indication
that Watts meant to restrict the 40- to 60-percent range to any
specific environment. It seems clear that the 40-to 60-percent range
refers to average values across a spectrum of occupational
environments.
IMC Global mistakenly attributed to MSHA ``the blanket statement''
that the same ratio of elemental carbon to dpm applies ``for all diesel
engines in different industries for all patterns of use.'' MSHA made no
such statement. On the contrary, MSHA agrees with Watts (and IMC
Global) that ``the percentage of elemental carbon in total diesel
particulate matter fluctuates'' depending on ``engine type, duty cycle,
fuel, lube oil consumption, state of engine maintenance, and the
presence or absence of an emission control device.'' (Watts, op cit.)
Indeed, MSHA acknowledges that, because of these factors, the
percentage on a particular day in a particular environment may
frequently fall outside the stated range. But MSHA is not applying a
single conversion factor to individual elemental carbon measurements
and claiming knowledge of the total dpm corresponding to each separate
measurement. Instead, MSHA is applying an average conversion factor to
an average of measurements in order to derive an estimate of an average
dpm exposure. Averages are always less widely dispersed than individual
values.

[[Page 5570]]

Still, MSHA agrees with IMC Global that better estimates of dpm
exposure levels are attainable by applying conversion factors more
specifically related to the separate categories within the trucking
industry: dock workers, truck drivers, and truck mechanics. Based on a
total of 63 field measurements, the mean ratios (in percent) of EC to
total carbon (TC) reported for these three categories were 47.3, 36.6,
and 34.2, respectively (Zaebst et al., 1991).\16\ As explained
elsewhere in this preamble, TC amounts to approximately 80 percent, by
weight, of total dpm. Therefore, each of these ratios must be
multiplied by 0.8 in order to estimate the corresponding percentage of
EC in dpm.
---------------------------------------------------------------------------

\16\ MSHA calculated the ratio for truck drivers by taking a
weighted average of the ratios reported for ``local drivers'' and
``road drivers.''
---------------------------------------------------------------------------

It follows that the median mass concentration of dpm can be
estimated as 2.64 (i.e., 1/(0.473 x 0.8)) times the geometric mean EC
reported for dock workers, 3.42 times the geometric mean EC for truck
drivers, and 3.65 times the geometric mean EC for truck mechanics.
Applying the 2.64 conversion factor to the range of geometric mean EC
concentrations reported for dock workers (i.e., 23 to 55 g/
m3) results in an estimated range of 61 to 145 g/
m3 in median dpm concentrations at various docks. Similarly,
the estimated range of median dpm concentrations is calculated to be
6.8 to 24 g/m3 for truck drivers and 18 to 102
g/m3 for truck mechanics. It should be noted that
MSHA is using conversion factors only for those occupational groups
whose geometric mean exposures have been reported in terms of EC
measurements.
Average exposures of railroad workers to dpm were estimated by
Woskie et al. (1988) and Schenker et al. (1990). As measured by total
respirable particulate matter other than cigarette smoke, Woskie et al.
reported geometric mean concentrations for various occupational
categories of exposed railroad workers ranging from 49 to 191
g/m3.
For comparison with the exposures reported for these other
industries, median dpm exposures measured within sampled mines were
calculated directly from the data described in subsections a, b, and c
above. The median within each mine is shown as the horizontal ``belt''
plotted for the mine in Figures III-1, III-2, and III-3.
Figure III-4 compares the range of median dpm concentrations
observed for mine workers within different mines to a range of dpm
exposure levels estimated for urban ambient air and to the ranges of
median dpm concentrations estimated for loading dock workers operating
or otherwise exposed to diesel fork lift trucks, truck drivers, truck
mechanics, and railroad workers. The range for ambient air, 1 to 10
g/m\3\, was obtained from Cass and Gray (1995). For dock
workers, truck drivers, truck mechanics, and railroad workers, the
estimated ranges of median dpm exposures are, respectively: 61 to 145
g/m\3\, 6.8 to 24 g/m\3\, 18 to 102 g/m\3\
and 49 to 191 g/m\3\. The range of median dpm concentrations
observed at different underground coal mines is 55 to 2100 g/
m\3\, with filters employed at mines showing the lower
concentrations.\17\ For underground M/NM mines, the corresponding range
is 68 to 1835 g/m\3\, and for surface mines it is 19 to 160
g/m\3\. Since each range plotted is a range of median values
or (for ambient air) mean values, the plots do not encompass all of the
individual measurements reported.
---------------------------------------------------------------------------

\17\ One commenter misinterpreted the tops of the ranges plotted
in Figure III-4. This commenter apparently mistook the top of the
range depicted for underground coal mines as the mean or median dpm
exposure concentration measured across all underground coal mines.
The top of this range (at 2100 g/m\3\, actually represents
the highest median concentration at any of the coal mines sampled.
It corresponds to the ``belt'' plotted for Mine ``G'' (with no
after-filters) in Figure III-1. The bottom of the same bar, at 55
g/m\3\, corresponds to the ``belt'' plotted for Mine H *
(with after-filters) in Figure III-1.

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[[Page 5572]]

As shown in Figure III-4, some miners are exposed to far higher
concentrations of dpm than are any other populations for which exposure
data have been reported. Indeed, median dpm concentrations observed in
some underground mines are up to 200 times as high as mean
environmental exposures in the most heavily polluted urban areas,\18\
and up to 10 times as high as median exposures estimated for the most
heavily exposed workers in other occupational groups.
---------------------------------------------------------------------------

\18\ It should be noted, however, that 24-hour environmental
exposures for a full lifetime are not directly comparable with
workday exposures over an occupational lifetime. If it is assumed
that air inhaled during a work shift comprises half the total air
inhaled during a 24-hour day, then the amount of air inhaled over
the course of a 70-year lifetime is approximately 4.7 times the
amount inhaled over a 45-year occupational lifetime with 240 working
days per year.
---------------------------------------------------------------------------

Several commenters objected to Figure III-4 and, more generally, to
MSHA's comparison of dpm exposure levels for miners against the levels
reported for other occupations. The objections to MSHA's method of
estimating ranges of median dpm exposure for job categories within the
trucking industry have already been discussed and addressed above.
Other objections to the comparison were based on claims of insufficient
accuracy in the RCD and gravimetric size selective measurements MSHA
used to measure dpm levels for miners. MSHA considers its use of these
methods appropriate for purposes of this comparison and has responded
to criticisms of the dpm measurements for miners in Subsections 1.a and
1.b of this risk assessment.\19\
---------------------------------------------------------------------------

\19\ One commenter pointed out that the measurements for miners
included both area and personal samples but provided no evidence
that this would invalidate the comparison. As pointed out in
Subsections 1.a and 1.b, area samples did not dominate the upper end
of MSHA's dpm measurements. Furthermore, Figure III-4 presents a
comparison of medians rather than means or individual measurements,
so inclusion of the area samples has very little impact on the
results.
---------------------------------------------------------------------------

Some commenters objected to MSHA's basing a characterization of dpm
exposures to miners on data spanning a ten-year period. These
commenters contended that, in at least some M/NM mines, dpm levels had
improved substantially during that period. No data were submitted,
however, to support the premise that dpm exposures throughout the
mining industry have declined to the levels reported for other
occupations. As stated in the proposal and emphasized above, MSHA's dpm
measurements were not technically designed as a random or statistically
representative sample of the industry. They do show, however, that very
high exposures have recently occurred in some mines. For example, as
shown in Figure III-2, more than 25 percent of MSHA's dpm measurements
exceeded 2000 g/m\3\ at underground M/NM mines ``U'' and
``Z''--and these measurements were made in 1996-7. In M/NM mines where
exposures are actually commensurate with other industries already,
little or nothing would need to be changed to meet the exposure limits.
IMC Global further objected to Figure III-4 on the grounds that ``*
* * the assumptions that MSHA used to develop that figure are grossly
inaccurate and do not make sense in the context of a dose-response
relationship between lung cancer and Dpm exposure.'' IMC Global
suggested that the comparison in Figure III-4 be deleted for this
reason. MSHA believes that the comparison is informative and that
empirical evidence should be used, when it is available, even though
the evidence was not generated under ideal, theoretical dose-response
model conditions. The issue of whether Figure III-4 is consistent with
an exposure-response relationship for dpm is addressed in Subsection
3.a.iii(4) of this risk assessment.

2. Health Effects Associated With Dpm Exposures

This section reviews the various health effects (of which MSHA is
aware) that may be associated with dpm exposures. The review is divided
into three main sections: acute effects, such as diminished pulmonary
function and eye irritation; chronic effects, such as lung cancer; and
mechanisms of toxicity. Prior to that review, however, the relevance of
certain types of information will be considered. This discussion will
address the relevance of health effects observed in animals, health
effects that are reversible, and health effects associated with fine
particulate matter in the ambient air.
Several commenters described medical surveillance studies that
NIOSH and/or the former Bureau of Mines had carried out in the late
1970s and early 1980s on underground miners employed in western,
dieselized coal mines. These commenters urged MSHA to make these
studies available and to consider the results in this rulemaking. Some
of these commenters also suggested that these data would provide a
useful baseline for pulmonary function and lung diseases among miners
exposed to dpm, and recommended that follow-up examinations now be
conducted to evaluate the possible effects of chronic dpm exposure.
In response to such comments presented at some of the public
hearings, another commenter wrote:

First of all, MSHA is not a research agency, it is a regulatory
agency, so that it would be inappropriate for MSHA to initiate
research. MSHA did request that NIOSH conduct a risk assessment on
the health effects of diesel exhaust and encouraged NIOSH and is
currently collaborating with NIOSH (and NCI) on research of other
underground miners exposed to diesel exhaust. And third, research on
the possible carcinogenicity of diesel particulate matter was not
undertaken on coal miners in the West or anywhere else because of
the confounding exposure to crystalline silica, also considered a
carcinogen, because too few coal miners have been exposed, and for
too short a time to conduct a valid study. It was not arbitrariness
or indifference on MSHA's part that it did not initiate research on
coal miners; it was not within their mandate and it is inappropriate
in any event. [UMWA]

Three reports summarizing and presenting results from these medical
surveillance studies related to dpm exposures in coal mines were, in
fact, utilized and cited in the proposed risk assessment (Ames et al.,
1982; Reger et al., 1982; Ames et al., 1984). Ames et al. (1982)
evaluated acute respiratory effects, and their results are considered
in Subsection 2.b.ii of this risk assessment. Reger et al. (1982) and
Ames et al. (1984) evaluated chronic effects, and their results are
considered in Subsection 2.c.i(1).
A fourth report (Glenn et al., 1983) summarized results from the
overall research program of which the coal mine studies were a part.
This health and environmental research program included not only coal
miners, but also workers at potash, trona, salt, and metal mines. All
subjects were given chest radiographs and spirometric tests and were
questioned about respiratory symptoms, smoking and occupational
history. In conjunction with these medical evaluations, industrial
hygiene surveys were conducted to characterize the mine environments
where diesel equipment was used. Diesel exhaust exposure levels were
characterized by area and personal samples of NO2 (and, in some cases,
additional gasses), aldehydes, and both respirable and total dust. For
the evaluations of acute effects, exposure measures were based on the
shift concentrations to which the examined workers were exposed. For
the evaluations of chronic effects, exposures were usually estimated by
summing the products of time spent in various locations by each miner
by concentrations estimated for the various locations. Results of
studies on acute effects in salt mines were reported by Gamble et al.
(1978) and are considered

[[Page 5573]]

in Subsection 2.b.ii of this risk assessment. Attfield (1979), Attfield
et al. (1982), and Gamble et al. (1983) evaluated effects in M/NM
mines, and their results are considered in Subsection 2.c.i(1). The
general summary provided by Glenn et al. (1983) was among the reports
that one commenter (MARG) listed as having received inadequate
attention in the proposed risk assessment. In that context, the general
results summarized in this report are discussed, under the heading of
``Counter-Evidence,'' in Subsection 2.c.i(2)(a) of this risk
assessment.
a. Relevancy Considerations
i. Animal Studies
Since the lungs of different species may react differently to
particle inhalation, it is necessary to treat the results of animal
studies with some caution. Evidence from animal studies can
nevertheless be valuable--both in helping to identify potential human
health hazards and in providing a means for studying toxicological
mechanisms. Respondents to MSHA's ANPRM who addressed the question of
relevancy urged consideration of all animal studies related to the
health effects of diesel exhaust.
Unlike humans, laboratory animals are bred to be homogeneous and
can be randomly selected for either non-exposure or exposure to varying
levels of a potentially toxic agent. This permits setting up
experimental and control groups of animals that exhibit relatively
little biological variation prior to exposure. The consequences of
exposure can then be determined by comparing responses in the
experimental and control groups. After a prescribed duration of
deliberate exposure, laboratory animals can also be sacrificed,
dissected, and examined. This can contribute to an understanding of
mechanisms by which inhaled particles may exert their effects on
health. For this reason, discussion of the animal evidence is placed in
the section entitled ``Mechanisms of Toxicity'' below.
Animal evidence also can help isolate the cause of adverse health
effects observed among humans exposed to a variety of potentially
hazardous substances. If, for example, the epidemiologic data are
unable to distinguish between several possible causes of increased risk
of disease in a certain population, then controlled animal studies may
provide evidence useful in suggesting the most likely explanation--and
provide that information years in advance of definitive evidence from
human observations.
Furthermore, results from animal studies may also serve as a check
on the credibility of observations from epidemiologic studies of human
populations. If a particular health effect is observed in animals under
controlled laboratory conditions, this tends to corroborate
observations of similar effects in humans.
One commenter objected to MSHA's reference to using animal studies
as a ``check'' on epidemiologic studies. This commenter emphasized that
animal studies provide far more than just corroborative information and
that researches use epidemiologic and animal studies ``* * * to help
understand different aspects of the carcinogenic process.'' \20\ MSHA
does not dispute the utility of animal studies in helping to provide an
understanding of toxicological processes and did not intend to belittle
their importance for this purpose. In fact, MSHA places the bulk of its
discussion of these studies in a section entitled ``Mechanisms of
Toxicity.'' However, MSHA considers the use of animal studies for
corroborating epidemiologic associations to be also important--
especially with respect to ruling out potential confounding effects and
helping to establish causal linkages. Animal studies make possible a
degree of experimental design and statistical rigor that is not
attainable in human studies.
---------------------------------------------------------------------------

\20\ This risk assessment is not limited to cancer effects, but
the commenter's point can be generalized.
---------------------------------------------------------------------------

Other commenters disputed the relevance of at least some animal
data to human risk assessment. For example, The West Virginia Coal
Association indicated the following comments by Dr. Peter Valberg:

* * * scientists and scientific advisory groups have treated the
rat bioassay for inhaled particles as unrepresentative of human
lung-cancer risks. For example, the Presidential/Congressional
Commission on Risk Assessment and Risk Management (``CCRARM'') noted
that the response of rat lungs to inhaled particulate in general is
not likely to be predictive of human cancer risks. More specific to
dpm, the Clean Air Scientific Advisory Committee (``CASAC''), a
peer-review group for the U.S. EPA, has commented on two drafts
(1995 and 1998) of the EPA's Health Assessment Document on Diesel
Exhaust. On both occasions, CASAC emphasized that the data from rats
are not relevant for human risk assessment. Likewise, the Health
Effects Institute also has concluded that rat data should not be
used for assessing human lung cancer risk.

Similarly, the NMA commented that the 1998 CASAC review ``makes it
crystal clear that the rat studies cited by MSHA should not be relied
upon as a legitimate indicators of the carcinogenicity of Dpm in
humans.'' The Nevada Mining Association, endorsing Dr. Valberg's
comments, added:

* * * to the extent that MSHA wishes to rest its case on rat
studies, Dr. Valberg, among others, has impressively demonstrated
that these studies are worthless for human comparison because of
rats' unique and species-specific susceptibility to inhaled
insoluble particles.

However, neither Dr. Valberg nor the Nevada Mining Association provided
evidence that rats' susceptibility to inhaled insoluble particles was
``unique'' and that humans, for example, were not also susceptible to
lung overload at sufficiently high concentrations of fine particles.
Even if (as has apparently been demonstrated) some species (such as
hamsters) do not exhibit susceptibility similar to rats, this by no
means implies that rats are the only species exhibiting such
susceptibility.
These commenters appear at times to be saying that, because studies
of lung cancer in rats are (in the commenters' view) irrelevant to
humans, MSHA should completely ignore all animal studies related to
dpm. To the extent that this was the position advocated, the
commenters' line of reasoning neglects several important points:
1. The animal studies under consideration are not restricted to
studies of lung cancer responses in rats. They include studies of
bioavailability and metabolism as well as studies of immunological and
genotoxic responses in a variety of animal species.
2. The context for the determinations cited by Dr. Valberg was risk
assessment at ambient levels, rather than the much higher dpm levels to
which miners are exposed. The 1995 HEI report to which Dr. Valberg
alludes acknowledged a potential mechanism of lung overload in humans
at dpm concentrations exceeding 500 g/m\3\ (HEI, 1995). Since
miners may concurrently be exposed to concentrations of mineral dusts
significantly exceeding 500 g/m\3\, evidence related to the
consequences of lung overload has special significance for mining
environments.
3. The scientific authorities cited by Dr. Valberg and other
commenters objected to using existing animal studies for quantitative
human risk assessment. MSHA has not proposed doing that. There is an
important distinction between extrapolating results from the rat
studies to human populations and using them to confirm epidemiologic

[[Page 5574]]

findings and to identify and explore potential mechanisms of toxicity.
MSHA by no means ``wishes to rest its case on rat studies,'' and it
has no intention of doing so. MSHA does believe, however, that
judicious consideration of evidence from animal studies is appropriate.
The extent to which MSHA utilizes such evidence to help draw specific
conclusions will be clarified below in connection with those
conclusions.
ii. Reversible Health Effects
Some reported health effects associated with dpm are apparently
reversible--i.e., if the worker is moved away from the source for a few
days, the symptoms dissipate. A good example is eye irritation.
In response to the ANPRM, questions were raised as to whether so-
called ``reversible'' effects can constitute a ``material'' impairment.
For example, a predecessor constituent of the National Mining
Association (NMA) argued that ``it is totally inappropriate for the
agency to set permissible exposure limits based on temporary,
reversible sensory irritation'' because such effects cannot be a
``material'' impairment of health or functional capacity within the
definition of the Mine Act (American Mining Congress, 87-0-21,
Executive Summary, p. 1, and Appendix A).
MSHA does not agree with this categorical view. Although the
legislative history of the Mine Act is silent concerning the meaning of
the term ``material impairment of health or functional capacity,'' and
the issue has not been litigated within the context of the Mine Act,
the statutory language about risk in the Mine Act is similar to that
under the OSH Act. A similar argument was dispositively resolved in
favor of the Occupational Safety and Health Administration (OSHA) by
the 11th Circuit Court of Appeals in AFL-CIO v. OSHA, 965 F.2d 962, 974
(1992).
In that case, OSHA proposed new limits on 428 diverse substances.
It grouped these into 18 categories based upon the primary health
effects of those substances: e.g., neuropathic effects, sensory
irritation, and cancer. (54 FR 2402). Challenges to this rule included
the assertion that a ``sensory irritation'' was not a ``material
impairment of health or functional capacity'' which could be regulated
under the OSH Act. Industry petitioners argued that since irritant
effects are transient in nature, they did not constitute a ``material
impairment.'' The Court of Appeals decisively rejected this argument.
The court noted OSHA's position that effects such as stinging,
itching and burning of the eyes, tearing, wheezing, and other types of
sensory irritation can cause severe discomfort and be seriously
disabling in some cases. Moreover, there was evidence that workers
exposed to these sensory irritants could be distracted as a result of
their symptoms, thereby endangering other workers and increasing the
risk of accidents. (Id. at 974). This evidence included information
from NIOSH about the general consequences of sensory irritants on job
performance, as well as testimony by commenters on the proposed rule
supporting the view that such health effects should be regarded as
material health impairments. While acknowledging that ``irritation''
covers a spectrum of effects, some of which can be minor, OSHA had
concluded that the health effects associated with exposure to these
substances warranted action--to ensure timely medical treatment, reduce
the risks from increased absorption, and avoid a decreased resistance
to infection (Id. at 975). Finding OSHA's evaluation adequate, the
Court of Appeals rejected petitioners' argument and stated the
following:

We interpret this explanation as indicating that OSHA finds that
although minor irritation may not be a material impairment, there is
a level at which such irritation becomes so severe that employee
health and job performance are seriously threatened, even though
those effects may be transitory. We find this explanation adequate.
OSHA is not required to state with scientific certainty or precision
the exact point at which each type of sensory or physical irritation
becomes a material impairment. Moreover, section 6(b)(5) of the Act
charges OSHA with addressing all forms of ``material impairment of
health or functional capacity,'' and not exclusively ``death or
serious physical harm'' or ``grave danger'' from exposure to toxic
substances. See 29 U.S.C. 654(a)(1), 655(c). [Id. at 974].

In its comments on the proposed rule, the NMA claimed that MSHA had
overstated the court's holding. In making this claim, the NMA
attributed to MSHA an interpretation of the holding that MSHA did not
put forth. In fact, MSHA agrees with the NMA's interpretation as stated
in the following paragraph and takes special note of the NMA's
acknowledgment that transitory or reversible effects can sometimes be
so severe as to seriously threaten miners' health and safety:

NMA reads the Court's decision to mean (as it stated) that
``minor irritation may not be a material impairment'' * * * but that
irritation can reach ``a level at which [it] becomes so severe that
employee health and job performance are seriously threatened even
though those effects may be transitory.'' * * * AMC in 1992 and NMA
today are fully in accord with the view of the 11th Circuit that
when health effects, transitory or otherwise, become so ``severe''
as to ``seriously threaten'' a miner's health or job performance,
the materiality threshold has been met.

The NMA, then, apparently agrees with MSHA that sensory irritations
and respiratory symptoms can be so severe that they cross the material
impairment threshold, regardless of whether they are ``reversible.''
Therefore, as MSHA has maintained, such health effects are highly
relevant to this risk assessment--especially since impairments of a
miner's job performance in an underground mining environment could
seriously threaten the safety of both the miner and his or her co-
workers. Sensory irritations may also impede miners' ability to escape
during emergencies.
The NMA, however, went on to emphasize that ``* * * federal appeals
courts have held that `mild discomfort' or even `moderate irritation'
do not constitute `significant' or `material' health effects'':

In International Union v. Pendergrass, 878 F. 2d 389 (1989), the
D.C. Circuit upheld OSHA's formaldehyde standard against a challenge
that it did not adequately protect against significant
noncarcinogenic health effects, even though OSHA had found that, at
the permissible level of exposure, ``20% of workers suffer `mild
discomfort', while 30% more experience `slight discomfort'.'' Id. at
398. Likewise, in Texas Independent Ginners Ass'n. v. Marshall, 630
F, 2d 398 (1980), the Fifth Circuit Court of Appeals held that minor
reversible symptoms do not constitute material impairment unless
OSHA shows that those effects might develop into chronic disease.
Id. at 408-09.

MSHA is fully aware of the distinction that courts have made
between mild discomfort or irritation and transitory health effects
that can seriously threaten a miner's health and safety. MSHA's
position, after reviewing the scientific literature, public testimony,
and comments, is that all of the health effects considered in this risk
assessment fall into the latter category.
iii. Health Effects Associated with PM2.5 in Ambient Air
There have been many studies in recent years designed to determine
whether the mix of particulate matter in ambient air is harmful to
health. The evidence linking particulates in air pollution to health
problems has long been compelling enough to warrant direction from the
Congress to limit the concentration of such particulates (see part II,
section 5 of this preamble). In recent years, the evidence of harmful
effects due to airborne particulates has increased, suggesting that
``fine'' particulates (i.e., particles less than 2.5

[[Continued on page 5575]]

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