Diesel Particulate Matter Exposure of Underground Coal Miners
Federal RegisterApr 9, 1998
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SUMMARY: This proposed rule would establish new health standards for
underground coal mines that use equipment powered by diesel engines.
This proposal 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 proposed rule for underground coal mines would require that
mine operators install and maintain high-efficiency filtration systems
on certain types of diesel-powered equipment. Underground coal mine
operators would also be required to train miners about the hazards of
dpm exposure.
By separate notice, MSHA will soon propose a rule to reduce dpm
exposures in underground metal and nonmetal mines.
DATES: Comments must be received on or before August 7, 1998. Submit
written comments on the information collection requirements by August
7, 1998.
ADDRESSES: Comments on the proposed rule may be transmitted by
electronic mail, fax, or mail, or dropped off in person at any MSHA
office. Comments by electronic mail must be clearly identified as such
and sent to this e-mail address: [email protected]. Comments by fax
must be clearly identified as such and sent to: MSHA, Office of
Standards, Regulations, and Variances, 703-235-5551. Send mail comments
to: MSHA, Office of Standards, Regulations, and Variances, Room 631,
4015 Wilson Boulevard, Arlington, VA 22203-1984, or any MSHA district
or field office. The Agency will have 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. The document will also be available for loan
to interested members of the public on an as needed basis. MSHA will
also accept written comments from the mining community at the field and
district offices, at the National Mine Safety and Health Academy, and
at technical support centers. These comments will become a part of the
official rulemaking record. Interested persons are encouraged to
supplement written comments with computer files or disks; please
contact the Agency with any questions about format.
Written comments on the information collection requirements may be
submitted directly to the Office of Information and Regulatory Affairs,
New Executive Office Building, 725 17th Street, NW., Rm. 10235,
Washington, D.C. 20503, Attn: Desk Officer for MSHA.
FOR FURTHER INFORMATION CONTACT: Patricia W. Silvey, Director; Office
of Standards, Regulations, and Variances; MSHA; 703-235-1910.
SUPPLEMENTARY INFORMATION:
I. Questions and Answers About This Proposed Rule
(A) General Information of Interest to the Entire Mining Community
(1) What Actions Are Being Proposed?
MSHA has determined that action is essential to reduce the exposure
of miners to a harmful substance emitted from diesel engines--and that
regulations are needed for this purpose in underground mines. This
notice proposes requirements for underground coal mines; by separate
notice, MSHA will soon propose a rule for underground metal and
nonmetal mines.
The harmful substance is known as diesel particulate matter (dpm).
As shown in Figure I-1, average concentrations of dpm observed in
dieselized underground mines are up to 200 times as high as average
environmental exposures in the most heavily polluted urban areas and up
to 10 times as high as median exposures estimated for the most heavily
exposed workers in other occupational groups. The best available
evidence indicates that exposure to such high concentrations of dpm
puts miners at significantly increased risk of incurring serious health
problems, including lung cancer.
The goal of the proposed rule is to reduce underground miner
exposures to attain the highest degree of safety and health protection
that is feasible.
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In underground coal mines, MSHA's proposal would require the
installation of high-efficiency filters on diesel-powered equipment to
trap diesel particles before they enter the mine atmosphere. Following
18 months of education and technical assistance by MSHA after the rule
is issued, filters would first have to be installed on permissible
diesel-powered equipment. By the end of the following year (i.e., 30
months after the rule is issued), such filters would also have to be
installed on any heavy-duty outby equipment. No specific concentration
limit would be established in this sector; the proposed rule would
require that filters be installed and properly maintained. Miner
awareness training on the hazards of dpm would also be required.
MSHA is not at this time proposing a rule applicable to surface
mines. As illustrated in Figure I-1, in certain situations the
concentrations of dpm at surface mines may exceed those to which rail,
trucking and dock workers are exposed. Problem areas identified in this
sector include 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, 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. Using tailpipe exhaust extenders, or directing
the exhaust across the engine fan, can dilute the high concentrations
of dpm that might otherwise occur in areas immediately adjacent to
mining equipment. Surface mine operators using or planning to switch to
environmentally conditioned cabs to reduce noise exposure to equipment
operators might also be able to incorporate filtration features that
would protect these miners from high dpm concentrations as well.
Completing already planned purchases of new trucks containing cleaner
engines may also help reduce the isolated instances of high dpm
concentrations at such mines.
The Agency would like to emphasize, however, that surface miners
are entitled to the same level of protection as other miners, and that
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.
(2) How Is This Notice of Proposed Rulemaking Organized?
The proposed rule for underground coal mines can be found at the
end of this Notice. The remainder of this preamble to the proposed rule
(Supplementary Information) describes the Agency's rationale for what
is being proposed.
Part I consists of twelve ``Questions and Answers.'' The Agency
hopes they will provide most of the information you will need to
formulate your comments. The first ten of these (Section A) cover
general topics. The last two (Section B) contain additional detail
about the proposed rule for the underground coal sector, and a
discussion of two alternatives on which the Agency would particularly
like additional comment.
Part II provides some background information on nine topics that
are relevant to this rulemaking. In order, the topics covered are: (1)
the role of diesel-powered equipment in mining; (2) the composition of
diesel exhaust and diesel particulate; (3) measurement of diesel
particulate; (4) reducing soot at the source--EPA regulation of diesel
engine design; (5) limiting the public's exposure to soot--EPA ambient
air quality standards; (6) controlling diesel particulate emissions in
mining--a toolbox; (7) existing mining standards that limit miner
exposure to occupational diesel particulate emissions; (8) how other
jurisdictions are restricting occupational exposure to diesel soot; and
(9) MSHA's initiative to limit miner exposure to diesel particulate--
the history of this rulemaking and related actions. Appended to the end
of this document is a copy of an MSHA publication, ``Practical Ways to
Reduce Exposure to Diesel Exhaust in Mining--A Toolbox,'' which
includes additional information on methods for controlling dpm, and a
glossary of terms.
Part III is the Agency's risk assessment. The first section
presents the Agency's data on current dpm exposure levels in each
sector of the mining industry. The second section reviews the
scientific evidence on the risks associated with exposure to dpm. The
third section evaluates this evidence in light of the Mine Act's
statutory criteria.
Part IV is a detailed section-by-section explanation and discussion
of the elements of the proposed rule.
Part V is an analysis of whether the proposed rule meets the
Agency's statutory obligation to attain the highest degree of safety or
health protection for miners, with feasibility a consideration. This
part begins with a review of the law and a profile of the coal
industry's economic position. This next part explores the extent to
which the proposed rule is expected to impact existing concentration
levels, reviews significant alternatives that might provide more
protection than the rule being proposed but which have not been adopted
by the Agency due to feasibility concerns, and then discusses the
feasibility of the rule being proposed. Part V draws upon a computer
simulation of how the proposed rule in underground coal mines is
expected to impact dpm concentrations; accordingly, an Appendix to this
discussion provides information about the simulation methodology. The
simulation method, which can be performed using a standard spreadsheet
program, can be used to model conditions and control impacts in any
underground mine; copies of this model are available to the mining
community from MSHA.
Part VI reviews several impact analyses which the Agency is
required to provide in connection with a proposed rulemaking. This
information summarizes a more complete discussion that can be found in
the Agency's Preliminary Regulatory Economic Analysis (PREA). Copies of
this document are available from the Agency and will be posted on the
MSHA Web site (http://www.msha.gov).
Part VII is a complete list of publications referenced by the
Agency in the preamble.
(3) What Evidence Does MSHA Have That Current Underground
Concentrations of DPM Need To Be Controlled?
The best available evidence MSHA has at this time is that miners
subjected to an occupational lifetime of dpm exposure at concentrations
we presently find in underground mines face a significant risk of
material impairment to their health.
It has been recognized for some time that miners working in close
contact with diesel emissions can suffer acute reactions--e.g., eye,
nose and throat irritations--but questions have persisted as to what
component of the emissions was causing these problems, whether exposure
increased the risk of other adverse health effects, and the level of
exposure creating health consequences.
In recent years, there has been growing evidence that it is the
very small respirable particles in diesel exhaust (dpm) that trigger a
variety of
[[Page 17495]]
adverse health outcomes. These particles are generally less than one-
millionth of a meter in diameter (submicron), and so can readily
penetrate into the deepest recesses of the lung. They consist of a core
of the element carbon, with up to 1,800 different organic compounds
adsorbed onto the core, and some sulfates as well. (A diagram of dpm
can be found in part II of this preamble--see Figure II-3). The
physiological mechanism by which dpm triggers particular health
outcomes is not yet known. One or more of the organic substances
adsorbed onto the surface of the core of the particles may be
responsible for some health effects, since these include many known or
suspected mutagens and carcinogens. But some or all of the health
effects might also be triggered by the physical properties of these
tiny particles, since some of the health effects are observed with high
exposures to any ``fine particulate,'' whether the particle comes from
diesel exhaust or another source.
There is clear evidence that exposure to high concentrations of dpm
can result in a variety of serious health effects. These health effects
include: (i) sensory irritations and respiratory symptoms serious
enough to distract or disable miners; (ii) death from cardiovascular,
cardiopulmonary, or respiratory causes; and (iii) lung cancer.
By way of example of the non-cancer effects, there is evidence that
workers exposed to diesel exhaust during a single shift suffer material
impairment of lung capacity. A control group of unexposed workers
showed no such impairment, and workers exposed to filtered diesel
exhaust (i.e., exhaust from which much of the dpm has been removed)
experienced, on average, only about half as much impairment. Moreover,
there are a number of studies quantifying significant adverse health
effects--as measured by lost work days, hospitalization and increased
mortality rates--suffered by the general public when exposed to
concentrations of fine particulate matter like dpm far lower than
concentrations to which some miners are exposed. The evidence from
these fine particulate studies was the basis for recent rulemaking by
the Environmental Protection Agency to further restrict the exposure of
the general public to fine particulates, and the evidence was given
very widespread and close scrutiny before that action was made final.
Of particular interest to the mining community is that these fine
particulate studies indicate that those who have pre-existing pulmonary
problems are particularly at risk. Many individual miners in fact have
such pulmonary problems, and the mining population as a whole is known
to have such conditions at a higher rate than the general public.
Although no epidemiological study is flawless, numerous
epidemiological studies have shown that long term exposure to diesel
exhaust in a variety of occupational circumstances is associated with
an increased risk of lung cancer. With only rare exceptions, involving
relatively few workers and/or observation periods too short to reliably
detect excess cancer risk, the human studies have consistently shown a
greater risk of lung cancer among workers exposed to dpm than among
comparable unexposed workers. When results from the human studies are
combined, the risk is estimated to be 30-40 percent greater among
exposed workers, if all other factors (such as smoking habits) are held
constant. The consistency of the human study results, supported by
experimental data establishing the plausibility of a causal connection,
provides strong evidence that chronic dpm exposure at high levels
significantly increases the risk of lung cancer in humans.
Moreover, all of the human occupational studies indicating an
increased frequency of lung cancer among workers exposed to dpm
involved average exposure levels estimated to be far below the levels
observed in underground mines. As noted in Part III, MSHA views
extrapolations from animal experiments as subordinate to results
obtained from human studies. However, it is noteworthy that dpm
exposure levels recorded in some underground mines have been within the
exposure range that produced tumors in rats.
Based on the scientific data available in 1988, the National
Institute for Occupational Safety and Health (NIOSH) identified dpm as
a probable or potential human carcinogen and recommended that it be
controlled. Other organizations have made similar recommendations.
MSHA carefully evaluated all the evidence available in light of the
requirements of the Mine Act. Based on this evaluation, MSHA has
reached several conclusions:
(1) The best available evidence is that the health effects
associated with exposure to dpm can materially impair miner health or
functional capacity.
(2) At levels of exposure currently observed in underground mining,
many miners are presently at significant risk of incurring these
material impairments over a working lifetime.
(3) The reduction in dpm exposures that is expected to result from
implementation of the proposed rule for underground coal mines would
substantially reduce the significant risks currently faced by
underground coal miners exposed to dpm.
MSHA had its risk assessment independently peer reviewed. The risk
assessment presented here incorporates revisions made in accordance
with the reviewers recommendations. 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).
The proposed rule would reduce the concentration of one type of
fine particulate in underground coal mines--that from diesel
emissions--but would not explicitly control miner exposure to other
fine airborne particulates present underground. In light of the
evidence presented in the Agency's risk assessment on the risks that
fine particulates in general may pose to the mining population, MSHA
would welcome comments as to whether the Agency should also consider
restricting the exposure of underground coal miners to all fine
particulates, regardless of the source.
(4) Aren't NIOSH and the NCI Working on a Study That Will Provide
Critical Information? Why Proceed Before the Evidence Is Complete?
NIOSH and the National Cancer Institute (NCI) are collaborating on
a cancer mortality study that will provide additional information about
the relationship between dpm exposure levels and disease outcomes, and
about which components of dpm may be responsible for the observed
health effects. The study is projected to take about seven years. The
protocol for the study was recently finalized.
The information the study is expected to generate will be a
valuable addition to the scientific evidence on this topic. But given
its conclusions about currently available evidence, MSHA believes the
Agency needs to take action now to protect miners' health. Moreover, as
noted by the Supreme Court in an important case on risk involving the
Occupational Safety and Health Administration, the need to evaluate
risk does not mean an agency is placed into a ``mathematical
straightjacket.'' Industrial Union Department, AFL-CIO v. American
Petroleum Institute, 448 U.S. 607, 100 S.Ct. 2844 (1980). The Court
noted that
[[Page 17496]]
when regulating on the edge of scientific knowledge, absolute
scientific certainty may not be possible, and ``so long as they are
supported by a body of reputable scientific thought, the Agency is free
to use conservative assumptions in interpreting the data * * * risking
error on the side of overprotection rather than underprotection.'' (Id.
at 656). This advice has special significance for the mining community,
because a singular historical factor behind the enactment of the
current Mine Act was the slowness in coming to grips with the harmful
effects of other respirable dust (coal dust).
It is worth noting that while the cohort selected for the NIOSH/NCI
study consists of underground miners (specifically, underground metal
and nonmetal miners), this choice is in no way linked to MSHA's
regulatory framework or to miners in particular. This cohort was
selected for the study because it provides the best population for
scientists to study. For example, one part of the study would compare
the health experiences of miners who have worked underground in mines
with long histories of diesel use with the health experiences of
similar miners who work in surface areas where exposure is
significantly lower. Since the general health of these two groups is
very similar, this will help researchers to quantify the impacts of
diesel exposure. No other population is as easy to study for this
purpose. But as with any such epidemiological study, the insights
gained are not limited to the specific population used in the study.
Rather, the study will provide information about the relationship
between exposure and health effects that will be useful in assessing
the risks to any group of workers in a dieselized industry.
(5) What are the Impacts of the Proposed Rule?
Costs. Tables I-1 and I-2 provide cost information. Some
explanation is necessary.
Costs consist of two components: ``initial'' costs (e.g., capital
costs for equipment, or the one-time costs of developing a procedure),
which are then amortized over a period of years in accordance with a
standardized formula to provide an ``annualized'' cost; and ``annual''
costs that occur every year (e.g., maintenance or training costs).
Adding together the ``annualized'' initial costs and the ``annual''
costs provides the per year costs for the rule.
It should be noted that in amortizing the initial costs, a net
present value factor was applied to certain costs: those associated
with provisions where mine operators do not have to make capital
expenditures until some period of time after the effective date.
Detailed information on this point is contained in the Agency's
Preliminary Regulatory Economic Analysis (PREA), as are the Agency's
cost assumptions.
The costs per year to the underground coal industry are about $10
million. Diesel equipment manufacturers would have a yearly cost
increase of about $14,000.
The Agency spent considerable time developing its cost assumptions,
which are discussed in detail in the Agency's PREA, and would encourage
the mining community to provide detailed comments in this regard so as
to ensure these cost estimates are as accurate as possible.
Table I-1.--Compliance Costs for Underground Coal Mines
[Dollars + 1,000]
Large mines (20) Small mines (g/m\3\ (roughly corresponding to a reduction of 25 g/
m\3\ in 24-hour ambient atmospheric concentration) could lead to
significant reductions in the risk of various acute responses,
including mortality. And chronic occupational exposure has been linked
to an estimated 30 to 40 percent increase in the risk of lung cancer.
All the quantitative risk models reviewed by NIOSH suggest excess risks
of lung cancer of more than one per thousand for miners who have long-
term occupational exposures to dpm concentrations in excess of 1000
g/m\3\, and the epidemiologically-based risk estimates suggest
higher risks.
Despite these quantitative indications, quantification of the
benefits is difficult. Although increased risk of lung cancer has been
shown to be associated with dpm exposure among exposed workers, a
conclusive dose-response relationship upon which to base quantification
of benefits has not been demonstrated. The Agency nevertheless intends,
to the extent it can, to develop an appropriate analysis quantifying
benefits in connection with the final rule.
The Agency does not have much experience in quantifying benefits in
the case of a proposed health standard (other than its recent proposal
on controlling mining noise, where years of compliance data and hearing
loss studies provide a much more complete quantitative picture than
with dpm). MSHA therefore welcomes suggestions for the appropriate
approach to use to quantify the benefits likely to be derived from this
rulemaking. Please identify scientific studies, models, and/or
assumptions suitable for estimating risk at different exposure levels,
and data on numbers of miners exposed to different levels of dpm.
(6) Did MSHA Actively Consider Alternatives to What Is Being Proposed?
Yes. Once MSHA determined that the evidence of risk required a
regulatory action, the Agency considered a number of alternative
approaches, the most significant of which are reviewed in part V of the
preamble.
The consideration of options proceeded in accordance with the
requirements of section 101(a)(6)(A) of the Federal Mine Safety and
Health Act of 1977 (the ``Mine Act''). In promulgating standards
addressing toxic materials or harmful physical agents, the Secretary
must promulgate standards which most adequately assure, on the basis of
the best available evidence, that no miner will suffer material
impairment of health over his/her working lifetime. In addition, the
Mine Act requires that the Secretary, when promulgating mandatory
standards pertaining to toxic materials or harmful physical agents,
consider other factors, such as the latest scientific data in the
field, the feasibility of the standard and experience gained under the
Mine Act and other health and safety laws. Thus, the Mine Act requires
that the Secretary, in promulgating a standard, attain the highest
degree of health and safety protection for the miner, based on the
``best available evidence,'' with feasibility a consideration.
As a result, MSHA seriously considered a number of alternatives
that would, if adopted as part of the proposed rule, have provided
increased protection--and would also have significantly increased
costs. For example, in underground coal mining, the Agency considered
requiring filtration of all light-duty diesel-powered equipment as well
as heavier equipment. The Agency concluded, however, that such an
approach may not be feasible for the underground coal sector at this
time, although it is asking for comment as to whether there are some
types of light-duty equipment whose dpm emissions should, and could
feasibly, be controlled.
MSHA also considered alternatives that would have led to a
significantly lower-cost proposal, e.g., increasing the time for mine
operators to come into compliance. However, based on the current
record, MSHA has tentatively concluded that such approaches would not
be as protective as those being proposed, and that the approach
proposed is both economically and technologically feasible. As a
result, the Agency has not proposed to adopt these alternatives.
MSHA also explored whether to permit the use of administrative
controls (e.g., rotation of personnel) and personal protective
equipment (e.g., respirators) to reduce the diesel particulate exposure
of miners. It is generally accepted industrial hygiene practice,
however, to eliminate or minimize hazards at the source before
resorting to personal protective
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equipment. Moreover, such a practice is generally not considered
acceptable in the case of carcinogens since it merely places more
workers at risk.
Other alternatives the Agency considered include: establishing a
concentration limit for dpm in this sector; requiring filters on some
light-duty equipment; and looking at the filter and the 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.
The Agency also spent a considerable amount of time studying whether it
could simply propose a concentration limit for dpm in underground coal
mines. Such an approach would provide underground coal mine operators
with flexibility to elect any combination of engineering controls they
wish as long as the concentration of dpm in the mine remains below a
set level. At this point in the rulemaking process, however, the Agency
is 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. As discussed in detail
in part II of this preamble, the problem arises because coal dust
contains organic compounds that might be mistaken for dpm in the
methods otherwise validated for use at lower dpm concentrations. The
Agency is continuing to explore questions about the measurement of dpm
in underground coal mines in consultation with NIOSH, and welcomes
comment on this issue. However, at this point in the rulemaking
process, the Agency believes that the best approach for the underground
coal sector would be one which does not require measurement of ambient
dpm levels to ascertain compliance or noncompliance.
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.
MSHA did consider 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.
The Agency believes, however, that these alternatives may be less
protective of miners than the alternative proposed, although it is
seeking comment on them. More information on these two alternatives can
be found in this part in response to Question 12.
(7) What Will the Impact Be on the Smallest Underground Coal Mines?
What Consideration Did MSHA Give to Alternatives for the Smallest
Mines?
The Regulatory Flexibility Act requires MSHA and other regulatory
agencies to conduct a review of the effects of proposed rules on small
entities. That review is summarized here; a copy of the full review is
included in part VI of this preamble, and in the Agency's PREA. The
Agency encourages the mining community to provide comments on this
analysis.
The Small Business Administration generally considers a small
mining entity to be one with less than 500 employees. MSHA has
traditionally defined a small mine to be one with less than 20 miners,
and has focused special attention on the problems experienced by such
mines in implementing safety and health rules, e.g., the Small Mine
Summit, held in 1996. Accordingly, MSHA has separately analyzed the
impact of the proposed rule on mines with 500 employees or less, and
those with less than 20 miners.
Table I-5 summarizes MSHA's estimates of the average costs of the
proposed rule to a small underground coal entity or small underground
coal mine.
Table I-5.--Average Cost per Small Underground Coal Mine
------------------------------------------------------------------------
UG Coal UG Coal
Size DPM g/
m3), the package would be acceptable without regard to the
efficiency of just the filter component. Alternative 2 would also
provide credit in filter selection for extra ventilation used in an
underground coal mine. If the bench test of the combined engine and
filter package was conducted at the name plate ventilation, a mine's
use of more than that level of ventilation would be factored into the
calculation of what package would be acceptable.
One practical effect of these alternatives would be to permit some
operators to save the costs of installing heat exchangers or other
exhaust-cooling devices on nonpermissible heavy-duty equipment. Such
devices are necessary in order for this equipment to be fitted with
paper filters--and as noted in response to the previous question, at
the moment these are the only filters on the market capable of
providing 95% and more filtration capability.
The appropriateness of Alternative 1 is not clear. With the proper
equipment to cool the exhaust, a 95% paper filter can be installed on
any piece of heavy-duty equipment in coal mines--and of course directly
on any permissible piece of equipment. And, as indicated herein, the
Agency is tentatively concluding that such an approach is economically
feasible as well. Installing a 95% efficient filter on an engine lowers
the dpm concentration in the mine more than would installing a less
efficient filter. Hence for engines whose emissions can, with a 95%
filter, be reduced below 120DPM g/m3 or
whatever other dpm limit is set under such an approach, the alternative
approach may result in less miner protection.
Moreover, it is not clear to MSHA that 95% filtration of the
engines used on the majority of permissible machines in underground
coal mines can meet an emissions limit of 120DPM g/
m3 using MSHA's name plate ventilation. These engines are of
older design and produce higher concentrations of diesel particulate.
Thus adopting a rule with such an emissions limit would in effect
require these engines to be replaced with cleaner engines. Of course,
it follows that such a rule would be more costly than the one proposed,
because it would require the 95% filters plus the replacement of these
engines.
The second alternative appears to be less protective in all cases.
To provide mines who need extra ventilation for other reasons (e.g., to
keep methane in check) with a credit for this fact in determining the
required filter efficiency would not reduce dpm concentrations as much
as simply requiring a 95% filter.
The Agency welcomes comments on these approaches and information
that will help it assess them in light of the requirements of the Mine
Act.
II. Background Information
This part provides the context for this rulemaking. The nine topics
covered are:
(1) The role of diesel-powered equipment in mining;
(2) Diesel exhaust and diesel particulate;
(3) Methods available to measure DPM;
(4) Reducing soot at the source--engine standards;
(5) Limiting the public's exposure to soot -- ambient air quality
standards;
(6) Controlling diesel particulate emissions in mining--a toolbox;
(7) Existing mining standards that limit miner exposure to
occupational diesel particulate emissions;
(8) How other jurisdictions are restricting occupational exposure
to diesel soot; and
(9) MSHA's initiative to limit miner exposure to diesel
particulates--the history of this rulemaking and related actions.
In addition, an Appendix at the end of this document reprints a
recent MSHA publication, ``Practical Ways to Reduce Exposure to Diesel
Exhaust in Mining--A Toolbox'', which contains considerable information
of interest in this rulemaking.
These topics will be of interest to the entire mining community,
even though this rulemaking is specifically confined to the underground
coal sector.
(1) The Role of Diesel-Powered Equipment in Mining. Diesel engines
now power a full range of mining equipment on the surface and
underground, in both coal and in metal/nonmetal mining. Many in the
mining industry believe that diesel-powered equipment has a number of
productivity and safety advantages over electrically-powered equipment.
Nevertheless, concern about miner safety and health has slowed the
spread of this technology, and in certain states resulted in a complete
ban on its use in underground coal mines. As the industry has moved to
realize the advantages this equipment may provide, the Agency has
endeavored to address
[[Page 17502]]
the miner safety and health issues presented.
Historical Patterns of Use
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 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 the diesel engine became an efficient
lightweight power unit. 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, however, 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 even 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, such
as: air compressor; ambulance; crane truck; ditch digger; foam machine;
forklift; generator; grader; haul truck; load-haul-dump machine;
longwall retriever; locomotive; lube unit; mine sealant machine;
personnel car; hydraulic pump machine; rock dusting machine; roof/floor
drill; shuttle car; tractor; utility truck; water spray unit and
welder.
Estimates of Current Use
Estimates of the current inventory of diesel engines in the mining
industry are displayed in Table II-1. Not all of these engines are in
actual use. Some may be retained rather than junked, and others are
spares. MSHA has been careful to take this into account in developing
cost estimates for this proposed rule; its assumptions in this regard
are detailed in the Agency's PREA.
Table II-1.--Diesel Equipment in Three Mining Sectors
------------------------------------------------------------------------
No.
Mine type No. Mines w/ No.
Mines Diesel Engines
----------------------------------------------\2\-----------------------
Underground Coal......................... 971 \3\ 173 \4\ 2,950
\1\ Small............................ 426 15 50
Large................................ 545 158 2,900
Underground M/NM......................... 261 \5\ 203 \6\ 4,100
\1\ Small............................ 130 82 625
Large................................ 131 121 3,475
Surface Coal............................. 1,673 \7\ 1,67
3 \8\ 22,00
0
\1\ Small............................ 1,175 1,175 7,000
Large................................ 498 498 15,000
Surface M/NM............................. 10,474 \9\ 10,4
74 \10\ 97,0
00
------------------------------------------------------------------------
Notes on Table II-1:
\1\ A mine with less than 20 miners. MSHA traditionally regards mines
with less than 20 miners as ``small'' mines, and those with 20 or more
miners as ``large'' mines based on differences in operation. However,
in examining the impact of the proposed regulations on the mining
community, MSHA, consistent with the Small Business Administration
definition for small mines, which refers to employers with 500
employees or less, has analyzed impact for this size. This is
discussed in the Agency's preliminary regulatory economic analysis for
this proposed rule.
\2\ Preliminary 1996 MSHA data.
\3\ Data from MSHA approval and certification center, Oct.95.
\4\ Actual inventory, rounded to nearest 50.
\5\ Estimates are based on a January 1998 count, by MSHA inspectors, of
underground mines that use diesel powered equipment.
\6\ The estimates are based on a January 1998 count, by MSHA inspectors,
of diesel powered equipment normally in use.
\7\ Based on assumption that all surface coal mines had some diesel
powered equipment.
\8\ Based on MSHA survey of 25% of surface coal mines.
\9\ MSHA assumes all surface M/NM mines use some diesel engines.
\10\ Derived by applying ratios (engines per mine) from MSHA survey of
surface coal mines to M/NM mines.
As noted in Table II-1, nearly all underground metal and nonmetal
mines, and all surface mines, use diesel-powered equipment. This is not
true in underground coal mines--in no small measure because, as
discussed later in this part, several key underground coal states have
for many years banned the use of diesel-powered equipment in such
mines.
Neither the diesel engines nor the diesel-powered equipment are
identical from sector to sector. This relates to the equipment needs in
each sector. This is important information because the type of engine,
and the type of equipment in which it is installed, can have important
consequences for particulate production and control.
As the horsepower size of the engine increases, the mass of dpm
emissions produced per hour increases. (A smaller engine may produce
the same or higher levels of particulate emissions per volume of
exhaust as a large engine, due to the airflow, but the mass of
particulate matter increases with the engine size.) Accordingly, as
engine size increases, control of emissions may require additional
efforts.
Diesel engines in underground metal and nonmetal mines, and in
surface coal mines, range up to 750 HP or greater; by contrast, in
underground coal mines, the average engine size is less than 150 HP.
The reason for this disparity is the nature of the equipment powered by
diesel engines. In underground metal and nonmetal mines, and surface
mines, diesel engines are widely used in all types of equipment--both
the equipment used under the heavy stresses of production and the
equipment used for support. By contrast, the great majority of the
diesel usage in underground coal mines is in support equipment. For
example, in underground metal and nonmetal mines, of the approximate
4,100 pieces of diesel equipment normally in use, about 1,800 units are
for loading and hauling. By contrast, of the approximate 3,000 pieces
of diesel equipment in underground coal, MSHA estimates that less than
50 pieces are for coal haulage. The largest diesel engines are used in
surface operations; in underground metal and nonmetal mines, the size
of the engine can be limited by the size of the shaft opening.
The type of equipment in the sectors also varies in another way
that can affect particulate control directly, as well as constrain
engine size. In underground coal, equipment that is used in face
(production) areas of the coal mine must be MSHA-approved part 36
permissible equipment. These locations are the areas where methane gas
is likely to accumulate in higher concentrations. This includes the in-
by section starting at the tailpiece (coal dump point) and all returns.
Part 36 permissible equipment for coal requires the use of flame
arresters on the intake and exhaust systems and surface temperature
control to below 302 deg.F. As
[[Page 17503]]
discussed in more detail elsewhere in this notice, the cooler exhaust
from these permissible pieces of equipment permits the direct
installation of particulate filtration devices such as paper type
filters that cannot be used directly on engines with hot exhaust. In
addition, the permissibility requirements have had the effect of
limiting engine size. This is because prior to MSHA's issuance of a
diesel equipment rule in 1996, surface temperature control was done by
water jacketing. This limited the horsepower range of the permissible
engines because manufacturers have not expended resources to develop
systems that could meet the 302 deg.F surface temperature limitation
using a water jacketed turbocharger.
In the future, larger engines may be used on permissible equipment,
because the new diesel rule allows the use of new technologies in lieu
of water jacketing. This new technology, plus the introduction of air-
charged aftercoolers on diesel engines, may lead to the application of
larger size diesel engines for underground coal production units.
Moreover, if manufacturers choose to develop this type of technology
for underground coal production units, the number of diesel production
machines may increase.
There are also a few underground metal and nonmetal mines that are
gassy, and these require the use of part 36 permissible equipment.
Permissible equipment in metal and nonmetal mines must be able to
control surface temperatures to 400 deg. F. MSHA estimates that there
are currently less than 15 metal and nonmetal mines classified as gassy
and which, therefore, must use part 36 permissible equipment if diesels
are utilized in areas where permissible equipment is required. These
gassy metal and nonmetal mines have been using the same permissible
engines and power packages as those approved for underground coal
mines. (MSHA has not certified a diesel engine exclusively for a part
36 permissible machine for the metal and nonmetal sector since 1985 and
has certified only one permissible power package; however, that engine
model has been retired and is no longer available as a new purchase to
the industry). As a result, these mines are in a similar situation as
underground coal mines: engine size (and thus dpm production of each
engine) is more limited, and the exhaust is cool enough to add the
paper type of filtration device directly to the equipment.
In nongassy underground metal and nonmetal mines, and in all
surface mines, mine operators can use conventional construction
equipment in their production sections without the need for
modifications to the machines. Two examples are haulage vehicles and
dump trucks. Some construction vehicles may be redesigned and
articulated for sharper turns in underground mines; however, the
engines are still the industrial type construction engines. As a
result, these mines can and do use engines with larger horsepower. At
the same time, since the exhaust is not cooled, paper-type filters
cannot be added directly to this equipment without first adding a water
scrubber, heat exchanger or other cooling device. The same is true for
the equipment used in outby areas of coal mines, where the methane
levels do not require the use of permissible equipment.
Future Demand and Emissions
MSHA expects there will be more diesel-powered equipment added to
the Nation's mines. While other types of power sources for mining
equipment are available, many in the mining industry believe that
diesel power provides both safety and economic advantages over
alternative power sources available today. Not many studies have been
done recently on these contentions, and the studies which have been
reviewed by MSHA do not clearly support this hypothesis; but as long as
this view remains prevalent, continued growth is likely.
There are additional factors that could increase growth. As noted
above, permissible equipment can now be designed in such a way to
permit the use of larger engines, and in turn more use of diesel-
powered production equipment in underground coal and other gassy mines.
Moreover, state laws banning the use of diesel engines in the
underground coal sector are under attack. As noted in section 8 of this
part, until recently, three major underground coal states,
Pennsylvania, West Virginia, and Ohio, have prohibited the use of
diesel engines in underground coal mines. In late 1996, Pennsylvania
passed legislation (PA Senate Bill No. 1643) permitting such use under
conditions defined in the statute. West Virginia passed legislation
lifting its ban as of May, 1997 (WV House Bill 2890), subject to
regulations to be developed by a joint labor-industry commission. This
makes the need to address safety and health concerns about the use of
such engines very pressing.
In the long term, the mining industry's diesel fleet will become
cleaner, even if the size of the fleet expands. This is because the old
engines will eventually be replaced by new engines that will emit fewer
particulates than they do at present. As discussed in section 4 of this
part, EPA regulations limiting the emissions of particulates and
various gasses from new diesel engines are already being implemented
for some of the smaller engines used in mining. Under a defined
schedule, these new standards will soon apply to other new engines,
including the larger engines used in mining. Moreover, over time, the
emission standards which new engines will have to pass will become more
and more stringent. Under international accords, imported engines are
also likely to be cleaner: European countries have already established
more stringent emission requirements (Needham, 1993; Sauerteig, 1995).
But MSHA believes that turnover of the mining fleet to these new,
cleaner engines will take a very long time because the mining industry
tends to purchase for mining use older equipment that is being
discarded by other industries. In the meantime, the particulate burden
on miners as a group is expected to remain at current levels or even
grow.
(2) Diesel Exhaust and Diesel Particulate. 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 being 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. Elevation, for example, is
a factor. 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) are worth
particular mention because in the atmosphere they can precipitate into
particulate matter. Thus, controlling the emissions of NOX
is one way that engine manufacturers can control particulate production
indirectly. (See section 4 of this part).
The particulate fraction of diesel exhaust--what is known as soot--
is made up of very small individual particles. Each particle consists
of an insoluble, elemental carbon core and an
[[Page 17504]]
adsorbed, surface coating of relatively soluble organic carbon
(hydrocarbon) compounds. There can be up to 1,800 different organic
compounds adsorbed onto the elemental carbon core. A portion of this
hydrocarbon material is the result of incomplete combustion of fuel;
however, the majority is derived from the engine lube oil. In addition,
the diesel particles contain a fraction of non-organic adsorbed
materials.
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. In underground metal and nonmetal
mines, a greater portion of the aggregates may be larger than 1 micron
in size because of the equipment used. Dust generated by mining and
crushing of material--e.g., silica dust, coal dust, rock dust--is
generally not submicrometer in size.
Figure II-1 shows a typical size distribution of the particles
found in the environment of a mine that uses equipment powered by
diesel engines (Cantrell and Rubow, 1992). The vertical axis represents
relative concentration, and the horizontal axis the particle diameter.
As can be seen, the distribution is bimodal, with dpm generally being
well less than 1 m in size and dust generated by the mining process
being well greater than 1 m. Because of their small size, even when
diesel particles are present in large quantities, the environment might
not be perceived as ``dusty''. Rather, the perception might be
primarily of a vaporous, dirty and smelly ``soot'' or ``smoke''.
[GRAPHIC] [TIFF OMITTED] TP09AP98.001
The particulate nature of diesel soot has special significance for
the mining community, which has a history of significant health and
safety problems associated with dusts in the mining atmosphere. As a
result of this long experience, the mining community is familiar with
the standard techniques to control particulate concentrations. It knows
how to use ventilation systems, for example, to reduce dust levels in
underground mines. It knows how to water down particulates capable of
being impacted by that approach, and to divert particulates away from
where miners are actively working. Moreover, the mining community has
long experience in the sampling and measurement of particulates--and in
all the problems associated therewith. Miners and mine operators are
very familiar with sampling devices that are worn by miners during
normal work activities or placed in specific locations to collect dust.
They understand the significance of sample integrity, the validity of
laboratory analysis, and the concept of statistical error in individual
samples. They know that weather and mine conditions can affect
particulate production, as can changes in mine operations in an area of
the mine. MSHA and the former Bureau of Mines have conducted
considerable research into these topics. While the mining community has
often argued over these points, and continues to do so, the
sophistication of the arguments reflects the thorough familiarity of
the mining community with particulate sampling and analysis techniques.
(3) Methods Available to Measure DPM. There are a number of methods
which can measure dpm concentrations with reasonable accuracy when it
is at high concentrations and when the purpose is exposure assessment.
Measurements for the purpose of compliance determinations must be more
accurate, especially if they are to measure compliance with a dpm
concentration as low as 200 g/m3 or lower. It is
with these considerations in mind that MSHA has carefully analyzed
[[Page 17505]]
the available methods for measuring dpm.
Comments. In its advanced notice of proposed rulemaking (ANPRM) in
1992, MSHA sought information on whether there are methodologies
available for assessing occupational exposures to diesel particulate.
Some commenters argued that at that time there was no validated
sampling method for diesel exhaust and there had been no valid
analytical method developed to determine the concentration of diesel
exhaust. According to the American Mining Congress, (AMC 1992),
sampling methods commonly in use were prototypic in nature, were
primarily being utilized by government agencies and were subject to
interference. Commenters also stated that sampling instrumentation was
not commercially available and that the analytical procedures could
only be conducted in a limited number of laboratories. Several industry
commenters submitted results of studies to support their position on
problems with measuring diesel particulate in underground mines. A
problem with sampler performance was noted in a study using prototype
dichotomous sampling devices. Another commenter indicated that the
prototype sampler developed by the former Bureau of Mines (discussed
later in this section) for collecting the submicrometer respirable dust
was difficult to assemble but easy to use, and that no problems were
encountered. Problems associated with gravimetric analysis were also
noted in assessing a short term exposure limit (STEL). Another
commenter (Morton, 1992) indicated the cost of the sampling was
prohibitive.
Another issue addressed by commenters to the 1992 ANPRM was ``Are
existing sampling and exposure monitoring methods sufficiently
sensitive, accurate and reliable?'' If not, what methods would be more
suitable? Some commenters indicated their views that sampling methods
had not been validated at that time for compliance sampling. They
asserted that, depending on the level of measurement, both the size
selective and elemental carbon techniques have some utility. The
measurement devices give a precise measurement; however, because of
interferants, corrections may need to be made to obtain an accurate
measurement. Commenters also expressed the view that all of the
sampling devices are sophisticated and require some expertise to
assemble and analyze the results, and that MSHA should rely on outside
agencies to evaluate and validate the sampling methods. An on-board
sampler being developed by Michigan Technological University was the
only other emission measurement technology discussed in the comments.
However, this device is still in the development stage. Another
commenter indicated that the standard should be based on the hazard and
that the standard would force the development of measurement
technology.
Submicrometer Sampling
The former Bureau of Mines (BOM) submitted information on the
development of a prototype dichotomous impactor sampling device that
separates and collects the submicrometer respirable particulate from
the respirable dust sampled (See Figure II-2).
[GRAPHIC] [TIFF OMITTED] TP09AP98.002
The sampling device was designed to help measure dpm in coal mine
environments, where, as noted in the last section of this part, nearly
all the dpm is submicrometer (less than 1 micron) in size. In its
submission to MSHA, the former BOM noted it had redesigned a prototype
and had verified the sampler's performance through laboratory and field
tests.
As used by the former BOM in its research, the submicrometer
respirable particulate was collected on a pre-weighed filter. Post-
weighing of the filter provides a measure of the submicrometer
respirable particulate. The relative insensitivity of the gravimetric
method only allows for a lower limit of detection of approximately 200
g/m3. Because submicrometer respirable particulate
can contain particulate material other than diesel particulate,
measurements can be subject to interference from other submicrometer
particulate material.
[[Page 17506]]
NIOSH Method 5040
In response to the ANPRM, NIOSH submitted information relative to
the development of a sampling and analytical method to assess the
diesel particulate concentration in an environment by measuring the
amount of total carbon.
As discussed earlier in this part, diesel particulate consists of a
core of elemental carbon (EC), adsorbed organic carbon (OC) compounds,
sulfates, vapor phase hydrocarbons and traces of other compounds. The
method developed by NIOSH provides for the collection of a sample on a
quartz fiber filter. The filter is mounted in an open face filter
holder that allows for the sample to be uniformly deposited on the
filter surface. After sampling, a section of the filter is analyzed
using a thermal-optical technique (Birch and Cary, 1996). This
technique allows the EC and OC species to be separately identified and
quantified. Adding the EC and OC species together provides a measure of
the total carbon concentration in the environment. This is indicated
diagrammatically in Figure II-3.
Studies have shown that the sum of the carbon (C) components (EC +
OC) associated with dpm accounts for 80-85% of the total dpm
concentration when low sulfur fuel is used (Birch and Cary, 1996).
Since the TC:DPM relationship is consistent, it provides a method for
determining the amount of dpm.
The method can detect as little as 1 g/m3 of
TC.
[GRAPHIC] [TIFF OMITTED] TP09AP98.003
Moreover, NIOSH has investigated the method and found it to meet
NIOSH's accuracy criterion (NIOSH, 1995); i.e., that measurements come
within 25 percent of the true TC concentration at least 95 percent of
the time.
NIOSH Method 5040 is directly applicable for the determination of
diesel particulate levels in underground metal and nonmetal mines. The
only potential sources of carbon in such mines would be organic carbon
from oil mist and cigarette smoke. Oil mist may occur when diesel
equipment malfunctions or is in need of maintenance. MSHA, currently,
has no data as to the frequency of occurrence or the magnitude of the
potential interference from oil mist. However, during studies conducted
by MSHA to evaluate different methods used to measure diesel
particulate concentrations in underground mines, MSHA has not
encountered situations where oil mist was found to be an interferant.
Moreover, the Agency assumes that full operator implementation of
maintenance standards to minimize dpm emissions (which are part of
MSHA's proposed rule) will minimize any remaining potential for such
interference. MSHA welcomes comments or data relative to oil mist
interference. Cigarette smoke is under the control of operators, during
sampling times in particular, and hence should not be a consideration.
While samples in underground metal and nonmetal mines could be
taken with a submicrometer impactor, this could lead to underestimating
the total amount of dpm present. This is because the fraction of dpm
particles greater than 1 micron in size in the environment of noncoal
mines can be as great as 20% (Vuk, Jones, and Johnson, 1976).
When sampling diesel particulate in coal mines, the NIOSH method
recommends that a specialized impactor with a submicrometer cut point,
such as the one developed by the former BOM, be used. Use of the
submicron impactor minimizes the collection of coal particles, which
have an organic carbon content. However, if 10% of coal particles are
submicron, this means that up to 200 micrograms of submicrometer coal
dust could be collected in face areas under current coal dust
standards. Accordingly, for samples collected in underground coal
mines, an adjustment may have to be made for interference from
submicrometer coal dust; however, outby areas where little coal mine
dust is present may not need such an adjustment.
NIOSH further recommends that in using its method in coal mines,
the sample only be analyzed for the EC component. Measuring only the EC
component ensures that only diesel particulate material is being
measured in such cases. However, there are no established relationships
between the concentration of EC 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 EC may vary). The Agency welcomes data and
suggestions that would help it ascertain if and how measurements of
[[Page 17507]]
submicrometer elemental carbon could realistically be used to measure
dpm concentrations in underground coal mines.
Although NIOSH Method 5040 requires no specialized equipment for
collecting a dpm sample, the sample would most probably require
analysis by a commercial laboratory. MSHA recognizes that the number of
laboratories currently capable of analyzing samples using the thermal-
optical method is limited. However, there are numerous laboratories
available that have the ability to perform a TC analysis without
identifying the different species of carbon in the sample. Total carbon
determinations using these laboratories would provide the mine with
good information relative to the levels of dpm to which miners are
potentially exposed. MSHA believes that once there is a need (e.g., as
a result of the requirements of the proposed rule), more commercial
laboratories will develop the capability to analyze dpm samples using
the thermo-optical analytical method. Currently, the cost to analyze a
submicrometer particulate sample for its TC content ranges from $30 to
$50. This cost is consistent with costs associated with similar
analysis of minerals such as quartz.
RCD Method
Another method, referred to as the Respirable Combustible Dust
Method (RCD), has been developed in Canada for measuring dpm
concentrations in noncoal mines. Respirable dust is collected with a
respirable dust sampler consisting of a 10 millimeter nylon cyclone and
a filter capsule containing a preweighed, preconditioned silver
membrane filter. Samples are collected at a flow rate of 1.7 liter per
minute. The respirable sample collected includes both combustible and
noncombustible particulate matter.
Samples collected in accordance with the RCD method require
analysis by a commercial laboratory. Total respirable dust is
determined gravimetrically by weighing the filter after the sample is
collected. After the sample has been subjected to a controlled
combustion process at 400 deg.C for two hours, the remainder of the
sample is weighed, and the amount of the particulate burned off
determined by subtraction. This is the RCD. The combustible particulate
matter consists of the soluble organic fraction, the EC core of the
dpm, and any other combustible material collected. Thus, only a portion
of the RCD is attributable to dpm. Oil mist and other combustible
matter collected on the filter are interferants that can affect the
accuracy of dpm concentration determination using this method. Because
the mass of RCD is determined by weighing, the relative insensitivity
of this method is similar to that obtained with the size selective
gravimetric method (approximately 200 g/m3).
One commenter (Inco Limited) indicated experience with this method
for identifying diesel particulate in their mining operations and
suggested that this technique may be appropriate for determining eight
hour exposures. Although this method was commonly used by the commenter
for assessing dpm levels, concerns for the efficiency of the cyclones
used to sample the respirable fraction of the particulate along with
interference from oil mist were expressed.
Canada is now experimenting with the use of a submicron impactor
with the RCD method.
Sampler Availability
The components for conducting sampling according to the
submicrometer and the RCD methods are commercially available, as are
those for NIOSH Method 5040, without a submicrometer particulate
separator (impactor).
A reusable impactor can be manufactured by machine shops following
the design specifications developed by the former U.S. Bureau of Mines
(BOM IC 9324, 1992). The use of the size-selective samplers requires
some training and laboratory time to prepare the impaction plate and
assemble the unit. The cost to manufacture the size-selective units is
approximately $35.
In addition, MSHA has requested NIOSH to develop and provide a
commercially available disposable submicrometer particulate separator
that would be used with existing personal respirable dust sampling
equipment. The commercially available separator will be manufactured
according to design criteria specified by NIOSH. It is anticipated that
other sampling instrument manufacturers will develop commercial units
once there is an established need for such a sampling device.
Use of Alternative Surrogates to Assess DPM Concentrations
A number of commenters on the ANPRM indicated that a number of
surrogates were available to monitor diesel particulate. Of the
surrogates suggested, the most desirable to use would be carbon dioxide
because of its ease of measurement. In 1992 the former Bureau of Mines
(BOM IC 9324, 1992) reported on research being conducted to investigate
the use of CO2 as a surrogate to assess mine air quality
where diesel equipment is utilized. However, because the relationship
between CO2 and other exhaust components depends on the
number, type and duty cycle of the engines in operation, no acceptable
measurement method based on the use of CO2 has been
developed.
(4) Reducing Soot at the Source--Engine Standards. One way to limit
diesel particulate emissions is to redesign diesel engines so they
produce fewer pollutants. Engine manufacturers around the world are
being pressed to do this pursuant to environmental regulations. These
cleaner engine requirements are sometimes referred to as tailpipe
standards because compliance is measured by checking for pollutants as
the exhaust emerges from the engine's tailpipe--before any
aftertreatment devices. This section reviews developments in this area,
and explains the relationship between the environmental standards on
new engines and MSHA engine ``approval'' requirements.
The Clean Air Act and Mobile Sources
The Clean Air Act authorized the Federal Environmental Protection
Agency (EPA) to establish nationwide standards for new mobile vehicles,
including those powered by diesel engines. These standards are
designed, over time, to reduce the volume of certain harmful
atmospheric pollutants emanating from mobile sources: 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 standards. New engines destined for use in
California must meet standards under the law of that State. The
standards are issued and administered by the California Air Resources
Board (CARB). In recent years, EPA and CARB have worked together with
industry in establishing their respective standards, so most of them
are identical.
Regulatory responsibility for implementation of the Clean Air Act
is vested in the Office of Mobile Sources (OMS), 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 OMS home page on
the World Wide Web at (http://www.epa.gov/docs/omswww/omshome.htm).
Information about the CARB standards may be found at the home page of
that agency at (http://www.arbis.arb.ca.gov/homepage.htm).
Engines are generally divided into three broad categories for
purposes of
[[Page 17508]]
environmental emissions standards, in accordance with the primary use
for which the type of engine is designed: (1) cars and light duty
trucks (i.e., to power passenger transport); (2) heavy duty trucks
(i.e., to power over-the-road hauling); and (3) nonroad vehicles (i.e.,
to power small equipment, construction equipment, locomotives and other
non-highway uses). Engines used in mining equipment are not regulated
as a separate category in this regard, but engines in all three
categories are engaged in mining work, from generator sets to pickup
trucks to huge earth movers and haulers.
New vs. Used
The environmental tailpipe requirements are applicable only to new
engines. In the mining industry, used engines are often purchased; and,
of course, the existing fleet consists of engines that are not new.
Thus, although these tailpipe requirements will bring about gradual
reduction in the overall contribution of diesel pollution to the
atmosphere, the beneficial effects on mining atmospheres may require a
longer timeframe, absent actions to accelerate the turnover of mining
fleets to the cleaner engines.
In underground coal mining, MSHA has already taken actions which
will have such an effect on the fleet. The diesel equipment rule issued
in late 1996 requires that by November 25, 1999, all diesel equipment
used in underground coal mines use an approved engine and maintain that
engine in approved condition. (30 CFR 75.1907.) MSHA expects this will
result in the replacement of about 47 percent of the diesel engines now
in the underground coal mine inventory with engines that emit fewer
pollutants. The timeframe permitted for the turnover was based upon
MSHA's estimates of the useful life in an underground mining
environment of the ``outby'' equipment involved.
Technology-Forcing Schedule
As noted above, the exact environmental tailpipe requirements which
a new diesel engine must meet varies with the date of manufacture. The
Clean Air Act, which was most recently amended in 1990, establishes a
schedule for the reduction of particular pollutants from mobile
sources. EPA and CARB, working closely with the diesel engine industry,
have endeavored to turn this into a regulatory schedule that forces
technology while taking into account certain technological realities
(e.g., actions taken to reduce particulate emissions may increase NOx
emissions, and vice versa). Existing EPA regulations for on-highway
engines (both for light duty vehicles and heavy duty trucks) and non-
road engines schedule the tailpipe standards that must be met for the
rest of this century. Agreements between EPA, CARB and the engine
industry are now leading to proposed rules for engine standards to be
met during the early part of the next century. These standards will be
stricter and will lower the levels of diesel emissions.
Light-Duty Engines
The current regulations on light duty vehicle engines (cars and
passenger trucks) were set in 1991. (56 FR 25724). EPA is currently
considering proposing new standards for this category. Pursuant to a
specific requirement in the Clean Air Act Amendments of 1990, EPA is to
study and report to Congress on whether further reductions in this
category should be pursued. A public workshop was held in the Spring of
1997. EPA plans provide for a draft report to be available for public
comment by Spring of 1998, and a final report completed by July 1998,
although a notice of citizen suit has been filed to speed the process.
Up-to-date information about the progress of this initiative can be
found at the home page for the study (http://www.epa.gov/omswww/
tr2home.htm).
On-Highway Heavy Duty Truck Engines
The first phase of the on-highway standards for heavy duty diesel
engines was applicable to engines manufactured in 1985. (40 CFR 86.085-
11.) For the first time, separate standards for NOX and
hydrocarbons were established. The nitrogen oxides and hydrocarbons are
precursors of ground level ozone, a major component of smog. A number
of hydrocarbons are also toxic, while nitrogen oxides contribute to the
formation of acid rain and can, as previously noted, precipitate into
particulate matter. In 1988, a specific standard limiting particulate
matter emitted from the heavy duty on-highway diesel engines went into
effect. (40 CFR 86.088-11). The Clean Air Act Amendments and the
regulations provided for phasing in even tighter controls on
NOX and particulate matter through 1998. Reductions in
NOX took place in 1990 and 1991 and are to occur again in
1998, and reductions in PM took place in 1991 and 1994. Certain types
of trucks in particularly polluted urban areas must reach even tighter
requirements.
On October 21, 1997, EPA issued a new rule for on-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 HC. The combined standard is set at 2.5gm/bhp-hr, which includes a
cap of 0.5gm/bhp-hr for HC. Prior to the rule, the EPA, CARB, and the
engine manufacturers signed a Statement of Principles (SOP) that agreed
on harmonization of the emission standards and the feasible levels that
could be achieved. The rule allows manufacturers a choice of two
combinations of NOX and HC, with a net expected reduction in
NOX emissions of 50%. The rule does not require further
reductions in tailpipe emissions of PM.
Non-road Engines
Of particular interest to the mining community is the EPA's
regulatory work on the standards that will be applicable to non-road
engines, for these include the engines used in the heaviest mining
equipment.
The 1990 Clean Air Act Amendments specifically directed EPA to
study the contribution of nonroad engines to air pollution, and
regulate them if warranted. 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 emission standards for land-based nonroad engines greater
than 50 horsepower (other than for rail use). Limits are established
for tailpipe emissions of hydrocarbons, carbon monoxide,
NOX, and dpm. The limits are phased in from 1996 to 2000:
starting in 1996 with nonroad engines from 175 to 750 hp, then smaller
engines, and by 2000 the larger nonroad engines. Moreover, in February
1997, restrictions on nonroad engines for locomotives were proposed.
(62 FR 6366.)
In September 1996, EPA announced another Statement of Principles
(SOP) with the engine industry and CARB on new rounds of restrictions
for non-road engines to begin to take place in this century. This led
in September 1997 to a proposed rule setting standards for almost all
types of engines in this category manufactured after 1999-2006 (the
actual year depends on the category). (62 FR 50151.) The applicable
standards for an engine category would be gradually tightened through
three tiers. They would set a cap on the combined NOX and HC
(similar to the on-highway), set CO standards, and lower standards on
PM. The implementation of the final tier of the proposed reductions is
subject to a technology review in 2001 to ensure
[[Page 17509]]
that the appropriateness of the levels to be set is feasible.
Will the Diesel Engine Industry Meet Mining Industry Requirements?
Concern has been expressed from time to time that the diesel
industry might not be able to meet the ever tightening standards on
tailpipe emissions, and might, therefore, stop producing certain
engines needed by the mining community or other industries (Gushee,
1995). To date, however, such concerns have not been realized. The fact
that the most recent regulations have been developed through a
consensus process with the engine industry, and that the non-road plan
includes a scheduled technology review to ensure the proposed emission
standards can really be achieved, suggests that although the EPA
standards are technology forcing, diesel engines will continue to be
available to meet the needs of the mining community for the foreseeable
future. In addition, the nonroad engine agreement with the industry
calls for development of a separate research agreement involving
stakeholders in the exploration of technologies that can achieve very
low emission levels of NOX and PM ``while preserving
performance, reliability, durability, safety, efficiency, and
compatibility with nonroad equipment'' (EPA420-F-96-015, September
1996). Also, Vice President Gore has recently noted that the
Administration is committed to emissions research that would clean up
both the diesels currently on the road, as well as enabling these
engines an opportunity to compete as a new generation of vehicles is
developed that are far more efficient than today's vehicles (White
House Press Release, July 23, 1997). It is always possible, of course,
that some new technological problems could emerge that could impact
diesel engine availability--e.g., confirmation that some of the newer
engines produce high levels of ``nanoparticles'' particulates and that
such emissions pose some sort of a health problem. Research of
nanoparticles and their health effects is currently a topic of
investigation (Bagley et al., 1996).
A related question has been whether the costs of the ``high-tech''
diesel engines will make them unaffordable in practice to the mining
community. MSHA believes the new engines will be affordable. The fact
that the engine industry has agreed to the new standards, and has some
assurance of what the applicable standards will be for the foreseeable
future, should help keep costs in check.
In theory, underground mines can control costs by purchasing
certain types of new engines that do not have to meet the new EPA
standards. The rules on heavy duty on-highway truck engines were not
applied to engines intended to be used in underground coal mines (59 FR
31336), and the new proposed rules on nonroad vehicles would likewise
not be mandatory for engines intended for any underground mining use.
In practice, however, it is not likely that engine manufacturers will
produce special engines once they switch over their production lines to
meet the new EPA standards, because there are few types and sizes of
engines in production for which the mining community is the major
market. Moreover, the larger engines (above 750 hp) are specifically
covered by the EPA nonroad rules (Engine Manufacturers Assn. vs. EPA,
88 F.3d 1075, 319 U.S. App.D.C. 12 (1996)).
MSHA Approved Engines
Acting under its own authority to protect miner safety and health,
MSHA requires that diesel engines used in certain types of mining
operations be ``approved'' as meeting certain tailpipe standards.
In some ways, the standards are akin to those of EPA and CARB. For
example, MSHA, CARB and EPA generally use the same tests to check
emissions. MSHA uses a steady state, 8-mode test cycle, the same as EPA
and CARB use to test engines designed for use in off-road equipment;
however, EPA uses a different, transient test for on-highway engines.
But to be approved by MSHA, an engine does not have to be as clean
as the newer diesel engines, every generation of which must meet ever
tighter EPA and CARB tailpipe standards. Approval of an engine by MSHA
merely ensures that the tailpipe emissions from that engine meet
certain basic standards of cleanliness--cleaner than the engines which
many mines continue to use.
The MSHA approval rules were revised in 1996 (as part of the 1996
rule on the use of diesel equipment in underground coal mines) to
provide the mining community with additional information about the
cleanliness of the emissions emerging from the tailpipe of various
engines. Specifically, the agency now requires that a particulate index
(PI) be reported as part of MSHA's engine approval. This index permits
operators to evaluate the contribution of a proposed new addition to
the fleet to the mine's particulate concentrations.
There is no requirement that approved engines meet a particular PI;
rather, the requirement is for information purposes only. In its 1996
rulemaking, MSHA explicitly deferred until this rulemaking the question
of whether to require engines used in mining environments to meet a
particular PI. (61 FR 55420-21, 55437). The Agency has decided not to
take that approach, for the reasons discussed in part V of this
preamble.
(5) Limiting the Public's Exposure to Soot--Ambient Air Quality
Standards. Pursuant to the Clean Air Act, 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 contributes 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 rulemaking on particulate
matter. For more detailed information, commenters are referred to ``The
Plain English Guide to the Clean Air Act,'' EPA 400-K-93-001, 1993, to
the ``Review of the National Ambient Air Quality Standards for
Particulate Matter: Policy Assessment of Scientific and Technical
Information'', EPA-452/R-96-013, 1996; and, on the latest rule, to EPA
Fact Sheets, July 17, 1997. These and other documents are available
from EPA's Web site.
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. It
is supposed to do a review 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.
[[Page 17510]]
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 pollution measurements 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''.
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 are mixed 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.
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 limit of 150 g/
m3, and a 24-hour limit of 50 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 those 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).
PM2.5
The next scientific review was completed in 1996, following suit by
the American Lung Association and others. A proposed rule was published
in November of 1996, and, after public hearings and review by the
Office of the President, 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 150 g/m\3\ (with some adjustment as to how this is measured
for compliance purposes), and a 24-hour ceiling of 50 g/m\3\.
In addition, however, a new NAAQS has now been established for ``fine
particulate matter'' that is less than 2.5 microns in size. The
PM2.5 annual limit is set at 15 g/m\3\, with a 24-
hour ceiling of 65 g/m\3\.
The basis for the PM2.5 NAAQS is a new body of
scientific data suggesting that particles in this size range are the
ones 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. (A chart of the
scientific review process is available on EPA's web site -- http://
ttnwww.rtpnc.epa.gov/naaqspro/pmnaaqs.gif). The proposed rule resulted
in considerable press attention, and hearings by Congress, in which
this scientific evidence was further discussed. Following a careful
review, President Clinton announced his concurrence with the rulemaking
in light of the scientific evidence of risk. However, the
implementation schedule for the rule is long enough so that the next
review of the science is scheduled to be completed before the states
are required to meet the new NAAQS for PM2.5--hence,
adjustment of the standard is still possible before implementation.
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. The
body of evidence of human health risk from environmental exposure to
fine particulates must, therefore, be considered in assessing the risk
of harm to miners of occupational exposure to one type of fine
particulate--diesel particulate. MSHA has accordingly done so in its
risk assessment (see part III of this preamble).
(6) Controlling Diesel Particulate Emissions in Mining--a Toolbox.
Efforts to control diesel particulate emissions have been under review
for some time within the mining community, and accordingly, there is
considerable practical information available about controls--both in
general terms, and with respect to specific mining situations.
Workshops
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. One 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
[[Page 17511]]
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).
Toolbox
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. Following comment, the toolbox was finalized in the
Fall of 1997 and disseminated. For the convenience of the mining
community, a copy is reprinted as an Appendix at the end of this
document.
The material on controls is organized as a ``toolbox'' so that mine
operators have the option of choosing the control technology that is
most applicable to their mining operation for reducing exposures to
dpm. The Toolbox provides information about nine types of controls that
can reduce dpm emissions or exposures: Low emission engines; fuels;
aftertreatment devices; ventilation; enclosed cabs; engine maintenance;
work practices and training; fleet management; and respiratory
protective equipment.
The Estimator
MSHA has developed a model that can help mine operators evaluate
the effect of alternative controls on dpm concentrations. The model 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. A complete
description of this model, referred to as ``the Estimator,'' and
several examples, are presented in part V of this preamble. MSHA
intends to make this model widely available to the mining community,
and hopes to receive comments in connection with this rulemaking based
on the results of estimates conducted with this model.
History of Diesel Aftertreatment Devices in Mining
For many years, the majority of the experience has been with the
use of oxidation catalytic converters (OCCs), but in more recent years
both ceramic and paper filtration systems have also been used more
widely.
OCCs began to be used in underground mines in the 1960's to control
carbon monoxide, hydrocarbons and odor (Haney, Saseen, Waytulonis,
1997). That use has been widespread. It has been estimated that more
than 10,000 OCCs have been put into the mining industry over the years
(McKinnon, dpm Workshop, Beckley, WV, 1995).
When such catalysts are used in conjunction with low sulfur fuel,
there is a reduction of up to 90 percent of carbon monoxide,
hydrocarbons and aldehyde emissions, and nitric oxide can be
transformed to nitrogen dioxide. Moreover, there is also an
approximately 20 percent reduction in diesel particulate mass. The
diesel particulate reduction comes from the elimination of the soluble
organic compounds that, when condensed through the cooling phase in the
exhaust, will attach to the elemental carbon cores of diesel
particulate. Unfortunately, this effect is lost if the fuel contains
more than 0.05 percent sulfur. In such cases, sulfates can be produced
which ``poison'' the catalyst, severely reducing its life. With the use
of low sulfur fuel, some engine manufacturers have certified diesel
engines with catalytic converter systems to meet EPA requirements for
lower particulate levels (see section 4 of this part).
The particulate trapping capabilities of some OCCs are even higher.
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 25%. Such systems are available for
larger diesel engines common in the underground metal and nonmetal
sector.
Other types of aftertreatment devices capable of more significant
reductions in particulate levels began to be developed for commercial
applications following EPA rules in 1985 limiting diesel particulate
emissions from heavy duty diesel engines. The wall flow type ceramic
honeycomb diesel particulate filter system was initially the most
promising approach (SAE, SP-735, 1988). 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 turned out to be unnecessary to comply with the
EPA standards of the time.
While this work was underway, efforts were also being made to
transfer this aftertreatment technology to the mining industry. 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 investigation 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. But as noted by one
commenter 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.'' (Ellington, dpm
Workshop, Salt Lake City, UT, 1995).
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.
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 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. In the case of some engines, a
choice of the two types is available; but depending upon horsepower,
this may not always be the case.
In the early 1990's, MSHA worked with the former Bureau of Mines
and a filter manufacturer to successfully develop and test a pleated
paper filter for wet water scrubber systems of permissible diesel
powered equipment. The dpm reduction from these filters has been
determined in the field by the former BOM to be up to 95% (BOM, IC
[[Page 17512]]
9324). The same type of filter has been used in recently developed dry
systems for permissible machines, with reported laboratory reductions
in dpm of 98% (Paas, dpm Workshop, Beckley WV, 1995).
ANPRM Comments
The ANPRM requested information about several kinds of work
practices that might be useful in reducing dpm concentrations. These
comments were provided well before the workshops mentioned above, and
before MSHA issued its diesel equipment standard for underground coal
mines, and are thus somewhat dated. But, solely to illustrate the range
of comments received, the following sections review the comments
concerning certain work practices--fuel type, fuel additives, and
maintenance practices.
Type of Diesel Fuel Required
It has been well established that the quality of diesel fuel
influences emissions. Sulfur content, cetane number, aromatic content,
density, viscosity, and volatility are interrelated fuel properties
which can influence emissions. Sulfur content can have a significant
effect on diesel emissions.
Use of low sulfur diesel fuel reduces the sulfate fraction of dpm
matter emissions, reduces objectionable odors associated with diesel
exhaust and allows oxidation catalysts to perform properly. The use of
low sulfur fuel also reduces engine wear and maintenance costs. Fuel
sulfur content is a particularly important parameter when the fuel is
used in low emission diesel engines. Low sulfur diesel fuel is
available nationwide due to EPA regulations. (40 CFR parts 80 and 86.)
In MSHA's ANPRM, information was requested on what reduction in
concentration of diesel particulate can be achieved through the use of
low sulfur fuel. Information was also solicited as to whether the use
of low sulfur fuel reduces the hazard associated with diesel emissions.
Responses from commenters stated that there would be a positive
reduction in particulate with the use of low sulfur fuel. One commenter
stated that the brake specific exhaust emissions (grams/brake
horsepower-hour) of particulate would decrease by about 0.06 g/bhp-hr
for a fuel sulfur reduction of 0.25 weight percent sulfur. The
particulate reduction effect is proportional to the change in sulfur
content. Another commenter stated that a typical No. 2 diesel fuel
containing 0.25 percent weight sulfur will include 1 to 1.6 grams of
sulfate particulate per gallon of fuel consumed. A fuel containing 0.05
percent weight sulfur will reduce sulfate particulate to 0.2-0.3 grams
per gallon of fuel consumed, an 80 percent reduction.
In responding to the question on whether reducing the sulfur
content of the fuel will reduce the health hazard associated with
diesel emissions, several commenters stated that they knew of no
evidence that sulfur reduction reduces the hazard of the particulate.
MSHA also is not aware of any data supporting the proposition that
reducing the sulfur content of the fuel will reduce the health hazard
associated with diesel emissions. However, in the preamble to the final
rule for the EPA requirement for the use of low sulfur fuel, EPA stated
that there were a number of benefits which could be attributed to
lowering the sulfur content of diesel fuel. The first area was in
exhaust aftertreatment technology. Reductions in fuel sulfur content
will result in small reductions in sulfur compounds being emitted. This
will cause the whole particulate concentration from the engine to be
reduced. However, the number of carbon particles is not reduced,
therefore, the total carbon concentration would be the same.
The major benefit of using low sulfur fuel is that the reduction of
sulfur allows for the use of some aftertreatment devices such as
catalytic converters, and catalyzed particulate traps which were
prohibited with fuels of high sulfur content (greater than 0.05 percent
sulfur). The high sulfur content led to sulfate particulate that when
passed through the catalytic converter or catalyzed traps was changed
to sulfuric acid when the sulfates came in contact with water vapor.
Using low sulfur fuel permits these devices to be used.
The second area of benefits that the EPA noted was that of reduced
engine wear with the use of low sulfur fuel. Reducing engine wear will
help maintain engines in their near manufactured condition that would
help limit increases in particulate matter due to lack of maintenance
or age of the engine.
Other questions posed in the ANPRM requested information concerning
the differences in No. 1 and No. 2 diesel fuel regarding particulate
formation; the current sulfur content of diesel fuel used in mines; and
when would 0.05 percent sulfur fuel be available to the mining
industry.
In response to those questions, commenters stated that a difference
in No. 1 and No. 2 fuel regarding particulate formation would be that
No. 1 fuel typically has less sulfur than No. 2 fuel and would
therefore be expected to produce less particulate. Also, the No. 1 fuel
has a lower density, boiling range and aromatic content and a higher
cetane number. All of these fuel property differences tend to cause
lower particulate emissions.
Commenters also stated that the sulfur content of fuels
commercially available for diesel-powered equipment can vary from
nearly zero to 1 percent. The national average sulfur content for
commercial No. 2 diesel fuel is approximately 0.25 percent. One
commenter stated that sulfur content varied from region to region and
the National Institute of Petroleum and Energy Research survey could be
used to get the answers for specific regions.
Commenters noted that low sulfur fuel, less than 0.05 percent
sulfur, would be available for on-highway use as mandated by the EPA by
October 1993. Also, California requires the statewide availability of
0.05 percent sulfur fuel for all diesel engine applications by the same
date. Although the EPA mandate ensures that low sulfur fuel will be
available throughout the nation, commenters indicated the availability
for off-road and mining application was uncertain at that time.
The ANPRM also requested information on the differences in the per
gallon costs among No. 1, No. 2 and 0.05 percent sulfur fuel; how much
fuel is used annually in the mining industry; and what would be the
economic impact on mining of using 0.05 percent sulfur fuel. In
response, commenters stated that No. 1 fuel typically costs the user 10
to 20 percent more than does No. 2 fuel. They also stated that the
price of 0.05 percent sulfur fuel will eventually be set by the
competitive market conditions. No information was submitted for
accurately estimating fuel usage costs to the industry. The economic
impact on the mining industry of using 0.05 percent fuel will vary
greatly from mine to mine. Factors influencing that cost are a mine's
dependence on diesel powered equipment, the location of the mine and
existing regulation. Mines relying heavily on diesel equipment will be
most impacted.
Another commenter stated that the price for 0.05 percent fuel is
forecast to average about 2 cents per gallon higher than the price for
typical current No. 2 fuel. Kerosene and No. 1 distillate are forecast
as 2 to 4 cents per gallon above 0.05 percent fuel and 4 to 6 cents
above current No. 2 fuel. A recent census of mining and manufacturing
dated 1987 showed mining industry energy consumption from all sources
to total 1968.4 trillion BTU per year. Coal mining alone used 9.96
million barrels
[[Page 17513]]
annually of distillate, at a cost of 258.1 million dollars. Included in
these quantities was diesel fuel for surface equipment and vehicles at
or around the mine site. The commenter also stated that applying a cost
increase of 2 cents per gallon to the total industry distillate
consumption would increase annual fuel costs by $24.3 million. For coal
mining only, the cost increase would be $8.4 million annually.
While MSHA does not have an opinion on the accuracy of the
information received in this regard, it is in any event dated. Since
the time that the ANPRM was open, the availability of low sulfur fuel
has become more common. Comments received at MSHA's Diesel Workshops
indicate that low sulfur fuel is readily available and that all that is
needed to obtain it is to specify the desired fuel quality on the
purchase order. The differences in the fuel properties of No. 1 and No.
2 fuel are consistent with specifications provided by ASTM and other
literature information concerning fuel properties.
Fuel Additives
Information relative to fuel additives was requested in MSHA's
ANPRM. The ANPRM requested information on the availability of fuel
additives that can reduce dpm or additives being developed; what diesel
emissions reduction can be expected through the use of these fuel
additives; the cost of additives and advantages to their use; and will
these fuel additives introduce other health hazards. One commenter
stated that cetane improvers and detergent additives can reduce dpm
from 0 to 10 percent. The data, however, does not indicate consistent
benefits as in the case with sulfur reduction. Oxygenate additives can
give larger benefits, as with methanol, but then the oxygenate is not
so much an additive as a fuel blend. Another commenter stated the cost
depended on the price and concentration of the additive. This commenter
estimated the cost to be between three and seven cents per gallon of
fuel.
Another commenter stated that some additives are used for reducing
injector tip fouling, other alternative additives also are offered
specifically for the purpose of reducing smoke or dpm such as
organometallic compounds, i.e., copper, barium, calcium, iron or
platinum; oxygenate supplements containing alcohols or peroxides; and
other proprietary hydrocarbons. The commenter did not quantify the
expected reductions in dpm.
The former Bureau of Mines commented on an investigation of barium-
based, manganese based, and ferrocene fuel additives. Details of the
investigation are found in the literature (BOM, IC 9238, 1990). In
general, fuel additives are not widely used by the mining industry to
reduce dpm or to reduce regeneration temperatures in ceramic
particulate filters. Research has shown aerosol reductions of about 30
percent without significant adverse impacts although new pollutants
derived from the fuel additive remain a question.
One commenter stated that a cetane improver and detergent additives
should not exceed 1 cent per gallon at the treat rates likely to be
used. The use of oxygenates depends on which one and how much but would
be perhaps an order of magnitude higher than the use of a cetane
improver. One commenter also added that any fuel economy advantages
would be very small.
In response to the creation of a health hazard when using
additives, one commenter stated that excessive exposure to cetane
improver (alkyl nitrates), which is hazardous to humans, requires
special handling because of poor thermal stability. Detergent additives
are similar to those used in gasoline and probably have similar safety
and health issues. Except at low load operation, additives are not
likely to result in any significant quantity in the exhaust. Another
commenter stated that the effect on human health of new chemical
exhaust species that may result from the use of some of these additives
has not been determined. Engine manufacturers also are concerned about
the use of such products because their effectiveness has not always
been adequately demonstrated and, in many cases, the effect on engine
durability has not been well-documented for different designs and
operating conditions.
MSHA agrees with the commenters that fuel additives can affect
engine performance and exhaust emissions. MSHA's experience with
additives has shown that they can enhance fuel quality by increasing
the cetane number, depressing the cloud point, or in the case of a
barium based additive, affect the combustion process resulting in a
reduction of particulate output. MSHA's experience also has shown that
in most cases the effects of an additive on engine performance or
emissions cannot be adequately determined without extensive research.
The additives listed on EPA's list of ``registered additives'' meet the
requirements of EPA's standards in 40 CFR part 79.
MSHA is concerned about the use of untested fuel additives. A large
number of additives are currently being marketed to reduce emissions.
These additives include cetane improvers that increase the cetane
number of the fuel, which may reduce emissions and improve starting;
detergents that are used primarily to keep the fuel injectors clean;
dispersants or surfactants that prevent the formation of thicker
compounds that can form deposits on the fuel injectors or plug filters.
While the use of many of these additives will result in reduced
particulate emission, some have been found to introduce harmful agents
into the environment. For this reason, it is a good idea to limit the
use of additives to those that have been registered by the EPA.
Maintenance Practices
The ANPRM requested information concerning what maintenance
procedures are effective in reducing diesel particulate emissions from
existing diesel-powered equipment, and what additional maintenance
procedures would be required in conjunction with anticipated
developments of new diesel particulate reduction technology.
Information was also requested about the amount of time to perform the
maintenance procedures and if any, loss of production time.
Commenters stated that some maintenance procedures have a very
dramatic impact on particulate emissions, while other procedures that
are equally important for other reasons have little or no impact at all
on particulates. Another commenter stated that maintenance procedures
are intended to ensure that the engine operates and will continue to
operate as intended. Such procedures will not reduce diesel particulate
below that of the new, original equipment. A commenter stated that the
diesel engine industry experience has demonstrated that emissions
deterioration over the useful life of an engine is minimal.
Commenters stated that depending on the implied technology, the
need for additional maintenance will be based on complexity of the
control devices. Also, time for maintenance will be dependent on
complexity of the control device. Some production loss will occur due
to increased maintenance procedures.
MSHA agrees with the commenters' view that maintenance does affect
engine emissions, some more dramatically than others. Research has
clearly shown that without engine maintenance, all engine emissions
will increase greatly. For example, the former Bureau of Mines, in
conjunction with Southwest Research, conducted extensive research on
the effects of maintenance on diesel engines which indicated this
result (BOM contract H-0292009, 1979). MSHA agrees that
[[Page 17514]]
emissions increase is minimal over the useful life of the engine only
when proper maintenance is performed daily. However, MSHA believes that
with the awareness of the increased maintenance, production may not be
lost due to the increased time that the machines are able to operate
without unwanted down time due to poor maintenance practices.
MSHA's diesel ``toolbox'' includes an extensive discussion on the
importance of maintenance. It reminds operators and diesel maintenance
personnel of the basic systems on diesel engines that need to be
maintained, and how to avoid various problems. It includes suggestions
from others in the mining community, and information on their success
or difficulties in this regard.
(7) Existing Mining Standards that Limit Miner Exposure to
Occupational Diesel Particulate Emissions. MSHA already has in place
various requirements that help to control miner exposure to diesel
emissions in underground mines--including exposure to diesel
particulate. These include ventilation requirements, engine approval
requirements, and explicit restrictions on the concentration of various
gases in the mine environment.
In addition, in 1996, MSHA promulgated a rule governing the use of
diesel-powered equipment in underground coal mines. (61 FR 55412).
While the primary focus of the rulemaking was to promote the safe use
of diesel engines in the hazardous environment of underground coal
mines, various parts of the rule will help to control exposure to
harmful diesel emissions in those mines. The new rule revised and
updated MSHA's diesel engine approval requirements and the ventilation
requirements for underground coal mines using diesel equipment, and
established requirements concerning diesel fuel sulfur content and the
idling, maintenance and emissions testing of diesel engines in
underground coal mines.
Background
Beginning in the 1940s, mining regulations were promulgated to
promote the safe and healthful use of diesel engines in underground
mines. In 1944, part 31 established procedures for limiting the gaseous
emissions 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
responded 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 was recommended for engines that have a properly adjusted fuel
to air ratio (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 nameplate
quantity for the vehicle with the highest nameplate air quantity
requirement; (b) 75 percent of the nameplate air quantity requirement
of the vehicle with the next highest nameplate air quantity
requirement; and (c) 50 percent of the nameplate airflow for each
additional piece of diesel equipment.
Diesel Equipment Rule
On October 6, 1987, MSHA published in the Federal Register (52 FR
37381) a notice establishing a committee to advise the Secretary of
Labor on health and safety standards related to the use of diesel-
powered equipment in underground coal mines. The ``Mine Safety and
Health Advisory Committee on Standards and Regulations for Diesel-
Powered Equipment in Underground Coal Mines'' (the Advisory Committee)
addressed three areas of concern: the approval of diesel-powered
equipment, the safe use of diesel equipment in underground coal mines,
and the protection of miners' health. The Advisory Committee submitted
its recommendations in July 1988.
With respect to the approval of diesel-powered equipment, the
Advisory Committee recommended that all diesel equipment except for a
limited class, be approved for use in underground coal mines. This
approval would involve both safety (e.g., fire suppression systems) and
health factors (e.g., maximum exhaust emissions).
With respect to the safe use of diesel equipment in underground
coal mines, the Advisory Committee recommended that standards be
developed to address the safety aspects of the use of diesel equipment,
including such concerns as equipment maintenance, training of
mechanics, and the storage and transport of diesel fuel.
The Advisory Committee also made recommendations concerning miner
health, discussed later in this section.
As a result of the Advisory Committee's recommendations on approval
and safe use, MSHA developed and, on October 25, 1996, promulgated as a
final rule, 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 October 25, 1996 final rule on diesels 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, maintenance requirements, fire
suppression, and design features for nonpermissible machines. While the
focus was on safety, certain rules related to emissions are included in
the final rule. For example, the final rule requires maintenance on
diesel powered equipment. Regular maintenance on diesel powered
equipment should keep the diesel engine and vehicle operation at its
original or baseline condition. However, as a check that the
maintenance is being performed, MSHA wrote a standard for checking the
gaseous CO emission levels on permissible and heavy duty outby machines
to determine the need for maintenance. The CO check requires that a
regular repeatable loaded engine condition be run on a weekly basis and
the CO measured. Carbon monoxide is a good indicator 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 either the regular maintenance was
missed or a problem has developed that is more significant than could
be identified by a general daily maintenance program.
Consistent with the Advisory Committee's recommendation, the final
rule, among other things, requires that virtually all diesel-powered
engines used in underground coal mines be approved by MSHA. (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, are designed to require
clean-burning
[[Page 17515]]
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. (Id.). To achieve the objective of clean-burning
engines, the rule sets performance standards which must be met for
virtually all diesel-powered equipment in underground coal mines (30
CFR part 7).
Consistent with the recommendation of the Advisory Committee, the
technical requirements for approved diesel engines include undiluted
exhaust limits for carbon monoxide and oxides of nitrogen. (61 FR
55419). As recommended by the Advisory Committee, the limits for these
gasses are derived from existing 30 CFR part 36. (61 FR 55419). Also
consistent with the recommendation of the Advisory Committee, the final
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. (61 FR 55420).
As recommended by the Advisory Committee, the ventilating air
quantities are required to appear on the engine's approval plate. (61
FR 55421).
The final rule also implements the Advisory Committee's
recommendation that a particulate index be set for diesel engines. (61
FR 55421). Although, as discussed below, there is not yet a specific
standard limiting miners' exposure to diesel particulate, the
particulate index is nonetheless useful in providing information to the
mining community so that operators can compare the particulate levels
generated by different engines. (61 FR 55421).
Also consistent with the recommendation of the Advisory Committee,
the final rule addresses the monitoring and control of gaseous diesel
exhaust emissions. (30 CFR part 70; 61 FR 55413). In this regard, the
final rule requires that mine operators take samples of carbon monoxide
and nitrogen dioxide. (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). Also consistent with the Advisory Committee's
recommendation, the final rule requires that diesel-powered equipment
be adequately maintained. (30 CFR 75.1914; 61 FR 55414). Among other
things, as recommended by the Advisory Committee, the rule requires the
weekly examination of diesel-powered equipment, including testing of
undiluted exhaust emissions for certain types of equipment. (30 CFR
75.1914(g)). In addition, consistent with the Advisory Committee's
recommendation, operators are required to establish programs to ensure
that those performing maintenance on diesel equipment are qualified.
(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).
Consistent with the Advisory Committee's recommendation, the final
rule also requires that underground coal mine operators use low sulfur
diesel fuel. (30 CFR 75.1901; 61 FR 55413). The use of low sulfur fuel
lowers not only the amount of gaseous emissions, but also the amount of
diesel particulate emissions. (Id.). To further reduce miners' exposure
to diesel exhaust, the final rule prohibits operators from
unnecessarily idling diesel-powered equipment. (30 CFR 75.1916(d)).
Also consistent with the recommendation of the Advisory Committee,
the final rule establishes minimum air quantity requirements in areas
of underground coal mines where diesel-powered equipment is operated.
(30 CFR 75.325). As set forth in the preamble, 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. (61 FR 55433). The final 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. (30 CFR 75.325 \2\).
---------------------------------------------------------------------------
\2\ On December 23, 1997, the National Mining Association and
Energy West Mining Company filed petitions for review of the final
rule. National Mining Association versus Secretary of Labor, Nos.
96-1489 and 96-1490. These cases were consolidated and held in
abeyance pending discussions between the mining industry and the
Secretary. On March 19, 1998, petitioners filed an Unopposed Joint
Motion for Voluntary Dismissal. This motion is still pending before
the Court.
---------------------------------------------------------------------------
The diesel equipment rule will help the mining community use
diesel-powered equipment more safely in underground coal mines. As
discussed throughout this preamble, the diesel equipment rule has many
features which, though it was not their primary purpose, will
incidently reduce harmful diesel emissions in underground coal mines--
including the particulate component of these emissions. (The
requirements of the diesel equipment rule are highlighted with a
special typeface in MSHA's publication, ``Practical Ways to Control
Exposure to Diesel Exhaust in Mining--a Toolbox'', reprinted as an
Appendix at the end of this document. An example is the requirement in
the diesel equipment rule that all engines used in underground coal
mines be approved engines, and be maintained in approved condition --
thus reducing emissions at the source.
In developing this safety 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 those exposure levels in underground coal mines. Moreover, the
rule does not apply to the remainder of the mining industry, where the
use of diesel machinery is much more intense than in underground coal.
Gas Limits
Various organizations have established or recommended limits for
many of the gasses occurring in diesel exhaust. Some of these are
listed in Table II-2, together with information about the limits
currently enforced by MSHA. MSHA requires mine operators to comply with
gas specific threshold limit values (TLV's) recommended by the American
Conference of Governmental Industrial Hygienists (ACGIH) in 1972 (for
coal mines) and in 1973 (for metal and nonmetal mines).
Table II-2.--Gaseous Exposure Limits (PPM)
----------------------------------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------------------------------
(1)
(1)MSHA limits
-------------------------
Pollutant
(1)Range of limits
(1)recommended Coal a M/NM b
----------------------------------------------------------------------------------------------------------------
HCHO........................................................ c 0.016 d. 0.3 2 2
[[Page 17516]]
CO.......................................................... d 25 50 50 50
CO2......................................................... c 5,000 5,000 5,000 5,000
NO2......................................................... c d e 25 25 25 25
NO2......................................................... f 1 d 3 5 5
SO2......................................................... c d 2 e 5 2 5
----------------------------------------------------------------------------------------------------------------
Table Notes:
a ACGIH, 1972.
b ACGIH, 1973.
c NIOSH recommended exposure limit (REL), based on a 10-hour, time-weighted average.
d ACGIH, 1996.
e OSHA permissible exposure limit (PEL).
f NIOSH recommends only a 1-ppm, 15-minutes, short-term exposure limit (STEL).
In 1989, MSHA proposed changing some of these 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 rule,
concerning control of drill dust, has been promulgated, but the other
components are still under review. To change a limit at this point in
time requires a regulatory action; the rule does not provide for their
automatic updating.
(8) How Other Jurisdictions are Restricting Occupational Exposure
to Diesel Soot. MSHA's proposed rule is the first effort by the Federal
government to deal with the special risks faced by workers exposed to
diesel exhaust on the job--because, as described in detail in the part
III of this preamble, miner exposures are an order of magnitude above
those of any other group of workers. But others have been looking at
the problem of exposure to diesel soot.
States
As noted in the first section of this part, few underground coal
mines now use diesel engines. Several states have had bans on the use
of such equipment: Pennsylvania, West Virginia, and Ohio.
Recently, Pennsylvania has replaced its ban with a special law that
permits the use of diesel-powered equipment in deep coal mines under
certain circumstances. The Pennsylvania statute goes beyond MSHA's new
regulation on the use of diesel-powered equipment in underground coal
mines. Of particular interest is that it 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/m3 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 what particulates are
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 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 (see, e.g., section 217-A(b)(6)).
West Virginia has also lifted its ban, subject to rules to be
developed by a joint labor-management commission. MSHA understands that
pursuant to the West Virginia law lifting the ban, the Commission has
only a limited time to determine the applicable rules, or the matter is
to be referred to an arbitrator for resolution.
Other Countries
Concerns about air pollution have been a major impetus for most
countries' standards on vehicle emissions, including diesel
particulate. Most industrialized nations recognize the fundamental
principle that their citizens should be protected against recognized
health risks from air pollution and that this requires the control of
particulate such as diesel exhaust. In November of 1995, for example,
the government of the United Kingdom recommended a limit on
PM10, and noted it would be taking further actions to limit
airborne particulate matter (including a special study of dust from
surface minerals workings).
Concerns about international trade have been another impetus.
Diesel engines are sold to an international market to power many types
of industrial and nonindustrial machinery and equipment. The European
Union manufacturers exported more than 50 percent of their products,
mainly to South Korea, Taiwan, China, Australia, New Zealand and the
United States. Germany and the United Kingdom, two major producers,
have pushed for harmonized world standards to level the playing field
among the various countries' engine producers and to simplify the
acceptance of their products by other countries (Financial Times,
1996). This includes products that must be designed to meet pollution
standards. The European Union (EU) is now considering a proposal to set
an EU-wide standard for the control of the emission of pollutants from
non-road mobile machinery (Official Journal of European Communities,
1995). The proposal would largely track that of the U.S. Environmental
Protection Agency's final rule on the Control of Air Pollution
Determination of Significance for Nonroad Sources and Emission
Standards for New Nonroad Compression-Ignition Engines at or above 37
kilowatts (50 HP)p (discussed in section 3 of this part of the
preamble).
A third impetus to action has been the studies of the health
effects of worker exposure to diesel exhaust--many of which have been
epidemiological studies concerning workers in other countries. As noted
in Part III of this preamble, the studies include cohorts of Swedish
dock workers and bus garage workers, Canadian railway workers and
[[Page 17517]]
miners, French workers, London transport workers, and Danish chimney
sweeps.
Below, the agency summarizes some information obtained on exposure
limits of other countries. Due to differences in regulatory schemes
among nations considering the effects of diesel exhaust, countries
which have addressed the issue are more likely to have issued
recommendations rather than a mandatory maximum exposure limit. Some of
these may have issued mandatory design features for diesel equipment to
assist in achieving the recommended exposure level. Measurement systems
also vary.
Germany
German legislation on dangerous substances classifies diesel engine
emissions as carcinogenic. Therefore, diesel engines must be designed
and operated using the latest technology to cut emissions. This always
requires an examination to determine whether the respective operations
and activities may be carried out using other types of less polluting
equipment. If, as a result of the examination, it is decided that the
use of diesel engines is necessary measures must be instituted to
reduce emissions. Such measures can include low-polluting diesel
engines, low sulphur fuels, regular maintenance, and, where technology
permits, the use of particulate traps. To reduce exposure levels
further, diesel engine emissions may be regulated directly at the
source; ventilation systems may be required to be installed.
The use of diesel vehicles in a fully or partly enclosed working
space--such as in an underground mine--may be restricted by the
government, depending on the necessary engine power or load capacity
and on whether the relevant operation could be accomplished using a
non-polluting vehicle, e.g., an electrically powered vehicle. When
determining whether alternate equipment is to be used, the burden to
the operator to use such equipment is also considered.
In April of 1997, the following permissible exposure limits (TRK
\3\) for diesel engine emissions were instituted for workplaces in
mining.
---------------------------------------------------------------------------
\3\ TPK is the technical exposure limit of a hazardous material
that defines the concentration of gas, vapour or airborne
particulates which is the minimum possible with current technology
and which serves as a guide for necessary protective measures and
monitoring in the workplace.
\4\ Colloid dust is defined as that part of total respirable
dust in a workplace that passes the alveolar ducts of the worker.
---------------------------------------------------------------------------
(1) Non-coal underground mining and construction work: TRK = 0.3
mg/m\3\ of colloid dust.\4\
(2) other: TRK = 0.1 mg/m\3\ of colloid dust.
(3) The average concentration of diesel engine emissions within a
period of 15 minutes should never be higher than four times the TRK
value.
The TRK is ascertained by determining the fraction of elemental
carbon in the colloid (fine) dust by coulometric analysis. Determining
the fraction of elemental carbon always involves the determination of
total organic carbon in the course of analysis. If the workplace
analysis shows that the fraction of elemental carbon in total carbon
(elemental carbon plus organic carbon) is lower than 50%, or is subject
to major fluctuations, then the TRK limits total carbon in such
workplaces to 0.15 mg/m\3\.
Irrespective of the TRK levels, the following additional measures
are considered necessary once the concentration reaches 0.1 mg/m\3\
colloid dust:
(1) Informing employees concerned;
(2) Limited working hours for certain staff categories;
(3) Special working hours; and
(4) Medical checkups.
If concentrations continue to fail to meet the TRK level, the
employer must:
(1) Provide appropriate, effective, hygienic breathing apparatus,
and
(2) Ensure that workers are not kept at the workplace for longer
than absolutely necessary and that health regulations are observed.
Workers must use the breathing apparatus if the TRK levels for
diesel engine emissions at the work place are exceeded. Due to the
interference of recognized analysis techniques in coal mining, it is
currently impossible to ascertain exposure levels in the air in coal
mines. As a consequence, the coal mining authorities require the use of
special low-polluting engines in underground mining and impose special
requirements on the supply of fresh air to the workplace.
European Standards
On April 21, 1997, the draft of a European directive that applied
to emissions from non-road mobile machinery was prepared. The directive
proposed technical measures that would result in a reduction in
emissions from internal-combustion engines (gasoline and diesel)
installed in non-road mobile machinery, and type-approval procedures
that would provide uniformity among the member nations for the approval
of these engines.
The directive proposed a two-stage process. Stage 1, proposed to
begin December 31, 1997, was for three different engine categories:
--A: 130 kW X) (g/ (PT) (g/
kWH) kWh) kWh) kWh)
----------------------------------------------------------------------------------------------------------------
130PPPX) (g/ (PT) (g/
kWH) kWh) kWh) kWh)
----------------------------------------------------------------------------------------------------------------
130PPPP2,
SO2 and RCD--respirable combustible dust which is mostly
dpm). These concentrations were divided by their then current
permissible exposure limits, and the sum of the several ratios
indicates the level of pollution in the mine atmosphere. The maximum
value for this Index was fixed at 3.0. This criterion was determined by
the known health hazard associated with small particle inhalation, and
the known chemical composition of dpm, among other matters.
Subsequently, in 1986, the Canadian Ad hoc Diesel Committee was
formed from all segments of the mining industry, including: mine
operators, the labor force, equipment manufacturers, research agencies
including CANMET, and Canadian regulatory bodies. The objective was the
identification of major problems for research and development
attention, the undertaking of the indicated studies, and the
application of the results to reduce the impact of diesel machines on
the health of underground miners.
In 1990-91, CANMET developed an RCD mine sampling protocol on
behalf of the Ad hoc Committee. Then current underground sampling
studies indicated an average ratio of RCD to dpm of 1.5. This factor
accounted for the presence of other airborne combustible liquids
including fuel, lubrication and particularly drilling oils, in addition
to the dpm.
The original 1978 French-Mildon study was updated under a CANMET
contract in 1990. It recommended that the dpm levels be reduced to 0.5
mg/m3 (suggesting a corresponding RCD level of 0.75 mg/
m3).
However, in 1991, the Ad hoc Committee decided to set an interim
recommended RCD level of 1.5 mg/m3 (the equivalent 1.0 mg/
m3). This value matched the then recommended, but not
promulgated, MSHA ``Ventilation Index'' value for dpm of 1.0 mg/
m3. Consequently, all of the North American mining industry
then seemed to be accepting the same maximum levels of dpm.
It should be noted that for coal mine environments or other
environments where a non-diesel carbonaceous aerosol is present, RCD
analysis is not an appropriate measure of dpm levels.
Neither CANMET nor the Ad hoc Committee is a regulatory body. In
Canada, mining is regulated by the individual provinces and
territories. However, the federal laboratories provide: research and
development facilities, advice based on research and development, and
engine/machine certification services, in order to assist the provinces
in their diesel-related mining regulatory functions.
Prior to the 1991 recommendation of the Ad hoc Committee, Quebec
enacted regulations requiring: ventilation, a maximum of 0.25% sulfur
content in diesel fuel; a prohibition on black smoke; exhaust cooling
to a maximum temperature of 85 deg.C; and the setting of maximum
contaminant levels. Since 1997, new regulations add the CSA Standard
for engine certification, a maximum RCD level of 1.5 mg/m3,
and the application of an exhaust treatment system.
Further, after the Ad hoc Committee recommendation was published in
1991 (RCDmax = 1.5 mg/m3), various provinces took the
following actions:
(1) Five provinces--British Columbia, Ontario, Quebec, New
Brunswick, and Nova Scotia, and the Northwest Territories, adopted an
RCD limit of 1.5 mg/m3.
(2) Two others, Manitoba and Newfoundland/Labrador, have been
adopting the ACGIH TLVs.
(3) Two provinces, Alberta and Saskatchewan, and the Yukon
Territory, continue to have no dpm limit.
Most Canadian Inspectorates accept the CSA Standard for diesel
machine/engine certification. This Standard specifies the undiluted
Exhaust Quality Index (EQI) criterion for calculation of the
ventilation in cfm, required for each diesel engine/machine. Fuel
sulfur content, type of aftertreatment device and rated engine load
factor are on-site, variable factors which may alter the ventilation
ultimately required. Diesel fuel may not exceed 0.50% sulfur, and must
have a minimum flash point of 52 deg.C. However, most mines in Canada
now use fuel containing less than 0.05% sulfur by weight.
In addition to limiting the RCD concentration, Qntario, established
rules in 1994 that required diesel equipment to meet the Canadian
Standards Association ``Non-Rail-Bound Diesel-Powered Machines for use
in Non-Gassy Underground Mines'' (CSA M424.2-M90) Standard, excepting
the ventilation assessment clauses. As far as fuel sulfur and
flashpoint are concerned, Ontario is intending to change to: Smax =
0.05% from 0.25%, and maximum fuel flash point = 38 deg.C from
52 deg.C.
New Brunswick, in addition to limiting the RCD concentration,
requires mine operators to submit an ambient air quality monitoring
plan. Diesel engines above 100 horsepower must be certified, and there
is a minimum ventilation requirement of 105 cfm/bhp.
Since 1996, the Ad hoc organization and the industry consortium
called the Diesel Emissions Evaluation Program (DEEP) have been
cooperating in a research and development program designed to reduce
dpm levels in mines.
World Health Organization (WHO)
Environmental Health Criteria 171 on ``Diesel Fuel and Exhaust
Emissions'' is a 1996 monograph published under joint sponsorship of
the United Nations Environment Programme, the International Labour
Organisation, and the World Health Organization. The monograph provides
a comprehensive review of the literature and evaluates the risks for
human health and the
[[Page 17519]]
environment from exposure to diesel fuel and exhaust emissions.
The following tables compiled in the monograph show diesel engine
exhaust limits for various exhaust components and illustrate that there
is international concern about the amount of diesel exhaust being
released into the environment.
Table II-3.--International Limit Values for Components of Diesel Exhaust Light-Duty Vehicles (g/km)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Region Carbon monoxide Nitrogen oxides Hydrocarbons Particulates Comments
--------------------------------------------------------------------------------------------------------------------------------------------------------
Austria..................... 2.1............ 0.62............ 0.25............ 0.124........... 3.5t; since 1991; from 1995, adoption of
European Union standards planned.
Canada...................... 2.1............ 0.62............ 0.25............ 0.12............ Since 1987.
European Union.............. 2.72........... 0.97 (with ................ 0.14............ Since 1992.
hydrocarbons).
1.0............ 0.7............. ................ 0.08............ From 1996.
Finland..................... ............... ................ ................ Since 1993......
Japan....................... 2.1............ 0.7............. 0.62............ None............ Since 1986.
2.1............ 0.5............. 0.4............. 0.2............. Since 1994.
Sweden, Norway.............. 2.1............ 0.62 (city)..... 0.25............ 0.124........... 3.5t; from motor year 1992.
0.76 (highway)
Switzerland................. 2.1............ 0.62 (city)..... 0.25............ 0.124........... 3.5t; since 1988; from 1995, adoption of
0.76 (highway) European Union standard planned.
USA (California)............ 2.1-5.2........ 0.2-0.6......... 0.2-0.3 (except 0.05 (up to Depending on mileage.
methane). 31000 km).
US Environmental Protection 2.1-2.6........ 0.6-0.8......... 0.2............. 0.05-0.12....... Depending on mileage.
Agency.
--------------------------------------------------------------------------------------------------------------------------------------------------------
Table II-4.--International Limit Values for Components of Diesel Exhaust Heavy-Duty Vehicles (g/kWh)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Carbon Nitrogen Hydro
Region monoxide oxides carbons Particulates Comments
--------------------------------------------------------------------------------------------------------------------------------------------------------
Austria............................. 4.9 9.0 1.23 0.4
Canada.............................. 15.5 5.0 1.3 0.25 g/bhp-h.
15.5 5.0 1.3 0.1 g/bhp-h; from 1995-97.
European Union...................... 4.5 8.0 1.1 0.36 Since 1992.
4.0 7.0 1.1 0.15 From 1995-96.
Japan............................... 7.4 5.0 2.9 0.7 Indirect injection engines.
7.4 6.0 2.9 0.7 Direct injection engines.
Sweden.............................. 4.9 9.0 1.23 0.4
USA................................. 15.5 5.0 1.3 0.07 g/bhp-h; bus.
15.5 4.0 1.3 0.1 g/bhp-h; truck.
15.5 5.0 1.3 0.05 g/bhp-h; bus; from 1998.
15.5 4.0 1.3 0.1 g/bhp-h; truck; from 1998.
--------------------------------------------------------------------------------------------------------------------------------------------------------
Adapted from Mercedes-Benz AG (1994b).
With respect to the protection of human health, the monograph
states that the data reviewed supports the conclusion that inhalation
of diesel exhaust is of concern with respect to both neoplastic and
non-neoplastic diseases. The monograph found that diesel exhaust ``is
probably carcinogenic to humans.'' It also states that the particulate
phase appears to have the greatest effect on health, and both the
particle core and the associated organic materials have biological
activity, although the gas-phase components cannot be disregarded. The
monograph recommends the following actions for the protection of human
health:
(1) Diesel exhaust emissions should be controlled as part of the
overall control of atmospheric pollution, particularly in urban
environments.
(2) Emissions should be controlled strictly by regulatory
inspections and prompt remedial actions.
(3) Urgent efforts should be made to reduce emissions, specifically
of particulates, by changing exhaust train techniques, engine design,
and fuel consumption.
(4) In the occupational environment, good work practices should be
encouraged, and adequate ventilation must be provided to prevent
excessive exposure.
The monograph made no recommendations as to what constitutes
excessive exposure.
International Agency for Research on Cancer (IARC)
The carcinogenic risks for human beings were evaluated by a working
group convened by the International Agency for Research on Cancer in
1988 (International Agency for Research on Cancer, 1989b). The
conclusions were:
(1) There is sufficient evidence for the carcinogenicity in
experimental animals of the whole diesel engine exhaust.
(2) There is inadequate evidence for the carcinogenicity in animals
of gas-phase diesel engine exhaust (with particles removed).
(3) There is sufficient evidence for the carcinogenicity in
experimental animals of extracts of diesel engine exhaust particles.
(4) There is limited evidence for the carcinogenicity in humans of
engine exhausts (unspecified as from diesel or gasoline engines).
[[Page 17520]]
Overall IARC Evaluation
Diesel engine exhaust is probably carcinogenic to humans (Group
2A).
(9) MSHA's Initiative to Limit Miner Exposure to Diesel
Particulate--a Brief History of this Rulemaking and Related Actions. As
discussed in part III of this preamble, by the early 1980's, the
evidence indicating that exposure to diesel exhaust might be harmful to
miners, particularly in underground mines, had started to grow. As a
result, formal agency actions were initiated to investigate this
possibility and to determine what, if any, actions might be
appropriate. These actions are summarized here in chronological
sequence, without comment as to the basis of any action or conclusion.
In 1984, in accordance with the Sec. 102(b) of the Mine Act, NIOSH
established a standing Mine Health Research Advisory Committee to
advise it on matters involving or related to mine health research. In
turn, that group established a 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 the
National Institute for Occupational Safety and Health (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 part, as a result of the recommendation of the Task Group,
MSHA, in April 1986, began drafting proposed regulations on the
approval and use of diesel-powered equipment in underground coal mines.
Also in 1986, the subgroup of the NIOSH advisory committee studying
this issue 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. (Interagency Task Group Report, 1986).
As noted previously in section 7 of this part, in discussing MSHA's
diesel equipment rule, on October 6, 1987, pursuant to Section 102(c)
of the Mine Act, 30 U.S.C. Sec. 812(c), MSHA 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 the Advisory Committee. As required by
Section 101(a)(1), MSHA provided the 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 should be promulgated.
In July 1988, the 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.'' The Advisory
Committee recommended that MSHA promulgate standards governing the
approval and use of diesel-powered equipment in underground coal mines.
The Advisory Committee recommended that MSHA promulgate standards
limiting underground coal miners' exposure to diesel exhaust.
With respect to diesel particulate, the Advisory Committee
recommended that MSHA ``set in motion a mechanism whereby a diesel
particulate standard can be set.'' (MSHA, 1988). In this regard, the
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. (Id. 64-
65). Instead, the Advisory Committee recommended that MSHA request
NIOSH and the former BOM to prioritize research in the development of
sampling methods and devices for diesel particulate. The Advisory
Committee also recommended that MSHA request a study on the chronic and
acute effects of diesel emissions (Id.). In addition, the 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 Advisory Committee further
recommended that particulate emissions ``be evaluated in the equipment
approval process and a particulate emission index repo
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