2
diesel particulate matter emission standards as specified in
Table 1 in the 30 CFR 72.502 (30). The diesel engines used
in the U.S. underground metal and nonmetal mines could
be MSHA-approved, or meet or exceed the power-class-
specific EPA standards as published in the table 57.5067-1
of 30 CFR 57.5067 (31): (1) the engines with power output
lower than 37 kW (50 hp) and higher or equal to 130 kW
(175 hp) must meet the EPA Tier 1 standards and (2) the
engines with power output between 37 kW (50 hp) and
130 kW (175 hp) must meet the EPA Tier 2 standards. It
is important to note that engines used in the underground
mining industry are exempt from complying with the EPA
nonroad regulations (29). Due to attrition and various
other reasons, the industry is gradually substituting “tra-
ditional” diesel engines that meet various superseded stan-
dards with “clean” diesel engines that meet EPA Tier 4 final
or more stringent standards.
The exposure limits for underground miners for DPM
(32,33,34) and criteria gases (35,36,37) emitted by diesel
engines were established on the basis of the pertinent occu-
pational health criteria and feasibility of implementation
of control technologies and strategies. The various substi-
tution, engineering, and administrative control technolo-
gies and strategies are used to control diesel emissions and
curtail exposures of occupations to diesel aerosols and gases
(8,38,39). Over the past couple decades, the exposures to
diesel contaminants have been primarily controlled using a
combination of the following engineering strategies (38):
(1) powering mobile equipment by engines with the lowest
possible particulate and gaseous emissions, (2) using “fresh”
air supplied by natural and forced ventilation systems to
dilute gaseous and particulate emissions (40,41,42,43,44),
(3) controlling tailpipe emissions by retrofitting “tradi-
tional” engines with exhaust aftertreatment devices, as well
as substituting petroleum-based fuels with alternative fuels,
and (4) improving maintenance practices. Lately, those
efforts are complemented with efforts on the substitution of
the “traditional” diesel engines with diesel and diesel/hybrid
power trains with “clean” engines that meet more stringent
contemporary standards (28,29, 45,46,47,48,49), and/or
on the elimination of diesel powertrains and replacement
of those with battery powertrains (50).
The integration of various emissions controls such as:
(1) improved combustion (51,52,53), (2) extensive use
of various exhaust aftertreatment systems based on die-
sel oxidation catalytic converters (DOC), diesel particu-
late matter filters (DPF), and selective catalytic reduction
(SCR) devices (39,54,55,56], and (3) improved control of
blow-by emissions via closed crankcase ventilation system
(57,58,59), were used in “clean” engines to substantially
reduce particulate mass and criteria gaseous emissions.
The reductions in particulate concentrations have been
complemented with substantial changes in the physical,
chemical, and toxicological properties of emitted aerosols
(60,61,62,63,64).
Based on those developments, the substitution of the
“traditional” diesel engines with contemporary “clean” die-
sel engines with substantially lower tailpipe and crankcase
emissions (56,63,65,66,67) has been expected to evolve
into an effective control strategy for the curtailment of
exposures to criteria pollutants in underground mines. So
far, the engineering challenges associated with the operation
of these complex powertrains in a harsh environment over
a wide range of duty cycles, higher cost (68), and poten-
tial for the inadvertent introduction of new health hazards
(39,69,70,71,72), are some of the factors that have so far
hindered wider implementation of “clean” engine technolo-
gies in the underground mining industry. The secondary
emissions of NO2 (72,73), sub‑23 nm aerosols (74), and
toxic metals (75,76) as well as a reduction in the size of
emitted aerosols (77) are identified as some of the issues
that require close scrutiny prior to deployment of these
control technologies in confined spaces of underground
mines, often ventilated with limited quantities of fresh air.
This study is conducted with the objective of evaluat-
ing the selected emissions from the selected engines that
comply with the EPA Tier 4 final standards (29) and use
the results to assess the viability and effectiveness of repow-
ering existing mobile equipment and powering new mobile
equipment with similar engines as a control strategy for
reducing the exposure of underground miners to criteria
pollutants.
METHODOLOGY
The analysis was performed on the results of the evaluations
of aerosol and gaseous emissions of three “clean” engines
(Engine 1, Engine 2, and Engine 3) that utilize various in-
cylinder control strategies and three different exhaust after-
treatment control strategies to meet U.S. EPA Tier 4 final
emissions standards for the corresponding power classes
(Table 1): (1) DOC (Engine 1), (2) DOC and the wall flow
monolith silicon carbide DPF (Engine 2), and (3) DOC,
diesel exhaust fluid (DEF) based SCR system, and ammo-
nia slip catalyst (ASC) system (Engine 3). For compara-
tive purposes, the emissions for these three “clean” engines
were contrasted to those of the “traditional” engine that
conform with the EPA Tier 2 emissions standards (Engine
4). The emissions for Engine 4 were previously evaluated
and reported [40] for three different exhaust configura-
tions: (1) muffler (Engine 4), (2) retrofitted with DOC
diesel particulate matter emission standards as specified in
Table 1 in the 30 CFR 72.502 (30). The diesel engines used
in the U.S. underground metal and nonmetal mines could
be MSHA-approved, or meet or exceed the power-class-
specific EPA standards as published in the table 57.5067-1
of 30 CFR 57.5067 (31): (1) the engines with power output
lower than 37 kW (50 hp) and higher or equal to 130 kW
(175 hp) must meet the EPA Tier 1 standards and (2) the
engines with power output between 37 kW (50 hp) and
130 kW (175 hp) must meet the EPA Tier 2 standards. It
is important to note that engines used in the underground
mining industry are exempt from complying with the EPA
nonroad regulations (29). Due to attrition and various
other reasons, the industry is gradually substituting “tra-
ditional” diesel engines that meet various superseded stan-
dards with “clean” diesel engines that meet EPA Tier 4 final
or more stringent standards.
The exposure limits for underground miners for DPM
(32,33,34) and criteria gases (35,36,37) emitted by diesel
engines were established on the basis of the pertinent occu-
pational health criteria and feasibility of implementation
of control technologies and strategies. The various substi-
tution, engineering, and administrative control technolo-
gies and strategies are used to control diesel emissions and
curtail exposures of occupations to diesel aerosols and gases
(8,38,39). Over the past couple decades, the exposures to
diesel contaminants have been primarily controlled using a
combination of the following engineering strategies (38):
(1) powering mobile equipment by engines with the lowest
possible particulate and gaseous emissions, (2) using “fresh”
air supplied by natural and forced ventilation systems to
dilute gaseous and particulate emissions (40,41,42,43,44),
(3) controlling tailpipe emissions by retrofitting “tradi-
tional” engines with exhaust aftertreatment devices, as well
as substituting petroleum-based fuels with alternative fuels,
and (4) improving maintenance practices. Lately, those
efforts are complemented with efforts on the substitution of
the “traditional” diesel engines with diesel and diesel/hybrid
power trains with “clean” engines that meet more stringent
contemporary standards (28,29, 45,46,47,48,49), and/or
on the elimination of diesel powertrains and replacement
of those with battery powertrains (50).
The integration of various emissions controls such as:
(1) improved combustion (51,52,53), (2) extensive use
of various exhaust aftertreatment systems based on die-
sel oxidation catalytic converters (DOC), diesel particu-
late matter filters (DPF), and selective catalytic reduction
(SCR) devices (39,54,55,56], and (3) improved control of
blow-by emissions via closed crankcase ventilation system
(57,58,59), were used in “clean” engines to substantially
reduce particulate mass and criteria gaseous emissions.
The reductions in particulate concentrations have been
complemented with substantial changes in the physical,
chemical, and toxicological properties of emitted aerosols
(60,61,62,63,64).
Based on those developments, the substitution of the
“traditional” diesel engines with contemporary “clean” die-
sel engines with substantially lower tailpipe and crankcase
emissions (56,63,65,66,67) has been expected to evolve
into an effective control strategy for the curtailment of
exposures to criteria pollutants in underground mines. So
far, the engineering challenges associated with the operation
of these complex powertrains in a harsh environment over
a wide range of duty cycles, higher cost (68), and poten-
tial for the inadvertent introduction of new health hazards
(39,69,70,71,72), are some of the factors that have so far
hindered wider implementation of “clean” engine technolo-
gies in the underground mining industry. The secondary
emissions of NO2 (72,73), sub‑23 nm aerosols (74), and
toxic metals (75,76) as well as a reduction in the size of
emitted aerosols (77) are identified as some of the issues
that require close scrutiny prior to deployment of these
control technologies in confined spaces of underground
mines, often ventilated with limited quantities of fresh air.
This study is conducted with the objective of evaluat-
ing the selected emissions from the selected engines that
comply with the EPA Tier 4 final standards (29) and use
the results to assess the viability and effectiveness of repow-
ering existing mobile equipment and powering new mobile
equipment with similar engines as a control strategy for
reducing the exposure of underground miners to criteria
pollutants.
METHODOLOGY
The analysis was performed on the results of the evaluations
of aerosol and gaseous emissions of three “clean” engines
(Engine 1, Engine 2, and Engine 3) that utilize various in-
cylinder control strategies and three different exhaust after-
treatment control strategies to meet U.S. EPA Tier 4 final
emissions standards for the corresponding power classes
(Table 1): (1) DOC (Engine 1), (2) DOC and the wall flow
monolith silicon carbide DPF (Engine 2), and (3) DOC,
diesel exhaust fluid (DEF) based SCR system, and ammo-
nia slip catalyst (ASC) system (Engine 3). For compara-
tive purposes, the emissions for these three “clean” engines
were contrasted to those of the “traditional” engine that
conform with the EPA Tier 2 emissions standards (Engine
4). The emissions for Engine 4 were previously evaluated
and reported [40] for three different exhaust configura-
tions: (1) muffler (Engine 4), (2) retrofitted with DOC