CONTROLLING AND MONITORING DIESEL EMISSIONS IN

UNDERGROUND MINES IN THE UNITED STATES 

Steven E. Mischler1

1

Corresponding Author. National Institute for Occupational Safety and Health, 

Pittsburgh Research Laboratory, PO Box 18070, Pittsburgh, PA 15236, 

smischler@cdc.gov Telephone: 412.386.6588 FAX: 412.386.4917 

and Jay F. Colinet2 

2

 National Institute for Occupational Safety and Health, Pittsburgh Research 

Laboratory, PO Box 18070, Pittsburgh, PA 15236, jcolinet@cdc.gov

ABSTRACT 

The exposure of mine workers to diesel particulate matter (DPM) and gases is an 

issue of great concern to the underground mining community in the United States. 

Approximately 30,000 underground miners are potentially exposed to high 

concentrations of DPM. In January of 2001, the U.S. Mine Safety and Health 

Administration (MSHA) promulgated rules setting compliance standards for both 

underground coal and metal / nonmetal mine workers. As industry works to achieve 

compliance with these standards, mine operators are looking for feasible methods for 

reducing DPM concentrations in their mines. In addition, the industry needs methods 

to accurately measure DPM to ensure that the control strategies they adopt are 

working successfully. 

The Pittsburgh Research Laboratory (PRL) of the National Institute for Occupational 

Safety and Health (NIOSH) conducts research to evaluate control technologies and 

monitoring instrumentation that can be used to reduce the diesel particulate matter 

(DPM) exposure of mine workers. An overview of the strategies being utilized in 

underground US mines to reduce DPM concentrations will be presented. Also, 

updates on the development of diesel monitoring instruments such as the continuous 

elemental carbon monitor or the Personal Dust Monitor for DPM measurement will 

be provided. 

1. INTRODUCTION 

The use of diesel-powered equipment by the underground mining community has 

continuously increased over the last several decades. In the United States for 

example, approximately 150 pieces of diesel equipment were being operated in 

underground coal mines in 1974 and by 1995 that number approached 3000 units 

(MSHA 2001a). A similar trend is seen in underground metal/nonmetal mines 
(M/NM), where the use of diesel equipment first started in 1936 and by 2001 there 

were over 4000 units operating in underground M/NM mines in the United States 

(MSHA 2001b). This extensive utilization of diesel-powered equipment generates the 

potential for exposure of underground miners to particulate matter and gaseous 

emissions from this equipment and creates an important challenge for the mining 

industry in the U.S. and worldwide to control these emissions. In recent years, studies 

have shown that long-term exposure to combustion-related fine particulate pollution, 

including diesel particulate matter (DPM), is an important risk factor for 

cardiopulmonary and lung cancer mortality (Pope, 2002). Therefore, health issues 

associated with exposure to DPM are receiving substantial attention from the public, 

government agencies, and academia. 

In January of 2001, the U.S. Mine Safety and Health Administration (MSHA) 

promulgated rules setting compliance standards for both underground coal and 

M/NM mineworkers. The underground coal rule [30 CFR 72.520] controls the 

exposure of the miners by limiting the emission rate from newly introduced and 

existing diesel-powered equipment. Engine emission rates are calculated using the 

emission rate determined through MSHA engine certification and the MSHAaccepted PM reduction factor for the emission control technology being 

implemented. An engine/control system must be verified to meet an emission rate of 

2.5 g/hr for permissible and heavy-duty or < 5 g/hr for outby light-duty equipment. 

MSHA determined that due to the absence of an accurate method for sampling DPM 

in underground coal mines, a performance rule was not feasible, thus air sampling, to 

measure DPM in the workplace is not required under this rule. 

The underground metal/nonmetal rule [30 CFR 57.5060] requires the mine operators 

to limit a miner’s personal exposure to DPM to an average eight-hour equivalent 

concentration of 160 ug/m3 total carbon, as measured by NIOSH Analytical Method 

5040 (NIOSH 1999). This limit went into effect on May 20, 2008. As industry works 

to achieve compliance with these regulatory limits, mine operators are looking for 

feasible methods for reducing DPM concentrations in their mines. In addition, the 

industry needs methods to accurately measure DPM to ensure that the control 

measures they adopt are working successfully. 

NIOSH-PRL has promoted an integrated approach to controlling DPM. This 

integrated approach adopts a holistic strategy of integrating all departments of a mine 

including management, production, maintenance, and safety. This paper will present 

an overview of the integrated approach and review the strategies being used by US 

mines to reduce the concentrations of DPM emitted from the tailpipe, as well as 

present results from research evaluating these strategies. It will not discuss, in detail, 

control strategies such as ventilation or enclosed cabs, which have been shown to 

successfully reduce DPM concentrations but are outside the scope of this paper. 
Finally, this paper will present information on two monitors being developed to 

enable the real-time measurement of DPM. 

2. INTEGRATED APPROACH TO CONTROLLING DIESEL 

PARTICULATE MATTER EMISSIONS 

The integrated approach to DPM control is a strategy, promoted by NIOSH in 

collaboration with our stakeholders, which systematically resolves issues associated 

with diesel emissions by integrating solutions, from each of the independent 

departments, throughout the mine as a whole. NIOSH has found that DPM exposure 

control is complicated but manageable when the proper people and proper system are 

put into place and allowed to succeed. With this approach mines learn how to 

properly understand the issues to be solved, tackle each issue systematically and 

thoroughly, research and try several different solutions, and finally implement the 

solutions that are most feasible for that mine. The integrated approach can be 

separated into five basic steps shown below: 

1) Find a management supported leader or DPM champion 

2) Get control over engine-out emissions (replace older/dirty engines, establish 

an emission’s based maintenance program) 

3) Look for administrative controls and gain an understanding of equipment 

inventory and usage, 

4) Ensure adequate ventilation, 

5) Examine additional control options including aftertreatment systems and 

alternative fuels. 

Finally, at each step in the process it is necessary to have a DPM measurement 

program that allows for documentation of the efficacy of each step in reducing the 

DPM concentration in the mine. The remainder of this paper will address the steps in 

more detail and end with a discussion of instrumentation which can be used to 

measure DPM. 

2.1 Management Supported Leader 

The management supported leader under the integrated approach serves as the focal 

point for the program and NIOSH has labeled this person the DPM champion. 

Successful management of worker exposure to diesel exhaust requires that the DPM 

champion has adequate expertise, the authority to manage and coordinate efforts 

within and throughout various mine organizational structures, and the respect and 

cooperation of the workers. The DPM champion must have the expertise to explain 

the intricacies of the diesel regulations as well as an understanding of the many 

control options to be used. Although many mines attempt to place a mechanic in this 

role, since they have the greatest knowledge on the workings of the diesel equipment, 

NIOSH has found that often a mechanic does not have the authority to institute all 
the necessary changes required in the integrated approach. Because it is the DPM 

champion’s responsibility to bring together all persons whose actions can influence 

the emissions of DPM, NIOSH has found that a person currently holding authority in 

the organization is the best choice. The DPM champion must have the ability to 

assemble all the people with influence over the departments affecting DPM 

emissions, lead the discussion on the DPM problems and their potential solutions, 

and work cooperatively with each department to reach solutions to address the 

ultimate goal of controlling DPM in the most cost-effective and reliable manner. 

2.2 Control Over Engine-out Emissions 

Gaining control over the engine-out DPM emissions is the important starting point 

for the integrated approach. A reduction in the amount of DPM emitted by the engine 

is a reduction in the amount of DPM which must be otherwise controlled using 

alternative control strategies. In many instances, reducing these engine-out emissions 

may be the only step necessary to meet DPM compliance standards. The two main 

approaches that can be used to reduce engine-out emissions are maintenance and 

administrative controls. 

2.2.1 Maintenance: Since the introduction of diesels into underground mining, the 

need for a good maintenance program has always been recognized. However, this 

recognition has not always resulted in the adoption and disciplined implementation of 

proper maintenance practices being applied to every diesel engine or vehicle in 

operation in underground mines. Nevertheless, it is extremely important to realize 

that the very first step on the path to reducing worker exposures to DPM is to 

implement an effective diesel vehicle/engine maintenance protocol and apply it to 

every diesel unit that operates underground. The early work in this area was 

performed by the U.S. Bureau of Mines [Waytulonis 1987]. The University of 

Minnesota’s Center for Diesel Research [Spears 1997] developed procedures for 

using tailpipe gas measurements as a diagnostic for engine maintenance. A 

comprehensive study on the relationship between diesel engine maintenance and 

tailpipe emissions was completed by McGinn [2000] under a research effort by the 

Diesel Emissions Evaluation Program (DEEP). McGinn developed a maintenance 

auditing procedure [McGinn et al. 2000] and guidelines [McGinn 1999], which were 

implemented in a hardrock mine with demonstrable results. The guidelines and 

training of the mine personnel involved participation by mine management, machine 

operators, mechanics, and most importantly the engine and vehicle manufacturers’ 

service representatives. Dramatic reductions in exhaust PM and CO emissions were 

observed in some cases when good maintenance practice was applied. These 

documents can be found on the DEEP website at www.deep.org/research.html. 

There are several important reasons to provide the best possible engine maintenance 

when considering or implementing control technology. The first reason is that the 
lowest emissions resulting from the application of any control technology are 

obtained when starting with the lowest possible engine-out emissions. The second 

reason is that ventilation requirements and PM emission rates determined through 

MSHA’s engine certification process were obtained using a properly tuned, wellmaintained (new) engine. It is important that the engines in the field have emission 

characteristics no worse than those of the certified engine so that calculations that use 

the MSHA ventilation and PM emission rates to ensure safe levels of toxic gases, to 

estimate workplace diesel particulate levels, or to compare particulate emission rates 

among engines are valid. In addition, excessive emissions from poorly maintained 

engines may jeopardize the performance of aftertreatment technologies. For example, 

excessive emissions of the ash caused by burning crankcase oil might result in 

clogging and premature failure of a diesel particulate filter (DPF). In summary, the 

very first step in applying control technology to reduce workplace exposures to diesel 

exhaust is to implement an effective maintenance program and closely monitor its 

effectiveness. 

2.2.2 Administrative controls: Effective administration of equipment usage can 

greatly assist in reducing the DPM concentrations in underground mines and is an 

important step in the integrated approach. To begin this process it is first necessary 

to evaluate the equipment inventory and equipment usage. Under this process the 

following steps are useful: 

1) List every piece of equipment being used, engine model, MSHA Particulate 

Index (PI) and ventilation number 

2) Know how and where each is used and its per shift fuel consumption (tied to 

total emissions) 

3) Be concerned with engines/equipment with high fuel consumption and high 

PI/horsepower (hp) ratio; consider replacing such engines/equipment 

4) Question the equipments necessity and see if it is possible to reduce the 

number of the fleet. In certain instances it may be possible to reduce the 

number of vehicles in a work area or reduce the size of the diesel engine 

being used, both instances may result in a reduction in DPM concentration 

in the work area. 

Once the equipment usage has been optimized there are several other administrative 

controls that may reduce emissions and DPM concentrations and these include 1) 

minimize engine idling, 2) avoid lugging engines (low RPM high load) and 3) 

maintain clean fuel and lube oil. Finally traffic control has been shown to be 

effective in reducing the DPM concentrations in work areas. This type of control 

would entail routing traffic away from a miners work area, routing haul trucks in 

return air especially when ascending ramps while loaded and limiting horsepower in 

a work area based on available ventilation. 
When considering administrative controls it is important for each mine to attempt 

different approaches and discover which administrative controls are most feasible for 

their circumstances. 

2.3 Ventilation 

Ventilation is the most widely used method for DPM control and the reduction is 

directly proportional to the increase in airflow. A doubling of the airflow into a 

working face will result in a 50% reduction in the DPM concentration at that face. 

As a guideline for estimating the amount of ventilation to control DPM, MSHA 

publishes a particulate index (PI) for each approved engine. This information can be 

found at http://www.msha.gov/01-995/dieselpart.HTM. The PI establishes the 

airflow quantity required to dilute DPM emissions to 1,000 μg/m3. The 

measurement of carbon dioxide is also a helpful tool in assessing the effectiveness of 

ventilation. The area CO2 concentration (increase over that in the incoming air) is a 

measure of the amount of ventilation air relative to the amount of total fuel being 

burned in the area (work being done and/or number of diesel powered vehicles) and 

is a very good measure of the adequacy of ventilation to dilute diesel exhaust. An 

increase in the CO2 concentrations in a work area can be an indication that the 

number of vehicles operating in that area is too high for the ventilation rate. 

2.4 Aftertreatment Technologies 

Aftertreatment technologies including diesel oxidation catalysts (DOC’s), diesel 

particulate filters (DPF’s) and disposable filter elements (DFE’s) are very effective in 

removing DPM from the exhaust of diesel-powered equipment (Johnson 2008). 

These aftertreatment systems are placed in the exhaust system just after the 

combustion chambers and are gradually becoming more utilized for underground 

mining applications [Bugarski, 2006a]. Figure 1 shows a schematic of the basic 

concept of filtering where engine emissions (blue arrows) enter at one end of the 

filter and then must physically flow through the filter wall, which removes the DPM, 

before exiting the filter. 

Figure 1: Basic concept of filtering 

 Figure 2 presents a picture of both the inlet and outlet of a 

filter showing that the black diesel soot is only seen on the inlet side of the filter. 

Disposable and non-disposable filters have been successful in efficiently removing 

DPM on mining equipment. 

 Figure 2: Entrapment of soot at inlet of filter 
NIOSH has completed extensive research on the effectiveness of DPF's, DFE’s and 

DOC’s to control DPM and a summary of the results from these studies are presented 

in Table 1. The results presented in Table 1 are from three types of DPF systems 

representative of the systems currently available to the underground mining industry 

to curtail DPM emissions from diesel-powered equipment. 

1. A DPF system manufactured by Catalytic Exhaust Products (CEP), Toronto, 

ON, Model 912-SXT with uncatalyzed Corning EX-80 Cordierite element (31 cell 

per cm2 and 0.3 mm wall thickness) (Cordierite DPF). 

2. A DPF system manufactured by DCL International Inc., Concord, ON, 

Model Minex Sootfilter 5.66×10 with uncatalyzed Ibiden silicon carbide element (31 

cell per cm2 and 0.36 mm wall thickness) (SiC DPF). 

3. A DPF system manufactured by Mann+Hummel GMBH, Speyer, Germany, 

Model SMF-AR with uncatalyzed sintered metal element (10 μm mean pore size, 

45% porosity, and 0.38 mm wall thickness) used with Satacen 3 fuel additive (SM 

DPF). 

The DPF systems with Cordierite and silicon carbide wall flow monoliths are listed 

by MSHA as being 85 and 87 percent efficient, respectively, in the removal of total 

DPM mass (MSHA 2007). The SM DPF system was recently added to the MSHA 

list as 81 percent efficient. As shown in Table 1 NIOSH results agree well with the 

MSHA efficiencies. 

Table 1: Efficiencies of DPF’s 

Cordierite DPF SiC DPF Sintered Metal DPF DFE

> 87% > 90% > 91% > 80%

When compared with DPFs and DFEs, the DOC produced relatively modest effects 

on aerosol mass concentrations. The effects of the tested DOC on total mass 

concentrations were found to be influenced strongly by engine operating mode. 

However, the most substantial reductions of 42 percent in mass concentration 

occurred when the engine was operated under the highest work load scenario 

(intermediate speed and 100% load). 

 

2.5 Biodiesel 

Although DPF systems are gradually becoming more utilized for controlling DPM 

emissions from underground mining vehicles (Bugarski 2006a, b) their acceptance 

has been hindered by their relative complexity, implementation issues and expense. 

Changing the fuel supply from petroleum diesel to biodiesel blends is considered by 

a number of underground mine operators to be a viable alternative for controlling 
DPM emissions. The major advantages of biodiesel over petroleum-based diesel 

fuels are greater cetane number, absence of aromatics and sulfur, and high oxygen 

content. In addition, biodiesel was shown (Williams 2006, Boehman 2005) to lower 

the balance point temperature of passively regenerated DPFs and therefore could 

potentially facilitate regeneration and the implementation of DPF systems in 

underground mines. 

In NIOSH testing, biodiesel fuels reduced total mass concentrations for all engine 

operating modes. With few exceptions, reductions in total mass concentrations rose 

with an increase in biodiesel fraction with 100% biodiesel reducing the DPM 

concentrations by slightly greater than 50%. 

3.0 MONITORING

The previous section in this paper discussed a strategy to be used to reduce the 

concentration of DPM in underground mines. However, as mines work toward 

implementing this strategy it is essential that they understand the importance of 

monitoring the effectiveness of this strategy. A proper monitoring program will 

enable the mines to identify and quantify problems with the implementation of their 

controls. A monitoring program should include a regular sampling schedule for both 

ambient concentrations of DPM and concentrations emitted from the equipment 

tailpipe. This data will allow the mine personnel to constantly assess the 

effectiveness of the DPM controls. Once the controls are implemented, continuous 

sampling will show a failure of these controls through a resulting increase in 

measured DPM concentrations. This section of the paper will present information and 

data about two different types of monitors that can be used to accurately measure the 

concentration of DPM or a reasonable surrogate. 

 

Diesel exhaust is a complex mixture made up largely of particulate elemental carbon 

(EC), commonly referred to as “soot”, and particle bound organic carbon (OC). 

Total carbon (TC) is the summation of EC and OC. In the US, DPM is regulated in 

M/NM mines through the measurement of TC. The standard sampling method 

requires time weighted personal samples to be collected during a work shift and then 

sent to a laboratory for NIOSH 5040 analysis. This process may take several weeks 

before a mine receives the sampling results making it difficult to ascertain the 

effectiveness of control strategies. As a result, NIOSH has been developing and 

testing two continuous monitors to give mine personnel real-time information on the 

effectiveness of implemented controls. These monitors are the DPMonitor and a 

personal dust monitor modified for diesel measurement (D-PDM). 

3.1 The DPMonitor 
The NIOSH developed DPMonitor is capable of measuring EC, at concentrations 

typically measured in underground mining operations, in near real time. This 

instrument uses a laser diode absorption technique similar to that used in 

conventional NIOSH 5040 analysis instruments. However, the DPMonitor is 

portable, lightweight and designed for near real time analysis. This instrument can 

be attached to a miner’s belt or to a piece of equipment to provide measurements of 

current EC concentrations which can then be plotted against time. This information 

can be used effectively when evaluating DPM control options. A picture of the 

DPMonitor is presented in Figure 3.

 

Figure 3: DPMonitor 

 

 

 Figure 4 presents data from the DPMonitor 

during tests evaluating the efficiency of an environmental cab. 

 

0

100

200

300

400

500

600

700

800

8:24 9:36 10:48 12:00 13:12 14:24 15:36

Time

EC (ug/m3)

inside cab

outside cab

 Figure 4: Interior and exterior cab EC 

concentration using a 5-minute running average 

during test 1. 

 

 

This data clearly 

shows that the environmental cab is effective in reducing the EC concentration and is 

an example of how this instrument can be used to assess the effectiveness of a control 

program. 

3.2 The Personal Dust Monitor 

A second real-time monitor being evaluated by NIOSH is a modified personal dust 

monitor (manufactured by Thermo Fisher scientific) or D-PDM. The D-PDM uses a 

tapered element oscillating microbalance to measure ambient submicrometer 

particles. Typically, more than 90% of submicrometer aerosols in underground mines 

are DPM. The D-PDM has the advantage of measuring the mass, in near-real-time, of 

many types of aerosols regardless of size, chemical composition, or refractive index. 

An example of results from preliminary tests of this modified instrument is shown in 

Figure 5. In this example the D-PDM data shows an increase in the concentration of 

submicrometer particles with the arrival of the diesel equipment (Gillies 2009). 
Figure 5: Diesel vehicle activities as measured by D-PDM 

4.0 SUMMARY 

As US mines continued to increase the utilization of diesel equipment in their mines, 

MSHA was enacting successively stricter diesel exposure limits. These factors 

created the need for improvements in diesel engine performance and control 

technologies. Through implementation of the integrated approach, US mining 

companies have substantially lowered the exposure of their workers to DPM. The 

continued development and refinement of real-time instrumentation to monitor diesel 

exhaust will further aid mining operations in their pursuit to limit exposures to DPM. 

 

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