1 INRODUCTION 

For the past seven years, the National Institute for 

Occupational Safety and Health (NIOSH) has been 

working closely with the underground mining industry, labor organizations, and the US mine enforcement agency – the Mine Safety and Health Administration (MSHA) – to assist in their understanding, 

development, and implementation of the alternative 

technologies to control and measure workplace concentrations of diesel exhaust contaminants. Control 

and measurement of diesel particulate matter (DPM) 

became the preeminent concern upon MSHA’s issuing proposed rules, and in January 2001 the promulgation of the two distinct diesel rules – one for underground coal (30 CFR 72) and one for 

underground metal and nonmetal mines (30 CFR 57) 

– that were designed to limit the exposure of underground workers to DPM. As one of its early efforts, 

the fledgling diesel team at NIOSH Pittsburgh in 

2000 produced an overview of the currently available control technologies in which their operating 

characteristics, performance characteristics, and 

limitations were described. This document emerged 

as a NIOSH publication IC 9462 (Schnakenberg & 

Bugarski 2002b) and is available for download from 

the NIOSH mining web site. The technologies that 

were covered included clean engine technology, alternative fuels (synthetic diesel, biodiesel, and water-fuel emulsions), diesel oxidation catalysts, disposable filter elements (DFE), and variously 

configured diesel particle filter (DPF) systems using 

wallflow monoliths of cordierite or silicon carbide. 

Some of these DPF systems, when engine exhaust 

temperatures were favorably high, would passively 

burn off the DPM as it was collected; other systems 

designed for application at prevailing exhaust temperatures, required an active application of a procedure to burn off the collected DPM. The process of 

burning off of the collected DPM in a filter is termed 

regeneration. 

In devising its DPM rule for metal and nonmetal 

mines, MSHA assumed that DPF systems would be 

necessary (66 Fed. Reg 2001, p 5713,). Because the 

implementation of this technology was not simple 

and because the entire concept of using filters was 

new to most of the mining industry, MSHA asked 

NIOSH in the fall of 2002 to help them develop a 

diesel particulate filter selection guide (DPFSG). 

The DPFSG was placed on the MSHA and NIOSH 

web sites in January 2003 with a minor revision in 

May 2003. This guide has received high praise from 

those with diesel control technology experience. 

During the period shortly after promulgation of 

the rules, NIOSH diesel researchers at Pittsburgh 

conducted several well controlled underground experiments designed to determine the effects of available control technology on diesel equipment emissions with the focus on DPM. These experiments 

An integrated approach for managing diesel emissions controls for 

underground metal mines 

G.H. Schnakenberg, Jr. 

National Institute for Occupational Safety and Health, Pittsburgh Research Laboratory, Pittsburgh, 

Pennsylvania, USA 

ABSTRACT: The National Institute for Occupational Safety and Health (NIOSH) has been working with diesel emissions control technology and the underground mining industry for a number of years. Underground 

isolated zone studies provided the emissions reduction performance of all of the alternative technologies currently available. A NIOSH/MSHA guide is available which provides mines with information and a process 

for selecting diesel particulate filters (DPF). Recent NIOSH experience suggests that more attention may be 

needed in managing the issues associated with diesel emissions and their control. The author argues that a holistic approach is needed which involves several key mine operations departments or disciplines by positing 

that workplace air can be considered as the product of a complex manufacturing process and examining how 

that process could be managed. 
were performed by operating a single unit with and 

without the control technology in place as it performed a repeatable work cycle that closely emulated a typical task performed by the vehicle. The 

equipment was run in an isolated part of a mine 

where the incoming ventilation rate and air quality 

were well controlled and could be measured. In sum, 

the results of these tests confirmed the beneficial effects of proper altitude adjustment of engine fueling 

rate and power matching for inby coal mine engines, 

and the laboratory performance for DPM and elemental carbon reductions obtainable with alternative 

fuels, disposable filter elements (DFE) and DPF systems. These tests also confirmed that DPF systems 

that utilized Pt-catalyzed washcoats to enhance regeneration also produce substantially elevated nitrogen dioxide (NO2) emissions (Schnakenberg & 

Bugarski 2002a, Bugarski et al. 2006a, b). Conducting these tests did not, however, throw much light 

on the issues concerning the implementation of these 

technologies into an actual production situation. Although the implementation is quite technology and 

mine specific, NIOSH is currently executing a study 

to expose many of the implementation issues in order to assess their impact and develop solutions. 

The implementation issue study currently underway, as well as a reflection on the situations experienced during the in-mine control technology testing, 

has emphatically shown that engine maintenance to 

keep emissions low is not a general or well understood practice. Aberrant engine emissions owing to 

maladjustment, use of an inappropriate replacement 

part, and a general failure to comprehend the concept were evident in the underground experiments 

noted above. The DPFSG recognized that emissionsbased maintenance is a necessary prerequisite for 

DPF implementation, but assumed that most mines 

had the resources and comprehension to readily 

adopt or had in place a sufficiently adequate engine 

maintenance program that controlled DPM emissions and as a result did not present the details of 

such a program other than by reference. 

Additionally, the DPFSG stated that the management of worker exposures to DPM emissions 

was not the exclusive responsibility of equipment 

maintenance department but required an integration 

and interaction of several departments including 

health and safety, ventilation, and production, in addition to equipment maintenance. However, the 

DPFSG did not go into much detail on this subject. 

This paper is an attempt to provide these details. 

2 AIR QUALITY MANAGEMENT 

One must consider that the deployment of diesel 

powered equipment into an underground mine creates a complex system involving several mobile and 

varying emission sources emitting of a variety of 

contaminants which are diluted and transported by 

the prevailing ventilation at the point of emission 

(equipment tailpipe). To this system is added the 

worker who is mobile (often coincident with a local 

source of contaminant) and is the consumer of the 

local contaminant concentrations, which may be 

mitigated by an environmental cab. One can take the 

view that this entire system can be modeled as a 

“manufacturing” process in which the final product 

is the air inhaled by the worker, and that air is “produced” by the interactions of the systems and process components mentioned. 

Considered thusly, the air quality, as measured by 

the level of diesel exhaust contaminants present in 

the inhaled air, is the responsibility of the manager 

of this “manufacturing process or plant” who must 

produce acceptable air quality at the lowest possible 

cost. This manager will have a team of process 

stream supervisors or specialists who are responsible 

for controlling the quality of their product as it is 

utilized and as they individually contribute to the 

quality of the final product. 

Although the “factory” for the production of 

“contaminated” workplace air is well established by 

virtue of operating just a single unit of diesel powered equipment underground, it is unlikely that any 

management system to control and assure the quality 

of workplace air was established at the same time. 

Continuing with the analogy, underground mining 

operations usually have the requisite management 

departments for the individual production processes 

contributing to the final product, but they are not organized or focused on integrating their efforts towards producing the workplace air product; rather 

they are focused on other objectives. Equipment 

maintenance, for example, is focused on maximizing 

equipment availability and is repair oriented. The 

tailpipe emissions, the very “raw” ingredient so to 

speak of workplace air quality, are not emphasized 

or treated as an important and necessary output of 

their efforts. 

3 DEPARTMENTAL ROLES 

The initial task for a manager of an underground 

mine utilizing diesel powered equipment is to recognize that controlling worker exposures to diesel 

emissions contaminants will require an integrated 
approach and is not the sole responsibility of one 

department or specialist. Because of the complexity 

and interactive nature of the underground diesel operation system, all departments or specialists which 

influence exhaust contaminant concentrations must 

work together. In many mines, this approach will be 

novel and most likely require an effort to shift the 

culture and focus of the affected departments. Mine 

management must be aware of the effort required 

and must prepare convincing arguments to effect the 

required changes for they have no other alternative if 

diesel emissions are to be controlled efficiently and 

effectively. 

3.1 Engine Maintenance 

The major contributor to workplace air quality, and 

a negative one at that, is the tailpipe emissions from 

the diesel equipment. It should be obvious that fresh 

air is being contaminated by the diesel emissions 

and, as a consequence, lower emissions are better 

and consistent with the air quality goal. Thus maintaining the tailpipe emissions of each piece of 

equipment to at or below its prescribed level should 

be a major objective of this department. Note that 

each piece of equipment should be assigned a prescribed level for each of the diesel contaminants. 

What these levels are will or may have been set by 

the analysis performed by production and ventilation 

departments in consort with the engine emission 

specialist. However, it should be rather clear from 

the cost of ventilation that in practice the maximum 

level for a particular engine’s emissions will not be 

much greater than that obtained for a properly running engine including properly installed and operating control technology. When exhaust aftertreatment 

systems are required, their maintenance is the responsibility of engine maintenance department as is 

the maintenance of any ancillary systems such as 

exhaust back pressure gages or monitors and filter 

regeneration systems required for the proper operation of aftertreatment systems. 

The above additional requirements may be considered to affect the “culture” of existing maintenance operations. The focus must shift from “doing 

what it takes to keep an engine running” to “doing 

what it takes to keep an engine running and running 

clean.” It is the responsibility of management to ensure that this latter goal is understood, implemented 

and rewarded. It is probably safe to state that, in 

general, the current maintenance departments are not 

adequately staffed with personnel sufficiently 

trained to perform the tasks required nor are adequate resources allocated to provide the required 

equipment and training. It is quite possible that finding and hiring suitable individuals to train is a problem in some areas of the country. 

Achieving the goals of engine maintenance cannot be done in isolation. The production department 

must understand that they cannot use a piece of 

equipment that runs but is not running cleanly. Their 

equipment operators need to be sensitive to their 

equipment’s emissions and report any changes such 

as the development of visible black smoke. 

3.2 Ventilation 

The role and objective of the ventilation department 

is to provide dilution and transport of the diesel exhaust contaminants released from the vehicle tailpipe so that the concentrations of these contaminants 

are within accepted limits. Despite the simple appearing objective, the efforts needed to achieve it are 

highly complex and involved, and the dealing with 

diesel emissions may be only one of the objectives. 

The details are too extensive to go into in this paper. 

For example, there are several diesel exhaust contaminants – the gases CO2, CO, NO, and NO2, and 

diesel particulate matter (DPM) – each with a spatially varying emission level as the equipment loads 

the engine differently as it moves throughout the 

mine with different prevailing airflows and each 

with its own acceptable air quality level. The tailpipe emissions may be altered by control technology 

which affect an entire fleet (in the case of an alternative fuel) or an individual piece of equipment as in 

the case of oxidation catalyst or exhaust filter. There 

will be a balancing act between the amount of ventilation that can be supplied to an area (and the quality 

of that air if it has been contaminated upstream) and 

the number of production vehicles that simultaneously occupy that area. The ventilation department 

must work closely with the production department 

who may want three trucks in a loading area when 

there is only ventilation enough to support two. 

Additionally, ventilation allocation is planned on 

paper, but must be carried out underground. Having 

proper ventilation at the required locations demands 

that the hardware which supplies that air not only be 

installed properly, but functionally verified and 

properly maintained. Torn tubing must be replaced, 

fans kept running, etc. In coal or gassy non-metal 

mines, ensuring and maintaining adequate ventilation to support diesel operation may be straightforward or at least has been a necessary and common 

practice because of the requirement to ventilate for 

methane. In most metal and nonmetal mines, however, ensuring adequate ventilation for the control of 

diesel contaminants at all times and locations can be 

a novel and difficult challenge. 
As noted above, diesels emit a limited variety of 

contaminants. The ventilation engineer must know 

what each of these are and how they are affected by 

control technology. He/she must know the occupational limits of the contaminants and work closely 

with the industrial hygienist or health and safety department. The ventilation engineer should be aware 

of the engine’s nameplate ventilation rate provided 

for MSHA certified engines, know how this rate is 

obtained, and know how to use such information to 

calculate ventilation air quantities. The use of aftertreatment device is not accounted for in the MSHA 

ventilation rate determination unless in a rare instance it is part of the engine. The almost ubiquitous 

use of diesel oxidation catalysts (DOC) which effectively reduce CO and hydrocarbons (when they are 

working) means that a low or undetectable level of 

workplace CO is no assurance that ventilation is 

adequate. On the contrary, the introduction of a new 

DOC or a platinum catalyzed exhaust filter may 

temporarily or permanently increase tailpipe NO2

concentrations to the point of requiring more ventilation air than that specified by MSHA for the engine without the DOC control. 

The ventilation engineer should also realize that 

one critical contaminant would remain if all other 

tailpipe emissions were reduced to an insignificant 

level. That contaminant is carbon dioxide. CO2 is an 

irreducible product of the burning of fuel diesel fuel, 

and as such leads one towards the rule that there always must be enough ventilation air to dilute the 

CO2 from the fuel being consumed. The monitoring 

of workplace CO2 concentrations is a little used but 

exceedingly useful tool for assessing the adequacy 

of localized (or general) ventilation to deal effectively with the localized (or general) burden of diesel equipment exhaust. Additionally, because CO2 is 

unaffected by emissions control technology yet is affected by ventilation along with the other tailpipe 

contaminants emitted with it, one can determine the 

effectiveness of a control strategy by simultaneously 

measuring CO2 along with the measurement or sampling of a controlled contaminant such as elemental 

carbon. For example, the use of a diesel exhaust filter on one or more pieces of equipment in a loading 

area should result in a drastic reduction in the EC to 

CO2 ratio. The ratios are independent of ventilation. 

Since tailpipe emissions and ventilation are inseparably linked, the ventilation engineer must be 

cognizant of vehicle deployment and utilization. The 

relationship between fuel burned and DPM emissions must be assessed for every vehicle or vehicle 

class. It is becoming more commonly known that the 

ubiquitous utility vehicle using low horsepower but 

rather dirty engines can be a major contributor to 

DPM burden and exposures. It seems that the ventilation department should perform the engineering 

calculations which will prescribe engine emission 

limits and, if needed or possible, the appropriate 

control technology for these vehicles. These limits 

are then transmitted to engine maintenance department who perform the necessary tasks to maintain 

engines to the prescribed emission levels. 

Since the objective of the ventilation department 

is to mitigate the effects of tailpipe emissions on 

workplace air quality, it will probably be their role 

to indicate when the ventilation system cannot adequately control DPM emissions to meet the compliance standard and the reduction of DPM emitted by 

the vehicle must be reduced using control technology. The selection of the most cost effective and appropriate control technology can be quite a complex 

decision which involves fleet-wide solutions (alternative fuels) and/or equipment-specific emission 

controls such as replacing the engine with a cleaner 

one or the addition of an exhaust filter. Once the 

need to control equipment emissions is realized, the 

development of a control strategy and selection of 

specific control technologies must be a collaborative 

effort of all departments. 

The above only touches the surface of the complex role of the ventilation department. They must 

work closely with those responsible for selecting 

new diesel powered equipment and control technology as well as with production department who need 

to utilize the equipment and with the health and 

safety department. The position is so pivotal for 

DPM control that it seems as if the ventilation department should assume the lead role for developing 

the overall mine strategy for controlling worker exposure to DPM. 

3.3 Health and Safety Department 

The health and safety department or industrial hygienist (IH) performs the quality assurance function 

by measuring workplace air quality and personal exposures to ensure that the air quality meets expectations. They must also work very closely with the 

ventilation department to convey to them the workplace contaminant limits for exposure and the relative toxicological importance of each. The IH and 

safety officials should be involved on an ongoing 

basis with those who are responsible for selecting 

control technology. In the process of considering a 

control technology, the IH needs to ask probing 

questions of the technology supplier as to how and 

what emissions are affected and let the ventilation 

engineer determine the impact on ventilation. The 
safety officials need to determine whether there are 

any safety issues with the technology. 

There is an obvious overlap between worker exposure measurements and workplace air quality 

measurements performed by the IH and ventilation 

department. The objectives of each department’s 

measurements are different and both are important. 

The measurements should not be the exclusive purview of one department; they should be coordinated 

when possible. Personal exposure measurements by 

the IH could be considered as proof that the air quality “production system” is functioning properly; that 

is, tailpipe emissions, vehicle deployment and ventilation together are controlling worker exposures. If 

exposures are not acceptable, then workplace or 

worker exposures to CO2 can be used to assess the 

adequacy of ventilation, and contaminant to CO2 ratios can be used to determine if control of tailpipe 

emissions (a malfunctioning engine or control technology failure) is the cause for unacceptable exposures. 

3.4 Production 

The obvious objective of production department is 

to get the most rock to the surface as safely and 

quickly as possible by efficiently utilizing available 

equipment and operators. After all, production is the 

money maker for the mine. Equipment availability is 

a prime concern and thus production supervisors 

push the maintenance department to service or repair 

equipment quickly. They may push the limits of the 

ventilation by wanting more pieces of equipment in 

an area than the local ventilation can support. However, when production goals cause engine maintenance and ventilation to less than adequately fulfill 

their objectives, the underground workers are the 

ones most affected by the decrease in air quality. 

The production department, as users of equipment, must be involved in air quality management. 

Their input on equipment deployment and utilization 

is essential for designing the ventilation system and 

equipment emission levels. On the other hand, the 

equipment operators must be instilled with an appreciation of the necessity to control air quality and 

DPM in particular. Altering driving habits (such as a 

using gentle application of the throttle) may reduce 

excessive DPM emissions. Having the equipment 

operators understand the importance of correct and 

continual operation of exhaust filters would increase 

equipment availability and filter longevity, for example. Equipment operators should be encouraged 

to perform a key function in detecting and reporting 

equipment malfunction such as excessive smoke, inoperative back pressure gages, etc. 

The production department is most likely heavily 

involved in decisions to rebuild old equipment and 

to select new equipment for purchase. These decisions should strive to obtain equipment using diesel 

engines with the lowest DPM emissions possible. 

This goal should be applied to any diesel-powered 

equipment being purchased. The intended purchase 

should be discussed with MSHA engine specialists, 

and the mine’s maintenance and ventilation departments. 

The production department must be involved 

when circumstances necessitate the utilization of 

diesel particulate filters because retrofitting of filters 

cannot be characterized as a “fit and forget” solution. How equipment is used, and the variability of 

use, greatly affects the selection and ultimate performance of DPF systems. DPF systems which passively regenerate can be successfully applied to relatively few vehicles and there is a consequence to 

ventilation from secondary emissions of NO2. DPF 

systems which must be “actively” regenerated – 

through either the application of a regeneration cycle 

to the DPF when the equipment is not in use or by a 

DPF exchange – have a significant effect on operational logistics, mine infrastructure, and equipment 

operator responsibility. The selection of filters obviously requires the input and agreement of all departments. 

4 SUMMARY 

This paper has presented a limited discussion supporting the need for an integrated interdisciplinary 

approach to control worker exposures to DPM in 

underground mines, and that the control of workplace air quality and worker exposure to diesel exhaust contaminants is a complex task and must be 

approached holistically. Using a factory or production analogy with the workplace air as the final 

product, the author identifies the typical mining operations departments involved in producing that 

product, discusses their involvement and roles, and 

shows that they all need to work together. It is the 

author’s view that the need for such an approach is 

not widely recognized within the metal and nonmetal underground mining industry, yet such an approach is necessary in order to control worker exposure to DPM to MSHA compliance levels. 

Management needs to form an integrated team of 

principals from equipment maintenance, ventilation, 

health and safety, and production departments and 

other areas which affect or are affected by measures 

required to control air quality. The ventilation de-
partment appears to be the most appropriate department to lead and manage the coordinated effort. 

REFERENCES 

30 CFR 57. Safety and health standards--underground metal 

and nonmetal mines. Code of Federal Regulations. Washington, DC: U.S. Government Printing Office, Office of the 

Federal Register. 

30 CFR 72. Health Standards for Coal Mines. Code of Federal 

Regulations. Washington, DC: U.S. Government Printing 

Office, Office of the Federal Register. 

66 Fed. Reg. 5706 (2001) Mine Safety and Health Administration: 30 CFR 57, diesel particulate matter exposure of underground metal and nonmetal miners; final rule 

Bugarski AD, Schnakenberg. GH Jr., Noll JD, Mischler SE, 

Patts LD, Hummer JA, and Vanderslice SE (2006a). In-situ 

Effectiveness of Selected Diesel Particulate Matter Control 

Technologies for Underground Mining Applications- Part I. 

U.S. Department of Health and Human Services Report of 

Investigation RI. In Press 

Bugarski AD, Schnakenberg. GH Jr., Mischler SE, Noll JD, 

Patts LD, and Hummer JA. (2006b) In-situ Effectiveness of 

Selected Diesel Particulate Matter Control Technologies for 

Underground Mining Applications – Part II. U.S. Department of Health and Human Services Report of Investigation 

RI. In Press. 

Schnakenberg GH, Bugarski AD (2002a) Effects of Fueling 

Rate and Filters on PM Emissions from Diesel Vehicles at 

High Elevations. In Proceedings of the Mining Diesel 

Emissions Conference (MDEC). Markham, Ontario, Canada: CANMET/NRCAN, 555 Booth Street, Ottawa, Ontario K1A 0G1. 

Schnakenberg G and Bugarski A (2002b). Review of Technology Available to the Underground Mining Industry for 

Control of Diesel Emissions. U.S. Department of Health 

and Human Services Information Circular IC 9262. 

[http://www.cdc.gov/niosh/mining/pubs/pdfs/ic9462.pdf]