Mine Safety and Health Administration
Protecting Miners' Safety and Health Since 1978
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U.S. Department of Labor Mine Safety and Health Administration Protecting Miners' Safety and Health Since 1978 |
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Practical Ways to Reduce Exposure TABLE OF CONTENTS Introduction Addressing the Problem: The Experience of the Mining Community The Reason For a "Toolbox" Approach The Toolbox Low Sulfur Fuel, Fuel Additives and Alternative Fuels Respiratory Protective Equipment Measuring the Concentration of Diesel Particulate Matter in Mines A Dozen Ways to Reduce Exposure to Diesel Particulate Matter Appendices A. Recommended Additional Reading C. Methods of Measuring Diesel Particulate Matter D. References to Relevant Regulations
The Mine Safety and Health Administration (MSHA) held a series of workshops in the fall of 1995 to obtain input from the mining community on ways of reducing miners' exposure to diesel particulate matter from the exhaust of diesel engines. MSHA thanks those who attended the workshops and willingly shared their ideas on practical ways to reduce exposure to diesel emissions in mining. These practical ideas have been utilized in producing this "Toolbox." A key objective of the toolbox is to facilitate the exchange of practical information on ways to reduce miner exposure to diesel exhaust emissions. Thanks are also extended to former U.S. Bureau of Mines scientists, from whose diesel-related publications the text of this handbook draws, and to Robert Waytulonis, Associate Director of the University of Minnesota's Center for Diesel Research. Credit is given to the following MSHA staff for their efforts in organizing the Diesel Exhaust Workshops, their role in selecting pertinent quotations from the workshop transcripts, and in contributing to or reviewing this manual: Kathy Alejandro, Janet Bertinuson, Teresa Carruthers, Jerry Collier, James Custer, George Dvorznak, Guy Fain, Ron Ford, Don Gibson, Hal Glassman, Jerry Lemon, Pamela King, James Kirk, Jon Kogut, Cheryl McGill, William McKinney, Ed Miller, Charlotte Richardson, Bryan Sargeant, Erik Sherer, Pete Turcic, and Sandra Wesdock. Thanks also to Liz Fitch and Mike Doyle for their help in reviewing early drafts, to Todd Taubert for help with the section on lugging, to Reggie McBee and Bria Culp for editorial support, to Anne Masters for graphic design support, and to Bill West for internet conversions. A special "thank you" to the mechanics, miners and other members of the mining community in Kentucky who took the time to review a draft of this publication for MSHA: Oscar Lucas, Ed Topping, Steward Stidham, William Peace, Bill Fields, Thurman Halcomb, West Sheffield, Robert Hoskins, Ronnie Stubblefield, Tracy Begley, and Ray Slusher. In addition, MSHA thanks other segments of the mining industry that provided comments for consideration in the Toolbox. Andrea Hricko, Deputy Assistant Secretary of MSHA, provided guidance in organizing the Diesel Workshops and worked closely with Winthrop Watts of the University of Minnesota, and Thomas Tomb, Chief of MSHA's Dust Division, as well as with Robert Haney and George Saseen of MSHA's Office of Technical Support, in creating this "Toolbox." Thanks to Peter Galvin for consolidating the final draft while on detail to MSHA from the Office of the Solicitor and to Keith Gaskill for shepherding the "Toolbox" through to publication. Special thanks to Winthrop F. Watts, Jr., Ph.D., of the University of Minnesota, Center for Diesel Research, for conceptualizing the "Toolbox"and for writing the first drafts of this manual under contract to the Mine Safety and Health Administration. Who should use this publication? If your mine uses diesel-powered equipment, or is contemplating its use, you will find this Toolbox to be a useful guide. So too will those who help mine operators select or maintain mining equipment. The Toolbox can be read cover-to-cover as a basic reference, or used as a troubleshooting guide by diesel equipment operators and mechanics. Some knowledge of engines is assumed, although a glossary is provided. Is this only of interest to underground mines? No. While some sections are of special interest only to underground mines (e.g., ventilation), most of this publication is of value to surface mines as well. Is the Toolbox useful in any type of mining? Yes. The ideas and concepts are just as relevant in metal and nonmetal mines as they are in coal mines, and many of the controls described are available to operators in both sectors. How can I find what I need quickly? The Table of Contents on the first page of this handbook can be used to quickly locate a topic of interest. Technical terms or materials are discussed or referenced in appendices.
If I follow the recommendations in the Toolbox, will I be in compliance with MSHA requirements? This publication is NOT a guide to applicable Federal or State regulations on the use of diesel engines, or the measurement or control of their emissions on mining property. Selection of an approach from the toolbox must be made in light of the need to comply with such requirements. Appendix D references some of the requirements which should be consulted. Please contact your local MSHA office if you have any questions about applicable requirements. As of the date of this Toolbox printing, MSHA is making final decisions on proposing some additional regulations about diesel emissions. These proposed new rules would help the mining community address the risks created by miner exposure to diesel particulate matter--the very small particles that are part of the diesel exhaust. The Agency expects to publish these proposed rules for comment early in 1998. While the requirements that will ultimately be implemented, and the schedule of implementation, are of course uncertain at this time, MSHA encourages the mining community not to wait to protect miners' health. MSHA is confident that whatever the final requirements may be, the mining community will find this Toolbox information of significant value. Does MSHA want my input on this subject? MSHA welcomes your suggestions on how to improve future editions of this Toolbox, and information on your experiences in reducing exposure to diesel emissions. Please direct any comments to: Chief, Pittsburgh Safety and Health Technology Center, Cochrans Mill Road, P.O. Box 18233, Pittsburgh, Pa. 15236. You may also fax them to 412-892-6928, or e-mail them to chiefpshtc@msha.gov.
Special Note on Regulations Involving the Use of Diesel-powered Equipment in Underground Coal Mines On April 25, 1997, certain key provisions of MSHA's final rule on the use of diesel-powered equipment in underground coal mines went into effect. Other provisions of that rule will go into effect over the next three years. Some of these regulations require the implementation of particular strategies recommended in this Toolbox. Since the mining community is still becoming familiar with these requirements, some of them are noted in the text at appropriate places, using italics. MSHA hopes this will serve as a useful reminder for underground coal mine operators, without being distracting to the remainder of the mining community. A compliance guide for the new underground coal mine diesel regulations, in the form of Questions and Answers, has been prepared by MSHA, and is being widely circulated. While this Toolbox is not a substitute for the compliance guide or a copy of the regulations, neither are the compliance guide or the regulations a substitute for this Toolbox--all three documents will be useful for underground coal mine operators and miners.
INTRODUCTION Diesel engines are widely used in mining operations because of their high power output and mobility. Many mine operators prefer diesel-powered machines because they are more powerful than most battery-powered equipment and can be used without electrical trailing cables which can restrict equipment mobility. Underground coal and metal and nonmetal mines currently use approximately 10,000 diesel machines and about 35 percent of these are used for heavy-duty mining production applications. The use of diesel equipment in mining is on the rise, as described by speakers at a series of Workshops on Controlling Diesel Emissions sponsored by MSHA in the fall of 1995: "In 1985, we had a total mine horsepower of 6,851 horsepower. Today, in 1995, our horsepower has risen to 14,885 horsepower in the mine." --David Music, "…Today we have over a hundred pieces of diesel equipment, large and small, anywhere from a Bobcat to large section scoops, generators, welders, compressors, trucks that are used on open highways, and diesel trucks." --Forrest Addison, The estimated distribution of diesel equip-ment in mining is shown in Table 1. An estimated 30,000 miners work at underground mines using such equipment and approximately 200,000 miners work at surface operations using such equipment. Table 1. Estimated Distribution of Diesel Equipment
There is a downside, however, to the use of diesel equipment, especially in the underground mining environment. The problem is the potential acute and long-term health effects of exposure to various constituents of diesel exhaust, which consists of noxious gases and very small particles. The gases in diesel emissions include carbon monoxide, carbon dioxide, oxides of nitrogen, sulfur dioxide, aromatic hydrocarbons, aldehydes and others. MSHA sets limits on miner exposure to a number of these gases. These limits are specified in Title 30 CFR § 75.322 and § 71.700 for underground and surface coal mines and § 57.5001 and § 56.5001 for underground and surface metal and nonmetal mines. The particles in diesel emissions are known as "diesel particulate" (DP), or "diesel particulate matter" (DPM). Diesel particulate matter is small enough to be inhaled and retained in the lungs. The particles have hundreds of chemicals from the exhaust adsorbed (attached) onto their surfaces. The mining community is very familiar with the specific hazards long associated with other particulates of respirable dimensions-like coal mine dust and dust that contains silica. A recent body of evidence, based on studies of air pollution, suggests that exposure to smaller particles (including those present in diesel exhaust) is likewise associated with increased rates of death and disease. Specific evidence has also been accumulating that exposure to high levels of DPM can increase the risk of cancer. In 1988, the National Institute for Occupational Safety and Health recommended that whole diesel exhaust be regarded as a "potential occupational carcinogen," and that reductions in workplace exposure be implemented to reduce cancer risks. In 1989, the International Agency for Research on Cancer declared that "diesel engine exhaust is probably carcinogenic to humans." In 1995, the American Conference of Governmental Industrial Hygienists (ACGIH) added DPM to its "Notice of Intended Changes" for 1995-96, recommending a threshold limit value (TLV®) for a conventional 8-hour work day of 150 micrograms per cubic meter (150 mg/m3 Note on Diesel Particulate Matter Measurements:Microgram v. Milligram In this Toolbox, measurements of DPM are expressed in micrograms (mg) per cubic meter of air. A microgram is one millionth of a gram. However, in many references, you may see the DPM measurements expressed as milligrams (mg) per cubic meter of air. A milligram is one thousandth of a gram. 1 mg/m3=1 milligram per cubic meter of air 1 mg/m3=1 microgram per cubic meter of air 1 milligram=1,000 micrograms. So if you want to convert from milligrams to micrograms, multiply by 1000-or move the decimal point three places to the right. For example, 0.15 mg/m3=150 mg/m3. Many non-mining workplaces where diesel equipment is used have levels of DPM well below the recommended ACGIH TLV®.In contrast, studies conducted by various scientific researchers demonstrate that exposures to DPM in mining environments can be significantly higher than exposures in the ambient air or in other workplaces. Figure 1 provides a rough visual picture of the range of DPM exposures of miners, as compared with the range of exposures of other groups of workers who routinely work with diesel-powered equipment. As can be readily seen, the range of exposures in mining environments are significantly higher than in other environments. Figure 1. Diesel Particulate Exposures in Several Industry Segments Range of Average DPM Exposures, mg/m3. 
Table 2 provides additional detail about the levels of exposure in U.S. mines. The higher concentrations in underground mines are typically found in the haulageways and face areas where numerous pieces of diesel equipment are operating, or where insufficient air is available to ventilate the operation. In surface mines, the higher concentrations are typically associated with truck drivers and front-end loader operators. Table 2. Measured Full-Shift Diesel
In 1988, MSHA's Advisory Committee on Diesel-Powered Equipment in Underground Coal Mines recognized a number of risks related to the use of diesel-powered equipment in such mines, including the potential risks of exposing miners to diesel emissions. The Committee made recommendations to address its concerns. Since that time, MSHA has taken several actions relative to diesel exhaust. In 1989, MSHA proposed "air quality" regulations which would, among other things, set stricter limits on some diesel exhaust gases. These regulations remain under review. In 1996, after notice and comment, MSHA issued final regulations for the use of diesel-powered equipment in underground coal mines. These rules will go into effect over a 3-year period. And in response to a specific recommendation of the Advisory Committee that, "The Secretary (of Labor) should set in motion a mechanism whereby a diesel particulate standard can be set…", MSHA is developing a proposed rule toward that end. There are some cases where alternative power sources (e.g., electricity or batteries) may be the solution. But when diesel engines are used, the mining community needs to understand the potential health risks they present and take steps to reduce the hazards. "…We're very dependent on diesel engines. At the same time, air quality in the mine is very important to IMC. We realized a long time ago that it affects both miner health and morale, and for us morale and productivity go hand in hand. So beginning in the 1970s we consciously undertook a program of improving our air quality…." --Scott Vail, Ph.D., "…Of all the health issues that we're dealing with in the mining industry, this issue is at the top of the list...As I travel across this country, I hear more about exposure to diesel exhaust than any other single issue in the mining industry." --Joe Main, The Experience of the Mining Community In 1995, MSHA established an internal working group to explore measures to reduce miners' exposure to DPM. This group organized a series of workshops to solicit input from the mining community. The workshops were designed to discuss the potential health risks to miners from exposure to DPM, ways to measure and limit DPM in mine environments, and regulatory or other approaches to ensure a healthful work environment. These workshops provided a useful forum to exchange views and concerns about limiting diesel exhaust exposure. More than 500 members of the mining community attended these workshops, providing evidence that reducing miners' exposure to diesel exhaust emissions, especially in underground mines, is a high priority for the mining industry. The experience of the mining community appears to support several conclusions: • The levels of exposure to DPM in mines depend upon engine exhaust emissions, the use of exhaust aftertreatment and its efficiency and, particularly in underground mines, ventilation rate and system design. • Engine emissions are governed by engine design, work practices, duty cycle, fuel quality and maintenance. Reducing engine emissions will decrease the amount of DPM that needs to be controlled by other means and will reduce the exposure of miners. • There is no single emission control strategy that is a panacea for the entire mining community. • Diesel engine maintenance is the cornerstone of a diesel emission control program. A major objective of this publication is to facilitate the exchange of practical information within the mining community on ways to reduce miners' exposure to diesel exhaust emissions. The Toolbox focuses on currently available methods of control as opposed to methods in the research and development stages. Each of the various technologies presented in the Toolbox will assist in reducing or monitoring worker exposure. Where possible, the Toolbox quotes specific examples of methods tested or used by the
mining industry to reduce exposure to diesel emissions. These quotations are taken directly from
public transcripts of the 1995 MSHA workshops, and were selected to provide a representative
sample of views expressed. All quotations are offset from the main text in bold lettering. The Toolbox also draws extensively from diesel-related publications prepared by former U.S. Bureau
of Mines scientists. Please note that key words and phrases are highlighted in bold type for easy
reference. MSHA hopes that the mining community will benefit from the exchange of this practical information and will take steps to reduce miners' exposure to diesel emissions, utilizing the variety of techniques described in this publication and other methods as they are developed. The Agency encourages an ongoing exchange of information on strategies to further reduce exposure to diesel emissions and to protect the health of miners. The quotations cited in this publication do not necessarily represent the views and/or policies of MSHA, nor of the organizations or companies at which the speakers work (or worked). MSHA recognizes that some affiliations have changed since the workshops. Names and affiliations at the time of the workshop are used. Finally, reference to specific manufacturers and/or products does not imply endorsement by MSHA or the U.S. Government.
THE REASON FOR A This publication introduces a "toolbox" approach to reducing miners' exposure to diesel exhaust emissions. A toolbox offers a choice of tools, each with a specific purpose. One tool after another may be used to find a solution to a problem or several tools may be tried at the same time. Reducing exposure to diesel emissions lends itself to a toolbox approach because no single method or approach to reducing exposure may be suitable for every situation. Examples of the "toolbox" approach to reducing exposure to diesel emissions in a mine were described at the 1995 MSHA workshops: "Since the mid-1980s Homestake has initiated a number of work steps and tests to control the diesel emission components, and these are engine alternatives, maintenance, exhaust aftertreatments, fuels, dilution ventilation and engine type….To summarize our experiences with diesel particulate matter, we've had good luck with respirators, maintenance and fuels. We've had mixed results with diesel particulate filters and with airflows. And results are still pending on engine type. We are going to continue working in all of these areas." --John Marks, "At Galatia a three-point approach is used to ensure safe and healthy diesel operating conditions. First, the mine is designed to provide vast volumes of air to all the active workings… Second, a well-conceived maintenance program strives to maintain optimum engine performance and thereby control diesel exhaust emissions. The maintenance program consists of regularly scheduled replacements of fluids and filters, operating performance evaluations and additional weekly permissibility inspections, a regularly scheduled emissions test…and…a training program to educate maintenance personnel in the engine operating recommendations and requirements. The third point in our approach is the use of control technology…All permissible vehicles…at Galatia use a wet scrubber for initial particulate reduction. Additionally, 10 Ramcars that are normally assigned to production units have been retrofitted with the pleated paper diesel particulate filter. Additional vehicles are being retrofitted during equipment rebuilds." --Keith Roberts, "…Ventilation is an important control…. Through clean-burning diesel engines, low sulfur fuels, and effective aftertreatment technology, we can reduce emissions at the engine." --Jeff Duncan, The Toolbox is divided into nine sections--  use of low emission engines
Each section covers specific methods that are being used to reduce emissions or exposure. Use of these methods will be determined by the specific circumstances found at each mine. "There is no single control that is a panacea for all the emission problems. Due to differencesin the mine design and the mine geology, the equipment types and sizes, and their duty cycles…different types of controls are used." --Robert Waytulonis, --Robert Haney, Low Emission Engines Low emission engines are produced by engine manufacturers to meet increasingly stringent Environmental Protection Agency (EPA) regulations. Mine operators can benefit from discussing the condition of their diesel fleet with diesel manufacturers prior to ordering new diesel engines. Moreover, benefits can be gained by replacing older model engines that require more maintenance with newer engines. In addition, lower emissions and greater machine availability (i.e., the machine does not break down as often) are normally achieved with a newer type engine. Low-emission engines typically operate at high fuel injection pressures which provide more efficient and complete combustion of fuel. These engines are frequently turbocharged to optimize power, performance, and emissions. After-cooling (cooling intake air that is compressed and heated by the turbocharger prior to induction into the combustion chamber) is used to reduce oxides of nitrogen (NOx). Electronic engine control is another technological improvement, which optimizes the fuel-to-air ratio resulting in lower emissions. As a result of EPA regulations in 1988, "on-highway" heavy duty diesel engine emissions have been significantly reduced. Emissions standards have driven particulate emissions levels for such engines from 0.6 grams per horsepower-hour (g/hp-h) in 1988 to less than 0.1 g/hp-h in 1994, and oxides of nitrogen emissions from 10.7 g/hp-h in 1985 to 5.0 g/hp-h in 1991. The EPA regulations provide a schedule for continued improvement. Pursuant to an agreement with the engine industry, the EPA has also proposed a new round of emission reductions in highway engines to begin with models produced in 2004. In 1996, the EPA established emission regulations for almost all land-based non-road ("off-highway") diesels, such as construction equipment. These regulations specify emission levels that non-road engines must meet depending on the horsepower of the engine. Currently, the regulations affect only non-road engines from 175-750 horsepower. For this category, the 1996 standard reduces particulate emissions from as high as 1.0 g/hp-h to 0.4 g/hp-h and oxides of nitrogen emissions to below 6.9 g/hp-h. The rule phases in limits for other horsepower engines. Modern engines developed for non-road use are expected to provide the mining industry with a greater choice of low emission engines for use underground. It should be noted that diesel engines used in underground coal mines are primarily indirect injection engines (pre-chamber), which in some cases could meet certain EPA non-road requirements. In September 1997, pursuant to an agreement with the engine industry, the EPA proposed a new round of emission reductions in non-road engines to begin with models produced in 1999. Engines that have been approved or certified by agencies such as MSHA, EPA or the state of California generally have lower emissions. Larger on-highway type engines built after 1988 and non-road engines built after 1996 have been designed to produce lower emissions to meet the stringent on-highway emission standards discussed above. For engines approved under Part 7, subpart E for underground mining applications, MSHA determines a particulate index (PI). The PI indicates the quantity of ventilation air required to dilute particulate emissions from a specific engine operated over a test cycle to a concentration of 1 milligram (1000 micrograms) per cubic meter of air. Mine operators and machine manufacturers of mining equipment can use the PI in selecting and purchasing engines. The lower the PI number, the lower the particulate emissions for the same horsepower engine. Mine operators may also use the PI to roughly estimate each engine's contribution to the mine's levels of total respirable dust in coal mines or the levels of diesel particulate in metal/nonmetal mines. In underground coal mines, all engines must be Msha-approved engines by November 25, 1999. "…Diesel engines continue to become cleaner; there will be more emission legislation out there in the future…. Diesel engine fuel efficiency has improved at the same time; power density has continued to climb; diesel engine life has steadily increased."
"In over the road truck engines, there has been about a 90 percent reduction in just going to cleaner engine technologies, and these are results that apply to well-maintained, new engines…"
"Now, this class of engines [modern, low emission engines] has high horsepower, typically from 250 hp up to 500 hp, so they are not suitable for all types of mining equipment.… They have the advantage of producing 80-90 percent less particulate than the conventional naturally-aspirated prechamber engines. They consume on the order of 25 percent less fuel. In the case of the Cat 3306 swirl, it's a drop-in replacement for some of the older 3306 technology."
"[Start] with buying a clean engine as opposed to some of these polluting engines that dump out all kinds of NOx's and carbon monoxide. Buy the cleaner engines…" "We felt that the problems we had with filters…were so severe and caused so many problemsthat it was a lot better to clean up the source, and so we got cleaner engines. We are using one manufacturer's engine. We're getting another--in fact, we're getting one of the new…Detroit Diesel engines with electronic controls just for that reason in the next machine we buy…. Utilization of highway-type diesel engines in our replacement engine program is providing us cleaner burning, reliable engines at a lower cost than the regular mining-type engines and a post-combustion device…"
USE OF LOW SULFUR FUEL, FUEL ADDITIVES AND ALTERNATE FUELS In general, emissions can vary from engine to engine and across different engine load conditions, even though all engines are operated using the same basic type of fuel and fuel additive package. Variations occur because the details of the combustion process differ with engine design and methods used to control fuel to the engine as well as with the duty cycle of the engine. Therefore, the following comments on fuel composition and additives should be viewed as generally applicable to an average diesel engine operated over a range of duty cycles. The quality of the 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 particulate matter emissions. In addition, it affects sulfur oxide (SOx) emissions, all forms of which are toxic. Moreover, SOx emissions can poison catalytic converters, and the continued use of high sulfur fuel will contribute to increased piston ring and/or cylinder liner wear. Cetane number affects all regulated pollutants, and fuel aromatic content affects DPM and nitrogen oxides (NOx). Therefore, it is important to provide fuel distributors with specific fuel specifications and recommended property limits when purchasing diesel fuel. Table 3 lists recommended property limits for diesel fuel. However, some of the property limits listed may not be commercially available in all areas at this time. Table 3. Recommended Property Limits
Use of low sulfur diesel fuel (<0.05 percent sulfur) reduces the sulfate fraction of DPM emissions, reduces objectionable odors associated with diesel use, and allows oxidation catalysts to perform properly. Another benefit from the use of low sulfur fuel is reduced engine wear and maintenance costs. Fuel sulfur content is particularly important when the fuel is used in low emission diesel engines. Low sulfur diesel fuel is available nationwide due to EPA regulations. As of April 25, 1997, diesel-powered equipment in underground coal mines must use low-sulfur fuel. "…There is an ASTM-975-93 specification [on low sulfur fuel] from the EPA. All you have to do is to specify that fuel on your purchase order, and this is the fuel they have to deliver. You just have to insist on it."
"…Homestake used a straight No. 2 diesel fuel with up to 0.5 percent fuel sulfur until 1991 when we switched to a premier No. 2 with 0.12 percent fuel sulfur. Since about the start of 1995 we've gone to the 0.05 percent No. 2."
"For fuel we use a low sulfur diesel fuel that typically averages 0.041 percent sulfur and a cetane number of 54."
The cetane number of U.S. diesel fuel can range between 40 and 57. Increased cetane number and volatility, (as measured by a fuel's distillation temperature characteristics) reduces both hydrocarbon emissions and the tendency to produce white smoke, which occurs when an engine is either cold or under low load. White smoke is mostly water vapor, unburned fuel and a small portion of lube oil. Fuel with a cetane number greater than 48 and a seasonably adjusted cloud point reduces cold-start hydrocarbon emissions, odor, noise, irritant and fuel system wax separation problems. "…Cetane number is very important--needed for good starting, good combustion and for emission performance of engine…. When cetane number is improved, either by cetane additive or base fuel composition…so that cetane number is improved from 45 to 55, there's a dramatic reduction in hydrocarbons…and…in carbon monoxide…and more than 10 percent reduction in particulates"
Typical No. 2 diesel fuel in the U.S. has an aromatic hydrocarbon content of 20 to 40 percent. Reducing the aromatic hydrocarbon content and the 90 percent distillation temperature of the fuel reduces the soluble organic fraction of DPM and NOx emissions. A variety of fuel additives are available to reduce emissions. For example, cetane improvers increase the cetane number of the fuel, which may reduce emissions and improve starting. Oxygenated additives increase the availability of oxygen needed to oxidize hydrocarbons in the fuel. Detergents are used primarily to keep the fuel injectors clean. Dispersants or surfactants prevent the formation of thicker compounds that can form deposits on the fuel injectors or plug filters. Lubricity additives are similar to corrosion inhibitors and are frequently added to fuel by petroleum producers. There are also stability additives which prevent the fuel from breaking down when it is stored for long periods of time. Only additives registered by the EPA are recommended for use, to ensure that no harmful agents are introduced into the mine environment.As of April 25, 1997, only diesel fuel additives that have been registered by the epa may be used in diesel-powered equipment in underground coal mines. "…There's a variety of different types of compounds you can add that contain oxygen. Typical diesel fuel doesn't have much oxygen…. [When significant quantities of oxygenates are added to fuel, the oxygen content of the fuel is increased], …You end up seeing…reductions in particulate emissions, hydrocarbon emissions and CO…, and NOx levels may increase or decrease slightly depending on the engine and load cycle."
"We took a very serious look at metal additives…for on-highway trucks…. We-Caterpillar-and the industry decided not to go that way…[One] concern was [that] these chemicals may actually cause health effects in their own rights…"
"…Detergent-type additives in the fuel primarily prevent coking or fouling [partial plugging] of the injectors. And if you don't use a detergent additive, pretty much all your emissions go up over time… [However] just using a detergent is not going to make up for an engine that's wearing out or isn't properly adjusted or maintained. …Metals as a group reduce the visible smoke output. …The problem with metal additives is they show up on the particulate. Metals don't burn up. …Metals are known to have some biological effects just like diesel particulates would. So I would not recommend that you [use] any of the metal additives for reducing [diesel particulates]."
Another promising control technology is alternative fuel, especially biodiesel fuels made from methyl esters derived from soybeans, although these are not readily available on the market. This type of fuel contains about 10 percent oxygen, has a high cetane number, and a much higher flash point. These properties improve combustion, starting, performance and safety characteristics of the fuel. To maximize the reductions in exhaust emissions, it is recommended that biodiesel fuels be used with a diesel oxidation catalyst. EPA has certified a biodiesel brand known as Envirodiesel®, which is being used in combination with diesel oxidation catalyst by urban bus transit operators. "The Bureau of Mines demonstrated that the combination of methyl soyate fuel and modern diesel exhaust catalyst is a passive control scheme that is very effective…. [In tests conducted at the Homestake Gold Mine], a Wagner load-haul-dump was operated using a 100 percent methyl soyate fuel and a modern catalyst. Compared to baseline emissions, a 70 percent reduction in the ambient levels of [diesel] particulate matter was achieved…."
"…Homestake cooperated with the [former]Bureau of Mines to successfully evaluate a soy methyl ester [biodiesel] fuel…miner acceptance was good, and the leftover [biodiesel] fuel was quickly used by our miners."
USE OF AFTERTREATMENT DEVICES Water scrubbers are basically a safety device used on "permissible" equipment in underground mines. Water scrubbers perform three functions: cool exhaust gases to safe temperatures, arrest sparks and arrest flames. The exhaust airflow from a diesel engine passes through water, making direct contact with the water. This direct contact with the water cools the air and quenches flames and sparks. Although not intended as an emission control device, scrubbers have been shown to remove about 30 percent of DPM from an engine's exhaust stream. Moreover, because water scrubbers cool the exhaust gases, they enable the equipment to be fitted with high efficiency paper filters that reduce DPM. Water scrubbers have no signifcant effect on gaseous emissions. "The water scrubber…is not an emission control, it's a safety control, but incidentally, it will remove 20 to 30 percent of the particulate…. They require frequent maintenance."
"Water scrubbers are not a pollution control, they are a fire control system…, but scrubbers create condensation in the air and increase mine air humidity…and with several pieces of diesel equipment using water scrubbers [on a section], the increased heat effect because of the humidity is a significant concern…."
The exhaust location can make a big difference in the concentration of pollution to which equipment operators and nearby miners are exposed. The location should be such that exhaust is directed away from the vehicle operator. The exhaust gas can be directed across the radiator, thus providing immediate dispersal by the radiator fan, or an exhaust extender can be used to redirect the exhaust away from the operator or nearby miners. These workers can be exposed to significant concentrations of diesel exhaust constituents before they can be diluted, even at surface mines. Exhaust dilutors can also be used in vented headings and tunnels. "Wouldn't it be nice if we could take that exhaust and put it somewhere else on the vehicle, so then, at the very least, the Ramcar operator is not subject to his own vehicle's emissions?"
Exhaust filtration devices capture DPM from the exhaust before it enters the mine atmosphere. Filters used to capture particulate or other exhaust constituents are called after-treatment devices.The most commonly used exhaust filtration devices are: disposable diesel exhaust paper filters and catalyzed or uncatalyzed diesel particulate ceramic filters. Particulate control systems using these components typically have removal efficiencies ranging between 50 and 95 percent; that is, they remove 50 to 95 percent of the particulate. It is important to note that an aftertreatment device that is 90 percent efficient is twice as effective for removing DPM as an 80 percent efficient device: only10 percent instead of 20 percent of the particulate would remain in the exhaust. The disposable diesel exhaust filter is similar to the intake air filter used on over-the-road haulage vehicles. It is placed downstream of a water scrubber or a water jacketed heat exchanger, capturing DPM from the exhaust stream. The filter is discarded after being loaded with DPM. Some states such as Pennsylvania require the loaded filters to be bagged and brought to the surface for disposal. Tests of the disposable diesel exhaust paper filters at two underground coal mines resulted in up to 95 percent reduction in DPM. Utilization of different filtration media and careful application of these filters combined with cleaning and reuse can extend the life of the filters. When used with a water scrubber, proper maintenance of the water level is necessary to eliminate the risk of hot exhaust gases igniting the filter. "…Disposable paper filters are installed on the Ramcars such that the exhaust first passes through the water scrubber, then through a water trap or baffle system to prevent water droplets from being carried by the exhaust stream to the filter, and then finally through the low-temperature paper filter. There's an exhaust temperature shutdown installed in front of the paper filter to prevent the exhaust gases from reaching 212o F, which is the maximum safe operating temperature of the filter. There's a back pressure gauge mounted in the operator's cab to help them know when the filters need to be changed out."
"Today, the best strategy to use on a diesel Ramcar is to use the changeable paper filters that many mining companies are currently using."
"…the Ramcar operators quickly accepted the filters and wanted them installed on all the face equipment. We have since installed the disposable diesel exhaust filters on our Wagner 25xs, Teletrams and Petitto Mule…. …We typically get about six hours off the Ramcar and Petitto Mules. On our Wagner systems we average approximately four hours of service life…."
"…In our experience, the lifetime of the filters has varied anywhere from 8 hours to 32 hours-provided that the engine on which the filter is installed is tuned properly so that it is not putting out too much soot. [The actual time between filter changes will vary depending upon the vehicle and engine's state-of-maintenance, duty cycle and other parameters.]"
Catalyzed or uncatalyzed ceramic diesel particulate filters currently available can reduce DPM emissions from 60 to 90 percent. Exhaust passes through the ceramic or metallic diesel particulate filter which traps the particulate matter. As exhaust continues to pass through the filter, filtering continues, and the filter slowly becomes clogged with DPM. Clogging increases the exhaust back pressure which can lead to engine damage unless the exhaust back pressure is lowered by cleaning the filter. Vehicles which have sufficiently high exhaust temperature (at least 325°C, 25 percent of the time) can automatically clean the filter using a process called autoregeneration or self-cleaning. During autoregeneration the high exhaust temperature causes the trapped DPM to ignite and burn, thus reducing the exhaust back pressure on the engine and allowing more DPM to be trapped. For other vehicles, regeneration can be assisted by the application of a catalyst to the filter, which lowers the regeneration temperature, or by the use of on- or off-board regeneration systems. "There are approximately 1,000 diesel particulate filters presently [being used] on mining vehicles throughout the world."
"In 1989 Homestake initiated a test on ceramic wall flow diesel particulate filters. Eight units were tested on a Cat 3306, different loaders from three different suppliers. One failed right away and was replaced by the supplier. Five lasted on the average about 2,000 hours, and two went over 3,000 hours. Miner acceptance was good when the filters were working properly."
"…Number one, while ceramic filters give good results early in their life cycle, they have a relatively short life, are very expensive and unreliable. Number two, other post-combustion devices are not readily available for the larger horsepower production equipment we are currently using. When evaluated for lower horsepower support equipment, they appear to be very costly with no proven reliability…" --Ray Ellington, Oxidation catalytic converters (OCCs) are used to reduce the quantity of carbon monoxide and hydrocarbons (including harmful aldehydes) in diesel exhaust. Oxidation catalytic converters also decrease the soluble organic fraction of DPM as well as gas phase hydrocarbons, which can reduce DPM emissions by up to 50 percent. The soluble organic fraction of the DPM exhaust contains known carcinogenic compounds such as benzo(a)pyrene and other polycyclic aromatic hydrocarbons. Use of low sulfur fuel (<0.05 percent sulfur) with OCCs is critical because air quality is harmed when fuel containing moderate or high sulfur (> 0.1 percent) is used. An OCC oxidizes sulfur dioxide to form sulfates which increase particulate emissions. OCCs can also oxidize nitric oxide to more harmful nitrogen dioxide. Modern catalysts are formulated to minimize the production of sulfate particulate matter and nitrogen dioxide, provided they are used with high quality low sulfur fuel. The OCC should be located as close as possible to the exhaust manifold to ensure maximum exhaust gas temperature. The catalyst formulation and its operating temperature are critical factors in converter performance. The temperatures required for 50 percent conversion of carbon monoxide and hydrocarbons are typically about 370°F and 500°F , respectively. As higher exhaust gas temperatures are attained, conversion efficiency increases. The use of high sulfur fuel reduces the life of catalytic converters. New catalyst technology and the availability of low sulfur fuel make the use of OCCs on underground mine vehicles an attractive tool for reducing diesel particulate emissions. "There are also over 10,000 oxidation catalysts that have been put into the mining industry over the years. …Sulfation is key in particulate control; you don't want a catalyst to cause any oxidation of the sulfur. I remem-ber once I was in India, and there was a complaint that they put a catalyst on and they were saying it caused smoke. And it did, a lot of smoke. I took a fuel sample and the fuel had 2.2 percent sulfur in it, not 0.25 percent. …Engine, fuel and aftertreatment control technology must work together." --Dale McKinnon, "The Homestake Mine has had extensive experience with oxidation catalysts…. We have always had them on our diesel units. And I know there's been a controversy on whether they might improve the work environment or harm it, but with low sulfur fuel I don't think there's any doubt they are a benefit. They oxidize the CO to CO2, and they burn off some of the unburned hydrocarbons and some of the components of diesel exhaust. We like them. The [modern] catalytic purifiers, to my knowledge, limit the NO-to-NO2 conversion, and with the low sulfur fuel you don't get the sulfates coming out. So we think we're better off with them." --John Marks, Dry system technology. An alternative to water scrubbers for meeting the exhaust gas cooling, spark arresting, and flame arresting requirements is the Dry System Technology (DST®). With this technology, the exhaust gas does not come into direct contact with cooling water, but it is indirectly cooled by a water-cooled heat exchanger such as a tube and shell heat exchanger. This cooling process does not involve the evaporation of water. Spark and flame arrest are provided by mechanical means. The DST® also includes a water-jacketed oxidation catalytic converter and a disposable diesel exhaust filter to reduce diesel emissions. The oxidation catalytic converter is located upstream of the water-cooled heat exchanger. Exhaust then passes through the water-jacketed heat exchanger, a paper filter and a flame arrestor. This system reduces diesel particulate by 95 to 98 percent. The DST&174; includes a complete set of diagnostic gauges to monitor system performance. The DST® has been approved by MSHA under 30 CFR Part 36. It can be used in coal or gassy metal and nonmetal mines where permissible equipment is required. In addition, the heat exchanger technology could be applied to nonpermissible engines in order to cool the exhaust gases so that disposable diesel exhaust filters (paper filters) could be used to reduce particulates. "This system [the DST®], I think, represents, from everything that I've seen, the state-of-art of the industry…the best technology on the market today…. This gives us the ability for the first time in a long time to change direction and try to solve problems [with exposure to diesel exhaust]." --Joe Main, The DST® has been tried on a number of vehicles retrofitted to use it. "…It was a welding truck, at Shoshone. It was put in November, 1992. That's coming up pretty close to three years. Has operated very successfully; have had no problems. There's a 913 scoop; that's at Twenty-Mile since January, 1994…. We retrofitted a 25X Wagner shield hauler…." --Norbert Paas, USE OF VENTILATION Today the primary means used to reduce exposure to diesel exhaust pollutants underground is to dilute exhaust pollutants with fresh air from the mine's ventilation system. The concentration of pollutants is inversely proportional to changes in ventilation air quantity; that is, as the air quantity increases the pollutant concentrations decrease. The mine ventilation system can work in conjunction with the other methods of contaminant control such as maintenance, exhaust treatment, etc. Any control system must then be supplemented with checks to ensure that all aspects are working as designed. One way to check the control system is to conduct periodic sampling of diesel contaminants to detect changes in the system. Mine ventilation systems where diesel engines are operated generally supply between 100 and 200 cubic feet of air per minute per brake horsepower (cfm/bhp). This air quantity is normally sufficient to dilute gaseous emissions from the diesel equipment to applicable standards for those gases. However, MSHA's experience in underground mines has shown that with these air quantities, DPM levels will still range between 200 g/m3and 1,800 g/m3. As a general reference, about 35,300 cfm of air are required to dilute one gram per minute of DPM to 1,000 g/m3. Therefore, to significantly cause a reduction of DPM concentrations in underground mines through ventilation, it may be necessary to supply air quantities above those currently being used. There are special ventilation requirements when diesels are used in underground coal mines. When a single piece of diesel equipment is operated, the nameplate airflow must be provided as at a minimum airflow requirement. For each individual piece of diesel equipment operating in a coal mine, the approval plate air quantity must be maintained in any working place where the equipment operates, at the section loading point, and in outby entries where the equipment operates. The MSHA regulations also allow the District Manager to add areas where the approval plate air quantity may be required, such as fueling locations. When multiple pieces of diesel equipment are operated, the minimum section airflow is the sum of the nameplate airflows for the individual pieces of equipment. This requirement was developed to reduce the gaseous diesel emissions. However, not all equipment is operated on a continuous basis and some equipment, such as transportation and supply vehicles, may be excluded from this calculation. (Prior to the1996 diesel powered equipment rule, a 100-75-50 percent guideline was used to establish minimum section air quantity requirements.) Any excluded equipment must be approved by theDistrict Manager and listed in the ventilation plan for the mine. The intent here is to allow for the exclusion of equipment that does not significantly add to the miners' exposure level. These air quantities must be maintained in the last open crosscut of working sections, the intake to longwall sections, and the intake to pillar lines. The multiple unit quantity also applies to the areas where mechanized mining equipment is being installed or removed. Quantities other than the multiple unit formula can be approved by the MSHA District Manager if samples show that such reduced quantity will not result in overexposures "…Ventilation can take care, in my opinion, of most diesel equipment in the main haulageway, even in the sub-mains. However, when you approach the face area, you don't have that velocity and that quantity of air; then the control of engine exhaust may be necessary depending on the size of the engine and the concentration." --Pramod Thakur, Ph.D., Metal and nonmetal mines can be ventilated in a variety of ways. In single level mines, working areas are generally ventilated in series. The exhaust of one area becomes the intake for the next area. Multilevel mines may have a separate air split to each level or to several levels. Separation between intake and exhaust air courses is essential to prevent leakage or loss of fresh air. Auxiliary and booster fans should be installed throughout the mine to optimize distribution of workplace airflow. Changing a mine's ventilation system to reduce pollutant exposure is frequently expensive and may require a long time to implement. Simple changes can include repairing an individual brattice or reducing leaks in an entire brattice line. However, significant improvements in air quality often are achieved only by complex changes such as redesigning the entire mining system to reduce airflow leakage, modifying the main fan installation, or adding a new air shaft. "The mine ventilation system must be designed to provide and distribute sufficient airflow to areas of the mine where diesel equipment is being used. Typical ventilation rates in metal and nonmetal mines range from 75 to 200 cfm per brake horsepower in use. In coal mines the name plate airflow has been used to determine plan airflow requirements." --Robert Haney, "Ventilation continues to be an important method of controlling diesel particulate matter concentrations, and our studies have shown that significant reductions can be achieved by changing the ventilation around in the section." --Jan Mutmansky, Ph.D., "Ventilation still remains the vanguard against diesel emissions. Toward the end of 1992 we reduced overall airflows to cut costs as part of a mine optimization process, and this summer we returned to those airflows. We currently have a mine migration of about 115 cfm/bhp. We designed with the 100 percent rule. We don't use 100 percent, 75 and 50 percent thereafter, although that's the way it sometimes works out. We try and keep all of our diesels on parallel splits as much as possible." --John Marks, "All permissible diesel face equipment is ventilated according to MSHA-required nameplate values. These are usually required to make in excess of 18,000 cfm in the last open break and 40,000 cfm on the section. In normal operation these values are 35,000 cfm in the last open break and 45,000 cfm on the section." --Chris Pritchard, "Looking a little closer at ventilation, in one of our larger panels, typically at any one time you'll see three Ramcars at 139 horsepower operating, a roof bolter, a powder wagon and roughly two service vehicles…for more or less a total horsepower of…610. With an air volume of 100,000 cfm, we have an effective air-to-horsepower ratio in an operating panel of 164 cfm. If you look at the entire mine, installed horsepower, the air-to-horsepower ratio is about 95 cfm. New Mexico has a standard of 75 cfm, so we're somewhat better than that." --Scott Vail, Ph.D., "We control air flow in the mine using air doors and air walls. …We will shotcrete or gunite some areas to prevent leakage. We build airwalls throughout the mine using waste rock and used conveyor belt. The rock is piled up half to two-thirds of the way to the back and conveyor belt is cut into strips and pinned to the back overlapping by about six inches. This produces a very efficient air wall in the mine." --Regina Henry, "Our stoppings consist of brattice cloth or waste salt piled to within 10 feet of the roof and brattice cloth. We have auxiliary fans located throughout the mine that mix the gases as they come off the sections. Our main intake ventilates all of the sections in B-bed, then returns to the production shaft. Right now our C-bed is on its own split of air, and we continue to keep it that way. Several years ago when our fans were old and running at a maximum capacity, we decided…to see what we needed to do to build a better ventilation system. We conducted several pressure and air quality surveys, and the results were put into a computer simulation model. From this model, we found out that we definitely needed new fans…. We also decided that when we were developing C-bed, that we did not want to continue with the way we were currently ventilating the mine. In other words, we did not want to have one single split ventilating all the sections. So at that time we sat down and we worked out a way to ventilate each section on its own separate split, which is what most coal mines do. We feel that this will give us a better air quality … and it will help clear the air out faster." --David Music, "…We believe mine design and ventilation is an important…control. The fact of the matter is, though, that… mine ventilation is not a stand alone system [for reducing exposure to diesel emissions]…. "Even coupled with the water scrubber exhaust cooling systems that have become the industry standard, we haven't reduced particulate exposure to [what we would consider] an acceptable level…." --Jeff Duncan, USE OF ENCLOSED CABS Properly designed and maintained environmentally conditioned cabs can reduce equipment operators' exposure to diesel emissions. Cabs should be pressurized and use high-efficiency particulate air (HEPA) filters. Many surface mines are currently using properly designed environmentally conditioned cabs and some efforts are being made to use enclosed cabs on underground mining equipment. The same principles apply to the use of underground booths designed to protect miners. Question: "I recently completed a study of a surface coal mine, and they were using pressurized cabs to minimize exposures…. Has this been given some thought in your design [of Ramcars] at Jeffrey?…." --Robert Wheeler, Response: "We may be getting very close to that, because just recently we produced the first Ramcar-type of vehicle ever with a cab, with some climate controls. …One of the problems with exposure in underground mines is not the operator of the machine. Because of the close confines, it's the people around the equipment and, of course, the pressurized cab does not affect them at all." --John Smith, DIESEL ENGINE MAINTENANCE Engine maintenance is an important part of a mine's overall strategy for reducing workers' exposure to diesel emissions. Without proper maintenance, diesel engines will perform poorly, thus reducing the effectiveness of all other emission control strategies. "It has been definitively proven, that when engine maintenance is neglected [especially if it involves regulating the fuel and air handling systems of engines] the particulate, and carbon monoxide, and hydrocarbons, all skyrocket."
"…We had a lack of maintenance on these pieces of diesel equipment. They were running the equipment until they broke down, and they would fix them, and they would run them again until they broke down…"
"We're having problems with respect to maintenance of diesels. We're having problems with untuned diesels. When we go to do longwall moves, we're working in an environment where the blue smoke is so heavy sometimes you can't see. We don't have a good maintenance system. We don't have a good inspection system."
A good preventive maintenance program will maintain near-original performance of an engine, and maximize vehicle productivity and engine life, while keeping exhaust emissions down. Engine maintenance activities which should be performed by mine maintenance personnel include maintenance of the following systems: air intake, cooling, lubrication, fuel injection and exhaust. These systems must be maintained according to manufacturer's specifications and on a regularly scheduled basis to keep the system operating efficiently. Measuring tailpipe CO emissions while the engine is under load provides a good indication when maintenance is required. However, daily checks of engine oil level, coolant, fuel and air filters, water tank, exhaust piping and gauges should be made. There are very specific requirements for maintenance of diesel equipment in underground coal mines; some are noted below. The air intake system removes airborne particles before they enter the engine and cause abrasion of internal engine surfaces. Intake air filters should be replaced when the pressure drop indicator exceeds the manufacturers' specifications, usually 20 to 25 inches of water. As of November 25, 1997, for diesel-powered equipment used in underground coal mines, intake air filters must be replaced or serviced when the intake air pressure device so indicates, or when the engine manufacturer's maximum allowable air pressure drop level is exceeded. "…Maintenance is extremely critical.… It takes two days to screw up the engine in the mine if you're running it without an air cleaner or a clogged air cleaner or if a cleaner was replaced by the wrong cartridge element that allows for some air to bypass the fuel filter."
"One of the most simplest things in maintenance is the intake air cleaner or filter. You could have emission increases by as much as 300 or 400 percent just having a clogged intake air cleaner."
"Maintenance: intake air and exhaust systems are checked at least once each day during their operation. Inspections are completed on a weekly basis. Inspections are done by competent persons assigned by the company to perform that work, and inspections are completed in a well-ventilated area. Results of these daily and weekly inspections are kept in a permanent record book."
The cooling system directly affects engine emissions by preventing scuffed cylinder walls and pistons, cracked heads, and burned valves. Liquid-cooled engines need to be kept free of mineral deposits and rust to ensure effective heat transfer. Mine water is generally high in minerals and salts, rendering it unfit for use in the cooling system. A 50 percent antifreeze and distilled water solution is optimal. Cooling fans, ducts and cowlings must also be maintained to ensure adequate cooling. Air-cooled engines discharge heat via cooling fins, and liquid-cooled engines rely on radiators. Be sure to keep cooling fins and radiators undamaged and free of oil and dust to ensure proper heat transfer. Adjust or replace slipping fan and pump belts to ensure proper air and coolant flow, thus avoiding excessive heat buildup. The fuel injection system can be damaged by contaminated fuel. To prevent this damage, fuel filters should be regularly replaced and fuel tanks should be periodically drained and cleaned. To avoid contamination, fuel should be properly handled, dispensed and the number of fuel transfer points minimized. Fuel tanks should be kept as full as possible to prevent condensation of water in the tank. Water should not be allowed to condense in fuel storage tanks. Water can be removed by the installation of fuel-water separators at the outlet of the surface storage tank, on the pump side of portable fuel trailers and on all engines. Water-absorbing additives may also be used. The fuel pump and governor should be set to the engine manufacturer's or MSHA's specifications prior to running the engine at the mine. In addition, the mine elevation must also be considered in the final adjustment of the fuel injection pump. Air density decreases with an increase in elevation; therefore the fuel-air ratio will change as elevation increases, thus causing an adverse effect on the engine emissions. If the engine is operated at elevations above 1,000 feet, the fuel rate should be reduced as specified by MSHA or the engine manufacturer. Turbocharged engines are an exception to this rule due to excess quantities of air available from the turbocharger. MSHA or the engine manufacturer specifies the maximum operating elevation of a turbocharged diesel. Above this elevation, engine derating is necessary. Caution should be observed in trying to increase the power output of engines: following manufacturer specifications can avoid significant increases in pollution. Minor increases in power that can be produced by adjusting the fuel-air ratio can also produce significant increases in particulate emissions. Similarly, too much advance or retardation of the fuel injection timing can have deleterious effects on NOx, hydrocarbon, or particulate matter emissions. The locks and seals on the fuel pump and governor must not be tampered with or removed. Faulty adjustment can result in overfueling and engine damage. Overfueling can increase emissions, especially black smoke, carbon monoxide, and particulates. [Engines used at high elevation must be properly sized to ensure adequate power.] "Due to our elevation of approximately 7,000 feet, the 150-hp engines are derated to approximately 115 hp. Unfortunately, horsepower at the wheels on the Ramcars is down to about 90 hp."
"…The first thing to do to reduce particulate emissions is to get the fuel injector pumps and the fuel injectors properly adjusted so they do not overfuel the engine. That will bring the particulate emissions down faster and more effectively than anything else…. It will also lower hydrocarbon and carbon monoxide emissions…."
Failure to maintain the lubrication system can lead to significantly increased particulate emissions, and eventually to catastrophic engine failure. Excessive heat lowers the viscosity of engine oil and results in lost lubricity and accelerated engine wear. The quality of the lubrication oil is also important and contamination must be avoided. Worn valve guides and piston rings allow lube oil to leak into the combustion chamber and cause white and/or blue-black smoke, and the creation of significant particulate concentrations. System failures are often caused by a component failure, such as seized bearings, lubricant breakdown, lubricant contamination or engine overheating. To prevent these failures it is important to regularly replace oil filters, maintain crankcase lubricant at recommended levels and to maintain the engine's cooling system. "…Any engine, regardless of whether it has mechanical controls or a sophisticated engine with electronic controls, if the engines have not been maintained, if they're burning oil, you will get plenty of blue smoke of all kinds…. I think we tend to confuse blue and black smoke sometimes. …But generally, a blue exhaust gas will indicate oil consumption, typically a low load operation, high oil consumption. Black smoke is more related to overfueling. In other words, we're talking about full-load overfueling of the engine, high temperature. It's basically the opposite of blue smoke."
The exhaust system must be periodically inspected and maintained to avoid the buildup of excessive exhaust back pressure and to ensure safe operation of the engine. Back pressure increases may result from a partially plugged water scrubber, flame trap, OCC, or filter or a dented exhaust pipe. Increased back pressure causes increased emissions and reduced performance. Back pressure should not exceed 27 to 40 inches of water or manufacturers' specification. The tanks of water scrubbers used on permissible equipment must be filled and the float valves must be operational to meet MSHA safety requirements. Proper maintenance also ensures safe operation of the disposable diesel exhaust filters located downstream of the scrubbers. "Water scrubbers are prone to mechanical failures, prone to maintenance problems. You can lose water, and you can have a filter catching fire…."
Because a diesel engine operates over a wide range of duty cycles, the most accurate way to assess the content of exhaust emissions during actual mining conditions is to take tailpipe samples while the engine is under load. As of November 25, 1997, weekly tests for CO in the undiluted exhaust are required for certain types of diesel-powered equipment in underground coal mines. A gas monitor can be used to measure the carbon monoxide level in the raw exhaust. A large increase in the carbon monoxide concentration is an indication that the engine has a maintenance problem that needs to be addressed. An increase in the carbon monoxide concentration is also a good indication that the diesel particulate concentration and observable smoke levels are increasing. Regular testing of an engine will provide information on the need for maintenance. Engine emissions during mining operations cannot be accurately evaluated at idle conditions. On certain types of mine vehicles, such as load-haul-dumps (LHDs) and scoops, a repeatable loaded condition can be readily placed on the engine. On clutched vehicles this may not be possible. Question: "At our mines, we've got a multi-gas testing system hooked up through…our mine monitor system, and from what I understand, unless you test these vehicles under load, it's more or less useless; is this correct?"
Response: "Well, [yes]…just about."
"…By tuning the engines on the dynamometer and making sure that we get the rated performance, the amount of smoke is greatly reduced, essentially eliminated."
Diesel engine maintenance is the cornerstone of a diesel emission control program. Proper maintenance includes compliance with manufacturers' recommended maintenance schedules, maintenance of accurate records and the use of proper maintenance procedures. Inadequate maintenance, improper adjustments, wear, and other factors will cause changes in diesel exhaust emission rates. As of November 25, 1997, diesel engines in underground coal mines must be maintained in compliance with the conditions of the MSHA approval, and examined weekly in accordance with approved checklists and manufacturer maintenance manuals. "…To control DPM, we've got a good strong preventative maintenance program. We bring equipment in on a regular basis on the 50, 250 and 1,000-hour intervals and do the recommended filter checks and changes as recommended by the manufacturer."
"…I just want to stress the importance of a good maintenance program… We have a very good maintenance program in that it's preventive maintenance as well as, you know, when problems arise on the job, we just get it fixed."
"The mine currently uses about 115 pieces of diesel equipment…. Although the mine has been slowly downsizing over the past five years, the number of diesel mechanics has increased, and we do this because we've upgraded our preventative maintenance. We seldom see a smoking diesel underground anymore, although once in a while, of course, we get one."
"…A well-conceived maintenance program strives to maintain optimum engine performance and thereby control diesel exhaust emissions. The maintenance program consists of regularly scheduled replacements of fluids and filters, operating performance evaluations and additional weekly permissibility inspections,…and a training program to educate maintenance personnel in the engine operating recommendations and requirements."
"There's a whole section in the MSHA advisory standards on diesel maintenance almost from A to Z. It could be almost verbatim from manufacturers' manuals themselves…. They've been laying in front of mine operators' faces for 15-16 years now. Some of them [mine operators] adhere to them religiously. Others have never even seen the standards, either voluntary or mandatory, have never even opened that section of the book."
It is worth emphasizing that if repairs and adjustments to diesel engines are to be done properly, the personnel performing such tasks must be properly trained. Operators of underground coal mines where diesel-powered equipment is used, are required, as of November 25, 1997, to establish programs to ensure that persons who perform maintenance, tests, examinations and repairs on diesel-powered equipment are qualified. "I think the mechanics need to be trained so they understand exactly what causes the emissions."
"It's also fundamental that the mechanics have proper and modern tools at their disposal and be trained in how to use them."
WORK PRACTICES AND TRAINING Work practices and training can have a significant effect on diesel exhaust emissions. Care must be taken to avoid contaminating diesel fuel and lubricating oils during transfer. Fuel contamination can result from transfers taking place in a dusty and damp environment or by using the same transfer pump for different fluids. Fuel contamination will increase emissions. Operators should avoid lugging the engine to low RPM. Lugging an engine is applying an increasing load (torque) against the engine, while the engine's fuel rack is at the maximum position, causing a decrease in the engine's RPM. An example of lugging is when a LHD operator drives the bucket into a muck pile with the accelerator to the floor and continues to work the engine causing the engine's RPM to decrease. If the engine operator continues to work the engine to a point where the engine's RPM are low but the torque demand on the engine is high, the engine may eventually stall. However, as the engine's RPM decreases and the engine torque increases, the engine's ability to efficiently burn fuel decreases causing the engine to produce excessive carbon monoxide and particulate emissions. For naturally aspirated engines and older turbocharged engines, an engine operating at a lower RPM and high load produces higher exhaust emissions than an engine operating at higher RPM and lower load. To avoid this situation, the vehicle operator should maintain higher engine RPM while performing the work. This might mean picking up a smaller load or carrying less material or shifting to a lower gear. The result will be a reduction in engine exhaust emissions. Operators should avoid idling the engine. Idling wastes fuel, increases emissions and may overcool the engine. Overcooling results in incomplete combustion, higher emissions and may lead to varnish and sludge formation. Unburned fuel washing down cylinder walls removes the protective film of lubricating oil and results in accelerated wear. The fuel dilutes the lubricating oil resulting in reduced lubricity. Engines should be shut down and not idled except as required in normal mining operations. As of April 25, 1997, idling of diesel-powered equipment, except as required in normal mining operations, is prohibited in underground coal mines. Operators of diesel-powered equipment must be trained on the operation of the equipment, in routine inspection and maintenance activities, and to promptly report any evidence of problems. For instance, operators should carry spare intake air filters, so that clogged filters can be changed as needed. As of November 25, 1997, operators of mobile diesel-powered equipment in underground coal mines must conduct a visual examination of the equipment before placing the equipment in operation. "Our operators all undergo a six-week training period underground on a training panel learning to efficiently and safely operate the equipment before we turn them loose in a production panel. A big part of that is awareness and reporting. They get on equipment, the power drops off or it's smoky, they know they're supposed to report it, and we do something about it. If air volume's dropping off, it's probably because the ventilation crew hasn't kept with the panel. It's reported, we address it. So we stay on top of things."
"We need education, education, education of the people who operate the equipment, of the people who maintain the equipment…and of the people that inspect the equipment for the enforcement agencies. A complete education process should start tomorrow."
"Equipment operation-my key thing is operators' training-to make the operator aware of exactly what a diesel machine is, what to look for, give them the ability to diagnose problems on the machine so that when he sees something, he can make a decision--should I call a mechanic in or not? Very important in the program. And a walk-around inspection?--It takes less than five minutes."
Operators and maintenance personnel should read and be familiar with the manuals covering the machines they operate and maintain. Besides specifying how a machine is to be operated and maintained, these manuals provide useful information on servicing methods and intervals. FLEET MANAGEMENT Diesel fleet management includes setting policies for operator and mechanic training, diesel usage, engine replacement and determining the types, numbers and horsepower of diesel engines used underground. Establishing such policies, and purchasing the needed equipment, is usually the role of upper mine management. Several participants at the MSHA workshops stressed that these management activities could play an important role in reducing diesel emissions. They suggested that mine management must actively support operator and mechanic training and ensure that adequate shop facilities are available to maintain the diesel fleet. "…We have service areas that advance with the panels underground because we're so spread out, and our main rebuild shop is also underground…."
RESPIRATORY PROTECTIVE EQUIPMENT While it should NOT be used as the primary method of control, use of respiratory protective equipment can help to reduce miner exposure to DPM until better controls can be implemented. It is generally accepted industrial hygiene practice to eliminate or minimize hazards before resorting to personal protective equipment. As indicated by the quotations in this Toolbox, various mines are taking a variety of approaches to minimize DPM emissions and to reduce DPM concentrations in mine atmospheres. However, using the correct respiratory protective equipment in areas of the mine which are difficult to ventilate and are currently subject to high concentrations of diesel pollutants can help to protect miner health. "Now, even before mechanization, slusher operators at Homestake wore half-face respirators as protection against the silica dust. Loader operators also are required to wear them. And with the organic mist and fume cartridges and filter pads, we figure that's removing 99 percent of any diesel particulate matter in the air."
MEASURING THE CONCENTRATION Monitoring DPM concentrations is the ideal way for a mine to track and evaluate its progress in implementing a DPM control program.Various methods for measurement are described in Appendix C of this publication.
"…The ultimate measure…is what the air quality is in the workplace, and I think that's an issue that we need to also consider. Just having cfm blowing through a place really doesn't
give you the true picture…. I want to be able to do the measurement on an ongoing basis…." "The Bureau of Mines, MSHA, NIOSH and others have been working with sampling technology that's been done in a prototype phase strictly within government control. We
need to take that technology and get it out in the field so people can evaluate what their own exposures are and evaluate how they might reduce those exposures." Mine operators who would like assistance in measuring or evaluating DPM exposures may
request help from MSHA's Office of Technical Support by contacting the MSHA District
Manager in their area. Assistance may also be obtained through the NIOSH Health Hazard
Evaluation Program by calling 1-800-35NIOSH.
A DOZEN WAYS TO REDUCE EXPOSURE TO
Use low sulfur fuel. Low sulfur fuel extends engine life, reduces emissions and allows catalyzed emission control devices to perform properly.
Use appropriate exhaust aftertreatment devices such as filters and oxidation catalysts,
and environmentally conditioned, enclosed cabs, where possible.
No ventilation, no operation. If ventilation in an underground mine is interrupted for any reason, all diesel equipment should be shut down.
Train miners properly. Miners must learn to recognize hazards, and to correctly operate and maintain diesel equipment. Designated maintenance personnel should be specially
trained in diesel repair.
Read operation and maintenance manuals. Deviation from maintenance and operation schedules and procedures will increase emissions.
Beware of black smoke. Black smoke from a diesel engine is a result of improper fuel to air ratio. Black smoke indicates that engine maintenance is needed.
No unnecessary idling.Idling wastes fuel, increases emissions, and may overcool the engine resulting in increased wear.
Keep it clean. Dirt and dust are detrimental to engines. Periodic maintenance of the intake air system is required for peak engine performance. The air cleaner must be changed to avoid an intake air restriction that will increase emissions.
Keep it cool.Engine overheating is a frequent cause of premature engine failures. Ensure that the lubrication oil is the correct viscosity and kept at the recommended levels, and that heat exchangers are clean and undamaged.
Do not operate the engine at high load and low speed (lugging), as this increases emissions. Operators should shift gears to operate the engine at higher speed to lessen the engine load.
No overpowering. The fuel injection pump governor must be set according to manufacturer's specifications or MSHA requirements. Tampering with the fuel system to boost power must be avoided.
APPENDICES
APPENDIX A: 1. Background Health Effects Institute. Diesel Exhaust: A Critical Analysis of Emissions, Exposure and Health Effects. April 1995. 2. Controls Mine Safety and Health Administration, transcripts of three workshops on Diesel Particulate control methods, Fall 1995. (For a copy, on paper or disk, available at cost, contact: MSHA, Office of Standards, Regulations and Variances, Room 631, 4015 Wilson Boulevard, Arlington, Va. 22203-1984, or call 703-235-1910.) 3. Measurement techniques Cantrell, B. K., Williams, K. L., Watts, W. F, and Jankowski, R. A., "Mine Aerosol Measurement", Chapter 27 in Aerosol Measurement: Principles, Techniques, and Applications, ed. K. Willeke, and P. A. Baron. Van Nostrand, 1993, pp. 591-611. Appendix B: Glossary of Terms Aftercooling Cooling intake air prior to induction into the combustion chamber to increase power and reduce the emission of oxides of nitrogen. Aftertreatment devices Devices such as filters which remove constituents of diesel exhaust as they leave the equipment. Approval plate quantity Quantity of ventilating air given in cubic feet per minute (cfm) that will dilute the concentrations of gaseous exhaust contaminants from a single diesel engine to specified limits for CO2, CO, NO and NO2. This is sometimes called the nameplate air quantity. Aromatic content Hydrocarbons in diesel fuel are numerous but generally fall into three families: paraffins, naphthenes and aromatics. Reducing fuel aromatic content will reduce hydrocarbons in the exhaust and the soluable organic portion of DPM. Autoregeneration Self-cleaning of a filter by an engine which has high enough exhaust temperatures to oxidize the diesel particulate matter captured on the filter. See "regeneration" below. Cetane number A number that describes the ignitability of diesel fuel. Fuels with high cetane numbers have low self-ignition temperatures. Fuels with low cetane numbers cause engine roughness. Cloud point The highest temperature at which the first trace of paraffin visibly separates in the liquid fuel. Diesel particulate matter (DPM) Small particles of matter in diesel exhaust, which can be collected on filters. The terms "diesel particulate", or "DP", mean the same thing. Elemental carbon Elemental carbon is sometimes used as a surrogate measure for DPM. It is composed of graphitic carbon, as opposed to organic carbon, and usually accounts for 40 to 60 percent of the DPM by mass. Exhaust back pressure Buildup of pressure against the engine created by the resistance of the exhaust flow passing through the exhaust system components. Fuel-to-air ratio The ratio of the amount of fuel to the amount of air introduced into the diesel combustion chamber. g/hp-h (Gram per horsepower-hour) The hourly mass of a contaminant in diesel engine exhaust emissions divided by the engine horsepower. Impactor Device used to separate particles by size. Nameplate quantity See approval plate quantity. Organic carbon Non-graphitic soluble organic carbon material associated with DPM. Oxygenates Fuel additives which contain a substantial fraction of oxygen by weight, e.g. ethanol, methanol, and methyl soyate. Permissible Equipment on which safety components and temperature controls have been added to prevent the ignition of methane or coal dust so that it can be safely used in areas of an underground mine where methane is likely to accumulate. Regeneration Process of oxidizing DPM collected on a diesel exhaust particulate filter to remove it. This process cleans the filter and reduces back pressure to acceptable limits. Respirable combustible dust (RCD) Method of measuring DPM using a combustion process. Threshold limit value (TLV®) Time-weighted average concentration (established by the American Conference for Governmental Industrial Hygienists) for a conventional 8-hour workday and a 40-hour workweek, to which nearly all workers may be repeatedly exposed, day after day, without adverse effect. Total Carbon Refers to the sum of the elemental and organic carbon associated with the diesel particulate matter and accounts for about 80-85 percent of the DPM mass. Turbocharge Process of increasing the mass of intake air by pressurization to the engine which allows more fuel to be burned and results in increasing the engine's power output. Volatility Measure of the ability of a fuel to vaporize. Wax separation Separation of the paraffinic portion of diesel fuel from the other components which occurs at low temperature. It can cause fuel flow problems.
Appendix C: DPM is comprised of solid elemental carbon particles, with adsorbed and condensed hydrocarbons and sulfates. The particles are arranged in chain aggregates that have a mass median diameter of about 0.2 micrometers. Several methods are available for determining DPM concentrations in the environment. They include: • Measuring the mass (gravimetrically) of the submicrometer portion of the respirable fraction of the aerosol. • Measuring the concentration (chemically) of the elemental and organic carbon fractions (total carbon) of either the submicrometer portion of the respirable dust aerosol or of the total respirable dust aerosol. • Measuring the mass (gravimetrically) of the combustible fraction of the respirable aerosol (often referred to as the RCD method). Measuring the mass of the submicrometer portion of the respirable dust sample is the most common method currently being used to determine the DPM concentration in coal mines. This method takes advantage of the facts that DPM in coal mines is generally less than 0.8 µm in size and that other mineral dust collected in a respirable dust sample is generally greater than 0.8 µm in size. Figure 2 shows a schematic of a sampling device that can be used to collect the submicrometer fraction of the respirable dust aerosol. The sampling device is similar to the standard respirable dust sampling device, which consists of a 10 mm nylon cyclone and a sample collection filter. However, the sampling device has been modified to incorporate an inertial impactor that separates particles greater than 0.8 µm in size from the aerosol sample. Particles greater than 0.8 µm are collected on an impaction plate. The submicrometer fraction (particles less than 0.8 µm in size) is collected on the filter. Depending on the type of filter used to collect the submicrometer fraction, the collected sample can be analyzed gravimetrically to determine the DPM concentration or chemically to determine the total carbon (elemental and organic) concentration of the submicrometer particulate. Figure 2. Personal Sampler Adapted for Submicron Sampling  For gravimetric analysis, the sample should be collected on a preweighed 5.0 µm pore size, vinyl Metricel® filter. If the submicrometer mass of the sample collected is less than 0.3 mg the DPM should be determined using chemical analysis. For the chemical analysis a preconditioned (heated in air at 400°C for 1 hour) quartz fiber-filter should be used. The total carbon content of samples collected on quartz-fiber filters can be determined using NIOSH's Analytical Method 5040. For metal and nonmetal mining operations, samples should generally be collected without the impactor because as much as 30 percent of the DPM in such mines may be greater than 0.8 µm.
About 80-85 percent of the dpm mass is total carbon (elemental and organic). The RCD method is applicable to certain metal and nonmetal mining operations. For the RCD method, the aerosol sample is usually collected using a typical respirable dust sampler. To measure the concentration of DPM, the respirable sample is collected on a preweighed, 0.8 µm pore size, silver membrane filter. The filter is preconditioned by heating at 400°C in an oven. After sample collection, the filter is first weighed to determine respirable dust mass and then is heated at 400°C in an oven to burn off the carbonaceous material. The sample is then reweighed. The loss in sample mass resulting from the heating represents the DPM. The RCD method should be used with caution when a hydrated mineral dust (e.g., gypsum or trona) or a carbonaceous material other than DPM collects on the filter. Such materials are chemically altered by the heating process and produce erroneous results unless properly accounted for. Also, the potential for metal oxide formation exists, which will bias the results. All of these methods have been used to determine the concentration of DPM in underground mines. Studies in metal and nonmetal mines of these methods have shown that DPM concentrations determined from gravimetric analysis of the submicrometer fraction of therespirable dust aerosol are approximately the same as those determined using the RCD method. Studies have also shown that in metal and nonmetal mines, total carbon concentration determined from the submicrometer fraction of the respirable aerosol is nearly equivalent to the concentration determined from the gravimetric analysis of the submicrometer fraction of the respirable aerosol. This may not be true for samples collected in mines containing other types of submicrometer combustible materials. For further information on the appropriate use of these methods contact MSHA. APPENDIX D: MSHA-Title 30, Code of Federal Regulations Underground coal, diesel-powered equipment regulations-published in the Federal Register on October 25, 1996, Vol. 61, Number 208, pp. 55412-55534. The Toolbox makes reference to the following requirements: • approved engines required 75.1907 • approval criteria Parts 7 & 36, revised • low sulfur fuel 75.1901(a) • fuel additives 75.1901(c) • maintenance of air filters 75.1914(d) • weekly CO testing of tailpipe emissions 75.1914(g) • compliance with manufacturer specifications 75.1909(a)(1), 75.1914(f)(1) • maintenance personnel qualifications 75.1915 • idling restrictions 75.1916(d) • visual exam by equipment operator 75.1914(e) Limitations applicable to certain diesel exhaust gases: • underground coal 75.321, 75.322 • surface coal 71.700 • underground metal/nonmetal 57.5001 • surface metal/nonmetal 56.5001 EPA standards for new diesel engines-Title 40, Code of Federal Regulations: •1988 "on-highway" engine standards 40 CFR 86.088-11 • 1996 "non-road" engine standards 40 CFR 89.112-96 Pennsylvania state standards for use of diesel-powered equipment in deep coal mines: Pennsylvania Act 182 of 1996, December 19, 1996. This Act adds a new article to the Bituminous Coal Mine Act, "Article II-A, Diesel-Powered Equipment." It took effect on February 17, 1997. For information, contact the Pennsylvania Bureau of Deep Mine Safety, 412-439-7469, or fax at 412-439-7324. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
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