USW Canada: Reducing Diesel Emissions in Mines

Diesel exhaust is a mixture of many gases, vapours and solid particles. Most of the components of diesel exhaust cause health problems. In the last ten years, a number of animal and human studies have shown that diesel exhaust can cause lung cancer.

Cancer is not the only problem associated with diesel. Diesel exhaust smells bad. It irritates the eyes, nose and throat. Workers exposed to diesel exhaust have more headaches, cough, phlegm, shortness of breath, chest tightness and wheeze than others. Some studies show increases in chronic bronchitis and asthma in diesel-exposed workers. Those who smoke are even more likely to have respiratory problems. Diesel exhaust causes safety problems as well as health problems, by interfering with visibility. The chart below shows some of the health problems associated with specific substances in diesel exhaust.

The Components of Diesel Exhaust

Diesel exhaust is a mixture of several types of harmful substances including: carbon dioxide, carbon monoxide, nitrogen oxides (NO_x ), sulphur oxides, hydrocarbon gases, and diesel particulate matter. Diesel particulate matter or soot consists of solid carbon particles, with various chemical contaminants absorbed onto the surface as shown below. These contaminants include oil and unburnt fuel (the "soluble organic fraction"), and cancer-causing hydrocarbons (PAH's).

A DIESEL EXHAUST PARTICLE

Based on new information about cancer caused by diesel exhaust, the American Conference of Governmental Industrial Hygienists has proposed a new, more protective exposure limit of 0.15 mg/m³ for diesel particulate matter. This is about ten times lower than existing limits in those few provinces which regulate diesel particulates. (The majority do not have a limit for the cancer-causing soot particles.) Average exposures in many Canadian mines are well above the proposed TLV.

Cancer, eye and throat irritation, effects on the lungs and heart -- these are all good reasons to reduce diesel emissions in mines. There are a number of ways to reduce emissions. No one strategy is foolproof. Some strategies only reduce one or two of these components of diesel emissions. Some strategies reduce certain emissions, but increase others. All of the strategies are will require the company to spend money. They also require vigilance. Our health is worth it.

A number of approaches to reduce or control diesel emissions are outlined on the following pages. A brief description of each approach is provided, along with some pros and cons to consider. An effective approach to reducing diesel emissions in the mines will probably involve a combination of approaches.

Electric-powered Equipment

Description

Some Canadian mines have equipment powered by electricity rather than diesel. In the Scandinavian countries, electric-powered equipment is much more common. This equipment usually operates at the end of long electric cables, although trolley-style electric couplings are also used. In the 80s, Inco experimented with an all-electric mine, but abandoned the effort after a few years.

Pros

Electric-powered equipment eliminates diesel emissions to equipment operators; although diesel generators may be used to produce electric power in the mine, the diesel emissions are usually confined to a location which can be controlled.

Cons

Electric cables and electric motors give off electromagnetic radiation, which has been linked to leukemia and brain cancer
electric-powered diesel vehicles have more restricted movement than diesel vehicles.
Electric cables are frequently damaged and require ongoing maintenance and repair.

Biodiesel Fuels

Description

Biodiesel fuels can be made from a number of different seed crops. In North America these fuels are generally derived from soybean or canola oils. They can be produced from used materials such as french fry oils or from soy or canola byproducts. They are essentially non-toxic to the environment. A spill of biodiesel biodegrades much more rapidly than petroleum-based diesel.

Biodiesel fuels have been tested on heavy-duty diesel engines in laboratories, on roads and underground in U.S. mines. Diesel particulate emissions in mines can be reduced by up to 70% just by switching to biodiesel fuel or a mixture of biodiesel and conventional diesel.

Pros

Biodiesel fuels produce much less cancer-causing smoke and carbon monoxide than conventional diesel.
There is no sulphur in biodiesel fuel, and so no sulphur oxides are produced by burning it.
Biodiesels can be blended with petroleum-based diesels or used straight with no major changes to existing engine technology; even 20% biodiesel can decrease emissions by 30% or more.
Biodiesels have a higher cetane number than petroleum diesels, which means they are more easily ignited, reducing hydrocarbon emissions, noise and odour.
Biodiesels have better lubricity than petroleum-based diesels and so causeless engine wear.
Biodiesels have a higher flash point than petroleum-based diesels and are less flammable .
Biodiesel exhaust odour is more pleasant than conventional diesel exhaust.

Cons

Engines run on biodiesel have about 10% less power than those using conventional diesel, and burn slightly more fuel.
Biodiesel is currently about 5 times more expensive than petroleum-based diesel.
Although a new canola biodiesel plant is now under construction in Saskatchewan, Canada does not yet have a good supply of the fuel.
Biodiesels are more negatively affected than petroleum-based diesels in cold temperatures.
Fuel lines may have to be replaced in some diesel engines to use biodiesel fuels.

Improvements to Petroleum-based Diesels

Description

Petroleum-based diesel fuel can be reformulated to reduce some emissions. For example, reduced sulphur contamination of fuel will reduce the emission of sulphur oxides. Diesel is now sold in two classes of fuel: "regular sulphur diesel fuel" which contains 0.50% sulphur and "low sulphur" fuel which contains less than 0.05% sulphur. Several provinces require sulphur content to be less than 0.25% in mine diesel fuel. Despite the health problems related to sulphur in diesel fuels, the average sulphur content of petroleum-based diesels used in mines may be on the increase. The Ontario Ministry of Labour recently reported that fuels contained 0.02% sulphur on average in 1990. In 1996, however, underground fuels contain an average of 0.04% sulphur, double the 1990 level.

Fuels with higher cetane numbers ignite better than those with lower numbers, and give off fewer particulates and NO_x emissions. Diesel fuel has an average cetane number of 40 to 43. However, cetane numbers from 55 to 60, which reduce emissions substantially, can be achieved in improved fuels.

Reducing the aromatic hydrocarbon content of diesel fuels also reduces the amounts and types of hydrocarbons produced in emissions. Aromatic content may range from 20-40% of diesel fuel by weight. Several researchers recommend limiting aromatic content of diesel to 20-25%. Oxygenating additives can also be added to the fuel to help it burn more completely.

Regulations may be necessary to drive these types of improvements in diesel fuels, although large mining corporations would probably be successful in demanding fuels with lower sulphur, higher cetane and lower aromatics.

Pros

Because of established production capacity and supply lines, and because U.S. EPA regulations are driving fuel producers to make improvements to on-road diesels, it may be easier to get improved petroleum-based diesels than switch to biodiesels, especially in the near future.
Reduced sulphur content of diesel fuels also reduces corrosion and oil fouling.

Cons

Low sulphur fuels have been shown to produce higher levels of cancer-causing PAHs than conventional fuels
Even major improvements in petroleum-based diesel fuels are unlikely to achieve the decrease in emissions which biodiesels offer .
Different engines have different sensitivities to reformulated fuels; some engines may not get dramatic improvements from reformulated petroleum diesel.

Modern, Electronically-Controlled Diesel Engines

Description

In 1994 the U.S. EPA set new emissions standards for heavy duty, off-road diesel engines. The particulate standard aims at a 90% reduction of emissions. Although diesels used in mining are excluded from these regulations, these engines have benefitted from improvements made by engine manufacturers who are trying to comply with the standards for on-road engines.

Designers have improved air motion in the cylinder and altered the combustion chamber so that fuel is burned more completely. New fuel injection systems combine high-pressure injectors, precise timing, control of injection rate and computer-controlled fuel metering to reduce all emissions.

In older engines, up to 50% of diesel particulate came from burning lube oils. Improved sealing technologies have reduced the oil fraction of diesel particulate to about 20%. Emissions research shows a steady improvement in diesel engines throughout the 1970s, 80s and 90s. Newly designed diesel engines first produced in 1994 (and first distributed in Canada in 1995) probably have the lowest emissions.

Some companies produce better engines than others. The U.S. Bureau of Mines recently reported that one electronically-controlled diesel engine from Detroit Diesel averaged 20% less NO_x emissions, and 47% fewer particulates than an equivalent Caterpillar engine which is not electronically-controlled.

Pros

New engines are clearly better than old ones, and should be replacing older models at an accelerated rate.

Cons

Independent research has yet to prove the claims of the diesel engine manufacturers. In fact, a recent study at Brunswick Mine indicated that an electronically-controlled diesel engine operating at 63% of maximum horsepower and using a catalytic converter still emitted 0.59 mg/m³ of respirable combustible dust, about 3 times the proposed new TLV for diesel particulate matter.
New diesel engines are very costly.
Electronically-controlled engines may be more difficult to repair and maintain.

Maintenance for Emissions Control

Description

With mechanization, mining has become increasingly dependent on maintenance operations to keep production going. A basic maintenance program includes preventive maintenance, periodic repairs and adjustments. Good maintenance can prolong or restore near-original efficiency of a diesel engine. Poor maintenance will result in higher emissions and will shorten the useful life of the diesel engine. Maintenance for emissions control requires special attention to air intake, cooling, fuel injection, lubrication and exhaust systems.

Mines should provide adequate conditions for good maintenance of vehicles, and should have sufficient mechanics on duty to be able to service vehicles at the recommended intervals. Mechanics should receive explicit training in cleaning, adjustment and repair of these systems to minimize emissions. They should have direct-reading instruments which allow them to measure particulate, carbon monoxide and NO_x emissions from vehicles on which they are working. Manuals for all relevant engines must be made available in underground garages. At one Canadian mine, these manuals are available to mechanics on-line, along with other information necessary for good servicing.

Where catalytic converters, particulate filters or other after treatment devices are used, they must be monitored and cleaned or replaced with the same careful attention necessary to maintain diesel engines in good working repair.

Pros

a good maintenance program is an essential part of any strategy to reduce diesel emissions; poorly maintained diesel engines will always emit more pollutants no matter what the original efficiency of the motor, the fuel or after treatment device used
good maintenance programs are particularly vital for older, heavy-duty equipment which emit more pollutants
a good maintenance program can reduce engine failures by more than half, saving the mine hundreds of thousands or even millions of dollars each year

Diesel Catalytic Converters

Description

Diesel catalytic converters are designed to convert carbon monoxide emissions to harmless carbon dioxide; they also convert hydrocarbons to carbon dioxide and water. Hydrocarbons attach to soot particles and can make up 70-80% of the weight of diesel particulates from engines built in the 1970s and early 1980s. Hydrocarbons are also found in gas form in diesel exhaust. So when catalytic converters work properly, they can reduce soot and the toxicity of diesel emissions. A majority of mine diesel engines in Canada use catalytic converters. A recent study claims decreases of more than 90% in cancer-causing hydrocarbons with the use of modern catalytic converters.

Average exhaust temperatures should be above 200^o C (392^o F) for converters to work effectively.

Catalytic converters should only be used with low sulphur fuel. Sulphates produced in the converter are harmful to health and reduce the efficiency and durability of the emission control systems.

Pros

reduce carbon monoxide, hydrocarbons and offensive odours in diesel exhaust
can reduce particulate emissions, by removing hydrocarbon component (especially important in older diesel engines)

Cons

diesel catalytic converters can convert the sulphur oxides in emissions to more harmful sulphates and sulphuric acid; enough sulphate may be produced to increase overall diesel exhaust emissions
catalytic converters do not lower NO_x emissions; they may increase the toxicity of these emissions by converting nitric oxide (NO) to more harmful nitrogen dioxide (NO₂ )
pellet-type catalytic converters can increase emissions of cancer-causing PAH's and should not be used
catalytic devices deteriorate with use, and must be monitored and replaced or cleaned at regular intervals to remain effective

Ceramic Particulate Filters or Traps

Description

Diesel particulate filters are designed to remove the particulate or soot emitted from diesel engines. Diesel exhaust is forced through a porous ceramic honeycomb structure, leaving the particulate deposited on the walls of the filter. This trapped particulate is burned off automatically if the vehicle is under heavy load and exhaust temperatures are very hot (usually more than 400^o C for 20% or more of the duty cycle). When vehicles fail to operate at this temperature, the particulate collets on the walls of the device, the exhaust flow becomes restricted and exhaust back pressure rises. The filter may be cleaned with compressed air, or the collected soot may be ignited and burned every 6-10 hours, "regenerating" the filter. Optional back pressure alarms are available to warn the operator of the necessity to burn off the collected soot.

A recent study at Brunswick mine reported decreases of 76% in respirable combustible dust (diesel soot and oil particles) with ceramic particulate filters. Despite this and other positive reports on the reduction of emissions, very few diesel particulate filters are used in mines. A 1996 survey on diesel engines in Ontario mines reported that only 7 filters are known to be used on more than 2200 diesel engines.

Pros

can be added to older diesel engines to reduce emissions especially on high-load equipment such as scoop trams
reduce engine noise by as much as half

Cons

require heavy duty cycle and high exhaust temperatures for auto-regeneration systems to burn off collected soot and prevent plugging; many diesel engines do not reach these temperatures
many diesel filters create back pressure problems in diesel engines and have to be retrofitted
uncontrolled regeneration can occur when excessive soot has accumulated, resulting in intense combustion and damage to the ceramic element; damage may not be noticed by the operator
can cost up to the price of a new diesel engine; it may well be more cost-effective to purchase new electronically-controlled engines rather than retrofit an older model with a diesel particulate filter
manual cleaning operations are frequent and may be time-consuming
filters may be fouled and plugged by engine oil leaks
filters deteriorate and may fail if hit with muck
some filters produce more mutagenic hydrocarbons than are found in unfiltered exhaust

Conclusions

Diesel emissions could be eliminated by using electric diesel equipment underground. However, electric equipment introduces a different hazard -- electro-magnetic radiation -- which should be assessed before introducing it into the mine environment.

Mine employers should consider an emissions-reduction program which combines the accelerated purchase of new, electronically-controlled engines using biodiesel fuels, supported by well-trained mechanics and a well-operated preventive maintenance program. Such a program should be backed by training of miners in operating practices which reduce emissions, good ventilation, and periodic air sampling for all major components of diesel emissions.

Because few mines will be persuaded to go to electric diesel equipment, or switch rapidly to new electronically-controlled diesel engines and biodiesel fuel, some other diesel reduction strategies may be necessary for the short- and medium-term, including improved petroleum-based diesel, modern catalytic converters and diesel particulate filters.

What action can we take?

The United Steelworkers union is actively involved in DEEP, the Diesel Emissions Evaluation Project along with mine operators, engine and equipment manufacturers, government inspectors, fuel suppliers, and researchers. The objective is to reduce our exposure to diesel emissions at work.

DEEP is raising money from industry and government to evaluate ways in which exposures can be reduced. Our role is to make sure that the research is done efficiently and effectively, and that our concerns as people working underground. Our union has a representative on both the management board and technical committee of DEEP to insure that our concerns are heard.

What can you do?

Keep on top of diesel emissions. Make sure that everyone is informed about the dangers of diesel as well as the strategies that can be used to reduce exposure. Encourage members to report problems with irritated eyes and throats as well as engines which smoke. Put our concerns on the table of the Joint Health and Safety Committee.
Inform union compensation representatives about potential claims if members have breathing problems, heart disease, or cancer which might be related to diesel exhaust exposures.
Support your union in its efforts to reduce diesel emissions. Get information on diesel exposures in your mine. FIND OUT IF YOUR EMPLOYER IS INVOLVED IN DEEP. Ask about what is being done in your area to reduce exposures. Let everyone know that YOU CARE ABOUT THE AIR YOU BREATHE.