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Statement of Need: The use of diesel-powered equipment in both surface and underground mines has increased significantly and rapidly during the past decade. It is currently estimated that approximately 30,000 miners are occupationally exposed to diesel exhaust emissions in underground mines and another 200,000 are potentially exposed at surface operations. ^PSeveral epidemiological studies have shown a positive carcinogenic risk associated with exposure to diesel exhaust. Other reported health effects associated with exposure to diesel exhaust include dizziness, drowsiness, headaches, nausea, decrement of visual acuity, and decrement in forced expiratory volume. In addition, studies by MSHA and the Bureau of Mines show that miners working in underground dieselized mining operations are probably the most heavily exposed workers of any occupational group. Based on the levels of diesel particulate measured in underground mining operations and the evidence of adverse health effects associated with exposure to diesel exhaust, MSHA is concerned about the potential health risk to miners. MSHA currently has no health regulations that specifically address the exposure of miners to diesel particulate.

Alternatives: Over the past 10 years, MSHA and the Bureau of Mines have conducted research on methodologies for the measurement and control of diesel particulate in the mining environment. This research has demonstrated that the use of low sulfur fuel, good engine maintenance, exhaust after-treatment, new engine technology, and optimized application of ventilating air all play a role in reducing miners' exposure to diesel particulate matter. MSHA, therefore, is considering whether or not to require any of these methods or other approaches (such as establishing a permissible exposure limit -- a PEL) to limit miners' exposure to diesel particulate. ^PTo obtain additional information and public input on health risks, measurement and control technologies, and alternative approaches applicable to limiting miners' exposure to diesel particulate, MSHA held public workshops in the fall of 1995.

Anticipated Costs and Benefits: MSHA is in the early stages of developing potential cost figures related to the various possible approaches in a proposed diesel particulate standard for surface and underground coal and metal and nonmetal mines. Costs will depend on the ultimate approach chosen, but will relate to the degree of implementation of engine control technology, fuel requirements, ventilation changes, sampling practices, and requirements for exhaust control devices on diesel-powered equipment. ^PThe projected costs of technology development are expected to be somewhat minimized by research and development conducted by the Bureau of Mines and others which has resulted in a number of exhaust control devices that have proven effective and safe when properly maintained. In addition, low sulfur fuel is readily available because of current Environmental Protection Agency (EPA) regulations. ^PBenefits to health and safety would result from reducing miners' exposure to diesel particulate in workplaces where diesel-powered equipment is used. One such benefit would be a reduction in the incidence of potential illnesses associated with exposure to diesel exhaust particulate.

Risks: Laboratory tests have shown diesel exhaust to be carcinogenic in rats, as well as toxic and mutagenic. In addition, several epidemiological studies have found that exposure to diesel exhaust presents potential health risks to workers. These potential adverse health effects range from headaches and nausea to respiratory disease and cancer. In the confined space of the underground mine environment, occupational exposure to diesel exhaust may present a greater hazard due to ventilation limitations and the presence of other airborne contaminants, such as toxic mine dusts or mine gases. The Agency believes that the health evidence forms a reasonable basis for exploring possible methods to reduce miners' exposure to diesel particulate.