A great deal of attention has been focused on the potential carcinogenic effect of diesel particulate matter (DPM) emitted in engine exhaust and its potential health impact on miners. In 1988, the National Institute for Occupational Safety and Health (NIOSH) recommended that whole diesel exhaust be regarded as a "potential occupational carcinogen" and that reductions in workplace exposure would reduce carcinogenic risks.(33) In 1989, the International Agency for Research on Cancer declared that "diesel engine exhaust is probably carcinogenic to humans."(34) In 1988, MSHA's Diesel Advisory Committee recognized the potential consequences of exposing miners to diesel emissions and recommended accelerating diesel research to minimize pollutant exposure.(35) Since then, MSHA has adopted new regulations for diesel engine approval and certification.(3)

In 1995, MSHA convened a committee to recommend regulations for minimizing DPM exposure and to consider a permissible exposure limit for DPM. The American Conference of Governmental Industrial Hygienists (ACGIH) added DPM to its List of Intended Changes for 1995-96 with a threshold limit value (TLV™) recommendation of 0.15 mg/m³.(38) Recently ACGIH extended the comment period through 1997. If this TLV™ is adopted as a permissible exposure limit, nearly all mines using diesel equipment in the United States and many mines in Canada would be out of compliance, and improved emission control technologies would be required.

DPM limits are already in place in Canada and the Federal Republic of Germany. British Columbia, New Brunswick and Ontario have adopted a 1.5 mg/m³ ambient level for respirable combustible dust and the Federal Republic of Germany has adopted technical exposure limits (TRK) of 0.3 mg/m³ for elemental carbon in underground noncoal mine and construction site environments. This limit is reduced to 0.15 mg/m³ when the DPM contains more than 50 % organic carbon.(39) No TRK has been adopted for underground coal mines because of limitations in the analytical method.

It has been demonstrated that engine faults resulting from inadequate or improper maintenance could increase engine exhaust concentrations of DPM by as much as 1000%.(1) Other studies have confirmed that engine faults can increase exhaust concentrations of undesirable emissions, including DPM. (2,16,17,18,23,25,27)

To reduce safety and health hazards to miners, MSHA requires periodic emission tests to ensure that engines are properly maintained.(3) Although the requirement specifies test performance criteria, it does not state a specific test procedure. This allows mine operators to implement a procedure that is appropriate for their mine(s). This report describes an "emissions-assisted maintenance procedure," or EAMP, that mine operators could use to comply with the performance criteria outlined in the regulation.