"Exposure to DPM is a significant public health concern, and underground miners are exposed to higher concentrations of DPM than any other occupational group," said David Dye, acting administrator for MSHA. "This final rule ensures enhanced protection for miners from the effects of diesel particulate matter."
Diesel particulate matter consists of tiny particles present in diesel engine exhaust that can readily penetrate into the deepest recesses of the lungs. The confined underground mine work environment may contribute to significant concentrations of particles produced by equipment used in the mine.
The final rule phases in the DPM final limit of 160 micrograms of total carbon per cubic meter of air over a 2-year period, based on technological feasibility information in the record:
- On May 20, the first phase of the final limit of 308 micrograms of elemental carbon will become effective.
- On Jan. 20, 2007, the DPM limit will be reduced to 350 micrograms of total carbon per cubic meter of air.
- The final limit of 160 micrograms of total carbon per cubic meter of air will become effective on May 20, 2008.
Mine operators must continue to use engineering and administrative controls, supplemented by respiratory protection when needed, to reduce miners' exposures to the prescribed limits, according to MSHA. Like the existing DPM limit, MSHA said it will enforce the final limits as permissible exposure limits (PEL).
The final rule also establishes new requirements for medical evaluation of miners required to wear respiratory protection, and transfer of miners who are medically unable to wear a respirator. It deletes the existing provision that restricts newer mines from applying for an extension of time in which to meet the final concentration limit.
MSHA first issued a rule establishing DPM exposure limits in 2001. Under the 2001 rule, an interim DPM concentration limit of 400 micrograms of total carbon per cubic meter of air was to become effective on July 20, 2002, followed by a final concentration limit of 160 microgram per cubic meter on Jan. 20, 2006.
MSHA issued a rule on June 6, 2005, converting the interim DPM concentration limit of 400TC (total carbon) to a comparable limit of 308ec (elemental carbon), which reflects a more accurate DPM exposure measurement. On Sept. 7, 2005, MSHA proposed a new rule revising the phase- in of the final DPM limit because of concern over mine operators' ability to meet the January 2006 deadline. MSHA also plans to initiate a separate rulemaking to convert the 350 and 160 total carbon DPM limits to elemental carbon limits.
The final rule, Diesel Particulate Matter Exposure of Underground Metal and Nonmetal Miners, is published in the Federal Register.