23 March 2007

After lengthy litigation, the US Mine Safety and Health Administration (MSHA) rule establishing exposure limits to diesel particulate matter (DPM) in underground metal/non-metal (i.e., non-coal) mines has been upheld by court. In a final ruling adopted last month by the US Court of Appeals for the District of Columbia, the court decided in favor of MSHA, and against the mining industry groups that challenged the regulation.

In a unanimous opinion written by Judge Sentelle, the court upheld the DPM rule in its entirety. Specifically, the court found:

  1. that MSHA’s risk assessment “was based upon evidence in the record that workers who are exposed to high levels of DPM face increased risks of lung cancer and other adverse health effects”;
  2. that MSHA’s selection of total carbon (TC) and elemental carbon (EC) as surrogates for DPM “was based upon evidence that TC and EC are closely correlated with DPM and that there are reliable conversion ratios between DPM, TC, and EC”; and
  3. that MSHA “offered more than enough evidence in support of its conclusion that mine operators can feasibly comply with the DPM exposure limits.”

The DPM rule was promulgated by MSHA on January 19, 2001. The regulation established two DPM exposure limits: (1) an interim limit of 400 µg/m3 effective 20 July 2002, and (2) a final limit of 160 µg/m3 effective 20 January 2006. Both limits were expressed as TC, according to NIOSH method 5040.

Following a court challenge by groups in the mining industry, negotiations started between MSHA, mine operators, organized labor, and other stakeholders which led to modifications of the rule:

  • In 2005 MSHA changed the interim limit from 400 µg/m3 of TC to 308 µg/m3 expressed as EC (based on a TC:EC conversion factor of 1.3).
  • On May 18, 2006, MSHA promulgated a final rule which:
    • Changed the interim limit to 350 µg/m3 EC and its effective date to January 20, 2007. This limit is being currently enforced by MSHA.
    • Extended the effective date of the 160 µg/m3 TC standard to May 20, 2008. This remains the effective date, as the 2006 final rule was also upheld by the court in that decision.

As applied to diesel, the 400 µg/m3 TC and 350 µg/m3 EC limits are of a similar stringency, but the EC measurement eliminates potential non-diesel sources of organic carbon particulates, for instance oil mist.

The final DPM exposure limit of 160 µg/m3 TC—now confirmed by the court—will be also converted to an equivalent EC-based limit in a separate rule to be issued by MSHA by the time of its effective date on May 20, 2008.

The final court ruling in the MSHA case can be significant to the mining industry throughout North America. In particular, it may prompt Canadian Provinces to adopt more stringent DPM exposure limits for Canadian mines, which use similar mining and diesel engine technology, but have rather relaxed diesel particulate matter exposure requirements.

Source: MSHA (Court ruling)