The U.S. Department of Labor’s Mine Safety and Health Administration (MSHA) recently published an emergency temporary standard (ETS) that revises the existing federal standard on maintenance of incombustible content of rock dust.

The decision, according to the agency, was based on a review of accident investigation reports of mine explosions in intake air courses that involved coal dust, as well as the National Institute for Occupational Safety and Health’s report “Recommendations for a New Rock Dusting Standard to Prevent Coal Dust Explosions in Intake Airways,” which can be viewed at

The ETS, effective immediately, applies only to underground bituminous coal mines and can be viewed on September 23 in the “special filings” section of the Federal Register’s Web site at The rock dust ETS will remain in effect until a standard is promulgated through the regular rulemaking process.
MSHA has also issued a program information bulletin that provides guidance on compliance with the new standard. The bulletin may be viewed on MSHA’s Web site at

The existing MSHA standard requires mine operators to maintain at least 80% total incombustible content (TIC) of combined dusts in return air courses and at least 65% TIC in all other areas. It also requires that the percent TIC of combined dust in all areas where methane is present in any ventilating current be increased. The 80% TIC must be increased by 0.4% for each 0.1% of methane in return air courses, and the 65% TIC must be increased by 1% for each 0.1% of methane present in all other areas.

The ETS revises the existing standard by requiring mine operators to increase the total incombustible content of the combined coal dust, rock dust and other dust from 65% to 80% in all accessible areas of underground bituminous mines, and an additional 0.4% for each 0.1% of methane where methane is present in any ventilating current.

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