The U.S. Mine Safety and Health Administration (MSHA) announced a new final rule that requires coal mine operators to maintain the percentage of incombustible content of the combined coal dust, rock dust and other dust at 80% in all accessible areas of underground bituminous coal mines, as well as an additional 0.4% for each 0.1% of methane where methane is present in any ventilating current. The new rule increases the total incombustible content for all areas of the mine, other than return air courses, from 65% to 80%.