 U.S. federal regulations require that rock dust be applied in all underground areas of a coal mine to mitigate the propagation of a coal dust explosion.Prior to September 2010, U.S. federal regulation () mandated that the nation’s coal mines maintain a total incombustible content (TIC) of at least 65% in nonreturn entries and at least 80% in the return airways.In September 2010, U.S.