Rock dust is crushed rock, often limestone, sprayed on walls inside underground coal mines to stop coal dust explosions. The dust helps absorb heat, reduces the amount of coal dust in the air, and prevents black lung disease. Rock dust has been used in coal mines since the early 1900s, and improvements in technology have been made over time.

U.S. federal rules require rock dust to be applied in all underground coal mine areas to stop the spread of coal dust explosions. Before September 2010, a rule called 30 CFR 75.403 required coal mines to have at least 65% incombustible dust in nonreturn entries and at least 80% in return airways. In September 2010, the U.S. Mine Safety and Health Administration (MSHA) created an emergency rule that raised the incombustible dust requirement in intake airways to 80%, which took effect on June 21, 2011. The 65% requirement was based on an average particle size called "mine-size dust," which came from samples collected from mines in the 1920s. To check if mines follow the rules, inspectors collect dust samples from underground coal mines and send them to the MSHA National Air and Dust Laboratory in Mount Hope, West Virginia, for testing to determine the incombustible content.