Recommendations for a New Rock Dusting Standard to Prevent Coal Dust Explosions in Intake Airways

Based on extensive in-mine coal dust particle size surveys and large-scale explosion tests, the National Institute for Occupational Safety and Health (NIOSH) recommends a new standard of 80% total incombustible content (TIC) be required in the intake airways of bituminous coal mines in the absence of methane. Mining technology and practices have changed considerably since the 1920s, when the original coal dust particle survey was performed. Also, it has been conclusively shown that as the size of coal dust particles decreases, the explosion hazard increases. Given these factors, NIOSH and MSHA conducted a joint survey to determine the range of coal particle sizes found in dust samples collected from intake and return airways of U.S. coal mines. Results from this survey show that the coal dust found in mines today is much finer than in mines of the 1920s. Explosion tests used medium-sized dust and indicated that medium-sized coal dust required 76.4% TIC to prevent explosion propagation. Given the results of the extensive in-mine coal dust particle size surveys and large-scale explosion tests, NIOSH recommends a new standard of 80% TIC be required in the intake airways of bituminous coal mines in the absence of methane. The survey results indicate that in some cases there are no substantial differences between the coal dust particle size distributions in return and intake air courses in today’s coal mines. The survey results indicate that the current requirement of 80% TIC in return airways is still appropriate in the absence of background methane.