Particle size and surface area effects on explosibility using a 20-L chamber

• The rock dust particle size distribution widely varies as well as the associated specific surface area.
• Some rock dusts meeting the U.S. particle size requirements do not inert PPC in the 20-L chamber.
• 20-L chamber tests were conducted with several rock dusts.
• The inerting effects of specific surface area are examined.
• A specific surface area of 260 m2/kg is a better specification than the percentage of material passing through 200 mesh.

The Mine Safety and Health Administration (MSHA) specification for rock dust used in underground coal mines, as defined by 30 CFR 75.2, requires 70% of the material to pass through a 200 mesh sieve (<75 μm). However, in a collection of rock dusts, 47% were found to not meet the criteria. Upon further investigation, it was determined that some of the samples did meet the specification, but were inadequate to render pulverized Pittsburgh coal inert in the National Institute for Occupational Safety and Health (NIOSH) Office of Mine Safety and Health Research (OMSHR) 20-L chamber. This paper will examine the particle size distributions, specific surface areas (SSA), and the explosion suppression effectiveness of these rock dusts. It will also discuss related findings from other studies, including full-scale results from work performed at the Lake Lynn Experimental Mine. Further, a minimum SSA for effective rock dust will be suggested.