An explosion which consists of a sudden pressure rise caused by the very rapid combustion of airborne dust. Ignition of suspensions of combustible dusts can occur in the following ways: (1) initiation by flame or spark, (2) propagation by a gas explosion or blasting, and (3) spontaneous combustion. Little is known about the last-named mechanism, which is relatively rare in mines. The most frequent causes of major coal mine explosions in the United States today are electric arcs, open flames, and explosives.