The Bureau of Mines has conducted research on the ignition of methane by sparks caused by frictional impact of aluminum alloys on rusty steel at typical coal mine fan speeds. The objectives were to establish the incendivity of aluminum alloys under these conditions, to investigate differences between aluminum alloys, and to evaluate substitute materials for the aluminum-steel combination. With a specially designed apparatus, three commercial aluminum casting alloys and a series of experimental aluminum alloys were tested for incendivity in frictional impact against rusted steel in flammable methane-air mixtures. All aluminum alloys tested produced some ingitions. In a series of experimental alloys, the harder alloys and those containing silicon tended to be more incendive than the others. Constructional steel, stainless steel, brass, and plastic did not cause ignition of methane-air mixtures in frictional impact against rusty steel. Some ignitions occurred with constructional steel at high speed in more flammable gas mixtures. It is suggested that other constructional materials than the aluminum-steel combination would minimize or eliminate this hazard.