Ignition of methane-air mixture by frictional sparks from light alloys

Industries handling flammable or explosive gases have to take measures against ignition sources due to mechanical friction and impact. One of the most hazardous ignition sources to methaneair mixtures are sparks induced by frictional impact from light alloys. The authors conducted a laboratory scale experiment to clarify the characteristics of frictional sparks, and the relation between the incendivity and practical conditions. A drop type testing apparatus was used, by which light alloy samples made an impact on a rusted steel plate. As a result, probability of ignition was greatly affected by some impact conditions, i.e., dropping height, weight of samples and surface roughness. The impact energy required to obtain 50% probability of ignition can be used as an index for estimating the incendivity of light alloys. Some correlation between the incendivity and the content of magnesium was found for three kinds of light alloys. The incendivity of light alloys became lower when a small quantity of beryllium was added to Mg base light alloys, but clear decrease of the incendivity did not appear as for Al-Si type light alloys.