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 o f the most hazardous ignition sources to methane-air mixtures are spar ks induced by frictional impact from light alloys. The authors conduct ed a laboratory scale experiment to clarify the characteristics of fri ctional sparks, and the relation between the incendivity and practical conditions. A drop type testing apparatus was used, by which light al loy samples made an impact on a rusted steel plate. As a result, proba bility of ignition was greatly affected by some impact conditions, i.e ., dropping height, weight of samples and surface roughness. The impac t energy required to obtain 50% probability of ignition can be used as an index for estimating the incendivity of light alloys. Some correla tion between the incendivity and the content of magnesium was found fo r three kinds of light alloys. The incendivity of light alloys became lower when a small quantity of beryllium was added to Mg base light al loys, but clear decrease of the incendivity did not appear as for Al-S i type light alloys.