The relative safety factors obtained by using various materials as spark electrodes in methane-air atmospheres

The authors seek to quantify the influence of various common materials (copper, aluminium, brass, zinc, tin, lead and cold-rolled and stainless steels) on the probability of spark ignition in 8.3% methane-air. Results presented indicate the current necessary to produce a probability of spark ignition of 10/sup -3/ for a specific material combination. By comparing currents that yield the same probability of ignition, the relative safety factors between various material combinations may be estimated. It is found that spark ignition safety factors (current ratios) vary considerably, with cadmium requiring the lowest ignition current at each voltage. These results indicate that other materials require higher currents to initiate spark ignition in resistive circuits than does cadmium. Thus, spark ignition approval criteria may be able to be relaxed, with respect to ignition current levels, without sacrificing safety.<>