The influence of using various materials as spark electrodes in the spark test apparatus

The degree to which various commonly used materials influence the probability of spark ignition in the standard spark test apparatus has been studied. These materials include aluminum, brass, copper, lead, tin, stainless steel, and cold-rolled steel. By comparing currents that give a probability of spark ignition of 10/sup -3/, a safety factor can be associated with each material relative to cadmium, which has been arbitrarily assigned a safety factor of 1.00. Results to date are summarized. Knowledge of the probability of ignition will allow a circuit designer to estimate the effect that the materials used to construct a device have on the ignition capability, which could lead to improved design and approvals processes. It is noted that if an electrical apparatus could be designed to preclude sparking to a cadmium electrode, significantly higher currents could be permitted in intrinsically safe circuits without sacrificing safety.<>