An investigation of the ignition hazards associated with various materials in the breakflash apparatus

The US Bureau of Mines Pittsburgh Research Center has completed an investigation of the degree to which various disk materials affect the probability of igniting a methane-air atmosphere using the breakflash machine. Data were generated for estimating currents (resistor or inductor circuits) and voltages (capacitor circuits) associated with a particular ignition level. Further analysis of these data was used to assign hazard levels for each material, with cadmium used as a reference material. From this, a safety factor was associated with each material. Presently, there are no construction requirements with regard to materials of construction. The worst case is always assumed (i.e., cadmium). Laboratory test results confirmed cadmium as the worst-case material among those tested for resistor and inductor circuits but not for capacitor circuits. In fact, aluminum testing illustrated lower ignition voltages than cadmium at 107 and 1310 mu F. For capacitor circuits, little, if any, safety was gained by using certain materials other than cadmium.<>