During investigations of automobile collisions involving fire, some cases were observed in which the sources of ignition were quite subtle. In one, the only liquid fuel available was coolant and the only ignition source near the observed burn damage was the internal sparking of a cooling fan motor. Questions raised from this example and others led to further research of minimum ignition energies of automobile underhood fluids and the spark energies available from electric motors.
Through laboratory measurements and analysis, the minimum ignition energy of ethylene-glycol-based coolant and spark energies available from operation of electric motors in automobiles were estimated. Comparisons of the spark energies available and the minimum ignition energy of underhood fluids confirmed the potential for ignition from motor sparks. Some questions still remain for further study.