Process: Evidence of Electrical Causation

Automotive fires are relatively infrequent events; hence those of electrical origin are even more rare. As such, it is prudent to carefully investigate the history of electrical problems with the vehicle. If a fire was caused by electrical means, there is some likelihood that the cause was related to a traceable history. Specific evidence of electrical causation may include:

History of fuse failure

Interviews with witnesses (the vehicle owner/driver or the person most responsible for maintaining the vehicle) may reveal a history of fuse failure and replacement that may give credence to a theory of electrical ignition source.

Wiring failure consistent with operating conditions and current

The investigator should attempt to determine if there was an electrical component in the car that reportedly malfunctioned, had been operating erratically, or had an odor prior to the fire. Was the electrical system energized? Could the available current from the system have caused the observed damage? Are there alternative explanations for the observed damage? Sometimes fires occur in parked vehicles after a significant period of time. In such cases, there is little chance that a hot surface on the engine could provide an ignition source. Electrical malfunctions or arson are the only likely possibilities.

Burn pattern: fuels and ignition sources

Sometimes the physical fire evidence suggests a possibility, or even likelihood, of electrical ignition. This could be in the form of arced connections, electrical overheating, beaded wires, internal heating, or other indication. Other times, by elimination, there is little possibility of any other form of ignition. For example, after a vehicle is parked for an hour, electrical malfunction and arson may be the only possible ignition sources. In any case, the investigator must strive to find consistency in all the evidence, including witness statements, to identify the ignition source. In an accidental fire, if there is no hot surface in the vicinity of the fire origin (and the fire origin is definitively located), then an electrical ignition source becomes much more likely. 

Arc damage

Arc damage or beading, may suggest a possible electrical origin. Arc damage may involve a transfer or loss of material. The investigator should look particularly carefully at the wiring in systems with a history of fuse failure, recent maintenance or problems in operation (e.g., reported intermittent function of electrical accessories or components).

Evidence of overheated wiring

Overheated wire should be carefully examined to determine (if possible) whether the heating was internal or external. If a wire has been overheated internally, its insulation will be affected along the entire length of the wire, from the current source to ground. If the wire was externally heated as a result of fire, there may be telltale areas where the wire was shielded from heat (such as behind a clamp). Sometimes disassembly of a wiring harness will give clues as to specific wires that may have overheated. If an overheated wire is found, the investigator should look for information about the related circuit. Is there any evidence of a problem with this circuit before the fire (owner report, maintenance, fuse replacement)? Was the circuit powered prior to the fire?