Heat Shadows

Burn patterns can be used to pinpoint fire origin by observing where the shadowing of heat has occurred. “Shadows” of relatively undamaged material may be visible in the area surrounding the heat source if those materials were blocked from the heat. An electrical conductor overheated by internal resistance will exhibit damage along its entire length from the power source to ground. Alternatively, an electrical conductor damaged by a fire may have insulation remaining in areas protected from the heat.

Engine compartment of Jeep Cherokee after non-collision fire; the bulkhead is to the left. An aftermarket alarm wire (at upper arrow) showed considerable heat damage. At the lower arrow, there was less damage to the alarm wire insulation because of heat shadowing from the larger wiring harness adjacent to it. This ruled out internal overheat of the wire as a potential fire cause.