From the Archives: Indeterminate Fire

Assigned to investigate a residence fire, the effort was made to determine if an active appliance caused the fire. Electrical components of the residence consisted of the circuit breaker panel, the electrical wiring in a pile of debris, and an air handling unit. The circuit breaker panel showed no evidence of malfunction. The appliances formerly energized with the wires in the debris could not be evaluated due to fire damage. The steel metal housing of the air handling unit was discolored and had both fused and alloyed with copper wire within the unit. The temperature of the fire in the vicinity of the air handling unit exceeded the melting temperature of steel (see table). The motor to the blower showed arcing; however, due to the temperature exceeding the melting temperature for copper, it could not be determined if the arcing occurred before (causing) or during the fire.

Often fire conditions obliterate the necessary evidence for evaluating the cause.

Table values from “Pocket Ref” by Thomas J. Glover, 3rd Edition, 2003, Sequoia Publishing, Littleton, CO.

Metal Melting Point (Celsius)
Aluminum 660
Copper 1085
Steel 1420