Electrical Systems and Appliance/Vehicle Fire Analysis
Electrical fire indicators
Most electrical fires involve resistance heating, overload, poor connections, or arcing. Arc mapping is a technique, not a cause determination: arcing at multiple points may show the fire traveled along a circuit, but arc sites can also be victims. Copper can melt and form beads from an arc, and distinguishing a fault arc from fire damage generally requires metallurgical examination. Beading does not prove the conductor caused the fire. Ground faults and short circuits leave characteristic patterns, and "electricity takes the path of least resistance" is an oversimplification that shows up as a wrong answer.
Appliances and vehicles
For appliances, determine whether the fire originated inside the unit (internal component failure) or the unit was damaged by an external fire. Examine the power cord, control board, and the relationship of fire damage to the appliance. Vehicle fires require checking the battery, alternator, wiring harnesses, fuel lines, and any aftermarket installation. Lithium-ion batteries can enter thermal runaway, producing venting, jet flames, and re-ignition; a fire that reignites after suppression suggests a battery. Document the vehicle's condition, mileage, and modifications.
TRAP: Concluding "electrical" because arcs were found. Arc beads are common in wiring destroyed by any fire.
RULE OF THUMB: Ask what the wiring looked like before the fire. Beads and melted metal downstream of the burned area are likely victims, not causes.