Fire Pattern

Investigation of automotive fires often involves the interpretation of burn or heat damage patterns on the vehicle body, in the engine compartment, passenger compartment (interior), or cargo space. Such patterns can provide clues as to the origin, cause or propagation path of the fire. However, the use of such patterns can be misleading and their interpretation must be used with care.

High-heat areas, such as portions of the body where all traces of paint have been burned off (and metal has often rusted) can provide clues as to the fire origin. This is especially true if a vehicle has not been burned extensively. High heat areas may also overpressurize sealed chambers, such as hood struts, hollow driveshafts, and other vessels that show distortion. The more limited the fire damage (from either self or external extinguishment), the greater the potential for identifying the fire origin based on fire patterns. Obviously, if fire is restricted to a small area, the fire origin is most likely within that region. The interpretation of fire patterns for purposes of identifying origin and cause must always be considered along with other evidence including observations, witness statements, analytical test results and the history of vehicle operation and repair.

This section will cover the interpretation of fire patterns and show examples of various features.

Toyota Camry collision fire. Note that fire spread from engine to interior, and heat radiated outward from passenger windows. Also, there was less exterior burn damage to lower area of rear doors.

Fire origin in the engine compartment can be identified even in some events with extensive burn damage. The following picture shows the engine compartment of a Toyota Camry with almost all combustibles consumed in a post-collision fire. With collision and fire damage this extensive, sometimes the origin of the fire can only be broadly identified.

A reliable identification of the engine compartment as the origin was possible in this case based on the following:

• Collision damage was limited to the engine compartment. It is likely that fire initiated in and around a damaged system.
• The burn damage in the engine compartment was near total; the burn damage in the passenger compartment was progressive from front to rear. If the fire had initiated in the passenger compartment it would be likely to have appeared to progress forward and rearward from the origin.
• Witness observations were consistent with fire initiating in the engine compartment. Even without the witness statements, identification of an engine compartment origin was justified.