Process of Investigation
- Collision fires are a small percent of all accidents and occur over a wide range of circumstances and severity. Be aware that collisions with negligible Delta V, under certain circumstances, may be sufficient to cause a fire.
- Pay close attention to the disruption of vehicle systems, especially those
containing flammable fluids. Trace each and every fluid system to see which
of them can be ruled in as a possibility or ruled out. Because so many
fluids exist in the engine compartment, it can be very challenging to make
this determination when there is substantial collision damage to the
underhood area.
- Examine electrical systems thoroughly, again focusing on any area of disruption or deformation. Look for evidence of arcing, shorting, or overheating that may provide clues as to electrical causes or involvement. Recognize that shorted wires are not necessarily a cause of fire; they often result from fire as well.
- Look for deformation that may have forced flammable materials into contact with a hot surface. For example, polymeric components normally separated by space may have been crushed into contact with hot exhaust components.
- During the collision, dynamic crush can be significantly greater than
static crush visible during a post-impact inspection. Note possible areas of
disturbance that may have taken place during the impact. For example, the
engine may be pushed rearward during the impact in a manner that deforms or
breaches a fuel rail between the engine and bulkhead. The engine position
may then restore when collision forces are removed leaving little direct
evidence as to the source of the damage to the fuel rail.
- Consider possible ignition sources such as mechanical sparks caused by collision with other vehicles or objects, and the possibility of metal dragging on the pavement. Also, consider that the ignition source may have been from another vehicle involved in the collision (light bulb filaments, parting arcs from broken electrical wiring) that may not be present at the inspection.
- Be aware that the first material to ignite may have been splashed or sprayed from its normal location to a distant location, vaporized by a hot surface, and ignited by yet another source distant from the hot surface. Such fires can be very complex and difficult to track.
- Interview witnesses, if possible, to learn details about exactly where the fire was first observed. Ask how much time elapsed between impact and ignition, whether there were any smells or sounds that preceded the eruption of fire (e.g., “poof”sound or explosion). Also inquire about the characteristics of the flames first observed (robustness, color, size), the nature of the how long it took for the fire to propagate from one place to another, what path the fire took, how long it took to be extinguished, and how it was extinguished.
