NFPA 921, Guide for Fire and Explosion Investigations, 2001 Edition, Chapter 22 is titled "Motor Vehicle Fires". This chapter provides basic information and background for investigating fires in motor vehicles. The information in the chapter is useful for investigating fires in automobiles, trucks, heavy equipment, and recreational vehicles. It does not cover fires in vehicles that travel by air, on water, or on rails.
When the type and quantity of combustible materials that make up motor vehicles are burned, they can produce a degree of damage that can initially give the appearance that there were incendiaries involved in the fire. Because the damage produced by the burned components in a motor vehicle can be so severe, the use of fire patterns to determine the nature of the fire and the point of origin can be confusing.
For instance, when the foam in the seats burn as a result of a fire that spread to them, the resulting fire is so intense that it produces patterns that show that the hottest part of the fire was in the cabin. This observation should not be interpreted to mean that the fire in the cabin burned the longest and therefore the origin must be in the cabin.
NFPA 921, Chapter 22, paragraph 22.1 Introduction states in part, "The use of fire patterns or degree of fire damage should be used with caution. The interpretations drawn from these patterns should be verified by witness evidence, laboratory analysis, service records indicating mechanical or electrical faults, factory recall notices, or complaints in service bulletins that can be obtained from the National Highway Transportation Safety Administration (N H T S A), or the Center for Auto Safety. The investigator should also be familiar with the composition of the vehicle, and its normal operation."
Fire Investigation Methodology
The methodology for investigating fires in vehicles has many similarities to the methodology used in the investigating fires and structures. The basic fire science of fire chemistry, heat transfer, and thermodynamics must be applied. However, the amount and type of combustible materials in a vehicle is much different in a vehicle as compared to a house.
For example, modern automobiles are constructed with many pounds of combustible plastic materials that burn with the intensity of a liquid fuel. Additionally, the size and shape of compartment sizes in vehicles will affect the growth of fires and the relative intensity of fires at given locations.
Motor vehicles often catch fire in locations where the burned remains of the vehicle cannot be left at the scene long enough for everyone interested in investigating the fire to get to the scene.
If a vehicle catches fire and burns along a roadway, public safety demands that the burned remains be hauled away and the roadway be cleared of debris. That makes it necessary for a vehicle fire investigator to go where the burned remains of a vehicle or stored to do an inspection.
In those situations, the investigator does not have the benefit of seeing how the scene affected the fire in the vehicle or how the fire in the vehicle affected the scene. Conditions at the scene may show that the fire actually originated outside the vehicle. Fire patterns at the scene may help the investigator determine the compartment of origin. It may be necessary to go to the scene even though the burned vehicle is no longer there.