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NFPA 921 Sections 15-1 and 15-3 through 15-5
Investigation of Motor Vehicle Fires

[interFIRE VR Note: Tables and Figures have not been reproduced.]

15-1. Introduction. This chapter deals with factors related to the investigation of fires involving motor vehicles. Included in this discussion are automobiles, trucks, and recreational vehicles (e.g., motor homes). While vehicles that travel by air, on water, or on rails are not covered, there are many factors relating to incident scene documentation, fuels, ignition sources, and ignition scenarios that may apply.

The burn or damage patterns remaining on the body panels and in the interior of the vehicle are often used to locate the point(s) of origin and for cause determination.

It was once felt that rapid fire growth and extensive damage was indicative of an incendiary fire. However, the type and quantity of combustible materials found in automobiles today, when burned, can produce this degree of damage without the intentional addition of another fuel such as gasoline. In the case of a total burnout, one cannot normally conclude whether the fire was incendiary on the basis of observations of the vehicle alone. The use of fire patterns or degree of fire damage to determine a point of origin or cause 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, or factory recall notices. The investigator should also be familiar with the composition of the vehicle and its normal operation. (See Chapter 4.)

The relatively small compartment sizes of vehicles may result in more rapid fire growth given the same fuel and ignition source scenario, when compared to the larger compartments normally found in a structure fire. However, the principles of fire dynamics are the same in a vehicle as in a structure and, therefore, the investigative methodology should be the same. (See Chapters 2 and 3.)

15-3. Ignition Sources in Motor Vehicle Fires. In most instances, the sources of ignition energy in motor vehicle fires are the same as those associated with structural fires, arcs, overloaded wiring, open flames, and smoking materials, for example. There are, however, some unique sources that should be considered, such as the hot surfaces of the catalytic converter, turbocharger, and manifold. Because some of these ignition sources may be difficult to identify following a fire, the following descriptions are provided to assist in their recognition.

15-3.1. Open Flames. The most common open flame in a carburetted vehicle is caused by a backfire through the carburetor. Ignition will rarely occur if the air cleaner is properly in place. Most vehicles today, however, use a fuel injection system that eliminates the need for a carburetor. Lighted matches in ash trays may ignite debris in the ash tray, resulting in a fire that exposes combustible plastic dashboard or seat materials. In recreational vehicles, appliance pilot flames or operating burners and ovens are open flame ignition sources.

15-3.2. Electrical Sources. The primary source of electrical power in a vehicle is the battery. With no battery, there can be no other electrical source of energy. With a battery, however, consistent energy can be produced by the generator or alternator, which is more than sufficient to cause a fire. Overcurrent protection devices, such as fuses, circuit breakers, or fusible links, are used on motor vehicles to provide safety. However, in some cases, breakdown of parts, improper use, or installation of additional equipment can defeat these safeguards.

15-3.2.1. Overloaded Wiring. Unintended high-resistance faults in wiring can raise the conductor temperature to the ignition point of the insulation, particularly in bundled cables such as the wiring harnesses or the accessory wiring under the dash where the heat generated is not readily dissipated. This can occur without activating the circuit protection. Faults and mechanical failures of high-current devices such as power seat or window motors can also result in ignition of insulation, carpet materials, or combustible debris that may accumulate under seats. Pre-fire history of electrical malfunction may be a clue.

15-3.2.2. Electrical Arcing. In postcrash situations, arcs can be generated through the crushing or cutting of wires, particularly battery and starter cables, which are not electrically protected and are designed to carry high currents.

The large amount of energy available in a battery can be enough to ignite materials such as engine grease, some plastic materials, and electric insulation. Significant arcing can also occur along with the crushing of the battery or batteries.

15-3.2.3. * Lamp Filaments of Broken Bulbs. Lamp filaments of broken bulbs are also a source of ignition energy especially for gases, vapors, or liquid fuels in a spray or mist form. Normally operating head lamp filaments have temperatures on the order of 2550F (1400C).

15-3.2.4. External Electrical Sources Used in Vehicles. While most electrical sources in vehicles are self-contained, in some situations electrical power is provided from commercial facilities. Examples of these sources are electrical hook-ups used in recreational vehicles and trailers and electric heaters for engines and vehicle interiors. Inspection for electrical power cords should be made when applicable, since an overload of the cord or failure of the appliance could be the cause of the fire. Where recreational vehicles are connected to commercial power, the branch circuit wiring should be inspected for indications that it was a possible ignition source.

15-3.3.* Hot Surfaces. Exhaust manifolds and components can generate sufficient temperatures to ignite diesel spray and to vaporize gasoline. Automatic transmission fluid, particularly if heated due to an overloaded transmission, can ignite on a hot manifold. Engine oil and certain brake fluids (DOT 3 and 4) dropping on a hot manifold can also ignite. The internal components of a catalytic converter have operating temperatures in the range of 1292F (700C) under normal operation and can be much higher if unburned fuel is introduced due to a fuel or ignition system malfunction. External temperatures of these converters can reach temperatures of 600F (315C) under normal operation and higher where ventilation or air circulation is restricted.

15-3.4.* Mechanical Sparks. Metal (e.g., steel and magnesium) to pavement sparking can generate enough energy to ignite liquid fuel vapors or gaseous fuels. Sparks generated at speeds as low as 8 km/h (5 mph) have been determined to have temperatures of 1470F (800C) (orange sparks). Higher speeds have produced temperatures of 2190F (1200C) (white sparks). Aluminum to pavement sparks are not an ignition source. Sparks can also be caused by moving parts such as pulleys rubbing against other metallic objects. Sparks from tools striking metals seldom cause ignition.

15-3.5. Smoking Materials. Modern upholstery fabrics and materials are treated with flame retardant and are generally difficult to ignite with a cigarette. Ignition may occur if a lit cigarette becomes buried in a crevice between seat cushions, paper, or other debris or if the seat material comes in contact with open flame.

15-4. Recording Motor Vehicle Fires. The same general techniques are employed for vehicles that are used for structural fires. Whenever possible, the vehicle should be examined in place at the scene. However, the investigator may not have the opportunity to view the vehicle in place or at the fire scene. For many reasons, the vehicle may have to be moved before the investigator reaches the scene. Frequently, part of the documentation takes place at a salvage yard, repair facility, or warehouse.

As the investigator commences the investigation, he or she should determine the following:

(a) Identify the vehicle to be inspected and record the information. This will entail describing it by make, model, model year, and any other identifying features. The vehicle should be accurately identified by means of the vehicle identification number (VIN). The composition of the VIN provides information on such things as the manufacturer, country of origin, body style, engine type, model year, assembly plant, and production number. The VIN plate is most commonly placed on the dash panel in front of the driver's position. It is affixed with rivets. If this plate survives the fire, the number should be recorded accurately. If it is rendered unreadable or appears to have been tampered with, then the assistance of one of the following should be requested:

1. A police auto theft unit

2. A member of the National Insurance Crime Bureau in the United States

3. A member of the Canadian Automobile Theft Bureau in Canada

These persons have the necessary expertise to identify the vehicle by means of confidential numbers located elsewhere on the vehicle. The VIN should be checked on either the National Crime Information Center (NCIC) or the Canadian Police Information Centre (CPIC) to ensure there is no record outstanding on it.

(b) Once the vehicle has been positively identified, the mechanical functions of that particular vehicle, its composition, and its fire susceptibility should be reviewed. To ensure that no details are overlooked, the investigator may examine a vehicle of similar year, make, model, and equipment, or the appropriate service manuals.

(c) Information regarding fires and fire causes in vehicles of the same make, model, and year can be obtained from the National Highway Safety Administration or from the Insurance Institute for Highway Safety, both located in Washington, DC. The Auto Safety Hotline number is 1-800-424-9393 or (202) 366-0123. In Canada, contact the Department of Transport, Ottawa; phone: (613) 998-1992.

15-4.1. Recording at the Scene. The investigator should make a diagram of the fire scene, showing points of reference and distances relative to the vehicle. The diagram should be of sufficient detail to pinpoint the location of the vehicle before its removal. The overall scene should be photographed showing surrounding buildings, highway structures, vegetation, other vehicles, and impressions left by tires or footprints. All fire damage to any of the above or any signs of fuel discharge that might help in the analysis of the fire spread should be photographed and documented. The location and condition of any parts or debris that are detached should be documented.

The vehicle should be photographed. The photographs should include all surfaces, including the top and underside. Both the damaged and undamaged areas, including the interior and exterior damage, should be photographed.

Any evidence showing the path of fire spread either into or out of any compartment (e.g., engine, passenger, trunk, cargo) or within any compartment should be photographed. As with structure fires, the path of fire travel may be difficult to determine in a totally burned out vehicle.

The cargo spaces should be photographed. The type and quantity of cargo and any involvement in the fire should be noted.

If possible, the removal of the vehicle(s) and any damage that may result from the removal process should be photographed. Also, the scene after removal of the vehicle(s) should be photographed, while noting burns on the earth or roadway and the location of glass and other debris.

Drawings and notes should be prepared to augment the photographs.

15-4.2. Recording the Vehicle Away from the Scene. If the vehicle has been removed from the scene, a visit should be made to the scene and any photographs that were taken at the scene should be reviewed. The basic process of documenting the condition of the vehicle is the same regardless of where it is. When the inspection is delayed and when it is located at a remote location, parts may be missing or damaged. Additionally, the vehicle(s) may have been damaged by the elements, and fire patterns, most notably those on metal surfaces, may be obscured. If outdoor storage is likely, arrangements should be made for the vehicle to be covered with a tarp or other suitable material.

Even if the vehicle was examined at the scene, there are advantages to inspecting a vehicle away from the scene. For example, it is easier to move or remove body panels that may be blocking a view of critical parts. Power is often available as are tools for disassembly if needed. Frequently, arrangements can be made to have equipment such as a forklift available to raise the vehicle for a more detailed inspection.

The vehicle should be thoroughly photographed as it is examined at locations away from the scene.

15-5. Examination of Vehicle Systems. For ease of discussion, the detailed examination is broken down by components or areas that have a common function. It is suggested that an attempt be made to develop a scenario of the events leading up to the fire as well as the progression of the fire itself. To do this, it is suggested that the operator of the vehicle, passengers, bystanders, the fire department personnel, and the police be interviewed separately. This information should be used to assist with the examination. Information regarding the operation of the vehicle immediately prior to the fire should be obtained from the operator and/or owner to determine the following:

(a) When the vehicle was last driven and how far

(b) The total mileage on the vehicle

(c) Whether the vehicle was operating abnormally (e.g., stalling, electrical malfunctions)

(d) When the vehicle was last serviced (e.g., oil change, repairs)

(e) When the vehicle was last fueled and the amount of fuel added

(f) When and where the vehicle was parked

(g) Whether the vehicle was seen again prior to the fire

(h) With what equipment the vehicle was equipped (e.g., radio, CD, CB, mobile phone, electrical windows, seats, customized wheels)

(i) What personal items were in the vehicle (e.g., clothing, tools)

If the vehicle was being driven at the time the fire occurred, the following additional points should be covered:

(a) How far the vehicle had been driven

(b) What the route of travel was

(c) If it was loaded, towing a trailer, being driven fast, and so forth

(d) When and where the smell, smoke, or flame was noticed first

(e) How the vehicle reacted (e.g., stalling, racing erratically, or showing indications of electrical malfunctions)

(f) What the operator did

(g) What was observed

(h) What attempts were made to put the fire out and how

(i) The length of time the fire burned before help arrived

(j) The total length of time the fire burned until it was extinguished

* A-15-3.2.3 For more information, see Severy et al., Automobile Collision Fires.

* A-15-3.3 For more information, see Cole, The Investigation of Motor Vehicle Fires: A Guide for Law Enforcement, Fire Department and Insurance Personnel.

* A-15-3.4 For more information, see Severy et al., Automobile Collision Fires, and API PUBL 2216, Ignition Risk of Hydrocarbon Vapors by Hot Surfaces in the Open Air.

For more information on mechanical sparks as an ignition source, refer to Campbell, Appraisal of the Hazards of Friction-Spark Ignition of Aircraft Crash Fires, and API PUBL 2214, Spark Ignition Properties of Hand Tools.

For more information, contact:
The NFPA Library at (617) 984-7445 or e-mail

Taken from NFPA 921Guide for Fire and Explosion Investigations 1998 Edition, copyright © National Fire Protection Association, 1998. This material is not the complete and official position of the NFPA on the referenced subject, which is represented only by the standard in its entirety.

Used by permission.

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