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
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
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
(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
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
(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
* A-15-3.3 For more information, see Cole, The Investigation
of Motor Vehicle Fires: A Guide for Law Enforcement, Fire Department and
* 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
For more information, contact:
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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
Used by permission.