Vehicle fires are among the most common fires that investigators encounter, yet they can be surprisingly difficult to analyze. A modern vehicle packs fuel, lubricants, high-temperature exhaust components, complex wiring and, increasingly, high-voltage batteries into a small space, and a fully involved vehicle can destroy much of the evidence in minutes. The Utah Chapter IAAI has long recognized the topic: the chapter's older Tools page offered investigators an automobile fires reference, a vehicle fire report form and a document on the ignition properties of automotive fluids. This article outlines a practical approach to vehicle fire investigation.
Safety at Vehicle Fire Scenes
Vehicle scenes carry hazards that differ from structure fires:
- Traffic: position yourself and your vehicle to minimize exposure, and use traffic control when working near roadways.
- Stored energy: bumper energy absorbers, hood and hatch struts, airbag inflators and seatbelt pretensioners can release suddenly when heated or disturbed.
- Fuels and fluids: leaking fuel and fluids can reignite or create slip hazards.
- Electric and hybrid vehicles: high-voltage batteries can remain energized after a fire and can reignite hours or days later through thermal runaway. Identify the vehicle's powertrain before examination, treat high-voltage components as energized, and follow manufacturer emergency response guidance.
- Toxic residues: burned plastics, composites and batteries produce hazardous residues. Use appropriate PPE and decontamination.
Our fire scene safety guide covers PPE and decontamination in more detail.
Identify the Vehicle
Record the make, model, year, vehicle identification number (VIN), license plate and mileage if it can be determined. Identification lets you research the vehicle's systems, service bulletins and recalls. The legacy version of this website linked to safety recall and product warning information; today, the U.S. National Highway Traffic Safety Administration maintains a searchable recall database by VIN. An open recall does not prove a cause, but it is important data to consider.
Documenting the Vehicle and the Scene
The scene
Photograph the location, surrounding surfaces, burn patterns on the ground, fluid trails, tire marks, debris and nearby exposures. Note whether the vehicle was parked, running or being driven when the fire started, and whether it may have been moved after the fire.
The vehicle
Photograph the exterior from all sides and corners, then each compartment: engine, passenger, cargo and undercarriage. Document the position of the windows, doors, ignition switch or push-button start, gear selector and keys. Our fire scene photography guide describes a systematic sequence that works well for vehicles.
Burn patterns
As with structures, patterns in and on the vehicle help identify the area of origin. Compare damage between compartments, look for the lowest and most intense areas of burning, and consider how openings such as broken windows affected ventilation. Remember that some materials, such as magnesium and aluminum components, can burn or melt intensely without indicating the origin.
A Practical Examination Sequence
- Complete the safety assessment and confirm the vehicle's powertrain type.
- Document the scene and the vehicle exterior before touching anything.
- Interview the owner, driver and witnesses as early as possible.
- Examine the least damaged areas first, then work toward the most damaged compartment.
- Examine fuel, fluid, electrical and exhaust systems in the area of origin, documenting each component considered.
- Develop and test hypotheses for each potential ignition source and first fuel.
- Preserve evidence and record custody before the vehicle is released or towed.
Where a vehicle has been towed before you arrive, document the tow route, storage conditions and who handled the vehicle, and return to the original location to examine the ground, debris and any parts left behind. Evidence that falls from the vehicle during towing can be lost if the original scene is not examined.
Common Accidental Ignition Scenarios
Automotive fluids and hot surfaces
Gasoline, diesel fuel, engine oil, transmission fluid, power steering fluid, brake fluid and coolant have different ignition properties. Some fluids can ignite on hot exhaust components such as manifolds, turbochargers and catalytic converters when they leak or spray onto them, while others are much less likely to ignite that way in open air. Published ignition temperatures are measured under laboratory conditions and do not by themselves prove or disprove hot-surface ignition; investigators must consider surface temperature, contact time, airflow and the form of the fuel.
Electrical failures
Battery cables, starter and alternator circuits, aftermarket accessories, poorly installed wiring, and components that remain powered when the vehicle is off can all fail. Look for arc sites, damaged fuses and signs of non-factory installations. The principles in our electrical fire investigation guide apply.
Mechanical failures
Failed bearings, dragging brakes, overheated catalytic converters and other mechanical failures can produce enough heat to ignite nearby combustibles. Parked vehicles can also ignite dry grass beneath hot exhaust components.
Interviews
The owner and last driver are key sources of information. Useful questions include when the vehicle was last driven and for how long, any warning lights, smells, smoke or performance problems, recent repairs or modifications, aftermarket equipment, fuel purchases, and who had access to the keys. Witnesses may describe where smoke or flames first appeared. See interviews and canvassing.
When a Vehicle Fire May Be Incendiary
Investigators should approach every case without assuming the answer. Where data suggest a deliberate fire, factors to consider include multiple unconnected areas of origin, ignitable liquids in the passenger compartment, missing items, and circumstances such as the vehicle's location. Any incendiary determination must be supported by evidence and tested hypotheses, as described in NFPA 921 and the scientific method, not reached simply because accidental causes were not found.
Evidence Preservation and Interested Parties
Vehicle fires frequently lead to claims involving manufacturers, repair shops or insurers. Preserve the vehicle and relevant components where possible, document storage and custody, and notify interested parties before destructive examination. The principles in our guide to evidence collection and preservation apply fully.
Vehicles Inside Structures
When a vehicle burns inside a garage, the investigator must determine whether the fire started in the vehicle or in the structure and spread to it. Careful comparison of damage, arc mapping of garage circuits and witness information are especially important in these cases.
Specialized Training
The IAAI offers a motor vehicle fire specialty credential, IAAI-(V), described in our certification guide, and online vehicle modules are available through CFITrainer.Net, listed on our Links page. Watch the Training page for chapter sessions, and explore more investigator resources.