Investigation of the Contributing Factors to Vehicle Fire

Contributing Factors to Vehicle FiresIn this article, Stan Bezuidenhout from IBF Investigations gives us the low-down on vehicle fires. As a Forensic Specialist with more than 20 years of experience responding to and investigating road traffic collisions, he has investigated more than his fair share of vehicle fires. This is his take on the most common causes of vehicle fires.

When investigating a burnt vehicle where intentional arson from a flammable liquid is suspected, several pieces of evidence can be found on the scene. Some of the key pieces of evidence that investigators look for include:

Burn patterns: Intentionally set fires often create distinctive burn patterns on the vehicle. For example, a fire that is started using a liquid accelerant will typically produce a "V" shaped pattern on the floor of the vehicle where the liquid pooled and burned.

Residue: The residue left behind by the accelerant can be found in the burnt vehicle. Accelerants leave behind distinctive patterns of burn marks and residue, and forensic scientists can use this evidence to identify the type of accelerant used.

Odour: A strong odour of gasoline or other flammable liquids may be present in the burnt vehicle. The odour can be an indication of the type of accelerant used and can help investigators identify the source of the fire.

Debris: Investigators may find debris from a container used to transport the accelerant, such as a gas can or a bottle, near the burnt vehicle.

Ignition source: Investigators will look for any evidence of an ignition source, such as a lighter or matches, that was used to start the fire.

Vehicle damage: The pattern of damage to the vehicle can also provide evidence about the origin of the fire. For example, if the fire started in the engine compartment, the damage will be concentrated in that area.

The characteristics of metals on vehicles can change depending on the heat they were exposed to or how long they were exposed to fire. Steel and aluminium, which are commonly used in vehicle construction, can have different reactions to heat and fire exposure:

Steel: When steel is exposed to heat or fire, it can undergo several changes. At around 300-400 degrees Celsius, steel can begin to lose its strength and start to deform. At around 550-600 degrees Celsius, steel can begin to soften and become more pliable. At around 900-1000 degrees Celsius, steel can start to melt and lose its structural integrity. In addition, prolonged exposure to fire can cause steel to corrode, which can further weaken its strength and structural integrity.

Aluminium: Aluminium has a lower melting point than steel, so it can start to soften and deform at lower temperatures. At around 300-400 degrees Celsius, aluminium can begin to lose its strength and start to deform. At around 600 degrees Celsius, aluminium can start to melt and lose its structural integrity. However, unlike steel, aluminium does not corrode when exposed to fire. Instead, it forms a layer of oxide on its surface that can help protect it from further damage.

The very first vehicle fire case I attended was back in February 2002. In that case, a lady was driving on a highway and came around a bend. There was a broken-down vehicle in the middle of her lane, so she collided with it. Her legs got entrapped and her vehicle caught alight. She thought she was going to die in the fire! She was relieved to see some people running towards her and expected them to rescue her. Instead, they literally punched out her teeth, stole her car speakers, and ran away! Fortunately, emergency services were on the scene quickly to put out the fire and extricate her.

Even back then, the first thing I did was to determine the possible cause of the fire. In this case, it was electrical. But you need to know what to look for, what kind of evidence to expect, and how to identify and interpret fire evidence.

In my approach to vehicle fire investigations, I typically look for the source of the fire - where it all started. This is easy when the fire is minor, as in this case, but not so easy when there is the destruction of the whole vehicle - especially when it is a truck or bus. Here are the top ten things I look for during a vehicle fire investigation, using examples for each:

Area of origin of the fire: The first step is to determine where the fire started in the vehicle. The origin point can provide valuable clues about the cause of the fire. In the above example, it was easy as the fire was localized. There wasn't much left to the imagination. All I had to do was inspect the area to determine what caused heat or ignition. Which led me to….

Signs of an electrical problem: Electrical problems are one of the most common causes of vehicle fires. I would look for signs of faulty wiring, short circuits, and other electrical issues. In the case of the Nissan 1400 LDV, the battery sits on the Right Front. During the collision, the wires shorted out and cause excessive heat, which led to the fire. Because the engine had died and because there was no high-pressure fuel supply, such as in fuel-injected vehicles, the fire was more local and easily controlled.

Fuel system problems: Fuel system problems can also cause vehicle fires. I would look for signs of leaks, damage to fuel lines or tanks, and other issues with the fuel system. In fuel-injected vehicles, the fuel is typically under extreme pressure. The moment anything happens to the fuel injection system, such as a pipe bursting or getting ruptured, the fuel is forced out into a fine mist, all over the engine compartment.

The following components are the hottest components on a typical petrol-powered vehicle and the approximate temperatures that might prevail under normal operation:


Typical Temperature Range

Exhaust manifold




Catalytic converter


Brake rotors


Engine block and head


The point at which a fuel/air mixture will easily catch fire is called the lower flammability limit (LFL), also known as the lower explosive limit (LEL). This is the lowest concentration of fuel vapour in the air that can sustain combustion. For petrol, the LFL is typically between 1.4% to 7.6% by volume. This means that if the concentration of gasoline vapour in the air is below 1.4%, there is not enough fuel to support combustion. However, as the concentration of gasoline vapour increases, the mixture becomes increasingly flammable and can ignite with a spark or flame.

However, gasoline vapour can also ignite spontaneously without an external ignition source when the temperature of the mixture reaches its auto-ignition temperature, which is the lowest temperature at which the mixture can ignite on its own.

The auto-ignition temperature of petrol vapour can vary depending on several factors such as the specific composition of the fuel, pressure, and the presence of other gases in the air. However, it generally falls within the range of 280-300°C.

So, if a fuel injection system is damaged, and gasoline is leaking and vapourizing into the air, there is a risk of the vapour igniting even if it only encounters a heat source. Since many components on a vehicle can get way hotter than this, the risk of a fire is ever-present whenever the fuel system is compromised.

You might think that this is only an issue with petrol, but it's not. Diesel vehicles are exposed to the same risks. Because the Flammability Limits of Diesel is between 0.6 and 6% and because its spontaneous combustion temperatures are only between about 400 and 450 °C, a modern Diesel Engine can also catch alight merely because of the presence of hot vehicle components.

If you consider the likely temperature ranges that might prevail on the brake systems alone, by vehicle class, we see the following:

Vehicle Type

During Regular Braking

During overheating




Light Motor Vehicle









If we keep this in mind, it can be seen that many components on vehicles get hot enough to cause a fire if the fuel system is compromised and the fuel is sprayed out all over the vehicle engine compartment or even underneath the vehicle.

Engine overheating: An overheating engine can cause a fire if it is not properly maintained. I would look for signs of coolant leaks, damaged or malfunctioning cooling systems, and other issues that can lead to engine overheating. As an example, I have investigated a truck fire case where the truck was forced to drive between a sequence of stop/go sections on the N7 In the Northern parts of the Western Cape. This was during summer, and there were only short stops (less than 15 minutes) at each stop/go section. The truck was heavily loaded and had to obviously comply with the traffic controls. While standing, the truck would be idling. Without the benefit of airflow, the engine temperatures would rise. Then, when traffic flow resumed, the truck had to accelerate and fully use its power.

High power demands at low vehicle speeds generate a lot of heat. Because the truck had to stop and start multiple times as it encountered the stop/go section, idled, and then accelerated from a standstill with a full load but never reached highway speeds, the turbo overheated. This resulted in excessive temperatures with inadequate cooling and resulted in vehicle components eventually catching alight. The whole vehicle was destroyed.

Without a working knowledge of the mechanical components, their performance during operation, and the thermodynamics that may prevail during different use scenarios, the determination of the cause of this fire would not have been possible.

Mechanical problems: Mechanical problems such as faulty brakes, bearings, or other components can cause a fire if they generate sparks or heat.

In another matter I investigated, a faulty Turbo was detected. In this case, there was no operational overheating, but rather a physical failure. Upon inspection, it was found that the turbine had contacted something that was sucked into the turbo housing. This caused excessive heat from friction, which lead to excessive temperatures around the area of the turbo.

Signs of arson: I would also look for signs of arson, such as the presence of accelerants, multiple ignition points, or evidence of tampering.

In a bus fire matter, I was appointed in, the claim was that the bus spontaneously caught alight overnight, while parked outside the owner's house. The bus was completely destroyed. Upon inspection of the bus, it was found that the diesel tank cap was missing. It was also found that the burn patterns indicated the source of the fire to be at or around the diesel tank area.

When we went to the scene of the fire, at the owner's house, we found the area where the fire occurred, but the undamaged diesel cap was found some distance from where the bus was, we found containers that could have contained chemicals and we detected the odour of diesel from them.

Vehicle Arson is a type of crime that is not very easy to conceal since vehicles are typically designed not to catch alight and would almost never spontaneously catch alight while parked.

If the initial investigation is not done right down to the component failure level, the cause of the fire could easily be misinterpreted.

This is why a Vehicle Fire Investigation should not be conducted by someone with little or no relevant experience, skills, or training. I have come across vehicle fire investigation reports that present as nothing more than a lay opinion on the extent of burns. Before you engage a fire investigator, ask about their relevant experience, skills, and training.

For a good example of how I approach Fire Investigation matters, feel free to read the article I wrote on the Boksburg Tanker Explosion, which can be found at

By Stan Bezuidenhout - IBF Investigations,

Stan Bezuidenhout is a highly accomplished and driven forensic specialist, court expert, tactical risk analyst, trainer, speaker, and author. He has dedicated his career to developing a deep understanding and expertise in a wide range of fields related to forensic investigation, risk analysis, and training. He has consistently demonstrated a strong commitment to excellence and a passion for delivering exceptional results in everything he does.

He is a highly qualified and respected professional in the fields of forensic science and risk analysis, with a strong reputation for his expertise and dedication to his work. He is confident in his ability to utilize his skills and knowledge to make a positive impact on any organization or project, and he is always seeking new challenges and opportunities to continue growing and advancing in his career.

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