What causes vehicle fires? The AA guide to preventing and dealing with car fires.

Graphic showing the silhouette of a car with a fire at the bonnet

How likely is your car to catch fire while you’re driving it? It’s the stuff of nightmares – seeing smoke or flames appear as you’re secured inside a moving vehicle. Thankfully, it’s not very likely. Despite the number of combustible materials that comprise a vehicle, most drivers won’t ever experience a spontaneous vehicle fire, and modern manufacturing has meant that vehicle fires on the road have dropped significantly in the past couple of decades. Even so, Irish fire brigades attended over 2,300 vehicle fires in 2019 and AA Roadwatch reported on average 1 or 2 vehicle fires a week affecting traffic on Ireland’s main routes between June 2020 and June 2021.

Not all of these turn into fully fledged fires – some of them are stopped quickly and others turn out to be false alarms. A Dublin Fire Brigade spokesman told us that “quite often steam from car’s radiator or dust from the safety air bags can be mistaken for smoke.” That said, better safe than sorry – you should treat any steam or smoke as a potential fire until you’ve confirmed it’s not.

What causes vehicle fires?

The biggest cause of vehicle fires attended by fire brigades is arson or vandalism of parked vehicles. Dublin Fire Brigade told us the majority of the car fires they attended in 2020 were due to arson, which is echoed by James Long, an Irish lecturer and President of the Society of Automotive Forensic Engineers, who said most fires he has investigated have had a deliberate cause. Figures for the UK show that around half of all vehicle fires between 2015 and 2020 were “deliberate”, and that’s before you count accidental fires caused by human activity.

While obviously a big problem, this means that it’s relatively rare for a vehicle to spontaneously catch fire while you’re driving. DFB say spontaneous fires caused by mechanical or electrical faults are a rarity, although they do happen. A study by the US National Fire Prevention Association found that the most common cause of “highway fires” – non-deliberate vehicle fires on the road or at the roadside – was mechanical faults, accounting for around half the highway fires in the US between 2013 and 2017. Electrical faults caused another fifth. With improvements in manufacturing and tighter regulations on roadworthiness, though, this type of fire is getting rarer – the US study shows they have dropped by 80% between 1980 and 2019.

Fires can also result from collisions, especially if the vehicle is badly damaged and fuel leaks onto hot components. DFB say that this is also, thankfully, rare: “modern car design takes in to account collisions, and as such, [they are] designed to prevent fire following a collision.” The data from the US showed that only 4% of car fires on the roads were caused by collisions, but those tend to be serious – two thirds of deaths associated with car fires happened when there had been a collision first.

While electric vehicles do not run the risk of fuel leaks, there is still a combustion risk from the lithium ion batteries, especially at hot temperatures. Fires caused by, or affecting, the battery of an EV may need different treatment, and a damaged battery could reignite hours later if it retained a charge.

Tyres can also catch fire, and are particularly hard to put out. Poorly inflated tyres rubbing against a solid surface on the chassis can reach ignition temperatures, or a failed brake lock system can cause heat too.

Surprising other causes

James Long identified a couple of surprising causes of vehicle fires too – a cigarette stub thrown out a window can be sucked back in as the vehicle moves and may burn in the backseat without a driver noticing. This has become much less likely to pose serious problems in recent years with flame-retardant seat covers a legal obligation for manufacturers, but could cause a problem if there were papers or some other flammable material on the back seat. Fallen autumn leaves or branches under a vehicle in a parking spot can also get drawn into a vehicle’s catalytic convertor as the driver starts the engine. Similarly, debris on the roadway can get caught in wheels or axles and cause friction fires – this can be a cause of truck fires, according to the Australian Road Transport Suppliers Association.

An extremely rare but possible cause of a fire in a parked vehicle is refracted sunlight from a reflective object – an non-tinted pocket mirror left on a seat for example, or in this unusual case, a bottle of water. This is unlikely to develop into a full fire, given than seat covers have to be flame-retardant, but could burn holes in upholstery if left unchecked.

What do I do if my vehicle catches fire, or I see smoke while driving?

Stop, pull in to safe place if possible, get all passengers out of the vehicle and call the emergency services. As James Long points out, “the electrical system can get compromised in a fire and that could affect your central locking”, so you don’t want to delay leaving the vehicle. If it’s safe, you could use an extinguisher to tackle a small external fire, but don’t put yourself at risk – as DFB remind us “a car can be replaced, you can’t”. Long also advises against opening the bonnet if smoke is coming out, as you could inadvertently make matters worse by introducing more oxygen to the flames.

Step away from the live lanes once you get out of the car, and get behind a crash barrier if there is one, because other drivers may not see you with smoke or flames in their line of vision. Stay well away from the vehicle – both DFB and James Long cite toxic chemicals as a risk to those near car fires, especially if the refrigerant or other fuels start to burn, and there is a danger of injury from smoke inhalation too.

DFB assure us that cars don’t tend to explode outside of Hollywood, but “tyres can pop and boot/bonnet struts can fire off like missiles”. There have also been recorded cases of gas springs shooting from the car, so you don’t want to stay too close. If you can see or smell fuel after a collision, it’s best to err on the side of caution and move away from the vehicle too.

It’s also worth telling the emergency services what type of vehicle it is from the offset and if you were carrying any flammable cargo that would require different treatment. A fire in an electric vehicle usually needs more water than an ICE one, and their batteries need careful treatment, as they have been known to suddenly reignite hours later.

How do you prevent a vehicle fire?

Keeping on top of your vehicle’s maintenance and getting it serviced regularly is the best way to avoid a spontaneous fire, given that around 2 in 3 of roadside fires are caused by mechanical or electric faults. Never ignore a warning light on your dashboard, and if your vehicle is ever part of a product recall, don’t wait to send it back. You might be avoiding some short-term inconvenience, but it could result in a much larger problem or even serious injury if a fire broke out. In Ireland, you can keep an eye on the Competition and Consumer Protection Commission’s website for recall notices, and check in with your manufacturer every so often.

The older your vehicle is, the more important it is to keep on top of your maintenance. In the US, roughly three quarters of the fires attributed to faults in 2017 involved cars that were at least ten years old. Also, some faults develop over time, rather than suddenly, especially if caused by fraying electrical wires or insulation, or rubbing of fuel lines. This means a regular service might catch the issue before it catches fire.

This blog is part of a series on road safety. See here for our guide to dealing with all types of road incidents, and here for how to change a puncture. If you’re looking for AA Car Insurance, you can get a quote here.