Car fires are more common than you think. What are the common causes?

Hamilton Spectator

25-05-2025

'There's a car fire somewhere in Toronto every day, but it rarely makes the news,' says Michael Wood, a Toronto Fire Services captain.
Despite high-profile incidents involving electric vehicles (EVs), North American fire services are preoccupied with a far more common menace: fires involving conventional gasoline-powered cars and trucks.
Here's a little-known fact: internal combustion engines grow more hazardous with age, especially as our vehicles become neglected and begin to leak flammable fluids.
Transport Canada estimates there are about 10,000 vehicle fires nationally per year. In the U.S., more than 170,000 vehicle fires occur annually on average, accounting for one in every eight calls to fire departments there.
EVs make up a tiny fraction of vehicle fires. The civil authority in Sweden reported 23 fires in 611,000 EVs in 2022, or 0.00004 per cent.
It's true the fires involving electric vehicles can be dramatic, serious and hard to control. An electric Mercedes-Benz EQE 350 sedan parked in an underground apartment garage in South Korea spontaneously caught fire and damaged some 140 other vehicles and left 200 families homeless for weeks. In Toronto, a Tesla Model 3 driven at high speed crashed into a bridge abutment, killing four occupants and starting a battery fire that smouldered for days.
They're just two incidents in a growing litany of events that have drawn attention to the challenges of an EV fire that sees its lithium-ion battery overheat or short-circuit, triggering a chemical reaction and fire that can last for days — even submerged under water.
'We're still learning to deal with EV fires,' explained Wood, who is co-ordinator of Centennial College's pre-service firefighter program. 'In the case of the Tesla crash, we put the car's battery into a dumpster, moved it to a secure location and poured sand over it to suppress the fire.'
There's little information conveyed about car fires on how they start and why. Proper automobile maintenance goes a long way in keeping your daily ride from going up in smoke.
Wood outlined many of the causes of vehicle fires and what he's seen on the job:
Leaky fuel system:
Fuel leaks are among the most common causes. Gasoline fires typically arise from old, worn fuel lines or faulty fuel line connectors, and leaky fuel-injection systems. Because gasoline vaporizes across a wide air temperature range, the fuel/oxygen mix present under the hood is ideal for ignition. All that's needed is an errant spark.
Today's fuel pumps aggravate the problem by working harder to compensate for the drop in line pressure, inadvertently feeding a potential fire. Wood watched a Ford F-150 pickup burn to the ground after it had been serviced (poorly) for a fuel leak. The aluminum hood and body panels melted away, but not before producing some lovely colours as the magnesium burned.
Electrical system faults:
Electrical system failures are another common cause of vehicle fires. Engines move on their mounts and virtually everything under the hood shakes to some degree, allowing cables to rub off their insulation or fray, and a short-circuit to develop, over time.
Battery and starter cables carry enough current to ignite combustibles in the event of a fault. A vehicle's 12-volt battery may produce hydrogen gas when charging, creating an explosion hazard.
Fuses, fusible links and circuit breakers provide an element of safety in case of overloaded wiring, but component faults or careless repairs can defeat these safeguards.
Overheating engines:
An overheating engine is not an uncommon occurrence as a neglected vehicle ages. A malfunctioning radiator or cooling fan is all it takes to send the engine temperature into the red zone and potentially crack the engine's head.
Combine an overheated engine with combustible liquids, such as motor oil, transmission fluid and brake fluid, and you have a recipe for disaster. The exhaust manifold on a hot-running engine can exceed 500C — that's high enough to ignite any liquids oozing from a leaking seal.
Aftermarket accessories:
Sloppy accessory installations can introduce an electrical fault and cause a fire down the road, according to Wood. Something as simple as a mounting screw contacting high-output stereo wiring can short circuit the system and light a fire. Many custom installations have two batteries to operate all of the sound equipment, which makes things doubly complicated.
Always get your aftermarket accessories installed by an authorized technician. Backyard mechanics can often overlook complex issues involving the vehicle's computers and wiring. Shortcuts can introduce unwelcome hazards.
Catalytic converters:
Catalytic converters in your car's exhaust system are tiny incinerators that operate at 700C-800C to convert the harmful exhaust gases into inert ones. A clogged catalytic converter can easily overheat, rising to more than 1,000C, hot enough to heat up the carpet and other combustibles under your feet.
Catalytic converters can be a magnet for road debris that catches on the heat shield protecting the converter and this can ignite. A flimsy heat shield may fall off after several years, leaving the catalytic converter exposed to debris, such as plastic or paper bags. (Wood noted that vehicles, especially farm machinery, parked on long dry grass, can set the field ablaze if the heat shield is missing.) Mechanics often throw away loose shields, but they really need to be reaffixed to keep combustibles away from the heat.
Pesky animals:
Auto technicians often remove nests and stashes of nuts that rodents love to store within the warm confines of an engine. Dried leaves, twigs and other nesting materials rodents bring into the engine compartment act as kindling that can create a fire under the hood, explained Wood.
The auto industry's zeal to adopt recyclable, organic materials has introduced a new problem: soy-based electrical wire insulation. This has become a rat treat. Toothy rodents can expose hot wires that may eventually cause a fire. You can buy wire wrap, infused with rodent-repellent, to address the problem.
Dangerous cargo:
Some people store spare fuel and combustible products in their car or truck. Unauthorized containers left in a hot car will allow fuel to expand, then leak and saturate the trunk liner or carpeting.
A motorist who kept pool chlorine in his trunk, along with a cardboard box saturated by a leaky container of brake fluid, saw smoke seeping from his trunk lid — right before watching his vehicle burst into flames, said Wood.
In the event of a collision, propane tanks and gas cans can fuel a big fire and endanger lives, he added.
Smoking and driving:
While just 11 per cent of Canadians are regular smokers, that's still enough of them to make driving and smoking a common hazard. Wood recited stories of motorists who have flicked their cigarette out the window, only to have the burning butt re-enter through the back window and land on the upholstery or carpeting, igniting the synthetic materials.
A variation of that, said Wood, involves pickup truck drivers who throw their cigarette out and it lands in the bed of the pickup. The smouldering butt can set fire to cargo, such as cardboard boxes, sawdust and spilled oil, on the bed floor.
Some cargo doesn't even need an ignition source, Wood noted. 'Somebody was hauling old manure in their pickup truck on a hot day, and the stuff generated enough heat on its own to spontaneously combust.'
No bull!