Nine Common Causes of Car Fires

We asked Michael Wood, an acting captain at Toronto Fire Services, about the common causes of vehicle fires.

According to the National Fire Protection Association, there were 173,000 vehicle fires resulting in 280 deaths in the U.S. last year. While the numbers have improved greatly compared to the totals 20 years ago (395,000 fires and 550 fatalities), it’s still a lot of vehicles turned to toast, and even one life lost is a tragedy. Yet despite the frequency of car fires – we hear about them in traffic reports almost daily – there is very little conveyed about how these fires start and why.

In reality, automobile fires are entirely preventable occurrences that are frequently the result of slipshod and even neglectful ownership. Proper maintenance goes a long way in keeping your ride from going up in smoke. We asked Michael Wood, an acting captain at Toronto Fire Services, about the common causes of vehicle fires and what he’s witnessed on the job.

Fuel System Leaks

Fuel leaks are the most common cause of automobile fires. Michael Wood points out that the flash point of gasoline is -43°C, which means it’s always evaporating to form a combustible concentration of gas. When it leaks and vapourizes into the air under the hood, the fuel/oxygen mix is ideal for ignition. All it needs is an errant little spark. And if the temperature rises above 257°C, say around a hot exhaust manifold, gasoline will auto-ignite without the need for a spark.

Gasoline fires typically arise from old, rotten fuel lines or faulty fuel line connectors, as well as leaky fuel-injection systems. Woods says today’s fuel pumps aggravate the problem by working harder to compensate for the drop in pressure in a leaky line, inadvertently feeding a potential fire. Wood and his crew watched a late-model Ford F-150 burn to the ground after it had been serviced (badly) for a fuel leak. The truck’s aluminum hood and body panels melted away, but not before producing some vivid colours as the magnesium burned.

Electrical System Failures

Electrical system failures are the second most common cause of vehicle fires. A car’s 12-volt battery can produce hydrogen gas when charging, creating an explosion hazard. Battery and starter cables carry sufficient current to ignite combustibles in the event of a fault condition. Even broken light bulbs are a source of ignition, since headlight filaments heat up to around 1400°C. Engines move on their mounts and virtually everything under the hood shakes to some degree, allowing cables to rub off their insulation or fray over time and a short circuit to develop.

Protection devices such as fuses, fusible links and circuit breakers provide an element of safety in case of arcs or overloaded wiring, but sometimes components breakdown, shoddy repairs or poor installation of aftermarket equipment can defeat these safeguards. And it doesn’t always have to occur in the engine compartment. Electrical faults in high-current devices such as power seat or window motors can result in ignition of insulation, carpets or even discarded paper accumulated under seats.

Overheating Engines

 An overheated engine is a common occurrence as a neglected vehicle ages. A worn-out water pump or cooling fan is all it takes to send the engine temperature high into the red zone. Combine an overheated engine with the numerous flammable liquids that allow a car to run, including motor oil, automatic transmission fluid, hydraulic brake fluid and engine coolant (ethylene glycol), and you have a recipe for disaster. The exhaust manifold on a hot-running engine can reach in excess of 500°C – high enough to ignite any of these liquids oozing from a leaky seal.

General Motors was forced to recall some older models – a second time – for oil seeping past deteriorating valve cover gaskets, causing oil to drip onto the hot exhaust manifold of its 3.8-L V6 engines, where it could ignite. In other instances, an engine may overheat by design or manufacture. Ford’s 1.6-L EcoBoost turbo four-cylinder engine is reputed to overheat and, reportedly, there have been some engine fires in both the late-model Fusion sedan and Escape crossover that use the engine.

Aftermarket Accessories

Amateur accessory installations can inadvertently introduce an electrical fault and cause a fire down the road. Something as simple as a mounting screw carelessly bored through high-output stereo wiring can short circuit the system and start a fire. Sound system and off-road lighting installations can go horribly wrong, more so today because the amperage required to run these aftermarket components is much higher. Many trucks and custom cars have two batteries to operate all of the entertainment gear, which makes things doubly complicated.

Always get your aftermarket accessories installed by an authorized technician and not your unemployed nephew, says Wood. Similarly, sloppy backyard mechanics that insist on fixing your car using little more than a wrench and a screwdriver often overlook complex issues involving the vehicle’s computers and wiring looms. Amateur repairs and short cuts can introduce unwelcome hazards in the engine compartment, which we have already seen is a dangerous place. As a smart advertisement once advised: Don’t open your hood to strangers.

Catalytic Converters

A catalytic converter, which resembles a muffler, is plumbed into a vehicle’s exhaust system to reduce the hydrocarbons and carbon monoxide in the exhaust gases by burning them over a platinum and palladium catalyst. Catalytic converters require working temperatures of 700-800°C to efficiently convert the harmful exhaust gases into inert ones. A clogged or overworked catalytic converter can easily overheat, rising to up over 1,000°C – hot enough to heat up the carpet and other combustibles located above it in the cabin.

Wood notes that the catalytic converter can be a magnet for road debris that catches on the converter’s heat shield and burns, ironically. A flimsy heat shield may fall off after several years, leaving the catalytic converter fully exposed to debris such as plastic or paper bags (paper auto-ignites at 451 degrees Fahrenheit, as sci-fi fans know). Wood says vehicles, especially farm machinery, parked on tall dry grass can set the field ablaze if the heat shield is missing. Mechanics often discard loose heat shields, when they should affix them properly so that they keep combustibles away from the catalytic converter’s intense heat.

 Pesky Animals 

Beware of mice bearing gifts. Automotive technicians often discover nests and stashes of nuts that rodents love to store within the warm confines of an engine. One tech found a bird nest in the air cleaner, easily a fire hazard judging by the charred twigs that were in there. Another car was the unfortunate victim of a squirrel that had jammed nuts into the air intake. Dried leaves, twigs and other nesting materials rodents introduce into the engine compartment act as kindling for a potential fire under the hood, says Wood.

The auto industry’s enthusiasm for recyclable, organic materials has introduced a new problem: soy-based electrical wire insulation, which is becoming a favourite treat of rodents under the hood. CTV reported that the issue is becoming commonplace as automakers such as Honda, Toyota and Subaru turn to soy-based insulation. In one example, rats chewed the wiring in a Honda CR-V, causing hundreds of dollars in damage for the owner to pay. Toothy rodents can expose hot wires and potentially cause a fire. There is wire wrap available infused with rodent repellant (chili pepper) to address the problem.

Dangerous Cargo

Some drivers think nothing of storing extra fuel and other combustibles in their car or truck. Unauthorized containers, such as plastic jugs, left in a hot car will allow fuel to expand, then leak and saturate the trunk liner or carpeting. One fellow who kept pool chlorine in his trunk along with a cardboard box saturated by a leaky container of brake fluid observed smoke seeping from his trunk lid and back seat – immediately before seeing his entire vehicle go up in flames. Mixed chemistry has a knack for doing things like that.

Wood advises never to store dangerous chemicals or materials in your vehicle. Propane tanks and gasoline jerry cans are common finds in an automobile trunk – potential time bombs waiting to ignite. In the event of a collision, they can fuel a needlessly big fire and endanger lives. Wood recalls seeing a car trunk full of hazardous industrial chemicals that the owner had pinched from his workplace, coveted for their cleaning power. It’s never a good idea to transport or keep toxic chemicals in a vehicle that’s not designed, and marked, for the task. 

Smoking and Driving

While the proportion of Canadians who smoke has steadily declined – it’s only about 15 per cent of the population today – there are still enough around to make driving and smoking a common hazard. Wood recites stories of motorists who have flicked their cigarette out of their window on a warm day, only to have the burning butt re-enter through the open back window and land on the upholstery or carpeting, where it can light the synthetic materials on fire. The unaware driver eventually senses the emergency when he or she feels an uncomfortable heat right behind them.

A variation of that scenario, says Wood, involves pickup truck drivers who throw their cigarette out and the still-burning butt lands in the bed of the pickup. The smoldering butt can light all kinds of cargo ranging from cardboard boxes to sawdust and spilled oil accumulated on the floor of the bed. Some cargo doesn’t even need an ignition source, notes Wood. “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!” 

Arson

It’s hard to surmise why anyone would set fire to a perfectly good automobile, but police have some plausible explanations. Random neighbourhood vandalism is a common occurrence when youth become bored. The cleansing action of a hot fire could be used to cover up a theft, or to destroy the evidence of another crime connected with the vehicle. Or it could be insurance fraud, motivated by someone in debt who hopes to engineer a nice payout courtesy of the automobile insurer. But it’s hardly an original idea.

Vehicle arson can be difficult to prove, particularly if the fire advances to the point where the entire vehicle is engulfed in flames. However, experts know a fire set in the passenger compartment will burn from the top down, starting at the top of the seats and working down towards the floor. Fire investigators also know there is no oxygen at floor level in an intense fire. If an accelerant such as gasoline was poured onto the floor, it likely wouldn’t burn off due to the lack of oxygen – leaving the residue in the vehicle’s burned-out hulk as evidence of wrongdoing.

Nine Troublesome High-Tech Features

Overheating Engines

 An overheated engine is a common occurrence as a neglected vehicle ages. A worn-out water pump or cooling fan is all it takes to send the engine temperature high into the red zone. Combine an overheated engine with the numerous flammable liquids that allow a car to run, including motor oil, automatic transmission fluid, hydraulic brake fluid and engine coolant (ethylene glycol), and you have a recipe for disaster. The exhaust manifold on a hot-running engine can reach in excess of 500°C – high enough to ignite any of these liquids oozing from a leaky seal.

General Motors was forced to recall some older models – a second time – for oil seeping past deteriorating valve cover gaskets, causing oil to drip onto the hot exhaust manifold of its 3.8-L V6 engines, where it could ignite. In other instances, an engine may overheat by design or manufacture. Ford’s 1.6-L EcoBoost turbo four-cylinder engine is reputed to overheat and, reportedly, there have been some engine fires in both the late-model Fusion sedan and Escape crossover that use the engine.

Aftermarket Accessories

Amateur accessory installations can inadvertently introduce an electrical fault and cause a fire down the road. Something as simple as a mounting screw carelessly bored through high-output stereo wiring can short circuit the system and start a fire. Sound system and off-road lighting installations can go horribly wrong, more so today because the amperage required to run these aftermarket components is much higher. Many trucks and custom cars have two batteries to operate all of the entertainment gear, which makes things doubly complicated.

Always get your aftermarket accessories installed by an authorized technician and not your unemployed nephew, says Wood. Similarly, sloppy backyard mechanics that insist on fixing your car using little more than a wrench and a screwdriver often overlook complex issues involving the vehicle’s computers and wiring looms. Amateur repairs and short cuts can introduce unwelcome hazards in the engine compartment, which we have already seen is a dangerous place. As a smart advertisement once advised: Don’t open your hood to strangers.

Catalytic Converters

A catalytic converter, which resembles a muffler, is plumbed into a vehicle’s exhaust system to reduce the hydrocarbons and carbon monoxide in the exhaust gases by burning them over a platinum and palladium catalyst. Catalytic converters require working temperatures of 700-800°C to efficiently convert the harmful exhaust gases into inert ones. A clogged or overworked catalytic converter can easily overheat, rising to up over 1,000°C – hot enough to heat up the carpet and other combustibles located above it in the cabin.

Wood notes that the catalytic converter can be a magnet for road debris that catches on the converter’s heat shield and burns, ironically. A flimsy heat shield may fall off after several years, leaving the catalytic converter fully exposed to debris such as plastic or paper bags (paper auto-ignites at 451 degrees Fahrenheit, as sci-fi fans know). Wood says vehicles, especially farm machinery, parked on tall dry grass can set the field ablaze if the heat shield is missing. Mechanics often discard loose heat shields, when they should affix them properly so that they keep combustibles away from the catalytic converter’s intense heat.

 Pesky Animals 

Beware of mice bearing gifts. Automotive technicians often discover nests and stashes of nuts that rodents love to store within the warm confines of an engine. One tech found a bird nest in the air cleaner, easily a fire hazard judging by the charred twigs that were in there. Another car was the unfortunate victim of a squirrel that had jammed nuts into the air intake. Dried leaves, twigs and other nesting materials rodents introduce into the engine compartment act as kindling for a potential fire under the hood, says Wood.

The auto industry’s enthusiasm for recyclable, organic materials has introduced a new problem: soy-based electrical wire insulation, which is becoming a favourite treat of rodents under the hood. CTV reported that the issue is becoming commonplace as automakers such as Honda, Toyota and Subaru turn to soy-based insulation. In one example, rats chewed the wiring in a Honda CR-V, causing hundreds of dollars in damage for the owner to pay. Toothy rodents can expose hot wires and potentially cause a fire. There is wire wrap available infused with rodent repellant (chili pepper) to address the problem.

Dangerous Cargo

Some drivers think nothing of storing extra fuel and other combustibles in their car or truck. Unauthorized containers, such as plastic jugs, left in a hot car will allow fuel to expand, then leak and saturate the trunk liner or carpeting. One fellow who kept pool chlorine in his trunk along with a cardboard box saturated by a leaky container of brake fluid observed smoke seeping from his trunk lid and back seat – immediately before seeing his entire vehicle go up in flames. Mixed chemistry has a knack for doing things like that.

Wood advises never to store dangerous chemicals or materials in your vehicle. Propane tanks and gasoline jerry cans are common finds in an automobile trunk – potential time bombs waiting to ignite. In the event of a collision, they can fuel a needlessly big fire and endanger lives. Wood recalls seeing a car trunk full of hazardous industrial chemicals that the owner had pinched from his workplace, coveted for their cleaning power. It’s never a good idea to transport or keep toxic chemicals in a vehicle that’s not designed, and marked, for the task. 

Smoking and Driving

While the proportion of Canadians who smoke has steadily declined – it’s only about 15 per cent of the population today – there are still enough around to make driving and smoking a common hazard. Wood recites stories of motorists who have flicked their cigarette out of their window on a warm day, only to have the burning butt re-enter through the open back window and land on the upholstery or carpeting, where it can light the synthetic materials on fire. The unaware driver eventually senses the emergency when he or she feels an uncomfortable heat right behind them.

A variation of that scenario, says Wood, involves pickup truck drivers who throw their cigarette out and the still-burning butt lands in the bed of the pickup. The smoldering butt can light all kinds of cargo ranging from cardboard boxes to sawdust and spilled oil accumulated on the floor of the bed. Some cargo doesn’t even need an ignition source, notes Wood. “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!” 

Arson

It’s hard to surmise why anyone would set fire to a perfectly good automobile, but police have some plausible explanations. Random neighbourhood vandalism is a common occurrence when youth become bored. The cleansing action of a hot fire could be used to cover up a theft, or to destroy the evidence of another crime connected with the vehicle. Or it could be insurance fraud, motivated by someone in debt who hopes to engineer a nice payout courtesy of the automobile insurer. But it’s hardly an original idea.

Vehicle arson can be difficult to prove, particularly if the fire advances to the point where the entire vehicle is engulfed in flames. However, experts know a fire set in the passenger compartment will burn from the top down, starting at the top of the seats and working down towards the floor. Fire investigators also know there is no oxygen at floor level in an intense fire. If an accelerant such as gasoline was poured onto the floor, it likely wouldn’t burn off due to the lack of oxygen – leaving the residue in the vehicle’s burned-out hulk as evidence of wrongdoing.

Nine Troublesome High-Tech Features


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