“Who brought the marshmallows?” Car fires are no laughing matter, however. According to the U.S. National Fire Protection Association, there were 174,000 vehicle fires in 2015 resulting in 445 deaths – many of which could be avoided.
By Mark Toljagic
It’s a caution we hear traffic reporters repeat day in and day out, so familiar it rarely registers with motorists, lame wisecracks and all. It goes something like this: “…watch out for the car fire on the shoulder just before the northbound exit ramp. Emergency crews are just getting on top of it now.”
Despite the frequent radio reports, there’s little information conveyed about car fires, in terms of how they start and why. In reality, automobile fires are frequent occurrences, although they shouldn’t be. Proper automobile maintenance goes a long way in keeping your daily ride from going up in smoke. We talked to Michael Wood, an acting captain at Toronto Fire Services and coordinator of Centennial College’s Pre-Service Firefighter program, about the causes of vehicle fires and what he’s seen on the job. Here’s what we learned.
Fuel leaks are the most common cause of automobile fires. Wood points out that the flash point of gasoline is -43°C, meaning that it’s always evapourating 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 or a sufficient heat source. 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 line pressure, inadvertently feeding a potential fire. Wood and his crew recently watched a late-model Ford F-150 burn to the ground after it had been serviced (badly) 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 failures are the second most common cause of vehicle fires. A car’s 12-volt battery may 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 have operating temperatures of around 1400°C. It’s important to note that 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 component 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 trash accumulated under seats.
An overheating engine is not an uncommon occurrence as a neglected vehicle ages. An old, malfunctioning radiator 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 keep a car running, including engine 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-litre V-6 engines, where it could ignite. In other instances, an engine may overheat by design or manufacture. Ford’s British-made 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. In one documented case, the engine head cracked from overheating, which sent oil to the hot turbo, igniting it.
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 current required to run these aftermarket components is much higher. Many trucks and custom cars have two batteries to operate all the entertainment gear, which makes things doubly complicated.
Always get your aftermarket accessories installed by an authorized technician and not your spouse’s unemployed nephew. Similarly, amateur backyard mechanics that insist on fixing your car using nothing more than a hammer and a screwdriver can often overlook complex issues involving the vehicle’s computers and wiring looms. Handyman repairs and short cuts can introduce unwelcome hazards in the vicinity of the engine, which we have already seen is a dangerous place. As a smart advertisement once counselled: Don’t open your hood to strangers.
A catalytic converter, which resembles a muffler in appearance, is plumbed into a vehicle’s exhaust system to reduce the unburned hydrocarbons and carbon monoxide in the engine’s exhaust gases by burning them over a platinum and palladium catalyst. Catalytic converters installed in all modern automobiles 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 above it in the passenger cabin.
Michael Wood points out that the catalytic converter can be a magnet for road debris that catches on the heat shield protecting the converter and ignites, 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 (Ray Bradbury reminds us that paper auto-ignites at 451 degrees Fahrenheit). Wood says vehicles – especially farm machinery – parked on long dry grass will often set the field ablaze if the heat shield is missing. Mechanics often throw loose heat shields away, but what they should do is affix them properly so that they keep combustibles away from the heat.
Beware the habits of our animal friends. Automotive technicians have often pulled nests and stashes of nuts and other treats that rodents love to store within the warm confines of an automobile 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” that creates fuel for a potential fire under the hood, says Wood.
Bizarrely, the auto industry’s zeal to adopt 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. The wire in this photo was chewed through by a rat. 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. Fortunately, there is wire wrap available that is infused with a rodent repellant to address the problem.
Inexplicably, some people insist on storing extra cans of fuel and combustible products 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 habit of doing things like that.
Wood advises never to store dangerous chemicals or materials in your vehicle. Propane tanks and jerry cans full of gasoline are common finds in an automobile trunk – all things that are just waiting for a spark. In the event of a collision, they can fuel a needlessly big fire and endanger lives. Wood recalls seeing hazardous industrial chemicals in an automobile trunk 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 private vehicle.
While the proportion of Canadians who are regular smokers has steadily declined – Stats Canada pegs it at just 20%of the population today – there are still enough around to make driving and smoking a hazardous combination. 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!”
It’s hard to surmise why anyone would deliberately set a perfectly good automobile on fire, but police – and Hollywood movies – present some plausible explanations. 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. Random neighbourhood vandalism can be a common occurrence when youth become bored. Or it could be insurance fraud, motivated by someone in debt who hopes to engineer a nice payout courtesy of his or her automobile insurer. But it’s hardly an original scheme.
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 realize 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 know there is no oxygen at floor level in an intense fire. If an accelerant (gasoline is a common one) were poured on 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.
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