Bob McKay travelled 185km east of Broome to investigate this Kenworth T909 fire.
Bob McKay travelled 185km east of Broome to investigate this Kenworth T909 fire. Contributed

Why do trucks catch on fire?

EVERY time Bob McKay hears about a heavy vehicle fire, he takes note.

That's because as a fire investigation technician, who specialises in motor vehicles, he's most likely going to get a call to say "come and tell us what happened”.

"Effectively, the purpose of my existence is to examine, determine the cause of the fire and report back,” he said.

Bob, McKay Investigation Services' managing director, has been working in the insurance investigation industry for almost 40 years and after getting "sick and tired” of seeing expert opinion reports that "didn't know what they were talking about”, he embarked on obtaining specialist fire investigation qualifications.

In 2016, he was granted specialist endorsement credentials for motor vehicle fires and is only one of 99 people who has that qualification.

"For a long time I did one thing, which was compensation, and then that morphed into motor vehicle investigation collisions, then stolen vehicles and then into heavy vehicles,” he said.

"I've had an association with heavy vehicles for I think 33 years, in one form of another, and because of that, I work for various insurance companies and they have me go and examine vehicles that have been on fire. And when I refer to a vehicle, it's anything that can be driven.

"If it doesn't move, I'm not interested, it's specialised.”

The largest machine he's ever worked on was a 2008 Komatsu PC1250-8R excavator, standing at nearly seven metres tall and almost 16 metres long.

It was in a holding area north of Kalgoorlie, awaiting pick up and was cleaned with pressure waters by staff. Three days later, when staff went to collect the excavator, it was burnt out.

"During examination, I found no evidence of an electrical fault, but did find that one of the windows of the operators cabin had been smashed before the fire,” he said.

"The fire had been maliciously set, but it did not involve the owners.”

2008 Komatsu PC1250-8R excavator.
2008 Komatsu PC1250-8R excavator. Contributed


So what exactly causes a truck, or another piece of heavy machinery, to actually catch on fire?

Well, according to Bob, there's a number of factors at play but the first point he wanted to make was that

heavy vehicles were designed to work in a broad range of temperatures and other variables came into play like whether the vehicle was moving or it was parked.

"If it's parked generally there are a couple of minor exceptions - if the engine is off there are only two reasons to burn, it's an incendiary fire or a mechanical fault,” he said.

"I'll establish what (the vehicle) was doing, whether it was rolling or moving or not and then consider the possibilities of what could have caused the fire. If it was parked, maybe an electrical fault. "If it was rolling, then I've got a whole raft of things I need to consider. That would include fuel delivery systems, fuel delivery hoses and turbo charges.

"I also need to look at rotary engine components, alternators, starter motors, air compressors, air conditioning, all those things in the truck.”

Then, if it wasn't due to any of those possibilities, he would consider electricals.

"We'd consider other components, tyre failure, wheel bearings, braking systems, brake locks in particular. I've seen trailers where one component failed and caused the trailer to burn down.”

Bob said faulty tyres also could be attributed to fires.

"There are situations where tyres, particularly when the one on the inside, deflates. If the driver isn't aware, the tyres are still turning and ultimately generates sufficient heat to catch on fire,” he said. "When you've got a tyre burning it's not long before the rest of it goes up.”

But Bob said there's always the question of what was in the load.

"I was looking at a couple of trailers that burnt down in Kallangatta in Victoria in 2017, there was a suspicious report,” he said.

"I mean these trailers were totally destroyed and looking through the manifest, the type of cargo that was on it was a small quantity of fish oil and a larger quantity of rosehip oil.

"Oils high in omega three fatty acids can, under the right circumstances, auto combust. A colleague of mine said if you take oil and it's good for you, it'll auto ignite. Everyone knows about linseed oil and they'll all do that under the right circumstances.”

The driver of this truck woke up to find it on fire.
The driver of this truck woke up to find it on fire. Contributed

"I tend to be able to work it out, but on some occasions I've had say this is what I think but I don't have evidence and we have to regard it as an undetermined fire,” he said.


  • Vehicle fires move fast. From the start of a fire in a truck, to the total destruction of the truck can take as little as 30 minutes. If you smell smoke, or think you smell smoke, stop immediately and investigate the cause.
  • Always remember, a battery isolator does not always completely isolate the batteries of a truck. Most modern trucks have certain circuits that are always energised. These circuits can cause a fire, even when the truck is parked.
  • If your vehicle has a fire in it, after the fire is out do not try to find out what caused the fire. You can destroy evidence, which could help an investigator determine the cause.
  • Be cautious if electrically powered devices, or the conductors to those devices get hot. This could be evidence of an electrical high resistance connection. An electrical high resistance connection can generate enough heat that the insulation on the conductors melts and catches fire.
  • If your truck or trailer has a fire in it and the tyres are already on fire, do not try to extinguish the fire with a fire extinguisher. You should also stand well away from the tyre, as it will explode with enough force to kill, or injure a person standing close by.
  • If you have, or suspect that you have a flat tyre, stop immediately, or drastically reduce you truck's speed until you can stop and change the tyre. A deflated tyre will generate enough heat, at normal road speed to cause a fire.
  • Fires due to electrical faults are often caused by a wiring harness abrading of metal fixtures. Inspect the electrical harnesses on your truck to make sure they are not rubbing against metal brackets of other components.
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