Though rare, fires in electric vehicles pose serious risks

It seems that whenever an electric vehicle catches fire, a headline is sure to follow — perhaps due to the novel technology involved.

Statistically speaking, however, EVs are much less likely to catch fire than vehicles powered by internal-combustion engines. But when they do, they can pose serious challenges to firefighters trying to extinguish the blaze.

“The data doesn’t show that it’s a very widespread occurrence, but sometimes it’s not the frequency; it’s the severity,” said Mark Stephenson, MPA, who teaches in Metropolitan State University of Denver’s Fire and Emergency Response Administration program.

Stephenson, who spent 36 years with Aurora Fire Rescue, said emerging technology, such as the high-capacity lithium-ion batteries used to power EVs, sometimes leads to dangerous consequences, which firefighters must deal with.

“To me, the EV fires are the latest in a long line of new duties that the fire service has had to assume,” Stephenson said.

Lithium-ion batteries, which power EVs, scooters and electric bicycles, have unique properties, said Tom Johnson, a captain with Aurora Fire Rescue and a graduate of MSU Denver’s Fire and Emergency Response Administration B.S. program.

“They have a potential, under fire conditions, to be involved in what’s called a thermal runaway,” he said. “One part of a battery cell ignites the next in a way that progresses faster than normal combustibles. From a firefighting tactical point of view, it requires more water than a normal combustible or the liquid fuels in an internal-combustion engine.”

Complicating matters, it can be hard to tell when an EV battery fire is fully extinguished. “There’s risk for reignition hours, days and even weeks later,” Johnson said. “That poses a risk to the secondary responders, such as towing companies or salvage yards.”

In addition, burning batteries may emit a cloud of toxic vapor that can catch fire. “There are reports of a vapor-cloud explosion or a sudden ignition,” he said. “From an owner’s point of view, they should be aware that if an EV is involved in a fire, there may be unexpected risks when compared to an internal-combustion fire.”

Should their EV catch fire, occupants should stay well clear of the burning vehicle until firefighters arrive, Johnson said. And because the EV components burn much hotter than those of an internal-combustion vehicle, a lot more effort will be needed to quench the flames.

Although EV fires may be tougher to put out, they’re comparatively rare, he said.

“I’ve read that an internal-combustion engine has a risk of fire of somewhere around 0.1% of likelihood, whereas these EVs run 0.001%,” Johnson said. “It’s significantly less risk. I’ve seen reports of significant fires or multiple fires in electric vehicles, so it was surprising to see how much safer they are in terms of likelihood of fire.”

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Johnson has not personally responded to a passenger EV fire, but given the popularity of the vehicles in Front Range communities, there is risk of one occurring. “We’re in a large city, running a large number of incidents, and we’re in an area of the nation that embraces EV technology,” he said.

Johnson has managed the response to a burning electric warehouse vehicle, however. “I dealt with that thermal-runaway consideration as that fire spread,” he said. “Once we were able to extinguish the fire in the involved vehicle, being aware of the thermal-runaway risk, we chained it and dragged it outside.”

To reduce risks, the best thing EV owners can do is to follow manufacturers’ instructions and make sure to have a licensed electrician install the code-compliant wiring necessary to safely power a home charging station, he said.

Meanwhile, front-line firefighters receive continual in-service training to prepare them for new challenges, Johnson said.

“As the landscape changes for firefighters, for what vehicles are on the road and what our tactics need to be to meet that challenge, the fire service across the nation is constantly growing, remaining adaptive to the changing risks,” he said.