Explainer: Electric vehicle fire risks

On Monday evening, a battery that was detached from an electric vehicle (EV) caught fire at Sydney Airport, destroying 5 cars in the process.

So how risky are electric vehicles, and what should you do if there’s a battery fire?

Why do lithium batteries catch fire?

Lithium batteries can occasionally catch fire while charging, or after being damaged. They’re prone to a process called “thermal runaway”: a chain reaction that happens inside the battery that releases heat.

It starts with dendrites: small metal filaments that can form from the metals in the battery.

“During charging of your lithium battery, or extreme charging, or in some cases, extreme discharging, you can get localised dendrites that will form within your battery. Once you get that, you can get a localised heating event that occurs,” says Dr Ruth Knibbe, a researcher at the School of Mechanical and Mining Engineering in the University of Queensland.

The heating triggers more heat-generating (or exothermic) reactions in nearby cells, causing the whole unit to get hotter and hotter.

“A small event can trigger a considerably more significant event in that process,” says Knibbe.

This makes battery fires very hot, and difficult to put out. Because batteries have different mixtures of chemicals in them, depending on the manufacturer, there can also be gases and other hazards released that are hard to identify from the outset.

“The seat of our fire is a chemical reaction [which is] confusing firefighters,” says Emma Sutcliffe, a firefighter and project director at EV Firesafe, a company researching the risks of EV fires.

That said, firefighters are working on best practice for dealing with battery fires: at the moment, the battery is cooled with water.

How common are electric car fires?

Extremely rare.

“It’s a bit of a myth doing the rounds on social media that electric vehicles catch fire all the time,” says Sutcliffe.

“It’s absolutely not the case. In fact, they’re far less likely to catch fire than an internal combustion engine vehicle.”

In Australia, Sutcliffe says there have been 7 EV battery fires in total (including the recent one at Sydney Airport).

“None have been spontaneous. There has always been human involvement to cause abuse to cells leading to thermal runaway and fire,” she says.

Globally, EV Firesafe has tracked 393 verified EV battery fires since 2010, plus 95 extra potential fires, out of 10 million total EVs on the road: that’s fewer than 5 fires per 100,000 vehicles.

This is because vehicle manufacturers have very high safety standards they need to meet before they can sell a roadworthy car. Agencies like the Australasian New Car Assessment Program (ANCAP) test EVs by running them through a range of crash scenarios, keeping an eye out for thermal runaway.

These safety features are comprehensive enough that batteries frequently don’t burn even when the rest of the vehicle catches alight from another source.

But smaller, less well-regulated vehicles, like e-bikes, e-scooters and hoverboards, are a different story.

“The quality of those can be very poor,” says Sutcliffe.

Battery packs in these e-bikes are less protected than those in cars, and the safety systems have less oversight.

“And then the owner of that electric bike brings that bike, or that battery pack, into their home to charge it up,” says Sutcliffe.

“So when it catches fire, the thermal event in that battery pack may be fairly short-lived because they’re a very typically very small pack, but it’s going to spread to your home very quickly.”

Sutcliffe says that EV Firesafe is seeing e-bike battery fires around the world “almost daily”, with dozens of fatalities worldwide in 2023 alone.

So: your road-registered vehicle is fine, but be wary of cheap e-bikes.

What should you do if there’s an EV fire risk?

Sutcliffe says that the first sign of thermal runaway in a lithium-ion battery is a “loud popping noise”. If you hear that happening to your cheap e-bike – or if the bike catches fire – you should leave the building as quickly as possible.

“As with any fire, and as any firefighter will tell you, don’t try to fight it yourself. Just get out and get everybody else out, raise the alarm, call an emergency number, and don’t re-enter the building,” says Sutcliffe.

For bigger EVs, the three scenarios where a fire is more likely are in crashes where the battery has been damaged; after the vehicle has been submerged (such as in a flood); or if the manufacturer has recalled the battery.

“If you’re in an electric vehicle, and you’ve been involved in a collision – particularly a collision where your airbags have deployed – then, if it’s safe and you’re able to do so, get out of the vehicle and move to a safe space and again, call emergency services,” says Sutcliffe.

If your vehicle has been flooded, you shouldn’t try to drive or charge it, she adds.

“And if your vehicle’s recalled, get it back to the dealership immediately. Follow the instructions that the dealer gives you, which will often include don’t park or charge it in your garage, keep it clear of structures, and get it fixed.”