Why Do Electric Cars Catch Fire?

If damaged or faulty, an EV battery may release its energy as heat, but explosions are rare.

Graphic showing car battery with only tires with fire aboveShutterstock

Modern EV battery packs hold enough energy to propel a vehicle for hundreds of miles at highway speed. If physically damaged or internally defective, though, some of the hundreds or thousands of cells that make up a lithium-ion battery pack may release the energy they’re storing, expanding and giving off heat. This can lead to thermal runaway, where the released heat causes a chemical reaction within a cell that generates even more heat to the point that the cell emits gas and possibly erupts into flame. One self-destructing cell can then affect its neighbors, causing a chain reaction that produces a large fire.

Carmakers have taken steps to try to prevent this. General Motors, for instance, divides the cells of its Ultium battery packs into a series of modules, which it spaces out to both improve cooling in normal operations and lower the risk of thermal runaway consuming the entire pack. The Ultium platform also uses a wireless battery-monitoring system to detect internal issues before they can lead to catastrophic failures.

How to Put Out an Electric Vehicle Fire

EV fires can be much more difficult to extinguish than gas-vehicle fires. According to an emergency-response guide published by Tesla, it can take between 3,000 and 8,000 gallons of water applied directly to the battery to get the job done. Trouble is, most firetrucks don’t carry that much water, and if a hydrant isn’t available (such as on a highway), what can you do?

The bigger challenge, though, is that even after it’s out, an EV fire can start up again, as happened twice in Texas last year. In both incidents, firefighters needed more than 30,000 gallons to kill resurgent flames in a crashed Model S (that’s about 40 times more water than you’d need to put out a regular car fire). And in 2018, California firefighters had to call in Tesla employees to help them disassemble a sputtering battery in a severely damaged Model X. They removed the exposed cells—making up about a quarter of the battery—and moved the car to an impound lot, where it reignited twice within 24 hours and once more several days later. At that point, Tesla engineers removed the remainder of the battery and submerged it in a vat of salt water.

Submersion is becoming more popular. In the Netherlands, for instance, firefighters have started to bring along car-sized shipping containers to crash sites. They fill the containers with water, drop in compromised EVs by crane, and tow the whole lot to an impound yard.

How Many Electric Cars Catch Fire Every Year?

Given the limited data we have, it’s difficult to draw conclusions about the frequency of EV fires, but Richard Billyeald, chief technical officer of Thatcham Research, told Forbes, “Our latest research indicates that the risk of a fire for all types of EV remains less likely than for [internal-combustion] vehicles."

As electric cars make up a tiny percentage of the vehicles on the road and getting timely crash data can be challenging, it will probably take a few years before we have statistically significant information to compare fire instances in EVs and gasoline-powered cars.

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Jordan Golson
Jordan Golson is a transportation reporter covering cars, trains, planes, future cities, mobility and more — basically, if it moves and doesn’t go to space, he's on it. He is especially interested in the intersection of transportation and technology, and that means he goes deep into electric cars, autonomous vehicle tech, sensors, safety, connectivity, and similar topics.