Incidence Rate of Combustion in Battery-Powered Autos: A Closer Look

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• Do EVs Catch Fire More Often Than Gas Cars?
• EV Fires Are Rarer, But More Difficult to Extinguish
• What Can Cause an EV to Catch Fire?
• Should You Worry About Electric Car Fires?

Given the intense stories about electric vehicle fires, and past disasters with overheating lithium-ion cell phone batteries , it’s reasonable to be concerned about an electric vehicle (EV) battery catching fire. But how often does that actually happen, and why?

Do EVs Catch Fire More Often Than Gas Cars?

Compared to how long gas cars have been around, there isn’t a ton of data on electric vehicle fires at the time of writing. But there is enough to make some determinations. AutoinsuranceEZ compared data from multiple sources to try and find an answer to the question of how often electric cars catch fire.

Their sources were:

• National Transportation Safety Board (NTSB)
• Bureau of Transportation Statistics (BTS)
• Recalls.gov

Per 100,000 vehicles sold, it was actually hybrids that had the most fires, and battery electric vehicles the least. As for the vehicle type with the highest total number of fires, it was far and away gasoline cars. Recall data showed a variety of components could cause a fire in a gas car, but with EVs and hybrids it was almost always the battery.

Overall, EVs were about 0.3% likely to catch fire, while gas cars were 1.05% likely to ignite. That should be good news for EV owners, but as the AutoinsuranceEZ report points out, car fires are dangerous no matter the cause.

EV Fires Are Rarer, But More Difficult to Extinguish

Though the data show EV fires to be rarer than fires in gasoline cars, EV car fires burn hotter and for a longer period of time. In gas cars there’s usually a single reaction, like a spark in a puddle of gasoline, that leads to the fire and that reaction eventually burns down. When an EV’s lithium-ion battery ignites the battery burns the energy stored inside, becoming the fire’s main source of energy and taking much longer to expend itself.

Related: How Does an Electric Vehicle Work?

Lithium-ion traction batteries are designed to contain a massive amount of energy in a very small space . Each cell inside it is filled with a flammable electrolyte, as well as electrodes that could short if they get damaged or are improperly maintained, causing the cell to overheat.

If one cell overheats, it can enter a process called thermal runaway -– basically, a positive feedback loop where it keeps making itself hotter very quickly — and ignite the neighboring cells in the battery pack until the whole thing goes up. Lithium-ion batteries can also reignite after they’ve been put out if moving them causes further damage to or new short circuits in the battery.

Since first responders are mostly trained in how to extinguish fires in a gasoline car, they can have trouble putting out an EV fire because it behaves differently. Instead of cooling down the part of the car a firefighter normally would, they need to direct water to the underside of the vehicle where the battery pack sits. Stored energy left over inside the battery, called stranded energy, can cause the battery to reignite hours or even days after the initial fire is extinguished if that energy is not properly dealt with.

What Can Cause an EV to Catch Fire?

Multiple factors can start a fire in an electric car, mostly pertaining to the battery. If the battery is damaged in a crash, for example, it can cause a short circuit in one or more of the lithium-ion cells and start a thermal runaway chain reaction.

If poorly maintained, components inside the battery pack may degrade to the point where a malfunction starts a fire. Manufacturing defects can also be the cause of car fires, both in EVs and gasoline vehicles.

Age may also be a factor. There isn’t enough data yet to show whether electric car batteries that are, say, 20 years old are more of a fire risk but it is something to be aware of as the components may degrade over time with hard use and poor maintenance.

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Should You Worry About Electric Car Fires?

The bottom line at the time of writing is that EV fires are far rarer than fires in gasoline cars. They’re also much hotter, burn for longer periods, and can therefore be very dangerous.

This doesn’t necessarily mean that all EVs are more dangerous than gas vehicles, just that standardized safety guidelines should be developed specifically to deal with these fires if and when they happen. If you own one, make sure you’re taking excellent care in maintaining the components so that the risk stays low.

Related: Why Does an Electric Car’s Battery Degrade?