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Officials in Florida warned residents to move their electric vehicles away from potential flood zones ahead of Hurricane Milton to avoid the risk that the cars could burst into flames after being submerged in saltwater for extended periods.
“Keep electric vehicles and lithium-ion batteries away from floodwaters and storm surge,” urged the Facebook page for Hillsborough County, which contains Tampa.
Electric vehicles contain lithium-ion batteries, which can also be found in e-bikes and scooters, wheelchairs, golf carts, electric lawn mowers and tools like cordless drills. If these batteries are soaked in saltwater, some can ignite after floodwaters subside.
It’s a relatively rare problem, but the risk is real.
Of the 48 lithium-ion battery fires attributed to Hurricane Helene, 11 were caused by electric vehicles, said State Fire Marshal Jimmy Patronis. The rest were electric wheelchairs, hoverboards, scooters and golf carts. The E.V.s that caught fire were a tiny fraction of the more than 254,000 electric vehicles that were registered in Florida at the end of 2023.
Why do batteries catch fire in floods?
If saltwater reaches the interior of a lithium-ion battery, it can cause the cells to short-circuit by conducting electricity between the positive and negative terminals. This generates heat.
In some cases, that heat can spur a chain reaction inside the battery called thermal runaway. Heat from one cell starts melting the plastic separators inside neighboring cells, which causes additional short-circuiting and generates more heat. The end result: a fire that can last for hours and is hard to extinguish.
Automakers design their lithium-ion batteries to be water-resistant. But if a vehicle is submerged in saltwater for an extended period, wear and tear or corrosion could allow saltwater to seep into the battery and cause a fire.
“This isn’t a risk for freshwater immersion” associated with heavy rainfall or river floods, said Albert Gore, the executive director of the Zero Emission Transportation Association, a trade group. “But in places prone to saltwater flooding and storm surges, it’s a risk to be aware of.”
How safe am I?
After Hurricane Ian hit southwest Florida in 2022, more than 3,000 electric vehicles were affected by floods, but just 36 were reported to have caught on fire, according to a January report by Idaho National Laboratory.
“It’s not super common,” said Thomas Barth, chief of a special investigations branch into highway safety at the National Transportation Safety Board.
Researchers have been dissecting and studying batteries that did catch fire after being flooded with saltwater to understand the causes, potentially allowing battery manufacturers to get better at preventing future fires.
“We’ve had 100 years to refine the safety of gasoline-powered vehicles, and we’re a little over a decade in terms of high-volume production of E.V.s,” said Alan Taub, director of the Electric Vehicle Center at the University of Michigan. “Events are rare but they catch a lot of attention.”
How can I protect my vehicle?
If you’re in the path of a hurricane, you can evacuate the area in your electric vehicle just as you would in a gasoline-powered car. In that scenario, you would want to make sure your car is fully charged before leaving.
If you’re not on the move but anticipate saltwater flooding or storm surge where your electric vehicle is parked, reduce your vehicle’s charge to 20 or 30 percent. A lower charge means there is less energy in the vehicle to cause thermal runaway.
Then, move the car to a place that’s less likely to be flooded, such as the top floor of a parking garage. If you don’t have that option, park it at least 50 feet away from structures that are flammable, like your house or garage or a stand of trees.
“If the worst does happen, then it’s only a car you end up losing,” said Greg Less, director of University of Michigan’s Battery Lab.
If you own an e-bike and can safely remove the battery, do it before the storm and place it in a secure, higher location that is unlikely to be flooded. But if the e-bike ends up being compromised, move it away from your home into a clear open space.
My E.V. was submerged. What should I do next?
If you know your E.V. was submerged in floodwaters, don’t drive the vehicle, even if it looks safe. Fires can start hours, days or even weeks after the floodwaters drain away.
Contact the manufacturer for an inspection. Be clear that your vehicle was submerged and needs to be assessed for flood damage. Often, a damaged electric vehicle will need to be towed away on a flatbed truck for further inspection.
“In spite of what might sound like dire warnings, we still believe E.V.s are safe to drive and safe to own,” said Dr. Less, who owns an electric vehicle.
Are battery fires a problem for firefighters?
Electric vehicles aren’t the only source of fire risk during a disaster. Gasoline-powered cars can, and often do, catch fire as well. But electric vehicle fires need to be dealt with differently.
Firefighters have to spray water in just the right places around the battery to reduce heat. “If you don’t get it right, you can spray all the water you want and it won’t stop the battery from reigniting,” said Andrew Klock, a senior manager at the National Fire Protection Association.
The association has educated about 350,000 firefighters in extinguishing electric vehicle fires, but there are roughly 1.2 million firefighters nationwide and more need training, he added.
Kate Christobek contributed reporting.
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