After having my car flooded last year in Northwest Florida during Tropical Storm Fred, the last thing on my mind was the thought of having to park the car away from structures, trees and other flammable material. That’s because it’s got an engine, not an electric powertrain.
But as the nation learned recently following Hurricane Ian in Southwest Florida, batteries in flooded EVs can ignite — sometimes days after being submerged — and create serious challenges for vehicle owners, firefighters and others.
“A typical car fire in the past would be one tank of water from our engine and would be less than an hour job. Pretty routine,” North Collier Assistant Fire Chief James Hammond told Fox Business after his department battled 10 EV blazes following the Sept. 28 storm. “And these we’re finding take hours to cool the batteries to keep them out of a runaway situation. It just ties up resources a lot longer, and in some cases where we don’t have a water source, we have to secure the area and let them burn.”
Footage of an EV fire that North Collier firefighters battled a week after Hurricane Ian shows traffic backed up on a major street while firefighters kept hosing the Tesla with water from a nearby hydrant. This after they emptied two tanker trucks with a combined 1,500 gallons of water.
Thankfully, no injuries were reported save for the anguish of those stuck in a traffic jam created by an EV fire that can take several hours to extinguish. And they’re not always over when firefighters think they’re over.
A deadly Tesla accident in Mountain View, California, in 2018 left behind a burning battery that firefighters and Tesla technicians thought had been finally extinguished after disconnecting the powertrain battery and exhausting the fire truck’s water tank. The car was towed away to a salvage yard where it reignited six days later. The incident so concerned Mountain View Fire Department Chief Juan Diaz that he penned a 13-page safety alert in which he wrote about the challenges of dealing with an EV battery fire.
One of the issues Diaz and his firefighters faced, just as Hammond’s crew faced four years later in Florida, was water availability in their trucks. A contemporary fire truck typically maxes out at upwards of 1,500 gallons (or about 12,500 pounds) of water, which was not enough to extinguish the Tesla fire in Collier County. Diaz’ contemplated shutting down Interstate 101 to drag a hose across the highway, but it had appeared that the battery had finally been extinguished. Or at least they thought.
When Googling online ‘how to extinguish an EV fire,’ 474,000 search returns emerge with water dominating the list of flame retardants. But in this case, it’s not so much a retardant as it is a cooling agent.
“Once a battery cell fails, it is impossible to extinguish the failed cell as the chemical reaction inside the cell happens far too quickly,” Captain Patrick Durham, a training officer at the Troy Fire Department in Michigan, writes in firerescue1.com.
“The only way to stop a thermal runaway is by directly cooling the cells involved to ensure that the failed cell does not cause the cells around it to also fail.”
Durham, who’s also a mechanical engineer, adds that “there is no simple solution or tool to stop a thermal runaway in an EV’s high-voltage battery. Directly cooling the battery cells is the best method, however the manufacturers do not give first responders direct access to the inside of the battery box. Trying to cool the battery cells from the outside will only extend a crew's time on scene.”
Ultimately, Durham advises that, if possible, the best course of action is to first let an EV fire burn itself out and then douse the vehicle to extinguish non-battery materials like seats, plastic and tires.
“If the battery box is intact and there are no exposures, the best solution is to simply wait for the battery to burn itself out, then extinguish the remaining class A fire,” Durham states. “While this strategy is not ideal – and not one favored by aggressive, proactive and eager firefighters – it’s really the best approach. It should only take an hour for the battery to burn itself out. The alternative will be to continually dump water on the vehicle for 6 to 8 hours.”
Tim Reeser, CEO and founder of Lightning eMotors, said letting an EV fire burn out is now a typical safety protocol because the fire’s burning slower. Unless the fire poses a threat to people or adjacent property “there’s no reason to keep dousing water on it,” Reeser said.
“What we hear when we talk to first responders is that they recognize that and so the answer is get people away from it and then just let it do its thing because it has a limited amount of energy so it will go out. It's not like it can burn for months,” Reeser added.
Obviously it’s wise to lean on advice from Durham, Reeser and other experts as EVs continue to roll out to fleets and consumers alike. A few years ago, Dana released a series of commercial EV maintenance training videos, which – among other things – recommended keeping an EV parked outside the garage overnight if it had been involved in a collision. Similar to a submerged battery pack, cells damaged in a wreck may ignite sometime later following the event.
It’s also wise to keep in mind which battery chemistries pose more flammability risks than others. Lithium iron phosphate (LFP) batteries are not as energy dense as nickel manganese cobalt (NMC), but the fire risk is much lower. Firefighters in Southwest Florida were battling NMC fires for instance. Major electric truck manufacturers like Kenworth, Peterbilt and BYD use LFP batteries. Ford announced in July that it would also be using LFP batteries "for Mustang Mach-Es sold in North America next year and F-150 Lightnings in early 2024." Tesla has added LFP to its battery chemistry lineup and Lightning eMotors announced last December that it would also be using LFP.
“There's a significant move to that even though there's a bit of an energy density trade-off," Reeser said and then added that in addition to increased safety, "it's much easier to get the iron and phosphate in the U.S. and meet the new Inflation Reduction Act requirements for mineral sourcing."
Yes, powertrain batteries are more complex than octane and cetane levels in contemporary fuels, but getting more familiar with battery chemistry can make all the difference when it comes to reducing risk and maximizing productivity.