By Janet Keyes, CIH
Who has heard of the dangers of electric vehicle fires? Yep – I see a lot of raised hands.
Who has thought about the dangers of gasoline vehicle fires?
Anyone ever have a car start on fire?
There’s an inherent fire danger with vehicles. Most have plastic containers full of gasoline, a liquid more flammable than paint thinner. The body might be steel, but the car has plenty of plastic. And while the plastic may not ignite easily, it certainly can burn. Many vehicles have aluminum or magnesium components. Aluminum and magnesium burn.
So why are we now so concerned about fires with electric vehicles? We’ve had years to figure out how to put out car fires. The standard fire extinguisher in your shop, an A/B/C or a B/C extinguisher, does an effective job with gasoline. Lithium-ion batteries, used for EVs, for many battery-powered tools, and for the cell phone in your pocket, are a new and different kind of fire hazard. And while they are usually less likely to ignite than the container of gasoline, they can be much harder to put out.
Lithium-ion batteries (Li-ion) have become widely used because they pack a lot of power in a small space. But some characteristics make them a special hazard in a fire.
Hybrid vehicles might have Li-ion batteries or nickel-metal hydride (NiMH) batteries. Because the latter aren’t nearly as powerful as Li-ion, they are no longer used in all-electric vehicles.
Batteries work by creating electrical current when ions move through an electrolyte, from an anode to a cathode. In a lead-acid battery, the electrolyte is a sulfuric acid/water solution. A NiMH battery uses an alkaline material such as potassium hydroxide for its electrolyte. Those won’t ignite. In a lithium-ion battery, the electrolyte is a flammable solvent.
What’s required for a fire? Fuel, a source of electrons, heat, and a chemical reaction. The Li-ion battery supplies the fuel and the source of electrons. Heat could be from a spark, from overcharging, from a short circuit caused by damage, or from a fire external to the battery.
If one battery cell generates more heat than it can dissipate, it can cause adjacent cells to fail and overheat. The overheated cell can lead to the barrier separating the anode and cathode to melt or distort, causing an internal short circuit. The cathode begins breaking down, releasing more heat and oxygen. And then cell temperatures keep rising – and you have thermal runaway. Eventually, all of the cells in the battery can heat up and ignite.
Lithium-ion battery fires are difficult to detect, difficult to control, and difficult to extinguish. You can’t use fire suppressants to remove oxygen, because the runaway reaction is generating its own oxygen. Cooling with water or foam works if it can get to the fire. But in newer vehicles, the batteries are in waterproof and fire-resistant protective cases, so firefighters can’t get extinguishing agents on the fire itself. Often, allowing the fire to burn itself out is the best option. Fire departments may be able to cover the vehicle with a special fire blanket, to protect the surrounding area and to contain the toxic and flammable gases given off in the fire.. Until the battery is completely discharged or destroyed, there’s still a chance of cells reigniting.
If you have a damaged EV:
- Assume the high voltage battery is energized and could shock you
- Treat the vehicle as a fire hazard. Store it outside when you can, fifty feet away from any structure or other vehicle.
- If you see any sparks, flame, or smoke, if there’s any leaking fluid from the battery compartment, if it seems hot, or if you hear noises (gurgling, popping, bubbling, hissing) from the high voltage battery, call 911 right away.
- If the vehicle’s on a lift, lower it before you evacuate. That makes it easier for the firefighters to deal with it.
- Don’t bother trying to use an extinguisher on a Li-ion car battery fire. You won’t succeed.
Keep in mind that Li-ion batteries in tools and phones can also undergo thermal runaway. The danger isn’t as great because of their small size. But make sure your technicians handle those with care. Don’t abuse or try to modify the batteries. Use only batteries and chargers okayed by the manufacturer. And if a battery is leaking, heating up, or making noise, get it outside, away from anything that can ignite. If one of these small batteries does ignite, call 911. If it’s safe for you to do so, you can try using an ABC or BC extinguisher on the small battery.
This article originally appeared in AASP-MN News (June 2025). It is intended to provide general information (no advice) about current safety topics. To discuss your specific concerns and how CHESS may help, please contact CHESS at 651-481-9787 or chess@chess-safety.com.