The Dangers Of Lithium Ion Battery Fires & The New Fire Class L
Think about everything you own that's got a LARGE battery! Your e-bike, your e-scooter, or that electric vehicle in your driveway. They all have one thing in common: a high capacity rechargeable lithium-ion battery. We sure love the amount of power it stores in such a compact space. But that same power makes them a serious fire hazard.
Large battery fires are hotter, faster, and more violent than anything seen before. Because of this, the International Organization for Standardization (ISO) officially created a new Fire Class L category this year.
What Exactly is Fire Class L?
In the world of fire safety, we use letters to group fires. Class A is for solid combustibles. Class B is for flammable liquids. Class C is for energized electrical equipment. Class D covers combustible metals like magnesium or lithium. And Class K is for cooking oils and fats used in kitchens.
Lithium-ion fires are so different in how they burn that they’ve recently got their own Class of fire. Fire Class L is used to describe fires involving lithium-ion batteries.
Why do they need special attention? Because a lithium-ion battery fire doesn’t behave like a normal fire. A typical fire needs oxygen from the air. A lithium-ion fire happens inside the battery, where a chemical reaction releases its own oxygen and heat. That means it can keep burning even when you try to smother it. Scary!
And here’s where it gets even more dangerous. A lithium-ion fire isn’t just one type of fire. It actually overlaps multiple fire classes. It can start as a Class A, B, and is always a Class C fire because the battery is an energized electrical system. But as the battery breaks down, it can also become a Class D fire, involving reactive metals like lithium. In reality, what people call “Class L” is a hybrid fire that combines regular combustibles, electrical and metal fire risks into one highly unstable event.
To add on to the complexity of these fires, inside every lithium-ion battery's casing, there is an anode and a cathode. They are kept apart by a very thin separator. If that separator fails because of an overcharge or physical damage, a short circuit happens. This starts a devastating chain reaction called thermal runaway.
ONLY THE FIRE DEPARTMENT CAN COMBAT A CLASS L FIRE
The Fatal Threat: Thermal Runaway
Thermal runaway is a chain reaction inside a lithium-ion battery where rising heat causes the battery to generate even more heat, uncontrollably. It can start from damage, overcharging, or high temperatures.
Once thermal runaway begins, the battery cells instantly overheat. The liquid electrolyte and flammable materials inside the battery pack turn into a pressurized gas that causes the fire to become inferno jets.
When this happens, the battery doesn't just catch fire. It explodes. This is a thermal runaway event, and it’s a nightmare for fire departments to contain. These fires release toxic gas and can even launch battery cells across a large distance like tiny rockets. This is why lithium-ion fires are considered a major product safety concern by the U.S. Consumer Product Safety Commission.
The Invisible Risk of Reignition
Even if firefighters are able to contain the initial flames, the danger is far from over. Lithium-ion batteries suffer from "stranded energy." This means that even when the fire looks out, the internal chemical reaction can continue to simmer.
A battery can reignite minutes, hours, or even days after the fire was "extinguished." To avoid further damage to surroundings, the battery packs must be kept in total isolation. In many cases, fire and rescue teams have to submerge the entire battery pack in a container of water for several days just to ensure it stays cool. A large battery fire remains a threat until a professional can safely dispose of it.
NO HAND-HELD EXTINGUISHER IS CAPABLE OF CONTAINING A CLASS L FIRE
Why Standard Extinguishers Aren't Enough
You might have a hand-held fire extinguisher in your home. You probably think it will protect you. But here is the hard truth: No portable fire extinguisher on the market today is capable of fighting a Class L fire. Because the fire is an electrochemical reaction happening inside the battery, standard extinguishants cannot reach the source of the heat. Even fire fighters often find themselves without the proper tools or specific training to be truly efficient at containing a lithium-ion battery fire. Most fire trucks are unprepared to fight a self-oxygenating chemical inferno. In many cases, the only thing a professional can do is try to keep the area cool and let the battery burn itself out.
A lithium-ion battery fire is a "Triple Threat" that portable fire extinguishers just aren't built for:
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It’s a Class A fire (the shell).
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It’s a Class B fire (any flammable liquids inside).
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It’s a Class C fire (the live power source).
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It's a Class D fire (lithium is a metal)
Pro Safety Tips: Understanding the Risks
To reduce the risk of a lithium-ion battery fire, you should always:
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Follow the manufacturer’s instructions. Never use a cheap, third-party charger.
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Never leave batteries charging on soft surfaces like beds or carpets. They need to stay cool.
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Charge outside your home whenever possible.
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Keep your e-bikes, e-scooters, or electric vehicles away from exits so you don't get trapped if a fire starts.
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When charging an electric vehicle at a public charging station, make sure it's always parked where you can easily and quickly exit the car. Electric car fires spread rapidly and you do not have much time to get to safety.
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Look for signs of damage or overheating, like a bulging battery case or a weird smell.
Frequently Asked Questions
Can a standard portable fire extinguisher put out a lithium-ion battery fire?
No. No fire extinguisher can. Nothing is rated for Fire Class L.
What is Fire Class L?
Fire Class L is a new classification created specifically for fires involving lithium-ion batteries. These fires are dangerous because they involve extremely high temperatures and produce their own oxygen.
Can any fire extinguisher put out a large lithium-ion battery fire?
No fire extinguisher can stop thermal runaway or contain a Class L fire. If you suspect a Class L Fire, you should immediately call the fire department and get yourself to safety.