Thermal Runaway: Why EV Fires Need Special Gear | EV Fire Solutions
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Explainer · How Battery Fires Work
Why You Can't Put Out an EV Fire With Water: Thermal Runaway Explained
Why does water often make an EV battery fire worse? It comes down to thermal runaway — here's what's really happening inside a burning cell, and what actually stops it.
It's the question we get asked most: if a battery catches fire, why not just hose it down? With a lithium-ion fire, water often makes things worse — and understanding why is the key to protecting yourself, your family or your workplace.
What is thermal runaway?
A lithium-ion battery stores a large amount of energy in a small space. When a cell is damaged, overcharged, overheated or manufactured with a fault, it can start to generate heat faster than it can shed it. That heat triggers a chain reaction — one cell overheating sets off the next, which sets off the next. This self-feeding cascade is called thermal runaway.
Once it starts, the battery is effectively fuelling its own fire from the inside. That's what makes these fires so different from a petrol or paper fire.
Why it's so hard to fight
- It generates its own heat. The reaction is driven by the battery's chemistry, so cooling the outside doesn't stop what's happening inside.
- It burns extremely hot and can spread to nearby vehicles, bikes or structures fast.
- It reignites. A battery can appear to be out, then flare back up hours later once trapped heat reaches the next cell.
- It releases toxic, flammable gas — dense smoke that's dangerous to breathe and can ignite.
So where does water fit in?
Firefighters do use very large volumes of water on EV fires — but the key word is volumes. It can take thousands of litres, applied continuously, to draw enough heat out of a large battery pack. A household hose or a standard extinguisher simply can't move that much heat, and a small amount of water on the wrong fire can spread burning material or create other hazards. For most homes and businesses, water is not a realistic first response.
What actually works
- A lithium-ion-rated extinguisher is formulated to cool the battery and knock the fire down, rather than just starving it of oxygen like a standard unit.
- A fire blanket smothers the fire and — just as importantly — contains the heat and burning material, limiting spread and buying time while the battery burns itself out under control.
The winning combination
Used together, an extinguisher and a blanket give an untrained person a genuine chance to control a small lithium-ion fire, or to contain it safely until the brigade arrives.
Be prepared with the right action plan
The single most important step is having the correct equipment where the batteries actually charge — the garage, workshop or charging bay.