The Smoke Is the Danger: Toxic Gases From Lithium-Ion Battery Fires

Battery fire science

When a lithium-ion battery fails, the flames are what people notice. What they breathe can be the bigger threat. Understanding what is in battery smoke changes how you respond, at home and at work.

What's in the smoke

In thermal runaway, a cell's electrolyte and internal components break down and vent a mix of flammable and toxic gases. Swedish researchers measured seven types of commercial lithium-ion batteries in fire tests and found they released between 20 and 200 mg of hydrogen fluoride for every watt-hour of battery capacity, plus 15 to 22 mg per watt-hour of another toxic gas, phosphoryl fluoride, in some tests (Larsson et al., 2017).

Put that in everyday terms. On that range, a typical 500 Wh e-bike battery could release somewhere between 10 and 100 grams of hydrogen fluoride, and a 60 Wh laptop battery between about 1 and 12 grams. Hydrogen fluoride is highly toxic and forms corrosive hydrofluoric acid on contact with moisture, including the moisture in your eyes, throat and lungs.

It isn't only hydrogen fluoride. A 2025 U.S. Coast Guard research paper found toxic gases often make up 60 to 70 percent of emissions from lithium battery fires, with hydrogen fluoride and carbon monoxide at levels immediately dangerous to life or health (MarineLink, 2025).

It can arrive before the flames

Describing the fire that caused NSW's first recorded lithium-ion battery deaths, at Teralba in 2024, Fire and Rescue NSW explained that a compromised cell overheats and gives off toxic gases before bursting into flames (pv magazine Australia, 2024). A hissing, venting or smoking battery is already dangerous, even if nothing is burning yet.

What this means at home

• Get out and stay out. Don't stay to watch, film or fan the smoke. Close doors behind you to slow its spread.
• Call 000 early, and tell them it's a lithium-ion battery.
• Keep away from the smoke outside too. Move upwind and keep others back.
• Get checked if you breathed it in. Tell medical staff it was a battery fire, as some effects of hydrogen fluoride exposure can be delayed.
• Only tackle a very small, early fire, and only with a clear exit behind you.

What this means at work

Where staff handle damaged or suspect batteries, in fleet workshops, e-bike repairers, warehouses, and waste and recycling sites, respiratory protection belongs in the battery fire kit alongside the extinguisher and blanket. The Sundström SR 200 full face respirator with ABEK1 + P3 filtration covers a broad range of gases and vapours plus fine particles, and the full face visor protects the eyes.

Be clear about its limits. A filtering respirator cleans the air you breathe, but it doesn't supply oxygen, and it isn't designed for atmospheres that are immediately dangerous to life or health. It is not for entering a burning room or a smoke-filled space; that is work for fire crews with breathing apparatus. It suits tasks such as moving an off-gassing battery to an outdoor quarantine point where it is safe to do so, and clean-up once the fire brigade has cleared the scene. Choose, fit and maintain respiratory equipment in line with AS/NZS 1715 (Standards Australia, 2009), and make sure staff are trained to use it.

Our Home & Warehouse EV Fire Safety Kit brings the respirator together with an extinguisher, blanket and signage, and our Lithium Battery Fire Safety Awareness course covers the warning signs of a failing battery for households and staff.

No extinguisher, blanket or respirator replaces the fire brigade. In any lithium-ion battery fire, get people clear and call 000.