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Lithium-ion battery fires: a new fire class

Anas SAHILI

The ISO 3941:2026 standard introduces fire class L, dedicated to lithium-ion batteries. A major step forward given the growing risk these fires pose in professional environments.

Why a new class?

Li-ion fires behave unlike any other:

- Rapid thermal runaway

- Re-ignition possible hours after initial extinguishing

- Toxic gases and extreme temperatures (>1000°C)

- Extinguishing can be complex, sometimes requiring thousands of litres of water

Point right Conventional extinguishers are insufficient. A dedicated class was needed.

What does Class L cover?

Only lithium-ion battery fires (not metallic lithium).

X Does not cover solid (A), liquid (B), gas (C), metal (D), or cooking oil/grease (F) fires.

Extinguishing methods:

- Massive water cooling

- Prolonged immersion

- Li-ion specific agents (in development)

- Post-fire monitoring mandatory

Impact on workplaces: training & risk assessments

Class L changes the game:

- Fire training must be updated

- Emergency procedures revised

- Charging and storage areas secured

- Risk assessments (RA / DUERP) updated to include “Li-ion Fires – Class L”

Where is the risk?

Virtually everywhere:

- E-bikes and e-scooters

- Power tools

- Cleaning robots

- Smartphones, laptops, tablets

- Electric vehicles

- Energy storage cabinets

- Batteries and cells

Prevention and training are now essential. Class L isn’t just another regulation – it’s a paradigm shift in fire safety.

  • It's also a money-making opportunity for somebody.

  • in reply to Simon Barker

    There may indeed be commercial implications, as with any new safety standard. However, the emergence of Class L reflects a genuine operational gap: Li-ion battery fires behave fundamentally differently from traditional fire classes, and recent incidents show that existing approaches are not always adequate.

  • Humm, I wonder about other battery chemistries. The only time I've personally seen thermal runaway was with a sealed lead acid battery in a UPS. Fortunately the problem was spotted early and it ended up being moved outside and left for several days before it cooled down. I have my suspicions it might have all been a lot more dramatic if it had been left in situ, connected to the supply, in a closed box in the middle of a not that well ventilated computer room (it had air con for cooling, but that just recycled air, there was no exchange with the outside, so any released hydrogen or other gasses couldn't have escaped easily).

       - Andy.

  • in reply to AJJewsbury

    Very good point, Andy. Thermal runaway and hazardous gas release are not limited to Li-ion systems.
    Sealed lead-acid UPS batteries can also overheat under fault or overcharge conditions, with significant hydrogen evolution.
    In enclosed or poorly ventilated plant rooms, this creates an additional explosion and fire hazard, especially if ventilation is only recirculated cooling rather than fresh air exchange.
    This highlights that battery fire safety must always consider the full installation context: chemistry, charging regime, enclosure, ventilation, and gas management not just the cell type.

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