The new fire class dedicated to lithium-ion batteries

Standard ISO 3941:2026 officially introduces fire class L, specifically dedicated to lithium-ion battery fires. This major development recognises the unique, electrochemical behaviour of these fires, which is fundamentally different from "conventional" fires.

Until now, standard ISO 3941:2007 classified fires by the nature of the fuel, into five categories:

• A: solid materials
• B: liquids or liquefiable solids
• C: gases
• D: metals
• F: cooking equipment

January 2026 marks a turning point

With its third revision, standard ISO 3941:2026 adds class L, dedicated to lithium-ion battery fires, confirming that these incidents can no longer be treated as conventional fires.

What does class L cover?

So-called "electrochemical" fires:

• Lithium-ion batteries and cells
• Without metallic lithium (to be distinguished from class D)

Why are these fires so critical?

They present specific hazard characteristics:

• Very high energy density
• Thermal runaway (extreme temperatures, projections, flaming jets)
• Massive release of toxic gases
• Difficulty extinguishing with conventional means
• High risk of re-ignition after extinguishing

An emerging, ever-present risk

Electric mobility, power tools, stationary storage, digital equipment… The spread of lithium-ion batteries across public-access buildings, car parks, workshops, logistics platforms and transport is turning this risk into a major fire prevention issue.

A challenge for the fire safety sector

This new class is both a regulatory advance and a call to action:

• Raise awareness of the risk of thermal runaway
• Evolve prevention, protection and response strategies
• Accelerate the adaptation of European and national standards (NF EN 2, NF EN 3-7)

Worth noting

Standard ISO 3941:2026 also provides enhanced information on the specific hazards associated with each fire class, improving the understanding and management of risks.

And you — are your sites ready to factor class L into your risk analyses and prevention plans?