In January 2026, the third edition of ISO 3941 introduced a significant and long-anticipated change to the way fires are classified internationally: the formal addition of Class L, covering fires involving lithium-ion batteries.
For an industry that has witnessed the rapid growth of lithium-ion battery usage and the rise in associated fire incidents, this development marks an important milestone.
But what does Class L actually mean? And how might it influence fire risk assessment, equipment selection, training and compliance?
A Brief Recap: Fire Classifications Under ISO 3941
ISO 3941 is an international standard that defines and designates classes of fire according to the nature of the fuel involved. Historically, these have included:
Class A: Solid materials, usually organic, such as wood, paper and textiles
Class B: Flammable liquids
Class C: Flammable gases
Class D: Combustible metals
Class F: Cooking oils and fats
The 2026 revision formally adds Class L, for fires involving lithium-ion batteries
The inclusion of Class L reflects both the scale of lithium-ion battery deployment across society and the distinct fire behaviour these batteries present.
Why Lithium-Ion Battery Fires Require Their Own Classification
Lithium-ion batteries are now embedded in everyday life, from handheld devices and power tools to e-bikes, e-scooters, warehouse equipment and electric vehicles. With that growth has come increased fire incidents across residential, commercial and industrial settings.
Lithium-ion battery fires are fundamentally different from traditional fuel-based fires.
Key characteristics include:
Thermal runaway: A self-sustaining chemical reaction within the battery cell that generates extreme heat.
Re-ignition risk: Even after apparent extinguishment.
High energy density: Resulting in rapid fire growth and intense heat release.
Toxicity: Production of toxic and potentially flammable off-gases.
Oxygen-independent combustion: Unlike Class A fires, they do not rely on atmospheric oxygen in the same way.
These factors mean that conventional suppression strategies are not always appropriate or effective. The formal recognition of Class L acknowledges that lithium-ion battery fires require specific understanding and response strategies.
What ISO 3941:2026 Says About Class L
The third edition of ISO 3941 highlights two key changes:
- The addition of a classification for lithium-ion battery fires.
- The inclusion of a clause providing further information on hazards related to fire classes.
This update aligns the classification framework with the evolving risk landscape. It also signals to regulators, manufacturers, insurers and fire safety professionals that lithium-ion battery risk is no longer peripheral; it is a central risk.
Implications for the Fire Industry
The introduction of Class L is more than a technical amendment. It has practical implications across several areas of the fire sector.
Fire Risk Assessments
Where lithium-ion batteries are present, whether in charging areas, storage facilities, transport operations or end-use environments, risk assessments may now need to explicitly consider Class L fire scenarios.
This includes evaluating several elements, including:
- Battery storage density
- Charging infrastructure
- Ventilation
- Compartmentation
- Emergency response planning
- Evacuation procedures
The presence of a defined class helps formalise these considerations for fire risk assessors.
Equipment Selection & Suitability
Historically, lithium-ion battery fires have often been addressed under existing classes (typically Class A or electrical risk categories). The addition of Class L may encourage clearer differentiation when specifying suppression or containment solutions.
It may also influence future product testing methodologies, labelling and performance standards, as well as insurance requirements and therefore procurement frameworks
As standards bodies respond, we may see further development of harmonised testing protocols specific to lithium-ion battery fire performance.
Training & Competency
The addition of Class L reinforces the need for education across the sector.
Many incidents involving lithium-ion batteries are exacerbated by a lack of understanding of thermal runaway, which can result in attempting to move or handle compromised batteries. Additionally, using unsuitable extinguishing media and failing to monitor for re-ignition have worsened some lithium-ion battery fire events.
Clear classification supports clearer training. Fire safety professionals, facilities managers and responsible persons must understand that lithium-ion battery fires are not simply “another electrical fire”.
Policy & Regulatory Development
While ISO standards are voluntary, they frequently influence national standards, building codes and regulatory frameworks.
The inclusion of Class L provides a foundation upon which national fire authorities, certification bodies and testing houses, as well as government departments, can build more detailed guidance.
This classification will likely shape policy conversations in the years ahead, particularly as electrification and decarbonisation strategies accelerate globally.
A Sign of a Changing Risk Landscape
The addition of Class L to ISO 3941 is a recognition that the risk environment is evolving.
Just as Class F was introduced in response to the specific risks of cooking oils and fats, Class L reflects the reality of battery-powered technology becoming integral to modern life.
For fire industry professionals, this change provides a clearer framework for discussion, a more accurate language for risk identification and a foundation for more appropriate mitigation strategies
It does not, on its own, solve the challenges posed by lithium-ion battery fires, but it does formally acknowledge them.
Simplifying Complex Topics
Fire safety is a complex and evolving discipline. As new risks emerge, so too must our understanding.
At Firechief®, we believe that complex topics should be explained clearly and responsibly. Through our CPD-accredited lithium-ion battery training courses, we aim to demystify the risks, outline practical considerations, and help fire professionals make informed decisions in an increasingly electrified world.
Because clarity, especially when it comes to fire safety, matters.
This blog is provided for general informational purposes. Readers should consult relevant national standards, regulatory guidance and competent fire safety professionals when assessing lithium-ion battery risks in their specific environment.