BS ISO 3941:2026: Class L Lithium Battery Fires
BS ISO 3941:2026: What the New Class L Fire Classification Means for Lithium-Ion Battery Fire Safety
🔋 Lithium-ion batteries are now part of everyday life. They are found in mobile phones, laptops, tablets, power tools, e-bikes, e-scooters, electric vehicles, battery storage systems, cleaning equipment, forklift trucks and many other rechargeable devices used across commercial, industrial, residential and education premises.
🔥 As their use has increased, so has the need to properly recognise the fire risks associated with them. BS ISO 3941:2026 has introduced an important update to fire classification by recognising a new category: Class L fires.
What is BS ISO 3941:2026?
📘 BS ISO 3941:2026 is the British adoption of the international standard for the classification of fires. Its purpose is to classify fires according to the nature of the material or fuel involved.
🧯 Traditionally, fire classifications have included familiar categories such as Class A for solid combustibles, Class B for flammable liquids, Class C for gases, Class D for metals and Class F for cooking oils and fats.
⚡ The 2026 update is significant because it introduces Class L for fires involving lithium-ion cells and batteries where no lithium metal is present.
What is a Class L fire?
🔋 A Class L fire is associated with lithium-ion cells and batteries. This is important because lithium-ion battery fires do not behave in the same way as many traditional fire types.
🔥 These fires can involve thermal runaway, rapid heat release, toxic and flammable gases, cell-to-cell propagation, re-ignition and difficult post-fire management. In simple terms, the battery can continue to generate heat internally, even when flames appear to have been reduced or extinguished.
⚠️ This is why lithium-ion battery fires should not simply be treated as a normal electrical equipment fire or a standard Class A fire involving plastics and packaging.
Why lithium-ion battery fires are different
🌡️ Lithium-ion batteries store a large amount of energy in a compact space. If a battery is damaged, poorly manufactured, overcharged, exposed to heat, incorrectly charged or abused, it can fail internally.
💨 When failure occurs, the battery may vent hot, toxic and flammable gases. In some cases, cells can rupture, eject burning material or spread heat to adjacent cells within the same battery pack.
🚫 This means that a small incident involving one device can develop quickly, particularly where multiple batteries are stored or charged together.
Where might Class L risks be found?
🏢 Many businesses now have lithium-ion battery risks on site without necessarily thinking of them as a specific fire hazard. Common examples include:
🔋 Staff charging e-bikes or e-scooters at work.
💻 Laptop, tablet and mobile phone charging areas.
🛠️ Cordless power tools and battery charging stations.
🧹 Battery-powered cleaning equipment.
🚚 Forklift truck and warehouse equipment batteries.
🚗 Electric vehicle charging points.
🏫 Schools, colleges and offices using large numbers of rechargeable devices.
🏭 Battery storage, recycling, repair, logistics or manufacturing environments.
Does BS ISO 3941:2026 mean every building now needs a lithium battery extinguisher?
🧯 Not automatically. This is one of the most important points for duty holders to understand.
⚠️ The introduction of Class L helps identify lithium-ion battery fires as a distinct type of fire risk, but it does not mean every extinguisher labelled as "lithium" is automatically suitable for every lithium-ion battery scenario.
✅ The correct approach is to assess the actual risk. This includes the type of batteries present, their size, quantity, location, charging arrangements, proximity to escape routes, surrounding combustibles, occupancy profile and whether any proposed firefighting equipment has suitable test evidence for the battery risk being protected.
🚫 For example, a small mobile phone battery risk is very different from a room containing multiple e-bike batteries, power tool charging racks or commercial battery storage equipment.
How does this affect BS 5306-8 fire extinguisher provision?
📘 The current British Standard for the selection and positioning of portable fire extinguishers is BS 5306-8. This standard remains the key reference document for fire extinguisher provision within buildings.
🔄 Following the introduction of the new Class L fire classification in BS ISO 3941:2026, BS 5306-8 is expected to be revised to take account of this new classification and to provide clearer guidance on portable fire extinguisher provision for lithium-ion battery risks.
🧯 Until the revised version of BS 5306-8 is formally approved and released, Kings Fire will continue to take a sensible, risk-based approach. This means considering the type, size, quantity, location and charging arrangements of lithium-ion batteries before recommending any fire extinguisher provision.
✅ Once the revised guidance is published, our engineers will follow the updated British Standard and provide customers with the necessary advice going forward.
What about CO₂ extinguishers?
⚫ CO₂ extinguishers can be useful for certain electrical equipment fires, particularly where live electrical equipment is involved. However, CO₂ should not be seen as a complete lithium-ion battery fire solution.
🌡️ The main issue with lithium-ion batteries is heat and thermal runaway. CO₂ does not provide the sustained cooling needed to deal with cells that are overheating internally or propagating to adjacent cells.
⚠️ Larger CO₂ extinguishers can also create oxygen displacement concerns in small or poorly ventilated rooms, so extinguisher selection must always consider both the fire risk and the safety of people using the equipment.
What should Responsible Persons do now?
✅ The introduction of Class L is a useful reminder that lithium-ion battery risks should be specifically considered within the fire risk assessment.
📋 Responsible Persons should review whether lithium-ion batteries are present, where they are stored, where they are charged and whether existing fire precautions remain suitable.
🔌 Charging should be managed carefully. Batteries should not be charged in escape routes, near combustible materials or in areas where a fire would quickly affect evacuation.
👀 Charging areas should ideally be visible, controlled and subject to clear rules. Staff should be told not to use damaged batteries, non-approved chargers or cheap replacement components from unknown sources.
🚪 Escape routes, staircases, corridors and final exits should be kept free from battery charging and battery storage wherever possible.
🧯 Fire extinguisher provision should be reviewed by a competent fire safety provider. The focus should be on risk-appropriate equipment, credible test evidence and clear user instructions rather than simply adding products because they are marketed as "lithium battery extinguishers".
📚 Staff should also understand what to do if a battery begins smoking, hissing, swelling, overheating or giving off an unusual smell. In many cases, the safest action is to raise the alarm, evacuate the area and call the fire and rescue service.
Practical steps for businesses
✅ Identify all lithium-ion batteries used, stored or charged on site.
✅ Avoid charging batteries in escape routes or communal circulation areas.
✅ Use manufacturer-approved chargers and charging leads.
✅ Remove damaged, swollen, leaking or overheating batteries from use immediately.
✅ Keep batteries away from combustible storage.
✅ Consider controlled charging areas for power tools, e-bikes, e-scooters and commercial equipment.
✅ Review fire detection provision where batteries are stored or charged.
✅ Review emergency procedures and staff training.
✅ Ensure your fire risk assessment specifically considers lithium-ion battery risks.
✅ Ask for proper evidence before installing any specialist lithium-ion battery firefighting equipment.
How Kings Fire can help
🧯 Kings Fire Ltd can help businesses review their lithium-ion battery risks as part of a fire risk assessment, extinguisher survey or wider fire safety review.
📋 We can look at where batteries are being used, stored and charged, whether they affect escape routes, whether additional controls are needed and whether existing fire extinguisher provision remains appropriate.
🔥 BS ISO 3941:2026 does not mean panic buying new equipment. It means taking a sensible, evidence-led approach to a recognised and growing fire risk.
📞 If your business uses lithium-ion batteries and you are unsure whether your current fire precautions are suitable, Kings Fire can help you review the risk and put practical measures in place. Call our friendly team on 01462 337037 or use the enquiry form below to contact us.