The use of Lithium-ion batteries has significantly increased over recent years, being used to power handheld power tools, laptops, mobile phones, electric vehicles, and for energy storage.
Despite the many benefits, there is a significant risk of fire from this technology, with close to 5,000 fires recorded in the UK over the past 4 years, with incidents growing rapidly. These are having significant impact to organisations and fire and rescue services that are having to adapt to the new and growing technology.
One method of adaption, is the introduction of class L firefighting equipment, including fire extinguishers designed specifically for Lithium-ion battery fires. Introduced in the 2026 revision of BS ISO 3941:2026, this new equipment will help fire and rescue services and organisations respond more effectively to these fires. However, care still needs to be taken due to the nature and characteristics of Lithium-ion fires.
WHAT IS A LITHIUM-ION FIRE?
A Lithium-ion fire is an intense, rapidly developing fire caused by the failure of a Lithium-ion battery. When a Lithium-ion battery experiences mechanical damage (puncture, crushing, dropping), faults, overcharging or using the wrong charger, manufacturing defects, exposure to heat or direct sunlight, internal short circuits, or poor battery management systems (BMS), it can result in a chemical reaction called thermal runaway.
Thermal runaway is where the battery overheats, internal temperatures rise uncontrollably, chemicals within the battery cells breakdown releasing flammable gases which then ignite along with the flammable electrolytes. Once thermal runaway begins, it is difficult to stop, and neighbouring cells can ignite in a chain reaction, and materials of the battery casing and surrounding area provide extra fuel.
WHAT ARE THE CHARACTERISTICS OF A LITHIUM-ION FIRE?
Lithium-ion fires have significant characteristics that need to be understood so suitable and sufficient firefighting measures can be identified and implemented. Lithium-ion fires have extremely high temperatures, exceeding 1,000°C within seconds, together with intense jet‑like flames that are emitted from the cell vents, Additionally, fires may reignite even after being “extinguished”.
HOW ARE THEY DIFFERENT FROM OTHER FIRES?
Lithium-ion fires differ from other fires in a number of unique ways, particularly in how they start, how they burn, and what is required to stop them. Whereas typical fires (Class A, B, C, etc.) are caused by external ignition sources such as sparks, flames, heat, or electrical faults, Lithium-ion fires can start without an external ignition source as a result of an uncontrolled chemical reaction. Lithium-ion fire also produce their own oxygen during the reaction, helping sustain the combustion.
There are a number of early indicators that a battery is at risk of igniting so prompt action could be taken. Signs include swelling or bulging of the battery casing, abnormal heat, hissing, popping, or cracking sounds, a sweet, solvent‑like smell, and white or grey smoke before ignition.
WHAT TYPE OF FIREFIGHTING PROVISION IS AVAILABLE?
There are a number of active firefighting provisions available to distinguish Lithium-ion fires. These include fixed suppression and water-mist systems, and portable fire extinguishers, which aim to rapidly cool the battery, and neutralise the chemical reaction.
Class L firefighting provision will contain additives F-500 EA or vermiculite to tackle the unique characteristics of a Lithium-ion fire. F-500 is an encapsulater additive that has been proven to provide rapid, deep cooling, encapsulate flammable electrolytes and gases, reduce explosive vapours and toxic emissions, and interrupt thermal runaway. Vermiculite will create a non‑flammable Oxygen Barrier, provide rapid cooling, and create a thermal and physical insulating layer. Both products are non-conductive and address the unique characteristics of a Lithium-ion fire.
Fixed suppression and water-mist systems are recommended by specialist fire‑safety professionals as one of the most effective methods, because they can cover a large area, and cool the battery safely and rapidly whilst also neutralising the chemical reaction. However, these systems are expensive to install and maintain and would not be suitable for small batteries and installations.
WHAT ABOUT PORTABLE FIRE EXTINGUISHERS?
Portable fire extinguishers are designed to provide immediate fire response against small fires, and for life safety including keeping evacuation routes clear of fire, smoke, and heat for the evacuation of occupants.
Conventional fire extinguishers may work on Lithium-ion fires. Class A, B, & D extinguishers could all work on Lithium-ion fires and surrounding areas where applicable and safe. However, it is not advised to use Class C extinguishers, as Lithium-ion fires produce oxygen during the chemical reaction, rendering CO2 extinguishers ineffective, and CO2 and wet chemical extinguishers will aid in the cooling of the battery, but do not stop the thermal runaway.
Class L fire extinguishers also contain additives F-500 EA or vermiculite to tackle the unique characteristics of a Lithium-ion fire. Class L extinguishers are currently the most effective purpose‑designed portable extinguishers for Lithium-ion battery fires because they are engineered specifically to address thermal runaway, rapid heat release, flammable gas venting, and re‑ignition risks; behaviours that traditional Class A, B, C & D extinguishers cannot control.
WHAT SIZE LITHIUM-ION FIRE WOULD CLASS L EXTINGUISHERS BE EFFECTIVE?
Due to the characteristics of Lithium-ion fires, and in most workplace, there are likely multiple batteries present, portable fire extinguishers found in most workplaces would still have limited effect, especially on larger systems. For e.g. – 1, 6-9 litre class L fire extinguisher would be needed to extinguish a power tool battery or a laptop battery. 2, 6-9 litre class L fire extinguishers would be needed to extinguish an e-scooter battery. Both are small scale and temporary solutions until the Fire and Rescue Service (FRS) arrive.
Portable extinguishers alone are not suitable for Electrical Vehicle (EV) and larger installations (Battery Energy Storage System (BESS)) fires but would be suitable for initial suppression and protecting people and escape routes. For EVs and larger installations (Battery Energy Storage Systems (BESS)), a full suppression or water mist system would be required for the long‑duration water cooling and neutralising of larger chemical reactions until the Fire and Rescue Service (FRS) arrive.
SHOULD YOU ADD CLASS L FIRE EXTINGUISHERS TO YOUR WORKPLACE?
Class L firefighting provision should be considered whenever Lithium-ion battery risks exist that cannot be adequately controlled through existing fire safety measures. To determine your risks and needs, a suitable and sufficient fire risk assessment should be undertaken by a competent Fire Risk Assessor and regularly reviewed.
Written by Daniel Prosser, MSc CMIOSH L4DipFRA OSHCR
Health, Safety and Wellbeing Professional