In brief
A fire in a lithium-ion battery starts with thermal runaway, in which heat inside the cell feeds itself and grows; flammable and toxic gases are released, and the fire can reignite after it has been extinguished. The way to reduce the risk is to charge with the manufacturer's charger in an area separated from combustible material, covered by detection and not blocking escape routes, and to quarantine damaged batteries. First response may be possible for a small power tool battery; if thermal runaway has started in a forklift battery, the right decision is to evacuate and call the fire brigade.
Why is a lithium battery fire different?
In warehouses, forklifts and pallet trucks with lithium-ion batteries are now used alongside forklifts with lead-acid batteries, and cordless power tools are common in workshops. When battery technology changes, the risks of the charging area change too. The prominent hazards in charging a lead-acid battery are the hydrogen released and contact with acid. A lithium battery fire, however, works through a different mechanism: thermal runaway.
Thermal runaway is a self-feeding chain in which heating that starts in one cell accelerates the chemical reactions inside it and those reactions produce more heat. The cell heats up, swells, releases gas and can ignite; the heat passes to neighbouring cells and the event spreads to the whole battery. During this process:
- Flammable and toxic gases are released. The smoke can contain irritant and toxic substances, including fluorinated compounds, and can accumulate in an enclosed charging room.
- The extinguisher does not stop the reaction inside the cell. Even if the visible flame is suppressed, the cells can continue to heat up.
- Reignition occurs. A battery thought to have been extinguished can reignite hours or even days later.
The main causes that trigger thermal runaway are mechanical damage (impact, dropping, puncture), an unsuitable charger or overcharging, external heating and manufacturing defects in the cell. Measures are built around these causes.
Which equipment is charged, and where?
The first step is to draw up an inventory of the lithium batteries at your workplace. Most businesses count only forklifts; yet the risk is much more scattered.
| Equipment | Typical charging location | Prominent risk |
|---|---|---|
| Lithium-ion forklift and stacker | Charging point inside the warehouse | Large battery, long charging, impact damage |
| Electric pallet truck | Loading ramp or corridor edge | Charging on an escape route, unattended charging |
| Cordless power tools (drill, grinder, screwdriver) | Workshop bench, cabinet | Mixed-up chargers, dropped batteries |
| Handheld terminals, radios, barcode scanners | Office and warehouse charging stations | Charging many devices together |
| Employees' e-scooters and e-bikes | Sockets inside the office or warehouse | Uncontrolled devices and chargers |
The last row is often overlooked. Employees charging their personal e-scooters and e-bikes inside the building means unattended charging of batteries of unknown quality. Set a rule for charging outside the building or in a designated area.
How should the forklift battery charging area be laid out?
Determine the layout of the forklift battery charging area through the risk assessment, according to the battery and charger manufacturer's instructions, the building's fire design and your insurer's recommendations. The following principles apply in every case:
- Separate it from combustible material. The charging point should not be next to pallet stacks, packaging material or easily ignited stock. This separation is especially important in textile and paper warehouses; see fire load in textile warehouses.
- Do not block the escape route. The charging point is not placed in front of an emergency exit door or in the only escape corridor. A burning forklift can block the exit completely.
- Provide detection and visibility. The charging area should be within the coverage of the fire detection system. This is especially important if charging is done outside working hours.
- Use the manufacturer's charger. A charger unsuitable for the battery can cause overcharging and heating. Chargers are matched to the equipment and labelled.
- Have the electrical installation inspected. The circuit feeding the charging points should be suitable for the total load. The internal electrical installation and earthing are subject to periodic inspection at least once a year under Annex III of the Work Equipment Regulation; forklifts are also subject to annual inspection under the same annex.
- Protect against impact. Barriers separating the charging point from forklift traffic prevent impacts to the battery and charger.
- Plan for extinguishers and cooling. An extinguisher is kept near the charging area; access by a fire hose cabinet or hydrant is important for cooling.
A battery charging room where lead-acid batteries are used needs ventilation against hydrogen and keeping ignition sources away; these rules are in our article on pallet trucks and stackers. If both technologies are used in the same room, the measures for both are applied together.
Damaged batteries and battery storage
A significant share of thermal runaway incidents start with a damaged battery continuing to be used or charged. A battery showing any of the following signs is taken out of service:
- Swelling, deformation, cracking or puncture
- Having been struck, dropped or submerged in water
- Heating more than normal, smell, noise or smoke
- Charging taking unusually short or long
A damaged battery is not connected to a charger and is not put back on a shelf inside the building. It is kept in a quarantine area away from combustible material, where it can be observed and in line with the manufacturer's instructions, and is handed over to the manufacturer or an authorised collection company. The battery storage area for spare batteries is set up on the same principles: separate from combustible stock, outside the escape route, within detection coverage. For how used cells and batteries start fires at recycling facilities, see our article on OHS at recycling facilities.
Extinguishing a lithium-ion battery fire: the limits of response
The most important information to give workers on extinguishing a lithium-ion battery fire is what they should not do.
| Situation | Do | Do not |
|---|---|---|
| A power tool battery is smoking | If safe, cut power to the charger, move away, raise the alarm; if trained, suppress the surrounding fire with an extinguisher and cool with water | Try to carry the battery by hand, lean over it |
| Smoke or flame from a forklift battery | Evacuate the area, call 112, tell the fire brigade it is a lithium battery and where it is | Try to move the forklift, go into the smoke |
| The fire has been extinguished | Keep the area closed, monitor for reignition, hand the battery over to authorised persons | Put the battery straight back on a shelf or into a waste container |
In these fires, water is the fire brigade's main tool because of its cooling effect; a portable extinguisher may suppress the visible flame but does not stop the heating inside the cell. Class D in our article on types of fire extinguisher is for metal fires; do not equate a lithium-ion battery fire with this class and prolong the response by relying on a special extinguisher. Because the smoke is toxic, no one enters an enclosed charging room without respiratory protection.
Risk assessment, emergency plan and training
Switching to lithium battery equipment is a change of technology and equipment that requires the risk assessment to be renewed (Art. 10 of Law No. 6331 on Occupational Health and Safety and the Regulation on OHS Risk Assessment). The assessment addresses charging points, storage areas, the decision on out-of-hours charging and the damaged battery procedure separately. A "battery fire in the charging area" scenario is added to the emergency plan: who will raise the alarm, who will cut the power, what information will be given to the fire brigade and through which door evacuation will take place are written down. For the general structure of the plan, see our article on how to prepare an emergency plan.
Forklift operators and those working in the charging area should learn the signs of a damaged battery and the limit of first response in practice. In our fire training service, Bursa Sistemer OSGB practises extinguisher use and the decision to abandon a response, and in our risk assessment service we enter charging and storage areas into the assessment. For other topics specific to warehouse businesses, see our logistics and warehousing page, and for forklift and electrical installation inspection dates, the OHS calendar tool.
Frequently Asked Questions
Can a lithium-ion forklift be left charging overnight?
This decision is made according to the risk assessment and the manufacturer's instructions. If out-of-hours charging is done, the charging area should be within fire detection coverage and separated from combustible material, the manufacturer's charger should be used, and a damaged battery should never be connected to a charger.
Which extinguisher is used on a lithium battery fire?
Portable extinguishers can suppress the visible flame but do not stop thermal runaway inside the cell. For a small power tool battery it may be possible to suppress the surrounding fire and cool with water; for large batteries the right decision is to evacuate and call the fire brigade.
What should be done with a swollen battery?
A swollen battery is not used and not connected to a charger. It is kept in a quarantine area away from combustible material where it can be observed, and is handed over to the manufacturer or an authorised collection company.
Do lead-acid battery charging room rules also apply to lithium?
Partly. With lead-acid batteries the prominent issues are hydrogen accumulation and acid splashes; with lithium batteries, thermal runaway, toxic smoke and reignition come to the fore. If both technologies are in the same area, the measures for both are applied together.
Fire classes, choosing the right extinguisher, hands-on extinguishing in a safe open area and an evacuation drill, all in one training.
Bursa SİSTEMER OSGB Technical Team — written from the field experience of our OHS specialists and workplace physicians. Legal information is valid as of the publication/update date; contact us for an assessment specific to your business.