Quick answers
What is thermal runaway in a lithium-ion battery?
Thermal runaway is a self-accelerating failure in which a lithium-ion cell generates heat faster than it can dissipate it. It can release flammable and toxic gases, cause fire and possible explosion, and spread heat to adjacent cells.
What are the warning signs of a failing lithium-ion battery?
Watch for heat, swelling, odour, leakage, hissing, popping, smoke or unexplained battery-management alarms. If these appear, warn others and evacuate immediately.
Can an ABC fire extinguisher stop a lithium-ion battery fire?
Assuming an ABC extinguisher can stop internal thermal runaway in a large battery system is a mistake. Extinguishing visible flames does not prove heat generation inside a cell has stopped, and cells can re-ignite.
How should damaged or swollen batteries be stored?
Quarantine swollen, hot, leaking, damaged, recalled or water-exposed batteries in an engineered location, separate from normal stock. Do not touch, carry or dismantle a suspect battery.
To protect against the dangerous possibility of thermal runaway, places where lithium-ion batteries are stored or made need special fire suppression systems.
What is Thermal Runaway?
Lithium-ion batteries are charged and drained to meet the grid’s energy needs. This flow of energy into and out of the batteries heats them up. When a battery is made wrong, a short can happen, which can cause thermal runaway.
Thermal runaway starts when a cell overheats and fails, producing heat it cannot shed. It can release harmful, flammable gases along with fire, and the heat can push the cells around it into the same failure. Fires in these batteries can get very dangerous, and they can start up again hours or days later because of thermal runaway.
Fire Suppression Systems
Because thermal runaway is so dangerous, battery areas need fire protection that is designed and tested for the exact batteries and layout. No single system suits every case:
- Water-based systems, such as sprinklers or water mist, can cool hot cells and limit spread when designed for the tested hazard.
- Gaseous systems, such as inert gas or clean agents, may knock down visible flames, but putting out flames alone is not enough: hot cells must be cooled or they can reignite.
- Large-scale fire testing, such as UL 9540A for battery energy storage, is used to check whether the chosen protection actually works.
Detection Systems
In places where lithium-ion batteries are stored or made, it is important to find a fire quickly. Some effective detection systems in these areas include:
- Off-gas detection, which senses gases a failing cell can give off before a fire develops
- Aspirating (air-sampling) smoke detection
What needs attention
- Extinguishing visible flames does not prove that heat generation inside a cell has stopped
- Gaseous agents may control surrounding flames but generally provide limited cooling of cells in continuing thermal runaway
- Water-based protection can provide important cooling and exposure control when designed and applied for the tested system
- Vent gases can be toxic and flammable before visible smoke or flame appears
- Early off-gas detection may add warning time but must be validated for cell chemistry, airflow and alarm thresholds
- State of charge, cell format and spacing materially change heat release and propagation behaviour
- Damaged, swollen, recalled, returned or suspect batteries need controlled quarantine—not normal stock storage
Controls that reduce risk
- Create separate inventories for cells, modules, finished packs, damaged returns and waste
- Record chemistry, model, state of charge, quantity and storage location in the emergency information pack
- Quarantine swollen, hot, leaking, damaged, recalled or water-exposed batteries in an engineered location
- Verify charger, BMS, fusing, contactors and temperature-monitoring compatibility
- Use representative propagation and fire-test evidence to approve rack spacing, barriers, ventilation and suppression
- Provide remote shutdown, clear signage, access and responder connection points
- Coordinate automatic detection, ventilation, suppression, alarms and shutdowns in one tested cause-and-effect matrix
- Plan extended thermal monitoring, safe dismantling, transport, disposal and contaminated runoff after an event
Common unsafe practices
- Calling the event 'thermal runway' instead of thermal runaway
- Listing inert gas, Novec, clean agent and water mist as equally effective universal solutions
- Assuming an ABC extinguisher can stop internal thermal runaway in a large battery system
- Designing from cell-level data when the installed rack or container has not been representatively tested
- Ignoring flammable off-gas accumulation and explosion pressure
- Mixing damaged returns with saleable stock or charging batteries in egress routes
- Placing emergency disconnects where responders must approach the hazard to use them
- Declaring the incident over immediately after flame knockdown without thermal monitoring and re-ignition planning
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