Sector·4 min read
Lithium-Ion Battery and Energy Storage Facility Fire Safety
Lithium-ion batteries and energy storage facilities (BESS) carry a self-sustaining hazard unlike a classic fire: thermal runaway. When a cell overheats and decomposes it releases heat and flammable/toxic gas and propagates to adjacent cells; the gases accumulating before flame can cause an explosion (deflagration). Because thermal runaway generates its own oxygen, gaseous suppression can knock down flame but cannot stop propagation or reignition. This article covers battery risks, off-gas and explosion hazard, and the most effective solution — water-based cooling — together with early gas detection, ventilation/deflagration control and layered design under NFPA 855 / UL 9540A.
A-Pro Engineering
Lithium-ion batteries and energy storage facilities (BESS) carry a self-sustaining hazard unlike a classic fire: thermal runaway. This article covers battery risks and the most effective and correct system against fire on a research basis.
Risk profile: thermal runaway
In energy storage the real hazard is not the flame itself but the uncontrolled heat reaction that produces it. A cell starts to decompose and produce heat due to overcharge/over-discharge, internal short circuit (manufacturing defect/dendrite), mechanical damage or over-temperature. This heat accelerates the reaction further — the loop feeds itself.
Critical point: thermal runaway can generate its own oxygen through cathode decomposition. So it does not depend on oxygen from the air; this fundamentally changes the suppression strategy.
Propagation: from one cell to the whole container
The most dangerous aspect of thermal runaway is propagation:
- One cell’s heat carries adjacent cells to threshold temperature,
- It advances cell to cell → module to module → rack to rack,
- A single defective cell can drag the whole facility.
That is why the design goal is not merely to extinguish flame but to remove heat and stop propagation.
Off-gas and explosion (deflagration) risk
Before they ignite, cells release a large volume of flammable and toxic gas (off-gassing): hydrogen, carbon monoxide, hydrocarbons, electrolyte vapors and, from the electrolyte, toxic HF (hydrogen fluoride).
- Inside an enclosed container/room these gases accumulate,
- On meeting an ignition source, a sudden combustion-explosion (deflagration) occurs,
- This is a deadly scenario especially for responding personnel.
That is why early gas detection is the key to noticing the event before flame and explosion become danger. We covered industrial facility safety in general in a separate article.
Why isn’t gaseous suppression enough alone?
Gaseous agents (CO2, FM-200, Novec 1230, inert gases) work mainly by diluting oxygen or interrupting flame chemistry. They knock down open flame quickly — but:
- Because thermal runaway generates its own oxygen and is an internal heat reaction,
- After the gas disperses the cells keep heating, propagation continues,
- The battery can reignite even hours later.
So a gaseous system extinguishes the “flame” but does not remove the “heat.” It can be a supporting layer for early flame control in enclosed electronic volumes, but it is not the real solution in energy storage. We covered gaseous agent selection in a separate article; we also examined the limits of in-cabinet aerosol solutions in our aerosol article.
The most effective solution: water-based cooling
The shared conclusion of large-scale test standards and research (UL 9540A, FM Global, NFPA 855) is clear: the most effective approach is water-based cooling that removes heat. Water’s heat-absorption (cooling) capacity is far higher than other agents; this way it:
- Slows/stops thermal runaway from propagating to adjacent cells,
- Suppresses reignition,
- Protects the structure and neighboring equipment.
Two main applications stand out:
- Automatic sprinklers at appropriate density — cool the area for a prolonged period and protect the structure (NFPA 13 / NFPA 855),
- Water mist — high cooling with less water; fine droplets increase surface area. See our water mist article.
Note: water requires design alongside high-voltage DC; insulation, drainage and contaminated-water management are part of the design.
The correct system: layered design
No single suppression is sufficient alone. The correct system is layered:
- BMS (battery management system) — prevents overcharge/over-discharge/over-temperature (first line of defense),
- Early gas/off-gas detection — warns before flame,
- Ventilation + deflagration control — keeps gas below the LEL; NFPA 68 (venting) / NFPA 69 (explosion prevention),
- Water-based cooling — removes heat with sprinkler/water mist, stops propagation and reignition,
- Cell/module spacing and compartmentation — physically limits propagation.
Standards
- NFPA 855 — installation of stationary energy storage systems (primary standard),
- UL 9540 / UL 9540A — system safety and the thermal-runaway propagation test (directly drives the design),
- NFPA 68 / NFPA 69 — deflagration venting / explosion prevention,
- NFPA 13 — sprinklers, IEC 62933 — energy storage.
UL 9540A test data directly determines cell/module spacing, fire separation, and ventilation and suppression needs. Since storage is often installed together with solar/wind, see also our solar plant fire safety article.
Summary
Lithium-ion/energy storage fire safety is designed against thermal runaway and cell-to-cell propagation together with off-gas/deflagration risk. Because gaseous suppression knocks down flame but does not remove heat in this self-oxygenating reaction, it is inadequate alone; the most effective solution is water-based cooling that removes heat (sprinkler/water mist). The correct system is layered: BMS + early gas detection + ventilation/deflagration control + water-based cooling + spacing/compartmentation — all under NFPA 855 and UL 9540A. We also covered which building needs which system in our general article. At A-Pro Engineering we design integrated gas detection, deflagration control and water-based cooling suppression for energy storage facilities; contact us for your project.
This content is for information only. Binding design must be done project-specifically based on the cell chemistry, system architecture and UL 9540A test results, and the editions in force of NFPA 855, UL 9540/9540A, NFPA 13/68/69 and BYKHY.
© 2027 A-Pro Mühendislik. This is original technical content produced by A-Pro Engineering; all rights reserved. Copying, reproducing or republishing it in whole or in part without attribution and permission is prohibited.
Frequently asked questions
What is the biggest fire risk in a lithium-ion battery?+
The biggest risk is not a classic fire but thermal runaway: a self-sustaining exothermic chain reaction that begins when the temperature inside a cell rises uncontrollably. A cell starts to decompose due to overcharge, over-discharge, internal short circuit (manufacturing defect/dendrite), mechanical damage or over-temperature; heat and flammable and toxic gases are released. This heat triggers adjacent cells too, propagating from cell to cell, module to module and rack to rack. The critical point: because thermal runaway can generate its own oxygen through cathode decomposition, it does not depend on oxygen from the air; so methods that only try to cut off oxygen are not enough to stop it. In addition, a battery can reignite even hours after being knocked down.
What is thermal runaway and how does it propagate?+
Thermal runaway is when the temperature inside a cell exceeds a threshold, accelerating chemical decomposition that produces more heat, and this loop feeds itself. Typical sequence: (1) the cell heats and first releases flammable/toxic gas (off-gassing) — the earliest warning before flame; (2) if the temperature keeps rising the cell ignites, with jet flame and dense smoke; (3) the released heat carries adjacent cells to threshold temperature, starting propagation. The most dangerous aspect of propagation is that a single defective cell can drag the whole module, then the whole rack and container. That is why the design goal is not merely to extinguish flame but to remove heat and stop propagation and reignition.
How does the explosion (deflagration) risk arise in an energy storage facility?+
During thermal runaway, cells release a large volume of flammable gas (hydrogen, carbon monoxide, hydrocarbons and electrolyte vapors) before they ignite. Inside an enclosed container or room these gases accumulate; on meeting an ignition source, a sudden combustion-explosion (deflagration) occurs. This is one of the deadliest scenarios in energy storage facilities and is especially dangerous for responding firefighters. That is why protection includes mechanical ventilation to keep gases below the LEL (lower explosive limit), deflagration vent panels where needed (NFPA 68) and/or explosion-prevention measures (NFPA 69). Early gas detection is the key to noticing the event before flame and gas accumulation turn into danger.
Why is gaseous suppression (CO2, clean agent) inadequate alone?+
Gaseous suppression agents (CO2, FM-200, Novec 1230, inert gases) work mainly by diluting oxygen or interrupting the flame chemistry. This can quickly knock down open flame; but because lithium-ion thermal runaway generates its own oxygen and is an internal heat reaction, after the gas discharges and disperses the cells keep heating, propagation continues and the battery can reignite. In other words, a gaseous system can extinguish the 'flame' but does not remove the 'heat' and does not stop propagation. So gaseous suppression can be a supporting layer for early flame control in enclosed electronic volumes, but what energy storage really needs is a water-based system that removes heat (cools). Similarly, some in-cabinet solutions (aerosol, direct injection) do not provide adequate assurance without cooling support.
What is the most effective suppression system for lithium-ion/energy storage?+
The shared conclusion of research and large-scale test standards (UL 9540A, FM Global, NFPA 855) is clear: the most effective approach is water-based cooling that removes heat. Because water's heat-absorption (cooling) capacity is far higher than other agents, it slows/stops thermal runaway from propagating to adjacent cells and suppresses reignition. In practice two main forms stand out: (1) prolonged cooling of the area and protection of the structure with automatic sprinklers at an appropriate density; (2) high cooling with less water via water mist. But no single suppression is sufficient alone; the correct system is layered: prevention with the BMS + early gas/off-gas detection + ventilation and deflagration control (NFPA 68/69) + water-based cooling + cell/module spacing and compartmentation. The final choice is made project-based according to the facility type (container/building), cell chemistry and UL 9540A test results.
Which standards and legislation govern energy storage facility design?+
The primary reference is NFPA 855 (Standard for the Installation of Stationary Energy Storage Systems); for system safety UL 9540 and the UL 9540A test method that measures thermal-runaway propagation are decisive. These are accompanied by NFPA 68 (venting) and NFPA 69 (explosion prevention) for explosion/deflagration, NFPA 13 for sprinklers, gas/flame detection standards and the international IEC 62933 (energy storage). UL 9540A test data directly affects cell/module spacing, fire separation, and ventilation and suppression needs. In Türkiye, design is based on these standards together with BYKHY and the relevant OHS/electrical legislation. In storage systems installed together with solar/wind plants, the relevant generation-facility requirements are assessed together.
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