In short
- A cell in thermal runaway makes its own heat and flammable gas; removing oxygen does not stop it.
- The response is separation (fire-rated battery rooms), early off-gas detection and water that has been tested at scale.
- NFPA 855:2026 requires sprinkler designs for systems above 50 kWh to be validated by large-scale fire testing.
- Plan drainage so firefighting water cannot reach live IT.
Why lithium-ion fires are different
When a lithium-ion cell overheats, through a defect, damage, overcharge or a neighbouring fire, its internal reactions release heat faster than it can escape. Temperature climbs, the cell vents flammable and toxic gases, and the heat spreads to the next cell. This chain is thermal runaway.
Because the reaction supplies its own heat and does not depend on room oxygen, a gas agent or inert atmosphere can suppress the flames above the battery while the cells inside keep heating. Re-ignition hours later is common. Only cooling, usually large amounts of water, stops propagation.
What recent incidents showed
| Incident | What happened | Lesson |
|---|---|---|
| Daejeon, Korea · Sep 2025 NIRS government data center | Lithium-ion UPS batteries ignited during maintenance; 384 batteries destroyed, about 22 hours to control, 96 of 647 public services hit | Maintenance is a risk moment; battery fires last for hours |
| Singapore · Sep 2024 Digital Realty SIN11 | Battery room explosion; later water ingress forced a server-room power shutdown | Firefighting water must be kept away from IT |
| Pangyo, Korea · Oct 2022 SK C&C, Kakao | Battery in the electrical room caught fire; services disrupted for days | Separate batteries from the power train they back up |
| Strasbourg, France · Mar 2021 OVHcloud SBG2 | Building destroyed; no automatic extinguishing, one-hour-rated wooden ceiling | Construction and suppression basics still matter |
Sources and details are in the lithium-ion section on the home page.
Separation: contain it in its own room
- Dedicated battery rooms with fire-rated boundaries, not batteries inside the data hall or the switchgear room. Fire and Rescue NSW (June 2026) asks for FRL 240/240/240.
- Spacing and barriers between battery cabinets so one rack cannot ignite the next, following the maker's large-scale test results.
- Explosion control: vented gases can accumulate; exhaust ventilation or deflagration venting may be required.
- Fire service access from outside, so crews do not have to cross the data hall.
Earlier warning: off-gas and aspirating detection
Cells vent gas before they burn. Off-gas sensors in the battery room, linked to the battery management system, give minutes of warning to disconnect a string before runaway spreads. Combine them with aspirating smoke detection and route both into the same alarm stages as the rest of the site.
Water that has been tested, and somewhere for it to go
NFPA 855:2026 requires sprinkler designs for energy storage above 50 kWh to be validated by large-scale fire testing, not assumed from ordinary densities. In practice this means a water design matched to the battery product, often with higher densities than ordinary hazard sprinklers.
Water then has to go somewhere. Floor drains, bunds and segregation keep it out of electrical rooms and data halls, the lesson of SIN11. A gas system can still protect the room against ordinary fires, but it is not the battery solution.
Six questions for a battery room design
- Is the battery room a separate fire compartment with the rating the authority asks for?
- Does the battery maker have large-scale fire test data for this exact product and layout?
- Are off-gas detection and BMS alarms linked to the fire alarm stages?
- Is the water design validated for the battery, and where does the water drain?
- Can the fire service reach the room without crossing live IT?
- Is there a written procedure for maintenance work on live battery strings?
Questions about battery fires
Can a gas system put out a lithium-ion battery fire?
It can suppress the flames, but it does not cool the cells, so thermal runaway can continue and re-ignite. Separation, early detection and water are needed.
Are VRLA batteries safer than lithium-ion?
They do not go into the same self-sustaining runaway and release less energy, but they are heavier, larger and last less long. Most new data centers still choose lithium-ion and design the room for it.
What is NFPA 855?
The US standard for stationary energy storage systems. The 2026 edition requires large-scale fire testing to validate sprinkler designs above 50 kWh.
Where should UPS batteries sit?
In their own fire-rated room, close to the UPS but separated from the data hall and the switchgear, with outside access for firefighters.
Sources
- Incident reports via W.Media, The Register and Data Center Knowledge, as listed on the home page.
- NFPA 855 (2026); Fire and Rescue NSW guidance, June 2026.
- Design measures are typical practice; the authority having jurisdiction and the insurer decide.