Energy storage system (ESS) fire safety rests on four layers: choose and package cells so a single failure stays small, lay out the site so a failure cannot spread, detect trouble early enough to act, and plan the response with the local fire service before the first container is energized. Suppression, the part most people search for, is the last and least reliable layer. Current U.S. guidance puts explosion prevention ahead of putting the fire out.
This guide is written for engineers, project managers and permit leads who specify or approve battery energy storage systems (BESS). It covers how thermal runaway works, what layout and ventilation do, how detection should trigger action, what suppression can and cannot do, and what operators should have in place.
TL;DR
- Thermal runaway is the root hazard: a failing lithium-ion cell can pass the 1600°F (871°C) mark and push neighboring cells into failure, so containing it early matters more than extinguishing it later.
- Layout and enclosure design come first: noncombustible enclosures, separation distances tied to chemistry and wall rating, and deflagration venting do more than any agent inside the box.
- Detection must do something: gas and temperature alarms should shut the system down and start ventilation, not just notify someone.
- Suppression has limits. U.S. Department of Energy guidance favors preventing explosions and controlling spread, and a battery can reignite long after a fire looks out.
- Write the emergency response plan during design and review it with the local fire department.
Table of Contents
- Why thermal runaway drives every ESS fire safety decision
- Layout, enclosure and ventilation: the first line of defense
- Detection: early warning that triggers action
- Suppression: what it can and cannot do
- Codes, standards and testing
- Emergency response planning
- Smoke, air quality and runoff
- Our perspective: engineer the box so the fire has nowhere to go
- Specifying storage with fire safety built in
- A practical ESS fire safety checklist
- FAQ
- Sources
Why thermal runaway drives every ESS fire safety decision
A lithium-ion cell that overheats can enter thermal runaway: a self-reinforcing chain of chemical reactions that releases heat plus flammable and toxic gases. According to EPRI’s explosion hazards research, cells can exceed 1600°F (871°C), eject glowing hot particles, and trigger neighboring cells through conduction, convection or radiation from vent gases. The failure can travel from a cell to a module and then a rack.
Two features make this different from an ordinary electrical fire:
- The fuel is inside the cell. The reaction does not need outside oxygen to keep heating, so cooling the outside of a rack does not stop what is happening within.
- The gas is the bigger danger. Vented gas is flammable. If it collects in a closed enclosure and then meets an ignition source or fresh oxygen, the result is a deflagration, not just a fire.
The 2019 McMicken, Arizona incident, where four firefighters were injured, is the standard case study. The DOE’s 2024 Energy Storage Safety Strategic Plan cites it as an example of what happens when oxygen enters an enclosure already filled with flammable gases. That event reshaped how designers and responders think about opening doors on a venting container.
Chemistry changes the picture. Lithium iron phosphate (LFP) and nickel manganese cobalt (NMC) cells have different onset temperatures and different gas behavior, which is why separation rules differ between them. Our comparison of LFP and NMC batteries for engineers covers the thermal thresholds.
Layout, enclosure and ventilation: the first line of defense
Most fire risk is decided on the drawing board. Three design questions matter most.
Where the system sits and how far apart
FM’s guidance recommends noncombustible enclosures, separation distances based on battery chemistry and wall ratings, and placing systems outdoors or in dedicated buildings or cutoff rooms (FM Data Sheet 5-33). The NFPA Research Foundation’s landscape report summarizes the numbers: at least 5 ft between outdoor LFP containers, and for NMC containers 13 ft where wall construction is unknown or rated under one hour, or 10 ft with a wall rating of at least one hour.
| Container type | Wall rating | FM recommended separation |
|---|---|---|
| LFP, outdoor | Any | At least 5 ft |
| NMC, outdoor | Unknown or under 1 hour | 13 ft |
| NMC, outdoor | At least 1 hour | 10 ft |
These are recommendations from an insurer-backed research body, not a substitute for the code that applies at your site. Your authority having jurisdiction may require more.
Deflagration protection
Because gas accumulation is the explosion route, enclosures need a way to relieve pressure and clear gas. The same FM data sheet addresses deflagration vents and air circulation, and NFCC guidance says containers should have explosion protection or deflagration venting suited to the hazard and the battery technology. Where mechanical exhaust is used to prevent deflagration, the design target is to hold the environment below 25% of the lower explosive limit.
Temperature control
HVAC is a safety system, not just a comfort system. FM’s guidance includes HVAC that maintains operating temperatures, because cells held within their design window are far less likely to start the chain reaction. Cold-plate design and temperature alarm limits are covered in our piece on BESS thermal management.
Siting and local rules
The U.S. EPA advises complying with state and local siting requirements, using remote monitoring (infrared, thermal and fire detection), and talking to local first responders to build emergency response plans. In practice that means the fire marshal should see your layout before you finalize it, not after.
Detection: early warning that triggers action
Detection is only useful if it is tied to a response. Two signals matter:
- Temperature. The battery management system (BMS) temperature reading is the first warning of thermal runaway, according to NFCC guidance on grid-scale storage.
- Off-gas. Cells vent gas before they burn, so off-gassing detection can give earlier warning than heat or smoke.
The same guidance says that when a gas detector senses flammable gas, it should alarm, shut down the BESS and start full exhaust ventilation. Notice the order: the detector does not wait for a person. A system that only sends a text message at 3 a.m. leaves the gas to build.
A practical detection checklist for a design review:
- Does a gas detection alarm cause an automatic shutdown and full exhaust?
- Are temperature thresholds set at module level, not only at the container average?
- Can the site be monitored remotely, with infrared or thermal sensing where the EPA recommends it?
- Do alarm signals reach someone who can act, and does the fire department know what the alarm means?
- Are detectors tested on a documented schedule?
Suppression: what it can and cannot do
Searches for ESS fire suppression usually assume a sprinkler or clean agent can end the event. The evidence is more cautious. Suppression is often limited by the inability to cool every cell or stop internal propagation, and it can create an explosion risk by trapping flammable gas in an enclosure, with a deflagration possible when oxygen is introduced (DOE Strategic Plan).
Water and cooling
Water has high cooling capability and may prevent further cell-to-cell propagation within a BESS. The catch is delivery: water has to reach the affected cells, and large volumes may be needed, which raises firefighting water management questions for the site.
The defensive strategy
The NFPA Research Foundation report notes that industry practice increasingly favors a defensive containment strategy: let the fire burn out in a controlled way to avoid gas accumulation and explosion, instead of suppressing it and risking stranded energy or reignition. The DOE describes this as a shift toward prioritizing explosion prevention over suppression, since uncontrolled gas buildup endangers responders more than an enclosure burning out. EPRI describes controlled-burn approaches as aimed at preventing gas clouds from forming in enclosed battery spaces.
What this means for design: protect the neighbors. Separation, barriers and venting exist so that one unit can burn without taking the next one with it.
Reignition and stranded energy
A BESS has no single point of disconnect. Disconnects de-energize selected parts, but batteries remain energized and can reignite long after the initial extinguishment. Any response plan needs a long monitoring period and a clear rule for who declares the site safe.
For more on how agents, water and containment fit together, see our deeper look at what actually works in BESS fire suppression.
Codes, standards and testing
No single document covers everything, and the requirements shift by jurisdiction. In the United States, NFPA 855 and large-scale fire testing under UL 9540A shape what a permit file must show. Internationally, UL 9540/9540A and IEC standards provide the testing and safety framework that the UK and Ireland build into their own guidance.
If you are preparing a submission, these pages go deeper:
- NFPA 855 compliance requirements that permit leads document
- UL 9540A test levels to resolve before submission
- 2026 BESS standards project managers file for permits
Two habits save time. First, ask early which edition of each code the local authority has adopted. Second, gather test reports from the equipment supplier before design freeze, because test data on the actual cell, module and rack configuration drives the separation and venting decisions above.
Emergency response planning
An emergency response plan (ERP) belongs in the design stage, not the commissioning checklist. UK government guidance says operators should develop the plan early, consult the local fire and rescue service and keep documentation on site (HSE-backed guidance). U.S. model templates follow the same logic: the South Dakota PUC template is meant to support coordination with local responders, and responding agencies should review the site layout information before entry where practicable.
Before an incident
- Share site maps, equipment data, gas and electrical hazards, and contact lists with the fire department.
- Hold a walk-through with responders, including how to approach a venting container.
- Agree on what staff do and do not do during an event.
During an incident
Staff should prioritize evacuation, call emergency services and stay away from enclosures until experts say it is safe. An ERP sets the perimeter rule plainly: do not enter the site perimeter during a fire or off-gassing event unless there is an imminent threat to life. Never open a door on a container that may be full of gas to “take a look.”
After an incident
Treat the site as energized. Keep monitoring for reignition, restrict access, and coordinate with the fire service and the equipment manufacturer before any cleanup or removal.
Smoke, air quality and runoff
Community concern about smoke is understandable, so operators should be ready with facts. A 2025 Fire & Risk Alliance assessment published by the American Clean Power Association reports that BESS fires mainly emit carbon monoxide, carbon dioxide and volatile organic compounds, with trace gases depending on chemistry. It finds that emissions generally dissipate quickly outdoors and that sampling from available incidents found no concentrations posing a public-health concern or requiring remediation.
That is a reassuring finding, but it does not remove the need for local air monitoring during an event, and the report is an industry-association publication. Runoff from large volumes of firefighting water should still be planned for in site drainage.
Our perspective: engineer the box so the fire has nowhere to go
We make energy storage containers, mobile storage systems and the steel structures around them, so we see fire safety as a manufacturing problem as much as a controls problem. Our view is simple.
The best response to a thermal runaway event is the one you never need. That depends on what happens before the unit leaves the factory: consistent in-house production, strict quality control and an enclosure built for the real conditions it will face. A steel container with predictable geometry makes venting, separation and access planning easier for the engineer and the fire marshal alike.
We also think project teams should stop asking which suppression agent to buy and start asking what the system does in the first minute: does gas detection shut things down, does ventilation start, are neighbors protected by distance and construction? Current U.S. guidance points the same way, and it matches the engineering we put into custom, project-specific designs.
Finally, involve the manufacturer in the emergency response plan. Responders need container drawings, vent locations and access details, and the people who built the enclosure can supply them.
— Hu
Specifying storage with fire safety built in
If you are scoping a project, bring the safety questions to the supplier at the start: enclosure construction, ventilation and venting provisions, how the unit fits your separation plan, and what documentation it supports for permits. Our range includes commercial and industrial energy storage systems, grid-scale battery energy storage and mobile energy storage systems, plus the mobile PV-BESS power station and E-House for projects that need integrated, transportable solutions. Tell us your site conditions and code requirements, and our engineers will work through the details with you. Start from our battery energy storage system page or contact us through gq-international.com.
A practical ESS fire safety checklist
Use this as a design-review prompt, not a code substitute.
- Chemistry and testing: Do you have cell, module and rack test data that matches the product being installed?
- Placement: Is the system outdoors or in a cutoff room, with separation set by chemistry and wall rating?
- Enclosure: Is it noncombustible, with deflagration venting sized for the hazard?
- Ventilation: Does exhaust hold the space below 25% of the lower explosive limit?
- Detection: Do gas and temperature alarms shut down the system and start ventilation automatically?
- Monitoring: Is there remote thermal or infrared monitoring, and a defined alarm response?
- Response plan: Has the fire department reviewed the ERP and the site layout?
- Recovery: Is there a reignition monitoring plan and a rule on who clears the site?
FAQ
Does a fire suppression system stop a BESS fire?
Not reliably. Suppression often cannot cool every cell or stop propagation inside a module, and sealing gas into an enclosure can create explosion risk. Current DOE-aligned guidance leans toward explosion prevention and controlled burnout, with neighboring equipment protected by separation and barriers.
How far apart should battery containers be?
FM’s recommendations cited by the NFPA Research Foundation are at least 5 ft for outdoor LFP containers, and 10 to 13 ft for NMC depending on wall rating. Your local authority and the adopted edition of the code can require more, so confirm before finalizing a layout.
What is the earliest warning of a battery fire?
BMS temperature readings are a critical first warning, and off-gas detection may signal trouble even earlier. Guidance says a flammable gas alarm should shut down the system and start full exhaust ventilation automatically.
Are the fumes from an ESS fire dangerous to neighbors?
An industry-commissioned 2025 assessment found that emissions usually dissipate rapidly outdoors and that incident sampling showed no contaminants of public-health concern. Responders should still follow local guidance and monitor air during an event.
Can a battery reignite after the fire is out?
Yes. Batteries stay energized after disconnects open, and reignition can occur long after apparent extinguishment. Plans should include extended monitoring and controlled site access.
Sources
- Battery Energy Storage Systems Explosion Hazards, EPRI
- Energy Storage Safety Strategic Plan, U.S. Department of Energy
- DS 5-33 Lithium-Ion Battery Energy Storage Systems, FM
- Landscape of Battery Energy Storage System Hazards, NFPA Research Foundation
- Battery Energy Storage Systems: Main Considerations for Safe Siting, U.S. EPA
- Grid scale energy storage system planning guidance, NFCC
- Emergency Response Plan template for BESS, City of Sumner
- Health and safety in grid scale electrical energy storage systems, GOV.UK
- Appendix G, Emergency Response Plan Template, South Dakota PUC
- Assessment of Potential Impacts of Fires at BESS Facilities