Fire Suppression Strategies for Battery Energy Storage Systems (BESS): Extinguish or Let It Burn?

Designing a fire suppression strategy for a Battery Energy Storage System (BESS) is one of the most debated aspects of modern energy safety engineering. Unlike typical industrial or electrical fires, lithium-ion battery fires behave unpredictably and can be extremely difficult—sometimes impossible—to extinguish once thermal runaway begins.

As a result, designers and authorities are increasingly rethinking traditional suppression methods. In many cases, the most effective and code-acceptable approach may not be to extinguish the fire at all, but to control and contain it safely—the so-called “let it burn” or controlled burnout strategy.

Why BESS Fires Are Different

Lithium-ion cells store energy through electrochemical reactions. When damaged, overcharged, or exposed to heat, they can undergo thermal runaway, an uncontrolled self-heating process that rapidly releases heat, flammable gases, and pressure.

These gases—typically a mixture of hydrogen, carbon monoxide, and hydrocarbons—can ignite violently once exposed to an ignition source. In many cases, the reaction inside the cell cannot be reversed or extinguished with suppression agents because it is driven by the internal chemistry rather than external oxygen.

This means that once thermal runaway begins, suppression efforts often cannot stop the reaction—only limit its spread to nearby cells or containers. That distinction shapes how BESS fire protection strategies are engineered today.

What Codes and Standards Require

Both the International Fire Code (IFC) Chapter 12 – Energy Storage Systems and NFPA 855 – Standard for the Installation of Energy Storage Systems establish fire suppression requirements based on system type and location.

According to IFC Section 1206.2.8 and NFPA 855 Section 4.10.4, BESS installations must include a means of fire control and suppression, unless the system is located outdoors in a remote area and the Authority Having Jurisdiction (AHJ) approves an alternative protection method.

This performance-based flexibility recognizes that not all BESS fires can be effectively extinguished and that in certain configurations, passive containment and defensive cooling can provide equivalent or even superior safety outcomes.

Common Suppression Approaches

1. Water-Based Suppression Systems

Water is still the most effective medium for cooling adjacent cells and preventing propagation. Automatic sprinklers or deluge systems can control external fires and reduce the temperature of neighboring modules.

However, water cannot stop the internal chemical reaction driving thermal runaway, and in some cases, application may spread contaminated runoff or create additional hazards. Therefore, water-based systems are most effective for indoor or mixed-use installations, where containment and drainage systems are in place.

2. Clean Agent and Inert Gas Systems

Clean agents (e.g., FM-200, Novec 1230) and inert gases (e.g., nitrogen, argon) are designed to remove oxygen or absorb heat. While they can prevent ignition during the early stages of overheating, they have limited effectiveness once cells begin venting or burning.

These systems are better suited to prevention—detecting and acting early—rather than suppression of full thermal runaway events.

3. Aerosol Suppression Systems

Condensed aerosol agents offer compact and easy-to-install protection for small modular BESS units. They can suppress incipient fires and reduce re-ignition risk but, like gaseous systems, they cannot stop cell-level thermal runaway. Their use is typically confined to small-scale or distributed systems where rapid activation and local control are priorities.

4. Passive Containment and Controlled Burnout (“Let It Burn”)

For outdoor or remote BESS installations, many fire protection engineers now advocate a controlled burnout approach—allowing the affected container to burn out while protecting surrounding units and exposures.

This strategy focuses on containment and cooling, rather than extinguishment. Key design measures include:

• Fire-rated enclosures to contain heat and debris

• Adequate separation distances between containers, per NFPA 855 and UL 9540A test data

• Deflagration venting and pressure relief systems to manage internal gas buildup

• Water supply for defensive cooling of adjacent containers

• Emergency Response Plans (ERPs) defining responder standoff distances and defensive tactics

The “let it burn” strategy is not a hands-off approach—it’s a planned, engineered response. It relies on validated test data, hazard analysis, and coordination with the local fire department to ensure that the fire can self-extinguish safely without endangering personnel or property.

Using UL 9540A Testing to Guide Design

UL 9540A testing plays a vital role in determining which suppression strategy is appropriate. The test evaluates thermal runaway propagation, gas composition, and fire spread between modules and containers.

By using UL 9540A data, engineers can:

• Verify whether suppression is effective for the chosen system type

• Justify omission of suppression under NFPA 855 Section 4.10.4

• Design adequate spacing and venting systems for containment

• Support performance-based approvals from the AHJ

This data-driven approach replaces assumptions with evidence—allowing suppression and containment systems to be tailored to real-world performance.

The Role of Fire Departments and Emergency Response Planning

Fire suppression strategies are most effective when integrated into the Emergency Response Plan (ERP) required by IFC 1206.9 and NFPA 855 Section 4.2.9. The ERP should outline:

• Site access routes, hydrant locations, and isolation zones

• Communication protocols and defensive firefighting tactics

• Monitoring for toxic gases and smoke plumes

• Post-incident cooling, inspection, and cleanup procedures

For controlled-burn strategies, early engagement with the local fire department is crucial. Responders need clear documentation on when to intervene, how to protect exposures, and when to allow the system to burn itself out.

Choosing the Right Strategy

There is no universal solution for BESS fire suppression. The right strategy depends on:

• Battery chemistry and configuration

• Installation type (indoor vs. outdoor)

• Available test data (UL 9540A results)

• Site conditions and exposure risks

• Local code requirements and AHJ preferences

Some sites may require active suppression, while others can justify a passive containment approach. The goal in both cases is the same: prevent escalation, protect responders, and maintain public safety.

Conclusion

Lithium-ion battery fires challenge traditional fire protection methods, but codes like NFPA 855 and IFC Chapter 12 now provide the flexibility to match suppression strategies to system behavior. Whether through sprinklers, gas suppression, or a controlled burnout approach, each method must be justified through analysis, testing, and planning.

Ultimately, the decision isn’t between extinguishing or letting it burn—it’s about understanding how to design for control, containment, and safety in a rapidly evolving energy storage landscape.

For any further inquiries regarding this topic, as well as for code consulting and fire engineering design support related to your project, please don’t hesitate to contact us via email at contact@engineeringfireprotection.com.