UL Solutions launches large-scale fire testing for Battery Energy Storage Systems

The new testing is conducted according to the sixth edition of ANSI/CAN/UL 9540A, the Standard for the Test Method for Evaluating Thermal Runaway Fire Propagation in Battery Energy Storage Systems. The updated method expands guidance for installation-level, large-scale fire testing, enabling UL Solutions to more closely replicate what happens when a fire starts inside an energy storage enclosure and how that fire might affect nearby equipment or buildings.

Thermal runaway is a battery failure condition in which overheating can cause the release of flammable gases and, in some cases, ignition. Understanding how this process unfolds at full installation scale is critical for evaluating the safety risks involved.

“Battery energy storage systems are being deployed at larger scales and closer to where people live and work,” said Wesley Kwok, vice-president and general manager of the Energy and Industrial Automation Group at UL Solutions. “This testing affords practising professionals the practical data they can use to evaluate site layouts, separation distances and fire protection strategies with greater confidence.”

Realistic installation conditions

During large-scale tests, UL Solutions intentionally initiates a fire within a BESS enclosure and observes how it develops under realistic installation conditions. The testing examines whether fire can spread between battery units, whether heat or flames could ignite nearby structures and how ventilation and gas release influence fire behaviour. It also evaluates how active and passive fire protection features perform when exposed to battery fires.

Test configurations are designed to mirror real installations, including outdoor containerised systems, indoor battery rooms and sites where multiple enclosures are grouped or stacked. Aligning test set-ups with actual layouts helps ensure results are practical and relevant.

The findings are documented in detailed reports that can be used by relevant authorities to evaluate installation proposals, review alternative design approaches permitted under current guidelines and assess whether manufacturer‑recommended clearances are appropriate. Battery energy storage system designers can use the same information to develop compliant and risk‑informed layouts, justify alternative designs and address permitting and relevant authority concerns early in the design process.

Fire and Rescue Services can also leverage the findings for hazard assessments, pre‑incident planning and response strategies.

Protecting firefighters and the public

“As communities expand their use of battery energy storage, we need to understand how these systems behave in a real emergency,” said Robert Sapien Jr, fire chief for the City of San José Fire Department.

He added: “Large-scale fire testing gives us the data we need to plan our response and protect both firefighters and the public. The insight gained is essential when it comes to adopting these systems safely.”

*Further information is available online at www.UL.com