UL Solutions Launches Large-scale Fire Testing for Battery Energy Storage Systems

• New large-scale fire tests show how battery energy storage system (BESS) fires can spread between units and to nearby buildings.
• Test results help code officials set separation distances and review fire protection plans using real-world fire data.
• Fire departments gain clearer insight into potential fire growth and response strategies for battery energy storage installations.

NORTHBROOK, Ill. - April 23, 2026 - UL Solutions (NYSE: ULS), a global leader in applied safety science, today announced enhanced large-scale fire testing for battery energy storage systems (BESS) to give code authorities and fire service professionals clearer, real-world information about how battery fires may start, grow and spread.

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 safety risks.

"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 gives authorities and fire departments practical data they can use to evaluate layouts, separation distances and fire protection strategies with greater confidence."

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 behavior. 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 containerized systems, indoor battery rooms and sites where multiple enclosures are grouped or stacked. Aligning test setups with actual layouts helps ensure results are practical and relevant.

The findings are documented in detailed reports that can be used by code authorities to evaluate installation proposals, review alternative design approaches permitted under fire and building codes and assess whether manufacturer-recommended clearances are appropriate. Battery energy storage system designers can use the same information to develop compliant, risk-informed layouts, justify alternative designs and address permitting and code authority concerns early in the design process. Fire departments can also leverage the findings for hazard assessments, pre-incident planning and response strategies.

"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 of the City of San José Fire Department. "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 to adopting these systems safely."

Learn more about how the latest edition of UL 9540A supports safer deployment of battery energy storage technologies through insights grounded in real-world fire scenarios: https://www.UL.com/services/UL-9540A-test-method.

About UL Solutions
A global leader in applied safety science, UL Solutions Inc. (NYSE: ULS) transforms safety, security and sustainability challenges into opportunities for customers in more than 110 countries. UL Solutions delivers testing, inspection and certification services, advisory offerings and software solutions that support our customers' product innovation and business growth. The UL Mark serves as a recognized symbol of trust in our customers' products and reflects an unwavering commitment to advancing our safety mission. We help our customers innovate, launch new products and services, navigate global markets and complex supply chains, and grow sustainably and responsibly into the future. Our science is your advantage.

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UL Solutions
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UL Solutions
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