UL 9540A Test Method for Battery Energy Storage Systems (BESS)

UL 9540A is the American and Canadian national standard for assessing fire propagation related to thermal runaway events in battery energy storage systems (ESS). We offer testing that aligns with both the 5th and 6th editions of UL 9540A, giving customers the flexibility to choose the edition that best matches their project and compliance strategy.

Testing to these national standard requirements is an essential element of due diligence. UL 9540A provides a methodology for testing a system’s safety-related behavior when the design or installation conditions of an ESS exceed the limits set by the National Fire Protection Association (NFPA) 855, NFPA 1, the International Fire Code (IFC), or the International Residential Code (IRC).

UL 9540A is the only consensus standard explicitly cited in NFPA 855 for large-scale fire testing and the only national standard in the U.S. and Canada for fire safety testing methods for battery ESS.

The 2026 edition of NFPA 855 introduces significant revisions that emphasize the importance of large-scale fire testing. A new section, Annex G.11, outlines expectations for this test, focusing on scenarios where fire could spread from one BESS to another. This addition reflects growing concerns among authorities having jurisdiction (AHJs) and fire safety professionals about real-world failure conditions and the need for robust evaluation methods. Annex G.11 provides guidance on initiating a developed fire condition, evaluating separation distances and considering the role of active fire protection systems.

UL 9540A has long been the benchmark for assessing thermal runaway and fire propagation in BESS. Its revisions continue to reinforce longstanding alignment with NFPA 855, allowing testing protocols to reflect the latest installation safety requirements. UL 9540A, Ed. 6, updates the installation-level test, introducing a challenging fire scenario and assuming a post-deflagration condition to evaluate enclosure design, separation distances and, for indoor systems, the effectiveness of building-based fire suppression systems.

• UL 9540, the Standard for Energy Storage Systems and Equipment.
• American and Canadian National Safety Standards for Energy Storage.
• International Code Council (ICC) IFC.
• NFPA 855, the Standard for the Installation of Stationary Energy Storage Systems.
• Various local, state and international building and fire codes.

UL Solutions conducts the UL 9540A test method at laboratories in the United States, China, Korea, Taiwan, Germany and other countries. For cell to large-scale fire testing, our battery safety experts will work with you to develop a test plan tailored to your specific needs. As a leader in battery safety technology, we offer:

• Full fire testing facilities, eliminating the need for subcontracting.
• Expert engineering and research teams with in-depth knowledge of battery chemistries and fire suppression.
• A proven track record serving fire departments, electrical inspectors and building officials.
• Proactive planning for project requirements and transparency in our proposals.