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

The UL 9540A test method is designed to meet stringent fire safety and building code requirements for battery energy storage systems.
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UL 9540A, the Standard for Test Method for Evaluating Thermal Runaway Fire Propagation in Battery Energy Storage Systems

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.

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NFPA 855: Reinforcing large-scale fire testing

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: Reinforcing longstanding alignment with NFPA 855

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 9540A Test Method - 5th Edition

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Cell-level test

Cell-level testing evaluates the thermal runaway characteristics of the cell as well as the composition and flammability of the gases.                                                                              

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Module-level test

Module-level testing evaluates the tendency of cell thermal runaway propagation, the heat and gas release rate of the module, and the potential danger of ignition or deflagration.

UL Solutions Battery Unit Illustration

Unit-level test

Unit-level testing evaluates the likelihood of fire spread between modules, the unit's heat and gas release rates, and the potential for deflagration or re-ignition.

UL Solutions Battery Installation Illustration

Installation-level test

Installation-level mainly evaluates the effectiveness of the fire protection system, as well as the heat and gas release rate of the system and the danger of deflagration or re-ignition.

UL 9540A Test Method - 6th Edition

Please note: Unit-level test will still be required for: residential BESS, non-residential BESS with an active Thermal Runaway Propagation Prevention System (TRPPS).

UL Solutions Battery Cell Illustration

Cell-level testing

Cell-level testing evaluates the thermal runaway characteristics of the cell as well as the composition and flammability of the gases.                                                                              

UL Solutions Battery Module Illustration

Module-level testing

Module-level testing evaluates the tendency of cell thermal runaway propagation, the heat and gas release rate of the module, and the potential danger of ignition or deflagration.

UL Solutions Battery Installation Illustration

Installation Level - Large Scale Fire Test

Installation-level mainly evaluates the effectiveness of the fire protection system, as well as the heat and gas release rate of the system and the danger of deflagration or re-ignition.

Download the UL 9450A Test Method infographic

Download the e-Book: An Inside Look at the Updates to UL 9540A:2025 (5th Edition)

e-Book: An Inside Look at the Updates to UL 9540A:2025

Explore the key updates in UL 9540A:2025, including enhanced testing methods and definitions to improve safety in battery energy storage systems and address fire hazards.

The UL9540A test method is recognized in multiple industry standards and codes, including:

  • 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.

Choose UL Solutions for UL 9540A testing

UL Solutions conducts the UL 9540A test method at laboratories in the United States, China, Korea, Taiwan, Germany and other countries. 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.

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Meet our experts

LaTanya Schwalb is an expert in product safety certification and UL Standards for stationary batteries, energy storage systems, fuel cells and hydrogen generators.

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LaTanya Schwalb

Principal Engineer, Energy and Industrial Automation
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Let’s work together

Contact us today to discuss your battery ESS and learn how our UL9540A test method can help you streamline your compliance process and enhance safety.

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