Recently, UL released the outline for UL 9540B Outline of Investigation for Large-Scale Fire Test for Residential Battery Energy Storage Systems. We anticipate many questions and are therefore providing answers in advance.

Q: What is the background for the development of UL 9540B?

A: Some Authorities Having Jurisdiction (AHJs) in the United States indicated that the UL 9540A test series alone was not sufficient to meet the requirements of the 2022 California Fire Code, necessitating additional large-scale fire testing. Therefore, UL 9540B was developed based on input from fire departments, incorporating UL 9540A testing experience, aimed at addressing concerns from various AHJs and fire departments.

Q: What are the differences between UL 9540A and UL 9540B?

A：

1. Scope: UL 9540B specifically targets residential energy storage systems of 20 kWh or less, excluding commercial or industrial energy storage systems.
2. Testing Content: UL 9540A requires testing at the cell, module, and unit levels, while UL 9540B only requires cell-level testing and fire spread testing.
3. Report: UL 9540A produces three test reports used to assess the system’s ability to manage thermal runaway propagation due to battery faults. UL 9540B produces one test report focused on evaluating fire spread and its thermal impact on the surrounding environment.

Q: If a product has completed UL 9540A testing, can any data be used for UL 9540B?

A: The UL 9540A cell-level test report can be used for UL 9540B cell testing. However, due to UL 9540B being a different testing method, fire spread testing under UL 9540B must still be completed.

Q: Are residential energy storage systems required to be tested under both UL 9540A and UL 9540B?

A: Not necessarily. To obtain UL 9540 certification, according to installation standards (NFPA 855, IRC), residential energy storage systems must meet the unit-level performance standards of UL 9540A when the spacing between individual battery energy storage systems is less than 0.9 meters. Some AHJs may require manufacturers to provide test data for large-scale fire testing based on local regulatory requirements, such as the California Fire Code. However, specific methods for large-scale fire testing have not yet been published. UL 9540B aims to provide a consistent testing method for large-scale fire testing to meet these AHJs’ requirements.

Q：How does UL 9540B help me get my products accepted into the US or other markets?

A: UL 9540 certification and UL 9540A testing are required in UL 9540 and NFPA 855 to get products accepted into the U.S. and other markets. However, some jurisdictions in North America do not consider UL 9540A to be representative of a large-scale fire test as required by their local fire code—the 2022 edition of the California Fire Code, for example. In those cases, the Code Authority requires an additional large-scale fire test for residential energy storage systems, and this is where UL 9540B fits in. UL 9540B was developed to address the concerns of code authorities related to fire propagation risks in a residential ESS experience due to a thermal runaway propagation event.

Q：Is UL 9540B intended to become a Standard?

A: Yes, there are plans to make UL 9540B the same standard as UL 9540A. Currently UL 9540B is released as an outline to address the immediate needs of the AHJ.