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UL 9540A establishes a new precedent in the energy storage system (ESS) testing and certification ecosystem

CSA Group comments from Dana Parmenter.

“The release of the 6th Edition of UL 9540A in March 2026 establishes a new precedent in the energy storage system (ESS) testing and certification ecosystem. This change will raise many questions for manufacturers around enforcement timelines, jurisdictional adoption, and how updated requirements may be interpreted by AHJs.

“This edition expands testing expectations and introduces large-scale fire (LSFT) testing requirements within the certification process. Section 10 requires LSFT to demonstrate that fire will not propagate between ESS units. This change is part of a larger trend across ESS standards, placing greater emphasis on LSFT as it relates to system-level safety.

“While UL 9540A addresses the safety testing requirements referenced by NFPA 855, Authorities Having Jurisdiction (AHJs) often request additional performance-based data to support site-specific evaluations. NFPA 855 Section 9.2.1.2.1 requires large-scale fire testing to characterise gas composition and demonstrate non-propagation between ESS units, which inherently involves gas analysis and calorimetric data such as heat release rate (HRR). Previous editions of UL 9540A did not explicitly incorporate large-scale fire testing. The 6th Edition now addresses spacing and fire propagation as safety considerations within the certification framework. Performance-based characterisation, including heat release rate, target unit measurements such as heat flux, operation of detection systems and BMS data, as well as a flexible framework for acquiring data needed for the fire protection engineer analysis, continues to be addressed through CSA/ANSI C800:25.

“NFPA 855 Section 9.2.2.2 requires interpretation of test results by a registered fire protection engineer, many of whom strongly recommend HRR and other measurements in CSA/ANSI C800 to support their analysis. CSA/ANSI C800:25 can be used alongside, and as an extension of, UL 9540A by providing additional performance and engineering-based data such as HRR, gas composition, detection response, and BMS data to support site specific installation requirements, engineering approvals, and AHJ review.

“UL 9540A and CSA/ANSI C800:25 now serve more distinct, yet complementary, roles within the ESS testing and approvals process. Looking ahead, both standards may be applied to support demonstration of alignment with NFPA 855. UL’s recent revisions to UL 9540A expand the scope of safety-focused requirements by incorporating certain performance-based considerations, such as those informing spacing and propagation mitigation, into the certification framework. While this approach reflects an increased emphasis on system-level safety, CSA/ANSI C800:25 continues to provide additional performance and engineering-based characterisation, including data elements that remain optional or out of scope under UL 9540A.”

Dana Parmenter, Commercial Vice President, Industrial at CSA Group