UL 9540 & 9540A 2025 Updates: Energy Storage Safety Standards

The March 2025 revisions to ANSI/CAN/UL 9540 and UL 9540A introduce significant updates for energy storage system safety. UL 9540 adds Appendix H, providing a template for residential ESS manufacturer installation instructions. UL 9540A, the test method standard for thermal runaway fire propagation, undergoes extensive changes including optional FTIR and mandatory hydrogen measurement at the unit level, a new continuous thermal temperature rise test method, and updated heat flux measurement requirements. Test configurations are adjusted, replacing the NFPA 286 test room with a test wall for residential units and revising thermocouple placements. Definitions are clarified, adding 'thermal runaway propagation' and distinguishing residential from nonresidential uses. New test methods cover lead-acid, nickel-cadmium, and high-temperature batteries, while flow battery requirements are updated. Pass/fail criteria for module tests are revised, and reference standards now include NFPA 855 and replace UL 1685 with UL 2556. Safety requirements remove noncombustible structure exceptions and add deflagration analysis. These updates enhance testing flexibility, expand battery type coverage, and strengthen fire risk assessment, marking a shift from passive fire prevention to active early warning in energy storage safety.