UL 9540A:2025 Standard for Battery Energy Storage Safety

The document details the ANSI/CAN/UL 9540A:2025 standard, which provides test methods for evaluating thermal runaway fire propagation in battery energy storage systems (BESS). It updates terminology, including definitions for non-residential and residential use, open parking garages, and thermal runaway propagation. The standard outlines testing at cell, module, unit, and installation levels. Key changes include continuous temperature measurement with 60-second averaging for surfaces but not for cell surfaces, and heat flux measurement with similar averaging. Cell-level testing requires charging to 100% SOC with a rest period of 1-8 hours, heating at 4-7°C per minute, and alternative methods like nail penetration if heating fails. A hold point at 5-15°C above separator melting temperature is specified, with exceptions if data is unavailable. Thermocouple placement is detailed, including under heaters, near positive terminals, and at vent areas. The standard enhances safety assessment for energy storage products.