Raising the Bar on BESS Safety: Lessons from Full-Scale Fire Testing Under the New NFPA 855

Synopsis

With the updated NFPA 855 now mandating Large-Scale Fire Testing (LSFT) for Battery Energy Storage Systems (BESS), system-level fire performance under real-world conditions has become a critical requirement for permitting, design, and risk evaluation. This presentation shares firsthand insights from a full-scale LSFT conducted on Trina Storage’s 5MWh Elementa 2 Pro platform in accordance with UL 9540A:2025-11 and aligned with the forthcoming NFPA 855:2026 framework. Executed by TÜV Rheinland with professional oversight from The Hiller Companies, the test deliberately exceeded minimum requirements—utilizing ultra-tight container spacing, 100% state of charge, disabled suppression systems, and intensified ventilation—to stress the system under extreme thermal conditions. Despite sustained fire temperatures exceeding 1300°C in the initiating container, no thermal runaway propagation occurred. Adjacent containers remained structurally sound and fully operational, and notably, the initiating container itself maintained structural integrity with no collapse and was safely lifted after the test. The results demonstrate how rigorous LSFT can validate robust BESS safety design, support regulatory confidence, and establish a practical benchmark for compliance with the new NFPA 855 standard.