Fault Tree Analysis for BESS Failures, Fires, and Explosions

This paper presents a practical method for constructing and quantifying fault tree analysis (FTA) for battery energy storage system (BESS) failures, fires, and explosions. It defines three precise top events: thermal runaway propagation, container fire, and container deflagration. The method clarifies boundary conditions, operating phases, and a reusable basic event classification system. Standard gate logic modes (OR, AND, combination, PAND, inhibit) are used, and protection layers (battery management system trip, isolation devices, HVAC/ventilation systems, suppression measures) are modeled via the PFDavg model combined with common cause factors. Through case analysis, the frequency magnitude of container deflagration is estimated, and minimal cut sets and importance measures are presented to prioritize engineering controls. Key aspects such as ventilation reliability, ignition control, isolation integrity, and commissioning/maintenance states are highlighted. Guidance is provided for data collection, quality verification, and integration with event trees, LOPA models, and consequence models, establishing a fault tree supporting design decisions, operational verification testing, and insurance assessment.