Since August 2017, 21 lithium-ion battery ESS fires have occurred in Korea alone, but only a portion of these incidents can be explained by battery cell defects alone. In many cases, the direct cause of fire spread was equipment outside the battery itself — the Balance of System (BOS) — such as missing surge arresters, defective wiring installation, or cooling/HVAC failures. With the release of the 2026 edition of NFPA 855, the National Fire Protection Association (NFPA) has shifted its evaluation criterion from "whether an internal cell defect exists" to "whether propagation to adjacent cells, modules, or racks is blocked." NFPA 855 is the Standard for the Installation of Stationary…