Forensic Analysis of Multi-Cell Lithium-Ion Battery Packs Exposed to Flashover Fire Conditions

Abstract

Lithium-ion batteries and battery packs found in the vicinity of a fire’s area of origin require evaluation to come to a reliable conclusion regarding the cause of the fire and what role, if any, batteries played in the ignition of the fire. With the proliferation of lithium-ion batteries found at fire scenes, the peer reviewed fire investigation methods put forth in NFPA 921 have occasionally been replaced by incomplete approaches that focus on the collection and analysis of lithium-ion battery packs found at fire scenes. Many fire investigators and engineers rely on the analysis of unique cell post-fire characteristics to establish the role a particular battery pack or cell may have had in a fire. To evaluate the efficacy of these analyses and further document the types of damage associated with fire damaged cylindrical cells, eighteen battery packs containing 18650 lithium-ion battery cells at various states of charge were exposed to a full scale, post-flashover room fire. Through documentation and characterization of the post-fire lithium-ion battery packs, many types of damage often alleged to indicate fire causation were observed in fire exposed cells including flat negative ends, ejected cell contents, localized damage to the windings, shifting of the cell contents, and rupturing of the cell can. The post-fire physical condition of the battery packs varies significantly depending on the state of charge of the battery pack and significant variation in the post-fire condition was observed in individual cells within the same battery pack. These findings highlight the necessity for a proper fire investigation, demonstrating that solely relying on post-fire comparative analysis of battery cells may incorrectly attribute characteristics associated with fire exposure as fire causal characteristics when an investigation is performed with incomplete or limited information.