A Review of Fire Extinguishing Test Methods for Lithium Metal and Proposal for a Standardized Test Procedure

Lithium metal is a combustible and water-reactive material that melts and forms mobile pool fires during heating. Existing Class D extinguisher tests are mainly based on metals such as magnesium or sodium and do not fully represent the geometry, melting, scattering, agent-metal interactions, and long-term reignition characteristics of lithium. This paper reviews domestic and international research, including experiments conducted by the Japan Atomic Energy Agency (JAEA), on molten lithium, early alkali-metal fire studies, commercial copper-powder extinguisher information, and existing Class D fire test standards and proposes a conceptual lithium-metal fire extinguishing test procedure based on a literature review. The comparison shows that the extinguishing performance should be evaluated not only by the disappearance of visible flames but also by agent compatibility, integrity of the agent cover, scattering of burning metal, thermal stabilization, and re-ignition. In the proposed foil-fire test, the agent discharge was initiated when the flames covered at least 50 % of the exposed Li surface. A previously considered criterion requiring at least 10 % unburned lithium was not adopted in this study because a reproducible analytical method for separating active lithium from oxides, nitrides, and agent residues has not yet been established. A performance framework based on flame extinction, controlled scattering, stable cover formation, four-hour re-ignition observation, and temperature history was proposed.