Fire Extinguishing Agents for Protection of Occupied Spaces in Military Ground Vehicles

Historically the US Army used Halon 1301 (bromotrifluoromethane), a chemical with high ozone depletion potential (ODP), to protect the crews of armored vehicles from the effects of peacetime and combat fires. Since the phase-out of Halon production the US Army has directed that zero ODP materials be used wherever possible. Subsequently, major new vehicle platforms have been deployed with automatic fire extinguishing systems (AFES) that rely on HFC-227BC, a zero-ODP-agent blend of HFC-227ea (heptafluoropropane) and sodium-bicarbonate-based dry chemical. Unfortunately, hydrofluorocarbons (HFCs) generally have high global warming potential (GWP)—thousands of times that of carbon dioxide on a weight basis. Hence, as part of a larger effort to reduce its carbon footprint, US Army Program Managers have asked that fire extinguishing agents that are more environmentally friendly be evaluated as part of ongoing vehicle modernization efforts. Several agents were investigated, including FK-5-1-12, water with additives, and dry chemicals. This report describes the findings of more than 150 live-fire tests using nine agents and four extinguisher technologies. The basic conclusion is that no alternate agent can yet be considered to be a practical replacement for Halon 1301 or HFC-227BC for this application. However, a blend of Halon 1301 and dry chemical has been found to be about twice as effective as Halon 1301 alone. Thus, pending confirmation tests on vehicles, it may be feasible to use less Halon in legacy systems without compromising fire protection performance.