Fire Safety Science Digital Archive

The fires suppressant CF3Br has been banned for most applications but it is still used in come critical applications for which suitable replacements have not yet been found. One such application is the suppression of cargo-bay fires in commercial aircraft. Recently, the agents C2HF5 (pentafluoroethane, HFC-125), and bromotrifluoropropene (C3H2F3Br, 2-BTP) have been evaluated in a mandated Federal Aviation Administration (FAA) test, in which a simulated explosion of an aerosol can must be suppressed by the agent. Unfortunately, unlike CF3Br, either agent, when added at approximately one half their inerting concentration, created a higher over-pressure in the test chamber than in tests with no agent present (thus failing the test). Similar combustion enhancement has been described in other experiments for certain conditions; however, explanation of the phenomena is lacking. As a first step in understanding this surprising result, the thermodynamics of the chemical systems are examined to predict the over pressure. For all of the cases examined, the over-pressure was predicted well by assuming that the fuel-agent-air ratio is that which produces the peak temperature, or peak [CO2]. The details of the three chemical systems are examined to provide insight into the anomalous behavior.