Fire Safety Science Digital Archive

Past research has identified three candidates as near term replacements for CF3Br in some aircraft total-flooding fire protection applications: CF3I, C2HF5 and C3F8. The behavior of these compounds when added to lean, stoichiometric and rich propane/air mixtures exposed to subsonic and supersonic combustion waves is examined using a 10 m long, 50 mm diameter detonation deflagration tube. Pressure and visible radiation are measured as a function of the amount of agent in the mixture to determine the pressure ratio across the incident shock wave and the speed of the radiation front. The results are compared to earlier studies using ethene, in which significantly higher pressure ratios and wave speeds were generated. The presence of the three extinguishing compounds in the propane/air mixtures causes the combustion either to be enhanced or suppressed, and depending upon the dynamical situation and the concentration of the agent, any of the three can outperform the others. For example, C3F8 is the most effective compound for attenuating combustion systems for all stoichiometries; C2HF5 reduces the threat by 90 % when its volume fraction is 11 %, the best performance of the three, but amplifies the severity of the deflagration the most at a volume fraction of 5 %; and the best agent for attenuating the pressure increase of the shock wave is CF31 under most conditions.