Fire Safety Science Digital Archive

An analysis is presented on the full-scale fire suppression experiments conducted on the F-22 engine nacelle simulator at Wright Patterson Air Force Base. Experiments investigated the relative effectiveness of halogenated agents and solid propellant gas generators (SPGG) in suppressing a series of spray fires with and without a fuel re-ignition source. Several agents were tested including CF3Br (halon 1301), C2HF5 (HFC-125), and two basic types of SPGG, including one that produced inert gases in conjunction with a fine solid particulate composed of K2CO3 and one that produced inert gases only. The measured agent effectiveness was compared to the predicted effectiveness based on results from cup burner suppression experiments. Estimates of the suppression effectiveness of the SPGG were based on the effectiveness of the components of its effluent. The mass fraction of SPGG effluent required to extinguish heptane cup burner flames was estimated as 0.15 and 0.29 as compared to previously measured values of 0.14 and 0.28 for CF3Br and C2HF5, respectively. The predicted suppression requirements (relative to CF3Br) agreed with the full-scale measurements within 35% for the halogenated compounds, whereas the SPGG performed as much as a factor of 3.3 better than predicted. This difference suggests that a large fraction of the SPGG performance may have been related to its fast deployment, which enhances flame straining and thereby reduces agent mass suppression requirements. The SPGG effluent that contained a significant percentage of K2CO3 particulate was particularly effective for re-ignition protection, a scenario that dominates agent mass requirements for the compressed halogenated liquids. In this case, the SPGG required 27 times less mass than CF3Br.