Full-Scale Testing of Fire Suppression Agents on Shielded Fires

Abstract

This report examines the relative effectiveness of water mist, water mist with class A foam concentrate added, and class A compressed air foam in the extinguishment of a shielded, post-flashover, compartment fire. This is to assist the New Zealand Fire Service in determining future firefighting tactics and equipment. Extinguishing agent application used hand lines operated by Fire Service personnel. Application of each of the three agents was for a fixed total period of ten seconds, with a constant flow rate of 2.8 litres/second. The class A solution was a wet foam with an expansion ratio of 1:2, and the compressed air foam was drier with an expansion ratio of 1:5. Measurement of the water content in the fire exhaust gases indicated peak moisture contents between 10% and 20%. No rise in water content was observed during suppression. Compartment temperatures peaked at 750°C to 820°C. Cooling to 200°C occurred within around 80 seconds of extinguishment. Cooling rates were similar for all three methods. The fires achieved peak heat release rates of up to 4500 kW. All three methods gave good initial extinguishment for fires of this size. Subsequent re-ignition occurred in most cases. No significant difference was found in the suppression performance of the three agents expressed in terms of heat release rate reduction, which was measured using oxygen calorimetry.