Experimental evaluation of fire suppression characteristics of twin fluid water mist system

This paper reports the results of experiments performed in a 1 m(3) chamber on suppression of n-heptane pool fires using fine water-mist (D-V50 similar to 23 mu m) generated from air aspirating twin fluid nozzles in continuous and pulsed mode. The effect of pulsing duration (1.0-1.4 s ON/0-1.3 s OFF), fire size (5-12.5 kW) and pre-burn duration (10-30 s) was studied for air and nitrogen as the atomizing fluid. During these experiments, fire suppression time, quantity of water for suppression and temperatures in the chamber were recorded. Fire suppression performance index (FSPI) was developed as an indicative measure of fire suppression effectiveness. It was observed that the best FSPI was achieved for a pulsing cycle of 1.3 s ON and 1 s OFF. Nitrogen as atomizing medium for mist generation was found to be more effective for fire suppression by 30-50%. Increase in pre-burn duration and fire size was found to reduce suppression time due to larger heat available in the chamber. Fire suppression for larger fire size was achieved with 25-30% of the combustion heat absorbed by the mist, indicating important contribution to fire suppression by other processes such as oxygen dilution and inerting due to water vapour. (C) 2012 Elsevier Ltd. All rights reserved.