Project Aquarius 4. Experimental Bushfires, Suppression Procedures, and Measurements

Abstract

Experimental bushfires were lit over three summers in Australian eucalypt forests with fuel loads (mean and range) of 11.3 (8-14) tonnes per hectare, in air temperature 25 (17-33)° C, relative humidity 47 (14-81)%, and wind speed 4.4 (2-9) m s-1. The McArthur Forest Fire Danger Index (FFDI) ranged from 2 to 18 and was evenly distributed between 'low', 'moderate', and 'high' fire dangers. Fires were lit on a crosswind ignition line of 50-200 metres, and were allowed to develop for 10-50 minutes before a seven-man hand-tool crew commenced its attack. Airborne infra-red imagery showed that head-fire intensity (averaged over 6 minutes) of most fires exceeded 1000 kW per metre of fire front (kW m-1) at some stage and ranged as high as 3280 kW m-1, challenging the crew in much the same way as summer wildfires and evoking similar uncertainty and apprehension. Firefighters were generally unable to suppress headfires with an intensity of more than 1000 kW m-1. Comprehensive measurements were made of the stresses the firefighters and scientific observers experienced, their physiological and subjective responses, and the firefighters' productivity and efficiency. In all, 23 km of fireline were constructed and 238 man-days of measurements were obtained — 179 on the firefighters, 59 on the scientists.