Project Aquarius 7. Physiological and Subjective Responses of Men Suppressing Wildland Fires

Abstract

The responses of four crews of 7-8 men were measured while they attempted to suppress well-developed experimental bushfires of intensities commonly faced by hand-tool crews, and also while they built fireline in the same way without fire, during three summers in dry eucalypt forests of SW and SE Australia. Average values were sweat rate 1,144 g h^-1, heart rate (HR) 152 beats min^-1, and rectal temperature (Tre) 38.2° C. Changes in the average temperatures of clothed and unclothed skin were negligible, indicating efficient evaporation of sweat. Firefighters considered the work 'somewhat hard', and felt 'just too warm' and 'wet' with sweat. By contrast, the responses of the scientific observers, doing less strenuous work in the same environment, were minimal: sweat rate 292 g h^-1, HR 80 beats min^-1, and Tre 37.6°C. Firefighters' responses were mainly due to exertion rather than fire, confirming an identical finding from measurements of their energy expenditure and thermal environment. Differences between attacks with and without fire were small in both groups (HR 8-9 beats min^-1, Tre 0.1-0.2 degrees C) except for sweat rate (firefighters 401 g h^-1, observers 181 g h^-1), and were usually present before the attacks began. All responses were highly consistent over the four crews, three summers, and two regions. The above findings show that the firefighters worked within their capacity and paced themselves to sustain their own preferred equilibrium levels of strain. They also demonstrate the effectiveness of the firefighters' clothing and work practices.