Project Aquarius 8. Sweating, Drinking, and Dehydration in Men Suppressing Wildland Fires

Firefighters' fluid balance was 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 Australian eucalypt forests. They consistently sweated at rates of 1-2 kg h-1 while building fireline and at half these rates for the whole work day. Drinking and dehydration were proportional to sweat loss: on average firefighters replaced 43% of their sweat loss during fireline construction and 63% for the whole work day. During fireline construction they dehydrated at an average rate of 654 g (0.9% body mass) per hour and a maximum rate of 2 kg per hour (2.6% body mass). The scientific observers sweated less than half as much as the firefighters but also drank less and became almost as dehydrated. These findings emphasise the need for work practices that guarantee an adequate water intake before, during, and after firefighting. Regression equations are presented for predicting sweat rate (hence water requirements) from activity, fire, body mass, and air temperature.