PROJECT-AQUARIUS .6. HEAT LOAD FROM EXERTION, WEATHER, AND FIRE IN MEN SUPPRESSING WILDLAND FIRES

Firefighters' thermal environment was continuously measured while they attempted to suppress well-developed experimental bushfires of intens ities commonly faced by hand-tool crews, and also while they built fir eline in the same way without fire, during three summers in Australian eucalypt forests. They worked far enough from the flames to avoid pai nful intensities of radiant heat (>2 kW m(-2)) on bare skin and usuall y experienced 1.6 kW m(-2) - little more than the intensity of sunligh t Fire had negligible effects on average air temperature, humidity, or wired speed. Exertion accounted for 71% of the total heat load, fire and weather for the remainder. Evaporation was effectively the sole me ans of heat dissipation, and predicted sweat loss exceeded one litre p er hour. Indices of heat stress usually exceeded occupational limits p roposed for heat-acclimatized men, although little additional strain r esulted. We conclude that firefighters should be fit and acclimatized, wear light and loose clothing that imposes minimal resistance to evap oration, and drink at least 1 litre of water per hour.