Project Aquarius .13. The thermal burden of high insulation and encapsulation in wildland firefighters' clothing

Light, heavy, and encapsulating clothing were compared in a climatic chamber during 60 minutes of moderate exercise (energy expenditure 382-464 W) in warm, dry conditions with no added radiant heat (air and mean radiant temperature 30 degrees C, relative humidity 33 %, air velocity 0.5 m s(-1)). The results showed that high insulation and reduced ventilation restricted the evaporation of sweat and thus hindered the dissipation of metabolic heat. These adverse effects were apparent in (1) a reduced cooling efficiency of sweat and hence a higher sweat rate; (2) increased heat storage, cardiovascular strain, discomfort, and fatigue; and (3) a failure to attain thermal equilibrium even after 60 minutes of work. Comparison with the effects of fire, previously reported, on lightly dressed firefighters showed that the above penalties would outweigh any benefit that extra insulation or encapsulation could confer during wildland fire suppression with hand tools.