Limited Effectiveness of Heat Acclimation to Soldiers Wearing U.S. Army and U.S. Air Force Chemical Protective Clothing.
ARMY RESEARCH INST OF ENVIRONMENTAL MEDICINE NATICK MA
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Heat acclilmation-induced sweating responses have the potential of reducing heat strain for soldiers wearing chemical protective garment. However, this potential benefit is strongly affected by the properties of the garment. If the clothing ensemble permits sufficient evaporative heat dissipation, then heat acclimation becomes helpful in reducing heat strain. On the other hand, if the garment creates an impenetrable barrier to moisture, no benefit can be gained from heat acclimation as the additional sweating cannot be evaporated. We studied 10 subjects exercising on a treadmill while wearing two different U.S. military chemical protective ensembles. Skin heat flux, skin temperature, core temperature, metabolic heat production, and heart rate were measured. We found that the benefit of heat acclimation is strongly dependent on an unimpeded ability of evaporative heat loss from skin areas. The evaporative potential EP, a measure of thermal insulation modified by moisture permeability, of the clothing ensemble offers a quantitative index useful to determine whether heat acclimation is helpful while protective clothing system. Our data show that when EP is less than 15, heat acclimation affords no benefit. An evaporative potential graph is created to aid in this determination.
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