Limitations to heavy work at 21 degrees C of personnel wearing the U.S. military chemical defense ensemble.

The purpose of this study was to determine the limitations to work of personnel performing heavy work at 21 degrees C (70 degrees F) while wearing the chemical defense ensemble (CDE) worn by all branches of the U.S. military. Male volunteers (N = 17) wearing the CDE performed an arm and leg work task yielding a time-weighted energy consumption rate of 450 W, under environmental conditions of 21 degrees C and 65-70% relative humidity. Each work bout was continued until one of the following limits occurred: volitional fatigue, rectal temperature (Tre) of 39 degrees C, or calculated heat storage (S) of 140 Wh. Subjects then rested until heat stored due to this work was lost, then repeated the work-rest cycles until refusal, or inability to restart work after a rest cycle. Over a total of 36 work cycles, subjects terminated work cycles for S on only two occasions, with the remainder almost equally divided between cumulative fatigue and high Tre. Intersubject variability was high for work and rest times, S, heat loss, and sweat production. U.S. Air Force Regulation (AFR) 355-8, which provides guidance for heat stress in the form of work/rest cycles, underestimated work tolerance under these study conditions.