Work tolerance and physiological responses to thermal environment wearing protective NBC clothing

Six young, healthy male subjects performed a series of experiments in a climatic chamber in different environmental conditions wearing protective ventilated NBC clothing. Ambient temperature, TA, ranged from -20 to 35 degrees C, relative humidity, RH, from 20 to 85%, and air velocity, VA, from 0 center dot 1 to 5 center dot 0 ms-1. In addition, thermal radiation, measured by the temperature of the globothermometer, TG, was artificially increased in some experiments. A total of 32 experiments were performed. The subject had to exercise on a bicycle ergometer at a mechanical power of 60 W for 120 min. Heart rate, HR, oxygen uptake, VO2, skin temperature, Tsk, and rectal temperature, Tre, were measured during the experiments together with the temperature of the space between skin and garment, Tmu. Sweat loss was determined as the difference of the body weight before and after the experiment. Tmu was well correlated with the chamber environmental parameters. During heat exposure work duration began to decrease progressively from a Tmu > 30 degrees C, reducing to 40 min at the highest thermal load. About the same value of Tmu marked the departure of HR, VO2, Tsk and Tre from the values measured during the same work load in neutral conditions. Also, during cold exposure at -20 degrees C work duration was reduced below 1 h, but the limit appeared to be the cold at the extremities. From these findings it appears that Tmu is a good indicator of the thermal load and is related to the environmental condition by the equation: Tmu = 9 center dot 93 + 0 center dot 56 TA + 0 center dot 023 TG + 0 center dot 14 RH (T in degrees C, RH in %). For better comfort and performance Tmu should be monitored whenever a subject has to work wearing an NBC garment and the ventilating system must be adequate to fulfil the needs imposed on the subject by an adverse environment, in particular a high relative humidity.