Effects of respirators under heat/work conditions

Physiological responses and perceived strain of five unacclimatized male subjects were studied. The subjects were exposed to heat during an exercise task and were evaluated while wearing half and full facepiece, cartridge-type, air-purifying respirators, and without a respirator. The exercise consisted of walking on a treadmill for a period of 1 hour in a controlled environmental chamber at each of two different energy expenditure levels (200 and 400 Kcal/hr) (approximately equal to 58 and 116 Watts) and two different heat exposures (air temperatures of 25 degrees C and 43.3 degrees C). The results indicated that wearing a full facepiece respirator imposed significant physiological strain added to that caused by the heat and workloads used in the study. Five of the six physiological measures show this increased physiological strain: heart rate; minute ventilation; oxygen consumption; energy expenditure; and oral temperature. There was no detectable effect on sweat rate. Although subjective ratings indicated more discomfort with increasing physiological strain, the observed correlations between such measures were low (Tb less than .60). The net consequence of the significant effects indicates that workers' tolerance to moderate or higher levels of work under hot conditions while wearing a respirator is reduced. The reduction is more pronounced when wearing a full mask than when wearing a half mask. Changes in respirator design which minimize respiratory dead space are suggested to alleviate this problem. Otherwise, prevention of excessive physiological strain from respirator use when working at moderate or higher levels at hot job sites could necessitate more rest breaks or limiting work time under such conditions.