"A study was conducted in sedentary human subjects of the temperature and humidity conditions under which wearing a respirator mask would be acceptable. Six healthy volunteers were studied during the summer months, when they were used to a hot environment. The experimental room was kept at one of the following combinations of ambient and dewpoint temperatures, in degrees-C: 25:11; 30:13; and 35:16. The subject remained sedentary and was given breathing air via a half facepiece respirator at a temperature of 27, 30, 33 or 36 degrees and a relative humidity of 47 percent (low) or 73 percent (high). Local skin temperatures and dew points were measured at several sites on the body, and the subjects provided ratings of acceptability (defined as desire to change or not change the respirator), thermal sensation, degree of discomfort, perceptions of sweating, and skin wettedness. All six subjects considered the respirator acceptable if the respirator air was 27 or 30 degrees at either humidity level, no matter whether the room condition was hot or not. At each level of environmental temperature, the acceptability of the respirator tended to decrease as either the temperature or the humidity of the respirator air increased. The acceptability of the respirator was related to the lip skin temperature and fell when this temperature exceeded 34.5 degrees or when the dew point of respirator air exceeded 20 degrees. Some subjects commented that they felt that breathing was slightly hard under conditions of high respirator temperature and humidity. High heat or humidity in the respirator air decreased the acceptability of the room environment for each level of room environment. The authors conclude that the heat and humidity conditions inside a respirator influence the acceptability of wearing a respirator. "

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