Evaluation of Comfort and Fatigue of Japanese Subjects in Extremely Low Humidity Air

Subjective experiments were carried out in a climate chamber using 16 Japanese subjects ofboth genders, in order to evaluate human comfort at very low humidity. Two levels ofabsolute humidity were set, 2.0 g/kg(DA) and 10.0 g/kg(DA). Three air temperatureconditions with absolute humidity of 2.0g/kg(DA), 20.0C/13%RH, 25.0C/10%RH and30.0C/8%RH, and 3 conditions with 10.0g/kg(DA), 20.0C/68%RH, 25.0C/50%RH,30.0C/38%RH, were examined. People were exposed in a chamber for 90 minutes withsedentary activity. Subjects rated their sensations and subjective fatigue on the questionnairesduring the exposure time. Skin moisture was measured on subjective left forearm by means ofmeasuring capacitance of the skin. Break up time (BUT) was measured by subjects with astopwatch.Absolute humidity has great impact on subjects skin moisture although air temperatureeffects on it were moderate. Subjective BUT got significantly shorter at extremely lowabsolute humidity. It was found that general dryness sensation at low absolute humidity wassignificantly higher than that at high absolute humidity. Subjects felt their eyes were dryer atlow air temperature, when keeping the same moisture content in air. In case of the constant airtemperature, low absolute humidity caused greater eye dryness sensation. Very low humidityair dry up the human mucous membrane and subjects perceived it as dryness sensation. Halfof subjects reported their palm of hand as wetted segment even at 25.0C/10%RH and30.0C/8%RH. Subjects felt more tired at very low absolute humidity under the cool andthermally neutral condition, while they complained more at high humidity in hot environment.