Experimental determination of the limiting criteria for human exposure to low winter humidity indoors (RP-1160)

Thirty subjects (female) were exposed for five hours in a climate chamber at 22 degrees C (71.6 degrees F) to clean air at 5%, 15%, 25%, and 35% RH. A comparable group was similarly exposed to air polluted by carpet and linoleum to the 35% RH condition and to 18 degrees C, 22 degrees C, and 26 degrees C (64.4 degrees F, 71.6 degrees F, and 78.8 degrees F) at an absolute humidity equal to 15% RH at 22 degrees C (71.6 degrees F). They performed simulated office work to ensure that they kept their eyes open and reported sick building syndrome (SBS) symptom intensity on visual-analogue scales. Nine objective tests of eye, nose, and skin function were applied. Subjective discomfort, though significantly increased by low humidity, was slight even at 5% RH. More rapid blink rates were observed at 5% than at 35% RH (P < 0.05), and tear film quality as indicated by the Mucous Ferning Test deteriorated (P < 0.05) at low humidity (5%, 15%) and at the highest air temperature 18 degrees C, 22 degrees C > 26 degrees C (78.8 degrees F). Low humidity was found to have reduced the rate of performance of three office tasks by 3%-7%.