The effect of evaporative cooling of respiratory protective devices on skin temperature, thermal sensation, and comfort.

High skin temperature of the face is a major source of discomfort while wearing respiratory protective devices. In this paper theoretical considerations of thermal exchange between the face and the environment with and without a mask are discussed to elucidate factors that may improve the design of masks to increase their acceptability. Comfort thresholds have been related to skin temperature for both resting and exercising subjects. Skin temperature below 34.5 degrees C at rest, and 31 degrees C during exercise, is rated as comfortable. In a previous study it was determined that evaporative cooling could reduce skin temperature and decrease discomfort in a dummy mask. In the present study evaporative cooling of a more sophisticated dummy mask and a modified Scott model 66 twin-cartridge respirator was tested in resting and exercising subjects. Skin temperature was significantly reduced when wet felt covered the surface of both masks and at rest the masks were rated as significantly more comfortable than with dry felt on the outer surface. It is concluded that evaporative cooling of an existing face mask can reduce skin temperature to the comfort threshold in resting subjects. Data suggest that similar results are attainable for exercising subjects.