When wearing a respirator the metabolic heat accumulated inside the mask affects the comfort of the wearer and thus the efficacy of respirator use. This study evaluated the change in respirator convective and evaporative heat flows occurring in response to the use of respirators of different facepiece design under activities of varying metabolic load.Methods
The study was performed in a climatic chamber with environmental temperature fixed at 25°C and relative humidity at 65%. In the experiment, each participant (13 males and 12 females) first exercised under specified activity for 30 min to thermally adapt and then with a respirator on continued the same activity for another 30 min. The specified activities included sitting in chair, walking on stairs, and jogging, representing exercises of low (70–130 W/m2), moderate (130–200 W/m2), and very high metabolic rate (>260 W/m2). Three models of half-mask respirators (two cup-shaped filtering facepieces, including one with and one without exhalation valve, and one elastomeric facepiece with valve) were tested.Results
The increase in the temperature of the respired air when wearing a filtering facepiece was approximately 1.7 to 2.0 folds of when donning the elastomeric facepiece. The change in the convective or evaporative heat flows as a result of wearing either of the filtering facepieces was significantly different among metabolic rates (p<0.001). For both the filtering facepieces, the gradient between the convective and the evaporative heat flows increased with increasing metabolic rate.Discussion
The increase in heat strain resulting from respirator use and metabolic demand heightened the requirement of heat dissipation, particularly if the wearers worked strenuously in hot environment. The elastomeric facepiece with an exhalation valve relieved the hot-and-humid air inside the mask more effectively than the filtering facepieces did in this study, lowering thermal discomfort and potential heat stress.