Abstract
The fit provided by natural and silicone rubber facepieces of the same brand and size of half-mask respirator were compared by performing multiple fit tests in random order with both face-pieces on 45 subjects. The tests consisted of a six-exercise protocol while measuring the penetration of ambient room aerosols with a condensation nuclei counter fit test device. Fit factors obtained by the two facepieces were compared by nonparametric statistical methods because fit factors for the silicone rubber face-piece were not lognormally distributed. The fit factors for the silicone rubber facepiece were found to be significantly greater than those for the natural rubber facepiece. Although the difference was statistically significant, it was not of the same magnitude as reported in previous studies. It was noted that the maximum and minimum fit factors obtained with the natural rubber facepiece were higher than those for the silicone rubber facepiece. The variability of fit factors for the silicone rubber facepiece was also found to be higher than that of the natural rubber facepiece. This would affect the calculation of fit factor lower tolerance limits and should be considered in estimating the lowest likely fit provided by a respirator for an individual or a group of wearers.