The protection level offered by filtering facepiece particulate respirators and face masks is defined by the percentage of ambient particles penetrating inside the protection device. There are two penetration pathways: (1) through the faceseal leakage, and the (2) filter medium. This study aimed at differentiating the contributions of these two pathways for particles in the size range of 0.03-1 microm under actual breathing conditions. One N95 filtering facepiece respirator and one surgical mask commonly used in health care environments were tested on 25 subjects (matching the latest National Institute for Occupational Safety and Health fit testing panel) as the subjects performed conventional fit test exercises. The respirator and the mask were also tested with breathing manikins that precisely mimicked the prerecorded breathing patterns of the tested subjects. The penetration data obtained in the human subject- and manikin-based tests were compared for different particle sizes and breathing patterns. Overall, 5250 particle size- and exercise-specific penetration values were determined. For each value, the faceseal leakage-to-filter ratio was calculated to quantify the relative contributions of the two penetration pathways. The number of particles penetrating through the faceseal leakage of the tested respirator/mask far exceeded the number of those penetrating through the filter medium. For the N95 respirator, the excess was (on average) by an order of magnitude and significantly increased with an increase in particle size (p < 0.001): approximately 7-fold greater for 0.04 microm, approximately 10-fold for 0.1 microm, and approximately 20-fold for 1 microm. For the surgical mask, the faceseal leakage-to-filter ratio ranged from 4.8 to 5.8 and was not significantly affected by the particle size for the tested submicrometer fraction. Facial/body movement had a pronounced effect on the relative contribution of the two penetration pathways. Breathing intensity and facial dimensions showed some (although limited) influence. Because most of the penetrated particles entered through the faceseal, the priority in respirator/mask development should be shifted from improving the efficiency of the filter medium to establishing a better fit that would eliminate or minimize faceseal leakage.

The aim of this study was to investigate respirator filter and faceseal penetration of particles representing bacterial and fungal spore size ranges (0.7-4 mum). First, field experiments were conducted to determine workplace protection factors (WPFs) for a typical N95 filtering facepiece respirator (FFR). These data (average WPF = 515) were then used to position the FFR on a manikin to simulate realistic donning conditions for laboratory experiments. Filter penetration was also measured after the FFR was fully sealed on the manikin face. This value was deducted from the total penetration (obtained from tests with the partially sealed FFR) to determine the faceseal penetration. All manikin experiments were repeated using three sinusoidal breathing flow patterns corresponding to mean inspiratory flow rates of 15, 30, and 85 l min(-1). The faceseal penetration varied from 0.1 to 1.1% and decreased with increasing particle size (P < 0.001) and breathing rate (P < 0.001). The fractions of aerosols penetrating through the faceseal leakage varied from 0.66 to 0.94. In conclusion, even for a well-fitting FFR respirator, most particle penetration occurs through faceseal leakage, which varies with breathing flow rate and particle size.

Breathing flow rate, particle size, and combustion material all had significant effects on the performance of the respirator. For the partially sealed and unsealed respirators, the penetration through the faceseal leakage reached maximum at particle sizes >100 nm when challenged with plastic aerosol, whereas no clear peaks were observed for wood and paper aerosols. The particles aerosolized by burning plastic penetrated more readily into the unsealed half-mask than those aerosolized by the combustion of wood and paper. The difference may be attributed to the fact that plastic combustion particles differ from wood and paper particles by physical characteristics such as charge, shape, and density. For the partially sealed respirator, the highest penetration values were obtained at MIF = 85 L/min. The unsealed respirator had approximately 10-fold greater penetration than the one partially sealed around the bridge of the nose, which indicates that the nose area was the primary leak site.