Performance of an N95 filtering facepiece particulate respirator and a surgical mask during human breathing: two pathways for particle penetration

Abstract

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.

FIGURE 1.. (A) Experimental setup for testing respirators/masks donned on a human subject; (B) Experimental setup for testing respirators/masks on a manikin equipped with the Breathing Recording and Simulation System. (Continued)

FIGURE 1.. Continued.

FIGURE 2.. Mean inspiratory flow rates (Q_MIF) recorded with the Breathing Recording and Simulation System for each fit test exercise. Each bar represents the average value of MIF and the standard deviation integrated over 25 subjects of the NIOSH fit testing panel.

FIGURE 3.. The exercise-specific breathing patterns recorded by the Breathing Recording and Simulation System from a selected subject exhibiting Q_MIF closest to the average values calculated for 25-subject panel: normal breathing (A), deep breathing (B), head side-to-side (C), head up and down (D), bending over (E).

FIGURE 4.. The panel-integrated particle penetration through the N95 facepiece respirator and the surgical mask as a function of particle size. Each point represents the average value and the standard deviation of 75 observations (25 subjects × 3 replicates).

FIGURE 5.. The panel-integrated FLTF ratio for the N95 facepiece respirator and the surgical mask. Each point represents the average value and the standard deviation of 75 observations (25 subjects × 3 replicates).

FIGURE 6.. The exercise-specific, panel-integrated FLTF ratio for the N95 facepiece respirator and the surgical mask. Each point represents the average value and the standard deviation of 75 observations (25 subjects × 3 replicates).