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 μm 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): ∼7-fold greater for 0.04 μm, ∼10-fold for 0.1 μm, and ∼20-fold for 1 μm. 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.

Keywords:

• aerosol
• breathing
• leakage
• penetration
• respirator
• surgical mask

ACKNOWLEDGMENTS

This research was partially supported by Cardinal Health, Inc., McGraw Park, Illinois. Hiroki Haruta's effort was funded by Koken Ltd., Tokyo. The authors appreciate this support. The authors also extend their gratitude to Linda Levin and graduate students Ashutosh Mani and Umesh Singh of the University of Cincinnati for their assistance in conducting statistical analyses.