Variability of the penetration of particles through facemasks

Abstract

COVID-19 is transmitted, at least in part, by airborne particles emitted by infected individuals. Wearing masks is one of the key actions that are required to prevent spreading COVID-19. To understand the variability in the performance, we evaluated the material performance of the whole mask, as manufactured, in terms of the penetration of particles, comfort and the quality factor of multiple copies of 29 different types. All masks were mounted to prevent leakage around the edges so the mask material and manufacture was tested, but the effects of the fit were not considered. The results of this study thus represent the upper bound of the performance of facemasks since leakage around the edges due to poor fit often overwhelms filtration through the mask material. The tests were performed at a steady flow rate of 30 L/min; mean values of the performance parameters were calculated for two different sizes; 0.12 µm and 0.3 µm. Of the masks tested, for 0.12 µm particles, N95 face filtering respirators consistently had the lowest peak penetration 1.7 ± 0.5%, while KN95 masks allowed 3.7 ± 2.6% penetration. In contrast, penetration through pleated procedure masks was 14.7 ± 16.9% due to one outlier - with that outlier removed, penetration decreased to 7.1 ± 4.3%; cloth masks allowed 26.4 ± 9.3% penetration. Tests on multiple copies of different masks demonstrated consistent performance of N95s, but considerably greater variability within the other classes of masks tested, leading to uncertainty in the degree of protection that they would provide.