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Variability of the Performance of Facemasks
BUDDHI PUSHPAWELA, Stavros Amanatidis, Yuanlong Huang, Richard Flagan, California Institute of Technology
Abstract Number: 153
Working Group: Infectious Aerosols in the Age of COVID-19
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 penetration of particles through the masks (a measure of risk), comfort (pressure drop), and the quality factor of 145 masks with multiple copies of 29 different types. The tests were performed at a flow rate of 30 L/min; mean values of the performance parameters were calculated for two different sizes; 120 nm and 300 nm. Of the masks tested, for 120 nm particles, the NIOSH-certified N95s respirators consistently had the lowest 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. The corresponding pressure drops at 120 nm for N95s, KN95s, procedure, and cloth masks were 22±4 Pa, 37±14 Pa, 14±5 Pa, and 32±10 Pa. The quality factors for different masks ranged from 15±3 kPa-1 to 274±28 kPa-1. Even within the different classes of masks, substantial variability was apparent, with coefficients of variation in penetration of 120 nm particles of 0.08-0.25 for N95s, 0.07-0.99 for KN95s, 0.11-0.42 for procedure masks, and 0.11-0.26 for cloth masks. The respective coefficient of variation of pressure drop was 0.03-0.12, 0.02-0.20, 0.05-0.15, and 0.01-0.20. 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. Therefore, quantitative testing is needed along with verifiable labeling to ensure that masks meet specific standards and, thereby, to control the large influx of inferior and counterfeit masks into the market.