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Measuring the Performance of Masks as Source Control Devices for Respiratory Aerosols
WILLIAM LINDSLEY, Francoise Blachere, Brandon Law, Raymond Derk, Justin Hettick, Karen Woodfork, William Goldsmith, James Harris, Matthew Duling, Brenda Boutin, Theresa Boots, Jamye Coyle, Timothy Nurkiewicz, Donald Beezhold, John Noti, National Institute for Occupational Safety and Health
Abstract Number: 27
Working Group: Infectious Aerosols in the Age of COVID-19
Abstract
Universal mask wearing is recommended to help control the spread of SARS-CoV-2, the virus that causes COVID-19. Masks reduce the expulsion of respiratory aerosols into the environment (called source control) and can offer some protection to the wearer. However, masks vary greatly in design and construction material, and testing is required to determine their effectiveness. Masks are often characterized using filtration efficiency, airflow resistance, and fit factors, which are standard metrics used to test masks and respirators as personal protective devices. However, none of these standard metrics are direct measurements of the ability of a mask to block aerosols during coughing and exhalation. We measured the source control performance of 15 cloth masks (which included face masks, neck gaiters, and bandanas), two medical face masks, and two NIOSH-approved N95 filtering facepiece respirators by determining their collection efficiency for aerosols ≤ 7 µm expelled during simulated coughing and exhalation. These measurements were compared with filtration efficiencies, airflow resistances, and fit factors on manikin headforms and humans. Source control collection efficiencies for the cloth masks ranged from 17% to 71% for coughing and 35% to 66% for exhalation. Filtration efficiencies of the cloth masks ranged from 1.4% to 98%, while the fit factors were 1.3 to 7.4 on the headform and 1.0 to 4.0 on human subjects. The correlations between the source control collection efficiencies and the standard metrics were statistically significant in all but two cases, but none of the correlations were strong. Our results suggest that a better understanding of the relationships between source control collection efficiency and metrics like filtration efficiency, airflow resistance, and fit factor are needed to develop simple quantitative methods to estimate the effectiveness of masks as source control devices for respiratory aerosols.