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Influence of Flow Rates on Pressure Drop and Penetration for Various Masks
PETER CHEA, Buddhi Pushpawela, Ryan Ward, Richard Flagan, California Institute of Technology
Abstract Number: 142
Working Group: Infectious Aerosols in the Age of COVID-19
Abstract
Mask-wearing emerged as the primary safety measure to prevent spreading COVID-19. To assess the viability of different materials in filtering aerosols when inhaling, we tested multiple copies of different mask categories: including NIOSH-certified N95 respirators, KN95 masks, procedure masks, and cloth masks. The intact masks were exposed to polydisperse NaCl aerosol of 30-800 nm, and tightly sealed within a chamber to get the upstream and downstream particle counts and pressure measurements. The pressure drop was measured for seven flow rates between 5 and 85 LPM. For all masks, it increased linearly with flow rate with r2 > 0.98. The KN95 and cloth masks had higher pressure drops than the other masks, causing reduced breathability. The penetration was calculated with counts from a differential mobility analyzer and condensation particle counter system for three flow rates: 5, 30, and 85 LPM. For all of the masks, the penetration increased with flow rate, while the most penetrating particle size (MPPS) generally decreased. However, N95 and KN95 electret masks did not exhibit a significant shift in MPPS when the flow rate increased from 5 to 85 LPM. Compared to electret masks, the shift in MPPS for procedure and cloth masks was significant. This behavior shows that, for increased flow rates, the effectiveness of diffusion and electrostatic attraction (mainly affecting small particles) decreases, while that of impaction (mainly affecting large particles) increases. The use of face masks at high flow rates increases the risk to the wearer, and reduces breathability. The reduction of breathability may cause the public to be hesitant to wear masks.