The Potential Efficacy of Double Masking

PETER CHEA, Buddhi Pushpawela, Ryan X. Ward, Richard Flagan, California Institute of Technology

     Abstract Number: 363
     Working Group: Control and Mitigation Technology

Abstract
Double masking generally decreases the penetration of particles and increases the pressure drop compared to the individual mask. When we wear the two masks the outer mask provides pressure to the edges of the inner mask, and therefore the inner mask fits more closely to the face and creates a better seal and an additional layer of protection. During the COVID-19 pandemic, the Centers for Disease Control and Prevention (CDC) and health experts recommended double masking to improve protection. However, the performance of double masks related to their particle penetration, pressure drops (breathing resistance or comfort), type of the masks, and combinations was limited in the literature. To address these limitations, we measured and compared the particle penetration and pressure drop of single and double masks (6 different combinations) that were fully sealed at a steady flow rate of 30 LPM. Of the double masks tested, N95 + procedure masks, N95 + cloth masks, KN95 + procedure masks, KN95 + cloth masks, and procedure + cloth masks showed 3-5% penetration, comparable with that of the N95s. The pressure drop measured for different double mask combinations varied between 38 and 83 Pa. These pressure drop values agreed well with the theoretical pressure drops estimated by the sum of the respective pressure drop values of single masks. The combination of procedure and cloth masks had similar pressure drops and penetration performance to a single respirator, making this double mask combination adequate in situations where respirators are less cost-effective or in limited supply. Therefore, the results of this study offer information to the community about the proper mask combinations that provide more protection than the individual mask.