Ballistic respiratory droplets impacting on facemasks: an overview

Facemask has become an integral part of our lives in protecting ourselves and others from CoVID-19. Proper use of facemasks blocks the ballistic respiratory droplets and liquid aerosols emanating from respiratory cavities and protects the user from inhaling the airborne droplets or aerosols. While N95 masks generally provide the best protection, single or multi-layered surgical masks, cloth masks, and other substitute masks have become popular during the pandemic. Naturally, their protection capability varies. In this talk, we will present an overview of what happens to ballistic large respiratory droplets when they impact single and multilayer masks. We will investigate both surgical masks and typical cloth masks. First, we will show that these droplets can penetrate the dry masks at certain conditions, generating many smaller atomized droplets. These smaller droplets can remain airborne for an extended period and hence, participate in disease transmission. Next, we will focus on wet masks. Indeed, long-term usage of masks leads to damp mask-matrix due to condensation of exhaled breaths. We will show how the wetness of the mask-matrix alters the penetration and atomization. Finally, we will present scaling analyses to explain the penetration dynamics for both dry and wet masks.