Penetration and aerosolization of cough droplet spray through face masks: A unique pathway of transmission of infection

The advent of the COVID-19 pandemic has necessitated the use of face masks, making them an integral part of the daily routine. Face masks occlude the infectious droplets during any respiratory event contributing to source control. In the current study, spray impingement experiments were conducted on porous surfaces like masks having a different porosity, pore size, and thickness. The spray mimics actual cough or a mild sneeze with respect to the droplet size distribution (20–500 μ m) and velocity scale (0–14 m / s), which makes the experimental findings physiologically realistic. The penetration dynamics through the mask showed that droplets of all sizes beyond a critical velocity penetrate through the mask fabric and atomize into daughter droplets in the aerosolization range, leading to harmful effects due to the extended airborne lifetime of aerosols. By incorporating spray characteristics along with surface tension and viscous dissipation of the fluid passing through the mask, multi-step penetration criteria have been formulated. The daughter droplet size and velocity distribution after atomizing through multi-layered masks and its effects have been discussed. Moreover, the virus-emulating particle-laden surrogate respiratory droplets are used in impingement experiments to study the filtration and entrapment of virus-like nanoparticles in the mask. Furthermore, the efficacy of the mask from the perspective of a susceptible person has been investigated.