An exposition of facemask efficacy against large size cough droplets

The usage of facemasks has been ubiquitously recommended worldwide as a physical barrier to the ejected droplet during respiratory events. This is an effective strategy for restricting various droplet-based disease transmission, as in the case of COVID-19. Although the N95 facemask has high efficacy against respiratory droplets, its accessibility/affordability for the general population is still deprived. As a possible solution, using a makeshift facemask (surgical or cotton facemasks) is generally advised by policymakers. Although such endorsement could be economical and accessible, quantitative analysis on the effectiveness of such facemasks is still lacking. Using a large-sized surrogate cough droplet, we identified an additional route of disease transmission, which involves atomization of large-sized cough droplets into numerous daughter droplets. It is shown that most of such atomized droplets are of sizes which is critical for aerosolization¹. This suggested that the amount of aerosol generated (thereby the risk of infection) through this mechanism is higher than the earlier predictions based on mask filtration efficiencies alone. A scaling argument based on the energy balance of impact dynamics was obtained and verified using experiments to identify a criterion for droplet penetration through a mask layer. The parametric analysis was also carried, which involves droplet impact velocities (corresponding to different respiratory events), impact angles (corresponding to different mask orientations), mask fabrics (surgical and cotton facemasks), and different washing cycles. The obtained results are discussed in detail, and a recommendation of the most suitable fabric for making homemade facemasks is presented.

 

References:

[1]       S. Sharma, R. Pinto, A. Saha, S. Chaudhuri, S. Basu, On secondary atomization and blockage of surrogate cough droplets in single- And multilayer face masks, in: Sci. Adv., 2021: pp. 1–26. https://doi.org/10.1126/sciadv.abf0452.