Research shows that high-momentum, large-sized surrogate cough droplets can penetrate single- or double-layer surgical masks to a significant extent1.
The penetrated droplets can then break into numerous much smaller droplets that could remain airborne for some time, an international research team has found.
Such airborne droplets can transport the coronavirus to a vulnerable person, the researchers say.
Previous studies on the efficacy of masks didn’t probe how cough droplets evolve, penetrate and eventually break into smaller droplets.
To better understand this, the scientists, including researchers from the Indian Institute of Science in Bengaluru, investigated the impact of large cough droplets on single-, double-, and triple-layer surgical masks. To simulate a coughing event, they used a droplet dispenser that could eject deionised water droplets.
The researchers found that the number of droplets penetrating through a double-layer mask is significantly less than that through a single-layer mask. A reduction in the effective porosity of the double-layer mask and its increased effective thickness caused the difference.
Droplets landing on the inner surface of the masks with a velocity of 10 metres per second could penetrate single- and double-layer masks. For a triple-layer mask, such droplets showed no or minimal penetration.
Next, the researchers used light-emitting nanoparticle-loaded droplets that mimic the fluid dynamics of virus-loaded droplets. They found that a triple-layer mask trapped a greater number of droplets than single- and double-layer masks.
This, they say, shows that a triple-layer mask could trap virus-loaded droplets more effectively than single- and double-layer masks.
References
1. Sharma, S. et al. On secondary atomization and blockage of surrogate cough droplets in single- and multilayer face masks. Sci. Adv. 7, eabf0452 (2021) doi:10.1126/sciadv.abf0452
