BENGALURU: What type of mask should one wear if he or she is coughing?
Researchers at the Indian Institute of Science
(IISc) in Bengaluru suggest wearing multilayered masks to prevent aerosol generation as these do not allow escape of droplet volume when the person coughs. The study carried out by IISc in association with scientists from UC San Diego and University of Toronto Engineering has been published in Science Advances.
According to IISc, when a person coughs, large droplets (>200 microns) hit the inner surface of a mask at a high speed, penetrate the mask fabric and break up or atomise into smaller droplets, which have a greater chance of aerosolisation
and thereby carry viruses like SARS-CoV2 with them. This study is important as it examines the happenings at the droplet-level and could be decisive in working out strategies to handle respiratory diseases.
The researchers used a high-speed camera (images were captured at 20,000 frames per second) and closely tracked individual cough-like droplets impinging on single, double and multi-layered masks. Taking note of the size distribution, researchers stated that most of these atomised droplets were found to be smaller than 100 microns for single and double-layered masks. Such droplets, they said, have the potential to become aerosols, which can remain suspended in the air for long, potentially causing infection.
“You are protected, but others around you may not be,” said Saptarshi Basu, professor at the department of mechanical engineering and senior author of the study. On the other hand, triple-layered masks (including those made of cloth) and N95 masks offered better protection as these successfully prevented atomisation, the experts added.
Shubham Sharma, a PhD student and first author of the study, said human cough was mimicked by using a custom droplet dispenser to pressurise a surrogate cough liquid (water, salt with mucin, and a phospholipid) and to eject single droplets on to the mask. The study team found single-layered masks could only block 30 per cent of the initial droplet volume from escaping and double-layered masks could block 91 per cent. However, droplet generation and transmission were either negligible or zero for triple-layered and N95 masks.