Disproving naysayers on the use of face masks, research conducted by a city-based cardiothoracic surgeon and his aerospace engineer-son has found that N95 masks are the most effective in reducing the horizontal spread of cough. And wearing any mask, including cloth masks, is better than wearing none.
Dr Prasanna Simha Mohan Rao, 54, from the Sri Jayadeva Institute of Cardiovascular Sciences and Research, and his 24-year-old son, Padmanabha Prasanna Simha, from Vikram Sarabhai Space Centre, Thiruvananthapuram, visualised and researched the cough flow fields under various common mouth-covering scenarios. Their paper, published in the journal Physics of Fluids on August 24, has elicited interest from The Optical Society of America, which has reached out to them.
The research findings come at a time when social media is awash with articles and videos on the “harms” of face masks. Speaking to DH, Dr Rao said the videos peeved him.
Jayadeva hospital director Dr C N Manjunath, who’s a member of Karnataka’s Technical Advisory Committee, said he planned to have the study findings on the meeting agenda of the committee so that a public advisory is sent out to naysayers spreading misinformation about masks.
Dr Rao and his son used Schlieren imaging, which shows the density of the cough droplets, their motion, velocity and spread.
“Schlieren imaging measures temperature and density gradients. When you cough, there is warm air, which is denser than the ambient air. So we could see how it travels. We positioned our subjects farther away from each other. When we cough, there is a contamination bubble around us where we can infect each other. With a three-ply surgical mask, the bubble is 0.5 to 1.5 metres,” Dr Rao explained.
Dr Rao, however, said they were not suggesting that everyone buy N95 masks. Wearing any mask, including cloth masks, is better than wearing none. An N95 mask is the most effective because it limits the spread of the salivary droplets between 0.1 and 0.25 metres, he explained. With a disposable mask on, the droplets travel up to 2.5 metres, and when the mouth is not covered, it could travel up to three metres. There is also a reduction of velocity in the droplets by up to ten times when one is wearing an N95 mask, he added.
The father-son duo started the study before the first lockdown in March when India was just beginning to report Covid cases. Dr Rao went on to explain that Indians tend to use their arms or elbows to cover their mouths while coughing which was proved to be ineffective during their study.