Due to the COVID-19 pandemic, everyone should wear a mask when visiting a crowded place so as not to spread cough drops. A fairly common advice is if you cough without wearing a mask, cover your mouth with your elbow or hand. But are these really plausible and effective?
To allay these doubts, Padmanabha Prasanna Simha, from the Indian Space Research Foundation, and Prasanna Simha Mohan Rao, from the Sri Jayadeva Institute for Cardiology and Research, conducted experiments to test the schools. the movement of coughing under a variety of common oral cover situations.
Simha argued that it would be beneficial for other healthy people if they could minimize the spread of droplets and reduce surrounding pollution. Density and temperature are also closely related, and coughing spells tend to get warmer.
Exploiting this connection, Simha and Rao used a technique called the Schlieren Imaging Method, to visualize changes in droplet density from test subjects. By tracking the movement of a cough through successive images, the team estimated the velocity and spread of the droplets that were expelled from the body.
In the experiment, 5 subjects coughed in different states and the researchers tracked the droplets’ movements in a series of images. With Schrilen Imaging, droplets can be seen as a ripple area in the image, as shown in the image below.
The subjects are “a: not wearing a mask”, “b: wearing a medical mask”, “c: wearing a N95 mask”, “d: holding mouth with one hand”, “e: covering with both hands. mouth “,” f: gag with a folded handkerchief “,” g: hand gag on a medical mask “,” h: elbow gag “and” i: use elbow with sleeve “.
Comparing the obtained image of a-b-c, it can be seen that the spread range of the droplets dropped clearly. According to the team, the droplets spread to 3 meters without a mask, but the range of transmission was reduced to 50 cm with a medical mask. When wearing the N95 mask, the initial speed of cough has decreased to 1/10, and the diffusion of the droplets is only about 10 to 25 cm.
On the other hand, comparing d-e-f, the results are as shown below. Droplets that could leak from the opening could be seen if only covered by pressing the mouth with the hand. But it seems that it is also possible to significantly prevent the spread of droplets by pressing a handkerchief against the mouth.
Finally, a g-h-i comparison. See that if you press on from the top of the medical mask with your hands, you can significantly prevent the spread of droplets. But because the drops get on the hand holding the mouth, if you touch other places with that hand, they will become infected.
If you cover your mouth with your elbow, where it is difficult to touch, but the droplets still have a chance of spreading out from the gap without long sleeves. And in the end if you wear long-sleeved clothing, the opening will fill up and the chance of the droplet spreading out is significantly limited.
Simha points out from the results of this study that even a mask cannot hold all droplets, but they work to prevent the droplets from spreading away. On the other hand, he also thinks that the mask is not perfect and it is important that everyone keep a sufficient distance from others.
Simha and Rao hope their findings will quell the argument that conventional fabric masks are ineffective, but they also insist that masks must continue to be used with social exclusion.
The research above has been presented in the journal Physics of Fluids.