Does it make sense to hold your mouth with your elbows or palms when you cough?
Due to the epidemic of the new coronavirus infection (COVID-19), it is a good etiquette to wear a mask when going to places where people gather and not to spread droplets (himatsu) when coughing or sneezing. If you cough or sneeze when you are not wearing a mask, it is recommended that you at least hold your mouth with your elbows, but the results of investigating whether it makes sense to actually hold your mouth with your elbows have been reported. I am.
Universal trends in human cough airflows at large distances: Physics of Fluids: Vol 32, No 8
Effectiveness of cloth masks depends on type of covering
https://phys.org/news/2020-08-effectiveness-masks.html
Since the new coronavirus (SARS-CoV-2) is contained in the droplets that spread when people cough or sneeze, the infected person should take measures such as wearing a mask to suppress the virus infection. Is said to be possible. Padmanabha Prasanna Simha of the Indian Space Research Organization and Prasanna Simha Mohan Rao of the Srijayadeba Institute for Cardiovascular Science investigate how droplets spread when coughing with various 'mouth coverings'. did.
Simha argues that if people can mitigate the spread of droplets and control pollution around them, it will benefit other healthy people. The research team used a technique called the Schlieren method to visualize the density of the droplets, taking advantage of the fact that the place where the droplets of the cough spread is warmer than the surroundings.
In the experiment, five subjects coughed in different states and tracked the movement of cough droplets in a series of images. With Schlieren imaging, cough droplets can be seen as a wavy area in the image, as shown in the image below.
The subjects were 'a: without a mask', 'b: with a medical mask', 'c: with an
Below is an image of the droplets visualized by Schlieren imaging. Comparing 'a: without mask', 'b: with medical mask', and 'c: with N95 mask', when the medical mask or N95 mask is worn, when the mask is not worn It can be seen that the spread range of the droplets is more clearly reduced. According to the research team, the droplets diffused up to 3 meters without the mask, but the diffusion range decreased to 50 cm with the medical mask. Furthermore, wearing the N95 mask reduced the initial velocity of the cough by up to 1/10, and the diffusion of droplets remained in the range of 10 to 25 cm.
On the other hand, comparing 'd: holding the mouth with one hand', 'e: covering the mouth with both hands', and 'f: holding the mouth with a folded handkerchief', it looks like this. Splashes may leak from the gap just by pressing the mouth with your hand, but it seems that you can considerably suppress the diffusion of droplets by pressing the handkerchief against your mouth.
'G: holding the mouth with a medical mask' 'h: holding the mouth with the sleeveless elbow of clothes' 'i: holding the mouth with the elbow with sleeves of clothes' looks like this .. If you press it with your hand from the top of the medical mask, you can considerably suppress the spread of droplets, but since the droplets will adhere to the hand that holds the mouth, if you touch other places with that hand, it will be contaminated with the virus. There is a danger. If you hold your mouth with your elbows, which are difficult to touch elsewhere, the droplets will spread through the gaps without sleeves, but if you wear clothes with sleeves, the gaps will be filled and the spread of droplets can be reduced. became.
Simha points out from the results of this study that even a mask that cannot catch all particles has the effect of suppressing the spread of particles far. On the other hand, he argued that the mask was not perfect, and that it was basically important to keep a sufficient distance from others.
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