Sep 02, 2020 19:00:00

Researchers visualize that 'face shield is less effective than masks in preventing the spread of viruses'

Many people wear masks to prevent the spread of the new coronavirus, but some people prefer to use a

face shield made of plastic because they do not like the oppressive feeling of the mask and the hidden facial expressions. However, an experiment conducted by a research team in the United States showed that 'a face shield is less effective than a mask in preventing droplet diffusion'.

Visualizing droplet dispersal for face shields and masks with exhalation valves: Physics of Fluids: Vol 32, No 9
https://aip.scitation.org/doi/10.1063/5.0022968

Face shields, masks with valves ineffective against COVID-19 spread | EurekAlert! Science News
https://www.eurekalert.org/pub_releases/2020-09/aiop-fsm082520.php

Visualization shows face shields may not protect against COVID-19 spread | Live Science
https://www.livescience.com/face-shield-visualization-covid-19-spread.html

Wearing a mask has been shown to be effective as a measure against the new coronavirus, as it prevents the virus contained in the body fluids of infected persons from spreading as droplets from the mouth and nose. It is not always necessary to wear a medical mask, and non-medical masks and homemade cloth masks also have a certain effect. As a method of investigating whether non-medical masks are effective against infectious diseases, a 'candle test' is proposed, in which the mask is worn and the candle is blown to the fire.

What is the 'candle test' to find out how effective non-medical masks are in combating infectious diseases? -GIGAZINE

However, 'wearing a face shield as an alternative to a mask is unlikely to be effective in preventing the spread of the virus,' said a paper published on September 1, 2020. To study the effects of various masks and face shields, a team of associate professor Siddhartha Verma at the University of Florida Atlantic has conducted an experiment that visualizes the spread of droplets splashing from the human mouth and nose.

The research team connected a nebulizer that emitted a vapor consisting of a mixture of water and glycerin to the head of the mannequin, and while using a mask and a face shield on the head of the mannequin, use a pump to eject the vapor, and a human cough I reproduced the state that I did. At this time, the green laser pointer was illuminated around the mannequin to visualize the spread of the droplets.

If you actually attach a face shield to the mannequin and use a pump to inject steam that imitates a cough...

Immediately after coughing, you can see that the droplets spread through the gap under the face shield. However, at least the droplets ejected in the forward direction are blocked by the face shield and do not appear to spread.

However, since the face shield does not capture small droplets, droplets that are small enough to float in the air will gradually spread.

Finally, the droplets spread about 0.9 meters before and after the mannequin, indicating that the face shield is not so effective in terms of suppressing the viral epidemic.

Verma says, 'When students go back to school or college, they may want to use a face shield that is more comfortable and easier to wear for a longer period of time.' What if it doesn't work? We'll put everyone in a tight space, with droplets that can cause infections to build up over time.' On the other hand, the face shield is not totally useless, and by using it in combination with wearing a mask, it can be expected to prevent the droplets of others from adhering to the eyes.

On the other hand, in the experiment conducted while the mannequin wore the

N95 mask ...

Immediately after the cough-like injection, it can be seen that the droplets spread from the upper gap.

However, the droplets do not spread further, and it seems that there is a sufficient effect to prevent the spread of the virus.

In addition, in an experiment conducted using a general mask...

After all, it was found that in addition to the liquid droplets spreading from the gap in the upper part, slightly fine liquid droplets also diffused from the front surface of the mask.

Still, the droplet spread is limited and there is no danger of inhaling the virus directly if you are far away. It should be noted that not all commercially available masks are necessarily effective, and it was shown that droplets spread more widely with another brand of mask that the research team experimented with.

This study is only a simulation and does not provide accurate data on the spread of the infection. But Verma pointed out that 'even the best masks have some leaks,' arguing that wearing a mask and maintaining a physical distance at the same time is important in mitigating the fashion.