How to cough with a mask? Expert experiments give conclusions-

Xinhua News Agency, Beijing, September 1 The use of masks has become an indispensable part of people's lives. Facts have proved that masks are an effective way to resist the spread of COVID-19. However, most people still have a question: to what extent can masks play a protective role? Should you cover your mouth with your hands or elbows even when sneezing or coughing? In order to dispel doubts, the staff of the Indian Space Research Organization conducted an experiment to visualize the cough flow field in various common scenes, from uncovered to wearing N95 masks. The research results have just been published in the monthly journal of Fluid Physics.

According to the website of Spanish newspaper Abesaibao reported on August 25th, experts pointed out that in a specific environment, consciously reducing the spread of pollutants can reduce the degree of environmental pollution, which will help to avoid other healthy people in polluted areas from being infected.

The density of liquid is closely related to temperature, and the area around the cough source is often warmer. Using this connection, the researchers used a photographic technique called schlieren method. This optical process used to capture the change of fluid density is called "schlieren effect". In the fields of aeronautics and ballistics, this technology is used to study supersonic airflow and also to photograph the airflow around moving objects.

The researchers used this technology to capture the cough images of five volunteers. By tracking the movement of cough in continuous images, the researchers estimated the propagation speed of discharged droplets. The researchers considered nine different scenarios: not wearing a mask; Wear a disposable surgical mask; Wear N95 mask; Cover with only one hand; Cover with both hands; Cover with a folded handkerchief; Wear a surgical mask and cover it with your hands; Don't wear a mask but cover it with your elbow; Put on a mask and cover it with your elbow.

As expected, the researchers found that wearing N95 mask is the most effective way to reduce the spread of cough. These masks greatly reduce the initial cough speed, limiting its spread range to 0. 1 to 0.25m ... In contrast, according to some studies, the spread distance of cough without masks can reach 3 to 5m. In addition, the distance can be shortened to 0.5 meters by using ordinary disposable masks.

Experts pointed out that even if the mask can't filter out all virus particles, with its protection, we can prevent these virus particles from spreading to far places. Wearing a mask is better than not taking any isolation measures. Even in the absence of a formal mask, any kind of mask is better than no mask, which can prevent the spread of the virus to varying degrees.

On the other hand, the researchers also considered the effect of covering your mouth with one hand, two hands or a folded handkerchief. In the first case, the airflow bypasses the only hand that can stop coughing and escapes through the upper respiratory tract; In the case of covering your mouth with both hands, the airflow escapes from fingers, upper limb gaps and upper respiratory tract, and the visible effect is even worse than covering your mouth with only one hand; Cover your mouth with a folded handkerchief than with your hand to block more virus particles.

However, the researchers also found some surprising conclusions. For example, wearing a mask and covering your mouth with one hand before coughing greatly limits the spread of cough, especially in the horizontal direction. When you don't wear a mask, it's a good choice to cover your mouth with your elbow and then cough, just as experts suggested in the early stage of the epidemic. But the researchers also pointed out that this action is only effective when the arm is covered with sleeves, because the bare skin can't seal the space around the mouth to prevent the airflow from escaping.