Long streams of droplets with Laden viruses can be caught behind infected individuals

The cough-generated points from an individual standing are distributed differently in a narrow corridor and an open space. In narrow corridors, the points are concentrated in a small bubble and left behind. Credit: Xiaolei Yang

Fast walking in narrow corridors can increase Covida-19 transmission risk.

Long streams of virus-laden points can crawl behind infected individuals walking down a narrow corridor, affecting safe social distancing guidelines.

Computational simulations have been used to accurately predict airflow and point distribution patterns in situations where COVID-19 can spread. In the diary Fluid Physics, by AIP Publishing, the results show the importance of the shape of space in modeling how virus-laden droplets move through the air.

Simulations are used to determine flow patterns following an individual walking in spaces of different shapes. The results reveal a higher risk of transmission to children in some cases, such as after rapid movement of people in a long narrow corridor.

Previous investigations using this simulation technique have helped scientists understand the impact of objects, such as glass barriers, windows, air conditioners and toilets, on airflow patterns and the spread of the virus. Previous simulations have usually taken up a large open space, but have not considered the effect of nearby walls, such as those that may exist in a narrow corridor.

Points generated by coughing Open Space

The cough-generated points from an individual standing are distributed differently in a narrow corridor and an open space. In an open space, the dots are distributed in a large range attached to the person. Credit: Xiaolei Yang

If a person walking down a corridor coughs, his breath exhales points that travel around and behind their bodies, forming an awakening in the way a boat forms an awakening in the water as it travels. The investigation revealed the existence of a “re-circulation bubble” directly behind the person’s trunk and a long awakening flowing behind them at approximately waist height.

“The flow patterns we found are strongly related to the shape of the human body,” said author Xiaolei Yang. “At 2 meters downstream, the awakening is almost negligible at mouth height and leg height, but is still visible at waist height.”

Once the airflow patterns were determined, the probe modeled the distribution of a cloud of droplets expelled from the mouth of the simulated person. The shape of the space surrounding the moving person is particularly critical to this part of the calculation.

Two types of distribution modes were found. In a way, the point cloud detaches from the moving person and floats far behind that individual, creating a floating bubble of virus-laden points. Alternatively, the cloud is attached to the back of the person, crawling behind them like a tail as they move through space.

Cloud of points

Either way, the droplet cloud stays at about half the height of the infected person before it reaches the ground, indicating a higher risk for children to inhale the droplets. Credit: Xiaolei Yang

“For the detached mode, the concentration of points is much higher than for the attached mode, five seconds after a cough,” Yang said. “This poses a major challenge in defining a safe social distance in places like a very narrow corridor, where a person can suck viral points even if the patient is far ahead of him.”

The risk is especially great for children, as in both ways, the point cloud hangs at a distance above the ground that is about half the height of the infected person – in other words, at mouth level for children.

Reference: “Effects of space sizes on the distribution of points created by cough by a person standing” by Zhaobin Li, Hongping Wang, Xinlei Zhang, Ting Wu and Xiaolei Yang, December 15, 2020, Fluid Physics.
DOI: 10.1063 / 5.0034874

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