Long streams of virus-laden drops can lag behind infected individuals

Long streams of virus-laden drops can lag behind infected individuals

Cough drops from the walking person scatter differently in the narrow corridor and open space. In narrow corridors, the droplets are concentrated in a small bubble and left further behind. Attribution: Xiaoli Yang

Walking fast in narrow corridors can be increased Covid-19 Transmission risk.

Long streams of virus-infected droplets can cause infected individuals to follow guidelines that maintain a safe social distance behind them as they walk through the narrow corridor.

Computational simulations were used to accurately predict ventilation and droplet distribution patterns in situations where COVID-19 could spread. In the journal Physics of fluids, AIP Publishing, The results show the importance of the shape of the space in modeling how virus-infected droplets move through the air.

Simulations are used to determine the flow patterns behind a person walking in differently shaped spaces. The results reveal high transmission potential for children in some cases, such as behind moving people fast in a long narrow corridor.

Previous experiments using this simulation technology have helped scientists to understand the impact of objects such as glass barriers, windows, air conditioners and toilets on airflow patterns and virus spread. Previous simulations have generally assumed large and open indoor space, but have not considered the effect of adjacent walls as they exist in a narrow corridor.

Cough Generated Drops Open Space

Cough drops from the walking person scatter differently in the narrow corridor and open space. In an open space, the droplets scatter over a large range attached to the person. Attribution: Xiaoli Yang

When a person walking down a corridor coughs, their breath expels the droplets that travel back and forth over their body, creating a wake in a way that creates a sensation in the water as a boat travels. The investigation found that there was a “re-circulation bubble” behind the man’s torso and that a long wave at waist height was flowing backwards.

“The flow patterns we found are strongly related to the shape of the human body,” said author Xiaoli Yang. “At 2 meters below, the wak is almost negligible at the height of the wak and the height of the legs, but it can still be seen at waist height.”

Once the airway patterns have been determined, the probe is modeled on the spraying of a droplet that is expelled from a person’s mouth. The shape of the space around the moving person is particularly crucial for this part of the calculation.

Two types of dispersal modes were detected. In one mode, the cloud of droplets separates from the moving person and flows from the back of the person, creating a floating bubble of virus-filled droplets. In another mode, the cloud is attached to the back of the person, moving behind them like a tail as it moves through space.

Cloud of drops

In both modes, the droplet travels at half the height of the infected person before reaching the ground, indicating a high risk for children to inhale the droplet. Attribution: Xiaoli Yang

“For the detached mode, the droplet concentration is much higher than the attached mode five seconds after a cough,” Yang said. “Determining a safe social distance in places like a very narrow corridor is a big challenge, and one can breathe viral drops even if the patient is far away in front of him or her.”

The danger is particularly great for children, because in both cases the cloud of drops travels about half the height of the infected person above the ground – in other words, at the level of the mouth of the child.

Reference: “The Effects of Space Sizes on Spraying Cough Drops on a Walking Person” Shaobin Li, Hong Hoping Wang, Xinlay Zhang, Ting Wu, Xiaoli Yang, December 15, 2020, Physics of fluids.
DNI: 10.1063 / 5.0034874

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