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

Cough drops from the walking person are distributed differently in the narrow corridor and in the open space. In narrow corridors, the droplets concentrate in a small bubble and continue to linger. 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 keep a safe social distance behind them as they walk down the narrow corridor.

Computer simulations have been used to accurately predict ventilation and droplet distribution patterns in situations where COVID-19 could spread. In the magazine Physics of liquids, AIP Publishing, the results show the importance of the shape of 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 show, in some cases, a high transmission potential for children, e.g. B. when people are moving quickly in a long, narrow corridor.

Previous experiments with this simulation technology have helped scientists understand the effects of objects such as glass barriers, windows, air conditioning, and toilets on air flow patterns and the spread of viruses. Previous simulations generally assumed a large and open interior space, but did not consider the effects of neighboring walls as they exist in a narrow corridor.

Cough created drops of open space

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

When a person walking down a corridor coughs, their breath expels the droplets that move back and forth across their body, creating a trail that makes the water feel like a boat is going. The investigation revealed that behind the man’s torso there was a “recirculation bubble” and that a long wave flowed backwards at waist height.

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

Once the airway patterns are determined, the probe is modeled on the spray of a droplet ejected from a person’s mouth. The shape of the space around the moving person is particularly important for this part of the calculation.

Two types of propagation modes have been identified. In one mode, the cloud of droplets separate from the moving person and flow off the person’s back, creating a floating bubble of virus-filled droplets. In another mode, the cloud is attached to the person’s back and moves behind them like a tail as it moves through space.

Cloud of drops

In either mode, the droplet moves halfway up the infected person before it hits the ground, indicating a high risk for children to inhale the droplet. Attribution: Xiaoli Yang

“For the detached mode, the droplet concentration five seconds after a cough is much higher than for the attached mode,” said Yang. “Determining a safe social distance in places like a very narrow corridor is a huge challenge, and virus drops can be breathed in even when the patient is way ahead of him or her.”

The danger is particularly great for children, since in both cases the cloud of drops moves about half as high as the infected person above the floor – in other words, at the height of the child’s mouth.

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

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