Long streams of virus-laden droplets may follow infected individuals.

The drops resulting from a cough from a walking person spread apart in a narrow corridor and an open space. In narrow corridors, the droplets are concentrated in a small bubble and released further back. Sincerely: Xiaoli Yang

Brisk walking in narrow corridors may increase COVID-19 Transmission risk.

Long streams of virus-laden droplets can pass through a narrow corridor behind infected individuals, affecting safe social security guidelines.

Computational simulations have been used to accurately estimate airflow and droplet dispersion patterns in situations where COVID-19 can propagate. In the magazine Physics of fluidsBy AIP publication, the results show the importance of space size in modeling how virus-laden droplets move through the air.

Simulations are used to determine the flow pattern behind a person moving in different size locations. The results highlight a high transmission risk for children in some instances, such as quickly moving people back in long narrow hallways.

Previous investigations using this simulation technique have helped scientists understand the effects of objects, such as glass blockages, windows, air conditioners, and toilets, on airflow patterns and virus outbreaks. Previous simulations have generally assumed a large, open indoor space, but have not considered the effect of nearby walls, which may be present in narrow corridors.

Cough drops open space

The drops resulting from a cough from a walking person spread apart in a narrow corridor and an open space. In an open space, the droplets are spread over a large range attached to the person. Sincerely: Xiaoli Yang

If a person walking in a corridor coughs, their breath exhales droplets that travel around and behind their body, forming a wave in the form of water in the boat that travels. Investigation has revealed that a “re-circulation bubble” is directly behind the person’s torso and a long waking behind them at approximately waist height.

“The flow pattern we have found is strongly related to the shape of the human body,” said Xiaoli Yang. “2 meters downward, wake at mouth height and foot height are almost negligible but still visible at waist height.”

Once the airflow pattern was determined, the probe modeled the spread of a cloud of expelled droplets from the fake person’s mouth. The size of the location around the moving person is particularly important for this part of the calculation.

Two types of dispersion modes were found. In one mode, a cloud of droplets separates from the moving person and floats far behind the person, creating a floating bubble of virus-filled droplets. In other modes, the cloud attaches to the person’s back, moving behind them like a tail as they move into space.

Drop cloud

In both modes, the cloud of droplets hovers at about half the height of the infected person before reaching the ground, indicating a greater risk for the drops to the children. Sincerely: Xiaoli Yang

“For different modes, the droplet concentration is much higher than for the attached mode, five seconds after coughing,” Yang said. “This is a major challenge in determining safe social distance in places such as a very narrow corridor, where one can inhale viral droplets, even if the patient is in front of or away from it.”

This danger is especially great for children, because in both modes, a cloud of droplets hovers at a distance above the ground that is about half the height of the infected person – in other words, at the level of the mouth for children.

References: “The Effect of Space Size on the Spread of Coughing Drops from a Walking Person,” by Zhobin Li, Hongping Wang, Xinlei Zhang, Ting Wu, and Xiaoli Yang, 15 December 2020. Physics of fluids.
DOI: 10.1063 / 5.0034874

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