Brisk walking in tight spaces behind a group of people can significantly increase COVID-19 risk of transmission, especially in children, according to a study that states that virus-laden respiratory droplets can drag infected individuals along as they move through these corridors.
The results of the computer simulation, published in the journal Physics of Fluids, underscored the importance of the shape of spaces in predicting how virus-laden droplets move in the air.
While previous studies have highlighted the influence of objects, such as glass barriers, windows and air conditioners on airflow patterns and the spread of the virus, scientists from the Chinese Academy of Sciences in Beijing have said that these simulations they usually assume large and open interior spaces.
However, the effect of neighboring walls, such as those that might exist in a narrow corridor, was not considered, the researchers added.
According to the current study, if a person walking down a corridor coughs, his breath expels droplets that travel around and behind his body, forming a wake in the same way a boat makes a wake in the water while traveling.
The research revealed the existence of a “recirculation bubble” directly behind the person’s torso and a long trail running behind them at about waist height.
“The flow patterns we found are strongly related to the shape of the human body,” study co-author Xiaolei Yang said.
“Two meters downstream, the trail is almost negligible at the mouth and leg, but it is still visible at the waist,” Yang said.
Once the airflow patterns were determined, the scientists then modeled the scattering of a cloud of droplets ejected from the simulated person’s mouth.
They said the shape of the space surrounding the moving person is particularly critical for this part of the calculation.
In a dispersal mode, the study found that the droplet cloud detaches from the moving person and floats a lot behind that person, creating a floating bubble of virus-laden droplets.
In another mode, it said that the cloud is attached to the person’s back, trailing behind them like a tail as they move through space.
“For the detached mode, the droplet concentration is much higher than in the connected mode, five seconds after a cough,” Yang said.
“This poses a great challenge in determining safe social distance in places like a very narrow corridor, where a person can inhale viral droplets even if the patient is far in front of him or her,” he added.
Scientists have warned that the danger is particularly high for children, as the cloud of droplets appears to hover at a distance from the ground that is about half the height of the infected person who is at the level of the children’s mouth.