Fast walking in narrow spaces behind a group of people can significantly increase COVID-19 transmission risk, especially in children, according to a study which says virus-laden respiratory droplets can trail behind infected individuals moving through such 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 through the air.
While earlier studies highlighted the influence of objects, like glass barriers, windows, and air conditioners on airflow patterns and virus spread, the scientists from the Chinese Academy of Sciences in Beijing said these simulations usually assumed large, open indoor spaces.
However, the effect of nearby walls, like those that might exist in a narrow corridor have not been considered, the researchers added.
According to the current study, if a person walking in a corridor coughs, their breath expels droplets that travel around and behind their body, forming a wake in the same way a boat forms a wake in water as it travels.
The research revealed the existence of a “re-circulation bubble” directly behind the person”s torso and a long wake streaming out behind them at approximately waist height.
“The flow patterns we found are strongly related to the shape of the human body,” said study co-author Xiaolei Yang.
“At two metres downstream, the wake is almost negligible at mouth height and leg height but is still visible at waist height,” Yang said.
Once the airflow patterns were determined, the scientists then modelled the dispersal of a cloud of droplets expelled 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 one mode of dispersal, the study noted that the cloud of droplets detaches from the moving person and floats far behind that individual, creating a floating bubble of virus-laden droplets.
In another mode, it said the cloud is attached to the person”s back, trailing behind them like a tail as they move through the space.
“For the detached mode, the droplet concentration is much higher than for the attached mode, five seconds after a cough,” said Yang.
“This poses a great challenge in determining a safe social distance in places like a very narrow corridor, where a person may inhale viral droplets even if the patient is far in front of him or her,” he added.
The scientists warned that the danger is particularly high for children, since the cloud of droplets seem to hover at a distance above the ground that is about half the height of the infected person which is at mouth level for children.