Past investigations utilizing a similar simulation technique have assisted scientists to better understand the influence of various objects, such as glass barriers, windows, air conditioners, and toilets, on airflow patterns and spread of viruses.
In most cases, those simulations only used large, open indoor spaces and didn’t consider the effects of nearby walls, which would be present in a narrow corridor.
The results revealed that when an individual coughs while walking quickly down a corridor, the expelled droplets were found to travel around and behind the body—and potentially infecting people trailing behind. In many instances, children had a higher transmission risk.
The study further showed the existence of a “re-circulation bubble” that is located directly behind the person’s torso and a long wake streaming out behind the individual at approximately waist height.
“The flow patterns we found are strongly related to the shape of the human body,” the study’s author Xiaolei Yang said in a news release.
“At two meters downstream, the wake is almost negligible at mouth height and leg height but is still visible at waist height.”
After determining the airflow patterns, the researchers were tasked with modeling the dispersal of a cloud of droplets expelled from the simulated person’s mouth. That is when the team noticed that the shape of the space surrounding the moving person was particularly critical in better understanding the varying risks of virus transmission.
In the end, two types of dispersal modes were found. In one, the cloud of droplets detaches from the moving individual and floats far behind, creating a floating bubble of virus-laden droplets.
In the other mode, the cloud of droplets is attached to the moving individual’s back, trailing behind as if it were a tail.
“For the detached mode, the droplet concentration is much higher than for the attached mode, five seconds after a cough,” Yang said.
“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.”
Children, in particular, had a greater transmission risk because in both modes the cloud of droplets often hovers at a height of roughly two to three feet—which is at the mouth level of many children.
Ethen Kim Lieser is a Minneapolis-based Science and Tech Editor who has held posts at Google, The Korea Herald, Lincoln Journal Star, AsianWeek, and Arirang TV. Follow or contact him on LinkedIn. Image: Reuters.