If you find yourself about to follow someone else into a narrow corridor or hallway, consider holding back for a few minutes or finding an entirely different route altogether.
An important new study from the American Institute of Physics reports infectious viral droplets tend to group together and linger longer in narrow indoor areas as opposed to more open spaces.
Troublingly, study authors speculate the usual six-foot social distancing rule may not be enough to ensure safety while walking behind someone else in a narrow hallway. If the person ahead of you happens to be infected with COVID-19 and ends up sneezing or coughing, it will likely result in a concentrated cluster of infectious viral particles waiting to greet you.
This risk appears to be especially high for children as well. In most simulations, the viral particles hovered above the ground at about half the height of the infected individual. That’s roughly mouth level for most young children.
Earlier studies had focused on how various items in a closed setting, such as windows, barriers of any sort, or air conditioners influence indoor viral airflow patterns in large, open rooms.
This research, however, is the first to focus on narrow hallways or corridors specifically. Considering how common such areas are in office buildings, restaurants, retail stores, and any number of other buildings, the importance of this work can’t be overstated.
Whenever a person coughs or sneezes while in a narrow hallway, that action produces numerous droplets that travel from the front to the back of the body. Researchers liken this phenomenon to how a boat will form a “wake” in the water as it moves. From there, they say the droplets form a “recirculation bubble” or trail that in many cases extends from the person’s torso to over six feet behind them. The farther this “bubble” travels, the closer to the ground it becomes.
“The flow patterns we found are strongly related to the shape of the human body,” says study author Xiaolei Yang. “At 2 meters downstream, the wake is almost negligible at mouth height and leg height but is still visible at waist height.”
Based on their calculations, the research team says viral spread in hallways usually happens according to two distinct “modes.” The first, called a detached mode, is when the droplets really spread out and float far behind the original cougher.
The second mode is characterized by the viral “cloud” being attached to the cougher’s back, essentially acting like an infectious tail joined to their backside.
“For the detached mode, the droplet concentration is much higher than for the attached mode, five seconds after a cough,” Yang explains. “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.”
Like so many areas of life that COVID has complicated, it isn’t reasonable to expect people to avoid hallways for the remainder of this pandemic. But, if you can opt for a more open route to where you are headed, try to stay away from narrow indoor areas the best you can. Similarly, the next time you inevitably find yourself trailing behind someone in a corridor, be sure to put a lot of distance between you and them.
The full study can be found here, published in Physics of Fluids.