Infected Person Hurrying Down A Narrow Hallway Leaves A 'Wake' Of Virus-Laden Droplets

A long stream of virus-laden droplets trails behind a coronavirus-infected person walking fast down a narrow corridor, a new computer simulation suggests.

When researchers modeled airflow patterns, they found it might be risky to walk down a narrow corridor behind someone else, even if current social distancing guidelines are followed, according to the report published in Physics of Fluids.

"The most important finding of this study is that the transmission of COVID-19 is highly influenced by the airflow and that a slight difference in the airflow can significantly alter the virus spreading pattern in the air," said study coauthor Xiaolei Yang, a professor in the institute of mechanics at the Chinese Academy of Sciences in Beijing. "In this study, the change of airflow is caused by a minor difference in the corridor width and the walking speed. However, such a change can also come from other factors, such as the indoor architectural structure, the temperature, the humidity, etc."

​

"There are two take-home messages for the public," Yang said in an email. "First, six feet is not enough for narrow corridors, and wearing a face mask is recommended even if you do not see people around. Second, the viral droplets behind a walking person tend to hover at the waist height, so short kids are exposed to higher risk than adults."

To take a closer look at how architectural features might impact the spread of the virus, Yang and his colleagues constructed a model of air flow using one set of equations. The dispersion of droplets expelled by a person breathing or coughing was modelled using Lagrangian equations of motion, which specifically look at the motion of particles.

The researchers' model showed that in the scenario of a fast walker in a narrow corridor a cloud of droplets emitted as a person coughs would expand in size as the walker progressed and pretty quickly start to lose velocity. Visually, it would resemble the wake of a boat traveling through water. After two seconds passes, the cloud drops to about waist height.

"For narrow corridors, six feet social distancing is not enough, so it is better to keep the maximum distance with the person in front and to wear mask even if you cannot see people around," Yang said. "When you are with a child, you may want to hold him/her in your arm to keep the child away from the virus hovering layer at adult's waist height."

The new study is "interesting," said Dr. Jessica Justman, an associate professor of medicine in epidemiology at the Columbia University Mailman School of Public Health in New York City.

"We haven't really paid much attention to what happens when we're standing behind someone who coughs, just in front," Dr. Justman said. "It's interesting to point out the theoretical risk of being behind someone who coughs."

Still, Dr. Justman said, "I'm not alarmed. But it does emphasize what we already know is important: wearing a mask."

—Linda Carroll

Source