MIT Scrutinizes Social Distancing Guidelines

Researchers propose a new approach to estimate the risks of COVID-19 exposure for indoor settings.

April 26, 2021

6ft distance floor sign

BOSTON—Two MIT professors have developed guidelines for indoor COVID-19 risk that suggest a limit for exposure time based on the number of people, the size of the space, the kinds of activity, whether masks are worn and the ventilation and filtration rates, according to a press release.

As businesses, schools and individuals try to gauge their own risks, Martin Z. Bazant, professor of chemical engineering and applied mathematics, and John W. M. Bush, professor of applied mathematics, say their model offers a detailed, physics-based guideline.

“As scientists, we’ve tried to be very thoughtful and only go with what we see as hard data,” said Bazant. “We’ve really tried to just stick to things we can carefully justify.”

The model provides an estimate of how long, on average, it would take for one person to become infected with the SARS-CoV-2 virus if an infected person entered an indoor space. For example, how long a person could safely expect to engage in an activity, whether it’s a few minutes in a store, an hour in a restaurant or several hours in an office or classroom.

“We argue there really isn’t much of a benefit to the six-foot rule, especially when people are wearing masks,” Bazant told CNBC. “It really has no physical basis because the air a person is breathing while wearing a mask tends to rise and comes down elsewhere in the room so you’re more exposed to the average background than you are to a person at a distance.”

Bazant also suggested that social distancing may have been “misplaced from the very beginning.” He said that the CDC and WHO “never really provided justification for it, they’ve just said this is what you must do and the only justification I’m aware of, is based on studies of coughs and sneezes, where they look at the largest particles that might sediment onto the floor and even then it’s very approximate, you can certainly have longer or shorter range, large droplets.”

In terms of distancing, the actual distance may not matter, suggested Bazant: “The distancing isn’t helping you that much and it’s also giving you a false sense of security because you’re as safe at six feet as you are at 60 feet if you’re indoors. Everyone in that space is at roughly the same risk, actually,” he said.

As for social distancing and wearing a mask outdoors, Bazant commented that it’s “kind of crazy.”

“If you look at the air flow outside, the infected air would be swept away and very unlikely to cause transmission. There are very few recorded instances of outdoor transmission.” he said. “Crowded spaces outdoor could be an issue, but if people are keeping a reasonable distance of like three feet outside, I feel pretty comfortable with that even without masks frankly.”