How risky are indoor spaces during COVID pandemic? This tool helps you figure it out

·3 min read

Since the beginning of the coronavirus pandemic, health officials have been telling the public to maintain a 6-foot distance from others to curb the spread of COVID-19.

Now, two professors from the Massachusetts Institute of Technology say such spacing doesn’t protect against contagious aerosols floating in the air and mixed throughout a room.

In fact, “people are no safer from airborne transmission at 60 feet than 6 feet” while indoors, they wrote.

So, the pair developed an interactive, physics-based “COVID-19 Indoor Safety Guideline” that provides individuals, businesses, schools and policymakers a tool to understand how long, on average, a person can safely engage in an activity in a certain room — restaurant, church, classroom, office, subway car, airplane, living room — before catching the coronavirus, given an infected person is in the space.

The website and phone app allows users to enter specific details about a scenario, such as the floor space size, ceiling height, number of people, type of ventilation, average age of the group, type of activity (exercising, whispering, singing), what kind of masks are being worn, if any, and the predominant coronavirus strain spreading in the area.

And that’s just in “basic mode.” Switch to “advanced mode,” and users can determine how long it would take for one person to get infected in a given room based on local coronavirus spread and immunity in a population from either vaccination or prior infection.

‘A false sense of security’

The team’s analysis assumes an indoor space has “well-mixed air,” but the condition may not apply to all rooms because it depends on many factors, such as people’s movements, forced convection from vents and fans, and “buoyancy-driven flows” from heaters, air conditioners or windows.

A study on the guidelines was published Tuesday in the journal PNAS.

“If you understand the science, you can do things differently in your own home and your own business and your own school,” study lead author Martin Bazant, professor of chemical engineering and applied mathematics at MIT, said in a statement. He developed the tool with mathematics professor John Bush.

“For airborne transmission, social distancing in indoor spaces is not enough, and may provide a false sense of security,” Bazant told The Washington Post.

Health experts have long acknowledged that airborne transmission — when coronavirus particles emitted from coughing, sneezing, eating or talking float in the air for long periods of time — plays a major role in COVID-19 spread.

Calculations for the model were based on data from various mass-spreading events, including the infamous two-hour choir practice in Washington state that led to 86% of seniors present becoming infected with the coronavirus, and two deaths.

“Efficient mask use’ is effective

In a hypothetical scenario in a restaurant where people aged 15-64 are dining without masks, 10 people could safely eat their meals for about three hours before potentially getting infected. If the restaurant has 25 people present, that safe exposure time drops to a little over an hour.

A screen grab of a hypothetical scenario in a restaurant using MIT’s “COVID-19 Indoor Safety Guideline.”
A screen grab of a hypothetical scenario in a restaurant using MIT’s “COVID-19 Indoor Safety Guideline.”

The tool suggests that if people spend approximately two hours in the same restaurant, occupancy should be limited to 15 people on the assumption that the space’s air is well-mixed.

“The risk would be higher if someone is positioned directly within a focused jet of particles emitted by a sneeze or a shout,” the researchers said.

The study’s main message: the “6-foot rule” doesn’t “reflect the full picture” of coronavirus risk in indoor settings.

“Efficient mask use is the most effective safety measure, followed by room ventilation, then filtration,” Bush told The Post. “And risk increases with the number of occupants and the exposure time, so one should try to spend as little time as possible in crowded indoor spaces.”

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