Researchers at the Massachusetts Institute of Technology have developed a model for understanding the risks of COVID-19 transmission in indoor settings.
It involves looking at factors like exposure time, number of people, size of the space and the types of activity, among others.
“What we are pointing out is the influence of what we call long-range airborne transmission, through tiny aerosol particles that are omitted when people are simply breathing, and are enhanced when they’re talking or singing or doing other activities such as that,” Dr. Martin Bazant, Professor of Chemical Engineering & Mathematics at MIT.
He noted that all respiration produces much smaller aerosol droplets that do not settle to the ground quickly and are carried away in the air currents. And that’s where social distancing becomes less helpful indoors, because any droplets produced while breathing travel throughout the entire indoor space regardless of where a person is standing.
Dr. Bazant said that many studies have already declared that social distancing indoors did not reduce the risk of COVID-19 transmission, and that people who were even six feet or more away from an infected person in an indoor space still contracted the virus. But he also said that the number of people in a room and the time spent in a room also play a factor in risk, as well as whether or not people wear their masks.
“So that’s our goal here, to provide some quantitative guidance, not only for individuals deciding to go to work or to school, or go to the grocery store, but also for policy makers,” Dr. Bazant said. “Because our analysis allows us to quantify how much safer would the space be. For example, if you were to increase the ventilation rates given the additional cost that would incur in terms of energy and carbon footprint, etc.”
Dr. Bazant and his team reflected their model in a new app site, which allows people to determine the latest COVID-19 guidelines for indoor spaces based on a range of room types, human behavior, age group and virus strain. People and policy makers can select different category filters to find out the best actions to take and what to keep in mind for different situations.
“The output of the app itself right now is in the form of simple text, where users who are not so technically inclined,” Dr. Bazant said. “And it also produces graphs of those quantities so you can look at it that way. And of course one can color code."
Dr. Bazant said that another extension of the app that his team is working on is to monitor carbon dioxide levels in a room.
“So this is an interesting approach that was proposed a number of years ago by other scientists, in which we have actually integrated with our guideline to give a measurement of or an interpretation of what would be a safe carbon dioxide level in that room,” Dr. Bazant said. “And the way that works is that, when people are in the room and exhaling, they’re producing carbon dioxide and that has been removed by ventilation flows. And so the average level of carbon dioxide you measure in a space reflects the balance of those two flow rates.”
Dr. Bazant hopes that in the near future public spaces like schools will have carbon dioxide sensors and color coding systems to inform of the risk level for that particular space.
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