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MIT researchers say time spent indoors increases the risk for Covid to 6 feet or 60 feet in a new study

Customers dine at Picos Restaurant, which was threatened after the announcement of its continued need for masks as the state of Texas prepares to lift its mask mandate and shut down business during the coronavirus disease (COVID-19) pandemic in Houston, Texas, to fully expand again. March 9, 2021.

Callaghan O’Hare | Reuters

The risk of exposure to Covid-19 indoors can be as high at 60 feet as it is at 6 feet in a room where the air is mixed – even if a mask is worn, according to a new study by researchers at the Massachusetts Institute of Technology, challenging social distancing guidelines adopted worldwide.

MIT Professors Martin Z. Bazant, who teaches chemical engineering and applied mathematics, and John WM Bush, who teaches applied mathematics, developed a method of calculating the risk of exposure to Covid-19 indoors that takes into account a variety of issues that have an impact could be transmission, including time spent inside, air filtration and circulation, immunization, variant strains, mask use, and even respiratory activity such as breathing, eating, speaking, or singing.

Bazant and Bush, in a peer-reviewed study published earlier this week in Proceedings of the National Academy of Science of the United States of America, question long-standing Covid-19 guidelines that require 6 feet of space between People from the Centers for Disease Control and Prevention recommend America. They say staying 6 feet away from someone else may not be enough if people are in the house for an extended period of time.

“We claim that the 6-foot rule really doesn’t have much of an advantage, especially when people are wearing masks,” Bazant said in an interview, since everyone in the room breathes the same air. “It really has almost no physical foundation as the air a person breathes while wearing a mask tends to rise and fall elsewhere in the room, leaving you more exposed to the average background than a person in the distance.”

Without the masks, however, Bazant said 6 feet would provide additional protection against Covid-19 versus 3 feet. This is especially true when a person is breathing directly towards you, creating something called a “plume of breath,” like a puff of smoke from a smoker. Their research was based on models that assume the air in the room is “well mixed” and that “the pathogen is evenly distributed,” they said in a follow-up statement to CNBC on Monday.

In well-mixed spaces, “60 feet are no safer with airborne pathogens than 6 feet,” they said.

The important variable that CDC and World Health Organization guidelines have overlooked is time spent indoors, Bazant said. The longer someone is in the house with an infected person, the greater the chance of transmission, he said.

Opening windows or installing new fans to keep the air moving could be just as effective or more effective than spending large sums of money on a new filtration system, he said.

Bazant also says the guidelines for enforcing indoor occupancy limits are flawed. He said 20 people who gathered for a minute are probably fine, but not over several hours, he said.

Small, poorly ventilated rooms, where many people spend a lot of time together, put people most at risk, he said.

“Unfortunately, the nursing home is one of those cases. When Covid patients live together around the clock, in some cases even in the same room, this is absolutely the worst scenario, especially given the vulnerability of this population,” Bazant added.

On the other hand, their analysis shows that many places that were closed didn’t necessarily have to close, he said.

“Often times the room is big enough, the ventilation is good enough, the time people spend together is such that these rooms can be operated safely even at full capacity, and the scientific support for reduced capacity in these rooms is real not very well, “said Bazant, quoting some of the university classrooms. “I think if you enter the numbers, even now, for many types of rooms, you will find that no occupancy restrictions are required.”

According to Bazant, social distancing and occupancy rules that have led to closed businesses and schools are oversimplified.

“That emphasis on distancing was really misplaced from the start. The CDC or the WHO never really provided a justification for it. They just said that this is what you have to do, and the only justification I know of is based on coughing and sneezing studies that look at the largest particles that could settle on the floor and even if it’s very approximate you can certainly have large droplets of greater or shorter range, “said Bazant.

“The distancing doesn’t help you that much, and it also gives you a false sense of security because you are just as safe at 6 feet as you are at 60 feet when you are inside and the air is mixed well. Everyone in this room is about the same At risk, “he noted.

Droplets laced with pathogens move through the air indoors when people are talking, breathing, or eating. Airborne transmission is now known to play a huge role in the spread of Covid-19 compared to the earlier months of the pandemic when hand washing was seen as the top recommendation to avoid transmission.

These droplets from a person’s warm exhalations mix with body heat and air currents in the area to lift and move throughout the room, bringing them all to a well-mixed room that is at risk of airborne transmission.

According to the study, people seem to be more exposed to this “background air” than distant droplets, such as B. Secondhand smoke.

For example, if someone infected with Covid-19 wears a mask and sings loudly in an enclosed space, a person sitting on the other side of the room will be no better protected than someone just 6 feet from the infected person sitting person. Because of this, the time you spend in the confined area is more important than the distance from the infected person.

Masks generally prevent transmission by blocking larger droplets. Therefore, larger droplets don’t make up the majority of Covid infections when most people are wearing masks. The majority of people who transmit Covid do not cough or sneeze, they are asymptomatic, Bazant said.

Masks prevent transmission indoors by both filtering out exhaled infectious droplets and blocking exhaled air jets. This is best illustrated by the idea of ​​someone exhaling smoke. Exposure to these infectious air rays results in a higher risk of transmission compared to the well-mixed background, according to Bazant and Bush in an earlier study.

Masks aid indoor transmission by both filtering out exhaled infectious droplets and blocking exhaled air jets that become visible when a smoker exhales. Exposure to exhaled rays of infectious air results in a higher risk of transmission compared to that of the well-mixed background, Bazant and Bush said.

Those who are in the same room as a smoker are severely affected by the second-hand smoke that moves and lingers around the enclosed area. The same logic applies to infectious airborne droplets in well-mixed rooms, according to the study. Indoors and when masked, factors besides distance can be more important to avoid transmission.

Although Bazant and Bush’s study didn’t specifically look at transmission outdoors, Bazant said that social distancing outside makes little sense because warmer air that is exhaled tends to rise and infected air to be swept away by the wind.

“Air follows the path of least resistance and often with many masks, that’s straightforward,” said Bazant. “Exhaled air is obviously much warmer than the background and tends to rise. By the way, that’s the main reason that there is almost no point in distancing yourself outside, and especially with masks, it’s kind of crazy because you really don’t . ” transferred to someone within 6 feet.

“When you look at the flow of air outside, the infected air is essentially being swept away and is very unlikely to cause transmission. There are very few recorded cases of outdoor transmission,” he said. Although rare, he said it was always possible to contract Covid-19 outdoors, especially in crowded places like concerts. “Crowded outdoor spaces could be a problem, but if people keep a reasonable distance of about 3 feet outside, I feel pretty comfortable with it even without masks.”

For variant strains that are 60% more transmissible, increasing ventilation by 60%, reducing the time spent indoors, or limiting the number of people indoors could offset that risk, he said.

Bazant also said a big question will be when to remove masks and that the study’s guidelines can help quantify the risks involved. He also noted that measuring carbon dioxide in a room can also help quantify how much infected air there is, and therefore the risk of transmission.

“We need scientific information that is conveyed to the public in a way that is not only frightening but actually based on analysis,” said Bazant. After three rounds of intense peer reviews, he said it was the most review he had ever been through and he hoped it would affect policy after it was published.

Bush and Bazant issued a statement Monday to CNBC clarifying some of Bazant’s earlier comments.

“Our study shows that the six-foot rule is not enough to limit the transmission of COVID-19 in indoor air: You also have to limit the time spent in an indoor area. Our study shows how this time limit is relevant Factors including room ventilation and filtration and face mask use, “they said, noting that” face masks can be an extremely effective indoor safety measure “.

Editor’s Note: The heading and article have been updated to add more citations and context to the researchers’ findings and opinions. Bazant said his comments on the outdoor broadcast were his opinion, not the formal results of the study.

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