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University of Michigan Experts Share Tips on Controlling the Spread of COVID-19 in Classrooms – WDIV ClickOnDetroit | Gmx Pharm

ANN ARBOR – As students return to classrooms this fall and transmission of COVID-19 continues, two University of Michigan experts share best practices for schools and teachers when it comes to keeping indoor spaces well ventilated.

Aerosol scientists Andrew Ault and Kerry Pratt have been advising public school systems on how to contain the transmission of COVID-19 in classrooms since the pandemic began.

They say social distancing is not enough to keep students from breathing in aerosols, which can remain airborne in a room for hours.

Associate Professors at UM’s Chemistry Department recently shared tips on how teachers can create the safest environment for their class. One way is to make a do-it-yourself air filter by gluing an oven filter around a box fan. Masks and open windows are also key to limiting exposure, the researchers said.

The university recently published this Q&A with Ault and Pratt.

Can you describe how airborne transmission of COVID works?

Airborne transmission means that a virus is spread through aerosols, which are tiny particles that we exhale into the air when we breathe and speak. The louder we speak or breathe harder, the more aerosols we emit. When someone has COVID, these aerosols contain viruses (SARS-CoV-2) that can infect others who breathe the aerosols. These aerosols are so small (100 times smaller than the diameter of a human hair) that they can remain in the air for hours.

How can humans visualize airborne transmission through aerosols?

You can think of the transmission of aerosols as cigarette smoke, which is similar in size to exhaled aerosol. Smoke travels through rooms and collects in poorly ventilated areas. Back when smoking was allowed in restaurants and bars, it didn’t matter if you moved a table or sat on the other side of the restaurant, everyone was inhaling the smoke.

How do aerosols move in closed spaces like classrooms?

Classrooms are like any other interior space. When infected children or adults are in the room, they exhale aerosols containing the coronavirus, and these aerosols hang in the air like smoke. The best thing you can do to prevent others from breathing these virus aerosols is to wear masks and improve ventilation by filtering and opening windows.

What affordable ways are there for teachers and school administrators to make classrooms safer for students?

There are a number of low-cost actions schools can take to clean the air and reduce transmission of COVID-19.

  • All students and adults should wear masks at all times indoors as respiratory aerosols are released through breathing. Masks reduce the amount of aerosol emitted into the room by an infected person (including asymptomatic people) and also reduce the amount of aerosol inhaled by another person (reducing the risk of infection). Mask fit is important, with the mask fitting snugly (i.e. not leaking) against your face to ensure the best protection. KF94, KN95 and N95 masks are readily available and offer an even higher level of protection than cloth and surgical masks by removing more than 90% of the aerosols exhaled by others when inhaled.

  • Eat outdoors and have students eat in individual, well-ventilated classrooms rather than large cafeterias during inclement weather to reduce the number of students exposed to an infected person.

  • Improve ventilation, which can be as cheap as opening a window. Steps beyond opening a window are to use fans to bring in fresh air and push dirty air out. Improving ventilation has the added side benefit of improving cognitive function by reducing carbon dioxide build-up.

  • Finally, a cool do-it-yourself option is to make a Corsi-Rosenthal Cube, a box fan with 5 MERV-13 furnace filters glued together that can be made for less than $100. Research shows that these filters reduce aerosol concentration and they are used in many schools across the country. Commercial HEPA air filter units are also available that cost more. There should be at least one HEPA air filter/cube in each classroom and multiple filters/cubes in larger indoor spaces. Portable HEPA air filters complement HVAC MERV-13 filters by filtering the air immediately around students.

Do not purchase ionizers, ozone generators, or products that claim to use ions/chemicals to remove viral particles. We in the indoor air community have tried to sound the alarm about this, but unfortunately many individuals and school districts have squandered large amounts of money on products that do not effectively remove viral aerosols but introduce other harmful gases. HEPA and MERV 13 level filtration is the best option for aerosol removal as used in hospitals.

How can teachers or school administrators monitor indoor air quality and determine if a room may have high aerosol concentrations?

A carbon dioxide monitor (about $250) will tell you how much exhaled air has accumulated in a room. With good ventilation, indoor and outdoor carbon dioxide concentrations should be similar (about 420 ppm). If the carbon dioxide level reaches more than 800ppm, it means the room is poorly ventilated and you are rebreathing the air that someone else was exhaling. This requires the need for increased ventilation (opening a window to mix in outside air) and adding an air filter unit to remove exhaled aerosol.

How will what we’ve learned about aerosol transmission of COVID affect how we deal with other illnesses like the flu or the common cold?

What we’ve learned about aerosol transmission of COVID can greatly improve the way we manage many other airborne respiratory diseases, such as influenza, and improve our overall health. By improving indoor ventilation, we reduce transmission of respiratory diseases, reduce exposure to air pollution and allergens such as pollen, and improve cognitive function (by reducing exposure to high levels of carbon dioxide). In many countries, even before COVID-19, it was common practice to wear a mask when ill to prevent infecting others.

We have received public health guidance on social distancing – what does this mean in the context of airborne transmission?

Just like standing next to a smoker, more aerosol is exhaled when close to a person, so social distancing reduces exposure, particularly to droplets. However, aerosols travel much further than 6 feet through rooms and accumulate in poorly ventilated spaces. To think of it another way, if you’re in a pool and someone pees in it, you don’t want to stay in the pool, even if you’re more than 6 feet away from them. This is why, in addition to social distancing, covering and airing indoors is so important.

What is the difference between exhaled droplets and aerosols?

Droplets are emitted when coughing and sneezing and are about the diameter of a human hair (100 times larger than aerosols). Droplets stay airborne for only a few seconds while traveling a distance of up to 6 feet. Since the early 1900s, most physicians thought that infectious diseases spread primarily through droplet and surface contact. This was partly because droplets and surfaces are easier to measure.

Over the course of this pandemic, we have found that thinking has become obsolete. Aerosols can remain airborne for hours in poorly ventilated indoor spaces, infecting people across rooms who inhale the previously exhaled aerosols. There is now overwhelming evidence that aerosols are the way COVID-19 is transmitted.

What is the Riskiest Part of the School Day for Transmission of COVID?

The riskiest part of the school day is anytime the students are inside and being exposed together. For students wearing masks, this risk comes with lunch or a snack. Having multiple cohorts (classrooms) of students together in a cafeteria/dining room increases the number of students exposed to an infected person as the aerosols travel throughout the room well beyond 3-6 feet. Eating al fresco is the best solution, but in inclement weather the next best thing is for small cohorts to eat in well-ventilated classrooms to reduce the number of students exposing each other to prevent outbreaks.

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