Opinion | Want to buy schools time? Open the windows. - The Washington Post
▻https://www.washingtonpost.com/opinions/2020/08/27/want-buy-schools-time-open-windows
For classrooms, we recommend aiming for five air changes per hour (that is, the full volume of air in the room is changed or cleaned every 12 minutes), but the perfect cannot be the enemy of the good. The massive costs of keeping kids out of school, the lower risk profile of kids, and universal mask-wearing and other risk-reduction strategies mean we shouldn’t set a bright line for keeping kids out of school. Four air changes per hour of dilution plus cleaning is good, five is excellent, and six is ideal.
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Opening windows is not a panacea and doesn’t mean we should not pursue other strategies. Buildings with mechanical systems should be set to the maximum amount of outdoor air possible, and schools should increase filtration to a MERV 13 filter or better on recirculated air. School officials should also be measuring flow rates and doing what they can to increase how much outdoor air comes inside.
If they can’t bring in enough outdoor air to hit the air-changes-per-hour target, they shouldn’t despair. There is always another way. Air cleaning through the use of portable air cleaners removes airborne viruses, providing four to six air changes on their own when sized correctly for the classroom.