The air in schools

As my epidemiological interests have shifted since the conversation has increasingly moved to schools and public places, indoor air quality experts Richard Corsi and Joseph Allen have been indispensible follows on twitter.  Here they team up to explain what we need to do, air quality-wise, if we’re going to let kids in schools.  Obviously, there’s lots of other concerns– especially amount of spread in the larger community– but insofar as many districts are sending kids back in person, period, we should have the best science guiding us on the air the kids are breathing and how that relates to viral transmission:

We have limited time and funds to get students and teachers back to school safely, but we can — and must — do it. Here’s how.

Start with the fact, as 239 scientists recently wrote to the World Health Organization (WHO), that airborne transmission of the novel coronavirus is happening. This is not to be feared; it just requires adding some new strategies to our arsenal in addition to hand-washing, distancing and other measures to keep community spread to a minimum. (Just because we reopen schools doesn’t mean we should reopen elsewhere.)…

A: Air cleaner in every classroom

Portable air cleaners, also known as air purifiers, may be the fastest way to clean the air quickly indoors. A portable air purifier with a HEPA filter that is correctly sized for the room can deliver three air changes per hour of clean air, meaning all of the air in the room is cleaned every 20 minutes.

R: Refresh indoor air

Every effort should be made to determine how much more outdoor air can be brought into schools, but there are limitations. In summer and winter months, the amount of air that can be brought in from outside will be limited by the cooling and heating capacity of existing HVAC systems. While bringing in twice as much as the minimum ventilation standard would be an excellent strategy, there may not be enough time or money to fix all of these school ventilation problems in the next 30 days before kids come back to school. That doesn’t mean we shouldn’t try.

Schools should also upgrade recirculated air filters to MERV13 or higher. If schools rely on natural ventilation, get those windows open and use simple box fans to pull in outdoor air.

It’s time get creative and re-imagine classrooms. We don’t need to think about ventilation rates if we hold classrooms outdoors. Yes, there will be inclement weather — kids and teachers will have to wear hats and gloves when it gets cold, and papers will occasionally get blown around. But this is still far superior to learning via Zoom. A massive mobilization of tents for schools, maybe by the National Guard, could get us there. Think this is impossible? We’ve done it before, during the tuberculosis epidemic.

And here’s all the key points in one handy graphic:


On a very personal, practical level, my school system is starting almost all on-line, but not the Special Education classes (for the obvious reasons).  So, thanks to these guys I’m going to make sure my son’s classroom has an air filter that exceeds 300 CADR.

If you want to learn even more about this, Allen has a terrific twitter thread where he links to all their efforts via Op-Eds, etc., on educating the public on how to make schools safer.

And here’s the whole Healthy Buildings report for schools which is terrific.

About Steve Greene
Professor of Political Science at NC State

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