Time for another thread on CO2 in classrooms:

 

TLDR:

Determine the time it takes for the CO2 concentration in EMPTY classroom to decline from 1200 ppm to 800 ppm:

Good: Less than 9 minutes

Bad: More than 30 minutes

In between: Meh…. better get filtering

https://threadreaderapp.com/thread/1509211030966132749.html