Thread by @CorsIAQ

1. Estimating w/ a conservative (overestimates for safety) model for different univ classroom scenarios an acceptable fraction of max capacity to avoid one infection from far field (not close contact) aerosols containing SARS-CoV-2 w/ 1 infector in room. (more)

2. For a large # of classrooms between 500 to 1,000 sq ft. Average room supply flow rates of 150 to 1,000 scfm with average outdoor air % ranging from 38 to 63%. Fall climate in Pacific NW. 75 min class periods - truncated 110 min lectures (more)

3. Fraction of max capacity determined for "as is" (scenario 1), replacement of MERV 8 with MERV 13 filters (scenario 2), & MERV 13 filters + a portable HEPA air cleaner w/ CADR = 250 scfm (scenario 3). (more)

4. Average fraction of max capacity for 75 min class period: scenario 1 = 0.18; scenario 2 = 0.31; scenario 3 = 0.49. Some variation between classrooms (COV slightly less than 0.25). 110 min class period approx 0.6 x of these values. (more)

5. Simultaneous increase of room supply air and outdoor air supply rate will also raise fractional max capacity above "as is", although with high starting OA% there is a short ceiling on increase. (more)

6. Scenarios did NOT include all students wearing masks nor did they include close contact (near field) effects.

Interestingly, scenario 2 leads to a fraction of max capacity that is similar to that obtained for 3 ft. radius (6 ft. distancing) in many classrooms. (more)

7. For situation described here, & accounting for conservative nature of the far field aerosol model, it appears that appropriate physical distancing, required use of masks, and "some" increase in ventilation/improved filtration will significantly reduce infection risk. (more)

8. But REMEMBER. This is for specific buildings w/ specific mechanical systems and classrooms in a specific climate zone. Results for the far field aerosol model will vary to some extent for other universities.

But proper physical distancing and use of masks should not!