Thread by @CorsIAQ

1/ New CDC recommendation on ventilation - as equivalent ACH (eACH). Aim for at least 5 air changes each hour and upgrade to MERV-13 filters. More thoughts below.

cdc.gov/coronavirus/20…

2/ It's a good start and should decrease inhalation dose of respiratory aerosol concentrations by between about 20% to 40% in many classrooms (based on my experience w/ typical starting points in schools --some w/ recirculation through MERV-13 filters already achieve 5 eACH).

3/ Importantly, it is NOT difficult to achieve MUCH higher than 5 ACH in classrooms - even approaching 10 equivalent ACH w/ ASHRAE 62.1 ventilation + a #CorsiRosenthalBox, or 6 ACH w/ 62.1 in a typical classroom & a good HEPA air cleaner.

4/ NIOSH reports 12.4 eACH on top of typical classroom ventilation with 2 CR Boxes in a classroom. That will often lead to 15+ eACH, pushing 80% reduction in inhalation dose of respiratory aerosol particles in tytpical classrooms w/ unit ventilation.

ncbi.nlm.nih.gov/pmc/articles/P…

5/ In my opinion, I would treat 5 equivalent ACH as a MINIMUM value (if not already there school districts are doing a disservice). 20 to 40% reduction in inhalation dose is better than 0%. 80% reduction in inhalation dose is better than 20 to 40%.

6/ Not rocket science, folks. Just do it!