Thread by @CorsIAQ

Portable HEPA Filter Systems.
1/ The cost of retrofitting EVERY public school classroom in the entire US w/ a portable HEPA air filter w/ CADR = 300 cfm is approximately $1 billion w/ recurring cost of about $300M/yr for replacement filters. To be clear, EVERY single classroom.

2/ For a classroom that holds 20-25 students, say 600 to 700 ft2 w/ ceiling height of 9 ft, this portable HEPA unit will yield approx equivalent increase in ventilation (equivalent ACH increase) of 3/hr. For a classroom under-ventilated to 2 ACH the bump up is to 5 ACH!

3/ That leads to a 60% reduction in inhalation dose of aerosol particles. Capacity exists. It can be done now.

4/ The cost to put a very good portable HEPA filtration system in every classroom in US is less than $10/student/year, with recurring filter costs of around $3/student/year. (Thanks to Mark Hernandez of CU Boulder for inspiring that analysis in our webinar today).

5/ That bears repeating. The cost to put a very good portable HEPA filtration system in every classroom in US is less than $10/student/yr, with recurring filter costs of around $3/student/yr. And a substantial reduction in inhaled dose. What's the cost of a textbook? Mic drop.

6/ Add 50% efficient masks on everyone (emitters and receptors) and the overall dose reduction is 90% (10 x reduction in inhalation dose). Just 2 steps in layered risk reduction. We have not even gotten to the hard stuff yet.

7/ If we layer universal mask wearing w/ portable HEPA and “reasonable” increased ventilation for many schools, it is not difficult to exceed 95% inhalation dose reduction (20 x reduction in inhalation dose). And that’s just 3 steps in layered risk reduction.

8/ I am just getting warmed up. But I think that I will stop here and conclude with the following .......

9/ We can do this. It is not rocket science. But schools are getting a lot of contradictory and confused messaging. I have spoken with many school districts. Many of them (not all) are confused beyond belief, and some are falling for unproven or ineffective technologies.

10/ Layered risk reduction. Simple steps. Proven technologies. @j_g_allen and I did the portable HEPA filter analysis in an Op-Ed in the Washington Post in July 2020. The US, Canada, and other nations have lost precious time and great opportunities to do this right. Just Do It!

Approximately $1B is actually on the high side as it assumes a $300 system. I recently purchased a large number of very good HEPA air filters for my college @Portland_State and received a bulk discount w/ actual cost < $200/unit.