Thread by @DrEricDing

HUGE—CDC just released NEW indoor air guidance for schools & #COVID19! Now emphasize: “Opening windows, using portable air cleaners, improving building-wide filtration are ways to increase ventilation in school or child care program.” Good, but caveats:🧵 cdc.gov/coronavirus/20…

2) “Bring in as much outdoor air as possible.
If safe to do so, open windows and doors. Even just cracking open a window or door helps increase outdoor airflow, which helps reduce the potential concentration of virus particles in the air.”

3) “Use child-safe fans to increase the effectiveness of open windows. Safely secure fans in a window to blow potentially contaminated air out and pull new air in through other open windows/doors.

4) “Consider having activities, classes, or lunches outdoors when circumstances allow.”

👏 YES YES YES 🙌 !!

5) “Ensure Heating, Ventilation, and Air Conditioning (HVAC) settings are maximizing ventilation.
Make sure your ventilation systems are serviced and meeting code requirements. They should provide acceptable indoor air quality, as defined by ASHRAE Standard 62.1

6) “Set HVAC systems to bring in as much outdoor air as your system will safely allow. Reduce or eliminate HVAC air recirculation, when practical and with expert HVAC consultation.*

7) “Increase the HVAC system’s total airflow supply to occupied spaces when you can. More air flow encourages air mixing and ensures any recirculated air passes through the filter more frequently.

8) “Disable demand-controlled ventilation (DCV) controls that reduce air supply based on occupancy or temperature. This way the air supply will remain constant throughout the day.

9) “For simple HVAC systems controlled by a thermostat, setting the fan control switch from “Auto” to “On” to ensure continuous air filtration and distribution. Consider running the HVAC system at maximum outside airflow for 2 hours before and after the building is occupied

10) “Filter and/or clean the air in your school or child care program.  
Improve the level of air filtration as much as possible without significantly reducing airflow.
Make sure the filters are sized, installed, and replaced according to manufacturer’s instructions.

11) “Consider portable air cleaners that use high-efficiency particulate air (HEPA) filters to enhance air cleaning wherever possible, especially in higher-risk areas such as a nurse’s office or sick/isolation room.

12) “Consider using ultraviolet germicidal irradiation (UVGI) in schools and non-home-based child care programs as a supplemental treatment to inactivate the virus that causes COVID-19, especially if options for increasing ventilation and filtration are limited.

13) “Use exhaust fans in restrooms and kitchens.
Ensure restroom and kitchen exhaust fans are on and operating at full capacity while the school or child care program is occupied and for 2 hours afterward.”

YES!!! Thank you on bathroom ventilation. Toilet plumes are real risk!

14) “Open windows in transportation vehicles.
Ventilation is important on buses and vans servicing schools and child care programs, along with other strategies such as mask use for people over 2 years old and physical distancing.

15) “Keep vehicle windows open when it does not create a safety or health hazard. Having more windows open is more helpful, but even just cracking a few windows open is better than keeping all windows closed.”

16) My take... I think this is a HUGE improvement from before when they only offered generic ventilation guidance for #COVID19 risk. But no guidance for schools specifically. It had lacked lots of things. cdc.gov/coronavirus/20…

17) And it’s an VAST improvement from the barely discussed or uttered ventilation in recent school reopening guidance.

https://twitter.com/drericding/status/1360343218177646597

18) As many of you know I’ve been advocating daily on this topic. That said the new guidance is missing a key thing — explicitly recommending a minimum or optimal AIR EXCHANGE RATE - the ACH per hour. We need explicit numbers on how much— an ACH target.

https://twitter.com/drericding/status/1364062371883470853

19) To be fair, the new CDC guidance indirectly directs people to ASHRAE standards for ventilation, and they do mention ACH. But this is very indirect and that website CDC links to is **behind a paywall**!

20) We need optimally 5 or more ACH per hour from combination of ventilation + air cleaning. Most school classrooms naturally have how much? Roughly ~2 according to @CorsIAQ and my @smartrestartaps colleagues at Arlington VA public schools. Some as low as 0.5!

https://twitter.com/DrEricDing/status/1364063590370713600

21) This is why we, led by @smartrestartaps, sent a letter to U Senator @MarkWarnerVA to follow the science and prioritize funding for ventilation/ indoor air quality. @APSHearOurVoice supported, as did teachers from Arlington and Fairfax, VA. Notably...

22) We asked that the Congress prioritize “school COVID safety expenditures for airborne transmission mitigation and rapid testing are legislatively prioritized ahead of other less effective school mitigation measures.”...

23) We had a 7 point priority list:

✅=in CDC guidance
✔️=mentioned elsewhere on CDC
📝=Experts

📌HVAC upgrades✅
📌Air cleaners ✅
📌Upper room UV for larger rooms✔️
📌outdoor / safe lunches✅
📌CO2 monitors📝
📌More school #COVID19 tests✅
📌Premium masks funding📝

24) Bottomline: Experts are heartened by the new CDC school air quality guidelines. But now, to make it happen— we need CONGRESS to step up and make sure it is **PRIORITIZED** in the #COVID19 relief bill’s $130 billion school support package.

25) And does HEPA filter air disinfection work? Heck yes. New recent study... 🧵

https://twitter.com/drericding/status/1363638390432948227

26) So if we advise aiming for 5 ACH per hour for a classroom, how do we calculate it from our HEPA? Using the CADR value of a portal air cleaner & dimensions of a room.

https://twitter.com/DrEricDing/status/1364066127182254081

27) here is the formula to use. This tells you how many Eq ACH your cleaner will add to ventilation.

CADR➡️ Equivalent ACH

Eq ACH = CADR *60/(A*Z)

A =floor area in square feet
Z =ceiling height in feet

*60 to convert CADR to cubic feet per hour

Eq ACH = air changes per hour.

28) The math is very simple for any regular classroom. Total ACH is then simply natural ventilation ACH + air cleaner equivalent ACH ==> target is 5 when summed together.

If less than 5? Use a HEPA with higher CADR rating, or just add another HEPA.

29) The EPA has pre suggested a few example room sizes and CADR minimums for a HEPA filter to cover such a room. If your CADR falls below the room area, then you might need to add 2nd HEPA (check math above).

P.s. I have no relationship or investments with any HEPA company.

30) for larger school venues like gymnasium, indoor pools, auditoriums, cafeterias (aka shouting + indoor dining galore) etc— they are too big for HEPA filters. For these, one needs “Upper Room UV”. And CDC does recommend Upper room UVGI in their other ventilation guidelines!

31) Again, remember this ACH/hour rule of thumb for indoor air quality we need:

📌4 is sorta okay

📌5 is what we should aim for

📌6 is ideal

P.s. Upper Room UV for large spaces can achieve >15 ACH/hour if done well!

32) More details of why air quality via ventilation and air cleaning is critical. This was written just below the new guidelines (top post above) came out overnight. I’ve been clamoring at this for month like many aerosol scientists.

https://twitter.com/drericding/status/1365543775167275009

33) critical urgency now: I’m told schools want to use the $130 bil (130k schools) to backfill budget deficits. But THATS NOT GONNA SOLVE the pandemic and make schools safer for kids.

Airborne transmission is real—we need air cleaning & ventilation now!🙏

34) And yes, we definitely want vaccinations for teachers ASAP. I’ve endorsed this position many times. But should it be a prerequisite to reopening? Not if we have premium masks, ventilation, and frequent testing. End of the day low transmission and airborne precautions better.

35) The good news is that $130 billion designated for schools is coming in the Democrat proposed bills! And it will offer funding for ventilation. But will it be prioritized?!?! We need to contact your US senators -& demand prioritize (earmark) ventilation in $1.9 mil COVID bill!

36) Here is the cost breakdown of one good portable HEPA filter per standard classroom. The total cost across 3 years is just $11/student. That is nothing compared to the cost of other school materials. this improves learning! We need to do this. We can afford it with new aid.

37) And workers who blow the whistle on workplace airborne transmission concerns and ventilation issues should not be muzzled or retaliated against, like being fired. This is also illegal under OSHA rules. Yet #TraderJoes did just that for advocating exactly CDC recs. Not okay.

https://twitter.com/drericding/status/1365840941605675010