Thread by @DrEricDing

AIR DISINFECTION—To reduce airborne #SARSCoV2 risk, new study finds HEPA cleaners, with total air exchange rate of 5.7  ACH/hour, after 2 hours in closed room with a highly infective person—the inhaled dose is 6x reduced!

➡️We need these for schools.🧵
tandfonline.com/doi/full/10.10…

2) In times when classes were conducted with windows and door closed, the aerosol concentration was reduced by more than 90% within less than 30 minutes when running the purifiers (air exchange rate 5.5 /hour)—and decreased by more than 95% within 37 minutes.

3) A **halving of the particle concentration was reached in 10.0, 7.0 or 5.4 minutes** (green, black and red lines, respectively), depending on the total flow of the purifiers.

The blue line shows a typical slow decrease when no purifiers were used.

4) Bottomline: Air disinfection cleaners can “reduce the aerosol load in a classroom in a fast, efficient and homogeneous way.”

(I have no relationships with any HEPA filter company)

5) “In situations when windows and doors are closed for a longer period of time a large reduction in the inhaled dose of particles containing virus RNA is achieved and therefore the risk of aerosol infection is likely to be lowered”

6) That said, ventilation is most key. VENTILATION is key. Both ventilation and masks needed to reduce risk indoors. But most buildings not ventilated well enough. Hence need for air cleaners like portable HEPA filters.

7) The good news is that there is $130 billion designated for schools in the Democratic proposed bills! And it will offer funding for ventilation. But will it be prioritized? I’m trying to work on this on behalf of schools. Will keep you all posted on the progress.

8) Meantime, there is another alternative poor-man’s Jerry rigged solution with a box fan + 4 or 5 MERV13 air filters... to create a “Corsi Box”!!! And it works great according to experts if you can keep it together well.

https://twitter.com/DrEricDing/status/1362895328459059200

9) Ideally, we want 5-6 air exchanges (ACH) per hour, via combination of air cleaning + natural ventilation. But many school classrooms have natural ACH of just 0.5 per hour... average was 2-2.5 for school classrooms sampled / assessed in Arlington, Virginia (personal comm).

10) Sadly, ventilation guidance in the CDC school reopening report was buried. It does exists but very weakly in the technical details.

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

11) That said, the CDC does give indoor air guidance for #COVID19 and recognizes ventilation, HEPA filters, and germicidal UV light (that avoid ozone).

cdc.gov/coronavirus/20…

12) Meanwhile, the EPA also give indoor air cleaning guidance. Depending on room size you should get a HEPA filter with certain minimum CADR (Clean air delivery rate) needed for your room. Go with 300 CADR level HEPA filter to be safe for most rooms.

epa.gov/sites/producti…

13) If you’re technical, there is calculator for what you need based on room size, ceiling height and ventilation situation. The higher the CADR, the more air changes per hour. Your goal is minimum three to five total air changes per hour. But 6 is ideal.

tinyurl.com/portableaircle…

14) Besides #COVID19 risk, there’s also small studies that show low ventilation rates in elementary schools correlate with low math scores. pubmed.ncbi.nlm.nih.gov/17100667/

15) To be clear, natural ventilation still best. Here is how to ventilate your school classrooms if unable to open window. #COVID19

16) Air disinfection for classrooms with portable HEPA is also very affordable— cost is just <$10 per student to start and only $11/student for 3 years, according to @CorsIAQ. Much less than cost of most school books.

https://twitter.com/corsiaq/status/1363734151271092224?s=21

17) The DIY Corsi Box (also called by some as the Comparetto Cube) as a low cost way to filter the air, is also a good kids learning activity.

Though nota bene—don’t touch the sides of the filter after it starts running. Virus particles can stick to it.
nbc12.com/2021/02/20/car…

18) We need CDC and OSHA standards for safe school & workplace ventilation and air cleaning guidelines!!! See my detailed 🧵 of what we need for safe schools!

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