Thread by @sri_srikrishna

GROUNDBREAKING + EPIC TEST: Bioengineers 👩‍🔬👨‍🔬 at CDC conducted world’s 1st “crash test” of Do-It-Yourself (DIY) air purifiers to check if they cab stop viruses 🦠 between test dummies. It’s like NHTSA running crash tests with dummies in cars 🚗 🚙. (1/16) sciencedirect.com/science/articl…

MAIN FINDING: CDC engineers validated 12+ air changes per hour (12 ACH) 🌪️ in a realistic size classroom of 6000+ cu. ft. but it takes more than one 🍇 DIY air purifier. Tested w/ most penetrating particle size (0.3 to 0.6 μm). 12 ACH is like a passenger jet inflight 🛫. (2/16)

CDC engineers found DIY air purifiers using single filter (DIY Ford) delivered about half of the air exchanges (CADR) of a four filter Corsi-Rosenthal box (DIY Cubes), give or take. Roughly consistent with my own tests: 2 x 1-filter = 1 x 4-filter. (3/16)

Most interestingly, CDC engineers tested 7 box fans and discovered an Air King model (Fan A) delivered 2x as much airflow (CADR) as other popular models. In addition to filter, the choice of fan (brand) matters more than perhaps been appreciated. (4/16) amazon.com/Air-King-9723-…

WHY did CDC do these “crash tests”? CDC engineers said biologically (1) infectious aerosols float🎈indoors for hours indoors (2) people can spread the virus 🦠 without symptoms 🤧 (3) vaccinated people 💉can have breakthrough 💘infections. Unambiguously in black and white. (5/16)

+ economically (4) too hard to improve airflow 💨 with HVAC in old buildings 🏡 (5) opening windows 🪟 easy but pulls in dust, pollen🤧, pollution 🔥, etc increases heating/cooling cost (6) varies depending on # of windows and outside conditions (7) HEPA purifiers costly. (6/16)

So CDC says they looked at DIY as potentially cost-effective solution due to “low cost, ease of construction and ready availability compared with higher cost and limited availability of
commercial HEPA air cleaners,”citing my own tests on this. (7/16) sciencedirect.com/science/articl…

They simulated people 👨‍👩‍👧 who were exhaling or inhaling aerosol particles into the room 🌬️ using a potassium chloride (KCl) solution (salt water🧂) at 1.25 L/breath and 12 breaths/minute = minute ventilation rate of 15 L/min. (8/16)

Another CDC insight is it takes 2x CR boxes to tango 👯‍♀️ or equally 4x 1-filter DIY 👨‍👩‍👦‍👦, “In addition to increasing filtration rate of the room air, using two DIY units instead of one also increased air mixing and produced a more uniform reduction in aerosol concentration.” (9/16)

One limitation of CDC study as authors acknowledge, “It should be noted the original Ford DIY air filtration units used 4” thick filters rather than the 1” and 2” used in our modified design; thus, the original design likely would have provided better performance” (10/16)

Just recently the EPA independently published evaluations of DIY air purifiers both citing my paper from last May. (11/16)

https://twitter.com/sri_srikrishna/status/1598955030408998913

This summer, @RanuDhillon @AbraarKaran and I wrote to CDC asking them to say clearly how many air changes per hour are necessary to slay Covid for good. (12/16) jamanetwork.com/journals/jama/…

CDC's said 5-6 ACH but 12 or more ACH maybe needed in some situations. Together with the new CDC and EPA studies, these are all making a case for use of DIY as a cost-effective solution for stopping spread of COVID and variants in 2023. (13/16)
jamanetwork.com/journals/jama/…

Last month my road trip 🚘 w/ my kids included N95 masks and 3-4 DIY air purifiers in the trunk of the SUV 🚙 for the hotel room 🏨 / Airbnb where masks 😷 must come off. Also lugged DIY on airplanes ✈️ as checked baggage 🧳 in cardboard boxes and they survive the flight. (14/16)

The USA 🇺🇸 gets stuff done. As CDC experts showed, with DIY the barriers to clean air 🌪️ are falling fast 🍃. Future is bright ☀️ if White House (@WHOSTP + @AshishKJha46) can 🙏🏽 break it down how to do 12 ACH w/ DIY in a crystal clear way so everyone can themselves. (15/16)

I'll breathe 🧘‍♂️ easier when airplane-like 12 ACH 🛫 becomes a minimum expectation in every room just like 120V electricity ⚡️. (16/16) @AbraarKaran @RanuDhillon latimes.com/opinion/story/…

@jljcolorado @j_g_allen @ShellyMBoulder @danaparish @PPEtoheros @EricTopol @ashishkjha @glagoudas @WBahnfleth @larrybrilliant @linseymarr @meghamama @betsyladyzhets @AlpertReyes @CorsIAQ @JimRosenthal4 @Don_Milton @MonicaGandhi9 @tanyalewis314 @changcon

“The DIY air filtration cube flow rate averaged 121% higher than the modified Ford DIY air filtration unit.”

@mtosterholm @DrEricDing @kprather88 @DFisman @drdavidmichaels

@trishgreenhalgh @zeynep

@CathNoakes @masknerd

Got the Air King (Fan A). Even on low speed, it is quite a bit more airflow but also much more noisy than the Lasko (Fan E). Subjectively, Air King on low is like Lasko on medium or high.