In flight to #AAAR to present a poster w/ my kids “Making Aerosol Precautions for COVID-19 More Easily Accessible and Affordable to Everyone” tysm @HuffmanLabDU. On flight ✈️ I brought tools (CO2, 0.3 μm OPC) to see what’s up here at 30,000 feet 👣 (1/3) aaarabstracts.com/2022/view_abst…
CO2 🧘‍♀️: compared to hair-raising reports of 2000+ ppm on other flights, CO2 has been relatively tame on jet bridge, while airplane ✈️ was on ground, and once in flight about 1000-1500 ppm. Still high relative to home 🏡 (800-1000 ppm) but not as high as I feared. (2/3)
0.3 μm particles⚡️ : much more interesting. After pilots 👩‍✈️🧑‍✈️ turned off seat belt sign, I ran a particle counter 💻 and it was ~10,000 per liter (typical for outdoor). An hour into flight it was ~300 which usually takes ~10 ACH at home. Inflight HEPA filtration at work! (3/3)
Having fun doing science experiments at 30,000 feet aboard the “clean room” environment on the airplane. The video shows 0.3 μm aerosol particle counts at ~300 per liter and then rising above ~800 within seconds of popping open a Coke can @adsquires @mikechenwriter @PlasticFull

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More from @sri_srikrishna

Oct 2
@WmHaseltine keenly points out a new CDC study (Aug 2022) found isolating in different rooms reduced transmission by over 80% during alpha + delta waves. Seems that is the real headline of the study, this data was buried in table 3 and not even mentioned in the abstract. (1/4)
Other things like using different bathrooms, avoiding close contact, also reduced risk of household transmission. Staying in separate room, avoiding close contact, and using own bathroom may be impractical in many cases e.g. large families living in small apartments. (2/4)
Data on mitigation (odds ratio of transmission)

Stayed in separate room (0.17)

Avoided close contact (0.33)

Used own bathroom (0.35)

Avoided sharing drinks and utensils (0.52)

Wore mask (0.81)

Slept in alone in room (0.82)

See Table 3 (3/4)
academic.oup.com/ofid/article/9…
Read 4 tweets
Sep 30
How do we reconcile expert differences about level of airflow needed to stop viruses? Lack of expert consensus responsible for ventilation ‘limbo’ from ASHRAE + CDC on what exactly we need to do for infection control in non-healthcare settings (schools, homes, offices). (1/16)
As early as Aug 2020, @ShellyMBoulder was advising 6-9 ACH, “most experts consider roughly 6 air changes an hour to be good… In a pandemic this should be higher.. an exchange rate of 9 times per hour reduced the spread of SARS, MERS and H1N1…” (2/16)

theconversation.com/amp/how-to-use…
Yet her coauthor from the classic paper on the Skagitt Valley superspreading event, @CathNoakes, just this week said to use volume-independent airflow not ACH (volume dependent). (3/16) onlinelibrary.wiley.com/doi/10.1111/in…
Read 18 tweets
Sep 23
Tracking Covid tests in classrooms in 2 waves (Delta + Omicron), Italy’s ventilation study best confirms aerosols as not just a possible route, but main route. Tech + epi details I learnt talking to Drs. Buonanno/Sabile, not obvious to me in preprint (1/) arxiv.org/abs/2207.02678
They analyzed database of SARS-CoV-2 transmission in ~10,000 classrooms (w/o extra ventilation) and w/ ventilation installed in 300+ classrooms. Database was handed to them directly by govt of Marche who invested in ventilation months before Delta/Omicron (not foreseeable). (2/)
In-classroom infection (“clusters”) was officially tracked as >= 2 infections per classroom *in a 5-day period* during Delta (Sept-Dec, 2021), and >=3 during Omicron (January, 2022). 5-day thresholds to define “clusters” standardized by govt. of Marche, not by researchers. (3/)
Read 7 tweets
Sep 23
Is there actually any evidence that ventilation 🌪 actually reduces Covid infection rates in humans 🦠? (1/9)
Yes some want more evidence from the US 🇺🇸. There are some very small-scale trials of air filtration (US/UK) I am aware of but data from these trials most probably won’t be available until next year. Even then their scale will be merely a few percent of data from Italy.
(2/9)
This week I spoke to 2 researchers on an Italian study of 10,000 schools 🇮🇹. From understanding their methods not apparent to me from reading their preprint, there is unlikely to be anything remotely close on the horizon from anywhere in world 🌎. (3/9) reuters.com/world/europe/i…
Read 11 tweets
Sep 16
Has there ever been a federal program in history where "hundreds of billions of dollars" remain unspent? Tens of billions in Emergency Relief (ESSER) money $$ intended to make schools 🏫🧑‍🎓👩‍🎓safe from COVID-19 🦠 remains unspent. Let's look into why it maybe. (1/12)
@AshishKJha46 noted school districts have “access to billions of dollars” from federal government 🦅 🇺🇸 to improve ventilation & filtration 🍃🪟 but why after 2 years hasn't it turned into 6+ ACH 🌪️in classrooms + eating areas where needed most? (2/12)
First, federal government handed money to states and didn't say how to use it. Data below says districts spent the largest share—about 29%—on academic interventions, not upgrading HVAC, ones who did faced delays due to labor + supply chain issues. (3/12) ncsl.org/research/educa…
Read 12 tweets
Sep 11
Why are the CDC webpages for ventilation inconsistent?? 🤡 This week I discovered CDC recommends 7.5 ACH of air filtration for homes 🏡 w/ 8 ft ceilings (6 w/ 10 ft), 2/3 of that for buildings 🏙(=5 ACH), 2-3 ACH air filtration in schools 🏫. Let’s break it down. (1/25)
If you look at the CDC webpage for homes, "When choosing a HEPA cleaner… look for one that has a Clean Air Delivery Rate (CADR) that meets or exceeds the square footage of the room(s) in which it will be used." (2/25) cdc.gov/coronavirus/20…
This means a ‘1/1 rule’ in which CADR (cfm) = Area (in square feet). For a typical 8 foot ceiling, this means if this scales with height (h) then CADR = Area x h / 8 = Volume / 8, so ACH = CADR * 60 / Volume = 60 / 8 = 7.5 ACH. (3/25)
Read 27 tweets

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