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Devabhaktuni
@sri_srikrishna
Jun 11 • 6 tweets • 2 min read • Read on X
Ceiling fan🌸OBLITERATED CLOSE-CONTACT 🧑‍🤝‍🧑 RISK:

In eLetter in Science, we suggested CEILING FANS might cut short-range risk (w/ ventilation for long-range).

Singapore lab found just that (2023): mannequin underneath fan 5 ft from cough 🌬️ inhaled ~ 95% FEWER particles.

(1/6)
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METHODS: To track individual particles as they flowed from cough to inhalation they DID EVERYTHING:

(1) LASER photography

(2) AEROSOL measurements in lab

(3) computer SIMULATIONS with computational fluid dynamics (CFD) on using parallel computation with 960 CPU cores

(2/6) Image
SETUP: The experiments tested how liquid aerosols EMITTED from a cough machine are TRANSPORTED to breathing mannequin placed 5 feet away directly underneath the ceiling fan, with the fan OFF versus ON

(3/6) Image
RESULTS: The fan ON was almost as good as wearing a well-fitting N95 (vs fan OFF):

95%, 94%, and 96% REDUCTIONS seen with aerosol measurements when mannequin was UNDERNEATH the fan.

(4/6) Image
The paper was PEER-REVIEWED and published Building and Environment in 2023 (paywall). Preprint below.

(5/6)

sciencedirect.com/science/articl…
Here is is the free pre-publication preprint

(6/6)

htps://papers.ssrn.com/sol3/papers.cfm?abstract_id=4269544

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More from @sri_srikrishna

Devabhaktuni
May 19
A 3000x breakthrough in H5N1 wastewater testing from Texas

Thread🧵

(1/25)
COVID-19 in wastewater was presumed to be from humans 👶👧🧒 but with H5N1 it maybe humans or animals (birds 🦆, cows 🐄 , etc.)

(2/25)
This week CDC rolled out a national influenza A wastewater dashboard 📺 similar to COVID-19 (3/25) cdc.gov/flu/avianflu/h…
Read 25 tweets
Devabhaktuni
May 17
Great, timely coverage by @susrust about a BREAKTHROUGH by Texas scientists @MikeTisza et al in wastewater testing for H5N1 where I was quoted,

“The Texas’ team approach exhibited “proof of principle” for employing metagenomic testing protocol for wastewater and air.”.
BACKGROUND: COVID-19 found in wastewater was presumed to be mostly from humans but with H5N1 it maybe humans or animals (birds, cows, etc).
THE PROBLEM: The wastewater testing in California and on the new national CDC dashboard amplify public worry about the fear of H5N1 spreading in humans without telling us whether it is human or animal origin, or if the
virus is starting to transmit efficiently among humans.
Read 5 tweets
Devabhaktuni
May 12
For EFFICIENT SPREAD of H5N1, this 2023 article by @kakape suggests the following list of 4 mutations are necessary (but not necessarily sufficient):

Thread 🧵

science.org/content/articl…
(1) PB2 —> E627K (single amino acids, glutamate to lysine)
(2) hemagglutinin —> Q226L (one nucleotide) + G228S (two nucleotides)
Read 6 tweets
Devabhaktuni
Feb 27
The trusty Temtop PMD 331 is ISO certified but PRICEY ($1399).

Are there cheaper particle counters to test DIY air purifiers that still work well at 0.3 μm or at submicron particle sizes?

Here is what I found.

(1/9)


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The Temtop PMD 331 is ISO-certified.

It enables testing performance of DIY and HEPA air purifiers at 0.3 μm using AMBIENT aerosols.

It was necessary to convince the peer-reviewers in my publication (2022).

(2/9)
sciencedirect.com/science/articl…
Image
I first found out about the Temtop PMD 331 in 2021 here on Twitter from a physics professor who (unfortunately) deleted his Twitter account.

Temtop PMD 331 is a GREAT PRODUCT and UNIQUE find, useful for many applications.

(3/9)

temtopus.com/products/temto…
Read 9 tweets
Devabhaktuni
Feb 13
MERV 16 vs 13: LONG TERM TEST 🏎️

— Summer ☀️ ‘23: 160 SAFE boxes installed in classrooms of middle school 🏫 in SF.

— Mix of 5” MERV 16 and 5” MERV 13 (both Lennox).

— TEST: Filtration💨 at 0.3 μm (%) before vs after 1 semester 📆 daily usage ⏳

Results below.

(1/8)
FILTERS CHOSEN FROM CLASSROOMS WITH DAILY USAGE ⏳:

To measure filtration efficiency (%), filters chosen from classrooms where teachers 👩‍🏫🧑‍🏫 self-reported daily usage in survey (Dec ‘23 ❄️).

Fans run 🔄 by teachers during school 🌞 turned off🎚️after school 🌙

(2/8)
FILTERS TESTED BY COMPARING INPUT VS OUTPUT @ 0.3 μm:

The test 🧪 method for SAFE boxes 📦 was described in my research 🧐 publication (section 2) using ISO-certified, factory calibrated optical ⚡️particle counter.

(3/8)

sciencedirect.com/science/articl…
Read 8 tweets
Devabhaktuni
Jan 12
SAVING FLOORSPACE: after we figured out low-noise air purifiers in 2022-23, surveys of teachers using 3+ SAFE air purifiers per classroom revealed need to take up less floorspace in cramped classrooms 🏫 .

Can stacking them TRIPLE the CADR in same real estate?

(1/8)
Image
Three SAFE boxes were needed to get 6 air changes per hour in a classroom at Aptos Middle School in San Francisco.

(2/8)

At first I used a $50 rack from Amazon

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Read 9 tweets

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