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Devabhaktuni
Devabhaktuni "Sri" Srikrishna
@sri_srikrishna
Working on how to stop spread of viruses since 2014. Founder https://t.co/HWrQJSBTiV: N95 + air purifier how-to. MS (EECS). Like, share, or retweet ≠ endorse.
4 subscribers
Dec 15 • 9 tweets • 3 min read
Few days ago I met a gentleman in a bar who asked me "why are you still wearing a mask (N95)", insisting "I'm not judging just trying to understand" but after I explained why (covid tx risks), he asked "why" repeatedly and said "that is crazy."

What is the best way to respond? Covid can be life threatening and it recently killed a physically fit, otherwise healthy friend of mine while he was undergoing cancer treatment. @michael_hoerger @anchari mercurynews.com/obituaries/jim…
Dec 11 • 6 tweets • 3 min read
Why Covid risk is flight-duration dependent (box model):

Airbus A321
200 people
1 infector
113 ft x 12 ft x 10 ft
12 air changes per hour (measured by me)

3d plot
Z-axis: infection risk (UC-Colorado estimator)
X-axis: hours of flight
Y-axis: infector's viral exhalation rate Image
Image Observations (consistent w/ study):

(1) Covid risk (by aerosol) is low for short flights (< 2 hrs)

(2) Risk rises duration-dependently for medium (4-6 hrs and long (> 10 hrs) flights

(3) Risk also depends on how fast virus is exhaled by infector (quanta emission rate)
Sep 21 • 4 tweets • 2 min read
HEAVENLY 😇 MATCH ❤️

U-C Berkeley put:

modest 🐇 ventilation 🌪️ (6.4 ACH)

+ slow 🐢 ceiling fans 🌸 (122 ft/min)

in conf. room w/ olive oil 🫒 aerosol released like breathing 🧘‍♀️

RESULT (vs 6.4 ACH 🌪️ alone):

-77 % (less) aerosol @ CLOSE-UP

+5% aerosol @ LONG-RANGE

(1/4) Image +5% increase in long-range exposure with ceiling fans at 6.4 ACH 🐇 was still 80% lower than at 1.6 ACH 🐌

For future experiments:

What would the reduction in exposure be at 12 ACH 🐎 like on passenger airplanes ✈️ ?

(2/4) Image
Sep 3 • 5 tweets • 3 min read
California (@CAPublicHealth) webpages on ventilation for schools vs skilled nursing facilities are night 🌙 and day ☀️

The school webpage obfuscates quantitative target + tech details needed for clean air in classrooms.

@CorsIAQ @kprather88 @RanuDhillon @AbraarKaran

(1/5) The CDPH webpage for ventilation in schools is a bunch of cartoons and lacks important quantitative details

(2/5)
cdph.ca.gov/Programs/CID/D…


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Jun 29 • 8 tweets • 3 min read
HAIR-RAISING ⁉️: @SF_DPH is “aware” of H5N1 in SF wastewater but doesn’t know where it is coming from: animals or humans 🤷‍♀️ 🤷‍♂️?

Timely and insightful coverage by @susrust

I’m quoted: This is concerning b/c of urban origin, not many dairy 🐄 or animal 🐓 farms in SF.

(1/8) Why don’t we know? SF is relying on OLD-SCHOOL 🏫targeted methods, kind of like a "magnifying glass," 🔎 to look for influenza A and H5.

(2/8)
Jun 11 • 6 tweets • 2 min read
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)
Image 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
Jun 7 • 25 tweets • 7 min read
Today, Science published my eLetter with @RanuDhillon critiquing the "per person" ventilation target of:

14 lps / person🧍(21 cfm / person)

proposed in Science article by Morawska et al. and replacing it with “per room” 🏡 + mixing targets.

(1/22)
science.org/doi/10.1126/sc… The eLetter cites CDC's Ventilation page + fundamental research by some of the authors (incl. @Don_Milton, @ShellyMBoulder, @CathNoakes, @jljcolorado, @linseymarr) to derive a potentially better and more efficient ventilation target than 14 lps / 21 cfm per person.

(2/22)
May 19 • 25 tweets • 6 min read
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)
May 17 • 5 tweets • 2 min read
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).
May 12 • 6 tweets • 1 min read
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)
Feb 27 • 9 tweets • 5 min read
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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Image 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…
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Feb 13 • 8 tweets • 3 min read
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)
Jan 12 • 9 tweets • 3 min read
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)

Jan 5 • 7 tweets • 4 min read
MASSIVE POLLUTION FROM A FROZEN PIZZA 🍕:

Since it is the new year I decided to relax 😎 and try out new brand of thin crust frozen pizza.

But I got totally smoked 🔥 .

(1/7) Image Directions are to place it directly on the center oven rack which I did.

(2/7)
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Dec 8, 2023 • 9 tweets • 2 min read
SURVEY of 18/18 teachers 👩‍🏫 🧑‍🏫 using DIY and HEPA air purifiers 💨 at Commodore-Sloat elementary school 🏫 in San Francisco 🌉:

89% using them DAILY 🕰️

11% using them WEEKLY 📆

(1/8) Why do you USE air purifiers in your classroom?

89% COVID 🦠

89% air circ. ♻️

83% Respiratory viruses besides COVID (e.g. flu) 😷

67% wildfires 🔥

56% air circ. when hot 🥵

50% air pollution 🚭

39% allergies 🤧

17% control odors 💩

11% industrial pollution 🏭

(2/8)
Aug 16, 2023 • 26 tweets • 8 min read
Today, Statnews published my new op-ed on WILDLY 🔥 INACCURATE BP READINGS sometimes with home BP machines. (1/25) statnews.com/2023/08/15/at-… HYPERTENSION is the #1 risk factor for death globally 🌎. It’s no surprise cheap BLOOD 🩸 PRESSURE (BP) MACHINES are in clinics + homes across the US 🇺🇸. “Get It, Slip It, Cuff It, Check It” makes it sound so simple 🤡. (2/25) Image
Aug 13, 2023 • 14 tweets • 4 min read
PARENTS: ARE YOU WORRIED 😟 ABOUT BAD INDOOR AIR QUALITY 💨🤧🔥IN YOUR KID’S SCHOOL?

A step by step guide on how to fix 🛠️it (with a little luck 🍀 🤞)

(1/14) Perhaps you “put the moose 🫎 on the table” in past but unaddressed b/c:

(1) school staff receptive but other things taking priority ✌🏽.

(2) staff opposed to better air quality😡.

(3) staff or district were sold on a bogus air cleaning tech 😍.

2, 3 harder, 1 easier.

(2/14)
Aug 12, 2023 • 23 tweets • 10 min read
CLEAN AIR IN *ALL* CLASSROOMS 🌎: This morning ☀️ I was so excited to address teachers at Aptos middle school (6-8) in SF about 160 DIY air purifiers. Congrats 👏to parents who built, installed 3 of them in ALL CLASSROOMS in summer. Below my notes, Q&A from morning talk. (1/23)

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Image TEACHER QUESTION #1: How long do the filters last? Best data from 1+ year operation at Commodore-Sloat Elementary school 📚 in SF ❤️ is the Lennox MERV 16 filters last over a year subject to ymmv based on environmental conditions 🔥 . (2/23) https://t.co/tBEjPfiSotmedrxiv.org/content/10.110…
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Aug 7, 2023 • 5 tweets • 4 min read
THE MAGIC 🦄 OF POSITIVE PRESSURE: At first I couldn’t believe it, 99% particle filtration (at 0.3 μm) w/ battery-powered 🔋 air circulating face shield AFTER CUTTING ✂️ BIG HOLE 🕳️ for easy access to mouth 👄 when hard to wear N95 (e.g. dentist, eating, etc). DO NOT TRY (1/5) Image
Image TREND AIRSHIELD PRO: This is an industrial helmet with “high efficiency solid particulate filtration” (HEPA-like) used primarily by woodworkers 🪵 and carpenters 🪚 to protect their face 😊 and lungs🫁 . (2/5) amazon.com/TREND-AIR-PRO-…
Aug 6, 2023 • 33 tweets • 13 min read
SHOUT OUT to @AirResources and @CAPublicHealth for INSPIRATIONAL leadership 💪 on DIY air cleaners to improve indoor air quality in California 🥑 and beyond. (1/) https://t.co/49V0XyNtJdww2.arb.ca.gov/protecting-you…
Image DIY: Parents 🙋‍♂️💁‍♀️+ school teachers/staff 👩‍🏫 👨‍🏫 are implementing CARB’s idea of BOX FANS + 5” MERV 13-16 FILTERS🌪️ for wildfire smoke + Covid mitigation at an elementary AND middle school in San Francisco ❤️ with @projectn95. (2/)
Jul 30, 2023 • 6 tweets • 3 min read
“Participants who reported a previous COVID-19 infection were 9.7 times as likely to have rapid abdominal aortic aneurysm growth (higher growth than the average of 2.7 mm per year). The average size of the abdominal aorta is 2 cm (0.79 inch).” newsroom.heart.org/news/abdominal… "People who have risk factors for developing abdominal aortic aneurysms, and those already known to have abdominal aortic aneurysms who are having their progression monitored, should know that COVID-19 infection may potentially alter the natural course or outcome of abdominal… twitter.com/i/web/status/1…