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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.
5 subscribers
Jul 21 • 8 tweets • 2 min read
UNFINISHED BUSINESS: ASHRAE 241, CDC 5 ACH are good, but not good enough, to stop viral 🦠 puffs 💨 .

Why?

Explained: Science published my eLetter, “Ventilation alone cannot address close-contact airborne transmission: dilution of exhalations is also needed” w/ @RanuDhillon Image My eLetter was responding to Science article by global IAQ experts on lessons learned from Covid pandemic.

They did not say how airborne virus 🦠 depends critically on the distance 📏 to infector if they are not wearing N95 or similar science.org/doi/10.1126/sc…
Jul 19 • 21 tweets • 8 min read
MEGA STUDY: ASHRAE 241 model just published 🌪️

Kudos to authors and anon peer-reviewers for achieving clarity + precision 🙏🏽.

Lot to LOVE in here 🎶.

But also some fatally FLAWED assumptions ☠️

Details below. First love 👍 then flaws 👎

h/t @effiegreathouse Bottom line up front: 241 is a SOLID contribution to MODELING airborne transmission indoors.

I am curious to see same modeling but with different assumptions as outlined below. Full paper here: sciencedirect.com/science/articl…
Jun 15 • 14 tweets • 4 min read
San Francisco school district (SFUSD): “INDOOR AIR QUALITY IS ESSENTIAL TO STUDENT SUCCESS” 👏

New memo shared thinking on classroom air quality 👏 (mentions old guidance by California Dept of Public Health but silent on 2024 CDPH standard).

What did it say? Image
Image #1 “MOST SFUSD buildings were designed to rely on PASSIVE ventilation, supplied through operable windows 🪟 (a window designed to open and close)” but… Image
Feb 1 • 10 tweets • 2 min read
Not too surprising that pollution 🔥 💨🚬 🚘 (PM 2.5) is linked to lung 🫁 cancer, but why would it increase risk of ANY CANCER?

“for every 10 microgram per cubic meter (µg/m3) of increased exposure to PM2.5, risk of dying from any cancer rose by 22 percent.” Image “The study enrolled 66,280 residents of Hong Kong, all of whom were age 65 or older when initially recruited between 1998 and 2001. The researchers followed the study subjects until 2011, ascertaining causes of death from Hong Kong registrations.”
Jan 19 • 24 tweets • 6 min read
Good q. If it smells toxic or VOC is a concern downwind of wildfires 🔥, below are 3 steps to protect from VOC in order of increasing cost $$.

@717imo @rockncasserole @StevenMathern VOC Step #1: As an upgrade from N95, P100 respirators with VOC cartridges like this one from GVS, also 3M and others can protect from chemical vapors. amazon.com/GVS-SPR485-Eli…
Jan 18 • 7 tweets • 2 min read
Caltech: “…preliminary data from particulate samplers located in Pico Rivera, south of Caltech's campus in Pasadena show significant amounts of both chlorine (from burning plastics like PVC) and lead in the air. (These samplers do not measure asbestos.)” “In addition to particulate, smoke contains a huge diversity of volatile organic compounds (VOCs). These are the source of much of what we are smelling in the air now.”
Jan 17 • 10 tweets • 3 min read
BIG NEWS: Yesterday California public health 🥑 just recommended to at least 5 air changes per hour in ALL ROOMS (occupied). Seismic. 🌎

Not just classrooms, but also evacuation centers, offices, homes, too. In agreement with CDC (May, 2023) “Given all of this information, CDPH is currently aligned with CDC and experts in recommending a minimum of 5 air changes per hour or 30 CFM/occupant of equivalent clean airflow, whichever is greater, in occupied indoor environments.”

cdph.ca.gov/Programs/CID/D…
Jan 12 • 6 tweets • 2 min read
“That air that’s being spewed is no longer just the kind of smoke that we used to see from wildfires, where it was natural vegetation that was burning,” said Becerra, a former California Attorney General. “Now you got a whole bunch of toxic materials that are getting burned and put into the air.” “It’s just a toxic soup,” Lisa Miller, a wildfire smoke expert at the University of California, Davis told NPR. “Think of all the synthetic fibers that are present in your living room—in your couch, in your carpet, in your clothes. All those things can be particularly toxic,” she said.
Dec 29, 2024 • 5 tweets • 2 min read
Clear explanation of CO2 vs ACH vs viral emissions in room by @ukhadds:

1. CO2 tracks occupant breathing (b/c ~4% of exhaled is CO2), but only indirectly tracks infector viral emission depending on if infector is there, how active (e.g. speaking, working out), and if masking. 2. CO2 can be used to estimate the air changes per hour (ACH) from ventilation only but not from air filtration (such as on airplanes). Air filtration reduces SARS-CoV-2 risk by removing aerosols but without decreasing CO2. Image
Dec 15, 2024 • 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, 2024 • 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)
Dec 1, 2024 • 20 tweets • 7 min read
SF Bay Area air quality just got worse from wood burning 🔥

5 things to consider:

#1 check @ThePurpleAir near you

#2 indoors < outdoors

#3 purifiers for home school office (at 5-10 ACH)

#4 HEPA for car

#5 N95 outdoors

From my LA Times oped last week.

Thread

(1/20) Image “Smoke from increased wood burning combined w/ light winds and cold overnight temps is expected to cause unhealthy air quality. High pressure over NorCal acts like a lid, trapping smoke at ground level.” — conditions likely to repeat in winter.

(2/20)

baaqmd.gov/en/news-and-ev…
Sep 21, 2024 • 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, 2024 • 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…


Image
Image
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Jun 29, 2024 • 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, 2024 • 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, 2024 • 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, 2024 • 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, 2024 • 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, 2024 • 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, 2024 • 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)


Image
Image
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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…
Image