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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
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…


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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)


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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, 2024 • 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, 2024 • 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, 2024 • 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)