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Dr. Alex Huffman Profile picture
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9 Mar, 7 tweets, 4 min read
Frequently questions about type of room air filtration & if #ionization is a useful upgrade.

Nearly always, simple filtration is sufficient for most people. Study here shows a bipolar ionizer also *not* useful at reducing PM2.5. Thx @JimRosenthal4. (1/x)
sciencedirect.com/science/articl…
2/ "[experiments] ... suggest that operation of the ionizer unit led to a small increase in loss rates for ultrafine particles (<0.15 μm) and a small decrease in loss rates for larger particles (>0.3 μm), but with negligible net changes in estimated PM2.5 loss rates."
3/ In contrast to relative ineffectiveness of ionization technology to reduce concentration of suspended particles in a room, simple #HEPA filtration does an *excellent* job. See e.g. examples in this 🧵 showing filtration in a school classroom.
4/ Keep in mind that a reasonable #DIY filter can also be made for <$40 with a furnace filter & standard box fan (useful against all kinds of particles, incl. respiratory & cooking aerosol, wildfire smoke). E.g. #boxfanfilter article by @JimRosenthal4.
wired.com/story/could-a-…
5/ If you're in the market for air filtration for yourself, your office, or school, find excellent resources here:
tinyurl.com/FAQ-aerosols

and a useful calculator to match your room volume to filtration needs:
tinyurl.com/portableaircle…
(Article HT @JimRosenthal4)

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Dr. Alex Huffman Profile picture
7 Mar
1/ More good support that indoor dining is challenging (no masks indoors = risky). Nice article by @RoniNYTimes, w/ comments from knowledgeable folk following a recent CDC #MMWR report.

Amazing this still needs to be news (but it is & still important).
nytimes.com/2021/03/05/hea…
2/ “You have decreases in cases and deaths when you wear masks, and you have increases in cases and deaths when you have in-person restaurant dining,” said #CDC director Dr. Rochelle Walensky
3/ Unfortunately, the Nat'l Restaurant Assoc called the #CDC report “an ill-informed attack on the industry hardest-hit by the pandemic.”

I feel for restaurant owners & workers. I honestly can't imagine the difficulty through the pandemic. But the challenge & risk is legitimate.
Read 5 tweets
Dr. Alex Huffman Profile picture
27 Feb
🧵1/ The #CDC update today (2/26) on "Ventilation in Schools and Child Care Programs" looks like good progress.

Details on #ventilation, #filtration, #bettermasks, w/ helpful links. Seems they're listening to @kprather88 @j_g_allen @CorsIAQ and others?
cdc.gov/coronavirus/20…
2/ The relatively short #CDC page seems to have more succinct, yet clear #K12 guidance & connection to other pages of support.

Though I admit, I haven't digested yet fully. What are your takes? (also e.g. @jljcolorado @linseymarr @ProfCharlesHaas @Don_Milton @ShellyMBoulder)
3/ I was pleased to see early mention that "Wearing a well-fitting, multi-layer mask helps prevent virus particles from entering the air or being breathed in by the person wearing the mask."

(BTW, need for good fit implies aerosols)

Links (twice) here:
cdc.gov/coronavirus/20…
Read 17 tweets
Dr. Alex Huffman Profile picture
27 Feb
Opening #K12 schools safely requires applying the right airborne prevention. This article interviews the right people; listen to them!

"The state of ventilation in schools in the United States right now is woefully inadequate": @CorsIAQ

HT @jljcolorado
cnn.com/2021/02/25/hea…
"Right now, schools are looking to CDC and they are not getting the answers to the kinds of things we are talking about." "All of them look to CDC." said @CorsIAQ
"If you look at all the high profile outbreaks -- same underlying factors -- no masks, low ventilation. It doesn't matter if it's spin class, ice hockey, camps, classrooms, choir practice or restaurants, (it's) the same underlying factors" said @j_g_allen
Read 4 tweets
Dr. Alex Huffman Profile picture
25 Feb
The more I read this story of #superspreading in a Chicago gym, the more outrageous it is, especially this late in the game. A few amazing quotes below.

So preventable: distance, wear good masks, improve ventilation & filtration.

HT @linseymarr (1/x)
cdc.gov/mmwr/volumes/7…
2/ Just amazing this can be true ...

"Overall, 43 (78%) attendees with COVID-19 participated in multiple classes while potentially infectious.* Twenty-two (40%) attendees with COVID-19 attended on or after the day of symptom onset."
3/ This is why #COVIDisAirborne education is critical:

"Patrons brought their own mats and weights and were stationed ≥6 ft apart."
"Mask use, temperature checks, and symptom screenings were required on entry"

"however, patrons were allowed to remove masks during exercise." 🤦‍♂️
Read 7 tweets
Dr. Alex Huffman Profile picture
19 Feb
1/ Here's a quick bite (< 2.5 minutes) of overview on infectious respiratory aerosol emissions, #ventilation, and using #CO2 monitors as a tool in the fight against COVID & for healthy indoor air.

Thx to @KateM_NYC @YahooNews for the interview. #COVIDCO2
news.yahoo.com/co-2-monitors-…
2/ I recently gathered several interesting stories from recent CO2 measurements as well as a simple example of how I had fun measuring the ventilation rate in my house.

Peruse #COVIDCO2 for many more examples.
3/ Measuring #CO2 to estimate ventilation rate is a quick way of approximating the amount of "rebreathed air" (the portion of air you breath that has already been in someone else's lungs).

See thread by @CorsIAQ for good details here.
Read 6 tweets
Dr. Alex Huffman Profile picture
19 Feb
1/ Another good preprint on mask efficiency tests; from a @NIOSH group that knows aerosols.

Lindsley et al.: "A comparison of performance metrics for cloth face masks as source control devices for simulated cough and exhalation aerosols"

HT @linseymarr
medrxiv.org/content/10.110…
2/ They explored a variety of respirators and masks. As expected, the collection efficiency of the N95 & surgical masks did very well. Masks with filters next, lowest filtration quality when only single-ply material used.
3/ The "fit factor"/FF (higher = better) is also critical. Look at the difference between the N95 and surgical masks in terms of fit (left).

Also see how much fit factor increased when more tightly fitted (below on right w/ ear loop adjusters to make snug).
Read 6 tweets

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