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Dr. Alex Huffman Profile picture
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19 Feb, 4 tweets, 3 min read
1/ More great work by @smogdr & team to test the performance of various kinds of #masks.

The (re)introduce mask "protection factor" (PF) as a fraction of particle mass that makes it through & also evaluate breathability, effect of mask construction, etc.
pubs.acs.org/doi/10.1021/ac…
2/ This is the thread of main points that @SmogDr put together associated with the now-published & #OpenAccess paper.
3/ And if you haven't already played around with the mask-testing data, @SmogDr & team built this interactive site (months ago) to look in detail at results from various masks.
jv.colostate.edu/masktesting/
4/ Their results support a key set of messages wrt masks ...


FIRST: any mask is better than no mask & that message is just critical.
SECOND: wear a mask with the best quality of both fit & filtration.

Another 🧵 on that topic:

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More from @HuffmanLabDU

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
Dr. Alex Huffman Profile picture
18 Feb
1/ Article summarizing a letter recently sent to the White House, CDC, NIAID, by a group of trusted colleagues.

“It’s time to stop pussyfooting around the fact that the virus is transmitted mostly through the air” said @linseymarr

Letter & quotes below.
nytimes.com/2021/02/17/hea…
2/ Read the short, important letter yourself:

"Immediate Action is Needed to Address SARS-CoV-2 Inhalation Exposure"
…ha-assets.sfo2.digitaloceanspaces.com/AIHA/uploads/P…
3/ "There is a pressing and urgent need for action. COVID-19 infections and deaths recently reached record levels. The roll-out of vaccines that started out in December rocky and slow is now improving, but it will be months before most of the population is vaccinated."
Read 9 tweets
Dr. Alex Huffman Profile picture
13 Feb
1/x Just can't shake my disappointment in yesterday's #CDC school opening guidelines: "Operational Strategy for #K12 Schools through Phased Mitigation"

A 🧵 with other thoughts, links, practical tips wrt #school COVID airborne health, beyond CDC guidance.
nytimes.com/2021/02/12/hea…
2/ First, here is the link to updated #K12 guidelines, as well as a few other key #CDC pages (w/ last update as of today).

K12 update (2/12): cdc.gov/coronavirus/20…

How COVID spreads (10/28/20): cdc.gov/coronavirus/20…

Ventilation in buildings (2/9): cdc.gov/coronavirus/20…
3/ So many lines of thought to follow, but I will direct you to short thread yesterday by @CorsIAQ for a good summary. The gist is simply that the #CDC guidelines leave out some of the most important, obvious help b/c they ignore the airborne component.
Read 24 tweets
Dr. Alex Huffman Profile picture
11 Feb
1/ Interesting paper showing high efficacy of portable HEPA #filtration to reduce aerosol concentration in a high school classroom during use.

By very experienced German aerosol group Curtius et al.; via @ASTJournal.

With short🧵on room air filtration.
doi.org/10.1080/027868…
2/ "In times when classes were conducted with windows and door closed, the aerosol concentration was reduced by more than 90% within less than 30 min. when running the purifiers (air exchange rate 5.5 ACH). The reduction was homogeneous throughout the room ..."
[note log y-scale]
3/ Figure 3: Highly reproducible reduction in aerosol particle concentration [uCPC] in a closed classroom without air purifiers (blue line) and with 3 or 4 air purifiers operating at speed 3 or 4 (max).
Read 15 tweets
Dr. Alex Huffman Profile picture
10 Feb
1/ You've surely seen constant recent messaging & articles imploring you to improve quality of both #mask fit & filtration, in part b/c of worrying COVID variants.

Good news that the #CDC is catching up w/ those messaging efforts w/ updated guidance today.

Short 🧵 of links.
2/ Another good summary thread of the CDC changes; by @AbraarKaran, who has been among ardent supporters lobbying hard for #bettermasks:
3/ One good example summarizing the new #CDC guidance changes on masks, w/ helpful infographics, interviews, and short video w/ CDC chief Dr. Walensky.

By @bylenasun & @FenitN
washingtonpost.com/health/2021/02…
Read 5 tweets

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