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Alex Huffman, Ph.D. Profile picture
@HuffmanLabDU
Jul 2, 2021 • 10 tweets • 6 min read • Read on X
Great new study on #HEPA air cleaners by Lindsley et al. out today via @CDCMMWR: masks reduced aerosol by 72%, HEPA by 65%, together by 90%.

Conclusions are consistent with messages for months, but important that #CDC amplifying this strategy.
Short 🧵
cdc.gov/mmwr/volumes/7…
2/ "The use of masks without air cleaners reduced the aerosol exposure of the receivers by 72%, and the use of air cleaners without masks reduced the exposure by up to 65%. When used together, the HEPA air cleaners and masks reduced exposure to respiratory aerosols by up to 90%." Image
3/ "These findings suggest that the use of portable HEPA air cleaners and universal masking can each reduce exposure to simulated SARS-CoV-2 aerosols in indoor environments, with larger reductions occurring when air cleaners and masking are used together."
cdc.gov/mmwr/volumes/7…
4/ The study used simulated SARS-CoV-2 aerosol emitted from a manikin in a fixed location, w/ two portable HEPA cleaners at varied locations in room. Also tested w/ & w/out mask use. Always caveats & limitations, but study highlights importance of both masks & room filtration. ImageImage
5/ The #MMWR report references several other studies to show similar efficacy of HEPA filters, e.g. the Curtius et al. study showing 90% reduction of aerosol w/in 5 min. in a classroom in Germany.
6/ And the study by Burgmann & Janoske "Transmission and reduction of aerosols in classrooms using air purifier systems"
aip.scitation.org/doi/10.1063/5.…
7/ The study could have also cited, among others, the nice, recent study by @KirstyBuising @RobynSchofield3 et al. showing reduction of aerosol in a hospital.
"Use of portable air cleaners to reduce aerosol transmission on a hospital COVID-19 ward"
cambridge.org/core/journals/…
8/ Addition of air cleaners like portable HEPA filters are an important part of keeping indoor air clean from infectious respiratory aerosols and all manner of suspended particles (like wildfire smoke, cooking aerosol, urban pollution PM).
9/ HEPA filters have been championed by indoor air experts as a key part of the strategy to offer in-person learning in the Fall and beyond. See this thread on an excellent example by NYC schools, with further comment & resources on filtration in schools.
10/ And if you like how well portable #HEPA filters work - just think of the tremendous benefit by adding to every school classroom in the US like @CorsIAQ & @j_g_allen have been saying for over a year.

Cost analysis from February:

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More from @HuffmanLabDU

Alex Huffman, Ph.D. Profile picture
Oct 7, 2022
Important article by @PatriciaFabianS & @jonlevyBU: investment in improving school air quality is critical.

Adds to reminder by @IAQinGWN at #AAAR2022 yesterday that investing in filtration can realize $10-100 return per $ spent e.g. via ⬇️ absences.
theconversation.com/investing-in-i…
Well-maintained HVAC filters or portable air cleaners can “also clean the air of pollen particles, mold spores & pollution from car exhaust and industrial operations. And in areas where wildfires are common, filters reduce the concentration of smoke particles inside buildings.”
[In schools that increase ventilation rate] “For kids and school staff, particularly those with asthma, allergies and sensitivities, this can mean fewer missed days of school, less medication, and fewer asthma attacks and subsequent trips to the hospital.”
onlinelibrary.wiley.com/doi/10.1111/in…
Read 4 tweets
Alex Huffman, Ph.D. Profile picture
Aug 18, 2022
"Indoor Air Management of Airborne Pathogens: Lessons, Practices, and Innovations" eventbrite.com/e/indoor-air-m…

Workshop by @theNASEM focusing on the current state of knowledge ➡️ practical lessons learned. Session 1 starting now.

Live-tweets below
#EHMI #NASEM #EnviroHealthMatters ImageImage
2/ @Don_Milton summarizes evidence that saliva PCR much better at catching COVID positive cases than PCR from nasal swabs. ImageImage
3/ @Don_Milton: It's the *combination* of masks, ventilation, filtration that can dramatically reduce spread Image
Read 66 tweets
Alex Huffman, Ph.D. Profile picture
Jul 6, 2022
A family emergency means I’m flying today for the first time since 2019. Fortunately I’ve got my N95 to reduce my inhaled dose as much as possible + my CO2 meter to gauge air.

Short 🧵 to occupy me while on a layover.

The CO2 was nicely & low in the Shreveport, LA airport (1/x) ImageImage
2/ On this tiny United commuter flight, 45 minute flight time from Shreveport to Houston, no one with N95 masks. Maybe 2 w/ surgical masks.

Boarding & taxi process, the #AirplaneCO2 briefly peaked at 1600 ppm, but mostly in 1100 range. Obviously higher than ideal, but not bad. Image
3/ Cruising (if you call it that for just a few minutes) was still in the 1000 - 1200 ppm range. At that upper level, roughly 2% of the air is likely rebreathed from others on board. But the ventilation is also filtering resp. particles from background air relatively frequently. Image
Read 23 tweets
Alex Huffman, Ph.D. Profile picture
Apr 4, 2022
Excellent OpEd by @linseymarr & @jljcolorado on the early and persistent confusion around the word "airborne" wrt the pandemic. It's a short overview on the effects of these miscomms across medical & disciplinary boundaries.
Some salient quotes, links (1/)
time.com/6162065/covid-…
2/ “This fundamental misunderstanding of the virus disastrously shaped the response during the first few months of the pandemic & continues to this day. We still see it now in the surface cleaning protocols that many have kept in place even while walking around without masks. …”
3/ “… There is a key explanation for this early error. In hospitals, the word “airborne” is associated w/ a rigid set of protective methods, incl. the use of N95 respirators by workers and negative pressure rooms for patients. These are resource-intensive and legally required.”
Read 11 tweets
Alex Huffman, Ph.D. Profile picture
Jan 14, 2022
CDC came out with another incremental update on #mask & #respirator guidance today: cdc.gov/coronavirus/20…

Clarifies N95s aren't in short supply & can be worn again!

It's still not perfect, but it feels like we're at least inching in the right direction. Some thoughts via a🧵.
2/ New statement that most respirators (i.e. #N95s) "are disposable and should be discarded WHEN they are dirty, damaged, or difficult to breathe through."

So you CAN #ReuseN95s‼️
See, e.g.:

That's *much* better guidance than to toss after a single use!
3/ Also clearly states that:
"Loosely woven cloth products provide the least protection ... and well-fitting NIOSH-approved respirators (including #N95s) offer the highest level of protection."

YES!!
Read 15 tweets
Alex Huffman, Ph.D. Profile picture
Jan 12, 2022
Really happy to see our paper led by @DaveyRachel1 just out in the #Forefront section of @AnalBioanalChem: rdcu.be/cEJN7

Improves a procedure to expose surrogate proteins to urban air (especially NO2, O3) to quantify changes in protein nitration ➡️ allergies, etc.
1/🧵 Image
2/ @DaveyRachel1 did a great job of quantifying & improving each step of the #bioanalytical procedure; ozone loss across PM filters, extraction & detection efficiencies, even good old analytical #FiguresOfMerit sensitivity & limit of detection.
rdcu.be/cEJN7 Image
3/ Possibly the most broadly useful piece is the data showing ozone loss across several filter types. The HEPA capsule scrubbed >60% of the ozone (bad if you're trying to quantify ozone). Kynar removed only 3%.
Important if using filter to remove PM, while quantifying O3 behind. Image
Read 6 tweets

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