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 🧵…
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."…
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"…
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"…
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:

• • •

Missing some Tweet in this thread? You can try to force a refresh

Keep Current with Alex Huffman, Ph.D.

Alex Huffman, Ph.D. Profile picture

Stay in touch and get notified when new unrolls are available from this author!

Read all threads

This Thread may be Removed Anytime!


Twitter may remove this content at anytime! Save it as PDF for later use!

Try unrolling a thread yourself!

how to unroll video
  1. Follow @ThreadReaderApp to mention us!

  2. From a Twitter thread mention us with a keyword "unroll"
@threadreaderapp unroll

Practice here first or read more on our help page!

More from @HuffmanLabDU

Apr 4
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/)…
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
Jan 14
CDC came out with another incremental update on #mask & #respirator guidance today:…

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."

Read 15 tweets
Jan 12
Really happy to see our paper led by @DaveyRachel1 just out in the #Forefront section of @AnalBioanalChem:

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. 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
Jan 6
If you have more experience & credibility than Dr. @brosseau_lisa on topics of industrial hygiene, aerosol science & mask use, etc. - then by all means speak up.
Otherwise, dispense w/ silliness that surgical masks are safer than N95s. Use #BetterMasks.
3/ Regarding new mask mandates:
“Once you go into a store & you know you’re gonna be there for more than a couple minutes, you’ve got to wear a respirator.”: @brosseau_lisa
Look for NIOSH stamp & a tight fit. "If it has ear loops, it's not a respirator."…
Read 4 tweets
Jan 5
It's frustrating to see pervasive misunderstanding that N95 masks (respirators) need to be fitted or they are useless. Some of the same people champion surgical masks instead.
Illogical - If N95s don't work unless prof. fitted, how could surgical masks w/ big gaps work better? 1/
2/ The chart & thread here gathered by @akm5376 helps add perspective. Yes, a professionally fitted N95 provides tremendous protection! But even a un-fitted N95 is better than almost anything else, b/c the filtration is great & fit is already good.
3/ This is a nice thread by @claire_horwell on the differences between surgical masks and respirators.
(BTW, Prof. Horwell has been on a tear lately with a great OpEd & a number of great threads - worth following!)
Read 6 tweets
Dec 17, 2021
Another good study simulating effects of masks, HEPA cleaners, ventilation in a small meeting room. By NIOSH team incl. Lindsley, et al.…

🔸 Masks reduced aerosol by 50% +
🔸 Additive further exposure reduction w/ any combo of HEPA, ventilation
Summary 🧵
2/ For reference, this is essentially the same NIOSH team that did some other really nice work on masks and air cleaners:
3/ The experimental team here used one aerosol source (0.3 - 3 microns) and three recipients, in various combinations. They used a relatively small room (54 m3) with 2 ACH on low fan speed in order to simulate a realistic meeting-type room.
Read 12 tweets

Did Thread Reader help you today?

Support us! We are indie developers!

This site is made by just two indie developers on a laptop doing marketing, support and development! Read more about the story.

Become a Premium Member ($3/month or $30/year) and get exclusive features!

Become Premium

Don't want to be a Premium member but still want to support us?

Make a small donation by buying us coffee ($5) or help with server cost ($10)

Donate via Paypal

Or Donate anonymously using crypto!


0xfe58350B80634f60Fa6Dc149a72b4DFbc17D341E copy


3ATGMxNzCUFzxpMCHL5sWSt4DVtS8UqXpi copy

Thank you for your support!

Follow Us on Twitter!