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.
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).
4/ "The measurements are supplemented by a calculation estimating the maximum concentration levels of virus-containing aerosol from a highly contagious person speaking in a closed room with and without air purifiers."
5/ "Figure 8: #CO2 mixing ratio measured in class during a school day. Even after venting the room for several minutes w/ door & windows wide open, CO2 levels do not drop < 1000 ppm. ... levels quickly rise to mixing ratios of 2500 to 2800 ppm at the end of the lesson." #COVIDCO2
6/ Study conclusions: "Measurements and calculation demonstrate that [portable] air purifiers potentially represent a well-suited measure to reduce the risks of airborne transmission of SARS-CoV-2 substantially."
7/ "Staying for two hours in a closed room with a highly infective person, we estimate that the inhaled dose is reduced by a factor of six when using air purifiers with a total air exchange rate of 5.7 ACH"
8/ "In summary, the operation of mobile air purifiers in classrooms seems feasible as a practical measure that can quickly be implemented during an epidemic."
#airpurifiers #aircleaners #HEPA #filtration
9/ "In order to reduce the risks of aerosol transmission for SARS-CoV-2 air purifiers can form an important additional measure of precaution, especially in cases where no fixed ventilation systems are installed and when windows cannot be opened properly." #aerosol
10/ The study conclusions are broadly consistent with lots of other experimental and modeling studies (i.e. portable filtration helps!). E.g. these are simple results I put together related to long-range aerosol risk modeling for classrooms on our campus:
11/ Practical follow-up to the study above.

Portable air filtration is an imp. component of layered reduction strategies against airborne viral infection. To learn more & est. right filtration for you, see tool by @ShellyMBoulder @j_g_allen @cedenolaurent
12/ And to answer further questions about room air filtration, see answers in section 10 of this helpful #COVID #aerosol transmission FAQ guide. Avoid ionizers & other gimmicks for portable units, stay with proven filtration.
13/ Another potentially good option for ~$40 is a #DIY version using a box fan + furnace filter combo. E.g. see article by @JimRosenthal4. #boxfanfilter
14/ This is a nice write-up on the DIY #boxfanfilter idea, via @JbcLiftec.
15/ A bonus of any good air filtration (central or portable) is that it can do a good job of removing all kinds of aerosol particles in a room, whether related to respiratory viruses, air pollution, or even wildfire smoke.

• • •

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

Keep Current with Dr. Alex Huffman

Dr. Alex Huffman 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

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
Read 5 tweets
9 Feb
This is why research & #scicomm now about virus transmission is so critical

"We’re going to have to be in a world that is more thoughtful about protecting ourselves from respiratory infection than we have ever had to be before.” Dr. Bloom, @HarvardChanSPH
(Starting at 2:31): “This is a global infection. A mutant or variant anywhere is a threat everywhere. And so we can’t be complacent and say because hopefully we start to do well by summertime in the US we will not be invaded by a new variant. So we really have to ..."
".. continue public health measures: wearing masks, reducing opportunities for spread, and being very careful, because even with vaccines, they’re not perfect, no vaccine has ever been perfect. ..."
Read 7 tweets
5 Feb
1/ In context of extra precautions against new COVID variants, some new questions pop up about #masks.

Article by @cwarzel @zeynep asks/answers some good questions to start. Other thoughts in a 🧵, e.g. N95s, fit (Tw7+ ⬇️), when to replace (Tw25 ⬇️), etc.
2/ Countless recent articles w/ interviews from relevant experts imploring people to still take mask-wearing & overall airborne COVID health seriously.

One of many, here by @skbaer w/ broad contribution. (Tw33 below has link to a compilation of more).
3/ Many good arguments recently towards motivating broader use of #bettermasks, i.e. #N95s. So if not using already, consider.

See e.g. this editorial by @j_g_allen: washingtonpost.com/opinions/2021/…

Or this opinion-piece by a group of excellent scientists:
Read 33 tweets
3 Feb
1/ Public admission by @mvankerkhove of #WHO that COVID transmission "goes through the air" is a *huge* turn-around from strong, incorrect statements to the contrary.

Strikes me as significant, even if subtle & played off as "we knew all along."

Full vid
2/ Earlier messages #WHO put out were blatantly wrong & dangerous ⬇️.

Many scientists globally have been working tirelessly to pressure @WHO to retract dangerously misleading statements like this & adequately educate that #COVIDisAirborne.
3/ Again, messaging efforts by WHO are critical b/c of their exposure & reach. By openly saying COVID isn't in the air & having press conferences w/o masks, have been undermining efforts to #MaskUp & prevent spread.

Baby steps today, still work to do!
Read 7 tweets
3 Feb
Updated preprint on COVID risk modeled from respiratory aerosol data

Notice ⬇️:
- No "safe" distance indoors, b/c aerosols travel
- Masks & ventilation increase safe time, but still risk

Graphs: below each line = safer

HT @linseymarr & @kprather88 (1/x)
2/ Study used the #WellsRiley model to estimate COVID risk from respiratory aerosols in a variety of scenarios, using particle size distribution data from previous studies.

Quanta: Statistical measure of avg infection probability; bigger value = easier to infect [~1 - e^-quanta]
3/ Bazant & Bush study supports broad consensus of observation & preventative steps:

✅No single action sufficient for COVID prevention
✅Steps compound reduction in risk, but never to zero
✅All important: distance, masks, reduced time, incr. ventilation
Read 6 tweets
1 Feb
Imp. perspective to remember.

"Excessive attention on making surfaces pristine takes up limited time & resources that would be better spent on ventilation or the decontamination of the air that people breathe": @linseymarr

By @dyanilewis HT @rye_b (1/x)
2/ A few other key quotes/reminders:
“It’s become clear that transmission by inhalation of aerosols — the microscopic droplets — is an important if not dominant mode of transmission,” says Prof. @linseymarr , who studies airborne disease transmission.
“You have to make up some really convoluted scenarios in order to explain superspreading events w/ contam. surfaces”
“If we’ve already paid attention to the air & we have some extra time resources, then yes, wiping down those high-touch surfaces could be helpful”: @linseymarr
Read 5 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

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

Donate via Paypal Become our Patreon

Thank you for your support!

Follow Us on Twitter!