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Joseph Allen Profile picture
@j_g_allen
Jul 19 • 6 tweets • 3 min read • Read on X
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NEW from our Harvard Healthy Buildings team

We used CFD modeling to evaluate the effectiveness of portable air cleaners to help remove airborne pathogens and mitigate disease transmission in schools

[tl/dr: portable air cleaners work]

THREAD Image
Portable air cleaners work!

We found that portable air cleaners w a clean air flow rate of 2.6 h−1 reduce mean aerosol intake of all students by up to 66% Image
Air mixing matters!

**A key benefit of using PACs is to facilitate
air mixing and movement in indoor environments with inadequate ventilation** Image
Placement matters!

Closest to infector is best (duh), but this is never known. So our results found that, in the absence of knowing who is infected, deploying a PAC at the
center of the room is recommended. Image
Discharge height matters!

We found that adjusting PAC flow discharge height to the breathing height of occupants (e.g., 0.9–1.2 m for seated people) can enhance their effectiveness in spaces with poor air mixing Image
There's a lot more that matters!

Have a read:


Big thanks and congrats to Dr. @Gen_Pei_ who led the work, alongside Dr. @parhamazimi_87 and Dr. @RimIAQ pubs.rsc.org/en/content/art…
Image

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More from @j_g_allen

Joseph Allen Profile picture
Sep 8
In @AMJPublicHealth I make an argument that adding in an economic lens is good public health practice, and I leverage an excellent article by @celinegounder and @Craig_A_Spencer.
🧵 Image
In the 1980s and 1990s, the then-new field of IAQ generated research documenting that ventilation rates above this minimum standard were associated with many health benefits.
Throughout the 1990s to 2000s, research efforts were also underway to evaluate—and expand—the understanding and value proposition of better indoor air quality.
Read 12 tweets
Joseph Allen Profile picture
Sep 7
The triple-digit temps in the southwest are catching headlines ("Record-breaking heat wave expected to extend stay in the West"). Dangerous heat, for sure, but, if you look at wet-bulb, you'll see that the headlines should be about the heat wave in the West **AND** Florida🧵 Image
How we talk about hot weather is seriously flawed. As heat waves become more intense and more frequent because of climate change, we need to change the way we think about outdoor temperatures.
We’re looking at the wrong measurement. What matters is not how hot the air is but how hot the weather is to a human body. For that, we need “wet-bulb globe temperature.”
Read 10 tweets
Joseph Allen Profile picture
Sep 6
In my Editorial for @AMJPublicHealth on the history of ventilation, I share a story not many people know...

--> In late 2020, the ASHRAE Epidemic Task Force convened a group of experts and gave them an explicit task of making recommendations on ventilation rate targets...
🧵 Image
This team submitted their first recommendations to the ASHRAE Epidemic Task Force in 2021...

...but the recommendations were never released to the public.
In the fall of 2022, the Lancet COVID-19 Commission released a report which revealed to the public the previously unreleased recommendations made by ASHRAE’s internal committee. Image
Read 9 tweets
Joseph Allen Profile picture
Sep 4
The history of ventilation is fraught, indeed. And it hasn't been told through a public health lens. I was invited to write an Editorial for @AMJPublicHealth. My reflections on how we got here, and what needs to happen next.
🧵 Image
We are in the sick building era, ushered in by a historic mistake in the 1970s with the promulgation of a standard that lowered ventilation rates in nearly every building we spend our time, and which represented a gross departure from earlier health-focused higher ventilation targets.
The year 2020 marked a major turning point in the history of ventilation. SARS-CoV-2, spread predominantly indoors, found an ally in buildings designed to minimal “acceptable” ventilation standards.
Read 4 tweets
Joseph Allen Profile picture
Aug 24
This is bad public health. "Everyone stay indoors after 6pm for the next six weeks" (also happens to be the absolute nicest time of year in Massachusetts...) Totally unrealistic, totally unnecessary, and also will just be ignored, anyway.
(A major contributing problem in Massachusetts is that we have **351** local boards of health...)
Read 4 tweets
Joseph Allen Profile picture
Jun 15
On H5N1, milk and this NEJM letter
There are some really important points being missed. It's worth reading the whole letter, including the supplemental info (the authors do a good job of explaining everything); it's not very long...
1/n
 nejm.org/doi/full/10.10…
Relevant background
There are two main commercial pasteurization approaches: 63C/30min or 72C/15 secImage
Things I find important/interesting in NEJM article:
The authors find that the 63C process works and "has a large safety buffer."Image
Read 13 tweets

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