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David Elfstrom Profile picture
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29 Apr, 4 tweets, 2 min read
U of T is making all classrooms achieve 6 ACH with #ventilation and #filtration, the same as for health care patient exam rooms. They measured air flow.
THIS should be the target for all Ontario daycare, elementary, and secondary schools too.
utoronto.ca/news/u-t-asses…
Children will be the last to be vaccinated. Schools & daycares will benefit immensely from reduced cold, flu, seasonal allergies by upgrading to 6 ACH. The time to start was a year ago. The next best time is tomorrow.
Big shout out to @ShellyMBoulder and the UC Boulder team that led the way on this last summer.
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More from @DavidElfstrom

David Elfstrom Profile picture
1 May
1/ I wear an N95 at locations outside of my home. I wear it to the grocery store, pharmacy and my doctor's office.

It's comfortable, doesn't hurt my ears, doesn't fog up my glasses, and easy to breathe through. I can wear it all day, anywhere. EXCEPT at the hospital! Photo of @DavidElfstrom wea...
2/ Many health care facilities require visitors to REMOVE their superior respiratory PPE and don a basic surgical ASTM Level 1 mask.

This practice must stop. Understanding the differenc...
3/ Here's my friend Annamaria's experience this past Thursday when she went to @NGHSimcoe for her second vaccination, shared with her permission👇 When I got there, I stood i...
Read 14 tweets
David Elfstrom Profile picture
28 Apr
This is bullshit policy @UHN. You won't permit a person to wear a clean N95 *respirator* (not mask) in your facility. You won't even allow someone to place your gappy surgical mask over top. Other health care facilities have no such problem. It's indefensible & unacceptable. /1 Image
Does a manufacturing facility say to a visitor "oh hey, take your safety shoes off and don our loafers".
Likewise, I've never been asked to remove my own provided hard hat in exchange for a bump cap or unprotected, as long as it meets sanitary requirements. /2
And you double down on it, even on April 22nd 2021. Can your Entrance Screening Working Group see their own logical fallacy?
If UHN wishes to maintain this policy, it should provide from a selection of pre-approved respirators. Charge a nominal fee if you must. /3 Image
Read 10 tweets
David Elfstrom Profile picture
10 Apr
LISTEN as highly influential Prof John Conly (upper left) of UCalgary, AHS CV19 sci advisory grp, Public Health Agency Canada, Chair WHO Infection Prevention & Control R&D Expert Grp. opposes N95 wearing citing acne harm vs @DFisman & @kprather88 precautionary principle. /1
"there's been decreased O2 concentrations in pregnant women" yeah, well here's the reference from one of his publications, dissected in fine form by @caruzycki /2
Here's an example of Prof Conly's influence by the dedicated @jmcrookston /3
Read 8 tweets
David Elfstrom Profile picture
9 Apr
Naaah, the massive gym outbreak couldn't possibly be lack of #ventilation. That rooftop unit is in excellent condition. 😬😬😬
I don't even know what I'm seeing. Is that charred polyisocyanurate spray insulation?
To be fair it's only one of six units, the others appear to be better.
Read 5 tweets
David Elfstrom Profile picture
7 Apr
What's the risk of COVID in apartment buildings? This review covers much of the basics but I believe the prevalence is much higher ... (THREAD) /1
ncceh.ca/documents/evid… Screen shot of PDF document
We've long known air flows throughout a building despite walls and floors because there's strong driving forces and little attention to air sealing, both on the building envelope, and between units. /2
Figure: Ueno, Lstiburek, Bergey 2012 buildingscience.com/documents/bare… Simplified diagram of stack effect in multifamily buildings
The three driving pressure forces are: Wind, Stack (chimney) effect, and Mechanical (both negative and positive). /3
Figure: Air Leakage Control for Multi-Unit Residential Buildings, CMHC 2017 agency.coop/media/747/down… Image from PDF showing the forces acting on buildings
Read 16 tweets
David Elfstrom Profile picture
18 Feb
#COVIDCO2 readings in an Ottawa classroom. Never reached a steady state. At 3152 ppm every breath contains 7.2% of other people's breath‼️‼️ 🤮. #DontShareYourAir #Onted
Classroom has below 0.4 air changes per hour.

Target MIN: 3-4, Good: 4-5, Excel 5-6, Ideal 6+
/1
For COVID, air changes from HEPA filtration are equivalent to outdoor air. Typical classroom portable HEPA air cleaner:
400 CFM on max at 65 dB adds 2.7 ACH
200 CFM on med at 55 dB adds 1.3 ACH.
Two on med would be 58 dB.

BUT there's still the cognitive impact of 3000ppm!
/2
Here's the back-calculation assumptions used to reach 0.4 ACH in a classroom. I'm assuming 12 foot ceilings for an older naturally ventilated school. Other values are typical as well. The calculator throws an exception in red at 19 students, but not at 18.
/3
Read 10 tweets

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