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9 Dec, 7 tweets, 4 min read
Swiss study finds SIX TIMES the cases in poorly ventilated classrooms (those with over 2000 ppm CO₂) compared to better-ventilated ones. #COVIDCO2
#Ventilate2Educate #COVIDisAirborne
H/T @SamJCauston
swissinfo.ch/eng/society/st…
More details on the Swiss CO₂ classroom study here: empa.ch/web/s604/covid…
For those school administrators who say “we have a ventilation system, it meets or exceeds ASHRAE standards”—That's not enough. You MUST monitor #COVIDCO2. My daughter's fully ventilated classroom, from her backpack monitor, yesterday vs today:
Frequency distribution of CO₂ in classrooms from the Empa study
Infection prevalence vs cumulative CO₂ in classrooms from the Empa study
Everything you need to know about measuring CO₂ in classrooms from @Poppendieck
All the other benefits of improved indoor air quality in schools:

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More from @DavidElfstrom

David Elfstrom Profile picture
9 Dec
While #Ventilate2Educate is geared towards schools, we can #Educate2Ventilate with simple directives for small businesses & organizations. Simple low-cost changes can make for an enormous indoor air quality improvement. Low-rise small commercial buildings are everywhere. Simplified schematic of small business rooftop unit: Maximiz
These simple ventilation actions and more are described on the CDC's Ventilation in Buildings Page: cdc.gov/coronavirus/20…
Idea for a local Business Improvement Area #Educate2Ventilate campaign: Team up with a local HVAC contractor and visit all the storefronts with a CO2 meter to promote simple changes to improve indoor air quality. Add energy efficiency measures too.
Read 5 tweets
David Elfstrom Profile picture
7 Dec
Uh oh @GEDSB. My daughter's classroom was doing well in the fall with CO₂ levels below 800 ppm, so I stopped sending the logger. After my presentation last night with @DFisman, I decided to check it again. #COVIDCO2 /1 Levels below 900 ppm until ...
This is a school with full mechanical ventilation. This room is centrally provided so air is shared with other classrooms.
Filters have NOT been upgraded to MERV-13 or better.
HEPA is only in the rooms required by the province. Not in this classroom. /2
The relative humidity is low.
The entire school day it was 25%–28%. WHO & CDC recommend 40%-60% for SARS-CoV-2, Health Canada recommends 30%–50% on account of our climate & buildings. /3
Read 8 tweets
David Elfstrom Profile picture
25 Nov
Genome sequencing analysis shows spread of new variant in HK in hotel quarantine between suites across from each other when the air flowed to the corridor. Here we go again—no amount of positive pressure in the suite is acceptable. /1
h/t @nzm8qs news.gov.hk/eng/2021/11/20…
If there is a 5 Pa positive pressure difference between the suite and the corridor, air will shoot out under the door continuously at an average velocity of 2.1 m/s (higher in the centre). No open door required. For a 10 mm bottom door gap, that's 19 L/s (40 CFM) of flow /2 Graph of average velocity (...
I verified the calculations with measurements in an earlier thread, illustrating why NSW Australia's IPAC guidance for quarantine hotels allowing up to +5 Pa was ridiculous and ignorant of physics: /3
Read 4 tweets
David Elfstrom Profile picture
7 Nov
#corsirosenthalbox flow tests for Lasko 3733 and 3M Filtrete 1900 20x20x1 filters.
Shroud optimization: 20 cm radius (15.75" diameter) /1
Effect of shroud size on outlet flow. Having a shroud is important, but don't stress over it. Without it, air flows backwards at the corners instead of through the filters. /2
The supply voltage makes a difference! Fan speed changes linearly with voltage. Here's the flow range for the accepted 110-125V variation of the nominal 120 V North American distribution supply: /3
Read 10 tweets
David Elfstrom Profile picture
5 Sep
Canadian Aerosol Transmission Coalition calls on federal party leaders for stronger, consistent COVID-19 protections:
1⃣Messaging on aerosol transmission and airborne protection,
2⃣clean air ventilation standard,
3⃣HEPA filtration, and
4⃣respiratory PPE. /1
Remember the prescient quote by the late Justice Archie Campbell, head of the 2003 SARS Commission:
📢“If we do not learn from SARS and we do not make the government fix the problems that remain, we will pay a terrible price in the next pandemic” /2
The Canadian Coalition on Airborne Transmission is a multi-disciplinary group includes physicians, health scientists, ventilation engineers, respiratory protection specialists and occupational health professionals. 6-minute video: /3
Read 13 tweets
David Elfstrom Profile picture
3 Sep
#COVIDCO2 monitoring success story 👇
You don't need to have permanent CO₂ monitoring in classrooms with mechanical ventilation. You can have The Littlest Hobo CO₂ that helps out for a few days and then moves on.
(Unintentional reference to an actual HOBO CO₂ monitor)
Read 4 tweets

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