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David Elfstrom Profile picture
@DavidElfstrom
Apr 12, 2021 • 11 tweets • 6 min read • Read on X
38/
 Almost six months later.
Why can't we do this here?
/39 adding this great thread from @marwa_zaatari:
/40 summary additional benefits of higher #ventilation and improved air quality in schools beyond airborne infectious disease transmission, from The Lancet COVID-19 commission, April 2021.
Link to document (PDF): static1.squarespace.com/static/5ef3652… Table 1. Additional benefit...
/41 Large or small, just do it.
Homewood IL District 153 (three schools) hiring engineers "to determine deficiencies of existing #ventilation systems, incl. lack of outdoor air, filtration, through visual inspection"
Should be measured. hfchronicle.com/article/2021/m…
/42 Back to Ontario, Waterloo RDSB is racing to complete #ventilation projects before end-of-year funding deadline. Capital intensive changes take a long time compared to adding some portable HEPA filters. Bravo @wrdsb for taking the long view! kitchener.ctvnews.ca/wrdsb-racing-t…
/43 @Fix_Our_Schools seeks crowd-sourced data for Ontario schools, 11 months after their initial survey of #ventilation in #schools. How was the money spent?
/44 Higher education is less encumbered by funding restrictions, and can unilaterally take action, like U of T is doing
/45 All classrooms in NYC to have TWO air purifiers next year. Why two?
My thoughts:
1. One on full speed is loud, two on half speed is quieter.
2. Have ability to increase flow when needed
3. Better air mixing/performance ny.chalkbeat.org/2021/6/23/2254…
/46 Also in NYC schools for fall 2021, any space not meeting strict requirements for ventilation will be shut down until repaired. This requires measurement, so CO2 meters will be distributed to school custodians.
/47 "It shouldn't be luck for students to end up in a new portable with a dedicated ventilation system versus an old classroom w/o any mechanical ventilation. That's not equitable." -me, based on a local school @GEDSB cbc.ca/news/canada/to…
/48 The indoor air quality experienced by a student and their educator shouldn't be randomly assigned when it directly impacts academic performance and health.
Every educational setting needs to be brought up to a minimum acceptable level. Costs $ but has $$$ benefits. Image

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More from @DavidElfstrom

David Elfstrom Profile picture
Mar 28
Three years ago on this day ASHRAE stated that Airborne transmission of SARS-CoV-2 is significant.

Today, WHO finally released a model () of #CovidIsAirborne risk by experts in the field. /1 iris.who.int/handle/10665/3…

Landing page for the WHO document titled: Indoor airborne risk assessment in the context of SARS-CoV-2: description of airborne transmission mechanism and method to develop a new standardized model for risk assessment
Four years ago on this day WHO said : "FACT: #COVID is NOT airborne."

Today, WHO finally released a model () of #CovidIsAirborne risk by experts in the field that warned of airborne even earlier, but were shut out. /2
iris.who.int/handle/10665/3…
WHO Tweet March 28, 2020 FACT: #COVID19 is NOT airborne. The #coronavirus is mainly transmitted through droplets generated when an infected person coughs, sneezes or speaks. To protect yourself: -keep 1m distance from others -disinfect surfaces frequently -wash/rub your hands -avoid touching your eyes / nose / mouth Cover page of Indoor airborne risk assessment in the context of SARS-CoV-2
This document has been a long time coming. As described by @jljcolorado, Lidia Morawska, co-chair of the group that published the new WHO airborne model, was previously cut off by John Conly when making the case that #COVIDisAirborne to WHO. /3
Acknowledgements: WHO ARIA Technical Advisory Group: First name: Lidia Morawska (Co-Chair) (Queensland University of Technology, Australia) (many other names) John Conly (University of Calgary, Canada)
Read 4 tweets
David Elfstrom Profile picture
Feb 23
Air purifier manufacturers say HEPA should always be the filter of choice, and their product's proprietary filter delivers. Which HEPA? ISO 35H at 99.95% or ISO 40H at 99.99%? Why not ISO 50U? That's 10x better at 99.999%. Why stop there? Go for ISO 70U at 99.99999%! /1
The answer is, single-pass filtration efficiency DOESN'T MATTER except in specific cases like Powered Air Purifying Respirators (PAPR), clean rooms, operating theaters, or nuclear laboratory exhaust—HEPA's original purpose. /2
For portable/in-room air cleaners, all that matters is the Clean Air Delivery Rate (CADR) for a target particle size and type, within acceptable for sound power and frequency characteristics for the people in the room. /3
Read 13 tweets
David Elfstrom Profile picture
Jan 3
Four years into this and we can't keep duct-taping in-room filter solutions for clean air. It's just filter(s) and a fan. We need open-source, optimized design, certifiable product, efficient, repairable using commodity filters and commodity components. /1
We need air cleaners assembled and distributed by not-for-profit community-based social enterprise. No more lock-in to proprietary filters. Verified replacement commodity filtration performance for safety. /2
Low income with donated CR boxes will pay over time in electrical costs for the duct-taped solution for clean air.
Power utilization for Smoke CADR, same filters:
Conventional CR Box: 4 CADR/W. (77 W)
PC fan array air cleaner: 24 CADR/W. (8 W)
/3
Read 4 tweets
David Elfstrom Profile picture
Aug 28, 2023
1/ Levoit Core 400S versus Austin Air HM400 in a challenge to see which portable air cleaner removes submicron salt particle aerosols the fastest! Which do you think will win, and by how much? Poll in next tweet below... A large indoor tent with taped seams on a concrete floor is shown. On the left is a bench with instruments. A webcam is mounted on the top of a chair facing the instruments. In the middle are two air purifiers: The cylindrical Levoit Core 400S and the larger boxy Austin Air HM400. In the back right corner is a circular floor fan pointed diagonally upward into the middle. At the front right is a chair holding what looks like a tiny pitcher with a spout. A long thin clear plastic tube is connected to the side of this device, and exits the frame. Power cords are on the floor.
2/ Which has a higher CADR (Clean Air Delivery Rate):
Levoit Core 400S, or Austin Air HM400?
See if you can find the manufacturer's claims for both, and then come back and vote:
[sarcasm] Not only is the Austin Air bigger and far heavier, it also draws way more power, is much louder, and more expensive. It couldn't possibly be *worse* than the Levoit, right? Right?
Read 13 tweets
David Elfstrom Profile picture
Jun 12, 2023
When to change the filter on DIY #CorsiRosenthalBox? Holder et al (onlinelibrary.wiley.com/doi/10.1111/in…) showed that performance degradation depends on contaminant: Dust reduces airflow. Smoke kills electrostatic properties. @JimRosenthal4 @joeyfox85 @CorsIAQ Table for MERV 13 single-fi...
@JimRosenthal4 @joeyfox85 @CorsIAQ Note the test substance for the CADR PM2.5 performance measurement was simulated wildfire smoke.
The same would likely apply to a commercial HEPA air cleaner. Monitor for clearing time for a fixed release of contaminant with a simple PM meter.
Read 6 tweets
David Elfstrom Profile picture
Apr 12, 2023
When an IAQ report for an elementary school states the acceptable industry CO2 guideline is 700 ppm above ambient, or 1200 ppm, ask why the professional is using Std 62.1-2016 Informative Appendix D that was DELETED in 2018 because of misuse and outdated 1950's data.
@O_S_P_E 's calculator will give a target steady state CO2 value based on Standard 62.1 minimum acceptable outdoor air ventilation rates. Hint: It's not 1200 ppm for an elementary classroom. Link: https://t.co/V1DwupuJ3xospe-calc.herokuapp.com
Key phrases identifying that the deleted Informative Appendix D was used:
-Target of 700 ppm CO2 above ambient
-ambient is 300-500 ppm
-majority of occupants be satisfied with respect to human bioeffluents
-uses 1.2 MET, 15 CFM (7.5 L/s), 0.31 L/min
Read 4 tweets

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