David Elfstrom Profile picture
Jan 11, 2022 15 tweets 10 min read Read on X
The air cleaner purchased by @nseducation for schools has a Clean Air Delivery Rate almost HALF of a common retail unit and may create secondary products by reacting with gas phase contaminants in a poorly ventilated room using photocatalytic oxidation #nspoli /1 Guardian Beyond Air F159E: ...
As seen in the photo, it's not running on its highest setting. For #ventilationequity in non-mechanically ventilated classrooms, should be a min 15 CFM per person, or 375 CADR for 25 people, AND at an acceptable noise level. How many per classroom? #DoTheMath! /2
Don't get me wrong, any filtration is better than nothing! But it's a mere band-aid over a gaping wound.
A DIY $120 #corsirosenthalbox will beat the air cleaners purchased by @nseducation AND can be used in STEM lessons! See cleanarair.com /3 Screen capture of web site
On the product claims of ActivePure® technology "to reduce over 99.9% of many common contaminants in the air and on surfaces", Dr. Brent Stephens who runs the Built Environment Research Group, has umm, "done the research". Link: built-envi.com/what-air-clean… /4 Image
But what about the use of photocatalytic oxidation? There are questions about chemicals that can be inadvertently created from this. I'll refer to the experts who wrote an open letter: medium.com/open-letter-to… /5
We should be requesting independent monitoring of the chemical composition of secondary products in both gas and particle phases in the rooms where these devices have been installed. You know, precautionary principle? /6
Stick with layering the basic triad of engineering controls:
#Ventilation
#Filtration (#FilterFitFlow)
#UVGI
please hold the bells & whistles /7 Image
Similar advice is from Johns Hopkins Center for Health Security in their letter released today.
#Ventilation 6ACH #Filtration MERV-13, #UVGI, #HEPA or build #Corsirosenthalbox, don't use unproven additive technologies: centerforhealthsecurity.org/news/center-ne… /8 Image
Take solace my NS friends, because your neighbors
@NLESDCA bought at least 3000 of the smaller Aerus Pure & Clean for schools, with a max flow of only 60 CFM (and presumably lower actual CADR rating, if it even qualified for the AHAM test) /9
Update on the cost: Nova Scotia spent $2.3M for 1600 units, or $1438 each. Compare with the Honeywell unit from Canadian Tire that has nearly twice the verified air cleaning performance for $329. globalnews.ca/video/8501732/… /10
If the Beyond Guardian Air was quieter, that might be worth the much higher cost, but it's not. It's the same noise level at full speed with almost half the air cleaning power as a much less expensive Honeywell. /11 Both the Honeywell HPA5350B...
There is a wide variety of air cleaners available. Many have significantly less noise and/or significantly more Clean Air Delivery Rate. @marwa_zaatari has collected info on many of them and their cost (USD) and noise level here: /12
Prof Jeffrey Siegel @IAQinGWN weighs in with this 7-minute interview, and I fully agree. While this unit might create byproducts using PCO, it's not as problematic as being undersized for a classroom without mechanical ventilation. Listen here: /13 cbc.ca/listen/live-ra…
@IAQinGWN These air cleaners are covered in this article /14 saltwire.com/atlantic-canad…
@IAQinGWN Summary table (excluding maintenance costs and the concerns about secondary products formed by Aerus' photocatalytic oxidation), includes suggested number of units for typical non-mechanically ventilated classroom. Take-home: Aerus is 8x higher cost. /15 Image

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More from @DavidElfstrom

May 31
Vancouver Coastal Health has released an updated Ventilation and Indoor Air Quality resource for Schools and Childcare Facilities () but their CO2 page needs some edits. vch.ca/en/document-li…
States high levels of CO2 and other contaminants ... can contribute to [list of five health effects, such as headaches, fatigue, difficultly concentrating], says CO2 should be below 1000 ppm, then says (incorrectly) that health effects from CO2 occur at levels above 5000 ppm. No, those effects can occur below 5000 ppm.  It also states the CO2 concentrations do not indicate a risk of infectious disease transmission in a space. No, ASHRAE's position statement on CO2 states that elevated CO2 concentrations CAN reflect higher risk. Obviously, because it indicates poor ventilation, which IS an i...
Vancouver Coastal Health "CO2 concentrations do not indicate a risk of infectious disease transmission in a space". No.
ASHRAE's position document on indoor CO2 says "higher CO2 conc correspond to lower ventilation and potentially increased risk of airborne transmission"
Vancouver Coastal Health "Note that health effects from CO2 occur at levels above 5000 ppm". Did WorkSafeBC interfere? Because that's contradicted by your Health Canada reference in the sentence immediately before it.
Read 10 tweets
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
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
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
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
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

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