David Elfstrom Profile picture
Apr 7, 2021 26 tweets 11 min read Read on X
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...
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 ...
The stack effect is a dominant factor in winter, and is directly related to the height of the building AND the temperature difference between indoors and outdoors. Remove the temperature difference and the stack effect is minimal. /4
Figure: Cdn building digest number 104, 1968 Image
Wind effect can exert very strong pressures that overwhelm other pressures, from minutes to hours, causing significant air movement within a building. /5
Figure: Handegord & Hutcheon, Building Science for a Cold Climate, 1983 Image
Dynamic pressures on a building can be very high. Note a 5 Pa pressure difference from a kitchen exhaust fan in a home is enough to backdraft a naturally aspirated hot water tank in the basement. /6
Figure: plot based on physics Plot of wind pressure vs wi...
Mechanical pressures: It depends. Nearly all MURBs use corridor positive pressurization with fresh air to make up air exhausted from suites from kitchen and washrooms. Typically these flows are not balanced between units at all. /7
Figure: CMHC 2017 agency.coop/media/747/down… Air movement in buildings i...
The implications are that in cold climates in winter, there are significant amounts of uncontrolled air movement between suites, sometimes substantially more than the intentional air supplied by mechanical systems. /8
Figure: Fitzgerald & Bohac, 2012 slideshare.net/mnceeInEx/mf-s… Image
*IF* any centralized exhaust fan is off, there is a potential for direct connection to other units with flows driven by wind, stack, and remaining mechanical pressures. /9
Figure: Center for Energy and Environment multifamily ventilation assessment 2016 cards.commerce.state.mn.us/CARDS/security…
In Ontario alone there have been outbreaks reported in the news of MURBs in London, Sudbury, North Bay, Collingwood. All of these had significant numbers, all were in winter. There are likely many more, but health units aren't aware of them because they are overwhelmed... /10
Dr. Alex Summers: A heavy load of case area-wide and the ability to notice trends contributed to delay. "It wasn’t until we had a few weeks of seeing this common address pop up multiple times, that we were able to see that trend and declare outbreak" /11 london.ctvnews.ca/why-did-it-tak…
So what can those in mid-rise and higher apartments do?
⛔️DO NOT cover up exhaust vents, or block the suite door, they exhaust stale air and provide fresh air!
✅Check with toilet paper for this necessary air movement out of and into the suite. /12 Toilet paper test at suite ...
✅Look for areas of uncontrolled leakage entering the suite from other suites. Pipe penetrations are common. /13
Figure: slideshare.net/mnceeInEx/mf-s… Gaps around sink plumbing
Pandemic or not, if kitchen & washroom exhaust fans are not functioning (toilet paper not sticking to the grill) or worse, slight air movement into the apartment, bring it to management's attention immediately.
/14 Toilet paper should easily ...
Remember, #COVIDisAirborne.
Properly functioning mechanical systems help.
Portable HEPA air cleaners will provided lasting indoor air quality benefits.
Open your windows a crack.
Wear a tight-fitting quality respirator outside your home.
Don't panic: Be aware of shared air. /15 Image
Whoops, forgot the figure. You want central exhaust fans to be operating. If not, there's potentially direct connection to other suites.
Image
Looking to other cold climates, 26 infected at an apartment in Norway
"I have no idea how I have been infected, because I have not mixed with anyone. I have almost only been to the store"
h/t @Lisbethsindag
nrk.no/sorlandet/smit…
Another outbreak. @cityofhamilton please engage engineers & building scientists ASAP to help stamp this out. globalnews.ca/news/7833640/c…
"While Rebecca Towers is the only apartment [in Hamilton] to see an outbreak so far, Richardson said there may have been smaller ones in buildings that the city couldn't detect with their systems". 10 new cases today. cbc.ca/news/canada/ha…
Tacking this on. Start looking for clusters in apartment buildings and you just might find them.
Streetlight effect again. "City staff admit they do not have a system in place to track outbreaks in residential buildings, as they do for workplaces. The city should immediately establish a system to track case counts in apartment buildings" thespec.com/opinion/contri…
Here's a list of apartment building outbreaks in Ontario from news reports. Many health units do not report them, or aren't looking for them, and are overwhelmed.
Link to Google Sheet: docs.google.com/spreadsheets/d… Screen capture of web site.
How to do it: ONE person tests positive for variant, entire apartment block locked down & tested. 10% infected (19 of 189 people). I think they should move those infected off-site to individual air-gapped accommodation to prevent additional infection. dailymail.co.uk/news/article-9…
Singapore. "Although the four units with confirmed cases are in the same stack, (vertically aligned), MOH said its initial assessment is airborne transmission highly unlikely." No reason given. Maybe they need a building sci engineer? HT @drkristenkc straitstimes.com/singapore/heal…
If it can happen between adjacent apartments outdoors then it can happen between adjacent apartments indoors driven through unsealed penetrations by zonal pressure differentials
An excellent thread by @markegilmore filled with photos and observations about how we might be sharing air between units, or be exposed to contaminated air from drainage systems in apartment buildings. Thank you Mark!!

• • •

Missing some Tweet in this thread? You can try to force a refresh
 

Keep Current with David Elfstrom

David Elfstrom Profile picture

Stay in touch and get notified when new unrolls are available from this author!

Read all threads

This Thread may be Removed Anytime!

PDF

Twitter may remove this content at anytime! Save it as PDF for later use!

Try unrolling a thread yourself!

how to unroll video
  1. Follow @ThreadReaderApp to mention us!

  2. From a Twitter thread mention us with a keyword "unroll"
@threadreaderapp unroll

Practice here first or read more on our help page!

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

Did Thread Reader help you today?

Support us! We are indie developers!


This site is made by just two indie developers on a laptop doing marketing, support and development! Read more about the story.

Become a Premium Member ($3/month or $30/year) and get exclusive features!

Become Premium

Don't want to be a Premium member but still want to support us?

Make a small donation by buying us coffee ($5) or help with server cost ($10)

Donate via Paypal

Or Donate anonymously using crypto!

Ethereum

0xfe58350B80634f60Fa6Dc149a72b4DFbc17D341E copy

Bitcoin

3ATGMxNzCUFzxpMCHL5sWSt4DVtS8UqXpi copy

Thank you for your support!

Follow Us!

:(