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David Elfstrom Profile picture
David Elfstrom
@DavidElfstrom
P.Eng, Energy management, measurement & verification. Born @ 327 ppm CO₂. Safer infrastructure, #ventilation, #CorsiRosenthalBox Also @ https://t.co/SDMtkE22wf, bsky, LinkedIn
9 subscribers
May 31 • 10 tweets • 3 min read
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"
Mar 28 • 4 tweets • 3 min read
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
Feb 23 • 13 tweets • 3 min read
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
Jan 3 • 4 tweets • 1 min read
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
Aug 28, 2023 • 13 tweets • 4 min read
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:
Jun 12, 2023 • 6 tweets • 3 min read
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.
Apr 12, 2023 • 4 tweets • 2 min read
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
Apr 12, 2023 • 9 tweets • 2 min read
I agree both COVID and climate have engineering solutions, but disagree that engineering is *the* approach for climate that will drive an economic boom, because it overlooks the underlying geological reason for the industrial revolution:
Energy. /1 Yes, engineering was the response to social need. As it was with aqueducts, for example.
However the enormous geological endowment of concentrated solar energy in fossil fuels is behind all expansion since the industrial revolution. /2
Jan 22, 2023 • 8 tweets • 3 min read
1/ Looking at the sharp rise in your #Enbridge #NaturalGas bill? Wondering how it compares to electricity? Here's the conversion factors for the energy content in m3 to kWh:
Enbridge South 1 m3 = 10.88 ekWh
Enbridge North 1 m3 = 10.78 ekWh 2/ The energy content of 1 m3 of natural gas changes over time. This web page has the historical annual average values: enbridgegas.com/storage-transp…
To convert between GJ per 1000 m3 natural gas and ekWh per m3, divide by 3.6.
(1 W = 1 J/s, and 1 hour = 3600 seconds) Enbridge web page snapshot: Unit of Measure Conversion infor
Dec 18, 2022 • 5 tweets • 2 min read
#PostNews is ableist by intent. When I made my first post I was astonished that I couldn't add an image description to an infographic.

It turns out this is not an oversight. It's intentional. #Accessibility. /1 Post by Taylor Lorenz @taylorlorenz@mastodon.social November The founder of Post says "We want to do it all but first, let's get everyone in."
Well, everyone in who is sighted, that is.
If #accessibility is not part of the design from the start, it won't be easily added in the future. /2
Dec 15, 2022 • 5 tweets • 2 min read
Pharmacies have empty shelves where children's fever medication once was and antibiotics are running low, yet there are overstock sales on respirator masks and air purifiers. The Canadian PPE industry is going to shut down without some large orders.
Nov 19, 2022 • 4 tweets • 2 min read
The #Mastodon search bar disappears on narrow screens, so click on the Explore (#) icon to reveal it. To find a specific person you need both their handle and server name, like mine: @DavidElfstrom@masto.ai /1 Mastodon on a narrow screen highlighting the # icon, which r On #Mastodon hashtags are very important, and you can subscribe to them in your feed! Enter the hashtag like #CorsiRosenthalBox in the search bar, click on the result link, /2 Explore icon is circled, #CorsiRosenthalBox hashtag is in th
Nov 9, 2022 • 4 tweets • 2 min read
1/ When writing to a school about #ventilation, I don't mention COVID at all. It carries a lot of baggage.
Focus on minimum standards first. Everyone can accept that poor ventilation results in poor academic outcomes. It's been proven, over and over. 2/ Use the same approach for #EnergyEfficiency. If people cared about the environment or saving money or the safety of others we wouldn't see people driving pick-up trucks everywhere. Focus on comfort or lifestyle.
Nov 9, 2022 • 4 tweets • 2 min read
Got a box of 3M VFlex 9105 #N95 respirators. Very comfortable, large surface area, easy to shape, VERY easy inhale. It seems to retain more heat from my own breath (good for winter!) and is a little bit harder to don/doff than the Eclipse Arc. Highly refined design. Hand holding a 3M VFlex respirator in front of a box of 50 o The fold over the edges of the 3M VFlex #N95 really adds to the comfort. View inside of the respirator. There is a gentle reminder of
Nov 5, 2022 • 5 tweets • 2 min read
As part of the rapid and deserving decanting of Twitter you can find me on #mastodon at @davidelfstrom@mstdn.social
mstdn.social/@davidelfstrom 2/ To give you a positive reason to join the Mastodon network, I'll be unboxing and testing this beast on there. Tall cardboard box in a bas...
Sep 8, 2022 • 5 tweets • 2 min read
Looks like this needs to be provided again to school administrators. Portable air cleaners do NOT interfere with the HVAC system. Mixing the air is beneficial in nearly all situations. /1 You can also read one of @joeyfox85's several threads that cover mixing and filtering, like this one: /2
Jun 25, 2022 • 4 tweets • 1 min read
My 7-year old daughter went to the movie Lightyear and was confused by what she saw and now I'm struggling to describe time dilation and special relativity Meanwhile Christian G Gonzalez @Chris...
May 30, 2022 • 4 tweets • 1 min read
I asked 7 year old if they had lunch outside since it was gorgeous weather, 29°C. “We had gym outside, then came inside for lunch, and went back outside for recess right after lunch”🤦‍♂️ Classroom CO₂. First dip to 600 ppm is morning recess, then back inside for math, second dip is gym outside, then lunch inside, third dip is recess outside right after lunch. Still low values, so not concerning.
May 29, 2022 • 7 tweets • 7 min read
#corsirosenthalbox TechTalk: Filter life and efficiency. Study of residential furnace filters in Toronto homes by Li & Siegel. Efficiency of MERV 8 improved, while MERV 11E, 14E (electret) dropped. @CappaSnappa @joeyfox85 @JimRosenthal4 @JbcLiftec DOI: doi.org/10.1080/237447… Figure 3 from: Tianyuan Li & Jeffrey Siegel (2020) Laborator @CappaSnappa @joeyfox85 @JimRosenthal4 @JbcLiftec Li & Siegel [@Amy_Tianyuan_Li & @IAQinGWN] also reported on the size resolved performance of the same filters in another study. Note the minimum occurring at 0.3 μm (300 nm) and is better on smaller sizes. DOI: doi.org/10.1111/ina.12… Figure 2 from Li, T, Siegel, JA. In situ efficiency of filte
May 25, 2022 • 4 tweets • 2 min read
Aerosol particle emission increases exponentially above moderate exercise intensity resulting in superemission during maximal exercise (2 W/kg+).
So spin class outbreaks weren't caused by droplets aerosolizing after hitting the bike's flywheel? [sarc]
pnas.org/doi/10.1073/pn… October 2020:
May 5, 2022 • 4 tweets • 2 min read
When your board of health hires an unqualified MOH who can only be Acting, you get a minimizer who ignores the 51%-80% prevalence of Post-Acute COVID-19 Syndrome and recommends treatment of chicken noodle soup and ginger ale. simcoereformer.ca/news/local-new… (May 4, 2022) Perfectly healthy, fully-va... Post-Acute COVID-19 Syndrome is no picnic. Link to PDF from Public Health Ontario: publichealthontario.ca/-/media/Docume… Screen capture of the top h...