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Jan 18 • 5 tweets • 1 min read
#HBA2021 - Antonios Tasoglou. Investigated electronic air cleaners using real time instrumentation. Used 30 m3 chamber, 25C and 50%. Limonene, formaldehyde and toluene as challenge gases. 1/5
Analyzed with ozone, PTRMS, DNPH, Tenax, particle counts as analysis methods. Example electronic cleaner with UVC/TiO2/HEPA/carbon filter. Limonene and toluene decreased to zero within an hour, formaldehyde did not decrease below 40 ppb after four hours. 2/5
Loss rates for limonene and toluene were 4-5/h. For formaldehyde the loss rate was only 0.7/h, as it is an oxidation product of toluene and limonene. 3/5
Clean air delivery rate was 20-30 m3/h (10-17 cfm) for formaldehyde and 130 to 160 m3/h (76-94 cfm) for toluene and limonene. 4/5
Byproducts detected: methanol, ethanol, and acetaldehyde, others. Concentrations still increasing after 4 hours. Up to 200 ppb. 5/5

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More from @Poppendieck

Dustin Poppendieck Profile picture
Jan 21
A thread on filtration:

Masks, portable filters, and HVAC filters are all the same.

They must account for three things to achieve EFFECTIVE, real-world filtration:

1) Fit
2) Flow
3) Filter Efficiency

(H/T @JimRosenthal4 for topic idea)

1/18
Let's start by clarifying this thread will be about mechanical filtration where the particles are removed via a physical process.

This thread is not about filtration technologies that rely on energy or chemical reactions to remove particles.

2/18
FIT:

Air must go through the filter to be effective. Whether on your face (N95s) or in a duct (MERV13) if there is a bad fit a majority of the air will not go through the filter.

Just like water finding the easiest path down hill,
3/18
Read 18 tweets
Dustin Poppendieck Profile picture
Jan 20
#HBA2021 Claire Barnett:

Children are not little adults.
Schools are not just little offices.
Schools are the second largest public building expenditure after roads.
Schools contain mainly women and children (>90%).

Schools were not COVID19 ready. CDC did not prioritize IAQ until May 2021. "Our schools are not designed to do that."

8 billion ft2 of schools >$3 Trillion in schools are not climate ready.
>12,000 schools are within 1 mile of a chemical hazard.

Heat waves: children do not test well or learn at high heat. Perhaps lower thresholds to send kids home?

Should schools operate during forest fires? Schools aren't designed to handle extreme particle levels.
Read 5 tweets
Dustin Poppendieck Profile picture
Jan 20
#HBA2021: Greg Whitely. What is the definition of clean? We clean materials to visual inspection to clean microbes we can't see.

We shed 40 million skin cells per day. We touch our faces 20-40 times a minute.
Superbugs in hospitals have not taken the last two years off.

Some microbes can survive in a viable form for years in biofilms.

Organisms you touch can remain on your fingers for up to 19 consecutive touches (and move to other surfaces).
The spread of microbes on surfaces is not uniform. If you use the wrong form of cleaning you can actually spread the microbes rather than remove them.

There are 9 variables in wiping a surface (pressure, disinfect to towel surface, frequency, etc.).
Read 6 tweets
Dustin Poppendieck Profile picture
Jan 20
#HBA2021. @anna_s_young. Sampled 231 office workers with wrist silicon wrist bands (only worn at the office) in US, UK, India and China. Analyzed for SVOC in 100 wrist bands by Heather Stapleton's group.

Exposure to chemical classes varied by location.
US workers exposed to PCBs that were banned 40 years ago. Exposures to PCBs in India higher. Paint likely a PCB source.
Brominated flame retardant higher in US and UK compared it China and India. People still exposed to flame retardants that have been banned over 10 years.
Read 4 tweets
Dustin Poppendieck Profile picture
Nov 5, 2021
Uncertainty in using CO2 for ventilation clues in Classrooms.

A LONG Thread... 1/
Short version:
High CO2: REAL BAD.
Low CO2: Meh...
In Between: Who knows... better get filtering.
2/
First lets talk about short versus long range transmission.

1) The highest COVID transmission risk is short range where the aerosols are highest in concentration. Well fitting masks and distancing are the best defense. 3/
Read 73 tweets
Dustin Poppendieck Profile picture
Sep 4, 2021
How do air change rate, ventilation rate and maximum carbon dioxide concentration in a room relate? Its complicated. But in general they relate like this:*

*Example classroom, the shape remains the same, while actual y-axis value change with room/age/activity. 1/7
If the maximum concentration in a room is above ~2,000 ppm we know that the ventilation rate/air change is BAD (flat part of curve). Small increases in ventilation will drop the carbon dioxide concentration quickly. 2/7
If the maximum concentration in a room is below 700 ppm we know the ventilation probably good (steep part of curve). Big increases in ventilation will only slightly drop the carbon dioxide concentration. 3/7
Read 7 tweets

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