Chris Iddon

a man wearing a top hat and a vest is standing in front of a pile of rocks .. ALT: a man wearing a top hat and a vest is standing in front of a pile of rocks ..

You're welcome

Want to know more about how airflow and risk modeling work? The full paper dives deep into the math, assumptions, and trade-offs 👉 doi.org/10.1016/j.bu...

#ventilation #indoorairquality #publichealth #ASHRAE241
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A great team effort from @benjonesieq.bsky.social, Marwa Zaatari, Pawel Wargocki and Richard Burns in providing this technical overview of the ANSI consensus process 10/n

Bottom line: ASHRAE 241 offers a science-informed way to reduce risk—but it’s not a silver bullet. Clean air helps, but vaccines, and reducing exposure time still matter too. 🏥🏢💨 9/n

Other expert groups might’ve made different modeling choices—but this is the consensus approach the ASHRAE 241 committee agreed on, based on current science and engineering judgment. 8/n

Important caveat: this only targets long-range airborne transmission. It doesn’t address close contact, surfaces, or time spent in spaces without increased airflow. And we still have limited real-world data on how much it reduces actual infection rates. 7/n

A major uncertainty is the viral load—how much virus an infected person emits varies by orders of magnitude. That makes precise predictions tough. The model aims for a good balance, not perfection. 6/n

So the modeling accepts that some rare cases (the other 4%) may still have higher risks—especially if someone is a high “emitter” of virus. Still, the chosen airflow levels drastically reduce risk most of the time. 5/n

One key thing: if there are no infected people in a room, the risk is zero. That seems obvious, but it shows why we can’t design for every worst-case scenario—doing so would require impractically high airflow. 4/n

We used the Wells–Riley model, a common tool in infectious disease modeling. But real-world variables—like viral load, breathing rates, and particle sizes—are full of uncertainty. So we used a probabilistic (Monte Carlo) approach. 3/n

The short answer: modeling. A group of experts used risk models—based on data from COVID-19—to estimate the odds of someone getting infected in an indoor space over 1 hour. Their goal? Keep that risk below 0.1% in 96% of cases. 2/n

ASHRAE Standard 241 sets guidelines for how much “clean air” (via ventilation, filtration, etc.) is needed in buildings to reduce the airborne spread of infectious diseases like COVID-19. But how were these numbers chosen? 1/n

New oped from @benjonesieq.bsky.social
& me
💨 The push for better school ventilation is well-meaning, but claims that it boosts cognition or learning lack strong, causal evidence. Many studies are low quality, poorly controlled, and often overstate effects. #IAQ #ventilation #education 1/5

The June issue of the #REHVA #Journal is out now! 📯

"#Education #Buildings: a Net Zero Transition Conducive to #Health and #Cognitive Performance".

📱 Read it online: www.rehva.eu/rehva-journa...

📨 Want to receive the #REHVA Journal in your inbox? Subscribe here: www.rehva.eu/newsletter-s...

Watched them as a teen and now with my kids

🔍 Conclusion: Better trials, not bigger fans. Until we have high-quality evidence, stick to standards, target known harms, and prioritize interventions with proven impact. #evidencebased #ventilation

rehva.eu/rehva-journa... 5/5

🏫 The real health risks in classrooms are known contaminants (e.g. PM2.5, NO₂, HCHO). Targeting these with harm-based IAQ metrics makes more sense than chasing broad ventilation increases. #healthfirst 4/5

🧪 Most ventilation-performance studies rely on weak observational data. Confounding variables, cherry-picked results, and overreliance on CO₂ (a poor proxy for IAQ) undermine conclusions. #scientificrigour 3/5

📉 Advocates often ignore the law of diminishing returns: more airflow ≠ proportionally more benefit. Beyond current standards, major upgrades need strong evidence—which we don’t yet have. #IndoorAirQuality 2/5

New oped from @benjonesieq.bsky.social
& me
💨 The push for better school ventilation is well-meaning, but claims that it boosts cognition or learning lack strong, causal evidence. Many studies are low quality, poorly controlled, and often overstate effects. #IAQ #ventilation #education 1/5

this is a hybrid-ventilation system, the fans are used for mixing incoming/outgoing air and are not the driving force. It is therefore considered that natural ventilation is the driving force and performance measured on this basis. This is set out in BB101

It takes ages to read the detail compared to a headline "scientists find air quality changes gut microbiome" or "improving gut microbiome could improve respiratory health, especially when air pollution is poor, says scientists"

No wonder you get the responses like you get from Trump...shame the baby gets thrown out in the bathwater tho 🙁

I naively thought it was the job of scientists to use a critical eye and assess the quality of research findings, but more and more I see it generating low quality observational guff that has little value.

tbh I think we've crossed that rubicon. But for those with deep held beliefs in a "science" such work just strengthens their faith - pass me another yakult/kimchee, it'll help me against air pollution now too, don't you know! Or it supports a grift. Ofc it's all BS if it doesn't support your bias

Is it that the green line went down from 6 to 2, whilst the red line went down from 5 to 2, so mask mandates are 1 better?

Whilst this paper shows promising improvements in air quality by replacing kerosene lamps with solar lamps in reducing respiratory symptoms, they suggest improving gut microbiome communities could be an answer thanks to p-hacking loads of gut flora! /end ehp.niehs.nih.gov/doi/10.1289/...

They suggest maybe it is the gut microbial communities that impacts the respiratory health, and poor IAQ changes these communities. So a therapeutic approach to countering poor IAQ if you can't replace kerosene lamps is to use microbiome-targeted therapies 🤯 7/n

Using solar lamps improved indoor air quality and reduced respiratory symptoms. But as the authors find some changes to different gut flora they also can find some correlations between gut flora species and respiratory symptoms, and wait for it, here's the discussion point: 6/n

The abundance of some bacteria went down and some went up. The abundance of some viruses went down and some went up 5/n