Chris Iddon
@chrisiddon.bsky.social
Music, walking, ventilation.
Research fellow
Chair of the CIBSE natural ventilation group
Research fellow
Chair of the CIBSE natural ventilation group
Kids also reported their perceived perception of the indoor air quality and their perception of the air quality improved with the presence of air cleaners, even when the air cleaners were off
A placebo effect - demonstrating the power of suggestion
A placebo effect - demonstrating the power of suggestion
November 21, 2025 at 5:49 PM
Kids also reported their perceived perception of the indoor air quality and their perception of the air quality improved with the presence of air cleaners, even when the air cleaners were off
A placebo effect - demonstrating the power of suggestion
A placebo effect - demonstrating the power of suggestion
6 schools and 27 classrooms under baseline, air cleaner off, HEPA on and SHAM (air cleaner on but no HEPA filter). Air cleaners also included activated carbon to remove TVOC.
If kids had symptoms they scored these, air cleaner reduces symptom severity with and without HEPA
If kids had symptoms they scored these, air cleaner reduces symptom severity with and without HEPA
November 21, 2025 at 5:49 PM
6 schools and 27 classrooms under baseline, air cleaner off, HEPA on and SHAM (air cleaner on but no HEPA filter). Air cleaners also included activated carbon to remove TVOC.
If kids had symptoms they scored these, air cleaner reduces symptom severity with and without HEPA
If kids had symptoms they scored these, air cleaner reduces symptom severity with and without HEPA
New study on HEPA air cleaners in Finnish school study.
Kids fill in daily diary of respiratory symptoms and the prevalence of symptoms reduced when the air cleaner was on.
However the prevalence also decreased when the air cleaner was on but HEPA removed 🧵
Kids fill in daily diary of respiratory symptoms and the prevalence of symptoms reduced when the air cleaner was on.
However the prevalence also decreased when the air cleaner was on but HEPA removed 🧵
November 21, 2025 at 5:49 PM
New study on HEPA air cleaners in Finnish school study.
Kids fill in daily diary of respiratory symptoms and the prevalence of symptoms reduced when the air cleaner was on.
However the prevalence also decreased when the air cleaner was on but HEPA removed 🧵
Kids fill in daily diary of respiratory symptoms and the prevalence of symptoms reduced when the air cleaner was on.
However the prevalence also decreased when the air cleaner was on but HEPA removed 🧵
During the COVID-19 pandemic in 2021, researchers monitored air quality in marquees and semi-outdoor venues at UK mass gatherings to understand ventilation and airborne infection risk — work that directly informed how such events could safely reopen. 🧵
November 6, 2025 at 1:44 PM
During the COVID-19 pandemic in 2021, researchers monitored air quality in marquees and semi-outdoor venues at UK mass gatherings to understand ventilation and airborne infection risk — work that directly informed how such events could safely reopen. 🧵
and on a tangent on this, if there is some discrepancy and the 4000cf is correct, then they have sized to provide an additional 6.4ach which exceeds the CDC guidelines at the time of 5ach. So I'd still argue that these filters have been well sized for the application
October 16, 2025 at 1:14 PM
and on a tangent on this, if there is some discrepancy and the 4000cf is correct, then they have sized to provide an additional 6.4ach which exceeds the CDC guidelines at the time of 5ach. So I'd still argue that these filters have been well sized for the application
I should clarify that the study did find that absences increased in those classrooms designated high viral load in the air, compared to low viral load. And that HEPA did not reduce your chance of being a high viral load classroom
October 15, 2025 at 8:26 PM
I should clarify that the study did find that absences increased in those classrooms designated high viral load in the air, compared to low viral load. And that HEPA did not reduce your chance of being a high viral load classroom
and so to the critiques - maybe they were turned off? Perhaps, but the data from the asthma study (ie the same data set) showed a 20-40% reduction in particulate material with the HEPA present. You wouldn't expect to see filters filtering if they were off! 9/n
October 15, 2025 at 7:33 PM
and so to the critiques - maybe they were turned off? Perhaps, but the data from the asthma study (ie the same data set) showed a 20-40% reduction in particulate material with the HEPA present. You wouldn't expect to see filters filtering if they were off! 9/n
The study provides no information on whether or not the presence of the HEPA had any impact on transmission of any of these respiratory illnesses or impacted absences. 8/n
October 15, 2025 at 7:33 PM
The study provides no information on whether or not the presence of the HEPA had any impact on transmission of any of these respiratory illnesses or impacted absences. 8/n
The results show an interesting spread of viruses that change in prevalence over the year (note there is no SARS-CoV-2 bcos this predates the pandemic, plenty of other coronaviruses tho) 4/n
October 15, 2025 at 7:33 PM
The results show an interesting spread of viruses that change in prevalence over the year (note there is no SARS-CoV-2 bcos this predates the pandemic, plenty of other coronaviruses tho) 4/n
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
July 14, 2025 at 11:10 AM
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
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
July 14, 2025 at 11:10 AM
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
🔍 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
rehva.eu/rehva-journa... 5/5
June 25, 2025 at 11:14 AM
🔍 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
rehva.eu/rehva-journa... 5/5
📉 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
June 25, 2025 at 11:14 AM
📉 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
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/...
June 6, 2025 at 1:19 PM
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
June 6, 2025 at 1:19 PM
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
The abundance of some bacteria went down and some went up. The abundance of some viruses went down and some went up 5/n
June 6, 2025 at 1:19 PM
The abundance of some bacteria went down and some went up. The abundance of some viruses went down and some went up 5/n
What if we also collect some 💩 and just look at all the bacteria and phages (viruses that infect bacteria) that we find and try and find some differences.
No difference in the diversity of bacteria, but some differences in the types of virus found 4/n
No difference in the diversity of bacteria, but some differences in the types of virus found 4/n
June 6, 2025 at 1:19 PM
What if we also collect some 💩 and just look at all the bacteria and phages (viruses that infect bacteria) that we find and try and find some differences.
No difference in the diversity of bacteria, but some differences in the types of virus found 4/n
No difference in the diversity of bacteria, but some differences in the types of virus found 4/n
And in this new study they show significant reductions in particulate pollution when using solar lamps as well as a reduction in respiratory symptoms esp dyspnea (shortness of breath). Reduced exposure to pollution correlates with reduced respiratory symptoms - great! but.. 3/n
June 6, 2025 at 1:19 PM
And in this new study they show significant reductions in particulate pollution when using solar lamps as well as a reduction in respiratory symptoms esp dyspnea (shortness of breath). Reduced exposure to pollution correlates with reduced respiratory symptoms - great! but.. 3/n
This is an extension of previous work that looks at the impact of changing from using kerosene lamps to solar lamps on indoor air quality in dwellings in rural Uganda. Burning of kerosene lamps creates a lot of particulate pollution as one might expect pmc.ncbi.nlm.nih.gov/articles/PMC... 2/n
June 6, 2025 at 1:19 PM
This is an extension of previous work that looks at the impact of changing from using kerosene lamps to solar lamps on indoor air quality in dwellings in rural Uganda. Burning of kerosene lamps creates a lot of particulate pollution as one might expect pmc.ncbi.nlm.nih.gov/articles/PMC... 2/n
This is represented for the different flu strains, suggesting that there is some difference between strains in their ability to confer infection via the aerosol route 10/n
June 5, 2025 at 1:28 PM
This is represented for the different flu strains, suggesting that there is some difference between strains in their ability to confer infection via the aerosol route 10/n
Triangles are direct inoculated and circles aerosols. As time from inoculation increases the amount of detected virus in supernatant increases, but at a faster rate in the direct inoculated 9/n
June 5, 2025 at 1:28 PM
Triangles are direct inoculated and circles aerosols. As time from inoculation increases the amount of detected virus in supernatant increases, but at a faster rate in the direct inoculated 9/n
More virus is detected quicker in cell lines inoculated directly compared to by the aerosol route and this is most likely because the cell lines are exposed to more virus in the direct inoculation compared to aerosol inoculation. Here serial dilutions of supernatant tested 8/n
June 5, 2025 at 1:28 PM
More virus is detected quicker in cell lines inoculated directly compared to by the aerosol route and this is most likely because the cell lines are exposed to more virus in the direct inoculation compared to aerosol inoculation. Here serial dilutions of supernatant tested 8/n
imo the virus still undergoes a stage where it moves from aerosol into the cell culture medium and then infects the cells, so I can't imagine any mechanical difference compared to the direct inoculation (tho i cld well be wrong) 5/n
June 5, 2025 at 1:28 PM
imo the virus still undergoes a stage where it moves from aerosol into the cell culture medium and then infects the cells, so I can't imagine any mechanical difference compared to the direct inoculation (tho i cld well be wrong) 5/n
A nebuliser is used to aerolise a viral solution, some of these aerosols containing virus deposit onto the solution covering the cells, and virus then infect the cells. Again incubated for a while before cells are washed and covered with virus free soln 3/n
June 5, 2025 at 1:28 PM
A nebuliser is used to aerolise a viral solution, some of these aerosols containing virus deposit onto the solution covering the cells, and virus then infect the cells. Again incubated for a while before cells are washed and covered with virus free soln 3/n
Here's a rough sketch of what was done, two types of cell lines are cultured on the bottom of a well in a plate. These cells need a solution with nutrients/antibiotics etc in to survive. In direct inoculation this fluid contains virus. Incubated for a while before washing 2/n
June 5, 2025 at 1:28 PM
Here's a rough sketch of what was done, two types of cell lines are cultured on the bottom of a well in a plate. These cells need a solution with nutrients/antibiotics etc in to survive. In direct inoculation this fluid contains virus. Incubated for a while before washing 2/n