Why don’t we just open the windows?

Dancer, Stephanie J.; Bluyssen, Philomena M.; Li, Yuguo; Tang, Julian W.

doi:10.1136/bmj.n2895

Cited by 13 publications

(11 citation statements)

References 17 publications

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“…anthrax), particulate pollution, allergens (pollen, dust, bacteria, fungi, etc.) but purifiers/ventilation can be expensive 71 and respirators can be difficult to wear for an extended period of time causing many organizations or households to hesitate. A design target is to meet or exceed 4 to 6 air exchanges per hour (ACH) recommended 58 by California Department of Public Health, or even exceed 15 ACH used in passenger aircraft where, as discussed below, several observers have noted that (published) super-spreading events are much more infrequent (fewer) than would be expected with such high occupant density.…”

Section: Introductionmentioning

confidence: 99%

“…Indoor ventilation upgrades, HEPA-purifiers, and respirators can reduce inhalation of SARS-CoV-2 and its variants, other airborne viruses, aerosolized bacteria, and particulate pollution, including allergens such as pollen, dust, bacteria, fungi, etc. However, purifiers/ventilation can be expensive 71 and respirators can be difficult to wear for an extended period of time causing many organizations or households to hesitate. To mitigate COVID exposures in non-healthcare settings (including businesses, companies, offices, restaurants, schools, faith-based organizations, etc.…”

Section: Introductionmentioning

confidence: 99%

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Can 10x cheaper, lower-efficiency particulate air filters and box fans complement High-Efficiency Particulate Air (HEPA) purifiers to help control the COVID-19 pandemic?

Srikrishna

2021

Preprint

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BackgroundSARS-Cov-2 aerosols have potential to accumulate in airspaces of poorly ventilated, indoor spaces such as classrooms, offices, homes, restaurants, and bars. Separately, toxic aerosol pollution (e.g. wildfires, wood burning) is frequently encountered in these locations with ventilation relying on outside air. Portable high efficiency particulate air (HEPA) air purifiers are useful to remove both types of aerosols without relying on outside ventilation. To meet or exceed recommended 4 to 6 air exchanges per hour (ACH), high price-points for select HEPA air purifier models without incurring excessive noise generation make them unaffordable for many households and communities. Do-it-yourself (DIY) alternatives with box-fans and HVAC filters can be much lower cost but their clean air delivery rate (CADR) and noise generation varies greatly depending on choices of filters, number of filters, and fan speeds.ObjectiveTo compare cost-effectiveness and noise-generation of aerosol filtration by commercially available, portable HEPA air purifiers and do-it-yourself (DIY) alternatives built from box fans and HVAC filters rated at MERV 13 or 14 using single and quad filter designs.MethodsThe comparison is based on three metrics: clean air delivery rate (CADR), the noise generated (dBA), and affordability ($$) using an ISO-certified aerosol measurement device to measure input/output particle filtration of particles sizes ranging from 0.3 microns to 10 microns, airspeed meter to measure airflow, and NIOSH sound meter app to measure noise.ResultsAccounting for reduced filtration efficiency of MERV 13/14 filters compared to HEPA, estimated clean air delivery rate (CADR) of a do-it-yourself (DIY) setup using 2” and 4” filters with a box fan running at fan speed 1 for tolerable noise was 278 cfm ($38) to 371 cfm ($58), comparable or better than a commercial HEPA air purifiers running at maximum speed with low noise generation at 282 cfm ($375). However the quad filter designs, popularly known as the Corsi-Rosenthal box, achieved gains in CADR of only 60% over a single filter design but in contrast to 200-250% gains reported by UC-Davis.ConclusionsDIY alternatives using single 1”, 2” and 4” MERV 13/14 filters compare favorably to commercially available systems in terms of estimated CADR and noise but at five to ten times lower cost. Compared to use of one filter, an improvement in CADR (air flow) was observed with a popular DIY configuration involving quad filter design, popularly known as the Corsi-Rosenthal box, not as high as reported by a recent study by UC-Davis

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Can 10x cheaper, lower-efficiency particulate air filters and box fans complement High-Efficiency Particulate Air (HEPA) purifiers to help control the COVID-19 pandemic?

Srikrishna

2021

Preprint

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“…It is hoped that public health leaders will develop practical guidance and “tilt” people and places closer to safety 31. Now, indeed, is the time for an indoor air revolution 3233…”

mentioning

confidence: 99%

Airborne SARS-CoV-2

Dancer

2022

BMJ

Self Cite

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Time for an indoor air revolutionStephanie J Dancer consultant microbiologist Debate over the exact mode of transmission of SARS-CoV-2 has been intense. 1 This is entirely reasonable, given that the mechanism of spread determines preventive and potentially lifesaving policies. But the choice between respiratory aerosol or droplet settled on short range droplets, which neatly circumvented any risk outside the fabled 2m zone. 1 This choice gave rise to social distancing, hand and surface hygiene, and masks, but not to improved indoor air quality.And so the debate smoulders on, as Duval and colleagues (

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“…Dancer and colleagues’ editorial is a valuable commentary on implementing controls for the airborne transmission of SARS-CoV-2 1. As they say, adding “ventilation” to policy documents is not enough: procedures are required, customised by each organisation and presented clearly for people who might not understand the aerodynamic behaviours of aerosols now known to be lethally infectious.…”

mentioning

confidence: 99%

Open the windows? It’s not that easy

Brown

2022

BMJ

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Open the windows? It's not that easyColin W Brown research studentformer GP Dancer and colleagues' editorial is a valuable commentary on implementing controls for the airborne transmission of SARS-CoV-2. 1 As they say, adding "ventilation" to policy documents is not enough: procedures are required, customised by each organisation and presented clearly for people who might not understand the aerodynamic behaviours of aerosols now known to be lethally infectious. Window opening, for example, is generally understood and seems quick to do. But the window and door patterns and timings required for air exchange are specific to each room, 2 including how to use its heating system to restore comfort after repeated five or 10 minute ventilation periods and how to manage occupancy. 2 -5 The role of carbon dioxide monitors in managing shared air, and the use of air filtration when ventilation cannot be improved, also require engineering based procedures at the individual room scale. Such procedures cannot be left to end users' experiments. Expertise lies with the heating, ventilation, and air conditioning industry, but business forces have failed to implement it so far on the scale required.Transforming ventilation policy into hundreds of standard procedures fit to implement in millions of rooms requires national direction. This crosses government departments, so new organisations may be needed, as if we were at war. We are.

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Why don’t we just open the windows?

Abstract: The evidence for preventing covid-19 is lost in translation

Cited by 13 publications

References 17 publications

Can 10x cheaper, lower-efficiency particulate air filters and box fans complement High-Efficiency Particulate Air (HEPA) purifiers to help control the COVID-19 pandemic?

Can 10x cheaper, lower-efficiency particulate air filters and box fans complement High-Efficiency Particulate Air (HEPA) purifiers to help control the COVID-19 pandemic?

Airborne SARS-CoV-2

Open the windows? It’s not that easy

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