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Redefining the home as a workplace and school environment 


The following was sent earlier this week to Dr. Ron Chapman, Yolo County Health Officer,  and the Yolo County Board of Supervisors:

“Dear Dr. Chapman and Supervisors,

This is a follow-up to my early queries and comments about advice on HVAC systems and ventilation of residences and more recently links I sent with evidence on how SARS-CoV-2 particles might be distributed even through normal respiration. It’s excerpted from what’s here.

Lately, many store workers in California have tested positive for COVID-19. There's now CDC guidance for essential workers that says to "... increase air exchange in the building.". The EPA also just sent out guidance on safety in school environments, which is still useful even though our schools are closed. It reminds schools to maintain their HVAC system. ASHRAE provides a link to an earlier version of the above-mentioned guidance from the CDC. Finally, there's also OSHA guidance on preparing workplaces for COVID-19. It's summarized here and says that the Engineering Control process includes "installing high-efficiency air filters" and "increasing ventilation rates in the work environment."

I call special attention to the terms in the above guidance: "Work environment" and "school environment". There's also multiple entities engaged in this issue beyond the CDC from which I presume you take the most guidance for decisions about Yolo County. In sum, they're all engaged in keeping people safe where they are or have to be. Right now, homes are workplaces for many, and for all children in Yolo County homes are their school environment. The clear spirit of the CDC, EPA, OSHA and ASHRAE(-supported) guidance is to improve air quality at home. It's where State and County Orders say that we must be outside of essential work and activities and recreation that maintains safe-distancing.

Therefore I urge the County to - at minimum - develop strong guidance with a robust communication element on reasonable strategies to improve the interior environment in residences. As to some extent the quality of interior air of the homes of renters may be out of their control, landlords must be required to communicate these strategies to renters.

This guidance can be on the same level, as it were, of what's happening with facial coverings, or from the first link I provide above. About the facial coverings as an example, a general DIY template has been provided. About residences, while some older homes in the area have whole house fans, most have central or by-room AC, not all of which provide a substantial amount of exterior air exchange. In this case the DIY template can be as simple as a box fan on one end of the home and an open window, on the other (and ideally in as many rooms as possible.) I suggested this several weeks ago and now there's more evidence that --  it's a good and very cheap solution. (I've also purchased some electronic timers so that fans can be run intermittently. The whole set up is about $40.) Many people already have box fans or similar fans that can be set up to exhaust air. I know that many in Yolo County have purchased these in the last two years in order to DIY interior air cleaners during the repeated wildfire fallout situations. We have three box fans and one standing fan in my house, and as for now supplies at e.g. Amazon seems to be considerable, likely in anticipation of the typical summer.

Thanks for your attention to this matter and for your hard work during the crisis in our local and broader community....

Todd Edelman, Davis


See also: “Stay 6 Feet Apart, We’re Told. But How Far Can Air Carry Coronavirus?” The New York Times, April 14, 2020.


Todd Edelman

Two more related stories appearing in the last couple of days!

Todd Edelman

Study examines spread of COVID-19 in restaurant | World News Tonight- ABC

Todd Edelman

"Where are people getting sick?

We know most people get infected in their own home. A household member contracts the virus in the community and brings it into the house where sustained contact between household members leads to infection.

But where are people contracting the infection in the community? I regularly hear people worrying about grocery stores, bike rides, inconsiderate runners who are not wearing masks.... are these places of concern? Well, not really. Let me explain.

In order to get infected you need to get exposed to an infectious dose of the virus; the estimate is that you need about ~1000 SARS-CoV2 viral particles for an infection to take hold, but this still needs to be determined experimentally. That could be 1000 viral particles you receive in one breath or from one eye-rub, or 100 viral particles inhaled with each breath over 10 breaths, or 10 viral particles with 100 breaths. Each of these situations can lead to an infection." -


Roberta L. Millstein

I agree with you Todd, but with a few clarifications. First, the risk of exposure is greater for people who work in grocery stores because of the length of time of exposure. Second, some stores are small with poor ventilation whereas others are larger with better ventilation. I think that matters also, especially depending on how many people are allowed in the store at one time. I suspect you agree on both of these points, but I thought it was worth clarifying them.

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