Joey Fox Profile picture
Nov 9, 2022 15 tweets 4 min read Read on X
Mitigating COVID Transmission in Your Home

You want to have friends over and avoid infection. What tools do you have? Here's a rundown of your options.

1/13
Aside from air quality, your other tools are vaccines, rapid tests and masks/respirators. The more layers the better.

For air quality, your tools are ventilation, filtration, ultraviolet light and humidity. So how do you use them?

2/13
@CPHO_Canada gives a list here (she's leaving out one major thing. Can you guess what it is?)

The 2nd and 3rd option are about running your furnace. I'll start with that.

3/13

Your furnace will supply about 30-70 cubic feet per minute per room. That's a tiny amount and not sufficient for mitigation. It's still worthwhile to ensure the air coming from your furnace is clean and run it. You can clean the air in the following ways:

4/13
-Attach an energy/heat recovery ventilator
-Upgrade filter to MERV-13 (my personal choice)
-Attach a HEPA filter to the furnace
-Place a UV lamp in the furnace (unsure how effective)

Do at least one of these and run your furnace.

5/13
Humidity

Humidity can be a helpful tool. Ultrasonic humidifiers can release mold, bacteria and other particles into the air. The best thing is a steam humidifier with distilled or reverse osmosis water. I have one attached to my furnace. Don't humidify past 40% RH.

6/13
The rest of the mitigation happens in each room:

Ventilation - windows are your tool. If it's cold, keep them cracked. You can boost air coming into the home by running an exhaust fan or making your own exhaust fan like Joe. (Be like Joe👍)

7/13

If you are exhausting air out, make sure there is a place for air to come in (open window). Your kitchen range hood is powerful, but usually loud. Bathroom fans are weak and not that effective for this.

8/13
Filtration

Run a HEPA filter or a DIY Corsi-Rosenthal Box. Not much more to say.

9/13
UV

If we want to get serious about mitigation, this is the best tool. The evidence we have is a 15 W far-uv lamp in a dining room gives you 30-60 air changes per hour. 1 lamp > 4 CR Boxes. I would use it if someone is symptomatic or when having guests (with consent).

10/13
Higher power far-uv will be more effective, but you need to do your research to ensure you aren't exceeding daily threshold exposure levels. You are very unlikely to exceed them if there is a 15 W lamp in your ceiling.
nature.com/articles/s4159…
11/13
Short range transmission

You need to dilute the concentrated air in your breathing zone with air from the room quickly. The way you do that is with increased air speed. Larger fans (ceiling fans) can do this more quietly. Smaller fans will be louder.

12/13
You can also use HEPA filters/CR Boxes to increase the airspeed in the room (they have fans). Combine that with effective air cleaning (windows, HEPA/CR box, far-uv) and you will create a VERY low risk environment. No guarantees, there is always some risk.

13/13
For stopping COVID in your home, you need extra tools. See this thread.

For basic indoor air quality in your home (not mitigating COVID), see this.

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More from @joeyfox85

Dec 14, 2023
The @NukitToBeSure Tempest

I was shipped this PC fan box and put it together. It looks really good. I think for many situations, this is the best option out there. Here are some thoughts about it.
1/11 Picture of the Tempest PC fan box.
I stated earlier on my blog: we need a PC fan air cleaner that is durable and looks good. While durability and looks are not the most important aspects of air cleaners, many companies want that. We now have it.
2/11 If a commercialized cleaner using PC fans similar to the aluminum fabricated PC fan CR box existed, it would provide an ideal solution for commercial spaces.
It took me about 1.5 hours to put together. It was a little more difficult than the @cleanairkits ones because Clean Air Kits uses plugs to snap the fans on instead of screws. This could be something adjusted in the future. 3/11 Image
Read 11 tweets
Oct 18, 2023
The blood libel is a deep scar from Jewish history. Jews were accused of slaughtering Christian children and baking their blood into the matzah we eat on Passover. It lead to pogroms against Jewish communities where many Jews were massacred.
We just witnessed a new blood libel created over the past day. Unverified claims by Hamas were promoted by MSF, the UN, politicians and many major media outlets.

We've seen the resurrection of all the classical antisemitism: pogroms, massacres, blood libels, death squads
This is a description of the Khmelnytsky massacres in Ukraine 1648–1649.

Nothing has changed. Rav Hanover describes the cruelty in great detail. He mentions the terrible killings which occurred in the towns of Pereyaslaw, Baryszowka, Piratyn, Boryspole, Lubin and Lachowce:   These persons died cruel and bitter deaths. Some were skinned alive and their flesh was thrown to the dogs; some had their hands and limbs chopped off, and their bodies thrown on the highway only to be trampled by wagons and crushed by horses; some had wounds inflicted upon them and were thrown on the street to die a slow death… They slashed the bellies of pregnant women, removed their infants and tossed them in...
Read 4 tweets
Sep 20, 2023
I've updated my post on Intro to Far-UV.

Since I first published this post, there have been multiple experiments showing ozone is a concern when using far-UV and needs to be taken into consideration.

itsairborne.com/intro-to-far-u…
In the post, I discuss how initially we didn't think it was a concern. I think ASHRAE needs to update their guidance on different UV wavelengths. ozone section in the blog post
I have far-UV in my house. I think for personal residential use, it can be used in a limited way if you understand the risks with ozone and mitigate it with open windows when in use. That's how I use it. Image
Read 5 tweets
Jul 6, 2023
ASHRAE 241 Equivalent Clean Airflow Rates

Here are the equivalent clean airflow rates from the recent ASHRAE Standard 241 Control of Infectious Aerosols. I've calculated the equivalent air changes per hour and the equivalent CO2 (if all the clean air was outdoor air).
These rates are doubled when there is "vocalization above a conversational level" (e.g. singing)

I'll be hosting a space with the chair of the committee @WBahnfleth to discuss these rates and more. Please join and message for any questions you have.
twitter.com/i/spaces/1gqGv…
To determine the ACH and CO2, I had to make assumptions about density and metabolic rate. I used values from ASHRAE standard 62.1 or found the closest approximation. If densities are different, the equivalent ACH would be different. It doesn't affect flow/person or CO2.
Read 4 tweets
Jul 6, 2023
What should you ask about your indoor air quality?

There are things individuals can do to improve the IAQ in their own space, but it ultimately falls on the building owners and operators to provide clean air. Here are some things you should ask to know about the IAQ.

1/10
1. Outdoor Airflow (OA)
- Is the system constant volume or variable volume?
- If it is constant volume, what is the airflow to the room (in cubic feet per minute [CFM] or liters per second [lps])
- if it's variable volume, what is the max and min airflow?

2/10
- what is the minimum OA % supplied during occupied hours?
- what is the occupancy schedule?
- is the system always running during occupied hours/auto mode?
- how often is it checked and maintained?

Learn about ventilation systems.

3/10itsairborne.com/intro-to-venti…
Read 10 tweets
Jun 27, 2023
"We need HEPA filtration, CO2 at 600 ppm and 100% outdoor air everywhere"

I see these types of comments non-stop. They are wrong and unhelpful. They show misguided ignorance about indoor air quality and what is actually required.
I'll start with filtration - you do not care about the filter efficiency. You care about the system effectiveness which is measured as a clean air delivery rate. MERV-13 with 300 cubic feet per minute (CFM) is identical to HEPA with 230 CFM. There's no reason to prefer HEPA.
Furthermore, air handling units can't handle HEPA filters. Demanding this is absurd when it will only increase cost and won't provide any benefit over MERV-13.

Having MERV-13 as the standard is sufficient for particulate matter issues.
Read 11 tweets

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