Table of Contents
How it spreads, preparing your house, humidity, symptom onset, positive test, isolation room, your furnace, sharing rooms, masks, filter location, exit.
It's transmitted when an infectious person and susceptible person are sharing air. There are 3 main scenarios: 1. Close range - they share the most air. This is the highest risk.
2. If they share a room, the virus particles they exhale can build up. As you inhale a higher dose (concentration, time, breathing rate), risk of infection increases. Virus can be removed through ventilation (windows) or filtration (HEPA/CR box).
3. Long range transmission - this is transmission with a lower dose and generally further away. It's not as common but still a risk if you are in a house with someone who is infected.
4/21
Before COVID Hits your Home
The one thing you can always do is keep the air clean. Keep the windows open as much as possible and run humidifiers, HEPA filters or CR Boxes. If someone is infected, you'll breathe in a lower dose.
You want relative humidity (RH) to be between 40-60%. Having good RH in your home does 3 things: 1. Viruses die quicker 2. With low RH, the droplet will evaporate quickly and stay suspended in the air. With good RH, it will fall.
2. Try to block any paths that the air can leak into the house at the door. 3. Create negative pressure in the room - turn on an exhaust fan in an adjacent bathroom or have a fan blowing air out a window. This will cause air to leak into the room and not out.
10/21
4. Run a humidifier in the room if the air is dry. 5. If a return vent is located in the isolation room, block it by taping plastic around it. They look like this:
11/21
You Home Furnace
Furnace filter: If it’s a 1” slot, use the Filtrete 1900. If it's a larger slot, get a MERV-13 filter that matches the slot size. If air can't reach the far end of the house or the furnace stops working, put back the old filter and reset the furnace.
12/21
Filtrete 1000 also works against aerosols, but 1900 is better. If you have a MERV-13/Filtrete 1000/1900 filter in your furnace, run your fan all the time to get the filtration. If your furnace filter has lower rating, leave it on auto.
13/21
Sharing a Bathroom
Leave the exhaust fan running between uses and keep the window open. It's best to wait between uses, especially if you are not wearing a mask (eg. shower). 25 minutes should be fine if exhaust fan is running. The longer the better.
14/21
PSA: Close the toilet lid before flushing. Inhaling aerosolized fecal matter isn't good for you, especially if it's virus laden. #CloseTheLid
As @DFisman says, air: it's the new poop.
When you're done, WASH YOUR HANDS!
15/21
Sharing other rooms, like a dining room is the same concept. If the infected person used it without a mask, open windows, run filters and wait before using it yourself.
16/21
Masks
Wear a N95 as much as possible, especially when not in the isolation room. If you need to take it off (eating, showering, sleeping), make sure the air is clean.
In the isolation room, it's lower risk to unmask and more comfortable for the infected person.
17/21
If you don't have a N95, use knot & tuck with a surgical mask.
Filter Location
If you only have 1 HEPA/CR Box or humidifier, I think it's best in the room with the infected person as source control and for their health.
18/21
You can place one outside their room to filter air that leaks out.
Otherwise, the best room for the filter is the one that you are in. They are portable, so you can carry them around.
19/21
Exiting
Don’t listen to US & Canadian Public Health and wait only 5 days. Best is to wait until symptoms resolve + 2 negative rapid tests on 2 days. At least wait for symptoms to resolve + negative rapid test.
20/21
N95s, filters, open windows, isolate, humidifiers - that's it.
Some can do more than others, but do what you can.
#COVIDisAirborne
If you know how it spreads, you know how to stop it.
Exposure is inevitable, infection isn't.
We aren't helpless.
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
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
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
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.
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.
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.
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.
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.
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?
"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.