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 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

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

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.

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…

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

"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.

If you want to use CO2 to gauge risk of airborne disease transmission, you need to know when it doesn't work. Here are 8 cases where it breaks down.
🧵 Case 1
A: Full classroom, 27 ppl, 200 litres per second (lps) of outdoor air, 1 infectious person, CO2 = 1100 ppm
B: Same classroom, 1 infectious person, 10 fewer people, CO2 = 840 ppm

They are equal risk, even with 1100 vs. 840 ppm. They have 200 lps for 1 infectious person.

To me, the way this study is framed is problematic. I've discussed many times how to use CO2 to gauge risk. My arguments are based on simple incontrovertible physics, not a model from only 3 cases of transmission.

Here's how you gauge risk and the role CO2 plays.
1/8

https://twitter.com/mdc_martinus/status/1668547669617197056

I list 18 factors that affect risk here. Air quality is one of them. Obviously not all these factors are equally important and I believe indoor air quality is one of the most important factors.
2/8

https://twitter.com/joeyfox85/status/1541527755367583746?s=20

The engineering and IAQ world was completely unprepared for this pandemic.

We had no standards for controlling infectious aerosols. The first official standard will be published soon. We needed it in 2020.
1/4 We also had no proper standard to ensure the safety and effectiveness of air cleaning equipment. That's why companies could sell useless garbage to uneducated consumers. Once equipment has to be reported in equivalent outdoor air delivery rates, these problems are solved.
2/4

"We have mechanical ventilation". Oh really? Standard ventilation rates are not designed for airborne diseases!

We actually have appropriate rates now. Let's see how the "mechanical ventilation" rates hold up.

1/19 Standard mechanical ventilation is calculated based on ASHRAE 62.1 - Ventilation and Acceptable Indoor Air Quality. I'll compare it to the CDC (5 air changes per hour), ASHRAE 241P draft for Control of Infectious Aerosols and OSPE/Lancet (6 air changes per hour).
2/19

Looking at the core recommendations for @O_S_P_E IAQ Advisory Group, it does a fantastic job at finding the middle of the road between the recent ASHRAE Standard 241 Draft and CDC Guidelines. It also addresses other IAQ issues. Here's how. 🧵
1/7 With the new CDC guidelines, they recommend 5 air changes per hour, where OSPE recommends 6. These numbers very close. However, they admit there are issues:
1. Places with high ceilings have rates too high
2. High risk spaces will have rates too low
2/7
cdc.gov/coronavirus/20…

The biggest medical failure of the pandemic was denying that COVID is airborne.

The biggest engineering failure of the pandemic was not providing a clean air delivery rate required for mitigating airborne disease. That failure has been addressed. We now have good values. 🧵
1/6 ASHRAE 241 Draft Review (Not finalized)
10-90 liters/second/person, depending on the risk of the environment.

Equivalent ACH was calculated based on occupant density in other standards. Higher density increases equivalent ACH.

2/6
osr.ashrae.org/Online-Comment…

Overview of Control of Infectious Aerosols
ASHRAE Standard 241P

ASHRAE released a standard for review. It can have significant impacts on designs, operations of new buildings how we move forward. Here's an overview of what's in it.
1/25
osr.ashrae.org/Online-Comment… To start, many of my threads in the past years are in line with the standard. After fighting all the misinformation, it was really cathartic reading though it. Note: This is not the final release, so things can change.

I predicted this by the way!

https://twitter.com/joeyfox85/status/1485096843474264064?s=20

2/25

ASHRAE Standard 241P Control of Infectious Aerosols
Infection Risk Management Mode (IRMM)
osr.ashrae.org/Online-Comment…

Understanding IRMM is essential to understanding what we can expect from buildings in the future. Here's a brief description. 🧵
1/9 Need to start with caveats, this is only the advisory public review and not the finished standard. I've read the standard twice and this thread is based on my understanding of the intent. I'll correct it if I'm wrong.
2/9

ASHRAE Control of Infectious Aerosols - Equivalent Outdoor Air Rates

The new standard is out and can be found here. osr.ashrae.org/default.aspx

Here's a quick review of the rates that are recommended.

1/5 The recommended equivalent outdoor air rates can be found in Table 5-1 on page 4. They are overall very high. For reference, WHO recommends 10 litres per second (lps)/person and OSPE and Lancet recommend 13.5 lps/person.

2/5

ASHRAE just developed a standard to mitigate airborne diseases. Once it's published, I'll do some threads explaining it. For now, I'll give a brief history behind this. 🧵

https://twitter.com/WBahnfleth/status/1656801859875532800?s=20

1/7 ASHRAE has had a standard for indoor air quality for many years (called 62.1). One major problem is that it never took into account airborne diseases. Andrew Persily explained why in last month's ASHRAE magazine.

2/7

I've written a post about air distribution. It seems like a technical and minor aspect of air quality, but it's extremely important. So much of the misinformation and bad decisions during the pandemic relate to misunderstanding air distribution.
1/15
itsairborne.com/air-distributi… Air distribution refers to how air mixes and is supplied throughout the space. You can get clean air into a room, but you only care about what people are breathing in. When that clean air bypasses people and gets exhausted, it's a useless waste of energy.
2/15

There's been a bureaucratic failure by Health Canada to protect Canadians from air pollution and it also hurt a lot of people throughout COVID. We should have had better filters in the air handling units, but didn't. Here's how the screw up occurred. 🧵 ASHRAE 62.1 primarily deals with outdoor airflow rates, but there's a section on filters. If national guideline on PM2.5 (fine particulate matter) is exceeded, MERV 11 or greater is required.

It's not as good as MERV 13, but still a good start. So what's the national guideline?

The UK Department for Education has a new document for use of CO2 monitors. It sets the cutoffs as:
<800 ppm - close windows
800-1500 ppm - consider opening windows
>1500 ppm - open windows and doors

Are these appropriate levels? What should it be? 🧵

https://twitter.com/LibDemPatrick/status/1651303759375368217?s=20

From an air quality/engineering perspective, CO2 is generally harmless does not tell you directly about other pollutants in the space. It only tells you the outdoor airflow per person. The goal is to verify the building is achieving the desired outdoor airflow per person.

What would I do if I was a dentist?

Can you make it low risk to be sitting in front of unmasked faces every day?

Believe it or not, you can. It takes 6 steps. 🧵 Step 1 - N95 Respirator + eye protection

This was obvious. Dentists usually wear a mask and some form of eye protection anyways. Wearing a better mask is low hanging fruit. If you want to learn more about masking, see these documents.

https://twitter.com/mariannelev/status/1598762864768057360?s=20

People have been asking if Beacon far-UV is effective. The cost right now is really low. The answer is I don't have enough info to make a definitive statement but it likely is effective and can have some very good uses. 🧵

https://twitter.com/beaconlightco/status/1646894347558813699?s=20

The best data we have was just a proof of concept experiment. I believe it used 15 W Ushio lamps, but they didn't publicize that since the goal was just proof of concept. 1 lamp gave 33-66 air changes per hour in a typical room in your home.
nature.com/articles/s4159…