Big thank you to @EricCarroll for pointing out this new WHO document on SARS-CoV-2 transmission.
This document is pretty complex, in-depth, dense, and I still expect it to evolve as we learn along the way. They have some of the correct people to be working on this, for once. Hello Lidia Morawska signing off on it at the beginning of the forward.
First, a tldr. If you don't care about how it came to be, or the science, and just want to know the outcome, here it is:
https://partnersplatform.who.int/tools/aria
Go to the calculator, enter your data, and come out with a probability of infection in a given situation along with the number of expected secondary infections from that interaction.
Here's the document itself if you want to follow along:
https://iris.who.int/bitstream/handle/10665/376346/9789240090576-eng.pdf?sequence=1&isAllowed=y
Disclaimer - This is evolving science.
I'm going to split this up in a thread, because I took a lot of notes of what stood out to me on a first read, and I hope to come back to it, and use it as a general reference moving forward.
Next up is ventilation and air cleaning. In the COVID cautious community I think we discuss this a lot and this is simply talking about the variables and how they work. In the intro they discuss that in hospital rooms under airborne precautions the standard in 12 air changes per hour(ACH) and show, mathematically, how 3, 6 and 12ACH differ for probabilities of infection(page 4 for those following along).
"Ventilation rate and air cleaning devices
The purpose of ventilation in buildings is to provide healthy air for breathing by diluting pollutants originating in the building with clean air, and by providing an airflow rate to change this air at a given rate [40]. A well-designed, maintained, and operated ventilation system can reduce the risk of respiratory pathogens transmission, including SARS-CoV-2, in indoor spaces by diluting the concentration of potentially infectious particles through ventilation with outside air and filtration and disinfection of recirculated air. Natural ventilation can provide similar benefits. i.e., opening of windows and/or doors [9]. The removal rate due to ventilation and equivalent ventilation is obtained from the amount of air (m3 h-1) supplied to the space and the volume (m3) of the room [104].
For filters that are portable and self-contained, the
rate of particle removal from air passing through
the filter is expressed as the clean air delivery rate (CADR), which is approximately equal to the product of airflow rate and the contaminant removal efficiency [105]. For the purpose of this document, air cleaning and disinfection devices, using filter category MERV (minimum efficiency reporting value) 14 / ISO ePM1 70- 80%, high efficiency particulate air (HEPA) and higher filtration efficiency filter [9], as well as UVGI technology [106], are considered as equivalent ventilation and the Clean Air Delivery Rate (CADR) (m3/h) is added up to the ventilation rate."
