Thread by @akm5376

The @WHO recently brought about ventilation related guidelines, focused on the #COVID19 #pandemic
A 🧵 with a tour through the document
apps.who.int/iris/handle/10…
1/n

2) Document entitled "Roadmap to improve and ensure good indoor ventilation in the context of COVID-19"
- very specific and focused name though in the document they also state that these steps will have long term benefits, non-Covid ones as well

3) Conflict declaration - The Advisory committee that helped craft this, among them there are people I know personally and some are my former supervisors, people who taught me what I know about indoor air, so my view could be biased

4) Limitation - As mentioned by @trishgreenhalgh, there is still the limitation that WHO's Infection Prevention & Control Research & Development Expert Group for COVID-19 needs to accept it

https://twitter.com/trishgreenhalgh/status/1366449715735367685

5) Into the document -
Context - crowded and inadequately ventilated spaces are pesky troublemakers. Hence, all this effort.
Also note that virus spreads by respiratory droplets and aerosols

6) Aerosols being produced by regular, everyday activity...

7) But immediately below that, as if they had taken a step too far...
a reference to AGPs for aerosol transmission. Put together with the above extract though, one could (like me) read everyday activities as AGPs

8) A nice tip of the hat to ventilation -

9) Standard disclaimer - WHO documents, to my understanding, are not intended to be prescriptive. Local governments always can override them, Hopefully, they won't for such clear guidelines.

10) Excerpt because it ran into another page.
Nice to see other respiratory viral diseases..
" Indoor ventilation is part of a comprehensive package of prevention and control measures that can limit the spread of certain respiratory viral diseases, including COVID-19."

11) Focus of the document
Ventilation for three broadly different settings

12) Ventilation in health care settings
Again, AGPs make an appearance and are given a better deal than normal patient rooms. How big is 160 liters per second, for every patient?
It would lead to indoor CO2 levels of ~460 ppm, assuming outdoors are at 425 ppm

13) Non AGP rooms, 60 L per person, every second, CO2 levels roughly 500 ppm.... I see what you did there ventilation people...

14) Now, one of my favourite parts - in-room filtration when you cannot serve ventilation needs otherwise

15) Good advice on air flow and the fact that flow direction matters

16) Now the part with my favourite word - whirlybirds
This is about extracting air from the room, using simple/cheap retrofits/add-ons.

17) This is pretty standard for ventilation design, but you would be amazed how many hospitals in less developed countries do not follow this

18) There is a very nice portion talking you through how to use or not-use non-ducted AC units (split units). Very important for many parts of the world.

19) Another nice part on use of heat recovery units. Heat recovery units got a bit controversial because they could involve contact between exhaust and intake airs. The document clearly delineates the kinds of heat recovery units where this is a concern and where it is not 👍🙏

20) Now, to non-residential settings
10 L (person.second) that would be about 4 ACH for average classrooms (@Poppendieck) and CO2 of ~950 ppm

21) Again local filtration to make up ventilation deficits
Filter ratings slightly lowered than for health care settings - all very sensible.

22) Now, my favourite things in a building, fans
Use of fans to increase dilution, but remember, only after you have met your ventilation goals. In a poorly ventilated room, a fan is just spreading contaminants to everyone - very democratic and very useless

23) Advice on pre- and post- ventilation, both very useful and often ignored ideas.

24) Same deal for mechanically ventilated spaces

25) Residences - the focus is on isolation area (where you have a patient)
Again, 10 L/(person.second)

26) How to increase ventilation in residences - tricky subject and very much needed since most residences do not have a dedicated ventilation system
Nice of them to provide some simple, actionable solutions.

27) Again, filtration if you cannot get in enough fresh air

28) For homes with mechanical ventilation -

29) Okay, that was supposed to be a short summary, but it dragged on a bit.
The document has some very practical, actionable items on its roadmap to good ventilation in different settings. Consider going through it. It is just 30 odd pages
/end