1/ A very good article in @elpaisinenglish about how to avoid becoming infected with COVID-19 by breathing the air exhaled by others:
(By the team that brought you "A room, a bar, and a classroom")
english.elpais.com/usa/2021-03-29…
(By the team that brought you "A room, a bar, and a classroom")
english.elpais.com/usa/2021-03-29…
2/ Humans exhale CO2. Our metabolism "burns" the foot we eat (carbohydrates, fats, proteins) into CO2 and other products (H2O, urea etc.) to extract energy.
Exhaled air has ~4% CO2 (40000 parts-per-million, or ppm). It is quickly diluted as it mixed w/ ambient air.
Exhaled air has ~4% CO2 (40000 parts-per-million, or ppm). It is quickly diluted as it mixed w/ ambient air.
3/ We get COVID when we inhale virus-containing aerosols exhaled by others.
Mainly in 2 situations: (1) in close proximity because we inhale much more of the exhaled air of the other person then.
Distance reduces infection mainly because we breathe less of that exhaled air.
Mainly in 2 situations: (1) in close proximity because we inhale much more of the exhaled air of the other person then.
Distance reduces infection mainly because we breathe less of that exhaled air.
4/ But distance does NOT eliminate transmission (it would, IF large droplets)
Although aerosols are much less concentrated in room than right in front of a person, they can build up over time and infect lots of ppl (choir, restaurant, bus and lots of other superspreading events)
Although aerosols are much less concentrated in room than right in front of a person, they can build up over time and infect lots of ppl (choir, restaurant, bus and lots of other superspreading events)
5/ So the other situation in which there is a lot of transmission in in shared room air.
CO2 and virus-containing aerosols (much larger than the virus itself) are exhaled together & behave very similarly in room air.
Drawing by @numeroteca (numeroteca.org/cat/en-el-aire/)
CO2 and virus-containing aerosols (much larger than the virus itself) are exhaled together & behave very similarly in room air.
Drawing by @numeroteca (numeroteca.org/cat/en-el-aire/)
6/ It'd be wonderful to have an instrument for $200 that beeped when there was virus in a room. Does not exist now
CO2 is only thing that we can measure at low cost, that serves as an indicator of infection risk. Which varies a lot btw locations and time. Not perfect, but good.
CO2 is only thing that we can measure at low cost, that serves as an indicator of infection risk. Which varies a lot btw locations and time. Not perfect, but good.
7/ Back to @elpaisinenglish. They use as an example a shared car. About the worst place in no ventilation, due to very small volume with high density of people. CO2 rises very very rapidly.
(And most of us did not pay attention to its ventilation in the past, only hot / cold)
(And most of us did not pay attention to its ventilation in the past, only hot / cold)
8/ But if we open a couple of windows a couple of inches, we get cross-ventilation. Then we can keep exhaled air (CO2) at much lower levels.
(Also works with car ventilation system, if set to strong + outside air)
(Also works with car ventilation system, if set to strong + outside air)
9/ @elpaisinenglish explains very clearly what level of CO2 corresponds to what percent of exhaled air.
An easy rule of 3 (400 ppm outdoor):
400 ppm - 400 ppm = 0 ppm ==> 0% exhaled air
40400 - 400 = 40000 ==> 100%
Your_Measurement - 400 = X ppm ==> Y %
An easy rule of 3 (400 ppm outdoor):
400 ppm - 400 ppm = 0 ppm ==> 0% exhaled air
40400 - 400 = 40000 ==> 100%
Your_Measurement - 400 = X ppm ==> Y %
10/ And we have to realize that the virus, like CO2, accumulates in indoor air, even if a person is alone in that space (as cigarette smoke would).
So we have to wear a mask indoors even if alone, if others will come into the space.
(Drawing by @numeroteca)
So we have to wear a mask indoors even if alone, if others will come into the space.
(Drawing by @numeroteca)
11/ So if we are going to enter a car where someone else has been for a while, best to ventilate it first.
And then keep the windows a little open (see graphic), or the ventilation system going with outdoor air.
And then keep the windows a little open (see graphic), or the ventilation system going with outdoor air.
12/ Indoor spaces have to be ventilated CONTINOUUSLY while people are present in them.
Many experiments show this, e.g. by @JbcLiftec, @franj_moya, or @felisi2punto0:
Many experiments show this, e.g. by @JbcLiftec, @franj_moya, or @felisi2punto0:
13/ Measuring CO2 also shows if an indoor space may have too many people, for the available ventilation.
E.g. in this bar in Zaragoza (Spain), per measurements of @JbcLiftec.
[Opening doors helped, but too many ppl so CO2 stayed too high]
#covidCO2
E.g. in this bar in Zaragoza (Spain), per measurements of @JbcLiftec.
[Opening doors helped, but too many ppl so CO2 stayed too high]
#covidCO2
14/ Article by @mariano_zafra and @javisalas, with development by @jacob_vx.
The team that brought you "A room, a bar, and a classroom." Which is a must read, if you missed it.
english.elpais.com/society/2020-1…
The team that brought you "A room, a bar, and a classroom." Which is a must read, if you missed it.
english.elpais.com/society/2020-1…
15/ And the same team also warned us recently about air communication within apartments in a building, and the potential risk of transmission through those.
english.elpais.com/science_tech/2…
[They deserve a medal for #scicomm when this is over]
#COVIDisAirborne #COVIDEstaEnElAire
english.elpais.com/science_tech/2…
[They deserve a medal for #scicomm when this is over]
#COVIDisAirborne #COVIDEstaEnElAire
16/ To learn more about CO2 (simple, big picture): section 9 of Scientist's FAQs: tinyurl.com/faqs-aerosol
To learn about the fine details (for scientists) see our preprint: doi.org/10.1101/2020.0…
[And I apologize for typo on #2: hopefully we are eating "food" and not "foot"]
To learn about the fine details (for scientists) see our preprint: doi.org/10.1101/2020.0…
[And I apologize for typo on #2: hopefully we are eating "food" and not "foot"]
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