The best indication is feeling sleepy. Once you become sleepy go outside and take deep breaths, then you understand the sensation difference between O2 and CO2.
I think some people are more sensitive to it than others.
I'm not disbelieving, just curious.
Unfortunately that doesn't seem to work for me.
Right now my room has > 1200ppm CO2 (due to closed
doors/windows) but I don't feel sleepy at all
In my case my face, specifically my forehead, feels warm. Not to the touch, but more to the nerves. I think it may be different for different people.
Has anyone here managed to? If so, do you have
any tips on how (or whether!) to do this
The easiest (only?) way to do this is simply to have a CO2 sensor, and pay attention to it. You'll quickly learn to intuitively correlate what you're seeing on the sensor with what you're experiencing. After a while you'll be able to vaguely approximate the CO2 levels without even looking at the sensor.
Of course, you won't be able to pinpoint an exact CO2 level, but you'll be able to tell when it's e.g. > 1000.
You've already been doing this your whole life, of course. You've already been distinguishing between "fresh" and "stuffy" air. "Stuffy" air is just our colloquial term for air with undesirably high CO2.
With respect to "stuffy" vs. "fresh" air, I don't know whether my sense of it is the same as others'. What I would call "stuffy" is probably affected by humidity, dust, odors, plants, etc. and not just CO2.
With respect to "stuffy" vs. "fresh" air, I
don't know whether my sense of it is the same
as others'. What I would call "stuffy" is
probably affected by humidity, dust, odors,
plants, etc. and not just CO2.
I know that when my wife turns on the gas oven downstairs I can definitely feel a difference even if I wasn't aware she was turning it on and the CO2 meter confirms the CO2 spike. But even then, maybe I'm just "sensing" it via proxy factors like smell.
In practice it probably doesn't matter all that much. Those proxy factors are really good proxies. It's hard to think of real-world scenarios where they wouldn't be.
Don't you think those 'experience correlations'
are based on proxy parameters?
Situations with high CO2 are usually situations with lots of warm, stagnant, exhaled air in rooms filled with people.
Would I be able to detect high CO2 levels in an environment with cool, well-circulated air? I'm not sure. Certainly not as well, and perhaps not at all.
In practice, it probably doesn't matter. I don't think there are many of those pathologically counterintuitive CO2 situations. If the air seems stuffy or stagnant then you can be fairly certain it's full of CO2 and/or airborne pathogens.
I also know people that don't own meters who think
they're in stale air as soon as it gets a warm in
a room and need to see an open window constantly
and then turn up the heating some more
The “my lungs are burning and I must breath” signal is actually caused by high co2. We can’t perceive blood oxygen levels at all.
This is actually something hospitals have to be aware of. A tiny sliver of the population (1-10000, maybe) have greatly reduced sensation of co2, so can literally stop breathing (while awake!) if placed on high flow 100% oxygen.
[1] https://events19.linuxfoundation.org/events/kvm-forum-2019/a...
[2] https://locations.filmfrance.net/location/lyon-convention-ce...
There are some other situations where non-"stuffy" air might have too much CO2, I guess. I guess you could pump CO2 into a room with cool, dry air.
But barring a contrived situation like that, stuffy=CO2.
Before I got a CO2 meter, I could always tell within hours when my building's flaky central ventilation fan had failed because I simply felt something was off.
Unless you are similarly cursed/blessed, just get a CO2 meter. I could not imagine learning this, it is like learning to feel temperature.