Comment by gpm
10 hours ago
I don't have the list of relevant studies I've read on hand atm but there was at least one where they simply pumped in CO2 (or didn't) and had an effect showing pretty directly that CO2 itself is problematic at reasonably low levels - as well as potentially being an excellent proxy for other air quality issues. Problematic in a "makes you drowsy/stupid" type of way - not a "kills you" type of way. Though there's also at least one correlative studies suggesting it might have long term health effects (which really wouldn't be surprising if it has any short term effects).
Besides which, proxy or directly high CO2 means you should ventilate...
the military has conducted studies where submariners were exposed to a PPM of 1000s with no ill effect. I suppose they were trying to determine how hard they need to scrub.
having said that, it's possible they omitted what other gasses and %s they used for advantage. there could be some mitigation possible there.
Submarines: 3000ppm. Here is a study with 5000ppm CO2 and no decision-making impediment was found: https://pubmed.ncbi.nlm.nih.gov/29789085/
I have to say, I'm not convinced those studies are legit.