[masklinn]

I'd be quite dangerous and very uncomfortable: exhaled air contains ~4% CO₂, 16% O₂ and is at roughly 100% humidity.

* at 4% CO₂ you'll be suffering from moderate CO₂ toxicity (narcosis, dizzy spells, increased heart rate & blood pressure, mild shortness of breath, exaggerated response to effort)

* at only 16% O₂ (but assuming atmospheric pressure), you're well into chronic hypoxia land, not quite sure lethal but not far, the hyperventilation from CO₂ poisoning will make this slightly better but nowhere near good

* the combination of hypoxia and CO₂ poisoning will make effort (let alone exercise) possibly to probably lethal

* the extreme levels of humidity will make the entire thing even worse as you'll have a hard time cooling down

You can probably live in this situation for a few days, but the CO₂ levels alone would make it lethal past a few weeks, the combination of all factors means likely no more than a pair thereof, at best.

[hamilyon2]

Can you please provide sources? I am very interested