Most gasses won’t make you choke the way something like dust or smoke will. In caves, gasses can pool at the bottom or top with now way to escape because they’re heavier/lighter than breathable air.
Thank you, I didn't consider it pooling at the top as well.
If oxygen nor included has taught me anything it's CO2 sinks because it is a heavier gas then O2.
So places with low airflow will accumulate the CO2.
A surprising place that O2 absent environment appears is telecom pits in the street. We had several safety courses about it.
That game is why I thought of it! I forgot to include in the post, I thought the reason we feel pain when suffocating is our lungs not liking CO2, but some gases like helium you'll just drop dead before you know what's happening?
One story that was told to us as kids is in the past some people put the barbeque grill back into the storage cellar still with red-hot and smouldering coals. Those would produce CO2 and more dangerously carbon monoxide, CO. Next person going in the cellar dies from CO poisoning, as does the next 2 people who go to check why the other ones take so long to get something from the cellar.
Oh yeah, that does ring a bell
Easier to type out this way