Anyone game to try that one?
There are a lot of variables, too many to be exact/safe without monitoring. People,,,their individual physical health, is a big unknown.
Co can kill you with 20% O2 available, it inhibits O2 exchange.
Co2 is widely variable, some can handle 5000-10000ppm, others???
There is a lot to it, and an enclosed space increases humidity, a very small space becomes miserable quickly. An open flame in a small space, is foolish.
4 exchanges per hour is 'minimum', although homes range 1-2/hr
A 10x10x8 foot room is 800cuft.
A bathroom 'fart fan' moves 50-70cuft/min
So 15min of run time an hour. How many people? hahaha
This may help:
Less than 18-19% O2 is not do-able for most people.
Less than 19.5% is not allowed under OSHA guidance.
Less than 17% mental impairment begins, for healthy people.
I got plenty more if you need it.
All bets are off if someone has bad gas, methane while not poisonous per se, does displace O2.
At 8000 feet, there is about 25% less oxygen. I have skied at such heights, hiked heavy packs through Haleakala at higher heights, and never had a problem.
So 15% (25% less than starting point of 21%) should be manageable for most people, especially if just sheltering in place.