Sorry, I added a 1 where I shouldn't have, meant to write "6%". Other points remain, if a person is in a room full of explosive gas the last thing that they'll be doing is attempting to read a newspaper.

21% is the amount of O2 in "normal" air. Any drop below that leads to to symptoms of O2 deprivation, dizziness, nausea, etc. A drop to 12% or less leads to unconsciousness, further drop ie, to 6% or less leads to rapid death.