If harmless, couldn’t it be breathed for maybe a minute — assuming the respiratory system doesn’t suffer some form of distress
Apparently not. The compressed gas safety training I get every other year is pretty clear that the extreme hypoxia sets in VERY quickly, and the victim usually is down before he knows what happened. Carbon dioxide buildup causes the panicky "GOTTA BREATHE" response; this does not occur when oxygen is displaced by some other inert gas.