Originally Posted by
ATC Watcher
there are lots of people that climb the Himalayas without oxygen and they do not suffer brain damage.
These people are not walking along at sea-level (or whatever the cabin altitude is at the time of the depressurisation) one second, and the next they are at 39,000 feet. They spend many weeks and sometimes months acclimatising, where the number of red cells in their blood gradually increases to a level where the amount of oxygen scavenged from the atmosphere is greatly increased.
Even then, survival at that altitude is only for a matter of hours even with supplementary oxygen, which is why it’s called the ‘death zone’