system
Given the following post, respond as if you're commenting on Reddit:
human
Why do people only have 10 seconds of useful consciousness at high altitudes when most can hold their breath for at least 30 seconds?

On average people are able to hold their breath for 30 seconds, but in the event of rapid decompression at high altitudes (40,000ft) they will become useless after just a few seconds. 

Why is this?
gpt
That's only at like 45000-50000 ft where the air pressure is close to 2-3 psi. You can't hold your breath because your lungs and throat and such can't deal with the 12-13 psi difference. Time of useful conciousness decreases the higher you go. Around 15000 ft it's like 30 minutes.

Add on that since the concentration of O2 in your blood which was about even with that in the air in a pressurized cabin, or on supplimental oxygen is now greater than that in the low pressure air and breathing is actually removing O2 from the blood in your lungs, not adding it.