system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is the death zone above 8000m still dangerous with supplemental oxygen?

Recently I have watched a number of documentaries about Mount Everest. It is always stressed how dangerous it is for the mountaineers to stay in the death zone above 8000m for too long, even if they use supplemental oxygen. Why does the use of oxygen not prevent altitude sickness and the risk of HACE and HAPE altogether? Should they not be fine for a long time, as long as they bring enough oxygen bottles?
gpt
The main difference between being at sea level and being at high altitude, besides it being cold as fuck, is that the air is much lower pressure. This effectively means theres less oxygen available for breathing which is why tanks are required, but it also reduces the oxygen pressure in the blood, referred to as partial pressure. Yknow how divers who come up too fast get bad things happening? That's cos nitrogen suddenly decompresses in the blood and forms bubbles. It's not as bad with oxygen on Everest cos the difference in pressure is much smaller, but it's still bad. Instead of forming bubbles, the effective maximum amount of oxygen in the blood reduces. This means even with an oxygen tank you have less oxygen than you do without a tank at sea level, and it's sufficiently low that if you stay for too long your brain explodes.