Why will people flying at high altitudes lose consciousness so quickly in a depressurization event when a human can normally hold their breath for much longer?
When you hold your breath, there’s still
more oxygen in the air you’re holding than at ultra-high altitudes. You can try, but there’s just not enough oxygen to hold. You go into hypoxia very quickly.
Your lungs are a bag of air, and inside that bag, there are lots of oxygen molecules bouncing around. Some molecules are bouncing randomly from the air into your blood, and some are randomly bouncing out of your blood into the air. But on average, *slightly* more are bouncing into your blood than out, because the oxygen molecules get snatched up by your red blood cells and carried off to be used.
There isn’t a huge, instant exodus of oxygen from your blood into the air when you hold your breath, because if a molecule bounces out of your blood, it’s pretty likely another one will bounce back in and balance it out. The slight imbalance caused by oxygen being carried away and used means that slowly more and more oxygen will bounce into your blood and never come back out, and this will slowly deplete the oxygen that’s bouncing around in your lungs until there’s none left. But you basically get to use it all.
In a near vacuum, there is just as much oxygen in your blood, but *no* oxygen in your lungs. That means that if an oxygen molecule bounces out randomly, there will be nothing to randomly bounce back in and balance it out. So all the oxygen in your blood very quickly gets “dumped out” in a hurry— it’s like the low pressure is “sucking” all the oxygen straight out of your bloodstream!
Basically all the blood that passes your lungs will be scrubbed of its useful oxygen, and from there it’s only a few seconds of travel to your brain. Your brain expects a continuous flow of oxygen to keep functioning, so the moment that supply cuts off, it’s basically an instant lights-out.
This balance of oxygen bouncing in vs. out is the “*partial pressure*” of oxygen against your lungs. When you’re holding your breath, the partial pressure is normal sea-level pressure. At high altitude, the partial pressure is very low, and it sucks all the usable oxygen out of your body.
More detailed than ELI5, good information. https://www.reddit.com/r/askscience/comments/dydt5x/why_is_tuc_time_of_useful_consciousness_so_short/
You won’t be able to hold your breath in a rapid depressurization. Anything full of air, like your lungs, is going to try to expand due to the lack of air pressure and will severely injure you if you don’t get rid of it. You have no choice but to let the air get sucked out of your lungs. You won’t be able to “store” some to use for the next couple of minutes, like you could while holding your breath.