"You have a few seconds to put this on your face before you're unconscious"
Is that correct? People can obviously hold their breath for longer than that. Is it something like panic causing you not to hold your breath?
Is that correct? People can obviously hold their breath for longer than that. Is it something like panic causing you not to hold your breath?
In a decompression event, the air is sucked out of your lungs. The air that remains has a low O2 partial pressure, and so oxygen can leak from your bloodstream into your lungs. As such the body's normal mechanisms for storing oxygen simply don't work.
Correction, sir. That's "blown out."
Male, 32 years, healthy, medium sporty.
Now, you have larger pressure differentials when scuba diving - every 10m of depth is an atmosphere of pressure - but the half atmosphere that you get from 10k vs 40k feet is probably still enough to cause some serious issues. (10k feet is ~0.69 atm, while 40k is ~0.19)
There is a thing where you deliberately hold your breath, which starts with taking a big lungful of air, which presumably is at normal pressure and contains 21-ish percent oxygen.
Even untrained individuals can hold their breath for a while like this.
There's another thing, which is what happens if the air you're trying to breathe either is at lower pressure, or has lower oxygen proportions. Either way, each breath has fewer oxygen molecules.
If you haven't prepared for this and try to continue breathing, you can quickly become short of breath, and then cognitive abilities become impaired, hampering your attempts to rectify the situation.
I wonder if the problem is that if cabin partially depressurizes by the time the masks drop, you may no longer be able to take a deep breath and hold it while taking your time putting on a mask.
I acknowledge that I do not have training in dealing with cabin depressurization. As luck would have it, my sister has worked for Air Canada for more than 30 years, I will ask her about it.
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I see some other comments about the oxygen actually coming out of your blood into your lungs at low pressure, and the air coming out of your lungs because the cabin is lower pressure than your lungs.
Those make sense, and had I trained for summiting 8,000m peaks instead of tech diving, I would have known that!
Suppose you're 2000 feet down, breathing hydrox or hydreliox. It's mostly hydrogen, maybe some helium, and less than 1% oxygen. You suddenly ascend to the surface. Instead of changing gas mixture, you try to hold the gas in your lungs and maintain the pressure.
You won't hold it in. As the pressure drops in your lungs, the dissolved gases in your blood will escape into your lungs. That drops the oxygen content in your blood.
But you only have a few dozen seconds before you become an idiot incapable of helping yourself. You can survive and be conscious for minutes in this state, but its "game over", you're not going to be helping yourself put on the oxygen mask once the critical period is up.
Given the tradeoffs of the situation (ie: your neighbor will be fine for minutes, although helpless), it makes far more sense to ensure the oxygen safety of yourself before helping other people.
No it isn't.
> you can survive and be conscious for minutes in this state
No you can't.
You are not going to remain conscious for more than a few seconds at 35000 or 40000 feet. You could potentially be between 15000 to 20000 feet but there's a reason oxygen supplementation is required above 10k feet in unpressurized cabins.
> It is the period of time from the interruption of the oxygen supply or exposure to an oxygen-poor environment to the time when useful function is lost, and the individual is no longer capable of taking proper corrective and protective action.
> It is not the time to total unconsciousness
35,000 feet is 30-seconds to 1-minute of total useful consciousness, half that for rapid decompression situations.
I stand by my estimate for "Dozens of seconds before you're an idiot". Most people will remain conscious after this time is up: they just will have become such idiots that its unlikely they will ever be able to fix their Hypoxia condition. (Slurred speech, unable to dexterously control your limbs, etc. etc. You're conscious, but no longer capable of putting on a mask even if it is dangling in front of you)
Wikipedia takes the table from an FAA document: https://www.faa.gov/pilots/training/airman_education/media/A...
There's pretty much no reason to measure "time to unconsciousness", because you're incapable of helping yourself long before you're unconscious.
At 40,000 feet, time of useful consciousness is 15-20 seconds.
See https://expertaviator.com/2012/04/19/oxygen-requirements-tim...
Basically the partial pressure of oxygen is low enough at altitude that the oxygen is driven out of your blood instead of in.
There are some breathing techniques that can offset that somewhat, but only if you are prepared and trained, which is unlikely in a sudden decompression event.
If I remember correctly, commercial aircraft are pressurized at about 8,000 ft. 25,000 ft is 5.45 psi, resulting in about 5.5 psi overpressure if you are depressurized. You might have a hard time, and you can injure your lungs doing that.
The time until you pass out will depend on your oxygenation situation before the loss of pressure, general health and fitness, activity level (panicking would be a bad idea), and a bunch of other things.
Depressurization means oxygen is quickly escaping, but that doesn't mean that people will rationally take a giant breath of air and hold it. I imagine most people continue breathing normally, or more rapidly due to increased stress. Not realizing that they are sucking in less and less oxygen, and begin to lose consciousness.