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Comment by foobarian | Hacker News Reader

BS. I can hold my breath for over 1 minute even without hyperventilating beforehand.

Your ability to hold your breath near sea-level does not invalidate the well-studied time-of-useful-consciousness effects from a rapid decompression in aviation.

https://en.wikipedia.org/wiki/Time_of_useful_consciousness

Most commercial flights are operating in the 30,000-39,000 range.

Worth noting that the quoted TUCs were for individuals who were healthy, rested, and expecting the depressurization.

FlightSafety International's training materials indicate that TUC could be cut in half if the decompression is explosive.

This personal anecdote doesn't really add to this conversation in a constructive way.

But, for sake of argument, it assumes a few things:

1) That your lungs are healthy enough to hold your breath for >= 1 minute (not all are)

2) You actually have the opportunity to breath in a lungful of oxygen-rich air (depending on the situation/timing, this might not be the case)

3) You have your wits about you while a very stressful situation unfolds around you (let's argue that you, personally, are cool and collected under pressure - this; however, is not universally true for all other passengers)

This comment is a master class in civil argumentation, and informative to boot. Thank you.

You can't hold your breath in a low pressure environment. Also the low partial pressure of oxygen causes it to diffuse out of your blood instead of in. Even people who can hold their breath for a couple minutes under normal circumstances will have severe hypoxia impairment in less than a minute above 30K feet. https://en.wikipedia.org/wiki/Time_of_useful_consciousness

I think the issue with rapid decompression is that you probably wouldn’t have any breath to hold in. And if you did your lungs would probably explode.

Hope you remember to hold your breath moments before an unexpected depressurization.

Smarter Every Day made a video about this in which he undergoes hypoxia training: https://www.youtube.com/watch?v=kUfF2MTnqAw

Most people start to panic after 10-15 seconds and feel immense discomfort and pain around 30.

Which lines up great with the linked time of useful consciousness chart: 15 to 30 seconds.

Can you hold your breath breathed out for that long? That's what happens in practice when the cabin depressurises.

I always assumed it was worse than this: when you breath out your lungs still contain a slightly lowered oxygen concentration at atmospheric pressure, so the partial pressure of O2 is still quite high. In a vacuum this drops to zero, meaning that your lungs become an oxygen sink.

So not only are you unable to get more oxygen, your lungs are actively sucking the remaining oxygen out of your blood.

Edit: as was pointed out in this comment a level up on this thread https://news.ycombinator.com/item?id=24495970

Try it. You can go about 30seconds in a calm situation where you know what to expect before the panic overwhelms you.

With a sudden event, you’d have about 15 seconds because there’s a lot to panic about.

Edit: just tried. 25s panic started, 30s my chest was trying to inhale, 36s I had to let myself breathe. This was at my desk while calm and in control.

On a plane I’d probably panic sooner and might be able to go a full minute before actually passing out.

Edit 2: I did use to freedive as a kid and am in very good shape (45 resting heart rate) so maybe that helps

36 seconds is actually not very good for someone that's calm, in a good shape, and not moving around much at sea level.

On the subject at hand, the best freediver in the planet would still have zero chance in a low pressure environment.

Your lungs operate based on partial pressure of each gas. So, effectively they operate in reverse in a low pressure environment.

Also, at 1ATM you have 14.7 lb/square inch in your lungs, at 30,000 feet that drops to 4.3 psi making trying to hold your breath dangerous on it’s own.

Your desire to breath is caused by the urge to expel CO2. At sea level you have a large reserve of oxygen.

It is a huge gamble that you would or could hold your breath at the opportune moment.

With a lack of oxygen in the air, you will quickly and painlessly blackout and then die.

https://expertaviator.com/wp-content/uploads/2012/04/TimeOfU...

The problem is that you probably won't notice the lack of oxygen. And after 1 minute you would not have enough mental capacity to put the mask on. There are some funny hypoxia videos: https://news.ycombinator.com/item?id=24495939

Would only work if you manage to breath out during depressurization and manage to not instinctively take a breath in the low oxygen environment.

Supposedly holding your breath is not advisable, and can actually make things worse.

Is there an issue of not being able to hold your breath in low pressure?

You must not. One of the most important rules of SCUBA diving is to never hold your breath. A breath of air at high pressure (deeper) expands quickly at lower pressure (shallower), which could cause you some problems (a ruptured lung).

Reply on news.ycombinator.com