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Comment by bjelkeman-again | Hacker News Reader

"He remained conscious for about 14 seconds, which is about the time it takes for O2 deprived blood to go from the lungs to the brain."

Why was that? Does the low pressure force oxygen out of the blood in the lungs and thereby having oxygen "free" blood arriving in the brain? If you hold your breath you can easily hold it for a minute without loosing consciousness. So the low pressure must be actively taking oxygen out of the blood, otherwise I can't see that you would loose consciousness in 15 seconds.

How long did it take for Dave Bowman to exit the pod and pressurize the airlock? :)

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How long did it take for Dave Bowman to exit the pod and pressurize the airlock? :)

(SPOILER if you haven't seen 2001: A Space Odyssey)

http://www.youtube.com/watch?v=e92vSua8XJY

In this clip, he ejects at about 0:20 and hits the lever around 0:27. You can see him go limp just after 0:34, before the chamber has finished pressurizing. 14 seconds.

So regardless of why the real-life (1965) test subject blacked out after 14 seconds, it appears that the makers of the (1968) film had done their homework!

There have been a couple of cases where crews on business jets were very quickly incapacitated after a loss of cabin pressure most famously the aircraft of golfer Paine Stewart. Unfortunately, unconsciousness does seem to occur pretty fast. Supplemental O2 wasn't used in that case, despite it likely being close to hand.

Also commercial jets: http://en.wikipedia.org/wiki/Helios_Airways_Flight_522

(It's a little embarrassing to count how many people have died because pilots have intentionally turned off power to warning systems that were warning of them of an actual problem. Here's another one: http://en.wikipedia.org/wiki/Northwest_Airlines_Flight_255. Same digits -- freaky.)

Crew on flights typically get a better chance due to the higher pressure and the presence of O2, despite the low pressure. However, typically euphoria kicks in anyway and, according to some of what I've read, can potentially be worse than a complete absence of O2.

If you hold your breath, your lungs are still filled with air, which contains oxygen. So there's still some oxygen being transferred into your blood, it just gets less and less.

But actually, I suspect that the far more important factor is CO2, which leaves the blood in the lungs when there is air present.

>>If you hold your breath, your lungs are still filled with air

Just let me note -- don't hold your breath when there are pressure differences between your lungs and the surroundings!!

You can find that in any scuba diving manual.

(Edit: I do realize the parent poster probably knows this.)

I've heard that when a diver surfaces quickly, they can expel a single breath all the way up. The air in their lungs continues to expand as they go through the pressure gradient.

Has anyone actually experienced this? I'm assuming it would have to be a really quick surface (ie: dropping your weights), and after only a short dive or on pure O2.

As a relatively experienced scuba diver I can say that the theory is correct. I haven't done an emergency ascent, as you describe, but standard practice is that you exhale on the whole way up or you will burst your lungs.

Look at this table [1]:

lung volume, depth m (ft) 2, 30m (99 ft) 3, 20m (66 ft) 4, 10m (33 ft) 8, 0 m (surface)

So by ascending from 30 meters to the surface you expand the volume of the air in your lungs four times. (Of course, you don't want to do this, as you will most likely get decompression sickness, aka the bends.)

[1] http://www.lakesidepress.com/pulmonary/books/scuba/sectionf....

You are absorbing only 25 percent of the oxygen, which suggests to me that having air still in you lungs can be very helpful in keeping you conscious. Is that right?

That's exactly what I meant.

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