Why can we survive much more, but not much less pressure?

[greypilgrim]

Hi.

In water, pressure increases with roughly 1 atm per 10 m depth, yet some divers can reach more than 100 m. Why can humans survive more than 10 times the atmospheric pressure, but will die a horrible death within seconds when released into a vacuum (e.g. outer space, even with oxygen for breathing provided)?

Similar question: Why don't deep-sea fish experience all those nasty things such as bursting blood vessels when brought to the surface?

 

[kuruman]

Think of all the air dissolved in one's blood suddenly forming expanding bubbles in the blood vessels and capillaries. Ugh!

 

[dRic2]

In vacuum the air in your lungs would be drained out (and you would suffocate), and perhaps your blood will start to flow off your skin because smaller veins will collapse

 

[Vanadium 50]

but will die a horrible death within seconds when released into a vacuum (e.g. outer space, even with oxygen for breathing provided)

Are you sure this is what happens? Within seconds?

 

[Dale]

Why don't deep-sea fish experience all those nasty things such as bursting blood vessels when brought to the surface?

They do. It is not exactly the same but they can easily suffer decompression sickness. Often their stomach becomes inverted and protrudes into their mouth.

 

[Nugatory]

Why can humans survive more than 10 times the atmospheric pressure, but will die a horrible death within seconds when released into a vacuum

Even much simpler systems will display this asymmetry. Consider the behavior of an inflated balloon: under pressure it compresses reversibly while in vacuum it bursts.

Humans are mostly liquid water, which is incompressible so that internal pressures can equalize against increased external pressure without doing irreparable structural damage (although a burst eardrum is seriously no fun). But being made of liquid water is a real handicap in a vacuum environment.

 

[Drakkith]

Why can humans survive more than 10 times the atmospheric pressure, but will die a horrible death within seconds when released into a vacuum (e.g. outer space, even with oxygen for breathing provided)?

Oh you'd puff up and swell a bit, but as long as you had a tight mask to provide air to breathe you would live for much, much longer than a few seconds. Human skin is airtight and would exert enough pressure to keep your insides on your insides without rupturing. Exposed tissue other than skin would likely suffer much worse. Your eyes, for example, would probably not fare very well in an extended spacewalk without protection. Without a mask, the saliva in your mouth would boil off and you'd lose consciousness in about 10-15 seconds as the oxygen is pulled from your blood through your lungs.

That's not to say that you'd be okay as long as you had a mask. I doubt you'd be able to survive for an extended period of time, but you'd last much longer than a few seconds.

 

[greypilgrim]

I have my information from this video, where that guy actually puts his arm in vacuum.

 

[Vanadium 50]

A YouTube video is not a very reliable source.

 

[Ibix]

Scientific American isn't a huge improvement, but at least references NASA research: https://www.scientificamerican.com/article/survival-in-space-unprotected-possible/

It says that survival times of dogs and chimps are a few minutes. Humans at least 27s.

 

[russ_watters]

In water, pressure increases with roughly 1 atm per 10 m depth, yet some divers can reach more than 100 m. Why can humans survive more than 10 times the atmospheric pressure, but will die a horrible death within seconds when released into a vacuum (e.g. outer space, even with oxygen for breathing provided)?

A lot happens to substances as the pressure drops toward zero. If you look at a phase diagram for, say, water, you will see that they tend to be displayed logarithmically.

Similar question: Why don't deep-sea fish experience all those nasty things such as bursting blood vessels when brought to the surface?

They do.

https://www.npr.org/sections/thesal...-are-learning-to-save-fish-that-get-the-bends

Caveat: I think the NPR article is wrong about barotrauma being the same as "the bends", but nevertheless they can get both.