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

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Discussion Overview

The discussion centers on the physiological effects of extreme pressure changes on humans and deep-sea fish, particularly why humans can survive high pressures underwater but face severe consequences in a vacuum. The scope includes theoretical considerations, biological responses, and anecdotal evidence from various sources.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants note that pressure increases in water by roughly 1 atm per 10 m depth, and question why humans can survive pressures exceeding 10 atm but not a vacuum.
  • One participant describes the potential for air dissolved in blood to form bubbles when exposed to a vacuum, leading to severe physiological effects.
  • Another participant suggests that in a vacuum, air in the lungs would be expelled, leading to suffocation and possible collapse of smaller veins.
  • There is a challenge to the claim that death occurs within seconds in a vacuum, with some arguing that survival could extend beyond a few seconds if certain conditions are met.
  • Concerns are raised about deep-sea fish suffering from decompression sickness when brought to the surface, with one participant stating they can experience inverted stomachs and other issues.
  • One participant compares human physiology to that of simpler systems, like an inflated balloon, to illustrate the differences in behavior under pressure versus vacuum.
  • Another participant argues that while humans might swell in a vacuum, skin could provide enough pressure to prevent immediate rupture, although exposed tissues would suffer significantly.
  • References to external sources, including a YouTube video and articles from Scientific American and NPR, are presented, with varying levels of reliability attributed to these sources.
  • One participant mentions that phase diagrams for substances like water illustrate the complexities of behavior as pressure decreases.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the physiological effects of vacuum exposure and the survival time of humans in such conditions. There is no consensus on the exact outcomes or the reliability of the sources cited.

Contextual Notes

Limitations include varying interpretations of physiological responses, dependence on specific conditions for survival in a vacuum, and unresolved details regarding the effects on deep-sea fish.

greypilgrim
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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?
 
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Think of all the air dissolved in one's blood suddenly forming expanding bubbles in the blood vessels and capillaries. Ugh!
 
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
 
greypilgrim said:
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?
 
greypilgrim said:
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.
 
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greypilgrim said:
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.
 
greypilgrim said:
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.
 
I have my information from this video, where that guy actually puts his arm in vacuum.
 
A YouTube video is not a very reliable source.
 
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greypilgrim said:
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.
 

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