9 ms·

Almost certainly not since the submarine is pressurized, just like how an airplane is.

by joshAg 15y ago

sopooneo 15y ago
So it starts out at as high a pressure as it will end up at the bottom? Because of course the problems of pressure are reversed in deep sea submersion as compared to high altitude flight. You have to pressurize a plane, the submarine will pressurize itself.
- elithrar 15y ago
  > the submarine will pressurize itself. It's a sealed unit, so presumably it's "pressurized" at ~1 atmosphere by the way of closing it up prior to launch.
  - panacea 15y ago
    Presumably if they set the initial pressure at something greater than 1 atmosphere, but still within the comfort level of a human they wouldn't need to engineer the hull to withstand as much?
    - maxerickson 15y ago
      Water is roughly incompressible and ~10 meters (33 feet) of it will generate 1 atmosphere of pressure, so at 6 miles deep, I would guess even a very small safety factor would dominate any gains from pressurizing the capsule (I don't know anything about diving, but Wikipedia says that saturation diving is good down to about 150 meters, and the most extreme experiments went down to about 700 meters).
    - DanBC 15y ago
      The pressure at that depth is immense. 36,000 feet deep == 16,000 psi (pounds per square inch.) That's over 1000 atmospheres. Lets say a human can cope with 10 atmospheres. (I have no idea what a human can cope with.) That still leaves 990, plus extra for safety margin. (http://www.extremetech.com/extreme/121183-the-tech-that-will-help-james-cameron-win-his-race-to-the-bottom-of-the-ocean http://www.extremetech.com/extreme/121183-the-tech-that-will...) (http://news.ycombinator.com/item?id=3680367 http://news.ycombinator.com/item?id=3680367) I agree with commentators here. This, and other deep sea stuff, is awesome. I'm fascinated that it's being done by private companies, and the competition between Cameron and Branson just adds to the awesomeness. (Branson appears to be losing badly.)
      - ars 15y ago
        > I have no idea what a human can cope with. I don't believe there is any specific limit, as long as you give enough time to change the pressure gradually. However at higher pressures you need to reduce the oxygen and co2 concentrations (since at higher pressures they dissolve too easily). (You want to keep the partial pressure constant, even though the absolute pressure goes up.)
- fleitz 15y ago
  No. Airplanes are not air tight therefore they require pressurization. Submarines are air tight therefore no pressurization is required. If the air in a submarine starts to 'pressurize' the last thing you're worried about is the bends. In a pressurization event on board a submarine you're going to be far more worried about how to get the ocean out. The other issue is that when the air pressurizes it heats up almost instantly, it's generally believed that a large leak in a sub would create a wall of flame.
  - D_Alex 15y ago
    "it's generally believed that a large leak in a sub would create a wall of flame." What complete and utter rubbish. Please provide a single reference for this "general belief". Or better still, apologise for posting crap. Air, and gases generally, do heat up when compressed adiabatically (without exchange of heat with surroundings). But filling half the sub with water - that's a large leak, right? - and hence doubling the pressure would only produce about a 60 degree increase in temperature - not quite enough for a wall of flame eh? - if no heat was lost from the air to such things as jets of cold water entering the sub in this scenario.
    - joshAg 15y ago
      http://www.physicsforums.com/archive/index.php/t-122838.html http://www.physicsforums.com/archive/index.php/t-122838.html "When the hull of a sub fails, it normally fails ni one location, and water shoots in through that spot, relieving the stress on the rest of the structure. That's why all the wrecks you see in video from actual crash sites look so intact. Of course, the inrush of water also has the effect of rapidly pressurizing the inside of the sub 'till it matches external pressure. This rapid compression of the air inside has the effect of drastically raising the temperature, so what the victems inside probably see is an explosion (big wall of flame rushing through the inside)." "Interesting point. Since compression is quick, it is adiabatic, PV^\gamma = K applies. So if the pressure doubles, the volume of air reduces to .6 of its original volume the temperature will increase by a factor of 1.2 (eg from 300K to 360 K) which is pretty warm but not enough to ignite anything. When the wall of water has consumed 80% of the volume, the temperature is up to 570 K (300 C). So the sailors at the end of the sub watching the oncoming wall of water get fried before they drown."
- D_Alex 15y ago
  This is far more accurate than the parent comment, no idea why it was downvoted.
- joshAg 15y ago
  > So it starts out at as high a pressure as it will end up at the bottom? Ignoring shrinkage of the chamber (not insignificant), yes the human chamber will be at the same pressure at the surface and at the bottom. Counting in shrinkage due to pressure, the absolute pressure change will be less than the absolute pressure change you experience when you get on an airplane. > Because of course the problems of pressure are reversed in deep sea submersion as compared to high altitude flight. Of course the pressure problems are reversed. But both the airplane and the submarine prevent humans from experiencing decompression sickness by keeping the absolute change in pressure small enough that decompression sickness isn't an issue.
  - sopooneo 15y ago
    It was the shrinkage of the chamber that I was thinking of, but I didn't really know how much it would be. Thank you for the information.
    - joshAg 15y ago
      here are some back of an envelope calculations i did yesterday, if you're interested: http://news.ycombinator.com/item?id=3730747 http://news.ycombinator.com/item?id=3730747
D_Alex 15y ago
Ugh... this can hardly be more wrong. Decompression sickness only occurs when a person is under elevated pressure for a period of time, and then the pressure is released. Pressurizing the sub could in fact cause the decompression sickness, not prevent it. For this sub, during descent the pilot's chamber compresses and air is drawn out of that chamber to keep the pressure constant (this from JC's site). Rather unlike the airplane, into which the air is pumped from the outside, usually from the engine compressor's bleed, to keep the pressure from falling too low as it ascends.
- joshAg 15y ago
  > Decompression sickness only occurs when a person is under elevated pressure for a period of time, and then the pressure is released. Pressurizing the sub could in fact cause the decompression sickness, not prevent it. Only a too rapid depressurization will cause decompression sickness. Unless the sub is pressurized to a much higher pressure than normal atmospheric pressure, decompression sickness won't be an issue. According to National geographic (http://news.nationalgeographic.com/news/2012/03/120308-james-cameron-deepest-mariana-trench-challenger-science-sub/ http://news.nationalgeographic.com/news/2012/03/120308-james...) the entire sub is only going to shrink by about 2.5 inches. If we assume that the shrinkage only occurs on the 43 inch pilot sphere, then the lost volume is only about 16% of the total original volume, which means pressure at the bottom is about 120% atmospheric pressure. Since most airplanes are pressurized to 10.9 psi, which is about 75% of atmospheric pressure at sea level (14.9 psi) I don't think decompression sickness will even be an issue. > For this sub, during descent the pilot's chamber compresses and air is drawn out of that chamber to keep the pressure constant (this from JC's site). Rather unlike the airplane, into which the air is pumped from the outside, usually from the engine compressor's bleed, to keep the pressure from falling too low as it ascends. I googled for James Cameron's website and couldn't find anything. Could you please provide a link? Yes, obviously an airplane is going to pump air in from somewhere to keep the chamber at a higher pressure than the ambient environment and a submarine with a shrinking chamber is going to remove air to keep the chamber at a lower pressure than the ambient environment. However, both an airplane and a sub are designed to keep a chamber at a specific pressure that is relatively close to normal atmospheric pressure, which prevents humans in the chamber from being at risk for decompression sickness, short of some sort of catastrophic failure.

Almost certainly not since the submarine is pressurized, just like how an airplane is.

by joshAg 15y ago

Almost certainly not since the submarine is pressurized, just like how an airplane is.

So it starts out at as high a pressure as it will end up at the bottom? Because of course the problems of pressure are reversed in deep sea submersion as compared to high altitude flight. You have to pressurize a plane, the submarine will pressurize itself.

elithrar 15y ago
> the submarine will pressurize itself. It's a sealed unit, so presumably it's "pressurized" at ~1 atmosphere by the way of closing it up prior to launch.
- panacea 15y ago
  Presumably if they set the initial pressure at something greater than 1 atmosphere, but still within the comfort level of a human they wouldn't need to engineer the hull to withstand as much?
  - maxerickson 15y ago
    Water is roughly incompressible and ~10 meters (33 feet) of it will generate 1 atmosphere of pressure, so at 6 miles deep, I would guess even a very small safety factor would dominate any gains from pressurizing the capsule (I don't know anything about diving, but Wikipedia says that saturation diving is good down to about 150 meters, and the most extreme experiments went down to about 700 meters).
  - DanBC 15y ago
    The pressure at that depth is immense. 36,000 feet deep == 16,000 psi (pounds per square inch.) That's over 1000 atmospheres. Lets say a human can cope with 10 atmospheres. (I have no idea what a human can cope with.) That still leaves 990, plus extra for safety margin. (http://www.extremetech.com/extreme/121183-the-tech-that-will-help-james-cameron-win-his-race-to-the-bottom-of-the-ocean http://www.extremetech.com/extreme/121183-the-tech-that-will...) (http://news.ycombinator.com/item?id=3680367 http://news.ycombinator.com/item?id=3680367) I agree with commentators here. This, and other deep sea stuff, is awesome. I'm fascinated that it's being done by private companies, and the competition between Cameron and Branson just adds to the awesomeness. (Branson appears to be losing badly.)
    - ars 15y ago
      > I have no idea what a human can cope with. I don't believe there is any specific limit, as long as you give enough time to change the pressure gradually. However at higher pressures you need to reduce the oxygen and co2 concentrations (since at higher pressures they dissolve too easily). (You want to keep the partial pressure constant, even though the absolute pressure goes up.)
fleitz 15y ago
No. Airplanes are not air tight therefore they require pressurization. Submarines are air tight therefore no pressurization is required. If the air in a submarine starts to 'pressurize' the last thing you're worried about is the bends. In a pressurization event on board a submarine you're going to be far more worried about how to get the ocean out. The other issue is that when the air pressurizes it heats up almost instantly, it's generally believed that a large leak in a sub would create a wall of flame.
- D_Alex 15y ago
  "it's generally believed that a large leak in a sub would create a wall of flame." What complete and utter rubbish. Please provide a single reference for this "general belief". Or better still, apologise for posting crap. Air, and gases generally, do heat up when compressed adiabatically (without exchange of heat with surroundings). But filling half the sub with water - that's a large leak, right? - and hence doubling the pressure would only produce about a 60 degree increase in temperature - not quite enough for a wall of flame eh? - if no heat was lost from the air to such things as jets of cold water entering the sub in this scenario.
  - joshAg 15y ago
    http://www.physicsforums.com/archive/index.php/t-122838.html http://www.physicsforums.com/archive/index.php/t-122838.html "When the hull of a sub fails, it normally fails ni one location, and water shoots in through that spot, relieving the stress on the rest of the structure. That's why all the wrecks you see in video from actual crash sites look so intact. Of course, the inrush of water also has the effect of rapidly pressurizing the inside of the sub 'till it matches external pressure. This rapid compression of the air inside has the effect of drastically raising the temperature, so what the victems inside probably see is an explosion (big wall of flame rushing through the inside)." "Interesting point. Since compression is quick, it is adiabatic, PV^\gamma = K applies. So if the pressure doubles, the volume of air reduces to .6 of its original volume the temperature will increase by a factor of 1.2 (eg from 300K to 360 K) which is pretty warm but not enough to ignite anything. When the wall of water has consumed 80% of the volume, the temperature is up to 570 K (300 C). So the sailors at the end of the sub watching the oncoming wall of water get fried before they drown."
D_Alex 15y ago
This is far more accurate than the parent comment, no idea why it was downvoted.
joshAg 15y ago
> So it starts out at as high a pressure as it will end up at the bottom? Ignoring shrinkage of the chamber (not insignificant), yes the human chamber will be at the same pressure at the surface and at the bottom. Counting in shrinkage due to pressure, the absolute pressure change will be less than the absolute pressure change you experience when you get on an airplane. > Because of course the problems of pressure are reversed in deep sea submersion as compared to high altitude flight. Of course the pressure problems are reversed. But both the airplane and the submarine prevent humans from experiencing decompression sickness by keeping the absolute change in pressure small enough that decompression sickness isn't an issue.
- sopooneo 15y ago
  It was the shrinkage of the chamber that I was thinking of, but I didn't really know how much it would be. Thank you for the information.
  - joshAg 15y ago
    here are some back of an envelope calculations i did yesterday, if you're interested: http://news.ycombinator.com/item?id=3730747 http://news.ycombinator.com/item?id=3730747

D_Alex 15y ago

Ugh... this can hardly be more wrong. Decompression sickness only occurs when a person is under elevated pressure for a period of time, and then the pressure is released. Pressurizing the sub could in fact cause the decompression sickness, not prevent it. For this sub, during descent the pilot's chamber compresses and air is drawn out of that chamber to keep the pressure constant (this from JC's site). Rather unlike the airplane, into which the air is pumped from the outside, usually from the engine compressor's bleed, to keep the pressure from falling too low as it ascends.

joshAg 15y ago
> Decompression sickness only occurs when a person is under elevated pressure for a period of time, and then the pressure is released. Pressurizing the sub could in fact cause the decompression sickness, not prevent it. Only a too rapid depressurization will cause decompression sickness. Unless the sub is pressurized to a much higher pressure than normal atmospheric pressure, decompression sickness won't be an issue. According to National geographic (http://news.nationalgeographic.com/news/2012/03/120308-james-cameron-deepest-mariana-trench-challenger-science-sub/ http://news.nationalgeographic.com/news/2012/03/120308-james...) the entire sub is only going to shrink by about 2.5 inches. If we assume that the shrinkage only occurs on the 43 inch pilot sphere, then the lost volume is only about 16% of the total original volume, which means pressure at the bottom is about 120% atmospheric pressure. Since most airplanes are pressurized to 10.9 psi, which is about 75% of atmospheric pressure at sea level (14.9 psi) I don't think decompression sickness will even be an issue. > For this sub, during descent the pilot's chamber compresses and air is drawn out of that chamber to keep the pressure constant (this from JC's site). Rather unlike the airplane, into which the air is pumped from the outside, usually from the engine compressor's bleed, to keep the pressure from falling too low as it ascends. I googled for James Cameron's website and couldn't find anything. Could you please provide a link? Yes, obviously an airplane is going to pump air in from somewhere to keep the chamber at a higher pressure than the ambient environment and a submarine with a shrinking chamber is going to remove air to keep the chamber at a lower pressure than the ambient environment. However, both an airplane and a sub are designed to keep a chamber at a specific pressure that is relatively close to normal atmospheric pressure, which prevents humans in the chamber from being at risk for decompression sickness, short of some sort of catastrophic failure.