extreme depth question

Question
I was watching the 1989 movie ' the abyss ' and it showed the main character using a liquid oxygen breathing system to drop down to what I think the movie suggested as around 18 - 20,000 feet. so first, is breathing liquid possible as a technology and second when they showed him going down the small ROV he took with him imploded under the pressure. and he wasnt wearing one of those full steel shelled suits for very deep dives...just fabric around his body. surely it isnt possible for the human body to simply have no reaction to 20,000 feet of pressure...the body would need some kind of protection like a hard shell correct?

Answer
Hi Simon,

You pose a couple of interesting questions and, although they're outside the scope of this category, I'll try to answer them for you.

First, the liquid Oxygen question.  In a nutshell, it isn't possible.  In order to keep pure oxygen in a liquid state, it must be kept at tremendously cold temperatures and/or extremely high pressures.  I don't have the temperature and vapor pressure tables handy so I can't give you exact values in this answer but the human lung cannot withstand either the low temperature or high pressure necessary to maintain oxygen in a liquid state.  If the temperature rises or the pressure falls, the liquid would immediately flash into vapor much like water turns to steam and the volume would expand and literally explode the lungs.

However there have been studies with lab animals that have used oxygen saturated saline water that was able to sustain life for a time while the animal was submerged in it and "breathed" the liquid.  To my knowledge, the animal was never conscious and could not be recovered back to air breathing.  I don't think there is a practical application at the present but at least it appears feasible.  Pneumonia is a medical condition where fluid accumulates in the lungs and can be fatal if not quickly removed.  So...filling the lungs with any kind of liquid would not be in the best interests of the person.  Great for science fiction but not practical in the real world!!

Your second question about withstanding the pressures found at 20,000 feet actually ties into your question about liquid oxygen.  The water pressure at that depth is around 8,900 pounds per square inch.  That is probably enough pressure to keep oxygen in a liquid state if the temperature at that depth is sufficiently cold.  Again, I don't have the necessary tables in front of me to give you an accurate answer but let's suppose it's sufficient.  Even so, at some point you've got to come back up and when the pressure drops sufficiently during ascent, your lungs would suddenly expand and pop.

More on pressure and the human body...Liquids do not compress very much so outside pressure has very little effect on them.  Most of our body is composed of water so it doesn't respond very much to increased pressure.  Fish can survive at great depths because they are composed of water and it doesn't compress.  However, there are lots of air spaces in our body and these are severely affected by changes in pressure.  Your ears pop when you fly due to changes in air pressure.  You have several sets of sinus cavities in your skull (not just your nose) and these are filled with air.  Of course, your lungs are also filled with air.  There is air in your digestive system as well.  All of these spaces must be able to equalize the air pressure within them to the same pressure as the water depth.  Any failure to equalize and the air space will implode from the crushing pressure.  The hard shell suits worn by deep divers keep the water pressure from contacting the body so these pressure problems are eliminated.  It's like a submarine that protects it's crewmen when they dive under the water.  All of the pressure is kept outside the hull of the submarine.

Whales are air-breathing mammals that can dive to depths of well over a mile.  However they have specially adapted lungs and rib cages that permit the lungs to compress and re-expand without damage.  Their blood and circulatory systems are also specially designed to carry more oxygen to the tissues to permit them to stay underwater longer without breathing.  Humans simply aren't built to do that so we have to improvise.

Technical deep divers can make dives to around 1000 feet without steel protective suits but they have to be highly trained and it's very dangerous.  Equalizing air spaces is critical and they must breath special gas mixtures.  I tell you this only to emphasize that the liquid and solid part of the human body isn't nearly as reactive to pressures as the air-containing spaces.

Science fiction writers take great liberties but it makes for some exciting movies, don't you think?

Thanks for writing, Simon!!

Mike Giles
Mike's Dive Center