I’m hungry.
The Houston Chronicle’s Energy Blog linked to this Infographic: Tallest Mountain to Deepest Ocean Trench.
Damn, that’s a deep well.
Thanks, Bridget. That’s beyond amazing. Gives us a whole new perspective on the well, and helps make me wonder what the hell we’re doing down there.
When I was in the Navy they announced when we passed over the deepest known portion (in 1966) of the Trench. Made me feel kinda dizzy when they told us it was nearly seven miles deep. Then they announced when we’d gone that distance on the surface. (6.8 mi, maybe 15-20 minutes)
That’s deep!
As a note, this was for diving in a traditional diving suit with helmet. The air is compressible, so the result is a massive squeeze. I’ve dived down to 100 feet in a wet suit using SCUBA and felt nothing, but in a dry suit I can feel suit squeeze even at 20 feet until I put in some gas. So the effect of water pressure on compressible substances is noticeable.
That’s the heart of the problem. The solid and liquid parts of our bodies are incompressible enough to survive to great water depths. At the deepest point in the ocean we’d hit problems for sure, but for substantial depth we’d be OK…
except for the air bits. Those cause problems. As someone pointed out in another message, there’s no combination of gases (that include O2) that are completely harmless.
Combinations of O2 and N2 are dangerous once you go past about 40% pp O2 because of oxygen toxicity; in short, too much high pressure O2 will kill you. The converse, raising N2, causes nitrogen narcosis. High pressure N2 also gets absorbed into your body and doesn’t come out all that easily. Come to the surface too quickly after a deep dive and you get the human body equivalent of Coke plus Mentos, which will ruin your whole day.
You can mix O2 and helium (He) more safely because He doesn’t seem to cause narcosis and doesn’t seem to get absorbed in the body as easily. It’s very expensive, though, and difficult to deal with. At the atomic level, He is only slightly larger than H2, and many times smaller than O2 or N2, so it has a tendency to leak out of anything you put it in. And once again, even with massive percentages of He to
O2 you still get to the point where you have O2 toxicity because of the pressure.
Someone mentioned a liquid breathing material. I think that it’s liquid Freon they’re thinking of. The Navy did some experiments with oxygen at normal pressure dissolved in liquid Freon. They found that dogs could survive on it.
I don’t know anything more about the Freon idea. I assume that it could deliver sufficient O2 up to significantly high depths. It might have some other problems, though.
They’ve observed fish in the deep abyss of trenches, so we know that the pressure isn’t fundamentally incompatable with vertebrate life, but the fish down there are presumably adapted to it. For something used to 15psi, the problem is probably that at extreme pressures the lipids in our bodies would start to solidify, or that the solubility of ions changes radically.
[stupid question]
Is it true that when you bring up fish from those depths that their eyes pop out?
[/sq]
These are being balanced by the pressured air you’re breathing. Divers periodically have to yawn or pinch their nose to balance the pressure as they descend.
In my own experience deep-sea fishing, I can tell you that some organ (swim bladder?) inverts itself and protrudes right out of their mouths like a giant inflated tongue. Their eyes looked kind of bulgy, but I don’t know if it could have been a bug-eyed fish in its natural state. So that’s not a stupid question at all.
Absolutely not Freon, because it is an aggressive solvent and would kill you and your equipment at any depth. You’re probably thinking of perfluorocarbon (which, although chemically similar to a CFC like Freon, will not kill you). Tests have been done, but according to the wiki linky it’s nowhere near ready for prime time for diving applications.
I have done that many times. It is a popular activity for oceanographers. The cup remains cup shaped, just smaller. By the end of a cruise there is usually a row of cups of different sizes in the wet lab marked with the depth they reached. 
It is very hard to know exactly what would happen to a human body at 5000ft, but besides being dead, not much physically. The pressure itself is balanced and so the body would stay approximately body shaped. The problems would be two-fold, relatively small differences in pressure would have significant effects on cell function and of course even if you had air compressed to that pressure it would be like breathing water. Gas exchange would be so messed up you wouldn’t be able to take or use a breath. But the corpse wouldn’t be crushed or anything. Fish for instance do just fine at 5000 ft. They don’t do so fine at the surface-the pressure change usually tears them apart-but if they are brought to the surface slowly enough they can survive.
eyes and other things.
yes.
it is due to the pressure change. Some marine biologists have developed reverse bathyscaphs-pressure chambers where the fish is enclosed and kept at pressure as it is brought to the surface. Not a good idea since it is essentially a bomb that has already detonated but hasn’t expanded yet…
Hey, another oceanographer, cool. Howzit.
Oh, there a lot of oceanographers. Just not so many who actually get to earn a living at it. Like forrest rangers. 
That would be true if it were filled with a compressible fluid, like air.
As long as it is filled with a low compressibility fluid, such as sea water, it doesn’t store very much energy, and failure does not result in an explosion. This is why high pressure gas vessels are first tested with high pressure water (hydrostatic testing) before being trusted to contain compressed gas.
Also, pressure vessels are mechanically stable, and as long as you don’t exceed the tinsel strength of the walls, they typically leak well before they fail catastrophically. Negative pressure vessels are another kettle of fish (heh!) and will buckle and fail in a heartbeat, thus they need much larger design margins.
So, they make nice Christmas tree ornaments?
CMC fnord!
OK, I have never seen one of these, just heard about them. I kind of wondered how in the world a bunch of marine biologists got the OK to try these out-perhaps they aren’t as dangerous as my friends and I assumed.
Still, I wouldn’t want to be too close when the lid comes off…
Hi There!
It has been a long time since I had the opportunity to go to sea. I kind of miss it. Been doing this for 30 years. It has been fun.
Wierdly, me too. I swapped careers as well.