Highest pressure a human can survive?

[Ender_Will]

If a person were to swim straight down, how deep could they get before the water pressure killed them? I'm willing to ignore things like the fact that this lucky diver would probably run out of air and other trivial details.

My friend arbitrarily decided that 2000 feet (roughly 60 atmospheres, or 867 psi) was a good number, and I agreed. However, Herbert Nitsch has gone to 600 feet and come back up, so now I'm thinking that 2000 feet may not be deep enough.

[groman]

It depends almost exclusively on the method of breathing on the way down. With surface air pressure in the person's lung it wouldn't be too long before your body can't hold it anymore. I wouldn't think anybody could make it past 1000 feet oxygen or not, but this is just a wild guess. However, the only way you're making it anywhere is if your body is pressurized. I don't know how well the lungs can engorge with plasma but if you have any surface air 14 PSI cavities left, the nice 400 PSI of water outside will deform you to compensate (Note: This might hurt)

If you don't mind proper compression and decompression, you should be able to go much deeper. You're almost a liquid with roughly the same compressibility and density as water -- as long as your gas exchange mechanisms are working and you don't die of hypothermia you should be able to keep diving. I think sperm whales can dive deeper than a mile, and I'm willing to bet the limit is that they can't ascend too quickly and they're pretty much holding their breath so it's a time issue rather than pressure.

My bet is that if you are provided properly pressurized breathing medium (a liquid of density similar to water would be best, but pressurized gas should do), sufficient time and sufficient heat then the answer is "the bottom of the ocean", but I am curious to see what diver/doctor dopers will say on the subject.

[Xema]

Originally Posted by groman

... the answer is "the bottom of the ocean"

Though I may not be popular for doing so, I'll note that in the one and only visit to the bottom of the ocean, small fish (sole & flounders) were seen there, which at least argues that flesh and blood can endure those pressures.

[groman]

Originally Posted by Xema

Though I may not be popular for doing so, I'll note that in the one and only visit to the bottom of the ocean, small fish (sole & flounders) were seen there, which at least argues that flesh and blood can endure those pressures.

But how long were they obs... OW OW OW...

People keep mentioning enduring these pressures but I am not convinced that there is anything to endure. Lots of biological processes are unable to withstand even slight changes of ambient pressure, but I can't think of any that just stop working at a certain pressure due to pressure alone. As long as you supply oxygen at marginally higher* than ambient pressure and protect the exterior of the body from the element by maintaining moisture, pH, temperature, why wouldn't it work?


*I'd say AT ambient pressure but then somebody would point out that you can't quite breathe 0 ATM oxygen if you're at 0 ATM.

[The Hamster King]

Originally Posted by Xema

Though I may not be popular for doing so, I'll note that in the one and only visit to the bottom of the ocean, small fish (sole & flounders) were seen there, which at least argues that flesh and blood can endure those pressures.

But that was just once, in 1960. For twenty minutes.

[scm1001]

I havent any figures for humans (the nazis did pressure experiments on humans), but many bacteria can survive to 600 atmospheres quite nicely, and spores, viruses etc to 6000 Atm when dry.

[Mangetout]

I think the pressures at which oxygen becomes a liquid (while remaining at room temperature) will set an absolute upper bound for human survival.

[coffeecat]

In Sphere, one of the characters mentions that you risk some horrible-sounding diseases if you spend a long time breathing high-pressure heliox. Does anyone know anything about this, or was Michael Crichton just talking through his hat?

[Ludovic]

Originally Posted by Mangetout

I think the pressures at which oxygen becomes a liquid (while remaining at room temperature) will set an absolute upper bound for human survival.

Maybe, maybe not. We've done liquid-breathing experiments successfully with mammals, so if human can breathe liquid as well it might not be a problem.

Pressure at which Co2 becomes a liquid, OTOH, might be more challenging: how are you to get the stuff out of your lungs?

[chorpler]

We've had some good threads on this before where we discussed things like High-Pressure Nervous Syndrome, whether the liquid breathing system shown in The Abyss is feasible for real use, whether your nerves and brain really do start malfunctioning at high pressures, etc. Unfortunately I can't find any of them right now because I have to leave.

[Mangetout]

Originally Posted by Ludovic

Maybe, maybe not. We've done liquid-breathing experiments successfully with mammals, so if human can breathe liquid as well it might not be a problem.

Pressure at which Co2 becomes a liquid, OTOH, might be more challenging: how are you to get the stuff out of your lungs?

I think the same problem will occur with the oxygen - at pressures sufficient for oxygen to be liquid, what's going to make it come out of the breathing solution?

[ralph124c]

Originally Posted by coffeecat

In Sphere, one of the characters mentions that you risk some horrible-sounding diseases if you spend a long time breathing high-pressure heliox. Does anyone know anything about this, or was Michael Crichton just talking through his hat?

yes, several divers who have spend long periods under high pressure (heliox saturation diving) have experience death of bone tissue (necrosis). Why this happens is unclear-perhaps the heliuminterferes with normal bone repair.

[Elendil's Heir]

Originally Posted by chorpler

We've had some good threads on this before where we discussed things like High-Pressure Nervous Syndrome, whether the liquid breathing system shown in The Abyss is feasible for real use, whether your nerves and brain really do start malfunctioning at high pressures, etc. Unfortunately I can't find any of them right now because I have to leave.

Here ya go: http://boards.straightdope.com/sdmb/...d.php?t=308429