Why doesn't swimming under water hurt?

[Nars Glinley]

WARNING: Stupid question follows.

If I were to lay on the ground and someone put a 6 foot column of water over me that was perfectly Nars Glinley shaped, I assume that with gravity and all, it would hurt like hell. Why can I go swimming and not feel the same effect? Gravity is still pulling me and the water above me toward the center of the Earth. If I were to lie on the bottom of the pool, it still wouldn't hurt.

What's the difference? Obviously I'm missing something obvious.

[Bill Door]

The water that you're under is under water as well. The same buoyancy that makes you float makes the water float as well.

[Nars Glinley]

OK. I'm going to have to try to wrap my tiny little brain around that one.

[Duckster]

The same reason why you don't feel the atmosphere crushing you.

[Baracus]

If you just put the water on top of you, it would tend to squish you flat. That would hurt because tissues would bend and stretch out of their usual positions. When you are underwater you experience the same pressure on your body from all directions at once. For swimming pool depths of water, this doesn't result in any significant distortion of your tissues and hence no pain.

[Absolute]

Atmospheric pressure is about 16 pounds per square inch (psi). You don't feel it because the inside of your body is at the same pressure - there is no net force pushing on you, and so you feel nothing.

As you dive in a pool, for the most part, your body (which is made mostly of solids and liquids) withstands the increasing pressures just fine (the solids and liquids react to the increased pressure without a significant change in volume, and so you feel no effect). However, gas does not resist compression without a significant change in volume, and so cavities in your body filled with gas will begin to collapse the deeper you go. At six feet in a pool, you can definitely feel the weight of the water on your ears and chest. At twelve feet, it begins to get uncomfortable, in my experience. It is possible to collapse a lung on a very deep dive, with improper technique, as well as do severe damage to your ears, sinuses, etc.

(note that trained divers use techniques to equalize the pressure in their ears and lungs with the ambient water pressure, relieving this discomfort - I'm referring to what happens if someone just jumps in a deep pool and swims to the bottom).

[Smeghead]

Right. If you have a column of water on top of you, all your bits and innards are going to go squish out the sides, because there's nothing holding them in. When you're under water, you're being pressed inward the same amount on all sides, so there's nowhere for your squishy bits to move. That's essentially the difference between pressure and weight.

[msmith537]

If you just put the water on top of you, it would tend to squish you flat. That would hurt because tissues would bend and stretch out of their usual positions. When you are underwater you experience the same pressure on your body from all directions at once. For swimming pool depths of water, this doesn't result in any significant distortion of your tissues and hence no pain.

Not to mention that you are mostly water. And liquids as you know, can't be compressed.

What can be compressed, however, are the various voids of air in your body. Mostly the lungs, inner ear, sinuses and so forth.

If you start swimming down around 10 -15 feet or so, you will start to notice the pressure.

[treis]

I disagree with the above answers. Well, I'd go so far to say they are flat out wrong and come from people that don't understand physics. Water doesn't hurt because it doesn't exert much pressure. 10 feet of water exerts a pressure of about 4 psi. To compare, my foot is about 12" x 4", which is 48 inches squared. Divide that into 200 pounds and you get about 4 psi. That's why it doesn't hurt. The weight is all there, but it is perfectly distributed over your body because water is a liquid.

To continue in this vein. Brief googling tells me that a human skull crushes at about 25,000 psi. If I am doing calculations right, that is about 6,000 feet of water. So somewhere between you swimming in a pool and having your skull crushed, I'd imagine it would start hurting.

[Blake]

10 feet of water exerts a pressure of about 4 psi. To compare, my foot is about 12" x 4", which is 48 inches squared. Divide that into 200 pounds and you get about 4 psi. That's why it doesn't hurt.


:eek:

You are saying that if you stood on my testicles it wouldn't hurt, because it is "only" 4 psi of pressure.

I calls bullshit. 4 PSI on the eyes, skull, solar plexus etc is more than enough to cause pain, yet as you point out, that is precisely the amount of pressure being exerted by 10 feet of water, yet it is utterly painless, indeed it is almost impossible to even feel.

So how do you explain that?

[barbitu8]

I disagree with the above answers. Well, I'd go so far to say they are flat out wrong and come from people that don't understand physics. Water doesn't hurt because it doesn't exert much pressure. 10 feet of water exerts a pressure of about 4 psi. To compare, my foot is about 12" x 4", which is 48 inches squared. Divide that into 200 pounds and you get about 4 psi. That's why it doesn't hurt. The weight is all there, but it is perfectly distributed over your body because water is a liquid.

To continue in this vein. Brief googling tells me that a human skull crushes at about 25,000 psi. If I am doing calculations right, that is about 6,000 feet of water. So somewhere between you swimming in a pool and having your skull crushed, I'd imagine it would start hurting.The extra pressure of even six feet causes more nitrogen to be dissolved in body liquids (present in our tissues). When you rise in the water too rapidly, the nitrogen comes out of solution and causes the "bends" which is quite painful, and possibly fatal. http://answers.yahoo.com/question/index?qid=20090920182042AAckRub

[treis]

:eek:

You are saying that if you stood on my testicles it wouldn't hurt, because it is "only" 4 psi of pressure.

Are your testicles 48 square inches? Because if they are anything like mine, they are 1x1/2 or 1/2 inches square at best, and round. Since they are round, they only contact part of the ground at one time. So if I step on your testicle, it's 200 pounds divided by probably 1/10th of a square inch at best, or 2000 psi.


I calls bullshit. 4 PSI on the eyes, skull, solar plexus etc is more than enough to cause pain, yet as you point out, that is precisely the amount of pressure being exerted by 10 feet of water, yet it is utterly painless, indeed it is almost impossible to even feel.

So how do you explain that?

You're wrong. 4 psi on the eyes, skull, solar plexus, etc does not cause pain as evidenced by people swimming with out pain.

[Blake]

Are your testicles 48 square inches? Because if they are anything like mine, they are 1x1/2 or 1/2 inches square at best, and round. Since they are round, they only contact part of the ground at one time. So if I step on your testicle, it's 200 pounds divided by probably 1/10th of a square inch at best, or 2000 psi.

Which is precisely what everybody else said, and precisely what you said was wrong.


You're wrong. 4 psi on the eyes, skull, solar plexus, etc does not cause pain as evidenced by people swimming with out pain.

Which is of course perfectly circular. Everybody else is wrong and you are right because clearly everybody else is wrong and you are right.

[treis]

Which is precisely what everybody else said, and precisely what you said was wrong.

No, we have people like you who say 4 psi will hurt. Which is absolutely flat out 100% wrong.


Which is of course perfectly circular. Everybody else is wrong and you are right because clearly everybody else is wrong and you are right.

No it's not:

You: 4 psi hurts
Me: No, it doesn't as evidenced by people swimming while experiencing 4 psi of pressure

[beowulff]

treis, you’re wrong.
Even a few PSI can cause pain to compressible areas of the body, like eardrums and sinuses. When you take SCUBA lessons, you lear about all the different types of “squeezes” that can occur to gas-filled areas of the body. The reason that these areas hurt and others don’t at the same pressure has to do with the compressibility of gasses.

[space_loner]

I disagree with the above answers. Well, I'd go so far to say they are flat out wrong and come from people that don't understand physics. Water doesn't hurt because it doesn't exert much pressure. 10 feet of water exerts a pressure of about 4 psi. To compare, my foot is about 12" x 4", which is 48 inches squared. Divide that into 200 pounds and you get about 4 psi. That's why it doesn't hurt. The weight is all there, but it is perfectly distributed over your body because water is a liquid.

You disagree with the above answers, then say exactly what they said?

[dracoi]

Let me try my approach to explain what some others have already said:

Tissues like our (solids and water-based liquids) adjust to pressure by increasing their own internal pressure. At sea level, we have 16 psi of air pushing down on our skin, and we have 16 psi of muscle/bone pushing up on our skin. In a shallow dive into your swimming pool, you might get up a total of 20 psi of water pushing down onto the skin, and now you have 20 psi of muscle/bond pushing up on the skin.

As long as the two are balanced, there's no pain. Even if you are talking hundreds of psi - or thousands. Sperm whales can go from 16 psi to 1,400 psi with no damage. (This doesn't work for humans because gas pockets change size under pressure and in people, this results in damage. Whales just let the gas pockets collapse. Maybe someday we'll do some genetic engineering that will permit free-diving to the ocean floor).

Using the OP's example of 4 psi of water placed on a person lying on the ground, you don't have even pressure. There is 16+4 psi pushing down (the water, and the air pushing on it), but only 16 psi pushing horizontally (the air to your sides). Your body can't find a happy medium there; if the internal pressure is at 16 psi, then the water crushes you from above. The internal pressure is at 20 psi, then your muscle/bone erupts horizontally. (i.e. you are squished).

To create another picture for the OP: imagine that you place a 4 psi amount of water in a hemispherical pile on top of you. Now the horizontal psi is the same as the vertical psi and there's no problem.

[Rhythmdvl]

What's really wrong with this thread is all this talk of testicle standing.

[treis]

treis, you’re wrong.
Even a few PSI can cause pain to compressible areas of the body, like eardrums and sinuses. When you take SCUBA lessons, you lear about all the different types of “squeezes” that can occur to gas-filled areas of the body. The reason that these areas hurt and others don’t at the same pressure has to do with the compressibility of gasses.

The reason these things hurt is that they are a lot more sensitive than the rest of your body. So yeah, a couple psi directly on your spinal cord is going to hurt like hell, but that's why it is protected. The only way your ear drums and sinuses are going to hurt is if their natural defenses fail. Besides, none of this answers the question of why swimming doesn't hurt.

You disagree with the above answers, then say exactly what they said?

:confused: They said you don't hurt because of the water's natural buoyancy and the fact that your body doesn't deform. That's different from it doesn't hurt because the water isn't pressing hard.

As long as the two are balanced, there's no pain. Even if you are talking hundreds of psi - or thousands. Sperm whales can go from 16 psi to 1,400 psi with no damage. (This doesn't work for humans because gas pockets change size under pressure and in people, this results in damage. Whales just let the gas pockets collapse. Maybe someday we'll do some genetic engineering that will permit free-diving to the ocean floor).

The reason people can't dive very deep has nothing to do with gas pockets expanding. It has to do with effects of breathing oxygen at such high pressures. Basically, at depth the air pressure is much higher, and this changes how much of the gases are dissolved in the blood. You get a high level of oxygen and all other gases in the blood, and this has detrimental effects. The bends are a different phenomenon and are only a problem on the way back up.

And, as noted previously, if you go down too deep your skull will crush like a tin can.

[msmith537]

I disagree with the above answers. Well, I'd go so far to say they are flat out wrong and come from people that don't understand physics. Water doesn't hurt because it doesn't exert much pressure. 10 feet of water exerts a pressure of about 4 psi. To compare, my foot is about 12" x 4", which is 48 inches squared. Divide that into 200 pounds and you get about 4 psi. That's why it doesn't hurt. The weight is all there, but it is perfectly distributed over your body because water is a liquid.



A ten foot high (by 1x1 ft) column of water weighs 640 lbs.

The ground pressure of an M1 Army tank is about 15psi, which is only equivalent to a depth of about 34 feet.

Mike Tyson can punch about 800-900 psi.


Given these options, would you rather get run over by a tank, have 600 lbs of scrap metal balanced on your head or punched by Mike Tyson?

[Rhythmdvl]

I would like to extend my sincere thanks for not including testicles in your rhetorical question.

I can breath again.

[treis]

A ten foot high (by 1x1 ft) column of water weighs 640 lbs.

The ground pressure of an M1 Army tank is about 15psi, which is only equivalent to a depth of about 34 feet.

Mike Tyson can punch about 800-900 psi.


Given these options, would you rather get run over by a tank, have 600 lbs of scrap metal balanced on your head or punched by Mike Tyson?

I don't see the point of this post.

[dracoi]

The reason people can't dive very deep has nothing to do with gas pockets expanding. It has to do with effects of breathing oxygen at such high pressures. Basically, at depth the air pressure is much higher, and this changes how much of the gases are dissolved in the blood. You get a high level of oxygen and all other gases in the blood, and this has detrimental effects. The bends are a different phenomenon and are only a problem on the way back up.

And, as noted previously, if you go down too deep your skull will crush like a tin can.

As noted previously... you are wrong. :)

Regardless of why humans can't dive that deep, my point was that whales can. And that the whales are able to survive without pain at both 16 psi and 1,400 psi.

If your insistence is that swimming in pools doesn't hurt because low pressure doesn't hurt, then explain how the whales withstand high pressure without pain.

[treis]

As noted previously... you are wrong. :)

Regardless of why humans can't dive that deep, my point was that whales can. And that the whales are able to survive without pain at both 16 psi and 1,400 psi.

If your insistence is that swimming in pools doesn't hurt because low pressure doesn't hurt, then explain how the whales withstand high pressure without pain.

Probably for the same reason polar bears can survive in Antarctica and I can't. Two different species. They're whales and we're humans.

[msmith537]

I don't see the point of this post.

The point is I will crush you!

Seriously, the point is that the pressure doesn't hurt because it's applied uniformly. The human body can actually survive a fair amount of uniform pressure.



The reason these things hurt is that they are a lot more sensitive than the rest of your body. So yeah, a couple psi directly on your spinal cord is going to hurt like hell, but that's why it is protected. The only way your ear drums and sinuses are going to hurt is if their natural defenses fail. Besides, none of this answers the question of why swimming doesn't hurt.

Are you kidding? The first thing you notice when you start diving is the pressure on your ears and sinuses. Then as you start reaching bottom of the Marianas Trench, your head implodes.

[Leo Bloom]

Note to OP: See how a naive question, with multiple disclaimers, can lead to scientific argument and rancor not seen since the AC versus DC- current wars?

Bad OP.

[Leo Bloom]

Mike Tyson can punch about 800-900 psi.
I've been trying to get this info for a while. Cite?

[BubbaDog]

I've been trying to get this info for a while. Cite?

I don't have a cite for this but I find it within reason. A very strong athlete can bench press possibly 350-400 pounds and fighters are trained to lean into punches and transfer their body weight into the force of a punch. Add speed to that equation and there is a lot of force (pressure) happening at the point of impact.

If you read on the fight forums people usually point out that Tyson never took a PSI measurement and the force of his punch is based on calculations. Even so I didn't see where any cites of specific measurements of any boxers were posted. Discussions of 600 to 1200 PSI punches seem to be prevelant.

[Xema]

And, as noted previously, if you go down too deep your skull will crush like a tin can.
Is there any evidence that a skull has ever been crushed this way?

For this to be true, there would have to be a pressure differential between the exterior and interior of your skull. Given that it's full of minimally compressible solids and liquids, how does such a pressure differential happen?

Various googling suggests that saturation diving has been done to depths exceeding 2000'. Mammals are known to reach depths around 10,000' with no evidence their skulls are close to being crushed.

[treis]

Is there any evidence that a skull has ever been crushed this way?

For this to be true, there would have to be a pressure differential between the exterior and interior of your skull. Given that it's full of minimally compressible solids and liquids, how does such a pressure differential happen?

It is probably true that your soft tissue will fail and equalize the pressure before your skull is crushed. But then you'd be dead, and not quite swimming.


Various googling suggests that saturation diving has been done to depths exceeding 2000'. Mammals are known to reach depths around 10,000' with no evidence their skulls are close to being crushed.

But they aren't humans. This is like saying Polar Bears are known to walk in the Arctic without coming close to freezing to death. What other mammals can do has little to no bearing on what humans can do.

[msmith537]

Your skull won't crush like a tin can at any depth. It's filled with a incompressible mostly liquid substance. Long before your skull reached crush depth, any air pockets would have also been filled with water.

Unfortunately, two of those compressible air pockets are your lungs, which you need for breathing and whatnot. Which gets harder to do when you have hundreds of pounds of water trying to compress you.

Diving limitations seem to have more to do with blood chemistry than physical forces.


I've been trying to get this info for a while. Cite?

Just some random message boards. Certainly nothing peer-reviewed. It seemed reasonable though.

[Baracus]

I disagree with the above answers. Well, I'd go so far to say they are flat out wrong and come from people that don't understand physics. Water doesn't hurt because it doesn't exert much pressure. 10 feet of water exerts a pressure of about 4 psi. To compare, my foot is about 12" x 4", which is 48 inches squared. Divide that into 200 pounds and you get about 4 psi.
Ok, yes it doesn't hurt your feet to stand on them. But what if a 200 pounder stood on your back? Or better yet as many could fit their feet on to apply a uniform 4 psi across your entire back? (For me that would be about six) Are you saying that that wouldn't hurt?

[treis]

Ok, yes it doesn't hurt your feet to stand on them. But what if a 200 pounder stood on your back? Or better yet as many could fit their feet on to apply a uniform 4 psi across your entire back? (For me that would be about six) Are you saying that that wouldn't hurt?

No. Well not because of the pressure on your back. People get massages where the masseuse walks on your back. It would hurt because your chest is 3-d, so that weight is going to be concentrated on your sternum at a much higher pressure.

Think about situations like weight lifting. I bench 185 pounds, and the bar doesn't contact with more than a couple square inches of my hand. That doesn't hurt, and certainly my back doesn't hurt supporting that extra weight.

[Xema]

What other mammals can do has little to no bearing on what humans can do.
Well, we tend to believe that physics are much the same across species. So what's different about the skull of a whale that keeps it intact at enormous pressures, whereas a human skull is crushed "like a tin can"?

And note that a can filled with water would not be crushed. Which tends to indicate that a human skull also would not be.

Note, too, that humans who have been to a depth of over 2000' do not seem to report symptoms of their skulls getting ready to collapse.

[treis]

Well, we tend to believe that physics are much the same across species. So what's different about the skull of a whale that keeps it intact at enormous pressures, whereas a human skull is crushed "like a tin can"?

As I said, this is not a good argument. Whales also manage to live in waters cold enough to kill humans. To answer your question, I would say there's a hell of a lot different between a human and whale skull.


And note that a can filled with water would not be crushed. Which tends to indicate that a human skull also would not be.

You're taking the analogy a little bit too far. While it is technically true that a perfectly filled can would not be crushed, your skull isn't a perfectly filled and sealed container. Even if it were, the pressure inside your skull would be 25,000 psi. Which I'd imagine would be very painful and fatal.


Note, too, that humans who have been to a depth of over 2000' do not seem to report symptoms of their skulls getting ready to collapse.

The ones that have been that deep were wearing fully contained suits.

[md2000]

Think of it this way.

If you take a balloon filled with air to 250 feet underwater, it wills hrink to half its normal diameter. (266 feet approx 8 atm, thus 1/8 the volume). But... it does this because it's air, and gases react to pressure accourding to the ideal gas law (Boyle's law) Pressure times volume is proportional to quantity of gas times temperature times a costant.

Solids and liquids are far less compressible. (as mentioned by earlier posts, for practical purposes they don't change volume under pressure.) A water-filled balloon would be the same volume at 250 feet as at 1 foot, and the same shape. It does not flatten, pressure is the same in all directions.

Same with you scuba diving. You don't flatten, because you are mostly water and otehr liquds, solids, and jelly mixtures... If you were full of hot air (hypotetically speaking) you would be crushed to half your former size. That's what would be painful. When someone puts a ton of lead on you , it's trying to deform you to look more like a pancake. If your testicles are in a vice or someone steps on them, they are being defomed to pancake shape. That's what's painful; the outer edges of the sphere are stretching well beyond normal size to try to reduce pressure on the overall structure. Pressure in only hurts if it stretches or squeezes the body in bad shapes. (How many PSI across your palms when you bench press 300 pounds? Or carry a person on your back, doubling the weight on your foot? Still it doesn't hurt...) Equal pressure from every direction at once equalizes without deforming your body.

In fact, in scuba diving, as you descend you inhale air at ambient pressure; if the air in your mouthpiece were not the same pressure, it would compress and h mouthpiece would fill with water. Instead, the regulator keeps leaking air until the pressure is greater than the surrounding water and it bubbles out. You suck this into your lungs, and your lungs have the same pressure of air as the water pressure around you. What hurts (speaking from experience) is the cavities that cannot adjust, your sinuses and ear tubes. There's a trick that you hold your nose and try to blow air into your ears to equalize the pressure. If it does not work, I know, your ear can hurt like hell. Of course, coming back up you have to reverse the process or blow an eardrum.

[Xema]

To answer your question, I would say there's a hell of a lot different between a human and whale skull.
Very true - the question is, what's the difference that allows one to have no problems while the other is crushed? Note that the whale skull is - like all vertebrate skulls - not a sealed container, so its contents are not shielded from ambient pressure.


... the pressure inside your skull would be 25,000 psi. Which I'd imagine would be very painful and fatal.
I don't dispute that you'd imagine it, but I'd like to see evidence it's true. (I know that I can imagine things that are ridiculous.)


The ones that have been that deep were wearing fully contained suits.
Well, they were fully exposed to ambient pressure.

[Qadgop the Mercotan]

Note to OP: See how a naive question, with multiple disclaimers, can lead to scientific argument and rancor not seen since the AC versus DC- current wars?

Bad OP.
I'd say it's more of an example of a Good OP. :D

The record scuba dive depth I was able to find was 1044 feet, wearing a compressible suit.

[msmith537]

Very true - the question is, what's the difference that allows one to have no problems while the other is crushed? Note that the whale skull is - like all vertebrate skulls - not a sealed container, so its contents are not shielded from ambient pressure.


The same thing that makes a submarine harder to crush than a soda can. It's bigger and thicker.




You're taking the analogy a little bit too far. While it is technically true that a perfectly filled can would not be crushed, your skull isn't a perfectly filled and sealed container. Even if it were, the pressure inside your skull would be 25,000 psi. Which I'd imagine would be very painful and fatal.

I think it would be but not because it would "pinch" your head. Your head isn't 100% water. I feel like at some point, the pressure would start to damage the cell linings and whatnot.

[Qadgop the Mercotan]

Actually, High pressure neurological syndrome (http://www.ncbi.nlm.nih.gov/pubmed/18008270) appears to be what limits how deep a person can go under water, as opposed to 'being crushed'. At depths below 300 meters, pressure effects on the nervous system starts causing significant dysfunction, and this only increases as depth increases.

[Xema]

The same thing that makes a submarine harder to crush than a soda can. It's bigger and thicker.
But the submarine is a sealed container, with a big pressure difference between outside and inside. A skull isn't.

[Leo Bloom]

Ok, yes it doesn't hurt your feet to stand on them. But what if a 200 pounder stood on your back? Or better yet as many could fit their feet on to apply a uniform 4 psi across your entire back? (For me that would be about six) Are you saying that that wouldn't hurt?
Testicles redux. ::sigh::

[Fish Cheer]

Probably for the same reason polar bears can survive in AntarcticaBut can they? I'm not aware of any observations supporting this.

[treis]

But can they? I'm not aware of any observations supporting this.

I realized my mistake and used Arctic in my second polar bear example :)

[Lemur866]

Take a tin can. Fill it full of water. Seal it. Take it down 1000 feet.

The tin can will not be crushed like a tin can. Neither will a steel can or an aluminum can.

If there are any air spaces in the tin can, those air spaces can be compressed and the tin can might bulge in by a small amount. But the water in the tin can will not be compressed by the water outside the tin can, any more than a given volume of water at the same depth is compressed by the water above it.

Yes, a can filled with air would be crushed. But a can filled with water would not be.

Note that the same can of water, could be easily crushed if you put it on the ground and put a 1000 foot column on top of it. It would split apart in microseconds. The exact same pressure has different results if the pressure is not evenly distributed.

A whale skull is not hundreds of times stronger than a human skull, and anyway, there are worms and soft-bodied creatures on the abyssal ocean floor a mile down. They aren't crushed by the pressure, and they don't have any sort of skeleton. The reason they aren't crushed by the pressure is the same reason the water-filled can isn't crushed. They don't have any compressible air spaces, and they aren't subjected to pressure changes. And so they live their wormy little lives at the bottom of the ocean.

What kills you when you are deep under the ocean are a couple of things. One, you aren't able to expand your lungs, even with a scuba tank. So you asphyxiate. Creatures that live down there have gills, so that doesn't matter, or their lungs can collapse, they don't "hold their breath" while underwater the same way humans do, instead they rely on oxygen dissolved in their tissues. Two, you have other air-filled spaces all through your body, and these will collapse. Three, you're experiencing pressure change, and so various substances in your body will change in solubility at different pressures. Note that high pressures tend to force gasses IN to solution, not out of solution. So you won't have nitrogen forming bubbles in your tissues from the pressure, rather the reverse, you get nitrogen bubbles when you remove the pressure.

So no, your skull won't be crushed like a beer can from the pressure, and neither will a beer can be crushed like a beer can. Yes, your lungs will collapse, your sinuses will collapse, your inner ears will collapse, any gas in your stomach and intestine will collapse. But 100 feet of water on your testicles won't feel like Mike Tyson punched you in the testicles, because your testicles aren't full of air. Note that if you set up a 100 foot tall pipe full of water and rested it on someone's testicles, then yes, their testicles would be crushed like a beer can, same as a beer can would be crushed like a beer can.

[Xema]

Convincing post, except for this part:

... you aren't able to expand your lungs, even with a scuba tank.
The SCUBA tank (and its pressure regulator) allow you to breathe air at the same pressure as the ambient water. So your lungs expand on inhalation and contract on exhalation, just as you'd like them to.