Can water pressure ever stop you rising to the Surface?

Question

I had this dream last night where I jumped from a high diving board into a pool and I could not rise back up again

In the dream I noticed the pool ventilation was switched off which I thought was the reason in the dream but I know that is not the answer.

I was at the bottom and I had to get over to the steps to drag myself up to the surface

Could this ever happen?

Can it happen at a particular depth or with a certain kind of water?

Answer 1

Well, now, interesting dream - and question!
Some people have answered it by thinking of differential pressure (feet as opposed to head, etc.). I don't think that's the point, here.
In fact, your dream is pretty much right. Most people are naturally buoyant at the surface, but as you go deeper, the increasing pressure compresses the air in your lungs, increasing the average density of your body and reducing your buoyancy. Below some depth, you could indeed find that you no longer float upward, but need to swim upward until you regain the point of neutral buoyancy. (It's unlikely to be so bad that you need steps!)
The depth at which this happens is (unless you're a very non-buoyant individual) deeper than most swimming pools, so you don't need to worry. Only deep divers need to take this -and lots of other things - into account.
Sea water being denser than fresh water, the effect kicks in even deeper in the sea than in a freshwater pool.

Answer 2

Possibly.

You are naturally buoyant. Air in your lungs, body fat, etc... all float. When your buoyancy is greater then the water pressure, then you will float, if it is not, you will sink.

But, wait, there's more...

Any water underneath you will be of a higher pressure then that above, so it will have the effect of pushing you upward. In order to continue sinking, your weight and the pressure above would have to overcome that upward pressure. Eventually, you would come to rest at some depth when neutral buoyancy is achieved.

And, that is exactly why SCUBA divers strive for. A well trained diver will be able to maintain a neutral buoyancy, and remain at a single depth for as long as they desire. They do this through the use of weights, an inflatable vest (called a buoyancy compensator or BC) and the air in their lungs.

By the way, the bends has nothing to do with getting stuck underwater. It is a side effect of breathing compressed air at depth. Your blood gets saturated with nitrogen, and as you rise to the surface, some of that nitrogen can form bubbles in your bloodstream. That is why divers always go to the surface very slowly, it allows that nitrogen to dissipate (off gas) without forming bubbles. It is called the bends because if bubbles form, they have a tendency to collect in the joints, and make a popping sound when you bend the joints.

Answer 3

No as water pressure increases with depth so does it's density.

The density of a person will always be slightly less or equal (depending on fat content) than the density of water.

Now if you breath in the water displacing the air in your lungs, that is a different story, you will sink like a rock.

In fact you can swim up from extreme depths on one breath of air constantly exhaling. The air in your lungs will expand with the pressure drop of going closer to the surface.

There have been instances where people have bailed out of a submarine at 150 feet deep or more and have survived with no SCUBA equipment.

Every 33.3 feet of water depth is the equivalent of one atmosphere of pressure and 1 cubic foot of air at sea level will be about 1/2 that volume 33 feet down.

Do not rise to the surface any faster than the bubbles that float up due to the risk of getting the bends.

For extended down time you need to surface in stages to allow your body to decompress.

The bends is what happens when you get dissolved nitrogen in your blood stream. When the pressure drops the nitrogen turns back into a gas.

Answer 4

I seems to notice when I was swimming in the med off a Greek Island that as I got deeper I seemed to
become less buoyant, that was a slightly worrying though for obvious reasons. I was down quite deep (free diving) not sure how deep probably around the 15 feet mentioned by another poster here, maybe a bit more, it did see quite a log way back up.
So I did fear becoming negatively buoyant (in case I passed out for example) it is probably the case you are less buoyant as you will be squeezed a bit smaller. I certainly felt it was easier to go down the further down I got.
I got down quite deep into a big hollow in the sea bed and then saw a huge fish, didn't look dangerous he seemed as afraid of me as i was of him, so I made a swift retreat to the surface!
I can't imagine people coming out of a submarine at great depth and not rising up.

However reading further about free diving negative buoyancy is mentioned a lot, although they generally do not give a depth, perhaps because it depends on a number of factors, your physiology and how much air is in your lungs. So they perhaps do not give a figure because it varies.

However............. I seem to remember that as a child when we went swimming to the local swimming pool it was possible to achieve negative buoyancy simply by breathing out. Indeed I seem to remember being able to lie on the bottom of the swimming pool in the shallow end, ie about 4 feet!!

I would add though that it is EXTREMELY DANGEROUS TO MESS ABOUT WITH YOUR BREATHING IN WATER.

IT IS POSSIBLE TO ACHIEVE NEGATIVE BUOYANCY AND FAINT, IN WHICH CASE YOU ARE *DEAD*
unless someone rescues you.

After a normal exhale you will find it is still possible to force air out of your lungs, so I think you can achieve negative buoyancy on the surface. I have just been exhaling and felt a bit weird, such stuff is dangerous even away from water in my opinion. In water it is exceptionally dangerous!! Knowing what I now know I won't be trying it again.

Answer 5

Yes, I believe at a depth of around 15 feet, the pressure acting on the area of the body will tend to stop you rising (Negative Buoyancy) without the assistance of actually swimming upwards. (This is also why, when swimming deep under water (not scuba diving), swimming fins are very helpful in getting you back to the surface).

(Experience in free-diving off the reefs of North Africa).
(By the way, ONLY if Scuba diving, (breathing compressed air), will rising too quickly cause the 'Bends', free-diving is no problem if you come up quickly).

Answer 6

The deeper you go the closer your body density approaches that of the surrounding water. If you breath out when diving then more so. Skin divers can reach depths of 100ft but don't breath out so that they remain positively buoyant even though their lungs are being restricted by the increased pressure. Scuba divers have buoyancy vests that they can fill with air to reduce density and so aid ascent.

If you go too deep you can become negatively buoyant and sink, unless you have the strength to swim upwards - if not you hit the bottom and start to decompose - but that's another story!

Answer 7

Hurricanes are a product of the interaction between hot and cold air over the ocean. In a high school science class, our teacher once suggested the idea to us of man being able to stop a hurricane by dropping a substance on it from above that would suck the water out of the storm completly. The only problem with this would be getting enough of the chemical to drop on the storm.

Answer 8

Great question coming from a dream!

The answer is "no". The thing that affects your ability to rise, is not simply the pressure, but the pressure _difference_ between the your head and your feet (assume you're in a vertical orientation).

The water presses on all sides of you, in a direction perpendicular to the surface of your skin. The water on top of your head pushes down; the water under your feet pushes up. The water on your left side pushes to the right, and the water on your right side pushes to the left.

Your "riseability" depends on how the downward pressure (on your head) compares to the upward pressure (on the soles of your feet). If the downward pressure is much greater than the upward pressure, you'll have a hard time rising.

But in fact, it's the _upward_ pressure on your feet that is always a little bit greater. This is true regardless of how far you descend. The reason is fairly simple: your feet are a couple of meters under your head, so they're a little bit deeper. Pressure is always greater at greater depths; so the pressure on your feet always exceeds the pressure on your head.

So, the pressure pushing up on you from below, will always (more than) counterbalance the pressure pushing down on you from above. The result is that great depth will never inhibit you from rising.

Answer 9

Yes.

The human body is compressible, at some depth the water pressure will be high enough to compress the body sufficiently that its density is greater than the water - then it will sink.

Answer 10

Only if you were very low down in the sea, I think they call it the bends. It's where you dont breathe properly so you sink or get crushed by the water pressure.