eli5: when a submarine exceeds its crush depth, and it’s crew is killed, what actually happens to them? Do they die instantly or are they squished flat? What happens ?
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They die pretty much instantly from being squished flat.
Exceeding crush depth means the structure of the submarine is no longer strong enough to hold out against the pressure of all the water around it, and well… [this happens](https://www.youtube.com/watch?v=Zz95_VvTxZM).
[Delta-P ain’t nothin’ to fuck with.](https://physicsfootnotes.com/footnotes/delta-p/)
EDIT: Note – the linked video is only 1 atmosphere of pressure difference. [Imagine what happens at 7 atmospheres (200 feet down)!](https://www.calctool.org/fluid-mechanics/hydrostatic-pressure)
At the titanic’s depth, the pressure is approximately 6000 PSI, so that’s 6000 pounds of force per square inch. An adult human’s body has a surface area of over 2500 inches, so that’s the equivalent of about 15 million pounds pushing on you. For reference, a typical passenger jet is less than half a million pounds, so about 35-40 airplanes stacked on top of a person
Water enters the submarine and they drown.
The water pressure will compress their lungs and cause oxygen and nitrogen concentration in blood to increase. Nitrogen will be at too high concentration, which would be problematic if they didn’t die of lack of oxygen first since it’s going to be consumed and not replaced.
It will not crush their body. Solids and liquids are not crushed by high pressure. They can change state (liquid to solid sometime or one crystal type to another like graphite to diamond) sometime, but the pressure in the ocean isn’t high enough for that. All parts of the human body that aren’t gas (so everything besides the lungs and potential small amount of gas in your dogestive system) will be unaffected.
Think of pressure change as a blast wave.
A blast wave is a change in pressure in the air. This might help visualize: https://www.researchgate.net/profile/Adi_Singh/publication/334784649/figure/download/fig2/AS:786638879875074@1564560732699/Pressure-propagation-of-a-sound-wave-through-air.ppm
When bomb goes off, the pressure wave travels outwards carries significant energy with it.
When a sub collapses, the pressure wave travels mostly inwards. But it’s still a blast wave.
Sound blast waves can pop eardrums, rupture liquid holding membranes (eyes, brains, bladders, etc) and even break bones.
If the hull integrity were to fail, they would be crushed like an egg. Instant death. If that’s what happened, they’re lucky. Worst case scenario, they’re trapped in the wreckage and still breathing.
Submarine crush depth is way lower (higher?) than a persons. When a submarine get crushed you get crushed, and fast.
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If catastrophic does not occur, there is the danger of a leaking weld or similar. This can allow a small amount of high-pressure water into the outer compartments.
Have you ever seen a high-pressure water-jet cutting metal and other materials?
Avoiding that sort of jet in a leaking compartment might be nearly impossible, and it could slice right through a person.
I’d take the instantaneous collapse any day.
To have an idea of what happens during explosive decompression, you can read about the Byford Dolphin oil rig diving bell accident. It gives you quite some vivid imagery regarding how people died, and that’s ‘just’ at 9 atmospheres of pressure.
https://en.m.wikipedia.org/wiki/Byford_Dolphin
I disagree with the squished flat part, yes your ribcage will be crushed and you’ll lose consciousness immediately, but your body remains mostly intact as it is also mostly water & bone.
The parts that get crushed are the soft external bits and everything containing air. Your lungs get flattened like pancakes but it’s not like you just stood under an acme anvil for wil-E coyote
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