If you take a submarine down 100 feet and open the hatch, you’re not going to die (from anything other than drowning or maybe your superior strangling you.) You’re at around 3 bar or 43.5 psi.

That’s literally at the low range of pressure that comes out of your tap.

Even at 200ft you’re looking at pressure that’s just barely enough to cause damage to your house plumbing, but nowhere near the pressure needed to hurt a human.

At about 500 feet, you’re looking at pressure that would come out of a fire hose. Not fun to get hit by, but not necessarily lethal. Most injuries would be from being pushed into things, not the water itself. And you’re definitely not becoming a paste.

Are you under the impression that the moment the hatch opens, the water instantly normalizes the pressure inside the vessel? Because that is by no means what happens.