10 meters of water is one atmosphere, so they're right - 0 on the inside and 1 on the outside is a pressure differential of one atmosphere.
"almost 4000 meters of water" is "almost 400 atmospheres". About 2.7 tons per square inch. I find that that absolutely unimaginable. - I can't find any equivalence that my brain can make sense of.
Well, sea level is at 1 atm already, so an increase to 2 atm isn't immediately catastrophic. However, if you took that tank filled entirely with sea level air and shoved it down 30 feet under the water the same thing would happen. It instantly crumples because its hollow. We're full of water with some air in a couple places. We'd crumple too if we were just a layer of skin over an air sac. But as it stands, the human body can withstand that pressure alright
Pressure equalizes as they descend slowly. It's different from descending 4000m inside an armoured can and have it all released upon you in a split second.
"almost 4000 meters of water" is "almost 400 atmospheres". About 2.7 tons per square inch. I find that that absolutely unimaginable. - I can't find any equivalence that my brain can make sense of.