The big thing to understand is that you gain a whole atmosphere of pressure every 10 meters underwater you go. So at 100 meters you are experiencing 11 atmosphe

The big thing to understand is that you gain a whole atmosphere of pressure every 10 meters underwater you go. So at 100 meters you are experiencing 11 atmospheres of pressure (over 150 PSI). It's a wonder humans can go there at all without a vessel!