I guess I was imagining a catastrophic failure of the inner tube door- "damn thing popped right off." At max depth, wouldn't the sudden compression zap anybody in the compartment?
(god forbid- I got pushed out of airplanes, and didn't mind that a whole lot...but the sub thing creeps me out. I even felt bad for our putative "enemies" the russians when they lost their sub.)
In the compartment it would be quick if it were at test depth--explosive. Near the surface but submerged it wouldn't be instantaneous. The next compartment would . . . probably . . . survive.