Nitrogen-induced hypoxia is painless, but in a sub like that CO2 might turn out to be a big problem, and that is not painless.
But yeah, the pressure vessel is (or, probably, was) fiberglass. It’s cheap to use but once it cracks it’ll absolutely shatter – this is why “real” subs tend to use metal – and that’s pretty much what I assume has happened. Either that or they’ve been bobbing on the surface with their air slowly running out, because the hatch can’t be opened from the inside.
Nitrogen-induced hypoxia is painless, but in a sub like that CO2 might turn out to be a big problem, and that is not painless.
But yeah, the pressure vessel is (or, probably, was) fiberglass. It’s cheap to use but once it cracks it’ll absolutely shatter – this is why “real” subs tend to use metal – and that’s pretty much what I assume has happened. Either that or they’ve been bobbing on the surface with their air slowly running out, because the hatch can’t be opened from the inside.