Thanks Hugh & Jon for the vote of
confidance.
I did qualify this with " In an emergency
situation". I think I have been
misunderstood.
You take your sub down to its 250ft limit with
several extra dive tanks on board.
At this point the outside of your hull is
experiencing round 125psi.
For every 33ft further you go down you add
14.7psi. The hull would always be experiencing
125psi from the outside as the pressure you're
adding would be countering the additional
pressure from additional depth.
So no pressure as such from the inside would be
pushing your view ports out.
The reason I said to increase the O2 flow into
the hull is the "bellows add" system based on
sensing a drop in pressure wouldn't work. In
that system the O2 flow is set below the users
normal O2 consumption & then topped up from
the bellows add system because if the O2
was set too high there would be a continual
pressure build up & 02 % increase.
You could safely bump up the O2 a tad as it
would be safer to have too much O2 than not
enough. This, as Jon said wouldn't matter much
because your time would be constrained by
decompression tables, & there would be
enough air in the hull to breath from.
So in a life or death emergency you
could take several air tanks into your hull & a set of
dive timetables, open the tanks by hand at the
250ft mark & go to 400ft.
Alan