Sub accident

[Axel Iehle <ai@augusta.cma.fr>]

A navy diver I know once told me the following story that
happened to one of his friends:

They were in a civil sub with lock-out capbilities to perform some tests for a 
new breathing mixture at depth (REAL depth I mean. Not were you go with 
standard air-tanks).
One guy went out of the sub.
The sub was already a little light since the beginning of the mission.
The test completed, the diver (connected to the sub with a 'narguile', I mean 
his breathing-fluid tube) went back inside the lock-out compartment.
But he couldn't manage to properly close the hatch to start emptying the water 
and begin the decompression phase. After multiple tries, the sub began to 
raise from the bottom where it was 'parked'. The pilot couldn't manage to 
stabilize the sub, and the sub started to move up. And as it is often the case 
underwater,
the ascent was getting faster and faster. The diver still inside the bell 
couldn't close the door and litteraly blew out before they reached the surface
(that's what he told me... but I'm not sure it's a real good description. 
Anyway the diver died. And not in a funny way. And the operator of the 
lock-out chamber inside couldn't do anything else than watching his mate 
dying).

After searching, it appeared that for a certain reason the diver didn't manage 
to close the hatch, and the gas he was rejecting in the water accumulated 
under the submarine in a ABS-plastic protection cover that was drilled with 
holes but not big enough to counterbalance the amount of gas realeased by the 
stressed diver.

The lesson is for me that when I'll build my sub, I'll avoid to the max
to have covers, or if I have, they'll present really huge venting holes
to prevent from an uncontroled accidental ascent.
OK my sub won't have a diver lock-out chamber, but this kind of accident
can also generate damages to your sub if you scratch a rock while going up.
In any case, underwater, you never want that things work differently than
what you designed them for, don't you?
Being positively buoyant is OK, if you designed your sub this way.

Axel IEHLE