Any Navy / Submariners here??
Was watching a program about submarine rescue this morning (i.e. rescue of personnel). The Navy currently uses a system which is comprised of two elements (the old DSRV's are now all decommissioned).
The first system is essentially a diving bell, called an SRM (submarine rescue module) lowered from a ship which mates onto the escape trunk of the submarine and allows for the rescue of 6 sailors at a time. The maximum working depth for this device is about 850' feet. Additionally, it requires the sub hull to be intact and the inside pressure to be the same as the surface pressure (i.e. sub not partially flooded and at different internal pressure than the surface). Okay, so this seems to work. Now let's look at the other part of this system.
If the sub is partially flooded, or below 850' feet, a different system is required, and this system is called the PRM (pressurized rescue module). Similar to the SRM, this is also lowered from a ship, but it is larger and can hold roughly 16 sailors at a time. The PRM has a maximum working depth of 2,000 feet (this is deeper than most subs crush-depth, but is widely publicized to submariners). The operation is the same in that it is lowered down, mates with the sub and people enter it through the escape trunk. Seems plausible at face value, but let's look a little closer.
So let's assume a downed sub is at 1,000 feet (just for easy numbers) and it is partially flooded. Forgetting water temperature for a moment, let's just look at pressures and this brings about my question...
If the internal pressure aboard the partially flooded submarine is below 200' feet, Nitrogen Narcosis is a certainty among all the personnel. If the internal pressure aboard the sub is below 400', oxygen is toxic unless all the nitrogen is removed and replaced with helium.
So what is the point of the PRM, unless being used on a perfectly intact submarine below 850'? Is this just a "feel good" measure published to make sailors less afraid? And why even bother publishing the 2000' number?? (not to mention the certain billions of tax payer dollars funding the development of such a system).
At the end of the day, when you consider the time it takes to locate a downed sub, the time it takes to airlift the system to the nearest country, the time it takes to put it on a ship, the time it takes to sail to the location...is there any practical hope that anyone could survive in a downed submarine?
And as a final note - Think about the downed Russian sub Kursk; a number of sailors actually did survive that incident (wrote letters even), but only for a few days, not the weeks it took to get the proper equipment to the scene.