Submarines?

[frank]

I know that this is not really scuba related, but it has become quite a curiosity issue for me. Is the air in a submarine mantained at 1 BAR pressure or do they become more pressurized at depth? Are there any decompression issues for men in a submarine? What sort of air do they breath? etc.. etc...

Any information or links to information would be greatly appreciated. As I said, this is merely a curiosity issue. After my scuba certification, and every thing I learned about nitrogen and pressure under water etc., I became curious about how submarines deal with these issues

Thanks
Frank

 

[rcohn]

I've been to test depth in a couple of Navy subs. There is no decompression involved. I never checked the air pressure so I don't know if it was exactly one bar but it must be fairly close. Pressure is not increased when they go deep, but they do station sailors at points in the sub to watch for leaks. That gave me a real sense of confidence.

Also they are happy to be shallower, when leaving test depth on one exercise they pulled a 19 degree up angle without warning. You quickly find out where gear hasn't been properly stowed.

Ralph

 

[Dr Deco]

Submarine rescue has been a topic of intense interest following the loss of the Kirsk. Submarines are at one atmosphere of pressure. Little would be gained by pressurization considering the great depths to which they dive, unless you were willing to add thirty atmospheres or so of pressure. This would help prevent hull collapse and reduce so leaks, but it would really add physiological problems such as nitrogen narcosis if air was used. Helium would eliminate narcosis but distorts the voice and plays havoc with sealed electronic devices. (Seawater leaks in submarines are handled by pumps, but only if the leaks are minimal ones.)

The fact that they are not normally pressurized does not mean that there are never any decompression issues, however. This can occur if partial flooding of the compartments should occur. Then the air is compressed in the “bubble” where the crewmembers will congregate. This will result in a decompression problem since it would not be unusual for the crew to become saturated after about 24 hours. Serious DCS can result fro decompression from about 20 feet of seawater when you are saturated. A submarine at a couple of hundred feet would present a real decompression challenge.

The modes of escape for the crew are essentially two:
[sp]Exit through an escape tower is possible up to about 400 feet (in a special suit), but this is only for minimal absorbed gas loads.
[sp]The other method is a rescue vehicle such as the Deep Submergence Rescue Vehicle, DSRV . This can mate with the submarine and then ferry about 15 crewmembers to the surface ship to mate with a deck decompression chamber. When many individuals are involved, space and decompression facilities are at a premium.

Considerable work is being performed by the US Navy at this time to devise ways to speed the decompression procedures; this is the DISSUB program.

 

[Warhammer]

So, if they were to pressurize a sub would it be possible for that sub and crew to reach the sea's greatest depth and return safely?

 

[Dr Deco]

The greatest depth in the ocean is the Challenger Deep in the Marianas Trench off Guam. At about 36,000 feet, it has altready been visited by a submarine of special design ("Trieste" in 1960) that carried its two crewmembers in a titanium sphere. The interior was not pressurized.

To increase the operational depth of a submarine, it would be possible to pressurize the interior to balance the outside sea pressure, but in practice, it is more practical [I suspect] to construct a smaller crew compartment and build a stronger hull. [Not being a marine engineer, I can not speak in depth to submarine design.]

Problems associated with pressurization of the interior are many, some of which would be:

[1.] Nitrogen is narcotic as the pressure is increased (“nitrogen narcosis”), so it would be necessary to compress with helium. Helium is however, notorious for being able to penetrate glass and metal with relative ease; every thing in the submarine that is electrical and would be bothered by helium and would need to be somehow protected. Anything with a vacuum inside would be particularly susceptible (e.g., cathode ray tubes and television tubes could not be used).

[2.] Pressure is not without its effects on living systems. Pressure changes the conformation (= shape) of molecules, and it can produce effects of its own – some detrimental. Thus large pressures on the interior could probably not be used.
[sp]Pigs have successfully gone to 5,000 in a chamber and been returned, so we know that this is physiologically possible. How this affected the mental status of the pigs is not known.

[3.] The higher the interior gas pressure, the greater the gas saturation of the crew, and the longer it would take to exit the submarine’s interior. If the sub were compressed with helium, a rule of thumb is one day per 100 feet of “depth” decompression time.

[4.] Everything connected with the climate control system would need to be redesigned. The interior gas would be very dense. Sound would travel better in this gas and might present a problem regarding passive detection of the sub by another enemy submarine.

Final comment is that, yes, it would be possible to compress to a certain point and then decompress and get the crew out. The deepest depth to date in a chamber run with humans, that I can remember, is a bit more than 2,000 feet. Decompression required three weeks.

 

[Warhammer]

Thanks for the info Dr. Deco, I find that fasinating. I had no clue that it had already been done. I didn't think we had the technology to construct a sub that could withstand the pressure at those depths. I wander what the crew was thinking when they passed the 30,000 ft mark.