I’ve heard a few journalists mention that if they ever get any of the crew into the rescue vehicle its a four hour journey to the surface because they have to decompress.
Now wait a minute.
Subs rely on the strength of their metal hulls to hold back the water’s pressure. And so do DSRVs (they’re just small subs). You couldn’t use a diving bell (a simple craft which relies on air pressure to balance the water pressure) for a sub rescue at depth because of the pressure difference between it and the sub. Open a hatch between them and WHOOSH! The bell & sub are both (nearly) at 1 atmosphere and the guys in the diving bell are dead. You could use an airlock, but why? A sub rescue device would simply be made to withstand high pressure thru hull strength.
So are the media guys just idiots (perish the thought)?
If the question is whether media guys are idiots…well that’s an easy one.
Regarding the sub-rescue, I thought the problem with the DSRV use was that the sub is at some funky angle that won’t allow a proper attachment.
I had honestly thought (no doubt incorrectly) that people aboard submarines were under 1 atm of pressure like at the surface (i.e. the massive hull held the water back, but I profess to being an idiot regularly on this board, so please don’t flame me when I’m clearly wrong :)) I heard the whole decompression thing too and was also confused by that because my thinking was…
Sub is at 1 atm
DSRV is at 1 atm
surface is at 1 atm
ergo…direct attachment of DSRV to sub, get people out, and be able to instantly go to the surface.
That said, I do remember a submarine guy here at work saying they have to do an exercise where they blow out yelling Ho Ho Ho like Santa Claus to keep their lungs from exploding in an emergency assent through the water which MUST imply they are ‘under pressure’.
the media idiots seem to be ignoring the pressure issue. We (USA) have a special rescue sub that attaches to a port on the stranded sub to allow the crew to get out. We gave the ruskies the design of this port so then could equip their subs w/ it. We don’t know if this sub has it or not - they didn’t ask us for our help even though it was offered.
I believe our rescue system will allow 1 atm or allow some pressure since a damaged sub might be leaking or might have to rase internal pressure for some reason. the ruskies I believe use (or tried to use) the diving bell method because that’s all they have. the crew member would have to equalize to the u/w pressure and trasnfer to the bell - not an easy task evident by the number of crew members that have been rescued
I think you’re right about the interior of the sub being kept at (about) 1 atmosphere. The rigid walls of the pressure hull bear the stresses caused by the pressure difference. Go down deep enough, and those stresses will be too much for the material…SQUISH.
The emergency ascents are generally made from what they call “escape trunks”, which are essentially airlocks. Two crewmen at a time (I think that’s all they’re big enough for) enter the escape trunk and shut the hatch in the floor that leads to the interior of the boat. In the ceiling is a hatch leading out. They then pressurize the trunk and fill it with water (in that order?), pop the exterior hatch, and rocket to the surface on their own buoyancy. Their last breath of air before leaving is at the pressure of that depth (many atmospheres), so if they didn’t exhale on the way up terrible things would happen as their lungs tried to expand drastically in volume.
So, basically, they’re not under local water pressure until they are just about to leave the boat, at which time they have to be - the escape trunk serves at the space in which the pressure is gradually brought up from 1 atm to whatever it is outside.
I’ve seen pictures of the Steinke hoods that they wear when doing this kind of escape, but I’ve never gotten a decent explanation of what they do, or why they help. Does anybody know?
Nope. The country that we spent zillions defending against was the Union of Soviet Socialist Republics. The country which currently has a sub stranded on the bottom of the Bering Sea, and which recently did finally request international help, is Russia. The land that is now Russia was once part of the USSR, but the government has changed, so it is no longer the same country.
The interior of the sub is at one atmosphere (about 14.7 psi).
If part of the sub is open to the ocean, the volume of the air trapped inside that part would be reduced to about 1/8 of the volume at 1 atmosphere, since the pressure would be about 9 atmospheres. That’s based on a depth of 320 feet. A lot of different depths have been reported by the media. (Maybe they don’t know the difference between meters and feet). That means that a compartment that is seven feet high would only have an air space of about .9 feet high. Not a lot of space for anyone trapped in it to expel carbon dioxide into . Note that the carbon dioxide build up would kill you before oxygen depletion would. You only use a small portion of the available oxygen in each lungfull you inhale, but exhale a significant amount of CO2. Rebreathers used by divers take advantage of that and remove the carbon dioxide while adding small amounts of air or oxygen back to the air that has been breathed. That allows them to stay underwater much longer (maybe 4 to 6 times as long) on one tank of air.
If the bell is pressurized to 9 atmospheres for the transfer, the four hour decompression time seems too long. I don’t have the tables here with me and I have never made a dive deeper than 125 feet, so I could be off on this, but as I recall, you can stay at 130 feet for 15 or 20 minutes before you incur a decompression obligation. You should have two or three minutes at 320 feet before decompression is required.
If the transfer to the bell took 20 minutes or so - which seems reasonable - I don’t think the decompression time required would be four hours. But I could be wrong about that.
A couple of follow up questions.
Assuming the pressure vesel has been breached (per your scenario above) since day one, wouldn’t the submariners have fully saturated their tissues with nitrogen by now ? Would oxygen toxicity be a factor ?
Steinke hoods are basically watertight hoods with a clear faceplate, which are put on in the escape trunk after pressurization. When the trunk is then flooded before the hatch is opened, the sailors have a small air space around their head. The Steinke hoods help because the “bubble” of air around your head is much more reassuring while you are “ho-ho-ho-ing” up to the surface than a bare-headed ascent would be. Also, the hood allows the eyes to be protected, so that the sailors can “steer” (theoretically) as they approach the surface at high speeds, avoiding collision with rescue vessels and their companions.
Here’s the thing about submarines: they are constructed as a series of watertight compartments. Between each two compartments are sealable doors which are capable of holding against the pressures expected to be encountered in a flooded compartment during a dive. In order to keep the rest of the boat from flooding, the bow compartment door would have been latched and sealed as part of the casualty response (along with all the other WT doors between compartments).
The pressure in the Kursk is probably very close to 1 atmosphere, but there are alot of variables (pressure in the boat at the time it came to rest, how much air has been released into the boat from compressed air tanks, temperature drop, etc.) The DSRV (assuming they can dock with the Kursk) will have to equalize pressure around the hatch, but there will likely be no tremendous difference, and there will certainly not be 9 atmospheres of pressure.
Oblio said “Assuming the pressure vessel has been breached (per your scenario above) since day one, wouldn’t the submariners have fully saturated their tissues with nitrogen by now ? Would oxygen toxicity be a factor ?”"
In areas that are breached, I believe the people would be dead in a short period of time from either the cold or from Co2 build up in the reduced volume of the trapped air space.
If they were somehow able to survive in a trapped air space oxygen toxicity might or might not be a problem.
I believe the current recommendation for the max oxygen partial pressure is about 1.4 atmospheres, but I did read the other day that the Navy was changing their recommendation to 1.2atmospheres.
At nine atmospheres the oxygen partial pressure would be about 1.8 atmospheres which is high enough to cause some people to have convulsions some of the time. However a lot of people have made dives to oxygen partial pressures of 1.8 and 1.6 atmospheres without problems. It’s one of those areas where we don’t have good models and can’t do a real good job of predicting what will happen.
xenophon41 said: “there will certainly not be 9 atmospheres of pressure.”
Please take another look at my post. I was talking about areas with trapped air that were open to the ocean. Those areas would have pressure equal to the ambient pressure of the seawater .
The more the things change the more they stay the same. The reason why the crew members are dead now is because Putin was too proud to accept help from his former enemies. I hope the family members stone him to death.
You’re quite correct, Diver, and I did not mean to imply that your information regarding a trapped air bubble was incorrect. My point was that, because the bow compartment would’ve been sealed off from the rest of the boat as a first action (and during training evolutions involving battle stations, the WT doors would’ve been sealed anyway) the remaining parts of the boat will not be at surrounding sea pressure. Any crew members trapped in the flooded compartment would have perished quickly.
Bad enough that you’re trapped underwater but I can’t imagine what it would be like to have to close the doors on your comrades to save yourself.
The way the news portrayed it the rescue craft would be blown off the Kursk upon docking.
This was covered in the Novel ‘Cryptonomicon’ by Neal Stephenson.
(VERY simplified explanation): Assume that a sub has a normal of one atmosphere. There is a hull breach, forcing the sub to sink… the sub goes down with the breach first, and the air ‘puddles’ at the other end. As the sub fills w/ water, via water pressure, the trapped air is forced into a smaller and smaller bubble, thus INCREASING the atmospheres. The body gets supersaturated w/ nitrogen, so if not decompressed properly while returning to the surface the sailors get The Bends.