Request for accuracy for a film...

[Wookie]

First. I would look skeptically at someone locking out of a chamber on a sub pressurized at 1 ATM and doing a free ascent. However, with the modern equivalent of a Momson lung, run of the mill US Navy submariners are taught exactly that. I don't know the effective usable depth of a Momson lung, it would take a submariner to know that. I was a surface guy.

Second. I would look skeptically at someone locking out of a submarine in street cloths at 400 feet and swimming to an open chamber. Not because SEALS don't do it all the time, they do. But they aren't wearing street cloths, they have a mask on to see underwater. Besides, at 400 feet, it's damn cold. Real cold. Cold is a real problem.

So, locking out of a pressurized submersible isn't a big deal, but having the correct tools to get to the surface or to a open bell is. Without the correct tools, chances of survival are in the realm of way less then 50/50. With the right tools the chances of survival are very high. Maybe you could give the hero a mask and make him drag the unconscious heroine through the water with a kraken chasing them to lessen the odds somewhat?

Sharks. Need to get sharks in there somewhere.

 

[MikkelBC]

I understand that freediving has less chance of the bends due to the time involved?

Freedivers don't get the bends because they don't breathe compressed air. It is the compressed air that causes the increase of dissolved nitrogen in your tissues that can then become bubbles when decompressing.

 

[pbnj]

This is kinda where industry people lose interest and tell you to just make things up. But I'd really rather not. If the movie were to be Mythbusted, I'd like it to at least grade 'Plausible'.

Let's MacGyver for a minute...

Proper equipment is not going to happen, or else there's no movie. Mylar space blankets are in supply on the vessel because of the temperature of the depths worked at. Let's not go full duct tape, but if these blankets were to be wrapped and sealed watertight, would they stand up enough as an improvised suit to reduce cold for an ascent? Not toasty warm, but I don't need it to be.

Tanks, rebreathers etc. are out, because loss of life support is what forces them out of their vessel. But what about a makeshift Steinke hood with enough captured air to help the ascent? Not all of it, but enough for a fighting chance?

---------- Post added May 5th, 2015 at 09:56 AM ----------

Freedivers don't get the bends because they don't breathe compressed air. It is the compressed air that causes the increase of dissolved nitrogen in your tissues that can then become bubbles when decompressing.

But taking your breath (or captured air) from inside a submersible pressurised to 1 ATM and then exiting to ascend would solve that problem?

 

[Storker]

But taking your breath (or captured air) from inside a submersible pressurised to 1 ATM and then exiting to ascend would solve that problem?

And how are you going to exit the sub before the pressure is equalized? That'd be pretty difficult. And it'll take time to pressurize the escape chamber, during which you need to breathe. While the pressure is increasing to match the outside pressure. So you will exit the escape hatch with pressurized air in your lungs. And during the ascent you need to allow that air to escape as it expands, otherwise your lungs will burst. But if you're lucky, your ascent is fast enough that any bends incurred will at least be survivable. As the saying goes: you may cure bent, but you can't cure drowned. If you make it to a submerged diving bell, you'll incur a deco obligation in the bell. That obligation will take quite some time to clear, and at the depths you're talking about that bell would be filled with a He mix rather than air.

Disclaimer: I don't know whether or not a free ascent from a stranded sub at depth will put you at a significant risk for bends. I'm just speculating and pointing out possibilities.

 

[Wookie]

You have to have a lock of some sort. If you were to slam out of a sub from any extreme depth and go from 1 ATM to 15 ATM would just mess your ears so bad that you wouldn't be able to tell up from down. Vertigo will be a big enough problem with the hit of ambient temp to something in the 30's. Your hero needs something to breathe on the ascent. Doesn't necessarily have to be breathable, but he needs his lungs operating correctly, otherwise the urge to breathe will drown him. Anything will work, 5 gallon bucket with air over his head, space blanket duct taped, whatever, but if the air volume is too large it will rip it from his hands.

 

[Yankee_Dive]

Following the MacGyver angle you might want to look at this:
http://balmaha.net/mnavy/l/orpheus_submarine_escape.jpg

It’s a newspaper article about a training exercise conducted in 1965, in which a group of 8 men (successfully) “escaped” in a free ascent from a sub at 500 feet. The article says “A one-man chamber in the torpedo space was used, and the escapees were fitted with a cotton fabric hood and plastic face plate”

More details can be found at the link just below, which is a fascinating document in its own right: “A Review of Submarine Escape Trials From 1945 to 1970, with Particular Emphasis on Decompression Sickness”
http://www.dtic.mil/dtic/tr/fulltext/u2/729735.pdf

Page 8:

Upshot IV (HMS OHPHEUS) July 1965
This trial was carried out in the open sea in July 1965. Maximal keel depth was 500 ft. (escape depth 475 ft.). The escapes, which were without untoward events, are detailed in Table 11. Compression (pressure doubled in constant time) was achieved in 25 seconds, time on bottom was 4 seconds, rate of ascent 3 ft. per second. Maximal SPdt was 207 h.f.s., an extremely safe figure at this depth as judged by previous human and goat experiments (see Figures 2, 3 and 4). Upshot IV emphasized the remarkable success and potential of this method of escape. No important narcosis was felt by the subjects, thus confirming the findings of Bennett, Dossett and Ray (21). The hood inflation system through the buoyancy stole worked extremely well. Lieutenant Commander Todd reported that he considered that no special ability or lengthy training was required by the escapers.

Note that your hero will still need a lock of some sort, to be able to pressurize to near the ambient water pressure at depth before leaving the submersible.

 

[pbnj]

In the absence of a lock, would flooding the whole submersible work if you were to capture air in an improvised hood first?

And if you were to go from a submersible at 1 ATM to 15 ATM outside and then to a bell pressurised at depth (maybe a little higher up at 10 ATM), stop for a few minutes to refill your hood and then go for the surface - would that stop in the bell and its He content really throw you off?

My thought was to stop at the bell, despite the risks, to retrieve life jackets to make the rest of the ascent faster. Or is this way off base?

And here's one that is completely Hollywood:

Would referring to PSI instead of ATM underwater be just absurd? It would be an embellishment for drama, because the more dramatic jump in numbers between atmospheres is easier for the average joe to derive tension from. Going from 220 PSI to 14 PSI sounds more dramatic than going from 15 ATM to 1 ATM.

Thanks again, guys - this is unbelievably helpful.

 

[CT-Rich]

The only combat escape from a sub in WW2 was from the USS Tang. Their boat made a couple kills in shallow water in the China Sea. The likelihood of surviving the escape was so low that several crew members decided to suffocate rather than make a swim for the surface. Here is a brief account of the escape. There is an excellent book about what they did and their time as POWs.
U S Sailors Escape from Sunk Submarine in World War II by being Trained | characterqualitystories.com
Get to a diving bell would be risky because you are unlikely to find it without a guide rope. The escape lungs are not really designed for staying at depth for very long. There some options that you could look at for getting out of a marooned sub. First and most likely is to have escape chamber that you pressurize and flood. This would be the way the sailors from the Tang escaped. The second would be to simply flood the hull and let the available air pocket be compressed and then swim out of the hull. This has been done but not without outside help. A Nigerian cook on a ship was the lone survivor of her sinking and was trapped in an airpocket for 3 days at 90 fsw. Divers found him, alive, kitted him out with a helmet and guided him to the a decompression bell. The final option would be to blow air into the hull (I'll assume there was a rupture of the ballast tanks that has permanently crippled the sub) and pressurizing the interior to ambient pressure and then swimming out. If you are going for realism, sink her in 100 fsw or so. The bends will almost guarranty a REALLY painful death from anything much deeper because they will accumulate nitrogen so quickly at deeper depths. Having them sit in a recompression bell and coming up from 300 fsw, they will need to breath helium (giving them squeaky voices), be managed by an expert in saturation diving and have them sit in a tin can for hours or days on end. If you don't think 100 fsw is impressive, stand at the base of a 10 story building and look straight up. Deep diving is a pretty hairy affair if not carefully planned. I would suggest reading up on what happened to the Rousses, very, very ugly death.
The Last Dive: A Father and Son's Fatal Descent into the Ocean's Depths: Bernie Chowdhury: 9780060932596: Amazon.com: Books
You may want to also read up on decompression diving with a book like Deco for Divers, which will give you an idea of the technical hurdles involved in being deep.
Deco for Divers: A Diver's Guide to Decompression Theory and Physiology: Mark Powell: 9781905492299: Amazon.com: Books
If you can find a reason to keep the sub shallow (like it is hung up on a oil rig or trying to infiltrate a harbor in war time, you will make your story much more believable. If the pressure hull cracks on a sub even at only 300 fsw, it is a death sentence. The likelihood of getting out alive is pretty much zero even for a trained submariner. The deepest recorded escape was one really lucky bastard in 1945. He made it to the surface from 210 fsw. Incidently, he also used my 2nd method of escape from his X11 mini-sub that was rammed near the surface.
You can read about him in his obituary:
Burgh man made deepest submarine escape

 

[Yankee_Dive]

Wow, the story of the escape from the X11 is amazing!

 

[CT-Rich]

In the absence of a lock, would flooding the whole submersible work if you were to capture air in an improvised hood first?

And if you were to go from a submersible at 1 ATM to 15 ATM outside and then to a bell pressurised at depth (maybe a little higher up at 10 ATM), stop for a few minutes to refill your hood and then go for the surface - would that stop in the bell and its He content really throw you off?

My thought was to stop at the bell, despite the risks, to retrieve life jackets to make the rest of the ascent faster. Or is this way off base?

And here's one that is completely Hollywood:

Would referring to PSI instead of ATM underwater be just absurd? It would be an embellishment for drama, because the more dramatic jump in numbers between atmospheres is easier for the average joe to derive tension from. Going from 220 PSI to 14 PSI sounds more dramatic than going from 15 ATM to 1 ATM.

Thanks again, guys - this is unbelievably helpful.

If you want a dramatic illustration of what happens.... kill someone. have a character die in an accident. An embolism will make it pretty clear what you don't want to have happen. air at 10 atm is one tenth the volume of what it would be at the surface a liter of air will compressed to 10 atm will expand to 10 liters at the surface. if you fail to vent that from your chest.... well, lets just say drowning will not be your big problem....

Soda will be flat at just a couple of atm. if you want to see something really graphic. watch some Youtube videos of a soda bottles with dry ice in them. they have a rupture pressure of aound 200 psi. they will easily take your hand off.
https://www.youtube.com/watch?v=Zu0lQyOpw_I