The Dive Bell effect?

[Arun Vajpey]

When the Titanic broke-up, the inter-deck spaces in the stern were exposed to the sea which would start flooding in very rapidly. But could the several bulkheads between the exposed area and the extreme aft section of the broken stern have temporarily slow down the flooding? If so, in those 20 or 30 seconds, the water-laden and sinking bow dragged down on the stern section at the still attached keel, forcing the stern into a near upright position. When that happened, would not any trapped air in the stern section displace to the extreme aft part? Then, when the stern itself started to sink, a lot of this air would escape through open portholes and other exposed spaces allowing water to flood in, but in the central-rear areas without an outer ‘hull wall’ might air be trapped a bit longer due to a “dive bell effect”? If so, could someone trapped in such spaces have remained alive for another 1 or 2 minutes after the stern sank beneath the surface before becoming overwhelmed by the flooding and/or implosion?

 

[Michael Kestner]

In short...yes, a scenario like what you described is very possible...and I can't imagine a more horrifying way to go.

 

[K9Thefirst1]

I'd say that is what happened. After all, such a pocket of air would lead to violent implosions, which is most likely what did most of the damage.

In short...yes, a scenario like what you described is very possible...and I can't imagine a more horrifying way to go.

Well, while for a while you would have known you were done for, the implosion itself would have been so quick that you wouldn't even know what happened.

Like Lovett said in the movie: "...if they go, it's 'saiyonara' in two microseconds."

 

[Scott Mills]

Yes. There is another thread on this somewhere you should read.

It is apparently possible, depending on the area of, the shape of, and strength of the surrounding materials creating the "dive bell", possible to very deep depths. I have a good friend who was formerly an engineer on an attack sub in the US Navy. He has told me his greatest fears were fire and being so trapped at a depth, far below crush depth, with no chance of rescue. Every other sinking eventuality did not scare him in the least, as the implosion would take him instantly and most likely without warning.

 

[TimTurner]

I'd wager that any living person who rode the Titanic down would have been knocked unconscious about the time the stern went vertical and sent everything inside flying. Also to consider, although the air pressure would keep the water out of "diving bells", those air pockets would still be exposed to full sea pressure, which would have been up to 6500 pounds per square inch 2.5 miles down. So anyone still onboard would have had the rapidly increasing pressure to deal with.

 

[Scott Mills]

I don't think a pocket, on Titanic, would survive to that depth (2.5 miles).

You'd have to talk to an engineer about this, but you'd be surprised at the pressure a human body can withstand. For instance, in water the human body would not feel the effects of pressure at all--if you were magically transported to Titanic your eardrums would burst, your lungs deflate and some unpleasantness would befall your sinus cavity, but after that you'd be fine and at equilibrium with the surrounding water--with the exception of being unable to breath.

The saving grace for someone trapped in a "dive bell" as Titanic sank would be the way in which gasses under pressure interact with the human body, and you'd eventually lose consciousness.

 

[Scott Mills]

Just checked on this. The human body will compensate and not be effected by mechanical pressure (in the air) until over 10,000 psi; However the Nitrogen and Oxygen start becoming highly toxic at about 15 atmospheres, or roughly 220 psi.

It wouldn't take long for you to become incopacitated after reaching this level, at about 500 or so feet underwater.

 

[TimTurner]

Adding to the discussion here, we'd need to account for the sinking velocity of the stern section, and the depth at which it imploded. I read here somewhere that it imploded several hundred feet down (very approximately ~500). If the Titanic sank at an average of 5mph (7.3 feet/sec) it would reach 500 feet in about 70 seconds. So not only would people be facing the increasing pressure, but the rate of increasing pressure, which would have substantial effects. This would be like airplane pressurization, but as much as 15 times the difference in pressure in about a minute).

Combine that with the diesel effect (increasing the pressure of a fluid rapidly increases its temperature). So I expect the trip might have been rather warm. I understand a standard diesel engine compresses it's fuel/air mixture by a factor of 15 or 20, I don't have the math, but from surveying the internet, the corresponding temperature could have been a couple of hundred degrees. After thinking this over, it's quite possible that the inside of the stern section was on fire by the time she imploded at about 500 feet.

As horrific as it might sound to be thrown sideways against the bulkhead of an upended sinking ship, then dragged in a blazing inferno into the frigid deep, while the air rapidly tried to equalize through your sinuses before the ship imploded, I think that was probably a more pleasant fate than slowly freezing to death on the surface. After the stern slipped under, this wouldn't have lasted more than a minute or two, and the adrenalin rush or lack of consciousness would have carried you through that.

EDIT: Not to say that I don't have a morbid fascination with the idea of actually reaching the bottom alive and having to wait for the air to run out, but I don't think the people trapped inside would have suffered as much as it is generally assumed.

 

[TimTurner]

Oh, and I didn't mean to suggest that there would be air pockets that survived all the way down to the sea floor in my earlier post. I just used the maximum pressure that would have been reached. Obviously the air pockets would have mostly disappeared at the point the stern imploded, and I didn't have an estimate for that depth when I originally posted.

 

[TimTurner]

Come to think of it, it may have been possible that the implosion was accompanied by a steam explosion. The water would have compressed the air inside, the air would have heated up to several hundred degrees, the hot air would have boiled the "surface water" of the air/water boundaries of the air pockets. The water would have expanded by over 1000 times, and the stern would have exploded.

Has anyone done any studies on this?

 

[Scott Mills]

Tim,

I wouldn't worry about being fascinated with such an idea. While, morbid, I think it is pretty normal for one's mind to wonder about this possibility. For instance, it has been years since I've seen the filme "Raise the Titanic," but as I recal this is portrayed in that film. In order for it to have occurred, however, one would have to be trapped in a sealed watertight portion of the ship where normal atmospheric pressure was maintained.

I somehow doubt this was possible at the pressures Titanic experienced, though it would, again depend on the size, area, shape and strength of the materials surrounding the sealed area.

 

[TimTurner]

I doubt any air pockets survived to the bottom. At 6500 psi, there aren't many man-made objects which can resist. Put that kind of pressure on a 10-foot wide wall, and it will crumple like saran wrap. The "air tight" cell in Raise the Titanic (about 10ft by 10 ft by 8 feet) would have had just under a million pounds per square foot pushing in on it. There just aren't any walls on Titanic capable of withstanding that kind of pressure, except maybe some parts of the hull.

Any air-tight space would have been crushed by the pressure. Any open pocket of air (such as would have formed in 3rd class open berthing, or the Seanman's berthing) would have been crushed to about 1/400th of it's original volume. Which is not impossible to survive in. However, I think the Diesel effect would have burned anything organic in an open air pocket.

 

[Scott Mills]

Right. And even would the Diesel effect not prove fatal, and a pocket 1/400 of its original volume still large enough for someone to stand in, somewhere between 500 and a 1000 feet anyone in the pocket would have succumbed to oxygen and nitrogen toxicity. So it is virtually impossible for anyone to have survived all the way to the bottom.

 

[Arun Vajpey]

Sorry to have resurrected this thread after over 2 years but for me somehow the possibility of some people surviving even for a short time within the stern section has become something of a horrific nightmare.

I accept that any air pocket would have lasted only till the stern section imploded. Accepting the above theories, if it occurred at around 500 feet, it would still have taken 70 seconds to reach that depth. To my thinking, that is a very long time for someone being pressurised to death or even be simply conscious in the darkness knowing what was to come.

Regarding 'flying objects' when the stern section became almost vertical, is that not unlikely in enclosed spaces (where we could expect air pockets)?. The stern was gradually rearing up earlier as the still intact Titanic sank from the bow and any loose objects would have gradually slid down towards the 'dependent' bulkhead. Although the stern dropped back after the bow section broke away, it did not completely regain the horizontal position and so it is theoretically possible that a few people deep inside the bowels of the ship were at the time uninjured and conscious in pitch blackness. Some of them might have survived for most of those 70 minutes and it is that scenario that haunts me.

For reasons that I simply cannot explain, I keep thinking that something like that happened to Finnish second class passenger Marta Hiltunen.

 

[Arun Vajpey]

Some of them might have survived for most of those 70 minutes and it is that scenario that haunts me.

Sorry, my bad. I meant 70 seconds, of course.

 

[Olblindman]

The more recent theories suggest that the stern did not raise up as high as previously thought before the ship ripped in half. That would allow water to rush in more uniformly, reducing the chance of air pockets, although certainly they were created. I doubt if anyone would have survived too long, either way. I doubt they would have made 70 seconds....

 

[TimTurner]

Arun asked me a year ago, and I've just opened my messages now. I've done the rough math, so I figure the community should benefit from it:

Mr Turner, I want to ask how much this effect would have affected any people trapped and alive in the stern section of the Titanic. There is a chance that a few of them would have been trapped in relatively small compartments at the extreme stern well within the bowels of the ship. In that case, those areas would have taken longest to flood and some air pockets probably still remained until the stern imploded at about 500 feet depth. Also, if there were no large loose objects there, the persons might have remained relatively uninjured and conscious.

If you hypothesise this scenario, what would be the air temperature gradient in those 70 seconds (I think you said elsewhere) that it took the stern to reach 500 feet?

Sorry, I have been gone for some time. - nearly a year.

If you are still interested, here is my answer:
The water pressure increase would have increased as the depth increased. This would have been nearly instantaneous (within probably 10 or 15 seconds, but hard to say). The water would have, in turn, pressurized the air. This would have been even more nearly instantaneous (a second or less). So the pressure of the air in the Titanic would have been almost the same as the water around it.

So the speed of pressure increase would have been the speed the Titanic sank. Seawater pressure is 1/2 pound of pressure per square inch every foot, as a general thumb rule (14.5 psi every 33 feet to be more exact). At 33 feet, the pressure is 14.5psi, at 100 feet it is 43.5 psi. (14.7 psi is the pressure humans are accustomed to from the weight of Earth's atmosphere, and we call this pressure "1 atmosphere" of pressure.)

We don't know for certain, but as general knowledge, the Titanic sank at about 30 mph and took about 5 or 6 minutes to reach the bottom. The Titanic is 12500 feet down, which means that it descended at about 2500 feet per minute, or 41.6 feet per second. That means the air pressure would have increased proportionally (41.6 divided by half) which gives us about 20.8 pounds per second.

We also need to remember that the Titanic didn’t fall at an even speed. It would have started slowly, picking up speed, until it hit Terminal Velocity of about 30mph in sea water (if you remember from High School physics, this is the speed at which the force of friction will equal the force of weight of the object, so downward acceleration stops. Friction is greater in water than air, so terminal velocity is much lower for a sinking ship than a falling airplane).

https://en.wikipedia.org/wiki/Gas_compressor#Temperature

Using the formula:
T2 = T1 (P2 / P1) ^((k-1)/k)
We can calculate the temperature. We must also use absolute temperature and pressure, so what we consider normal air pressure is actually 14.7 psi, and we must add the weight of this air to all our water figures, too (because the atmosphere is pressing down on the ocean water). We also will need absolute temperature. I’ll use Rankine degrees, because the math is simpler conversion to Fahrenheit (just add about 460).

K is a constant, which is about 1.4 for air.

If we assume the air temperature below decks on Titanic was 50 Fahrenheit degrees (+460 = 510 Rankine degrees), and 14.7 psi at the surface. At 500 feet (reached in about 12 seconds) pressure would have been about 220 psi (plus 14.7 atmosphere). We can calculate:

T2 = T1 * (P2 / P1) ^((k-1)/k)

T2 = 510 * (234.7 / 14.7) ^((1.4-1)/1.4)

T2 = 510 * (15.96) ^(.2857)
The 15.96 is our compression ratio. A typical diesel engine has a compression ratio of about 14-22 (source wikipedia).

T2 = 510 * 2.2

T2 = 1125 Rankine degrees

-460 to convert back to Farenheit

Gives us 665 Farenheit degrees final temperature (351 C). That’s a 615 F increase over 50 F (10 C). This would have happened in about 12 seconds so, 51 F per second (28 C per second). Or using the original 70 seconds, 9 F per second (5 C per second)

Granted , this is rough math. We don’t know the interior temperature of the Titanic before the sinking, but we can assume it was mostly around 50-60 F degrees. 70 F is normal room temperature. Exterior temperature was recorded as 48 F degrees, and we know they were turning heaters on because they felt cold, in 1st class and the bridge so we can assume that 3rd class probably wasn’t too much warmer than outside air (at least, somewhere between 48 F and 70 F).

We must also remember that the seawater was near or below freezing. This would have sucked heat out of the Titanic, like putting a boiling hot pot in the freezer. It won’t stay hot for long.

Finally, the Titanic started sinking slowly, then picked up speed. It probably took a bit longer than 12 seconds to reach 500 feet. Probably closer to 30 seconds or a minute. It’s maximum speed was about 30 mph. If it was 70 seconds, that would be a bit less than 9 F per second (5 C per second).

Which means it was a very hot ride down, and if you hadn't already passed out from the pressure and heat, you were probably grateful when the ship imploded in the crushing embrace of freezing waters.

Yes, morbid, I know, but something a submarine sailor thinks about.

 

[Christophe Puttemans]

I'm still trying to imagine what would happen to somebody trapped in the giant air pocket when the stern broke free from the bow and started to sink. Let's place this person in the First Class Smoking Room, and assume that room was torn apart at the first big implosion which caused the stern's pitch to level off. Would he still be alive by then, conscious and wondering what the hell was happening, or would extreme heat and pressure have killed him already?

 

[TimTurner]

I doubt the 1st Class smoking room would not have formed much of an air pocket, the large glass windows would have burst, and doors would have let the air out very quickly. When I think of air pockets, I usually think of 3rd class berthing down on F and G decks, perhaps some of the food storage spaces.

I don't know that anyone has studied the question deeply. You'd want a doctor to fully answer that. I don't know about the pressure - hopefully it would knock you out. But rapid pressure would probably damage your ears, lungs, and eyes, and be extremely uncomfortable to very painful. That would probably be overshadowed though, because the temperature would be hotter than an oven, and at some point the floors and woodwork (possibly your clothes) might catch on fire.

I would guess most people would be in pain for 30 or 40 seconds before passing out, and some people might have been alive for a full minute or two before the stern exploded and everyone died, but I certainly don't know.

 

[Christophe Puttemans]

Thanks, I know enough for now on that topic.