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  #1  
Old 29 May 2007, 07:08 PM
TuFurg TuFurg is offline
 
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Default Ocean water pressure and LOST

This question is regarding debate over a scene from LOST.

Bascially in this scene, a good guy is in an underwater station and has locked himself in a room with a window about 2/3 up the wall. A bad guy blows open the window and water floods in drowning the good guy.

There is discussion on the net about how the water should not have come into the room past the height of the window, while others are saying that the pressure of the water would squeeze out the air. Without knowing the exact depth of the station, is there a way to tell which case would actually happen in real life?

While the exact depth is unknown the station can be scene from the surface if directly above it (I'm guessing at least 200 feet down), and the station would be several hundred yards from the shore. IMO the room is probably about 50 or so square feet with a ceiling of no more than 8 feet.

Anyone care to comment?
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  #2  
Old 29 May 2007, 07:16 PM
Bryan With a 'Y''s Avatar
Bryan With a 'Y' Bryan With a 'Y' is offline
 
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As I understand it, water pressure wouldn't squeeze out the air (force it out the window below), but it could squeeze the air (compress it). That assumes that the room isn't already pressurized for its depth. That would require much sturdier engineering, but would likely be the case if the air supply is connected to the surface. If there were some form of ventilation in the ceiling, presumably one without an easily removable grate that a person could fit through, the pressure of the water could force the air back through the ventilation system, filling the room and killing your good guy.

But I'm a social scientist, so make of that what you will.
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  #3  
Old 29 May 2007, 07:45 PM
Alchemy Alchemy is offline
 
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Bryan's right; if the room is sealed all the air below the breach will be exchanged for water and all the air above the breach will be compressed.

At 200 feet below sea level, pressure is about 7 atm. If the room was at 1 atm, the volume of the air left would be compressed to 1/7th the original volume. So if the breach was 28 inches below the ceiling, the water would compress the air into a space about 3 inches below the ceiling.
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  #4  
Old 29 May 2007, 08:12 PM
Pseudo_Croat
 
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Quote:
Originally Posted by Alchemy View Post
At 200 feet below sea level, pressure is about 7 atm. If the room was at 1 atm, the volume of the air left would be compressed to 1/7th the original volume. So if the breach was 28 inches below the ceiling, the water would compress the air into a space about 3 inches below the ceiling.
Now here's the next question: Assuming you survived the initial onrush of water into the room, would it be possible for a person to breathe the now-highly-compressed air in the top of the room (say, to prepare oneself for swimming to safety)?

- Pseudo "ay, air's the rub" Croat
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  #5  
Old 29 May 2007, 08:20 PM
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Keeper of the Mad Bunnies Keeper of the Mad Bunnies is offline
 
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However, the station in Lost is already established as not being connected to an outside air source. It is pressurized enough to support the 'moon pool'. This pressure is throughout the station as the door was open to the moon pool room.

As such, the water should have stopped within a reasonable distance above the port hole that was removed. There is no place for the excess air to go. if it went into the room with the moon pool, then the water would have risen in the moon pool and come to an equilibrium (the same as if the door had been left open).

James Powell
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  #6  
Old 29 May 2007, 08:23 PM
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Quote:
Originally Posted by Alchemy View Post
Bryan's right; if the room is sealed all the air below the breach will be exchanged for water and all the air above the breach will be compressed.

At 200 feet below sea level, pressure is about 7 atm. If the room was at 1 atm, the volume of the air left would be compressed to 1/7th the original volume. So if the breach was 28 inches below the ceiling, the water would compress the air into a space about 3 inches below the ceiling.
Quote:
Originally Posted by Pseudo_Croat View Post
Now here's the next question: Assuming you survived the initial onrush of water into the room, would it be possible for a person to breathe the now-highly-compressed air in the top of the room (say, to prepare oneself for swimming to safety)?

- Pseudo "ay, air's the rub" Croat
If the pressure was high enough to compress the air significantly, I believe the human body would not survive. You would not have to worry about breathing the compressed air because you would already be crushed.

At lower pressures, there would be no harm in breathing the slightly compressed air.

James Powell
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  #7  
Old 29 May 2007, 08:23 PM
jimmy101_again jimmy101_again is offline
 
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Quote:
Originally Posted by Alchemy View Post
Bryan's right; if the room is sealed all the air below the breach will be exchanged for water and all the air above the breach will be compressed.

At 200 feet below sea level, pressure is about 7 atm. If the room was at 1 atm, the volume of the air left would be compressed to 1/7th the original volume. So if the breach was 28 inches below the ceiling, the water would compress the air into a space about 3 inches below the ceiling.
Based on the design of the submerged building the pressure in the room started off at 7 ATM. (Or whatever it would be based on it's depth.) The building is basically an inverted cup with air trapped inside. The pressure of the air is the same as sea pressure at the depth of the water inside the cup measured back up to sea level.

The building could not be as deep as 200 feet, I seriously doubt if your average joe can free dive to a depth of 200 feet. Besides, you cant see anything through 200 feet of sea water. A more reasonable estimate is probably 50 feet or less to the bottom of the station.

The room would have filled with water until the water was at the top edge of the window. There would have been enough air trapped at the top of the room for Charlie to breath (assuming the top edge of the window was not at the cieling) and it would have been at about the pressure the room was at before the window was broken. Charlie should have been able to swim out the window (if he could fit through it, and it sure looked like he could), and to the surface, once the water had stopped flowing.

The water would not have entered the room as a solid stream as shown. It probably would have gone "galunk-galunk-galunk" as air and water took turns going through the broken window.

The only way that things could have happened as shown would be if the explosion blew out the window and cracked/broke the structure somewhere above the window. Then you would have had water coming in the window as air exited through the higher breach in the room. The room would have filled with water up to the level of the breach. If the breach was in the cieling then the room would have filled completely with water.
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  #8  
Old 29 May 2007, 08:25 PM
Deepfrydegg
 
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My Two Cents
1) I watched the episode, I don't think they were 200 feet below, but that is subjective and kind of irrelevant.

Quote:
Originally Posted by Alchemy View Post
Bryan's right; if the room is sealed all the air below the breach will be exchanged for water and all the air above the breach will be compressed.
We are assuming the door (water tight, when sealed) was the only way Air was getting in. I would propose that there was another way for air to enter the room, and a way for air to escape so the water would fill the space.
I could be wrong on that, I am not an engineer in underwater design.

Quote:
Originally Posted by Pseudo_Croat View Post
Now here's the next question: Assuming you survived the initial onrush of water into the room, would it be possible for a person to breathe the now-highly-compressed air in the top of the room (say, to prepare oneself for swimming to safety)?
I don't see why you couldn't breathe air at ~7 ATM. In theory, the entire submersed facility would already be at 7 ATM (or at least above 1 ATM). Balancing the internal and external pressures. I mean it is easier to pump more air into a room, rather than design the structure to withstand greater outside pressure.
Problem with Breathing air at that pressure comes when you try to escape to the surface. The drop in pressure around you will cause the Bends (microscopic bubbles of air will expand inside the body and cause problems) and probably kill you.
Oddly enough, going from Low to High pressure quickly does minimal damage to people, but the other way is usually lethal AFAIK.
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  #9  
Old 29 May 2007, 08:30 PM
Troodon Troodon is offline
 
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One ATM is about 15 pounds per square inch. With the pressure inside the person being 1 ATM and the pressure outside the person being 7 ATM, perhaps physical trauma could be a cause of death even if suffocation were not an issue.

Edit: it may be that I'm not understanding the design of this hypothetical underwater station. If it is simply a roof keeping in a bubble of air which is open to the water at the bottom, then the air will already be compressed until its pressure equals the water pressure.

Also, from the internet:

Quote:
Mark Ellyatt (UK) currently holds the (unconfirmed) world record for the deepest dive using SCUBA. The dive of 313m beat the previous record set by the late John Bennet of 308m (confirmed).

The above records were set using 'recreational' SCUBA. Commercial dives to depths greather than 500m have been made using specialised commercial and military diving equipment and support systems.
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  #10  
Old 29 May 2007, 09:03 PM
DaGuyWitBluGlasses DaGuyWitBluGlasses is offline
 
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The human body has trouble handling the amount of nitrogen in air at/above 3 atm of pressure.
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  #11  
Old 29 May 2007, 09:28 PM
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Quote:
Originally Posted by Keeper of the Mad Bunnies View Post
If the pressure was high enough to compress the air significantly, I believe the human body would not survive. You would not have to worry about breathing the compressed air because you would already be crushed.

At lower pressures, there would be no harm in breathing the slightly compressed air.

James Powell
AFAIK, there's no particular problem with your body being 'crushed' until some astonishingly high pressures. When you're at equilibrium, the air in your lungs is at the same pressure as the air around you. The rest of your body is water and solid, which doesn't compress much. The big problems you have deal with gas solubility (the nitrogen/oxygen issue that's been mentioned) and with sudden changes in pressure that create a pressure gradient between, say, the environment and your lungs or inner ear.
So while your body could be crushed by extremely high pressures, you'd be long dead by then. I hope that's comforting.
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Old 29 May 2007, 09:30 PM
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Keeper of the Mad Bunnies Keeper of the Mad Bunnies is offline
 
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Quote:
Originally Posted by Bryan With a 'Y' View Post
AFAIK, there's no particular problem with your body being 'crushed' until some astonishingly high pressures. When you're at equilibrium, the air in your lungs is at the same pressure as the air around you. The rest of your body is water and solid, which doesn't compress much. The big problems you have deal with gas solubility (the nitrogen/oxygen issue that's been mentioned) and with sudden changes in pressure that create a pressure gradient between, say, the environment and your lungs or inner ear.
So while your body could be crushed by extremely high pressures, you'd be long dead by then. I hope that's comforting.
However, you were postulating a non-equilibrium situation, with the air at 1 atmosphere and the incoming water at 7 atmospheres.

Of course you would not be crushed in an equilibrium situation. Otherwise, deep diving would not be possible.

James Powell
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  #13  
Old 29 May 2007, 09:34 PM
Griffin2020
 
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Quote:
Originally Posted by DaGuyWitBluGlasses View Post
The human body has trouble handling the amount of nitrogen in air at/above 3 atm of pressure.
Not true. I have personally been deep enough for long enough to have forced decompression upon ascent. What happens is that the gasses dissolved in the blood and tissue (especially nitrogen)increases with depth. If the diver ascends to quickly, or does not stop to acclimate (decompress) the gasses (nitrogen) will come out of solution forming microscopic bubbles in the tissue. These bubbles will tend to gather at the joints causing the painful ailment known as "the bends".

Pressure increases 1 atm for every 33 ft of depth. So, 66ft would be 3 atm.

The deepest dive I have ever done was 130ft.

Here is an example deco table for 130ft (dug-up from Wiki, but it is fairly accurate), since I do not have dive tables or a dive computer with me:

Quote:
A dive to 130 ft on air for 10 minutes (the NDL is 5 minutes)

Waypoint at 130 ft for 10:00 (13) on Air, PPO2 1.036, END 130

Deep Stop at 110 ft for 0:20 (13) on Air, PPO2 0.909, END 110

Deep Stop at 100 ft for 0:20 (14) on Air, PPO2 0.845, END 100

Deep Stop at 90 ft for 0:20 (14) on Air, PPO2 0.782, END 90

Deep Stop at 80 ft for 0:20 (15) on Air, PPO2 0.718, END 80

Deep Stop at 70 ft for 0:20 (15) on Air, PPO2 0.655, END 70

Deep Stop at 60 ft for 0:20 (15) on Air, PPO2 0.591, END 60

Deep Stop at 50 ft for 0:20 (16) on Air, PPO2 0.528, END 50

Deep Stop at 40 ft for 0:20 (16) on Air, PPO2 0.464, END 40

Norm Stop at 20 ft for 4:00 (20) on Air, PPO2 0.337, END 20

TOTAL DECO TIME: 7 minutes. DIVE RUN TIME: 20 minutes.
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  #14  
Old 29 May 2007, 09:38 PM
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I think DaGuyWitBlueGlasses may have been referring to Nitrogen Narcosis, rather than the bends.
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  #15  
Old 29 May 2007, 09:40 PM
jimmy101_again jimmy101_again is offline
 
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Quote:
Originally Posted by Troodon View Post
One ATM is about 15 pounds per square inch. With the pressure inside the person being 1 ATM and the pressure outside the person being 7 ATM, perhaps physical trauma could be a cause of death even if suffocation were not an issue.
Nope, if the pressure outside the body is 7 ATM then the pressure inside the body is ~7 ATM. Besides, it took several seconds for the room to fill with water. That is slow enough for the parts of the body that care to pressure equilibrate. The inner ear, and lungs for example, the rest of the body really wouldn't much notice the pressure change.

Besides, the design of the building is such that the air inside it is already at whatever the water pressure is at that depth. The pressure in the room would not have changed much because of the broken window. This building is not a submarine. In most subs the pressure in the sub is maintained at about 1 ATM. Because of the constant pressure submariners have no problems diving to hundreds of meters then surfacing quickly. No issues with the bends. The cost of maintaining a 1 atm pressure is that the sub's hull must be incredibly strong to withstand the pressure.

The submerged building in the Lost episode could be of fairly flimsy construction since it is not maintained at 1 atm. Heck, to get the required hydrodynamic strenght all you would need is a big plastic or canvas bag.
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  #16  
Old 30 May 2007, 01:08 PM
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Regardless of the depth and compression, the water should have gone up to just the top of the broken window unless there were some other structural damage that allowed the air to escape above that mark.

If the building was set up to allow all of the rooms to be at the same pressure as the moon pool, then as the water flowed in from the broken window it would displace the same volume of air as the water entering. When the internal water level reached the top of the window sill or the top of the breach, the air which had already been compressed to the proper pressure would not be able to leave and the inflow of water would stop. It can't flow uphill.

If the room he was in was not set up to equalize pressure with the outside ocean, then the first inrush of water would start to compress the air and none would escape until the air pressure equalized with the water pressure. If it was at 50 feet, based on the ratios discussed above, it would be almost 3" of water to 1" of air. If it was at 200 feet it would be 7" of water to 1" of air. Once the air pressure equalized (and it would really hurt your eardrums and sinuses - but probably not kill you) then the air would start to escape through the hole and the same situation as above would occur.

Short answer, he would have air at the top of the room for a while, at least.

His survival would depend on how deep he was when he started. He could have made the surface from either depth if the opening were big enough to get through. If he had been at 200 feet for any length of time, even just a few minutes, he would not have been able to decompress on the way up and would have died very painfully shortly after surfacing. If he was at 50 feet for less than a few hours he would probably survive, but anything longer than that also requires decompression.

Basically without air tanks, he's gonna die.
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  #17  
Old 30 May 2007, 03:27 PM
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What they said. If he was 200' down and was only exposed to that pressure for a short time he could easily free ascend to the surface without any ill effects. And no he will not be crushed, jeeze. Now the bigger issue is the very rapid buildup of CO2 in the air pocket, very low concentrations in a pressurized pocket can and will kill. The other issue is pressurized air in the lungs as you ascend. If he holds his breath he will explode his lungs. We were taught to go "HO HO HO" like Santa Claus (not like Don Imus) on ascending. So the answer is he should survive if he is quick in getting out and does not hold his breath.
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Old 30 May 2007, 03:30 PM
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If the structure had a moonpool, and a window was breached, wouldn't the air have rushed out the broken window and the water rushed in the moonpool, rather than the water rushing in the window?
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Old 30 May 2007, 04:01 PM
diving_cecil
 
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One other thing did occur to me. If there was a moon pool and it was at 200' then there is no way to survive. This would mean that he was saturated and unless he did a very long, very slow decompression his blood would have turned into a fizzy drink on ascending.
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  #20  
Old 30 May 2007, 04:13 PM
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After watching, in a lost moment, only a few short snatches of the program -- just long enough to rank it as one of the most ridiculous series I've ever seen -- I can only say that it surprises me that anyone would try to find even a trace of logic in the whole thing.
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