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Author Topic: depressurization vs decompression  (Read 9227 times)
zarrina
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« on: March 20, 2014, 12:54:57 AM »

Recently,  I was questioned about depressurization and decompression, searched in Google and found out that there was no difference between these two words, but a friend of mine is insisting that depressurization occurs in pilot's cockpit and decompression occurs in  passengers' salon. huh
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swa4678
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« Reply #1 on: March 20, 2014, 03:03:11 PM »

Ask your friend how a collection of molecules we collectively refer to as "air" knows whether it resides in the pilot's cockpit or not. Then ask him to define the two words. Then we might be able to describe how the two differ.
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InterpreDemon
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« Reply #2 on: March 20, 2014, 06:50:58 PM »

Generally, depressurization is when (in aircraft so equipped) a pressurized cabin reaches equilibrium with the atmosphere surrounding it, for example when an aircraft descends to below 8,000 feet, or lands... or a cargo door blows open at 35k feet. If one were to be a pedantic word smith, one might think that a "compressed" cabin would be one where the pressure outside the vessel exceeded the pressure inside, for example if you trimmed the wings down to a stub, put the engine in the tail and converted your airplane into a submarine, which leads to...

Decompression. That is when a diver who has been "compressed" at depths (or a miner working a very deep mine) has absorbed excess nitrogen in his blood and needs to be slowly "decompressed" (by coming back to the surface in stages) to allow that nitrogen to be naturally exhaled rather than boiling in the blood stream ("the bends").

Decompression is also when one comes home from work, grabs a glass and a bottle of Chivas Regal, slumps in the recliner and tunes in "Family Guy" or "The Bugs Bunny, Road Runner Hour".
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winglover1
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« Reply #3 on: March 21, 2014, 11:59:33 AM »

I would think there should be a big difference between a slow ""depressurization"" and and a more sudden rapid and radical ""decompression"".  Letting the air out of a balloon at the neck making a squealing noise, versus a more rapid pin prick and POP!

In the case of the Hawaiian airline loosing a 15 foot section of fuselage, accompanied by massive decompression and one Flight Attendant was blown out of the plane. That was probably not a very pleasant way to go.

One question I have is what would happen if someone replaced the O2 supply on the airplane with C02? Are there sensors monitoring C02 levels on the plane?
Curious...
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InterpreDemon
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« Reply #4 on: March 21, 2014, 12:55:25 PM »

Actually, if you concur with the theory of this engineer ( http://the.honoluluadvertiser.com/2001/Jan/18/118localnews1.html ) which I do, she probably never knew what happened to her. I read about this guy ten years ago and his theory about fluid hammer explains things perfectly. Basically a 10" square relief panel failed right overhead the attendant, her head and arm were sucked into the air stream and hole, but then her body momentarily blocked the flow, resulting in overpressure at the front of the cabin and the roof blowing off.
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svoynick
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« Reply #5 on: July 03, 2014, 06:27:30 AM »

I would think there should be a big difference between a slow ""depressurization"" and and a more sudden rapid and radical ""decompression"".  
Perhaps, but this distinction is predicated upon your assumption that the definition of "depressurization" includes slowness, and that the definition of "decompression" includes radical speed.  I don't accept that these are inherent in standard usage.

Case in point:  when divers decompress (and they do use that term) they virtually NEVER do it quickly - that's the whole point.  



One question I have is what would happen if someone replaced the O2 supply on the airplane with C02? Are there sensors monitoring C02 levels on the plane?
Curious...
Kind of a weird question...  What's your context for this? Why would it make sense specifically to have CO2 sensors?  You could ask the same question about replacing the O2 supply with Nitrogen (another abundant diatomic molecule) or Argon (a noble gas), or any other available gas, but unless you're the Joker in a Batman movie, it doesn't make much sense.  

Also, note that the passenger O2 supply in many passenger aircraft is not simply pressurized bottles of Oxygen gas, but rather chemical oxygen generators that initiate a highly exothermic (heat-producing) reaction that evolves oxygen.  Due to the nature of these items, they don't look much like pressurized gas bottles, and so would be difficult to surreptitiously replace with a different gas.

If one were to be a pedantic word smith, one might think that a "compressed" cabin would be one where the pressure outside the vessel exceeded the pressure inside, for example if you trimmed the wings down to a stub, put the engine in the tail and converted your airplane into a submarine, which leads to...
Ha ha... pedantic word smith that I am, I might suggest an alternate interpretation, which is that it's not necessarily the container which is compressed from the outside, as in a submarine, but the air within the container, which is (in a pressurized cabin) still arguably compressed, relative to the air outside.
« Last Edit: July 03, 2014, 06:34:21 AM by svoynick » Logged
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