Depressurizing airplanes

[Alpo]

They tell you in an airliner that in the event of an emergency, which I assume means the plane depressurizes, the oxygen masks drop out of the ceiling.

 

But does anyone know at what pressure?

 

I'm watching a TV show about DB Cooper. He jumped out of the airplane at 10,000 feet. And I just wondered why, when he opened the door of the plane, the oxygen masks did not fall out of the ceiling.

 

I don't know what artificial height the airplane is pressured to. But I have been up in the mountains to a mile, and I had the damnedest time breathing, because there ain't hardly no air there.

 

I think I read somewhere that airplanes are pressurized to 3500 feet. I know I never had trouble on short hops of about an hour, but the one 3-hour flight I made, I was running out of air. The last 20 minutes I could barely breathe. I was giving serious consideration to asking the stewardess to bring me an oxygen bottle.

 

Y'all that are laughing - get over it. I live at sea level, with 15 pounds of air pressure, and I am used to having oxygen in my air.

 

So anyway - if the plane is pressed to 3500 feet, and they open the door at 10,000 feet, it seems to me that the plane would think it was having an explosive decompression.

 

They probably did not have the masks hang down because it would have been a pain in the butt for the television show.

 

But it made me wonder what would really happen. Anybody know?

[Gateway Kid SASS# 70038 Life]

Not laughing, but when I lived in Denver my house was at exactly 5,280 feet. My current home is at almost 4,600 feet in Grand Junction. My wife has crested 27 of the 54 fourteeners (14,000 feet plus mountains) in Colorado and I have completed 20 of them. Much younger and better shape then but oxygen content not really a problem. Like they say pressure is relative. Couple of friends skydive occasionally will have to ask at what altitude they jump and whether their aircraft even has oxygen masks. 
Regards

    

Gateway Kid

[Marshal Mo Hare, SASS #45984]

I never had a problem at 12,000 ft.

[Larsen E. Pettifogger, SASS #32933]

All I know is when James Bond shot the window out of the plane Goldfinger got sucked out.  Not sure of the altitude but no oxygen masks fell.

[Marshal Mo Hare, SASS #45984]

3 minutes ago, Larsen E. Pettifogger, SASS #32933 said:

All I know is when James Bond shot the window out of the plane Goldfinger got sucked out.  Not sure of the altitude but no oxygen masks fell.

Yeah, but that “plane” was on a sound stage.  I’d say an oversight by the director.

[Still hand Bill]

I believe they pressurize to around 8000-10,000ft.   Can’t be lower pressure than that or some people start having issues.   I believe faa requires oxygen starting around 12,000

[Alpo]

Wiki says the max allowable cabin pressure is 8,000 feet, and the average seems to run between six and seven.

 

https://en.m.wikipedia.org/wiki/Cabin_pressurization

[Marshal Mo Hare, SASS #45984]

10 minutes ago, Alpo said:

Wiki says the max allowable cabin pressure is 8,000 feet, and the average seems to run between six and seven.

 

https://en.m.wikipedia.org/wiki/Cabin_pressurization

OMG, he does look things up!

[Father Kit Cool Gun Garth]

9 hours ago, Larsen E. Pettifogger, SASS #32933 said:

All I know is when James Bond shot the window out of the plane Goldfinger got sucked out.  Not sure of the altitude but no oxygen masks fell.

I remember it well.

 

That's why I don't sit in a window seat when I fly. 

 

[Marshal Mo Hare, SASS #45984]

That plane had squarish windows. Planes intended for pressurization have had round or oval windows since about the fifties after three plane crashes were attributed to fuselage stress failures caused by square windows.

 

I’d expect Blofeld to have been stuck in the window rather than sucked out.

[Cholla]

I have read that there is the same amount of oxygen at different elevations. The difference is the pressure that presses it into the lungs decreases at higher elevations. With less pressure there is less rate of exchange. 

[sassnetguy50]

15 minutes ago, Cholla said:

I have read that there is the same amount of oxygen at different elevations. The difference is the pressure that presses it into the lungs decreases at higher elevations. With less pressure there is less rate of exchange. 

Close.  There is the same ratio of oxygen in the air.  The amount of oxygen molecules per volume is decreased as the pressure and air density decreases.  

[Still hand Bill]

46 minutes ago, Cholla said:

I have read that there is the same amount of oxygen at different elevations. The difference is the pressure that presses it into the lungs decreases at higher elevations. With less pressure there is less rate of exchange. 

The % of each component is the same independent of altitude.  As the pressure is less the distance between molecules becomes larger and there are fewer oxygen molecules per a given volume.  Also there is less pressure differential between your lungs and the outside air so the lungs may not fill as well.  The lower pressure may also slow absorption into the blood.   For a engine, performance is approximately half at 11,000 ft vs sea level.  I expect the body is similar.  
 

having tried to do physical activity at 14,000 ft I can say it slows you down a lot.  That was even when I lived at 7400 ft and had extra red blood cells. 

[Abilene Slim SASS 81783]

13 hours ago, Alpo said:

I think I read somewhere that airplanes are pressurized to 3500 feet. I know I never had trouble on short hops of about an hour, but the one 3-hour flight I made, I was running out of air. The last 20 minutes I could barely breathe. I was giving serious consideration to asking the stewardess to bring me an oxygen bottle.

They're pressurized at 8,000 ft. Lack of oxygen, called hypoxia, usually doesn't cause shortness of breath as the volume of air remains the same - it just has fewer oxygen molecules. As oxygen levels decrease with altitude, a person will experience mental confusion and sleepiness. If left uncorrected, you'll eventually drop off to sleep. The condition most often goes unnoticed and is what killed golfer Payne Stewart and pilot. Their plane gradually lost pressurization and they drifted off to sleep. The plane continued flying on autopilot until it ran out of fuel. 

 

 

[Sixgun Sheridan]

3 hours ago, Father Kit Cool Gun Garth said:

I remember it well.

 

That's why I don't sit in a window seat when I fly. 

 

 

You do know that the idea of being sucked out of a broken plane window like that is just a myth, right?

[Abilene Slim SASS 81783]

13 hours ago, Alpo said:

So anyway - if the plane is pressed to 3500 feet, and they open the door at 10,000 feet, it seems to me that the plane would think it was having an explosive decompression.

Cooper jumped out the rear stairwell of a 727. Since the stairwell doesn't open instantaneously, the airplane doesn't decompress explosively. There's a helluva rush of air though!

[Abilene Slim SASS 81783]

3 minutes ago, Sixgun Sheridan said:

 

You do know that the idea of being sucked out of a broken plane window like that is just a myth, right?

Depends on where you're sitting. This woman had a window seat.

 

https://www.chicagotribune.com/business/ct-southwest-flight-fatality-details-20181114-story.html

[Crazy Gun Barney, SASS #2428]

I for one prefer not to roll down my window during the flight.  I have little enough hair left and prefer not to have it blown off. 

[Alpo]

Y'all can insist that there is the same amount of oxygen in the air is 6,000 ft as there is in the air at 14 ft. My lungs do not agree.

[Abilene Slim SASS 81783]

12 minutes ago, Alpo said:

Y'all can insist that there is the same amount of oxygen in the air is 6,000 ft as there is in the air at 14 ft. My lungs do not agree.

There is not the same amount.

 

The air we breathe is 78% nitrogen, 20% oxygen and 2% carbon dioxide. A cubic foot of air contains a given number of molecules of those elements at sea level. At 6,000' MSL, a cubic foot contains fewer molecules of those elements.

 

[Father Kit Cool Gun Garth]

1 hour ago, Sixgun Sheridan said:

 

You do know that the idea of being sucked out of a broken plane window like that is just a myth, right?

[Utah Bob #35998]

1 hour ago, Sixgun Sheridan said:

 

You do know that the idea of being sucked out of a broken plane window like that is just a myth, right?

Not exacly. The myth is that a bullet will cause it. The Mythbusters tried it years ago. a bomb will definitely do it. or a structural failure.

 

[Sixgun Sheridan]

I believe a bomb or other sudden structural failure results in the slipstream pulling things out of the plane. The Goldfinger scene assumed that there is such a huge pressure differential between the inside of the plane and the outside air that it creates a suction like a vacuum cleaner, which is false.

[Dubious Don #56333]

It's not pressurization, it is pressure differential. In flight the airpacks, provide cabin air altered for suitable temperature and pressure at altitude. At sea level, air pressure is about 14.7PSI. At 5600 feet it's 12PSI. At 18,000 it's down to 7.3PSI. The "line" is 10,500 above which flight crews must be on oxygen or, have pressurization AND have oxygen available in specific way by regulation. Hypoxia (lack-A oyygen) is cumultive and insidious. You don't even realize you're going out. You just....fall asleep. 

 

Most commercial aircraft have doors that open outboard. It is physically impossible to open them in flight. The Boeing 727 has an aft stair and THAT door is capable of being opened in flight. In order to do that, you have to be at an altitude where the pressure differential between inside/outside is low enough to open it. Which is why DB Cooper picked a flight on a 727.

 

No. A bullet hole is not going to blow out a window or take out a section of the plane. It makes a small hole. NONE of those things are perfectly airtight anyway. They all leak air LOL. On the other hand, there are documented cases of structural failure caused by crosseyed mechanics, inspectors, corrosion and the like. Aloha airlines.

[Trailrider #896]

In the Air Force, I had the chance to go into the altitude simulation chamber.  They asked for a volunteer to take of the oxygen mask at simulated 25,000 ft. Some idiot, later called Trailrider, volunteered.  They had a block of wood with various-shaped holes and blocks to fit them.  First they had me put the blocks into the holes with the oxygen mask on.  Then I took the mask off at "25,000 ft." and attempted to repeat that exercise with the blocks.  After 29 seconds, I could no longer co-ordinate.  I could hear the airman tech telling me to put my mask on, but couldn't do it!  That was 56 years ago, and I was younger and in better condition.  I had 29 seconds of useful conscienses (and could spell any better then either with oxygen).  This is why the airlines tell you if you have someone with you who probably can't manage a mask, to put yours on first before assisting them.  Oh, and above 45,000 feet you can't just suck oxygen in from a mask, your diaphragm isn't strong enough to expand your lungs! You have to have pressure breathing do it, and must forcibly exhale.  I understand that military fighter pilots now are pressure fed O2 from the start, which can be very tiring, and may lead to hyperventillating.

[Marshal Mo Hare, SASS #45984]

Btw, The Armstrong limit is the altitude at which your blood boils if you don’t have a pressure suit, about 69,000 ft.  I said that without looking it up, I could be off a tad.

 

 

 

[Abilene Slim SASS 81783]

1 hour ago, Trailrider #896 said:

In the Air Force, I had the chance to go into the altitude simulation chamber.  They asked for a volunteer to take of the oxygen mask at simulated 25,000 ft. Some idiot, later called Trailrider, volunteered.  They had a block of wood with various-shaped holes and blocks to fit them.  First they had me put the blocks into the holes with the oxygen mask on.  Then I took the mask off at "25,000 ft." and attempted to repeat that exercise with the blocks.  After 29 seconds, I could no longer co-ordinate.  I could hear the airman tech telling me to put my mask on, but couldn't do it!  That was 56 years ago, and I was younger and in better condition.  I had 29 seconds of useful conscienses (and could spell any better then either with oxygen).  This is why the airlines tell you if you have someone with you who probably can't manage a mask, to put yours on first before assisting them.  Oh, and above 45,000 feet you can't just suck oxygen in from a mask, your diaphragm isn't strong enough to expand your lungs! You have to have pressure breathing do it, and must forcibly exhale.  I understand that military fighter pilots now are pressure fed O2 from the start, which can be very tiring, and may lead to hyperventillating.

 

That's for breathing underwater as in scuba diving. Expanding your lungs (inhaling) requires pressure from the tank to overcome pressure exerted by the water. 

[Wyoma]

The passenger oxygen masks drop at 14,000' pressure altitude.  The airplane can be depressurized at any altitude by manually opening the outflow valve from the cockpit.  Commercial airliners are pressurized to 8.3 psid.  DB had the crew depressurize the aircraft before lowering the stairs.  After this incident all 727's were retro fitted with what became known as a "DB Cooper" lever which would not allow the stairs to be lowered manually while in flight.