AlitaliaORD
Topic Author
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Pressurization

Sun Jan 25, 2004 2:53 am

What does it actually mean to lose cabin pressure. I always used to think it meant there was a hole in the plane while it was in flight. What happens as a result of losing cabin pressure? For anyone who has ever been on a flight when this sorta of thing has happened is it noticible? Can it be restored after it has been lost?
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DLKAPA
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RE: Pressurization

Sun Jan 25, 2004 2:56 am

When the Oxygen Masks come down, you tend to notice it then.

DLKAPA
And all at once the crowd begins to sing: Sometimes the hardest thing and the right thing are the same
 
fritzi
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RE: Pressurization

Sun Jan 25, 2004 2:57 am

"What happens as a result of losing cabin pressure?"

The air pressure inside the cabin will decrease, as the air pressure outside the aircraft is lower than inside, during flight of course.
The pilots will decent to around 14,000 feet immedietly so that you wont pass out from hypoxia.
 
AlitaliaORD
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RE: Pressurization

Sun Jan 25, 2004 2:59 am

DLKAPA,
hahaha, i meant can you feel changes (besides difficulty of breathing)
Joy To The World, All The Boys and Girls, Joy to the Fishes in the Deep Blue Sea, Joy to You and Me
 
DLKAPA
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RE: Pressurization

Sun Jan 25, 2004 3:22 am

14,000, hell I could breathe without the Oxygen mask at that altitude, and I have before, climbing Mt Elbert, at 14,334 ft.

DLKAPA
And all at once the crowd begins to sing: Sometimes the hardest thing and the right thing are the same
 
air2gxs
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RE: Pressurization

Sun Jan 25, 2004 4:57 am

I was on a jumbo frieghter in 90 when an R5 window blew out while climbing through 21000. I felt the pressure change in my ears. The aircraft pressurization system "caught up" to the pressure loss and tried to maintain the pressurization schedule. Of, course we turned around and went right back into JFK to get it looked at.

It really wasn't un-comfortable at all. We never went on O2 because the aircraft was able to stabilize the pressure.
 
fritzi
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RE: Pressurization

Sun Jan 25, 2004 7:44 am

DLKAPA,

Thats why they decend to that altitude!

The use of O2 masks will not be necessary then.
 
liamksa
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RE: Pressurization

Sun Jan 25, 2004 9:37 am

For anyone who has ever been on a flight when this sorta of thing has happened is it noticible?

An explosive decompression in the cruise definitely won't go unnoticed. The air will be forced out of your lungs, the partial pressure of oxygen won't be high enough to get any oxygen into the bloodstream (hypoxia) and you'll have a time of useful consciousness of around 15 seconds (FL400).

The less severe case is the slow loss of cabin pressure which would probably go unnoticed by passengers initially. Indications to the flight crew would be a positive rate of climb on the cabin VSI accompanied by (obviously) an increasing cabin altitude indication. Modern aircraft have a built in warning system which alerts the crew when the cabin altitude exceeds a preset value.

On the photo below you can see the cabin altimeter and VSI:

View Large View Medium
Click here for bigger photo!

Photo © John Miller



Rob.
 
Inbound
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RE: Pressurization

Sun Jan 25, 2004 12:08 pm

I thought O2 supply followed this rule...??

human body can survive for 30 minutes at 10,000 feet.
and nothing past 13,000 feet.

or is that just for Canadian standards?
Maintain own separation with terrain!
 
DLKAPA
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RE: Pressurization

Sun Jan 25, 2004 3:02 pm

When climbing Mt Elbert I was above 13,000 for almost Four hours.

DLKAPA
And all at once the crowd begins to sing: Sometimes the hardest thing and the right thing are the same
 
FredT
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RE: Pressurization

Sun Jan 25, 2004 8:03 pm

And the pressure in your bowels will be way higher than ambient... that you'll notice as well, but chances are you will be too preoccupied to care much.

Ah, the glamour!

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
pilotpip
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RE: Pressurization

Mon Jan 26, 2004 12:14 am

Your ears and bowels can tell you the difference in as few as a thousand or less feet. Flying light aircraft that aren't pressurized will make you an expert at popping your ears and letting out a timely burp, or worse  Big thumbs up

DLKAPA, Many people don't have the luxury of having that sort of ability. People with health problems, smokers, and people like me, who live at a low altitude often can't handle high alitude environments like that. I've seen a guy start getting hypoxic at 6,000 feet. I consider myself to be in decent shape. I work out at least 3 times per week and durning the summer I ride my bicycles as much as 200 miles per week. I have no trouble doing this around St. Louis, about 500ft MSL. However, when I took a trip to Utah a couple years ago and was riding regularly at over 7,000 feet I found myself much more fatigued after a ride than I do at home.
DMI
 
BMAbound
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RE: Pressurization

Fri Jan 30, 2004 7:19 am

I spent 3.5 hrs flying unpressurized at 12000 ft.

I think I was alive most of the time.

johan
Altitude is Insurance - Get Insured
 
prebennorholm
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RE: Pressurization

Fri Jan 30, 2004 7:50 am

Rules of thomb for playing safe with complete pressure loss:

Below 15,000 ft: No problem.

15,000 to 25,000 ft: You are on O2 and descend to 15,000 before O2 supply runs out.

25,000 to 50,000 ft: You are on O2 and descend below 25,000 ft. ASAP.

Above 50,000 ft: Better wear at least a partial pressure suit, or you are in danger.

And finally above some 65,000 ft: You wear full pressure suit (space suit), or your blood boils and kills you instantly.

Happy landing, Preben Norholm
Always keep your number of landings equal to your number of take-offs
 
sovietjet
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RE: Pressurization

Sat Jan 31, 2004 1:43 am

Why does blood biol over 65000 feet? At 40000 the temperature is like -55 degrees celsius does it rise to boiling in 25000 feet?
 
ben
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RE: Pressurization

Sat Jan 31, 2004 3:46 am

Sovietjet,

The boiling point is related to atmospheric pressure.

As the pressure decreases, the boiling point also decreases.

For instance, at an altitude of 10,000 feet (lower pressure), the boiling point of water is about 10 degrees celsius colder than at sea level (higher pressure). There are anecdotes about not being able to make a good cup of coffee or boil an egg when camping on high mountains.. basically, the water will be boiling at a lower temperature and wont cook the egg as fast (I don't understand the relevance to coffee tho)

If you take that analogy to it's logical end and take the water up to 60,000 feet or beyond, it will boil at lower and lower temperatures until it boils at only a few degrees. Same with blood, which if you aren't asphyxiated already, will be at about +37 degrees C, not -55.

There is a calculator on this page that shows boiling points of water, but it only does imperial measures sorry. http://www.biggreenegg.com/boilingPoint.htm
 
L-188
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RE: Pressurization

Sat Jan 31, 2004 2:35 pm

Same with blood, which if you aren't asphyxiated already, will be at about +37 degrees C, not -55.

You are thinking of the Armstrong line, can't recall what altitude that actually occurs at.


Think if it as an extreme case of the bends, the gasses in your blood boil out because the atmospheric pressure isn't there.
OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
 
delta-flyer
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RE: Pressurization

Sun Feb 01, 2004 3:28 pm

Preben ... at 37C, what would be the boiling pressure of blood? Water would not boil at that temperature even at zero pressure, and I don't think blood would either. You would need a pressure suit only if you are going to be exposed to reduced or zero gravity in addition to low pressure.

Pete
"In God we trust, everyone else bring data"
 
L-188
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RE: Pressurization

Sun Feb 01, 2004 5:47 pm

Pete and Preben.

Blood boiling has nothing to do with temperture and everything to do with altitude.

All fluids have some amount of gas in them, if you take a fluid with a pressure and suddenly lessen the pressure, those gases will come out of solution violently. Do you want to see a real time example of this? Get a can of Soda, Pop, Seltzer water and pop the top, those bubbles are carbon dioxide gas comming out of the solution because the pressure in the can has suddenly been reduced to atmospheric and the gasses are comming out of solution.


Man in pressure suit in altitude chamber in which the pressure has been lowered to 63000 feet. The beaker holds ordinary water.


For human blood the equivlent pressure altitude is known as the Armstrong Line, like I mentioned in my earlier post. I have seen did a little checking and found out that for human blood will "boil" at 63000 feet depending on the circumstances.

But keep in mind your not going to exlode like you see in some space movies, what you end up with is the aeronautical equivelent of a case of the bends that divers get.

Same idea, they go down to a depth (higher pressure) their blood gets gasses in it at that same pressuere, when they come up they have to stop at various depths to give their blood a chance to get used to the lower pressure.

That is why they say you shouldn't fly after you dive.

Here are a couple of links to help you figure it out.

http://www.sff.net/people/Geoffrey.Landis/vacuum.html

http://www.sff.net/people/Geoffrey.Landis/ebullism.html


OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
 
Bellerophon
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Pressurization

Sun Feb 01, 2004 5:58 pm

Delta-flyer

…at 37C…Water would not boil...even at zero pressure...I don't think blood would either…

The pressurized aircraft we have today are a direct result of the pioneering work done by Dr Harry Armstrong at Wright Field in the late 1930’s.

It was there he discovered, amongst other things, that at 63,000 feet pressure altitude, blood will boil at body temperature, an altitude limit still know to this day as the Armstrong Line.

If you would like to know more about Dr Armstrong try this link:

http://www.nationalaviation.org/museum_enshrinee.asp?eraid=4&enshrineeid=329


Regards

Bellerophon
 
L-188
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RE: Pressurization

Sun Feb 01, 2004 6:07 pm

Bellerphon, thanks for the historic notes.

But i can't get that link to work.

Use this one instead.

http://www.nationalaviation.org/website/index.asp?webpageid={F3401AC2-408C-42A7-AD0F-CDDC7942F110}&eID=329
OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
 
delta-flyer
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RE: Pressurization

Mon Feb 02, 2004 1:34 am

L-188 .... I can buy the dissolved gas theory -- I didn't think of that, although I should have, as I suffer with it regularly in the context of dissolved air in hydraulic fluid coming out of solution when the inlet pressure to a pump is reduced.

Bellerphon, thanks for the info ... I couldn't open the link, either. In any event, as I said, I overlooked the dissolved gas content of blood. I don't disagree with Preben's comments in that case.

Pete
"In God we trust, everyone else bring data"
 
Bellerophon
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Pressurization

Mon Feb 02, 2004 10:39 am

L-188

Thanks for your help with the link.

Regards

Bellerophon
 
DrJetMech
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RE: Pressurization

Tue Feb 03, 2004 1:51 am

I was on a flight from Tinker AFB heading to Turkey, about an 18 hr flight and 2 in-flight refuels. Well, I was sleeping about 4 hours into the flight and all of a sudden I hear a loud bang. I woke up and my ears were hurting, I looked around and all the flight crew had put on there O2 masks. whatt happened was the Auto mode of the press. controller had fualted and opened the outflow valve to full opened in a hurry.
The flight eng. performed the correct actions and went to manual mode and closed the outflow valve even faster. The whole ordeal took no more than 2 minutes, but I did start feeling a little woozy becuase by the time I realized what had happened it was to late to put on O2. It was on a boeing 707 E-3 AWACS, the best looking A/C flying today.
 
prebennorholm
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RE: Pressurization

Wed Feb 04, 2004 7:39 am

I have been away from this thread for some days, and it really surprises me that it is not common knowledge that water boils at +37C at extreme altitude pressure.

In fact water (H2O) acts exactly the same way as carbon dioxcide (CO2). Only the temperature values are different. With CO2 we can observe the process at ambient temperature at sea level atmospheric pressure.

CO2 freezes to white ice at around -70C (H2O at zero). In a telescope we see the CO2 atmosphere on Mars freeze on the North and South poles as Martian winter and summer alternates.

Our bar tender keeps it as a liquid in a pressurized container, but when he blows it into our drink, then it boils.

Same way we can take butane gas (C4H10) as used in a cigaret lighter. It boils at normal ambient temperature and that way builds up pressure so it can be kept in liquid state in the lighter.

But put the lighter into your freezer, and then try to light it. It won't. C4H10 boils at sea level pressure at just around zero degrees C, so no gas will flow when the valve is opened on your frozen lighter.

The gasoline you put on your car is basically a mixture of C6H14 and more complex hydrocarbon molecules which boils at between roughly +40 and +200C. It needs the heat from the compression in the cylinder to boil and evaporate so the spark plug can ignite it.

But back to the Armstrong line: Well above 60,000 feet your blood will boil. Steam bobbles will form and obstruct the blood flow within you brain, and you will die very quickly.

At such altitude a pressure suit (space suit) or pressurized cabin is absolutely mandatory for man to survive.

Happy landing, Preben Norholm
Always keep your number of landings equal to your number of take-offs
 
OE-LDA
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RE: Pressurization

Wed Feb 04, 2004 10:55 am

I have to disagree with Preben Norholm: Altitudes between FL100 and FL 150 cannot be described as "no problem". In fact, everything above FL 100 has to be considered as dangerous, not for all, but for many persons. Symptoms differ from person to person: fatigue, headache, nausea and so on. You have to try it to find out how your own body reacts. When I personally did my "high altitude flight" during my training I went up to FL 115. My symptoms there were like under the influence of small amounts of alcohol. I felt great, talked a lot and thought I just had invented aviation, in one word: enthusiasm.

Some quotes from my student pilot textbook:

Above 6500/10000 ft: first reactions based on reduced oxygen pressure: slower reactions, fatigue.

Above 13/16000 ft: Physical malfunctions due to oxygen deficit, reduced ability for quick and logical decisions.

So as a summary, above 10000 feet flying alone, without oxygen mask, is considered to be unsafe. And then there may be no more "Happy Landing".

Regards, OE-LDA
I am totally missing basics and clueless about airline flying!
 
delta-flyer
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RE: Pressurization

Wed Feb 04, 2004 12:47 pm

I have been away from this thread for some days, and it really surprises me that it is not common knowledge that water boils at +37C at extreme altitude pressure.

OK, smart guy, rub it in! After digging through the long-neglected archives of my brain where I stored this data 35 years ago, yes I agree - water will boil at 37C, probably around 1 psia. And that's probably the pressure that corresponds to 65,000 feet.

Peter, it looks like you can't leave the thread even for an hour, lest we ignorant fools muck everything up!

Pete
"In God we trust, everyone else bring data"
 
vikkyvik
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RE: Pressurization

Wed Feb 04, 2004 4:36 pm

According to the standard atmosphere tables in one of my textbooks, the pressure at 65,000 feet is 118.93 psf, or 0.826 psi. Outside air temp is ~ -56 deg C. Just some info for those who care....
~Vik
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".
 
prebennorholm
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RE: Pressurization

Thu Feb 05, 2004 8:15 am

Thanks OE-LDA for the detailed information. Sure your data are valid.

When I wrote "Below 15,000 no problem", then I was more or less thinking about the physical safety of a passenger on a plane. I agree that it is certainly not recommended that pilots fly unpressurized without oxygen at FL150.

If a passenger suffers any danger at FL150, then he has a serious health problem. In the Andes Mountains there are people who live above FL150. But they adapt slightly by building up a higher concentration of red blood cells than for instance Danes like me who are born almost below sea level.

But a pilot should never accept any unnessessary degradation of physical or mental capability due to lack of oxygen.

That said, the highest I have climbed in the Alps (which I assume you know  Big thumbs up ) is 12,826 ft. (Switzerland). It was a non-event (except for the fantastic view), and we met a lot of happy people up there doing skiing in mid summer. Our only real concern was sunburn.

But I do remember that we were warned in advance that unfit people should not do what we planned to do.

Happy landing (and I mean it!)
Preben Norholm
Always keep your number of landings equal to your number of take-offs

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