Pressure loss in airplane

[Don Burke]

String once bubbled... http://www.usatoday.com/weather/wstdatmo.htm

was the source for the altitude pressure tables.

I found a few on the internet that agreed with those values although was a little confused as 12hPa even on 100% O2 shouldnt sustain life and people have gone much higher.

There are two sets of tables on that page.

People have gone to the top of Everest without oxygen, so it isn't impossible. The Air Force people will go to 40,000 or so on O2 and beyond that a bit with a positive pressure mask. B-17s made runs at 25-30,000 feet and sometimes a bit higher.

The body will function quite well on about .17ATA of oxygen as long as the exertion level isn't too high. The real deal breaker at those altitudes is the cold, which is downright brutal. Fortunately, the airlines get lower before the full effect of the temperture is felt.

Even so, that 8,000 feet throws an additional pressure change of 1:1.35 into your deco problem. Going from 8,000 to 30,000 throws another 1:2.5 into the fray. That could get pretty ugly.


BigJet,

Do the airliners coming back from dive locations ask for lower altitudes just in case?

 

[Dr Deco]

Dear Scuba Board Readers:

Pressure Changes

When considering the pressure changes in an airplane and the relationship of these to diving, one must recall that the pressure change ratios change with absolute pressure. There is a depth dependence to the Haldane ratios (or M-values), and these ratios increase as you go to lower absolute pressures. An allowable pressure jump to altitude will be greater than an allowable change at saturation when at depth.

Equilibrium Processes

As far as the consequences of the pressure changes are concerned, we must always think in terms of the “time course” or the rate of the process. The bursting of a balloon is essentially instantaneous, but most other events are not. There is a long times scale (tens of minutes) for dissolved nitrogen to diffuse to a micronucleus and cause it to grow.

Thus, the sudden loss of cabin pressure in an airline will not bring instantaneous retribution from the Diving Gods because of the slowness of the processes involved. In actuality, 30,000 feet for an hour is not exactly horrible with respect to DCS for seated subjects. I certainly could not image the plane remaining at that altitude except in a Hollywood movie.

Lung rupture could occur if someone were to take a deep breath just prior to pressure loss and hold it all through the pressure drop. Again, except for Hollywood movie, not likely.

Dr Deco :doctor:

 

[BigJetDriver]

Don Burke once bubbled...


BigJet,

Do the airliners coming back from dive locations ask for lower altitudes just in case? [/B]

Fraid not, Don! For one thing, the Air Traffic Control structure is not set up for it. The routes, or lanes, for aircraft arriving and departing specific airports are preset both in terms of direction and altitude. For another, once you drop below a certain altitude, jet aircraft are HUGE pigs when it comes to sucking fuel!!:huh:

 

[Don Burke]

BigJetDriver69 once bubbled... Fraid not, Don! For one thing, the Air Traffic Control structure is not set up for it. The routes, or lanes, for aircraft arriving and departing specific airports are preset both in terms of direction and altitude. For another, once you drop below a certain altitude, jet aircraft are HUGE pigs when it comes to sucking fuel!!:huh:

That's what I suspected. ATC could set up the flight levels to make it easier for a homeward bound plane to descend, but that would probably be too hard.

 

[adder70]

Remember that not long ago divers still used in water recompression therapy. While this is obviously not the ideal prectice, you can simply realize that returrning to sea level pressures is similar to having a diving related DCS hit and correcting it by visiting a chamber. So while you may be slightly bent from the sudden pressure reduction, returning to sea level is almost like very long term hyperbaric therapy.

 

[dtdiver]

"People have gone to the top of Everest without oxygen, so it isn't impossible.
......
The body will function quite well on about .17ATA of oxygen as long as the exertion level isn't too high. "

without acclimatization, unconciousness will result from acute exposure to the low pO2's at high altitude. the mountaneers take weeks to months to acclimatize prior to their ascent.
even as such the hypoxia is so extreme that they WILL DIE if they don't return to lower altitudes (hence the name "death zone" above 24,000 feet), even though they can survive there for short periods of time.
even without exertion, there isn't enough oxygen present to support metabolic function- the body consumes itself to generate enough energy to survive.

even going from sealevel to 10,000 ft leaves most people short of breath with minimal exertion. a sign of hypoxia. i'm not sure i'd call that functioning " quite well"

dt

 

[Don Burke]

dtdiver once bubbled... "People have gone to the top of Everest without oxygen, so it isn't impossible.
......
The body will function quite well on about .17ATA of oxygen as long as the exertion level isn't too high. "

without acclimatization, unconciousness will result from acute exposure to the low pO2's at high altitude. the mountaneers take weeks to months to acclimatize prior to their ascent.
even as such the hypoxia is so extreme that they WILL DIE if they don't return to lower altitudes (hence the name "death zone" above 24,000 feet), even though they can survive there for short periods of time.
even without exertion, there isn't enough oxygen present to support metabolic function- the body consumes itself to generate enough energy to survive.

even going from sealevel to 10,000 ft leaves most people short of breath with minimal exertion. a sign of hypoxia. i'm not sure i'd call that functioning " quite well"

dt

Quite a bit of this is taken out of context.

Much of the quoted message dealt with breathing pure oxygen at altitude.

Just doing some thumbnail math will tell you that 18,000 feet would be about .10ATA of oxygen, so I'm having trouble seeing how 24,000 feet is relevant to this discussion. .17ATA of oxygen translates to less than 2000 feet above MSL on a standard day. Unless I'm working pretty hard, I deal with that pretty well.

 

[Don Burke]

Make that 2000 meters in the last message. I still do pretty well.

 

[BigJetDriver]

adder70 once bubbled...
Remember that not long ago divers still used in water recompression therapy...

And as a minor note, we still do in settings where the boat, and personnel are configured for it, and the chamber is extremely difficult to get to.=-)

 

[Padipro]

Dr Deco once bubbled...
Dear SCUBA SOURCE Readers:

Flying and Pressure Loss

Fortunately, the pressure loss is not instantaneous. Any hole that would allow the aircraft to retain any structural integrity would prevent the loss of cabin pressure in less than a part of a minute, certainly not one or two seconds.

During this time, one would be able to position the oxygen mask. The plane will begin the descent and all will be fine. If you were skimpy with the FAD interval, you could be in for trouble.

Dr Deco :doctor:

Sorry Doc but that's not entirely correct. Remember the Aloha Airlines Boeing 737 jet that decided to become a convertable at FL240? According to the NTSB there was an "Exlposive Decompression" where nearly 18 feet of cabin skin and structure departed the aircraft. One Flight Attendant was killed and several passangers were injured but the aircraft made a safe landing.

If an aircraft window or door were to depart in flight, not likely but also not impossible, there would most certianly be a rapid decompression in a very short period of time and most likely the aircraft would remain airworthy. As was mentioned earlier in the thread there isn't much time at high altitudes to get the O2 mask on before one would pass out. This is the reason the Flight Attendants tell everyone in their breifing to get their own mask on first before assisting someone else.

When I was in the Air Force I had the oppertuinity to go through the altitude chamber. It's like a recompression chamber in reverse. The air is sucked out to simulate a higher altitude. One of the tasks we had to preform was to successfully survive a rapid decompression. Two chambers, linked by a system of vavles and ducts, were brought up to altitude. One chamber to 30,000 feet or so and the other to around 8000 ft to simulate the cabin of an aircraft. We were in the 8000 foot side with no idea when the valves would be opened to equlize the two sides to about 23,000. All at once there was a big BANG, everything fogged up so bad you couldn't see your hand in front of your face and we had to put our O2 masks on and go to 100% O2 on the regulator panel. No one was injured no lungs burst no ears bled. It all happened so fast they said there was little chance for injury.

In fact the only incident that occured was my case of pulminary oxtox from prebreathing 100% for several hours a day, several days in a row while in training.

Scott