Pressure loss in airplane

[ScubaRon]

Every time I watch the safety video in an airplane and see all the oxygen masks pop from the ceiling I wonder what happens if the pressure would be lost at say 30,000 feet altitude.

I would expect that the pressure loss would create instant pneumothorax and embolism, so what is the point of the masks?

Can anyone explain this to me?
ScubaRon

 

[FredT]

The O2 is there to keep you alive and conscious until the plane gets down to where there is enough O2 in the air to do it on it's own.

The screaming will keep the unwashed masses from breaking a lung. As a trained diver you know enough to keep your lungs open to keep from breaking one, and you'll probably even equalize your ears.

The pressure drop will result in a certain percentage of bent passengers, but even a bent passenger will still be breathing. As long as they keep breathing, bent is usually treatable with at least some success.

FT

 

[Dr Deco]

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:

 

[DA Aquamaster]

Even at 30,000 ft, getting bent is not really the issue. It is more of a concern at higher altitudes and military pilots expecting to fly higher (50,000 ft plus) will pre breathe O2 before the flight and stay on o2 during the flight to avoid getting bent in the event of a loss of cockpit pressurization. If they are sustaining flight at those altiudes they will be in a pressure suit to ensure they can function in the event of cabin depressurization, but the suit pressure is still much less than sea level pressure and getting bent would be a concern without prebreathing O2.

An airliner losing cabin pressure at 30,000 ft will make a immediate and dramatic descent because at that altitude even 100% 02 will not be very effective at ambient pressure through the cheap constant flow masks provided for airline passengers. They are required to have at least a 10 minute supply on board for each passenger if they operate above 25,000 ft.

The flight deck crew normally use a more advanced pressure sealed demand mask similar in function to military pressure demand masks. These maintain some positive pressure and allow the pilot to function for extended periods to about 35,000-37,000 ft.

The problem with 100% 02 at very high altitudes is that the partial pressure is just so low that it just won't pass into the blood stream. Pressure demand masks extend this altitude a bit but do not remove the need to decend if cabin/cockpit pressure is lost above 35,000 ft.

At or above 35,00O feet the pilot or co-pilot must be on O2 at all times as in the event of a rapid cabin depressurization, a pilot without O2 will be concious for only about 7 seconds - not normally enough time to don an O2 mask. Both pilot and copilot are required to be on O2 at or above 41,000 ft.

Regardless of the regulation it's a good idea have one of the fligth crew on O2 at altitudes well below 35,000 ft. The Payne Stewart tradgedy is a good example of what can happen when an aircraft loses pressure at high altitude.

 

[BigJetDriver]

Here's what really happens:

The "CAUTION" message comes up on the EICAS (an electronic status indicating system), and the Master Caution light illuminates! We say: "CR*P!" and start looking at things to find out what's going on. The "WARNING" message comes up along with the Cabin Pressurization Checklist, and the Master Warning Light. The bell goes off, literally! We say: "Sh*t!!!" and grab our masks!

The presure demand masks we now have are easy to don. They look an awful lot like the "face-hugger" creature from the movie "Alien"!:wacko:

We begin the process of notfying ATC (Air Traffic Control), turning off the airway, closing the throttles, putting out the speedbrakes, and pointing the nose down for our rapid descent.

In the cabin, there are lots of, as mentioned earlier, "cries of amazement" (understandably so), and lots of fumbling around with the "rubber jungle" that has fallen out of the overhead!

We will be down to 10,000 feet MSL shortly, and we will then be able to remove the masks, and begin sorting things out. The process will involve diverting into a suitable near-by airfield, and having maintenance fix the problem. We will then proceed on to our destination, albeit somewhat grumpy at having been delayed.

All of us will proceed EXCEPT, however, for those of us who have pushed the limits of the Flying After Diving rules, especially those who practice the infamous "Wet Hair" procedure. As has been aptly pointed out by Doc Deco, they will be going to whatever location has the nearest hyperbaric chamber for treatment of their now evident pain and suffering!ity:

Thus endeth lesson Number #1 in Aircraft depressurization Basic Procedures!

 

[Epinephelus]

ScubaRon once bubbled...
I would expect that the pressure loss would create instant pneumothorax and embolism, so what is the point of the masks?

As a PMCF (Post Maintenence Check Flight) pilot in tactical jets, one of the checks I had to perform was to dump cabin pressure at 40,000' - which artificially creates an explosive decompression situation - takes about a second. I suppose that had I taken a deep breath just before, and held it during the decompression I could have induced an embolism - but by just breathing normally the decompression event falls into the "no big deal" pile.
Surprise, surprise, Hollywood lies...
Now DCS is a different matter entirely, and to avoid that I prebreathed pure oxygen prior to the check flight and all during the check flight - and it became positive pressure breathing at 40,000 when cabin pressure was dumped. Others have already mentioned that those who've shaved their FAD interval close are at increased risk of DCS in the event of a cabin depressurization incident - but embolism just isn't a problem.
E.

 

[BigJetDriver]

We now have actual testimony available on this board from one of our members who cut short his time from diving to flying, and did get bent as a result. One can read his testimony in Basic Scuba Discussions under the heading: "I just got bent!" In his particular case, there was NO pressure loss in the aircraft. Had there been, he would have had much less of a chance of recovery!

 

[DandyDon]

FredT once bubbled...
The screaming will keep the unwashed masses from breaking a lung. As a trained diver you know enough to keep your lungs open to keep from breaking one, and you'll probably even equalize your ears.

FT

That'd be a reverse sqeeze, won't it? Hate those! :errrr: Have to remember to exhale fully and equalize before I bend over to kiss goodbye. :smooch:

don

 

[BigJetDriver]

Heck, DD,

They are almost non-events! By the time the haze clears, you slap the kid in the seat next to you, and untangle your mask that he was trying to steal, it's almost all over.

You don't even get to see Gert Frobe fly down the aisle and out the window a la James Bond!

Darn the luck!=-)

 

[Diver0001]

FredT once bubbled...
<snip>

The pressure drop will result in a certain percentage of bent passengers, but even a bent passenger will still be breathing. As long as they keep breathing, bent is usually treatable with at least some success.

FT

How do you reach that conclusion?

R..