Cabin depressurisation

[Tallbloke]

I am looking for some advice.
My question is this: What happens to cabin temperature in the event of depressurisation at normal cruising altitude?

I am writing my thesis on Long Range Operations. Manufacturers are promototing the use of onboard oxygen generators to preclude a descent in the event of cabin depressurisation, the idea being that if the aircraft need not descend, it is permissable to fly over higher terrain, thus opening new routes for example over the Himalayas, where a descent to <10,000 feet is not possible. However, this is academic if the pax are going to freeze to death. Any opinions would be appreciated.

[Bre901]

Although I am not an aerospace engineer, I feel I could at least fuel some discussion. The answer would be : it depends.

If A/C & heating is still operating and can cope with some increased flow (after all the cabin pressure is regulated through a bleed valve), temperature control would still be possible.

Otherwise, let us assume an adiabatic expansion of the air in the cabin (probably some sort of worst case). Starting with a cabin altitude of 8000 ft (2438m), the ISA pressure would be 75264 Pa, temperature=20 deg C (293K). Depressurizing to 41000 ft (12496m) would drop the pressure to 17874 Pa. The adiabatic expansion yields T.P^(1-1/gamma)=constant, hence the final temperature will be = 293*(17874/75264)^(1-1/1.4)=194K=-78deg C.

This is well below the ISA temperature (-55degC) at this very altitude. Maybe the temperature would not drop below -55 degC if there is still some venting available, but the SLF would still be a little stiff in the end.

Hope this helps

[Seat1APlease]

I am highly sceptical. Firstly aircraft normally carry drop out oxygen which will keep the passengers alive for about fifteen minutes until the emergency descent is complete. To carry oxygen necessary to continue in cruise for another hour or so would be prohibitively heavy and technically complicated. Many passengers would have suffered ear damage or other medical problems and the thought of continuing in cruise for another hour or so pretending that everything is fine just doesn't bear thinking about. The aircraft may have suffered structural damage and all considered needs to get on the ground as soon as possible.

Now if the manufacturers are considering carrying slightly more O2 in case an immediate descen to <10,000ft is impractical in less than 20 minutes then that is a different matter.

[smandkjc]

We interviewed a number of the survivors from flight UA811. A United Airlines 747-200 that had suffered an explosive decompression at 22000 ft on 24th Feb 1989.
The shock wave from the decompression burst a number of the passengers eardrums especially in the lower first class cabin.
A number also suffered damage to their teeth as airpockets in fillings expanded. some passengers also ingested insulation material an other airborne particles.
The cabin also filled with mist.
Cant recall anyone actually saying they froze but maybe the sudden adrenalin rush of having an aircraft fall apart around you helps to keep the cold at bay.

[Tallbloke]

Thanks for the input, further research indicates that the oxygen generation system is to allow further flight without diversion in the event of single or double engine failure on 4 engine a/c. Quite what is proposed in the event of depressurisation is not so clear. Thanks again everyone.

[SRB]

Nobody has mentioned the risk from decompression illness (DCI) which is very real and potentially fatal. The aircraft would have to descend to at least below 18,000 ft to remove this risk, so for this reason alone continuing the flight at normal cruise altitudes, even with supplemental oxygen and alternative cabin heating, is a non-starter.