crew oxygen?

[wingtip777]

could anyone tell me this: how long can the crew oxygen be used in case of depresurisation on the boeings(eg. B777)?

another question:at 20000feet, how long does it take a person to be unconscious?

[Golden Rivet]

Until it runs out ?

A lot longer than it takes you to descend to a breathable altitude.

At 20 000 ft you've got approx 25mins or less before hypoxia symptoms become apparent. ( loss of muscular control, judgement,reasoning, memory and time sense, emotional outbursts)

At 40 000 ft you've got approx 15-20 secs (10 secs under rapid decompression ), until loss of consciousness.

Also smokers will encounter symptoms 2000ft to 7000ft earlier than non-smokers

regards

[18-Wheeler]

At 20 000 ft you've got approx 25mins or less before hypoxia symptoms become apparent.

I beg to differ - I've actually done it, and no no physical exertion I was rapidly heading towards being a blathering idiot in a mere ten minutes. (Hard to tell from the normal state though, I must admit! :) )

I guess that's a pretty average normal figure in the real world.
I did it in an Aerostar 601P endorsement, for the express purpose of knowing what hypoxia feels like. I've never forgotten it, so I'm always aware.

[JEP]

I agree with 18-wheeler - 25 mins at 20.000 ft is too optimistic.

My book on Human Factors says 12 min of useful consciousness while sitting quitely and 5 min during moderate activity - it also says it varies considerably depending on physical condition, smoker/nonsmoker.

[Straight Up]

25 minutes sounds a bit hopeful to me as well.

When I did the course at Boscombe Down the chamber was depressurised to 25,000 ft, and the three of us on the course took it in turns to do jigsaws, and after 2.5 minutes I was trying to fit two pieces together with one of them vertical, so I don't think I would have been much use at the controls. (I wouldn't be that much use anyway, as I'm not a pilot, but you get the idea).

It was an interesting experience, and bloody good fun as well.

[Human Factor]

Having 'survived' a decompression to 25000ft, courtesy of RAF North Luffenham, useful conciousness at that altitiude is two to three minutes. Gibbering idiocy begins shortly thereafter.

[Empty Cruise]

AFAIK, flight deck must be supplied with not less than 15 min. of oxygen at 100% (mask overpress.).

Where does it say so? Beats me...

Empty

[TheDrop]

Since the original question was for a transport category aircraft (FAR25) the specs can be found in FAR25 to be as I remember a total of 2 hours, of that 10 minutes to descend to some altitude, then stay there for 1:50.

Have a look in either JAR25 og FAR25, it should be the same.

[saudipc-9]

Human,
Think TUC is 4-6 minutes at 25'000. Concur with gibbering idiocy begins shortly thereafter:D

[GlueBall]

Factors of physical health and altitude acclimatization influence time of useful consciousness. Persons who live at high altitude cities such as La Paz, Quito, Bogota, Denver, Jo'burg...etc, would have an easier time breathing at FL200. Some folks have climbed Everest without oxygen; and all Everest climbers have made base camp at 24,000 feet without oxygen.