I've just read a news article on the depressurization incident that happened today in Australia. How much time did the pilots have before they lose consciousness if they hadn't used their oxygen masks? This incident is said to have happened at FL 340.
According to: Time of useful consciousness:
- Altitude (measured barometrically) - TUC
- FL150 (15,000 ft; 4,550 m) - 30 minutes or more
- FL180 (18,000 ft; 5,500 m) - 20 to 30 minutes
- FL220 (22,000 ft; 6,700 m) - 5-10 minutes
- FL250 (25,000 ft; 7,600 m) - 3 to 6 minutes
- FL280 (28,000 ft; 8,550 m) - 2.5 to 3 minutes
- FL300 (30,000 ft; 9,150 m) - 1 to 3 minutes
- FL350 (35,000 ft; 10,650 m) - 30 secs to 1 minute
- FL400 (40,000 ft; 12,200 m) - 15 to 20 seconds
- FL430 (43,000 ft; 13,100 m) - 9 to 15 seconds
- FL500 (50,000 ft; 15,250 m) - 6 to 9 seconds
Time of useful consciousness tables are useful as a first order approximation.
The reality is that there is a great degree of difference between individuals, and also their conditioning. In one chamber ride, nearly an hour after explosive decompression (which can be very disorienting, even when anticipating it), I was still performing the cognitive exercises while my chamber partner was copying my kneeboard results and acting real silly.
I can also say that when spun in a centrifuge (no G suit) at 4G I was able to maintain consciousness at a pressure altitude of 30,000. As soon as I was spun up to 6G things got ugly fast, and there is a video to prove it.
The operators would also have us spin at some G level and then explosively decompress the spinning chamber. LOC happens very fast in that case.
If one has the ability to adjust the Gs, it is possible to play with your oxygenation. For example, performing the M1 maneuver, we would play with Gs and cause our vision to start to tunnel, to a soda straw tunnel, and then ease off on the Gs to get a more wider view of the world. The same thing is possible without the abdominal muscle maneuvers and working bladders in a G suit, just a lower Gs.