I did the "physiological flight training course" at Edwards AFB several years ago in preperation for a skydive from 30,000ft. I would recomend it to anyone who is serious about flying. Until you have experienced hypoxia for yourself it is hard to comprehend how dangerous it is and hard it is to tell that you have it. On the course we did the following:. .. .Chamber ride to 24K to observe symptoms of hypoxia. . .. .We were supposed to wait until we observed one or more physical symptoms and then start breathing oxygen. Even though this was a training course and the whole point of the excercise was to become hypoxic several people didn'y put their masks on in time and started spacing out.. .. .A demonstration of how bad night vision is at altitude without oxygen. . .. .Above 7,000ft night vision and the ability to distinguish colors is severely degraded if you aren't on oxygen.. .. .Depressurisation. .. .We were depressurized from 7000ft to 24,000ft in about 3 seconds. Two notable things: In the event of a rapid depressuriasation you will start to exhale even if you were inhaling as the air in your lungs expands. Also expect all the water vapor to condense into fog and then dissapate a few seconds later.. .. .As for long term harm - there's a big difference between taking people to the onset of hypoxia at 24,000ft and allowing them to be hypoxic for prolonged periods of time at 30,000.. .. .theRolfe