Hmmmm... From Canada, joined May 1999, 2095 posts, RR: 5 Reply 2, posted (10 years 9 months 3 weeks 12 hours ago) and read 4173 times:
Canadian air regulations stipulate that, in Canada, no person shall fly an unpressurized aircraft between 10,000 and 13,000 ft. ASL for more than 30 minutes unless there is, available to each person, an oxygen mask and a supply of oxygen, nor shall anyone fly an unpressurized aircraft, for any amount of time over 13,000 ft., unless there is an oxygen mask and a supply of oxygen available for each person.
Those are the legal limits, but that also gives you a good idea of what the practical limits are.
An optimist robs himself of the joy of being pleasantly surprised
Kay From France, joined Mar 2002, 1884 posts, RR: 3 Reply 8, posted (10 years 9 months 2 weeks 6 days 23 hours ago) and read 4004 times:
Scientifically, 12,500ft is the max altitude after which oxygen lacks. More than 30 minutes up there and one suffers hypoxia and other lack-of-oxygen related symptoms.
Very dangerous. You can become unconscious.
"Hmmmmm", 10,000ft is the legal limit in Canada, but not the practical limit! I spend quite some time around that altitude with a max of 10,500ft in the 172.
Radarbeam From Canada, joined Mar 2002, 1310 posts, RR: 5 Reply 10, posted (10 years 9 months 2 weeks 6 days 22 hours ago) and read 3977 times:
The truth is that hypoxia can start at different levels depending on the person and other factors, such as the time of the day. For example during day time one could become hypoxic at 7,000ft or 8,000ft if the person is in bad physical condition or if the person is a smoker. And during night time assuming the person is in good health condition (non-smoker) hypoxia could start as low as 5,000ft.