On: How often do plane stowaways fall from the sky?

[pdx]

    Above 33,000ft (10,065m) the lungs require artificial 
    pressure to function normally.

So, you don't know either. Why did you respond then? The pressure from an oxygen canister can be down regulated to anything you choose, including 1ATM.

[praptak → pdx]

I doubt that human lungs can withstand this much difference between inside and outside pressure. I haven't found the maximum non-harmful difference but a quick google found that maximum expiratory pressure in men is 97 cmH2O. This is only about 0.08 atm.

So I wouldn't count on the canister alone, unless it is connected to a full-body suit.