Dr Ian Millar, hyperbaric medicine unit director at The Alfred hospital, said: "If there was an emergency and the pilot took nitrogen instead of oxygen, instead of gaining control of the aircraft he would black out and it would be all over. It's a pretty serious mistake."
Is Dr Millar assuming the tanks were 100% full of Nitrogen?
When oxygen tanks are serviced, are they not simply topped up? Therefore would it not be fair to say that the tanks would be something like 95% Oxygen, and 5% Nitrogen?
Considering air is 78% Nitrogen, and 21% Oxygen, perhaps claiming that instant death would be inevitable is overstating it somewhat.
Of course I am not saying it is a serious matter, of course it is! I'm just pointing out that it may not be AS bad as first thought. (The partial pressure of oxygen is still 95% of what it would have been had it been serviced with oxygen bottles).
http://en.wikipedia.org/wiki/Earth's_atmosphere