Kimoki/JetII,
Sorry for sounding off a little,so I`ll backtrack.
Time of useful consciousness at FL300 is--30 secs
at FL350 is--20 secs
at FL400 is--15 secs
Now,you may be young and exuberant,and may be able to stretch those times a bit,but not a lot!
So,think about what will happen if you are alone on the flight-deck,and a w/s cracks,a cargo door/emergy. exit pops/smoke/fumes in the cockpit? If it`s a rapid decomp the a/c will probably fog out,it will be spaghetti junction in the cabin,SLF will be panicking,and your other crew-member may not be able to get back onto oxygen, or get to the flight-deck.
This may be painting a bleak picture ,depending whether you are flying SLF or just freight;with minimum crew on a freighter it could be said that the situation could be worse if the other crew is down aft- if so I would suggest that he should have a walk-around oxygen bottle and mask anyway!!
Once it has happened to you on a dark night,you will not forget---guaranteed!
You should sanitise your mask b4 and after flight anyway,when you check that it is working and stowed correctly.If you suspect it is leaking then you dont fly!!
I hope you will always be ready,but never have to put it to the test
Sycamore