Nitrogen narcosis involves many ever-changing variables that will
affect when and if it will happen. Speed of descent, temperature,
depth, physical fitness of diver only name a few.
I recently was narced at a depth that I had dived many dozens of times
with no symptoms at all. The bottom line, it is not something we can
predict. The best way to prepare for the narcs is to be aware of the
symptoms in yourself and be aware of your buddies behavior.
Just a thought from me! :)
"...pardon my appearance while I decompress"