Lee Bell wrote:

> As much as I scoff at PADI's delineation of open water versus deep diving
> levels, they've done a fairly good job of defining the level, about 60 feet,
> above which the vast majority of divers, on the vast majority of their
> dives,  do not need to monitor narcosis effects.

I thought narcosis was not the determining factor in setting the
20m limit. I don't remember all the explanations I read about the
"why" of this limit but the one I found most convincing was that
diving above 20m was a quasi guarantee that a beginner/not so
advanced diver would not exceed his NDL when diving with a single
12 lt tank.
Anyone in the know as for the real "why"?

Jean-Marc