Bobb,
The basics of this issue ARE suposed to tought in o/w course. I'll give you a schem of things, anyone else may add to it or reffer to it ofcourse.
Deapth
meters
0 -Surface.
6 -No decompression depth (to shalow to develop DCS).
18 -Beginning of Narcosis, unfelt by most people.
30 -Narcosis get's up another stage,functionality is reduced.
42 -Every one is narked here, rec. dive limit.
55 -Nark is STRONG, I had halucinations.
70 -Risk of O2 tox.
Deep diving:
It is highly none-recomended for none very experienced divers to go beyond 30 meters. Narcosis get's strong, and inflicts there everyone. Beyond 42 meters the risk of narcosis is VERY big.
About no deco times:
If I remeber correctly, there are no deco time up to 70 meters. It stays 5 minuets, but only getting there will take a few minuets.