Goby....Your welcome for the link.
I just returned from my TDI Nitrox class, and Warhammer is correct, from the safety standpoint, there is not that much statistical difference for DCI between air and Nitrox for 50 feet or less.
Looking at my PADI Recreational Dive Planner, the no deco limit (NDL) for 50 feet on air is 63 minutes. And from what I have observed, heard, and studied, 1 hour is typically how long an "average" diver can make an aluminum 80 tank last at that depth (considering a square profile, and average or less exercion).
If you were to replace air with Nitrox for 50' (or less), it would, in theory, provide more no deco time, but your limiting factor is the quantity of air in your tank. You would run out before you could appreciate the bottom time extension afforded by the increased 02.
Nitrox is mostly used to extend your NDL (no deco limit) for deeper dives. For the new divers following along, you remember that standard air is 21% O2 and 79% nitrogen. And if you were to consult your dive tables, you would see that at a depth of say, 80' you can stay down 25 minutes with no deco.
With EAN36 (Enriched Air Nitrox with 36% oxygen), your gas mix is 36% O2 and 64% nitrogen. In other words, the gas you are breathing has 15%
less nitrogen. An immediate benefit is that since you are inhaling less nitrogen, there is less being forced into your bloodstream. Thus the reduced chance of DCS. And your no deco bottom time is nearly doubled.
(Warhammer, check me on this please. I think I explained this right, but I've only had one class and no nitrox dives, yet.)
Finally, if I can sway your choice of agencies to obtain your nitrox cert, please consider TDI (Technical Diving Institute). With their sister agency (Scuba Diving International, or SDI
http://www.tdisdi.com) they are rapidly becoming one of the more "realistic" training agencies out there. By realistic I mean they are not so rigid in what and how they teach. They acknowledge the current trends and technologies in diving and include that in their information and methods. Plus, if you have a desire to be certified in some of the advanced diving areas (wreck, nav, cavern/cave, etc), then TDI/SDI will do an excelent job of training.
Good luck in your upcoming class, and be sure to keep us informed of the fun you are having.
--TM