Although Advanced Nitrox and Deco Procedures are written as two different courses, the instructor is allowed to combine them and treat them as a single course, with required dives done in a different order than if the courses were done consecutively. It makes a lot of sense to do it combined, because, frankly, a stand alone advanced nitrox class makes very little sense, and the combined system (which is spelled out) works much better. If a course is taught that way, you may indeed be doing decompression dives before you are technically done with the Advanced Nitrox class.
In the above paragraph, I said you may be doing decompression dives rather than you will be doing decompression dives because, unless the rules have changed since I left TDI, Decompression Procedures certification does not actually require doing any decompression dives.
Open Water Execution:1. Four dives are required, 2 of those dives must be deeper than 30 Metres/100 Feet.2. If Advanced Nitrox is taught in conjunction with decompression procedures* only a total of 6 dives are required.
I always taught the combined class with a minimum of 10 dives, and the last 3 were actual decompression dives where the deco time did not exceed the bottom time.
Even when I started to split the class into two, AN and DP, we still did 10 dives.
5 for AN and 5 for DP made a significant difference in their skill levels and retention of the materials.
I'd do AN one weekend, focusing hard on bottle handling, team skills, and emergency procedures in less than 30 feet of water. We'd rack up 8 to 9 hours of good bottom time. And we'd cover some of the DP skills here. It was an AN/DP class.
Just with a break between sessions.
I'd then have the students go off and practice for a month or so. However many dives they did was up to them, but 99% of them tried to get more than a half dozen dives in.
When we'd get back together for DP they were solid and diving like a team.
We'd do one I guess you could call it refresher dive kinda shallow and the 1st part of the skills to critique anything.
2nd dive would be to 100 ft and do the required skills at that depth. Air share and emergency back up deployment.
Dives 3, 4 and 5 were actual decompression dives.
We did plan them using a lot of conservatism so that in actuality dive 3 could, if the stuff hit the fan, fall back on a no deco bailout. Never had that happen.
But 4 and 5 did not have that option even at the level of conservatism we were using.
Deco was required.
And the water temp at depth was usually in the low 40s.