Part of that is the idea some instructors have of dragging the student to the limits of the cert on the checkout dives with no real purpose other than to go there. In a combined AN/DP course, that means 150' on something like 25% nitrox with 1 or 2 deco gasses - usually 1 if the instructor or course progression wants to save some bottle management skills for normoxic trimix.
On the other hand, it's not all bad if the instructional intent is to have the student figure out they are narc'd beyond any useful ability at 150' and thus learn to scale it back a bit to somewhere in the 100-110 ft range, and doing the dives in a fairly controlled environment, but that does not always happen.
However, an AN'DP cert does not require the student to got to 150' - a 30-40 minute dive to 110-120' would work just as well for the deco, planning and bottle management skills. What ever flaws AN/DP may have, the advantage is that a progressing cave diver completes AN/DP and learns how to do decompression planning and masters the in water and bottle skills before showing up for a full cave class. In N FL full cave nearly always means doing dives that end up with a decompression obligation and the use of O2. While it's very common for full cave candidates to do this absent any formal decompression procedures training, it is in my opinion a situation where the student is then diving beyond the limits of his/her training during the class, and will continue to do so after the class.
I think taking AN/DP and understanding the problems with high ENDs is a much lesser evil than taking full cave absent AN/DP.
If you are talking about mix in an "AN/DP" course you are really talking about an extended range class with trimix for the last two dives, and that makes little sense as a) AN/DP is often a re-req and b) normoxic makes a lot more sense than extended range. I'd rather have a student do two more trimix dives and call it normoxic than do deep air dives instead and call it extended range.
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In any case, to the OP, the intent is to acquire the dive planning and bottle management skills required before you get to the point of doing decompression dives, especially in a cave. And having the training in advance reduces the stress and general ask overload that will occur in a cave class anyway. And whether you are certed to 150' or not, the max END in a cave should be no more than 130' per even the more liberal agency standards and most cave divers who've tried ENDs in that range, with or without mix, will probably suggest a max END of 100-110' instead.



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