I appreciate the feedback, but do feel that you are misrepresenting what i was saying a bit. I was not trying to say these were not decompression dives - I was pointing out that they were not planned as such. We were not told prior to the first dive that this would be the case so I was concerned when I saw my NDL ticking down to zero at ~21 minutes into the dive and we were not yet ascending - which is why I let the DM know my state.
First, let me apologize in advance because my online demeanor can come across as ... brusque. This may come across as really beating you up on this and I don't mean any of it with any rancor. But, I do think it is a very important subject that merits direct and clear communication. It may not change your mind at all, but I'm also thinking of other people who may come along later and read all this and I hope it will at least help some of them make the best decisions they can.
I also did not think it was "perfectly fine" - but what would you suggest I do??
First (on that), you said the DM explained things after the first dive and "I was then prepared for this situation on the subsequent dives." That sounds like you thought it was fine. You did more dives of the same nature, right?
As for what I would suggest: Use your best judgment. If it was better, on that first dive, to stay with the group than to ascend, well, there's a couple of things about that.
If you didn't have a buddy that would ascend with you, that is a problem.
If it was a group dive and the group would not have ascended with you, then that is a problem.
If you were diving where the Golden Rule was not in effect, that is a problem. "Anyone can thumb a dive, at any time, for any reason, with no repercussions." It sounds like you did not feel like you could thumb the dive. And, from what you've posted so far, I suspect that your training is "when your computer shows an NDL of 0, you should be ascending to the surface." So, you didn't follow your training. Notice I did not say "you should be ascending." I said "you should be ascending to the surface." Another problem.
Regardless of how you handled it during the first dive, my suggestion would be to not engage in any more of those type of dives after that, once you understand that they are taking you on dives that are beyond your training and putting you in danger (of which you are not even fully cognizant, because you don't know what you don't know and - worse - you think you DO know).
Leave the group and ascend into a ripping current with limited viz (I'd have lost sight of the group for sure) in the middle of a pass with standing waves and boat traffic on the surface?? I did not think that was a good idea and I still had plenty of gas, so felt that the best choice at that point in the dive was to trust the DM who takes divers on these dive profiles many times each day and was indicating to me that it was OK. I had read "Deco for Divers" so understood basics of deco and what my computer was telling me and why - so I knew what was happening (we had stayed deep long on the front end). I also knew we would start ascending once we got through the pass and into shallower water. In any event, I would have headed for the stop depth if my gas supply had required it.
You also need to understand that these were not significant deco obligations: the first alert called for 1 min @ 9.8 ft. That increased to 3 min @9.8 ft, before shifting to 1 min @ 19.7 ft and then finally settling at 5 min @ 9.8 ft which counted down to 1 min and before going away and being replaced with the Safety Stop timer by the time I had ascended to 22 feet. So, the deco obligation that was accumulated would have been cleared with my safety stop and final ascent. Therefore, I was only concerned for a short period when it appeared to be increasing - once we started ascending 5 min later and I saw the deco stop diminishing, I had no real concern.
After the dive, I spoke to the DM about my concern and he went over the typical profiles and the fact that we might see these small deco obligations pop up. However, the deco obligation would be early in the dive when we had plenty of air to satisfy it if we needed to ascend to the surface for some reason and it would clear fully in the normal, planned profile otherwise. Once I knew that, I had no concern with that type/level of deco popping up on subsequent dives (had 1 or 2 min @ 9.8 ft pop up and clear well before safety stop depth was reached on 3 subsequent dives).
Deco for Divers is a great book. But, it is only a foundation for understanding the training that comes in TDI Advanced Nitrox and Decompression Procedures (or equivalent). Understanding what that book teaches you is NOT a basis for thinking that you know how to safely execute decompression dives (i.e. dives with mandatory deco stops). And your statements make it clear that you actually do NOT know how to do that.
You described having a mandatory stop for 1 minute at 19.7 ft. You further described that as "not significant" as a deco obligation. The politest thing I can say is that I respectfully disagree.
I happened to do a deco dive yesterday where my first stop was at 20 feet. At the time that my computer clicked over from a 10 foot stop to having a stop for 1 minute at 20 feet, my SurfGF was 131%. Had I ascended directly to the surface right then, I would have gotten there with my leading compartment at 30% OVER the M-value! That is NOT "insignificant". Further, if your computer was set to less conservative settings than I was using yesterday (which, mine were fairly conservative), then your SurfGF would have been even higher.
I hope your understanding gleaned from Deco for Divers informs you on how significant a SurfGF of 131% is. I am COMPLETELY confident that, had I ascended directly to the surface just then, even at a normal ascent rate, I would have been very bent when I got there or soon after. I say that from actual experience, not just book learning. Unless you have your computer set on some ridiculous, unrealistic level of conservatism, once you have built up enough deco to have a stop at 20', you are well into SERIOUS deco territory. Not "you're going to die" territory (probably). But, "serious pain and a chamber ride" territory, anyway.
I honestly see no reason for me to get trained for deco diving to manage this type of dive profile now - I know what I need to know.
Again.... I respectfully disagree. Not based on anything you have posted, anyway.
I'll add that I have not had that situation arise again in almost 200 dives since Rangiroa and would normally avoid it by shallowing up, if at all possible.
The last thing I'll say on the topic is that I still personally believe that there is a huge difference between my example of what I get were actual deco dives (albeit unplanned) with very small (safety stop like) deco obligations and planned deco dives where the stops (#/depth/time) can be complex/significant and require advanced planning to ensure sufficient gas supply/backup and possible surface support. I get that requires special training to do safely but I have no interest in ever doing that type of diving.
You were DOING that type of diving. And despite thinking that you know what you need to know, you didn't even know you were doing that type of diving - much less how to do it safely. Reading Deco for Divers and an explanation from a Divemaster is not an adequate substitute for formal training on how to safely execute the exact kind of dives you were doing. "They do them all the time" is not an acceptable validation that diving like that is safe.
This is TEXTBOOK Normalization of Deviance. This kind of thinking is a signifcant factor in many diver deaths.
You do you, but I hope this discussion at least helps someone that reads it, some day, to avoid engaging in the same behaviors.
Anyway... I am bowing out of this now. Unless you ask me a specific question, I will just leave this alone now. I think I have killed the horse.
ps. Again, I apologize if that all came across as being a jerk or being overly harsh. If you read it and try to hear in your head a sincere and concerned tone of voice - not an angry tone of voice - you will maybe understand how I am trying to "speak".
