Overshooting NDL and mandatory deco stops

[tursiops]

In my experience, when we were expected to go into 5 min of deco, due to short surface interval and 25m+ consecutive dives, the guide said to the three of us, to flag her when we reached 5 min deco on our dive computers. As soon as someone hit 5 min deco, we would end our dive and proceed to the safety stop.

For the dive computer, it can be set to have Deep Stops or not:

If Deep Stops are set, then the computer will indicate a depth and duration for the mandatory stop(s). Once you're within the depth plus a bit of tolerance, the dive computer will start counting down. You're clear when the computer gets to zero. After completing all the Deep Stops, you would proceed to the normal safety stop and do the typical 3 min at 5m.

If Deep Stops are not set, then you would likely proceed to the normal safety stop depth of 5m and wait out the mandatory stop. The computer would count down until the mandatory stop is complete... then it will start counting down from 3 min for the normal safety stop. Maybe some computers will combine the two counts.

If you're low on air, going progressively more shallow will gain you some time.

As the others have said, know your dive computer. It will tell you your obligations.

Sorry, this post has so many inaccuracies in it that it should be ignored.

 

[JackD342]

Sorry, this post has so many inaccuracies in it that it should be ignored.

It kind of makes some sense if you substitute "NDL" for "deco." I suspect that is what @divinh meant.

 

[almostDIR]

When using PADI DSAT RDP:
Exceed NDL < 5 min, then 8 min deco at 15ft, no diving for next 6 hours.
Exceed NDL >= 5 min, then 15 min deco at 15ft, no diving for next 24 hours.

my padi air table says 'exceed NDL>= 5min, then no less than 15min deco at 15ft, no diving next 24 hours' so they suggest at least 15min needed in any case and don't want to calculate any further.

I guess one could use deco software to get some estimates for longer stays for emergency purposes (just in case) even if not deco trained and if trying to do NDL dives. but most computers should tell the same info in these cases I believe

 

[tursiops]

It kind of makes some sense if you substitute "NDL" for "deco." I suspect that is what @divinh meant.

Perhaps, but that doesn't fix the nonsense about deep stops and deco stop depths.

 

[JackD342]

I'm not going to start running scenarios on my RDP, but I try to imagine what kind of a dive profile would allow me to both exceed my NDL and still have enough air left for a 15 min deco stop if using a standard AL80.

I don't think that is likely to happen if you just accidentally overstay your depth by a few minutes on a typical recreational dive. Sounds more like a scenario of repetitive deep dives with abbreviated surface intervals, so would be more likely to occur if pushing some other limits too.

 

[KenGordon]

Caveat this has not happened to me and im not going to do it. But if someone else has in the dive what would be the time for a mandatory deco stop? And im only asking the question as im sure it does happen to divers I just want to know the process.

If a diver were at 100ft depth and for whatever reason lost track and overshot the NDL by say 2 minutes and started up then at what depth would the mandatory stop be and for how long? On air. I assume if you hit the NDL on 32 nitrox it would end up being the same thing you were just at 100ft longer to get there.

Also do all modern dive computers automatically warn you at NDL and then tell you when and how long to stop?

Obviously if theres not enough air left you are going to avoid a mandatory stop of course.

Depending on the brand and type the computer may show the total ascent time (TTS, or time to surface).

From a minute stop (ie immediately after NDL expires) from 30m that will be 7 or 8 minutes (2 or 3 to reach 6m, 1 minute mandatory stop, 3 minute safety stop and 1 minute to reach the surface.

That can be a surprise, and worrying if you think it is telling you you need to spend 7 minutes at a mandatory stop.

 

[NAUI Wowie]

Lot of info here and interesting takes. I have a perdix A.I. computer. I also personally now have 2 120 HP steels and I know some divers in monterey even use 133s.

Im paranoid about my air consumption and always check every few minutes so this scenario wont happen to me unless I have to chase someone down to help.

It looks like there really isnt much extra time at shallow depth to blow off the excess nitrogen if you go over NDL by about five minutes but then it says dont dive for six hours or 24 hours.

That part doesnt make much sense based on the total time on stops and some of the stop time being going up slowly so its not much.

I havent in past really hit up on any NDL limits as I dove mostly AL80s and shallow 40 to 60 ft but Monterey has some areas where with my 120 tanks I am pretty sure I can hit NDL limits.

 

[JackD342]

Lot of info here and interesting takes. I have a perdix A.I. computer. I also personally now have 2 120 HP steels and I know some divers in monterey even use 133s.

Im paranoid about my air consumption and always check every few minutes so this scenario wont happen to me unless I have to chase someone down to help.

It looks like there really isnt much extra time at shallow depth to blow off the excess nitrogen if you go over NDL by about five minutes but then it says dont dive for six hours or 24 hours.

That part doesnt make much sense based on the total time on stops and some of the stop time being going up slowly so its not much.

I havent in past really hit up on any NDL limits as I dove mostly AL80s and shallow 40 to 60 ft but Monterey has some areas where with my 120 tanks I am pretty sure I can hit NDL limits.

The number one take away you should have from this discussion is to NOT mix and match rules and procedures. If you are diving with your Perdix computer and exceed the NDL of that computer, then follow the deco procedure and the minimum surface interval(s) defined by that computer. Do NOT exceed a computer NDL and then decide to use PADI RDP emergency deco and surface interval rules. Or any other such combination.

 

[NAUI Wowie]

The number one take away you should have from this discussion is to NOT mix and match rules and procedures. If you are diving with your Perdix computer and exceed the NDL of that computer, then follow the deco procedure and the minimum surface interval(s) defined by that computer. Do NOT exceed a computer NDL and then decide to use PADI RDP emergency deco and surface interval rules. Or any other such combination.

Oh yes definitely. Its part of the reason I got the perdix after my suunto zoop basic computer. I wanted something that will give me more information while easier to navigate through. That suunto was a pita to even do basic changes like gas changes from air to nitrox. Hated it. Still have it though and clip it to bcd as a backup

 

[uncfnp]

Lot of info here and interesting takes. I have a perdix A.I. computer. I also personally now have 2 120 HP steels and I know some divers in monterey even use 133s.

Im paranoid about my air consumption and always check every few minutes so this scenario wont happen to me unless I have to chase someone down to help.

It looks like there really isnt much extra time at shallow depth to blow off the excess nitrogen if you go over NDL by about five minutes but then it says dont dive for six hours or 24 hours.

That part doesnt make much sense based on the total time on stops and some of the stop time being going up slowly so its not much.

I havent in past really hit up on any NDL limits as I dove mostly AL80s and shallow 40 to 60 ft but Monterey has some areas where with my 120 tanks I am pretty sure I can hit NDL limits.

So you are concerned that you may accidentally hit your NDL with your new bigger tanks? The obvious answer is just watch your time.

If you really want to know how to handle deco, accidental or purposeful, take a deco course. Otherwise know your computer. Chances are if you just touch deco your recommended safety stop will become mandatory.

Curious, what GF settings do you use?