Quiz - Recreational Dive Planner - Exceeds NDL By 6 Minutes

[scubadada]

Was that before the new high presure cylinders at 207bar (3,000psi).

Yes, these were steel 72s @2475 psi with the + rating, 2250 psi without, 72 and just short of 65 cu ft respectively. My RMV has always been good, I would routinely hit my NDL below 60 feet. We used USN tables, a bit more liberal than any of the tables today. I started diving in 1970.

 

[scubadada]

Yes, these were steel 72s @2475 psi with the + rating, 2250 psi without, 72 and just short of 65 cu ft respectively. My RMV has always been good, I would routinely hit my NDL below 60 feet. We used USN tables, a bit more liberal than any of the tables today. I started diving in 1970.

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That's funny, my SPG from 1972 only went to 3500 psi, all go to 5000 psi today

 

[TMHeimer]

I got it correct because I couldn't recall anything from past manuals/courses mentioning "3 hours".
I guess you could surface late due to equipment malfunction too. Once my SPG got stuck on 1000 PSI. I finished the shallow shore dive asap after realizing the needle was stuck. Got a new SPG.

 

[Steve_C]

How do you exceed NDL by six minutes and not discover it until after you surface?

Case in point she did not know how to read a computer in terms of NDL. All prior dives were with folks using AL80s who called the dive because of remaining air. She always ended with lots of air. This time she was deeper and with folks diving nitrox and also diving HP100s. I asked to see her gauges to see how she was doing on air which was when I discovered she was already a few minutes over NDL but had lots of air. I immediately thumbed the dive for the three of us and indicated to her she should stay with us and we slowly went up and did a longer safety stop.

She just followed our direction. On the boat we explained what had happened and how to read her rental computer. If you do not remember NDL from a class you had a couple years ago and after 30 or so dives then you don't know until you have been told.

In this case we did not surface until her computer had cleared. But she would have happily (maybe not) surfaced owing a lot more than 6 minutes if we had not acted. She was an air sipper and very relaxed in the water.

 

[Pedro Burrito]

Spoiler: Answer

d. Remain on the surface, rest and be monitored for signs/symptoms of decompression sickness; wait at least 24 hours before diving again.

 

[scubadada]

@Pedro Burrito

Good one, I look forward to them

 

[Brett Hatch]

She was an air sipper and very relaxed in the water.

Relaxed indeed! To the point of being cavalier if you ask me. Happy to hear that you and your buddies were around to keep this diver safe, great job. Surprised and dismayed however to hear that she went on some 30 dives not understanding how to read the NDL on her computer... if you are going to understand how to read literally anything on it, the NDL is top of the list for me.

 

[dmaziuk]

How do you exceed NDL by six minutes and not discover it until after you surface?

More to the point, if you didn't realize it at any time during the dive, what did you find on the surface that opened your eyes and woke you up?

 

[lowflyer]

Your question is about what happens if you surface after exceeding NDL by 6 minutes. The other case is if you discover you have exceeded NDL by more or less than 5 minutes but have not yet surfaced. In this case, I like the rule of "3 and 5". Normally it is a 3 to 5 minute safety stop at 15'. If you exceed NDL by less than 5 minutes then you add 3 to 5 so it is 8 minutes at the safety stop. If you exceed NDL by more than 5 minutes then you multiply 3 by 5 so it is 15 minutes at the safety stop. In both cases after you surface you have a wait time before reentering the water: 6h and 24h respectively. Those times are chosen to monitor for DCS and to wash out the excess nitrogen.

When you say "exceed NDL by more than 5 minutes," I think what is lacking with this formula is how far beyond 5 minutes it applies.

 

[tursiops]

When you say "exceed NDL by more than 5 minutes," I think what is lacking with this formula is how far beyond 5 minutes it applies.

Why does that matter? The explicit recommendation is to stay at 15 ft for at least 15 mins, longer if you have gas to do it. It is of course a long deco stop for those who are not trained in deco. When you finally get to the surface, you monitor for DCS, and if it shows you move into O2, etc. And stay out of the water for 24h, because (1) most DCS occurs with in the first 6h and almost all occurs within 24h, and (2) in 24h you have off-gassed enough to get back in the water.
And, all that time at 15 ft, and 24h out of the water, is being put in the penalty box for having been so careless in the first place.
What more would you like to see?