As a rec diver, what to do if I breach my computer's NDL???

[Tigerman]

Aw, I hope you weren't referring to my comment about "it's in MY computer's manual." But how to handle a few minutes NDL violation is well-described out there--if not in one's computer manual then elsewhere. I also recall being given a rule-of-thumb procedure in a PADI Deep class.

Theres even one printed on the padi RDP if you have that handy..

 

[victorzamora]

Theres even one printed on the padi RDP if you have that handy..

I had never noticed that, but sure as shootin' there's one in there. 8min mandatory stop at 15ft for <5min over NDL. 15min mandatory stop at 15ft for>5min over NDL. It's pretty basic, and not NEARLY exact enough....but it's a good starting point, and absolutely better than running straight to the surface.

Edited to add: Minimum SI for <5min NDL breach is 6 hours, minimum SI for >5min breach is 24 hours....both as recommended by PADI's RDP. Check the RDP on the "reverse" side (repetetive dive side) for PADI's official wording.

 

[ianr33]

Excellent synopsis.

Only thing I would add is be sure to surface SLOWLY from that 10/15 foot stop. DO NOT do 20 minutes of deco then instantly pop up to fresh air. Once on the surface just relax for 10 minutes if possible. No need to immediately climb bouncy ladders or haul tanks up hillsides.

 

[victorzamora]

Good point! I'll add that if I can.

 

[boulderjohn]

I had never noticed that, but sure as shootin' there's one in there. 8min mandatory stop at 15ft for <5min over NDL. 15min mandatory stop at 15ft for>5min over NDL. It's pretty basic, and not NEARLY exact enough....but it's a good starting point, and absolutely better than running straight to the surface.

This "rule of thumb" has been a part of the RDP since it was created. It covered in the academic materials for the course if the student is taking the table version of the OW course. It's on the final exam. Allow me to explain the reason for it.

The PADI RDP was designed to be a no-stop required table. It does not include any diving requiring true decompression stops. They intentionally made it different from the Navy tables that preceded it on the theory that recreational divers doing recreational profiles should be governed by different rules from Navy divers. The Navy tables do include decompression stops for dives in excess of NDLs. The RDP is designed to allow recreational divers to have multiple dive days. Divers who stay within those guidelines can do multiple dives without unduly long surface intervals. Before that, divers following the Navy tables had to stay out of the water a very long time between dives.

Because the PADI RDP does not include decompression stops in its calculations, it has to have a way of dealing with people who violate NDLs unintentionally. Because it does not include decompression, it has no way of calculating surface intervals in the event that the diver does into decompression. It must therefore clear you so you can start over again on the table the next time you dive. Victor mentions that with <5 minutes of deco, you are supposed to do an 8 minute stop. He did not mention that you are then supposed to stay out of the water for 6 hours. That is because that surface intervals are based on the 60 minute compartment, which clears in 6 hours. (Look at the surface interval chart to see the 6 hour maximum.) If you go >5 minutes, you are supposed to stay out of the water for 24 hours. That is because they have to cover all possible bases on that rule, including situations in which much longer compartments might be appropriate.

Students taking the computer version of the PADI OW course are taught to follow the directions on their computers, not only for the length and depth of the stop but also for the surface interval.

 

[Lorenzoid]

Oh? Pray-tell mon ami, and what would that rule of thumb be?

See Boulderjohn's thorough explanation.

 

[victorzamora]

John, I'm sure it's been there forever....I had simply never noticed it. The reasoning makes sense, and you're right....I did forget to mention the minimum SI's mentioned. I only stole the part that I did to show how rudimentary it was, not for it to be used as a deco planner . The reasoning is pretty interesting, as well, as I had never really thought about it.

As far as that being taught in the tables class, I wasn't taught it when I took my OW (2004) and I was taught the tables. What's funny, though, is I remember the tables being an optional class....with no option if you didn't take it. I don't remember computers being mentioned at all. Then again, it was nearly half my lifetime ago....so it was probably different than how I remember it now!

 

[rhwestfall]

From a "techreational Diver" - The thing I am having a hard time dealing with is "accidental deco". SITUATIONAL AWARENESS.... thats more important than anything!

Now, quite honestly, if you are leaving the bottom with a few minutes of NDL time remaining, or, even into a very light DECO obligation, it is likely to clear on the ascent (just please understand what the "Magic Bracelet" is telling you). I'd also add that if you have thirds for gas reserves, or utilized a RB calculation, you are more than likely going to be okay to handle the potential of a light DECO obligation..... it just gets "messy" if something else happens....

Now, I am also right now doing an Intro-2-Tech to get my head around this more, and will likely be stepping it up to Adv. Nitrox and DECO procedures as a next step (or whatever gets me to that).

 

[Colliam7]

what you think of my synopsis.

Yes Vic, I'd say that's about right on topic.

I agree, I think the synopsis is very appropriate.

One thing that was mentioned on another thread was this: dive nitrox with your computer set to air, and then a backup computer set to your real mixture. Dive your air (primary) computer into deco and watch what it says. Make sure your backup doesn't go into deco and make sure you don't exceed MOD. Then, ascend and watch what your computer does. It's a way of simulating deco while not actually putting yourself in that situation. It also proves whether or not you could handle a deco stop. e.g. If you lock out that computer, you're "bent"...purely do to lack of skill.

This is a very instructive exercise, and I encourage divers, who have access to two computers, to try it. I have divers who complete their Deep Diver certification with me, do something very similar as a 'fifth' dive.

What you often find is that, if you exceed your NDL by no more than a few minutes, your computer will clear well before you reach your safety stop. I have done this at 130 feet - stayed there until my air computer went into deco, and accumulated a 5 min obligation, then executed a normal ascent and my air computer cleared by the time I reached 70 feet.

Your post has stimulated some good discussion.

 

[Nwcid]

I will add since I did not see it in here is UNDERSTAND what your computer is telling you.

On the other thread one poster stated his computer told him to go to 10' regardless of depth. I do not have that unit and can not speak to what it says, but in my limited knowledge (all from reading) that is not seem like a good deco profile. My old computer showed a 10" symbol but what it was telling you was to ascend 10' (or more if you were more then 10' below your next stop) and stop till the computer cleared. Once it clears again ascend until the next stop is shown. This fits in with the Deco profiles I have seen.

My new computer handles it differently showing carried depths not just "10".

As stated I have hit deco once. It was not an accident, but not planned either. We were critter searching and found what we were looking for with about 2 min of NDL. On the way up (contour shore dive) the computer easily cleared with no need for extra stops.