Exceeded NDL by a bit, but computer cleared me. What should I do?

[The Chairman]

that people can get bent even when they follow the computer,

Limits. Your PDC isn't your only limit. Treating it as such will cause problems. Exercise immediately after a "safe" dive is one of many factors that can result in trauma.

 

[jborg]

You'll note that your initial screenshot (with variable ascent rate) misses the deco ceiling if you extend the ascent rate established just prior to the safety stop.

If NDL was calculated with that stop in mind, the bottom time would increase when enabled. When I check it, bottom time in the table on the right is unchanged.

Yeah, agreed.

What I see is what happens when that isn't possible -- for example if I ask for a 5 minute dive to 70m. If "safety stop" is unchecked it will correctly mark the dive as red -- not an NDL dive:

However, if you check "safety stop" it resolves into a green "NDL dive" with the safety stop:

So it will indeed try to clear deco without a safety stop, but will accept having to do one. In either case, I think it's arguable that these are not in fact NDL dives...

Of course these are extreme samples maybe pushing the algorithm unfairly, but I think the suggested plan for a more recretational-ish 40m dive is still what most here would consider a deco dive? Or anyway, that was the discussion in the thread, whether a deco dive is a dive where we do deco stops, or one where we have a deco ceiling at some point. If the definition is to avoid having a ceiling, these are not NDL dives...

I was surprised to see the rec planner extending the dive like this instead of beginning the ascent in time to avoid the ceiling.

 

[Boarderguy]

Limits. Your PDC isn't your only limit. Treating it as such will cause problems. Exercise immediately after a "safe" dive is one of many factors that can result in trauma.

Off topic: how you holding up down there in whirly weather alley?

 

[Subcooled]

I was doing a guided dive to 30m today and was roughly following the guide. I have a habit of checking my computer often, but it’s not 100% there, and I have just started diving deep. Excuses, I know.

My aqualung i300c has a deep stop that triggers automatically, which I didn’t notice this time, but at some point I show the NO DECO and the dive time remaining flashing. I thought it was my DTR alarm triggering and paid no attention (there was no audible alarm). The computer didn’t instruct me to do a Deco stop. I did the usual three minute safety stop at 5m and then surfaced.

When I synced the dive to the Dive Log plan, I see that it has marked a point with red, saying decompression (see image). I am not 100% sure if it is using another algorithm or if it’s picking up NDL data from the computer.

Should I be worried? What should do better next time, apart from monitoring my computer closer next time, and perhaps start Nitrox diving?

Looks good.

The dive logging software warns you about a mandatory decompression stop at 3m (9ft) for 2 min. It's not a lot and you are not very deep and you are on your way up, so things are gradually getting better. Please note that the amount of conservatism does vary from model to model. And then there are things that are not modeled at all (like your BMI or hydration status). Hence, it's an inexact science. The computer is only a rough guide - more on the safe side though. Your software could have even wider safety margins.

Ways to increase safety include staying fit (good aerobic shape and not excessively fat), limiting repetitive diving, drinking plenty but not excessive amounts of water during the whole week (good hydration), slowing down ascent during the last 30ft, spending extra time at 18ft or shallower, drinking water after the dive, avoiding hot showers and steam baths and physical excercise (e.g. lifting heavy loads) after the dive... So, there are many things you can do to increase safety besides watching a dive computer screen.

 

[L13]

If NDL was calculated with that stop in mind, the bottom time would increase when enabled. When I check it, bottom time in the table on the right is unchanged.

You are right. I was experimenting with SubSurface and got the same impression that @jborg did, that it affected NDL. I could have sworn it changed the NDL time, I must have done something else and fooled myself. However I just verified that I was wrong and it works just like you say. (I am using 5.08 as well)

 

[inquis]

I was surprised to see the rec planner extending the dive like this instead of beginning the ascent in time to avoid the ceiling.

That's the thing, it didn't extend the bottom time at all. The "planner" takes over at the end of your defined profile. I'd say that leaving the yellow warning triangle in place would be a better UI choice when the user has forced the bottom time beyond NDL and checked "safety stop".

 

[jborg]

it didn't extend the bottom time at all

I was talking about the last screenshot here though, where I asked for 3 min @ 40m (the white dot in the diagram) and the planner extends it to 9 min @ 40 min, with a ceiling. I realize that the rec planner algorithm is "make the dive as long as possible without deco stops required to get to the surface", and hence plans the dive so that deco clears during the ascent. Nonetheless, that does result in a fairly significant ceiling for part of the dive.

 

[inquis]

Oh, I gotcha. I suppose that some planners could dictate that a bolt to the surface shouldn't break the ceiling, but I don't know of any that do it that way. (Hardly a comprehensive survey, though!) I certainly prefer that it use the rate I gave it, but I would guess opinions vary.

 

[scubadada]

So, the OP, @Orestis82, has not been in this thread since post #4 on Aug 22. I don't know if he has benefitted from the 10 pages of responses to his simple question.

He did a dive that was confusing to him, and retrospectively found out that he might have had a short deco obligation that cleared on ascent when he downloaded his computer to a 3rd party log application. He never confirmed that the computer's onboard log also showed he was in deco.

There are several simple lessons from this story

• Understand how your computer works, how to set it, and what alerts it might give you.
• Pay attention to your computer while you are diving
• Keep it simple, set the proper FiO2, make sure alarms are set appropriately or turned off, avoid unneeded complications like deep stop.
• If you go into deco, you are in deco and have an obligation to satisfy. If the obligation is very short, it may clear on ascent, if not, you have a deco stop to perform.
• If you have not performed appropriate gas planning, it would be better to avoid an unplanned deco obligation.
• You are diving your computer, not a download app or a planning app, again, pay attention to your computer.

That would probably do it for most, mainly no-stop, divers

 

[DeepSeaExplorer]

Some folks still do not seem to understand. No, you do the deco required by your computer at the end of your dive

Your misunderstanding. I’m saying if you intended to do a deco dive, but didn’t actually end up going into deco, you don’t still do the now unnecessary deco.