Past NDL. And then this???

[kafkaland]

There are two fundamental aspects to your question. First, what kind of dive profile, and consequently Deco/NDL are you comfortable with. There is no universal answer to this, only you can decide. There are very aggressively algorithms, especially when it comes to multiple dives, like DSAT. On the other hand, you can dive much more conservatively, with ZHL-16 and 30/70 gradient factors, for instance. Only you can decide how much risk you are willing to take, and if there are any factors that advise caution, like cold water, strong currents, you being older or out of shape, or having a hangover from the night before. After you have done a few dives near the NDL for your chosen algorithm, ask yourself routinely how you feel, and if there's any indication of fatigue or such, go more conservative the next time.

The second part is the team aspect. The rule is that the most conservative choice of NDL or deco algorithm detemines the ascent profile for all. So when you're reaching your limit, signal to your buddies, and they ought to ascend with you, on your schedule. And no reason for you to feel bad about this. That's how diving in a team works. It might not be a bad idea, though, to discuss this with your dive buddies before you splash, especially if you dive a very conservative or very aggressive algorithm, so that everyone knows what to expect.

Oh, and if you're routinely scratching at the NDL, consider getting deco training. It's very liberating to think more about ascent profiles and contingency plans instead of a rigid NDL number when planning your dive.

 

[azstinger11]

My (obviously naive/newbie) understanding is that once past the NDL there is already more than the safe amount of gas in my tissues. Don’t I risk turning that gas to bubbles by going up “fast” ??? And obviously by fast I don’t mean faster than 30 feet-10m/min.

Obviously I was slow, but subsurface’s algorithm was happy with it (0 deco once I reached 4m). Of course that was much later, being totally dry in the comfort of my desk.

I will try to upload the profile once I find out how (I am new to the forum).

Thanks a lot

Was it your first dive of the day/trip or had you had other dives in the last 24 hours? If you ran the numbers on a repetitive dive like you did on a first dive then yes you could be deeper for longer with no deco obligation. That's why dive computers are great, they keep a very accurate accounting of what you did. Which is why the DM faking data bothers me. Your dive computer thinks your body did something very different from what it actually did.

 

[DevonDiver]

A pertinent example of why recreational divers should respect and restrain themselves within no-stop limits.

I'm glad nobody got hurt. DCS isn't a hypothetical construct.

I get the feeling that some novice divers view DCS as a type of ficticious "boogie-man" tale meant to scare them away from breaking agency 'rules'.

Let's knock that cynical notion on the head... people get hurt by DCS every year. Sometimes that injury is life changing.

People learn "something" off internet sites like Scubaboard, or from diving peer groups, and self-professed, unqualified 'experts'; but then it all goes wrong in-water. Go figure....

A little knowledge can be a bad thing - worse than no knowledge at all.

In this case, ALL that needed to be known was to ABORT the dive immediately by ascending and following the computer directions exactly.

That didn't happen because the victim of the incident had "a little knowledge".

That "little knowledge" made them chose a totally different course of action than that taught by their dive agency, and that demanded by their dive instrument.

I'll forgoe an explanation of what and why happened from a deco modelling perspective. This incident teaches a more important lesson than deco assumptions...

I'd suggest that a qualification in decompression diving would be an adequate starting point from which to begin discussion on what should have been done.

Let's, instead, look at why this incident occurred..

As an diver, don't be deluded that "Scubaboard time" etc etc counts toward your diving competency.

No recreational diving programme educates divers to second-guess decompression instruments; either yours or your buddies.

For the OP:

- No clarity is necessary on the behaviour of your instrument.

- No clarity is necessary on deep stop implementation.

- No clarity is necessary on algorithm A vs algorithm B.

This incident was entirely due to HUMAN FACTORS.

Bad decisions were made. Those diver decisions over-ruled both agency training and the in-water dive instrument directions.

That incorrect decision making was potentially exacerbated by an over-confidence and complacency empowered by an internet browser or peer group quasi-education.

This lesson wasn't learned at the time - hence the mistaken quest for 'decompression model clarity' by the OP... more peer group quasi-education... that, again, illustrates little comprehension of where things actually went wrong.

The CLEAR lesson is to respect what you are actually TAUGHT at your level of diving... and have the disciple and moral courage to restrain yourself within those limits.

Human Factors....not equipment glitch.

A secondary lesson is that dive operators can act very irresponsibly at time. The DM leading that dive absolutely failed to act to protect your safety and further endangered your safety with his "clearing your computer" shenanigans.

I've run several dive centres and I'd have sacked a DM for such gross failings in their professionalism and duty-of-care.

 

[boulderjohn]

My (obviously naive/newbie) understanding is that once past the NDL there is already more than the safe amount of gas in my tissues. Don’t I risk turning that gas to bubbles by going up “fast” ??? And obviously by fast I don’t mean faster than 30 feet-10m/min.

People have already said you ascended much too slowly, and you did. What I want to do is clear out two misconceptions you show in this statement. You are acting as if you only have one kind of tissue in your body, and you are assuming it that once it has too much nitrogen in it, things can't get any worse.

Your body has a wide variety of tissues, and they take on nitrogen and release nitrogen at hugely varying rates. As you gain nitrogen, some of the fastest tissues become saturated (meaning they have all they can take at your depth at that moment, but others are still slowly taking it on. As you ascend, the ones that are saturated will begin to let off nitrogen, but the ones that aren't will continue to absorb nitrogen. If you ascend too slowly more and more tissues will take on nitrogen, meaning you will acquire more and more decompression time.

 

[stepfen]

Was it your first dive of the day/trip or had you had other dives in the last 24 hours? If you ran the numbers on a repetitive dive like you did on a first dive then yes you could be deeper for longer with no deco obligation. That's why dive computers are great, they keep a very accurate accounting of what you did. Which is why the DM faking data bothers me. Your dive computer thinks your body did something very different from what it actually did.

Before that day I had 3 days with 3 dives each day. The dive with the incident was the last (3rd) dive anyway of the fourth day. The following day (5th) was my last diving day and I did 3 more dives.

 

[boulderjohn]

A couple of years ago I wrote to the Divers Alert Network (DAN) about this article, which I believe is dangerous.
Alert Diver | Ascent Rates

In it, they talk about safe ascent rates. They talk about a 2009 study that compared a 60 FPM rate with a 30 FPM rate, concluding that the faster rate was more dangerous. The article then goes on to say that you should use slower rates rather than faster rates, but it does not quantify that. Although it does not say it per se, it strongly implies that there is no rate that is too slow--the slower the better! Take a week if you want!

I asked DAN when an ascent rate is too slow, and they did not respond. I guess they stand by the "slower is always better" credo.

 

[azstinger11]

Before that day I had 3 days with 3 dives each day. The dive with the incident was the last (3rd) dive anyway of the fourth day. The following day (5th) was my last diving day and I did 3 more dives.

Unless you put all of that data into subsurface then yeah, subsurface would probably show a no deco dive. You exited the dive before the deco diver at a much higher pressure group then you started the trip/day in.

I'd be willing to bet if you had done an absolute perfect recreation of that dive as the very first dive of your trip you'd be fine and not in deco.

 

[DevonDiver]

Or get a more liberal computer.

Does that come with "a more liberal physiology" included as standard?

I mean, seriously,... you read what scenario the OP managed to get himself in... and your advice is that he gets a less forgiving computer?!?

Manufacturers make recreational computers so conservative EXACTLY BECAUSE of the sort of incompetent diving behaviour so clearly illustrated in this thread.

If people dove a little more responsibly, with some sincere respect for their limits and the agency recommendations they're given.... then perhaps the long trend wouldn't have been for manufacturers to make dive computers ever more and more conservative...

 

[stepfen]

A pertinent example of why recreational divers should respect and restrain themselves within no-stop limits.

I'm glad nobody got hurt. DCS isn't a hypothetical construct...

People learn "something" off internet sites like Scubaboard, but then it all goes wrong in-water. Go figure....

A little knowledge can be a bad thing - worse than no knowledge at all.

In this case, ALL that needed to be known was to ABORT the dive immediately by ascending and following the computer commands exactly.

That didn't happen because of "a little knowledge".

I'll forgoe an explanation of what and why happened from a deco modelling perspective.

I don't think this thread is the time and place for it... read on.

I'd suggest that a qualification in decompression diving would be an adequate starting point from which to begin such a discussion.

As an AOW diver with minimal experience, don't be deluded that "Scubaboard time" counts toward your diving competency.

You aren't educated (even remotely) sufficiently to second-guess decompression instruments; either yours or your buddies.

No clarity is necessary on the behaviour of your instrument.

No clarity is necessary on deep stops.

No clarity is necessary on algorithm A vs algorithm B.

This incident was entirely user error.

That user error was greatly exacerbated by an over-confidence and complacency empowered by an internet browser quasi-education.

This lesson wasn't learned at the time - hence the mistaken quest for 'clarity' in the OP... more internet browser quasi-education... that, again, illustrates little comprehension of where things actually went wrong.

The CLEAR lesson is to respect what you are actually TAUGHT at your level of diving... and have the disciple and moral courage to restrain yourself within those limits.

A secondary lesson is that dive operators can act very irresponsibly at time. The DM leading that dive absolutely failed to act to protect your safety and further endangered your safety with his "clearing your computer" shenanigans.

I've run several dive centres and I'd have sacked a DM for such gross failings in their professionalism and duty-of-care.

Thanks a lot for all the advices. I do take them all seriously. Just one clarification. All I knew before was what I was taught during my certifications and that was the rule "don't go past ndl -or even near it DOT". I didn't even know scubaboard or similar forums existed online. Sh*t happens though (yes it's me to blame and only me) and so after what happened I started searching about it - just in case for next time. I did some homework/search myself (I could have done more obviously) during which I became aware of SB and hence I asked the question here to get some more advice.

 

[stepfen]

Unless you put all of that data into subsurface then yeah, subsurface would probably show a no deco dive. You exited the dive before the deco diver at a much higher pressure group then you started the trip/day in.

I'd be willing to bet if you had done an absolute perfect recreation of that dive as the very first dive of your trip you'd be fine and not in deco.

The whole trip was on subsurface as downloaded from my computer! I know that surface intervals make huge difference in all these.

Thanks a lot guys. I got to go get some sleep for now.

It was a pleasure and I hope by tomorrow I will have plenty more replies to study.