Past NDL. And then this???

[uncfnp]

Your ascent rate was dangerously slowly. Slow isn't safer

Guys. This is not an ascent rate issue. He did not ascend when he hit the NDL. He continued his dive but at gradually shallower depths. Just as some divers "ride" the NDL he attempted to ride his deco. Doesn't work as he found out.

 

[tursiops]

My computer went to DECO “mode”.

I remained calm knowing that that it was not the end of the world (eg my fellow divers had several minutes NDL left, I had plenty of gas etc) and continued a slow but now steady ascent (no more looking around for fish etc – just focusing on the ascent, my gas, the computer and the group).

Guys. This is not an ascent rate issue. He did not ascend when he hit the NDL. He continued his dive but at gradually shallower depths.

Seems like HE thought he was ascending. That does make it an ascent rate issue.
In reality, of course, he was continuing to dive, as you say.
But the "issue" was his failure to actually ascend at a reasonable rate, i.e. 30 fpm.

 

[uncfnp]

I remained calm knowing that that it was not the end of the world (eg my fellow divers had several minutes NDL left, I had plenty of gas etc) and continued a slow but now steady ascent (no more looking around for fish etc – just focusing on the ascent, my gas, the computer and the group).

Seems like HE thought he was ascending. That does make it an ascent rate issue.
In reality, of course, he was continuing to dive, as you say.
But the "issue" was his failure to actually ascend at a reasonable rate, i.e. 30 fpm.

Yes its semantics which I hate but..
He was ascending but he was not ascending to the SS (now a deco stop) to end the dive. He was ascending during the dive, but continuing the dive, hoping this would clear the deco.

The issue here is not ascent rate but judgement and perhaps lack of experience and knowledge. He knew he was in deco and I *think* all agencies teach to safely end the dive at that point. Not to continue the dive and try to clear deco by ascending shallower.

By calling it an ascent rate (or focusing on the algorithm too for that matter) we are ignoring the real problem with this dive, judgement.

 

[tursiops]

Yes its semantics which I hate but..
He was ascending but he was not ascending to the SS (now a deco stop) to end the dive. He was ascending during the dive, but continuing the dive, hoping this would clear the deco.

The issue here is not ascent rate but judgement and perhaps lack of experience and knowledge. He knew he was in deco and I *think* all agencies teach to safely end the dive at that point. Not to continue the dive and try to clear deco by ascending shallower.

By calling it an ascent rate (or focusing on the algorithm too for that matter) we are ignoring the real problem with this dive, judgement.

Agreed. Dive judgement problem. Good judgement comes from experience. Experience comes from lack of good judgement.

 

[Nianne]

PADI rescue knowledge review c1q1 :

1. What is the most common cause of diver emergencies?
- Poor judgment.

 

[Michael Guerrero]

There was NO problem whatsoever with the computer, the issue is the end user.
What would Petrel or Perdix do when the diver refuse to take note of the info given to him? Physically take him up and start the deco!!!

For your first sentence: Doesn't sound like it to me. The OP said he punched the entire series of dives for the trip into Subsurface to validate the ascent/deco schedules, resulting in a no-deco dive. He said his dive buddies who were with him on the trip all had no deco obligation for the same dive--1hr+ surface intervals between repetitive dives.

That tells me that whatever algorithm his current computer is using is giving him outsized deco obligations for relatively innocuous dives.

For your second: Nothing. But you may want to calm down a bit. All those exclamation points make it seem like you're getting excited .

 

[Michael Guerrero]

Cressi RGBM is arguably the most conservative of the commonly used commercial decompression algorithms.

Definitely arguable. Didn't we have a bunch of studies that have demonstrated the problems with bubble models?

 

[Michael Guerrero]

I'll include this again, as I was adding/editing it to a previous post as you typed your reply.

Andy, I think you've really hijacked this thread to shout down what you feel is bad and dangerous behavior in a diver, rather than answer the basic question.

Did the diver ignore his computer? Yes. Is this bad? Maybe, but with the OPs level of understanding of deco theory and physiology, probably yes.

Did the diver know from past experience that his computer will tell him he has a shorter NDL than his diver partners? Yes. Is this different than the many thousands of technical divers out there who "negotiate" the ascent curve and length of their deco profiles, and will lengthen or shorten those stops, and thereby deviate from the algorithms? Not so sure.

When I dive my gradient factor (GF) 70/70 profile and my buddies dive their equivalent of a 10/85, and we get out of the water at different times, running different ascent curves, and are all unbent, is that wrong? No.

This thread is riddled with unnecessary histrionics.

If the diver can run through Subsurface with his entire dive trip to see the impact of repetitive dives and what the expected decompression obligations should be for those dives, and then he finds that based on the chosen GF he should not have been in deco, my question is why does he have a question? Clearly, his computer is running an algorithm that he seems to feel is excessively conservative.

So my question to the OP is: Now that you have validated to yourself that your computer has a questionable implementation of a decompression algorithm, what are you going to do about it?

My recommendation is that if you want to continue to use a computer you should use one that implements a standard algorithm. An algorithm proven to introduce less decompression stress and sickness in a number of recent studies performed by leading decompression scientists and researchers and national navies. One that also allows you to change the "conservatism" based on what you're comfortable with. The commercial algorithm that does that is Buhlmann (ZH-L16C) and the best line of computers on the market with that algorithm is Shearwater (Petrel, Perdix, etc.). Case closed.

 

[Michael Guerrero]

As I mentioned a page ago...

With such an aggressive and extended diving history, there would be so much variance between divers that a comparison of algorithm performance would be near-irrelevant.

Andy, I don't agree. First, that this is an aggressive dive schedule. Three dives to relatively shallow depths over the course of a few days is not aggressive, particularly with SIs in excess of an hour. Second, if the diver has stayed with his buddies, then the tissue loading should be relatively similar. The major reason for any significant difference in NDL times would be algorithm implementation, which I have remarked on in another post.

Additionally, the OP has indicated that he "knew" his computer was more "conservative" in its NDL calculation, which indicates that over a period of time and a number of dives, this has been shown relative to his dive buddies. He has also indicated with his post that he stays with his dive buddies. Once again, tissue loading should be similar and following the algorithm of his buddies computers vs. his own is not unreasonable.

Let's not kid ourselves that there are clear bright lines between what will get you bent and not. And let's not spread that falsehood to the newer divers among us. I'm not arguing against your recommendation for being conservative and not pushing your NDLs on a routine basis without understanding deco theory and physiology. People should be informed, and it is their own responsibility to make themselves informed. But to say that always diving to your NDLs is aggressive (and by implication dangerous) is just not true. The NDLs established by recreational dive computers are substantially more "conservative" than the pure algorithms developed for military and commercial divers. And even those algorithms have very low likelihoods of DCS.

 

[Michael Guerrero]

Why would you let other computers interfere with your own one? It is none of their business.
I haven't been diving long, ~21 yrs, never ever compare the ndl of my computer with others. What is the point? It had given you false sense of security in this case!!!!

This is nonsense.

Technical divers routinely compare ascent rates and deco obligations. They also routinely change both of those as they see fit--sometimes based on old and disproven theories, unfortunately.

NDLs, deco times, etc. are always a range. And you are doing yourself a service, not a disservice, to inform yourself of some of the calculated ranges. Saying that you will only stick to your own computer because it must be right is just foolish nonsense. That said, making these kinds of adjustments without understanding their potential implications because one has failed to inform themselves is just as nonsensical and foolish.