Which deco stop to skip?

[Nirvana]

I understand the issue.

he problem is that people who see it as "bubble model" vs. "Haldanian" are missing something important.

The bubble model does not discount the Haldanian approach. It is not one against the other. Bubble models accept that the Haldanian theory--modified by later theorists like Workman and Bühlmann--is also true. many people therefore more accurately refer to the "bubble model" as "dual phase," meaning that we have to use a balanced approach that deals with nitrogen in both phases--dissolved and free gas. Thus, shifting the emphasis from bubble control to dissolved gas control is really not an abandonment of one theory for another. It is exactly what I suggested--merely a shift in emphasis.

I now understand your point. Thank you for the clarification.

 

[dumpsterDiver]

---------- Post added April 25th, 2013 at 06:35 PM ----------



No, not all computers will do this, but many will. The Shearwaters will.

The fact that you don't know much about this does not mean it is not true.

Your post was this: Moreover, if you are following a planned ascent and using a computer as backup, if you do shave time off your deep stops, the computer will adjust for you as you ascend. The computer can thus become your primary guide rather than the backup. On the other hand, if you hold to the deep stops and risk running out of gas on the shallow stops, the computer can do you no good whatsoever.

You reference "a computer" which I think people might assume ANY computer. Apparently you were talking only about YOUR computer. I think that is an important distinction.

Does it really say in "your computer" manual that you can blow off any deeper decompression stops you want and as long as you do shallow stops and follow the computer "as a primary guide" that all will be well?

 

[DevonDiver]

The point would make sense if bubble models merely added deeper stops to a Haldanian ascent... but they don't. The dissolved gas calculations have a direct and tangible effect on the 'Haldane stops' in the shallows.

We aren't talking about voluntary deep/Pyle stops.

Remove the deep 'bubble-collapsing' stops and you don't have an amended bubble model... you have a Haldanian model. You are now only concerned with off-gassing nitrogen through a process of maximizing gas differential across the tissues/blood/lungs, without exceeding a state of super-saturation in the process - you are no longer limiting/reducing initial bubble growth with the predicted impact that has on the later requirement to off-gas.

Another crass analogy: Removing two wheels from a car doesn't make it a motorbike. It's just a useless car.

 

[boulderjohn]

[/B]
You reference "a computer" which I think people might assume ANY computer. Apparently you were talking only about YOUR computer. I think that is an important distinction.

Since this was posted in the technical diving forum, I assumed that all readers would understand that when I was talking about using a computer like the Liquivision X-1 or the Shearwater Predator, I was talking about a computer deigned to handle decompression algorithms. I guess I should have made it clear that I was not talking about a basic Mares Puck or a Suunto Zoop. I forgot who I was responding to. My apologies to anyone else who was confused.

 

[DevonDiver]

... if you do shave time off your deep stops, the computer will adjust for you as you ascend.

In reference to the debate on the need to surface ASAP... the computer would (depending on model) adjust... it'd give you longer in the shallows.
Is that a better, or worse, solution given a finite gas supply and/or restricted time for stops?

From my perspective, it runs the risk of failing both bubble and Haldanian model demands... you miss the deep stops , but your still finite gas supply may still prevent you from completing the (now longer) shallow stops. You can end up with incomplete deep and shallow stops.

I still think the answer remains in having a worst-case scenario deco plan/s. Those plans depend on the dive/gas.

So... when putting together a contingency plan.... do you formulate a 'max-aggressive' plan using your primary model (likely a bubble model), or do you refer back to Haldane and abandon the deep stop/bubble control concept altogether?

When I used to dive in Thailand, we had surface supplied O2 at 6m on the deco bar (redundant to our carried deco gas/ses). That made a strong argument for a Haldanian ascent direct to the shallows. The availability of support divers makes that same argument. Loss of back-gas and retention of a rich deco gas makes the same...

If, however, we lose deco gas, and have to ascend and decompress using only a deeper gas, then it's not so clear-cut IMHO. We have to choose... so do we put emphasis on the benefit of bubble elimination... or the benefit of avoiding super-saturation for as long as possible? (assuming that, without gas, we can't avoid it entirely).

If we have ample gas for all phases of the ascent, but another factor demands that we exit the water ASAP, then we have a range of options. There are certain factors that may make a Haldanian profile preferable. That said, there are situations where speed of exit, rather than 'being shallow' is the only demand. In that case, amending (making very aggressive) your existing approach might be the best option.

 

[rjack321]

You guys can sure belabor your points, with no evidence that any one strategy is superior to another...

 

[DevonDiver]

You guys can sure belabor your points, with no evidence that any one strategy is superior to another...

I think it's a great discussion. Enjoyable. Interesting to see other's views...and challenge them....and likewise, be challenged. Presenting one option in a debate doesn't necessarily mean it is someone's 'point'. I'd like to think that most of us were pretty open-minded in this debate... just explaining our understandings, or lack of.

As you say... it's not about being right or wrong... just about sharing and discussing concepts.

 

[Peter69_56]

Firstly, thank you all for your answers.

Now, to address some of the issues raised. As some of you have pointed out, there is no need to say "you should never skip any deco". I think it is pretty obvious to anyone with a minimum of scuba diving knowledge that missing decompression stops puts you at serious risks. It follows pretty clearly that contingency plans must not include omitting decompression. The original question was thought of in a scenario of some imperative need to ascend more quickly than would be desirable, such as in the case of a developing medical issue (not DCI).

Best regards.

Nirvana, given I was one who said "Plan your Dive and Dive your plan" etc etc. I have to agree with the response it generated, what I suggested is the theory of what ideally one should do on every dive, and your question (in retrospect by me) was if it all turns pear shaped what's the best way out etc etc. You are right, , one should think about the what if’s after one recognises that they know the theory of what should be “normally” followed and why..

My reaction (in retrospect) was based on something I saw recently and I have posted this elsewhere. Regarding your comment above about “I think it is pretty obvious to anyone with a minimum of scuba diving knowledge that missing decompression stops puts you at serious risks” I would like to think that all divers who have a basic understanding appreciate this, however I saw a recent example of a young guy (OW cert and just recent) who was quite happy to say he had been diving 5-6 dives per day, found his computer locking up (due to deco breaches) so was swapping it for a spare, then when the second locked up didn't bother with a computer and was diving to >40m on hooker for extended periods with no plan or deco plan etc etc. On challenging him about the very high risk his response was, well my mates all say its ok (they are not certified and are diving with him), and also stated if he gets into trouble with a “buildup of the bends he will go to a deco chamber once a year to relieve the pressure. Yes he gets pains in his shoulders and arms sometimes, etc etc” . Then when I tried to explain the huge risk he was exposing himself to, and that he was probably already bent and it will get worse, he simply walked out of the shop so he didn’t have to hear it. A walking dead person I would suggest, or a future cripple.

So when you say “Its pretty obvious...”, I would suggest its only obvious to those who chose to use their grey matter a little. There are some who chose to ignore all their training and sound logic and so I am always cautious about saying things like (and I don't suggest you actually did, its just an example) “well you can shorten and miss a deco stop and probably get away with it............but risks go up” (or something which deviates from training) in open forums as they (by their strange interpretation) could and probably would interpret it as , “well thats ok deco stops are like safety stops, something nice to do" because divers more experienced than me (in a scuba forum) have, said it. Hence my initial post about following the plan etc etc.

We are trying to have a discussion and our audience is the extremes from the newbie with perhaps only pool experience to the super experienced who first dived from Noahs Arc on the maiden voyage.

Anyway I stand corrected on the matter, you obviously have your grey matter well around deco and risks and I missed the point you were trying to make, and would also say, it’s something I hadn’t thought about until you broached the subject, and would be guided by people more experienced than me.

 

[ajduplessis]

Your post was this: Moreover, if you are following a planned ascent and using a computer as backup, if you do shave time off your deep stops, the computer will adjust for you as you ascend. The computer can thus become your primary guide rather than the backup. On the other hand, if you hold to the deep stops and risk running out of gas on the shallow stops, the computer can do you no good whatsoever.

You reference "a computer" which I think people might assume ANY computer. Apparently you were talking only about YOUR computer. I think that is an important distinction.

Does it really say in "your computer" manual that you can blow off any deeper decompression stops you want and as long as you do shallow stops and follow the computer "as a primary guide" that all will be well?

No use. Mr Ph.D here feeds of his own assumptions and views. I know believe in "outcome based education"

 

[dumpsterDiver]

Since this was posted in the technical diving forum, I assumed that all readers would understand that when I was talking about using a computer like the Liquivision X-1 or the Shearwater Predator, I was talking about a computer deigned to handle decompression algorithms. I guess I should have made it clear that I was not talking about a basic Mares Puck or a Suunto Zoop. I forgot who I was responding to. My apologies to anyone else who was confused.

Thanks but where is MY apology?