Dive computers - how conservative?

[Kern]

This is true, but however sophisticated the algorithm, at the end of the day, they do just "spit out a number". If that number is consistently smaller than both other algorithms, and what practice has shown to be safe, then that number is less useful that one which is consistent with both those things.

As I can't think of a recreational computer that doesn't use a Haldaneian or neoHaldaneian model at its base, I feel that's as reasonable a way as any to make such a decision when deciding on which one to use.

You can increase the conservatism of a liberal dive computer to meet your needs, however, you can do nothing to make a conservative computer more liberal.

With the earlier recreational computers that use a so called RGBM model this was true, but some of the newer models offer the option of going to 50% RGBM so it's not always the case these days.

 

[jd950]

There is a new computer, an "OC1" from Oceanic which offers a choice of algorithms. Set for whichever model you want or even change algorithms depending on situation or dive buddies. I am not sure, but Oceanic probably also still has their "conservative" setting which would then increase flexibility even more.

 

[Kern]

You seem to get a choice of 2. Either Pelagic DSAT or Buhlmann ZH-L 16C. According to the table, ZH-L 16C as represented by the Nitec Duo & Pelagic DSAT as represented by the Oceanic, Aires, Genesis etc. computers, would appear to be almost exactly the same once you pass 40'.

I wonder if that says something about the table, or the OC1, or maybe they've tweaked 1 or both of the algorithms to give a more substantial difference.

 

[maged_mmh]

just a personal perspective; but the RGBM rationale is the most of these "theories/concepts/constructs" that makes sense to my taste.

 

[scubadada]

There are an infinite number of nuances here, computer manufacturers have obviously recognized this. To each their own. The reading list previously posted is a good start.

As I can't think of a recreational computer that doesn't use a Haldaneian or neoHaldaneian model at its base, I feel that's as reasonable a way as any to make such a decision when deciding on which one to use.

With the earlier recreational computers that use a so called RGBM model this was true, but some of the newer models offer the option of going to 50% RGBM so it's not always the case these days.

Except for the RGBM or other bubble model algorithms

Reducing the RGBM for Suunto computers is the only exception to reducing conservatism that I'm aware of. As these computers are among the most conservative of all recreational computers, I do not know the relative effect of this change.

You seem to get a choice of 2. Either Pelagic DSAT or Buhlmann ZH-L 16C. According to the table, ZH-L 16C as represented by the Nitec Duo & Pelagic DSAT as represented by the Oceanic, Aires, Genesis etc. computers, would appear to be almost exactly the same once you pass 40'.

I wonder if that says something about the table, or the OC1, or maybe they've tweaked 1 or both of the algorithms to give a more substantial difference.

With the Oceanic OC1, for only $1500 without AI or $1850 with AI, one can switch between deco algorithms after a 24 hour lockout (not too useful on a single dive trip). The Pelagic Pressure Systems/DSAT algorithm is the one I'm very fond of from my Pro Plus 2. The conservative Seiko algorithm (Dive Rite Nitek Duo, Zeagle N2ition, Tusa IQ-700 Hunter, Cressi Archimedes 2, Apeks Quantum...) is a modified Buhlman ZHL-12. The Pelagic Z+ is a Buhlman ZHL-16c. The NDL times for the PZ+ are slightly less conservative than my Dive Rite Nitek Duo but are much more conservative than the Oceanic algorithm to considerably deeper than 40 feet ( 50 feet 81 vs 65 minutes, 90 feet 24 vs 19 minutes...).

just a personal perspective; but the RGBM rationale is the most of these "theories/concepts/constructs" that makes sense to my taste.

The OC1 also has a conservative factor (elevation of 3000 feet), a deep stop option, and a programable safety stop. Between the 2 algorithm options and other variables, this could please most everyone except those desiring a RBGM algorithm. I guess the next option will be 3 NDL algorithms.

Personally, I think all of the available dive computers and NDL algorithms are quite safe. Whether you take a deep stop and/or a safety stop and the degree to which you push your computer toward the NDL, are your own choice. We must all operate within this grey zone of some uncertainty. Risk tolerance is a personal decision. A well educated decision is a good decision.

Good diving to all,

Craig

 

[RAWalker]

just a personal perspective; but the RGBM rationale is the most of these "theories/concepts/constructs" that makes sense to my taste.

It is also the newest and most conservative model but surprisingly there is no evidence that a more conservative model was needed. This is particularly interesting if you consider that many of the models using the older more established model already had the ability to be put into a conservative mode.
So the question arises why have another more conservative model?
Usually the simplest answer to a question of this type is true. That answer would seem to be that by having a more conservative model manufacturers can play upon consumers fears and sell them the product as safer. Does the product actually have benefit? Maybe, to a small number of customers then again maybe not. But if the customer believes it does that in itself may be enough to lessen anxiety and keep them from feeling negative effects brought on by anxiety.

 

[maged_mmh]

I got your point but mine was about the scientific basis of RGBM vs. "classical" tissue compartments

 

[scubadada]

It is also the newest and most conservative model but surprisingly there is no evidence that a more conservative model was needed. This is particularly interesting if you consider that many of the models using the older more established model already had the ability to be put into a conservative mode.
So the question arises why have another more conservative model?
Usually the simplest answer to a question of this type is true. That answer would seem to be that by having a more conservative model manufacturers can play upon consumers fears and sell them the product as safer. Does the product actually have benefit? Maybe, to a small number of customers then again maybe not. But if the customer believes it does that in itself may be enough to lessen anxiety and keep them from feeling negative effects brought on by anxiety.

Most simply, the greater the exposure, the greater the risk of DCS. This may practically be the difference between extremely uncommon and extremely, extremely uncommon. I would refer you to Bove and Davis' Diving Medicine, Saunders, 2004. Chapter 7 on Mechanisms and Risks of Decompression is very enlightening. Based on contemporary computers of the time, they estimated the risk of DCS to be 52/10,000 dives using the Suunto Vyper or DCIEM tables versus 68/10,000 dives using Oceanic computers with the considerably less conservative PPS/DSAT algorithm.

There's a lot of valuable information out there, we should all use it, I do. One can avoid the risk of DCS completely by not diving.

Good diving, Craig

 

[RAWalker]

Most simply, the greater the exposure, the greater the risk of DCS. This may practically be the difference between extremely uncommon and extremely, extremely uncommon. I would refer you to Bove and Davis' Diving Medicine, Saunders, 2004. Chapter 7 on Mechanisms and Risks of Decompression is very enlightening. Based on contemporary computers of the time, they estimated the risk of DCS to be 52/10,000 dives using the Suunto Vyper or DCIEM tables versus 68/10,000 dives using Oceanic computers with the considerably less conservative PPS/DSAT algorithm.

There's a lot of valuable information out there, we should all use it, I do. One can avoid the risk of DCS completely by not diving.

Good diving, Craig

But does the research show the Oceanic computers to be set to their normal mode or conservative mode of operation?
I would assume the research was based on the default mode of operation and since. Their is a conservative mode of opeartion built into the Oceanic computers which is not the default mode we really can't say the Suunto computers are any safer.

 

[gcbryan]

But does the research show the Oceanic computers to be set to their normal mode or conservative mode of operation?
I would assume the research was based on the default mode of operation and since. Their is a conservative mode of opeartion built into the Oceanic computers which is not the default mode we really can't say the Suunto computers are any safer.

I don't know what model of Oceanic computer you are referring to and I didn't check to see when this research was conducted but I've had several Oceanic computers...the last being the Veo 200 and it had no option to make the computer more conservative other than to set an alarm or something. It has no setting comparable to the conservative computers that also can be made more conservative with a setting of 0-whatever.

Maybe the newer models have this?