Decompression Models

[ArcticDiver]

This is a general question on just how reliable the newer decompression models are. To me it doesn't make any difference whether the model is presented in a table or in a computer on my wrist. It is the same table.

In fact, to me, the ideal would be an air integrated wrist computer that would show appropriate data and information from each of my on board tanks.

When I look at the information about currently popular tables I see such phrases as(paraphrased): "Experimental", "Beta Test", "The manufacturer takes no liability for anyone using these tables", etc. The tables are clearly stated as being based on someone's theories without much, if any, scientific testing.

Yet these seem to be tables that people use routinely as a baseline for their dive planning. Then to compound the table's lack of precision, divers insert a fudge factor they call "degree of conservativism".

Now I know that with the possible exception of the work your folks have done Doc and the recent work of the US Navy all the traditional tables are based on empirical data. We know they work because literally millions of successful dives have been made from them.

The Navy's recent work I understand is scientifically based but not available to the public.

So, three questions:
What are people using the newer tables when they are so clearly labeled as being experimental and for which the manufacturer's take no liability instead of tables that are empirically based and for which there is a large body of supporting data?
Second, is there any chance the scientificly based new Navy Tables will be available to the diving public any time soon?
Third, is there a table existent, or soon to be existent, that incorporates the data and information derived from your experiments, Doc?

 

[Snowbear]

Every time we dive we're testing the theories. Not just the new ones - the "older" tables are based on theory as well. Every once in a while someone proves that they don't work for every person on every dive. More often, some parameter was not met (hydration, ascent rate, stop time, etc...) and it's called an "undeserved hit."

 

[String]

The tables i dive were based on someone killing/injuring a statistically small number of goats but i still dive them


On a serious note, ALL tables are a statistical average and just like anything else based on this they are based on the bell curve type effect meaning that although it satisfies MOST users there will always be those operating within those limits who will suffer.
Obviously newer theories based on better modelling and more data may be more accurate but even these are just a statistical sampling - no table is 100% accurate for 100% of people 100% of the time and never will be.

Just to highlight that, over here in the last few years, most DCS incidents have come from people diving within the NDLs for their various tables/computers.

 

[BigJetDriver]

This is a general question on just how reliable the newer decompression models are. To me it doesn't make any difference whether the model is presented in a table or in a computer on my wrist. It is the same table.

"The manufacturer takes no liability for anyone using these tables", etc. The tables are clearly stated as being based on someone's theories without much, if any, scientific testing.

Yet these seem to be tables that people use routinely as a baseline for their dive planning. Then to compound the table's lack of precision, divers insert a fudge factor they call "degree of conservativism".

Now I know that----all the traditional tables are based on empirical data. We know they work because literally millions of successful dives have been made from them.

So, three questions:
What are people using the newer tables when they are so clearly labeled as being experimental and for which the manufacturer's take no liability instead of tables that are empirically based and for which there is a large body of supporting data?

Artic Diver, et al,

Okay, your first point is a good one, and is mis-understood by many. The algorithm is the same, whether installed in a wet-computer or a desk-top, unless something has been left off due to the amount of coding and the performance of the micro-processor. Usually the latter is not so, due to the fact that the designer needs for the performance "in vivo" to match the performance "in vitro" so to speak.

Your second statement should not surprise any of us in this litigious environment. It is as automatic as: "Closed course. Professional driver. Do not attempt." The second part of that statement depends entirley on which model you are talking about.

You are mistaken, however, about the use of conservatism factors. This is simply a method to allow the diver to tailor the operation of the algorithm to his or her particular circumstances. If you are 20 years old, immortal, strong like ox, and full of beans, you can set it to operate in a less conservative mode. If the water is extremely cold, you are older, or a bit out of shape, you can adjust for that. You are making the operation of the model MORE precise, not less.

Now the comment about "empirical data" is an interesting one. As another writer here pointed out, that original empirical data came from the ol' goat-bender and his goat-bending son, the Haldanes, pere et fils. After that, a lot of that data was produced by both the Royal and the U.S. Navies using "crash-test dummies". This, of course, is code for "sailors". As we know, historically, it was a case of: "Oops, he doesn't look so good! Maybe we'd better try something else!" Finally, in the modern age, we have come to analyze things through mathematical study using computers. Believe me, both the goats and the sailors are thankful.

Finally, some modern models, after the super-computers have done their analysis, HAVE undergone many empirical trials. The RGB Model, for instance, has had many hundreds of dives performed on it by some very good technical people and has been found to be very effective, especially for deep and cutting-edge dives using helium and rebreathers. So, at least in this case, to insist that it has not been tested is just not correct. (Should anyone doubt this, you may check with Tim O'Leary of NAUI's Technical Research Group.)

You may choose your weapon at your will, so to speak, but I have no problem choosing to dive my re-breather while running RGBM on both my desktop, and my wet computer, with the latter linked to a fourth O2 sensor.

Cheers, all!


BJD :anakinpod

 

[DepartureDiver]

I just posted this in another forum, but when I saw this thread I thought it may be of some interest too. The timing of this is fitting considering the letter just posted from Dr. Hills' who influenced my approach heavily. The post in general shows a high degree of similarity between some different bubble models including their stops and total deco times. While there are naturally some differences, all predict virtually the same first stop depth and are relatively close in their total deco times.

 

[BigJetDriver]

Nice post, Brian. Thanks for the comparison article!

BJD

 

[MarcHall]

What are people using the newer tables when they are so clearly labeled as being experimental and for which the manufacturer's take no liability instead of tables that are empirically based and for which there is a large body of supporting data?

It's my body and I would rather run a clean deco curve, then a deco curve generated by a "tested" traditional model. I am not all that concerned about having a manufactuer to sue if I happen to get bent. I would rather dive a deco curve where I will fill better at the end of the dive and have less chance of suffering decompression sickness.

Liability concerns often dictate what makes it to market.

Take care

Marc Hall
www.enjoythedive.com

 

[DepartureDiver]

Thanks for the suggestion Marc. I took you up on it and redid the graphs by including traditional half-time profiles for comparison purposes. I also put larger versions of the graphs at the end without the "half-time" model. I term it a traditional style half-time model since the bubble models also use half-time compartments, but in a different way. These profiles shows the longer "first pull" (to use Dr. Hills terminology) to the first stop with the half-time model as compared to the bubble models. This can result in significant bubbling and is the old "bend them and mend them" approach. Until longer extreme profiles are done, it is found that the half-time model often generates the same total decompression time as the bubble models with deeper stops. This is actually expected using the idea that deeper stops are better for the diver, so the diver should not get penalized for doing the deeper stops whereas a traditional half-time model would penalize a diver and require even longer decompression time.

 

[Dr Deco]

Hello Readers:

Why are people using the newer tables when they are so clearly labeled as being experimental and for which the manufacturer's take no liability instead of tables that are empirically based and for which there is a large body of supporting data?

• All tables are “without warranty” when it comes to DCS. Thus, all tables carry the same disclaimer whether expressed or not.
• All tables are empirically based. Some will purport to accord more directly with physical reality, but this is difficult to demonstrate.
• Because all are derived from roughly the same dive data, they are in reality very similar, despite what the manufacturer might say in the promotional literature.
• No table or decompression theory to my knowledge has actually predicted a certain type of very novel outcome; they all start with the result and work backwards.
• Despite what they say, the database is not published (except for the Recreational Dive Planner (PADI).

Second, is there any chance the scientifically based new Navy Tables will be available to the diving public any time soon?

• I am not aware of any new US Navy tables currently under development.
• I know that the Navy is testing procedures dealing with the rescue of sailors from a downed submarine, but this is not really of particular utility to recreational divers.
• I do know of some Navy work because I review diving research proposals from them; it would not be proper to discuss this work outside of the Navy, as you can imagine.
• Navy tables generally are decompression schedules for deep diving with externally supplied air, and would probably not interest SCUBA divers.

Third, is there a table existent, or soon to be existent, that incorporates the data and information derived from your experiments, Doc?

• The work that I have performed for NASA does not lend itself to SCUBA tables; it describes safe procedures controlled by the diver.
• These procedures involve not straining or lifting; the whole is described as “limited lifetime nuclei generated by stress assisted nucleation.”

Dr Deco :doctor:

 

[ArcticDiver]

Hello Readers:

Why are people using the newer tables when they are so clearly labeled as being experimental and for which the manufacturer's take no liability instead of tables that are empirically based and for which there is a large body of supporting data?

• All tables are “without warranty” when it comes to DCS. Thus, all tables carry the same disclaimer whether expressed or not.
• All tables are empirically based. Some will purport to accord more directly with physical reality, but this is difficult to demonstrate.
• Because all are derived from roughly the same dive data, they are in reality very similar, despite what the manufacturer might say in the promotional literature.
• No table or decompression theory to my knowledge has actually predicted a certain type of very novel outcome; they all start with the result and work backwards.
• Despite what they say, the database is not published (except for the Recreational Dive Planner (PADI).

Second, is there any chance the scientifically based new Navy Tables will be available to the diving public any time soon?

• I am not aware of any new US Navy tables currently under development.
• I know that the Navy is testing procedures dealing with the rescue of sailors from a downed submarine, but this is not really of particular utility to recreational divers.
• I do know of some Navy work because I review diving research proposals from them; it would not be proper to discuss this work outside of the Navy, as you can imagine.
• Navy tables generally are decompression schedules for deep diving with externally supplied air, and would probably not interest SCUBA divers.

Third, is there a table existent, or soon to be existent, that incorporates the data and information derived from your experiments, Doc?

• The work that I have performed for NASA does not lend itself to SCUBA tables; it describes safe procedures controlled by the diver.
• These procedures involve not straining or lifting; the whole is described as “limited lifetime nuclei generated by stress assisted nucleation.”

Dr Deco :doctor:

I've used your post Doc as a reply format because it is without a doubt the best organized response I've seen in a long while.

Thanks everyone for your confirming replies. There is so much snake oil of one flavor or another in this sport that it is sometimes difficult to get actual facts.

Also, there is a paucity of actual failure data and actual injury and death data. While some places purport to report such information, since I personally know of events that never made it into the data base I am extremely suspect of their presentation and conclusions.

Doc, since I haven't looked at all decompression tables I could only make a guess at their differences, or lack thereof. I suspected that differences were more in the snake oil regime than that of science.

At the same time tables such as the Navy and its' immediate derivatives present themselves as being empirically based on a large number of human dives supported by explanatory experimentation and theorization. That is quite different from a table based on theory and labeled as experimental. After your explanation since I assume you have looked at all these tables, I think the hype may be a byproduct of snake oil.

As far as the New Navy tables: Some time ago I read an article in one of the journals that the Navy had conducted some pretty significant medical testing on Seals and other shallow water divers. The result of that testing was a set of tables that were based on reliably gathered medical information. However, that information was to be held private to the Navy. Shortly after I read that a computer company had been contracted to produce dive computers incorporating those tables and that those computers were not to be made publicly available. It could be that this is another case of military paranoia and overclassification. Or, it could be they actually have information that would change our diving habits. I don't know. I was hoping you, or someone would.

Thanks for your explanation about your research.

Oh yes, I do understand that every time I go off road here at home, or dive somewhere the outcome is far from certain. But, I have a saying that pertains: I don't mind getting hurt from a human mistake, or if the odds just go against me. It royally ticks me off to get hurt from ignorance or stupidity!