Decompression Tables

[gcbryan]

To clarify:

1. Many algorithms were used to create the DCIEM Model
2. The Aladin and Monitor dive computers are based on the DCIEM Model
3. Other algorithms were used to make up the DSAT Model
4. The EDGE and SkinnyDipper computers are based on the DSAT Model
5. Other algorithms were used to develop the VPN-B, VPN-BE Models
6. These Models have been combined into the Liquivision X1 tech computer.

Again:

Which decompression tables do you use? If you use a computer, are you aware of the Table in-which the computer algorithms are based?

Do you build any "fudge factor" into your bottom times? If not, why not?

Do you know how the Table you use compares with others?

DCIEM is an algorithm. It was a serial model as I recall rather than parallel (regarding the compartments).

VPM (not N) is a bubble algorithm and is one of several software models available for the Liquivision.

I just read your next post and now I at least kind of get where you're coming from.

The answer regarding recreational computers is that it would be good to know what algorithm they use but for the most part the manufacturers don't really say.

They may say Buhlmann such as the ZHL-16C or Neo Haldanean but Buhlmann and everyone else except for VPM and RGBM is Neo Haldanean (DCIEM would be other one of course). So all the manufacturers of recreational computers pretty much use some form of Buhlmann's work since he published a book that actually showed enough of his work that one could derive a working program from it.

It's a good question or topic but for the most part it's only tech computers where you might be told exactly what is in the computer and in many cases it's still Buhlmann based although sometimes it's VPM.

The fact of the matter is for recreational computers the differences are for the most part how the manufacturer modified the original algorithms to make them more "conservative" or "liberal". In many cases, particularly Suunto (in my opinion) they just screw things up with too many "penalties" for coming up too fast or for sometimes just raising your arm too fast (the computer doesn't always know the difference).

My interest is just in the theory of decompression however. I don't have any interest in technical diving per se. I have V-Planner, and several dive computers and as you know V-Planner is VPM-B or VPM-BE and the dive computers are both some variety of Buhlmann and that's about all the manufacturers will say.

 

[tgsmith]

What computers do you and your buddies use?

During the dive, if our computer(s) clear first we stick with the generated tables. If we complete the decompression schedule and our computer(s) has not cleared, we stay until it does. Perhaps, that is our 'fudge factor'

 

[Meng_Tze]

I think that 'models' and 'algorithms' can and are used interchangeably.

Haldane created empirical tables, Buhlman and others created mathematical models based on that. Yet others branched off and created other models based on the same principles of gas coming out of solution, but needing control of bubble growth.

Based on these (mathematical) models, algorithms (in this case computer instruction sets based on real time or variable input) were created and implemented in different computers and published on printed tables.

Why do people use/buy as they do? Because 99% of all recreational divers learn to use basic tables. To certify, they do not need to know the model/algorithm behind these, just how to get two dives off of a table.

The next step is that they buy computers, as most dive operators nowadays require people to use computers. The majority of computer manufacturers have made these things so conservative that it is hard to get into trouble if you follow the profile. This is when other features (air integration, etc) become more important.

So the short of it is, recreational divers are not required/enticed to learn the models behind the tables/computers. The industry has set itself on a path where this is less important than following instructions as given by tables/computers.

The tech diving world is different where most do have a basic understanding of the models they run and how these change with different settings (G/F and conservatism). But even there, there are many who just follow what they are told by tables/computers.

In effect, we all follow what we are being told by our tables/computers, but some have an understanding why it is telling us that, others don't.

 

[HenrikBP]

As a rookie I'd very much like to see some discussion of the various models, how they affect decompression/off-gassing, the justification for each model, which computers use what etc.

Henrik

 

[Colliam7]

What computers do you and your buddies use?

Three of us dive an X-1. Two of us also have Nitek HEs. And two of us dive Vytecs.

 

[rongoodman]

As a rookie I'd very much like to see some discussion of the various models, how they affect decompression/off-gassing, the justification for each model, which computers use what etc.

Henrik

"Deco for Divers" by Mark Powell is current and quite readable.

 

[DCBC]

What computers do you and your buddies use?

Too many I'm afraid, including:
1. U.S. Navy Tables (Air)
2. U.S. Navy Tables (HeO2)
3. DCIEM Standard Air
4. DCIEM HeO2 to 100 metres
5. Meta Model experiments as a test diver at DCIEM
6. Oceaneering International (OI) Alpha tables
7. OI Yankee Bell Tables
8. SubSea SSM7 (modified Buhlmann) Bell Bounce Tables
9. SOSI Bell Bounce Tables to 200 metres
10. EBSDC (Component 2) Saturation to 400 meters
11. Meta Model experiments as a test diver at DCIEM
12. Others (When teaching SCUBA I use the Tables adopted by the training agency)

The main reason why there's such a large selection, is that it's up to each Commercial Operator to prescribe the Table to be used to meet the situation at-hand (liability). Also, different Tables were used at different times in my diving career.

When using a computer (recreational diving) I like the Liquivision X1 (VPM B, B/E, +2 conservatism)

 

[DCBC]

As a rookie I'd very much like to see some discussion of the various models, how they affect decompression/off-gassing, the justification for each model, which computers use what etc.

Henrik

That's what I was hoping for too. Thanks for your comments.

 

[DCBC]

I think that 'models' and 'algorithms' can and are used interchangeably.

Haldane created empirical tables, Buhlman and others created mathematical models based on that. Yet others branched off and created other models based on the same principles of gas coming out of solution, but needing control of bubble growth.

Based on these (mathematical) models, algorithms (in this case computer instruction sets based on real time or variable input) were created and implemented in different computers and published on printed tables.

Why do people use/buy as they do? Because 99% of all recreational divers learn to use basic tables. To certify, they do not need to know the model/algorithm behind these, just how to get two dives off of a table.

The next step is that they buy computers, as most dive operators nowadays require people to use computers. The majority of computer manufacturers have made these things so conservative that it is hard to get into trouble if you follow the profile. This is when other features (air integration, etc) become more important.

So the short of it is, recreational divers are not required/enticed to learn the models behind the tables/computers. The industry has set itself on a path where this is less important than following instructions as given by tables/computers.

The tech diving world is different where most do have a basic understanding of the models they run and how these change with different settings (G/F and conservatism). But even there, there are many who just follow what they are told by tables/computers.

In effect, we all follow what we are being told by our tables/computers, but some have an understanding why it is telling us that, others don't.

Each agency uses Decompression Tables based upon different models (as do the various computers). ACUC International uses the DCIEM Table which allows a maximum NDBT on the 1st dive to be a maximum of 15 minutes at 100 FSW. PADI Tables on the other hand allow 20 minutes. The U.S. Navy Tables (1993) allow 27 minutes and the French Navy Tables 30 minutes.

Personally if divers took a more cautious approach to the tables, there would be far less accidents. It's not if you can do the dive, it's how long you need to decompress if you've gone over the NDT. With the global rate of injury and death resulting each year from DCS, isn't this something worthy of discussion? Just a thought...

Thanks for your answer.

 

[fire_diver]

I use V-Planner, becuase it does have varying levels of conservatism to choose from. I keep mine at +2 as a rule.

I really don't think it matters which algorith you use. Quite frankly the combination of biomechanics, fluid dynamics, biochemistry, immune function, and a dozen other factors that control our bodies during dives is too complicated to even begin to understand without years of focused schooling. The experts who have developed the current models understand this about as well as can be understood. The fact of the matter is, you can grossly violate current deco theory and be fine, or follow it to the letter and take a type 2 hit. It just depends on how lucky you are that day. Obviously, the more of a chance you take, the faster your number will get punched.

I pick what is recommended to me by those who are my mentors.