So you want to purchase a Decompression Computer...

[DCBC]

To-date, no Decompression Computer made can provide a totally safe decompression calculation for every diving scenario. Another problem is that there is no gold standard of decompression safety in-which one computer can be compared. Ultimately, decompression safety rests upon what the user judges to be an acceptable incidence of DCS.

So what is acceptable? The U.S. Navy Tables followed to the letter, will result in a mild case of DCS in 2% of the dives. For the Navy, 0.1% is good enough when it comes to serious DCS. In Commercial Diving, the figure drops to less than 0.1% for mild DCS and 0.025% for serious DCS (industry requirements Gulf of Mexico). Acceptability is defined by the user/organization.

I find it interesting that if a Diver uses a computer for decompression calculation, they often are unaware of the decompression algorithm their computer uses. It seems that Decompression Computer Manufacturers often don't provide/advertise this information to their customers. Nor are they necessarily aware of the impact their chosen algorithm will impacts the risk of DCS. Perhaps this is partially due to the fact that Decompression Computers aren't regulated. In-fact, Decompression Computers are not even required to be validated! This would be an expensive and complicated proposition. Also much of the data that would be required to reduce risk isn't easily attainable.

So why did you select a particular make and model of computer? Is it equipped in such a way that allows you to build in conservation into the computer program? If not, why not? Keep in-mind the DCS statistics of the Navy Tables. If you don't have the body and fitness of a SEAL, you need conservation. If you are a SEAL, you've already accepted the statistics that you may have a minor case of DCS in 50 dives. Makes a person pause to think doesn't it?

 

[rongoodman]

My computers use either Buhlmann GF or VPM. Either allows modifying the amount of conservatism in a well understood manner.

 

[Lorenzoid]

Good thread/poll. I have been a purely no-deco diver, but having read more about deco and how some computers allow the user to modify M-values and such, I have been starting to think about this very issue. I assume they would cover this in a deco course?

 

[rongoodman]

Good thread/poll. I have been a purely no-deco diver, but having read more about deco and how some computers allow the user to modify M-values and such, I have been starting to think about this very issue. I assume they would cover this in a deco course?

It will be touched on, but for more depth, I'd strongly recommend Mark Powell's "Deco for Divers" if you haven't got to it yet.

 

[rhwestfall]

My original PDC was chosen (many years ago) because it was one of the very few that didn't just lock you out if it went into a required decompression event on a dive (remember those times?). It also allows for a manually input conservatism.

When it went into "paperweight mode" due to me storing it without any batteries for an 8 year absence from diving, the manufacturer gave me a very, very, very good deal on an upgrade to the new model, so I stayed with them.

The manufacturer states the Algorithm as "20 Tissue Adaptive Modified Haldanean", but supplies little additional information (so i chose "don't know algorithm"). It can be upgraded for mixed gasses (He) and gas switches if desired. For my diving, I am comfortable with it, but if I was doing much more advanced types of diving, I might consider other options.

 

[Lorenzoid]

It will be touched on, but for more depth, I'd strongly recommend Mark Powell's "Deco for Divers" if you haven't got to it yet.

I've read it. But it's theoretical and doesn't advise you about the hows and whys of actually mucking with the algorithm settings on a dive computer that has that kind of flexibility.

 

[gurnie]

Should be an option for "I use a Computer, know the algorithm used, apply conservation and back it up with tables".

 

[DCBC]

Should be an option for "I use a Computer, know the algorithm used, apply conservation and back it up with tables".

Yes, I actually thought of that, but didn't have anymore room. I thought I would change it, but thought the better for it because I'd have to retype the whole thing over... Me bad.

 

[TSandM]

I can't answer the poll, because none of the answers fit. I plan my dives using Ratio Deco. I wear a Liquivision X1 running V-planner, which is VPM-B, with the conservativism set at +3. This generates profiles that are fairly similar to my RD profiles in total stop time, although the X1 usually wants more time shallow. At any rate, if the dive is executed as planned, the computer is happy. I figure the gauge is a last-ditch piece of insurance against either a dive that for some reason is completely different from what I planned, or a dive where something has reduced my processing power to where I need to lean on something else to do the math. (It's also kind of interesting to look at it on cave dives, where the profiles are often quite odd and one wonders if average depth use is really all that valid.)

 

[Abdullah]

I plan my dives with V-Planner VPM with GF's and +4 conservancy (same modeler my dive buddies use). My computer uses Buhlman with GF. I set it to +3 conservancy. On deco dives, my buddies and I dive the more conservative of our tables with a simple BT: My computer is along for the ride as a dynamic, well informed aid for unforeseen emergencies.