setting to nitrox to reduce over conservatism on dive computers

padudle · Jun 25, 2014

A common complaint I hear is that newer dive computers are overly conservative. The reason given is that computer manufacturers are afraid of litigation.

I encountered one diver who had adapted to the problem by setting his new computer to a few percent of enriched oxygen. He could test the setting by running the computer in dive planning mode and comparing bottom times with what his old computer allowed. In effect, he used the nitrox adjustment to create a less conservative setting on his new dive computer that matched his old computer.

This was my first exposure to the technique. I am wondering how common it is in the dive community.

Pedro

DaleC · Jun 25, 2014

I am not a fan of diving to the edge of NDL's as a habit rather than the exception. But then again, I am an older diver who solo's and cannot afford to take a hit in an isolated setting. I get it that there is a class of diver who only gets out so often and wants to maximize their underwater time every dive but it's a risky way to roll the dice for DCS, especially on multi day multi dive trips after long lay offs.

As to the question. I haven't heard of anyone doing this and would shy away from someone who did. Sub consciously I would be wondering what else they were fudging. I have heard of people setting their computers to air while diving EAN as a form of additional conservatism. As long as one knows the real MOD's this does not seem to be a problem.

NAM001 · Jun 25, 2014

Is there a difference between air adn using nitrox mode with 21%?

DaleC · Jun 25, 2014

If you're asking me I meant diving mix such as 32% but treating it as air.

Rick Murchison · Jun 25, 2014

padudle:
A common complaint I hear is that newer dive computers are overly conservative... he used the nitrox adjustment to create a less conservative setting... I am wondering how common it is in the dive community.

First I've heard of it.
Not a good idea, for I guarantee that the new, "conservative" algorithm with a little oxygen added will *not* match the apparently less conservative older computer over its entire operating envelope, and since the person who tries it is likely to dive the corners of that envelope (after all, that's why the fudging in the first place, eh?) it's a recipe for getting hurt.
If I want to dive outside the envelope of a particular computer, I don't use that computer.
There are plenty of new computers that use the "old" algorithms, and plenty of legitimate tables and computer programs a diver can use to maximize bottom time if that's what a diver wants. Trying to make an algorithm give a desired answer by feeding it false info will eventually produce bad answers.
GIGO applies.
Rick

claymore · Jun 25, 2014

I do not see the push to run on the ragged edge of the curve. Spend more time at a shallower depth where there is more to see or get the training, to plan and execute, and the equipment to do the deco dives.

Being an older diver and diving cold water at home I prefer a more conservative profile. Unless there is specific reason to change the nitrogen setting I leave it at 21% if I am diving a nitrox mix or air to give me a little more conservatism when diving Nitrox. I do label my tanks Nitrox mix and put the MOD and contingency depth on the label. My shop banks 32% so my mixes are generally 30% to 32% so that will take me to any rec depth I will be diving even if I push PPO2 of 1.6 for a short time.

Rick Murchison · Jun 26, 2014

KWS:
Is there a difference between air adn using nitrox mode with 21%?

There's no difference in the computer's nitrogen calculations, but some computers display different information when in Nitrox mode than they do in Air mode. The specifics vary...
So why set the computer to 21% instead of just putting the computer in Air mode? All the computers I know of won't allow a switch to Air until a 24 hr surface interval after a nitrox dive, I reckon because in air mode the algorithm that tracks oxygen exposure isn't active.

Rick

Dr. Lecter · Jun 26, 2014

Sounds quite similar to using RD to approximate a given model, since he's trying to match another known algo using pre-dive planning. It's probably not going to harm him and undoubtably adds to his redundancy, but diving both computers set correctly and following the more conservative one would be safest.

His life, his choice...but I've never heard of anyone trying this specific approach. It does echo another practice of which I'm aware involving trimix and deco diving, but that's a whole different kettle of fish.

BRT · Jun 26, 2014

Why not just get the nitrox and have the best of both worlds?

DiamondD · Jun 26, 2014

BRT:
Why not just get the nitrox and have the best of both worlds?

That was my exact thoughts. Not to mention the way nitrox makes many of us, me included, feel better after a dive.

setting to nitrox to reduce over conservatism on dive computers

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