Nitrox and partial pressures

[tarponchik]

The computer was functioning perfectly (it's settings were just wrong); he did not know how to use it. But when he realized something was wrong, why should he assume it is JUST the N2 and O2 that are wrong? After all, pressure sensors fail too, and clocks. You are arguing he had a dive plan. What was his plan? Set the computer and follow it. Bad plan.

Since one can safely stay at 75 ft breathing NITROX-36 for about 100 min, a 2-tank dive of approx 50 min each with a ~1 hr surface interval is guaranteed to be safe and it is quite possible to leave your comp at home for such dives. All you need is a depth gauge and your watch to do the safety stop.

 

[JMarc]

The computer has a setting that resets Nitrox to 50%

No. From the manual citation above the computer switch to a safe but non coherent behavior where it use 50% O2 for MOD warning and 79% N2 for deco computation. I find that surprising, would not expect someone to know about it without referring to the manual and can understand how it could be missed or forgotten even after having read the manual.

RGBM is defective? This is news to me. Then why Atomic, Mares, Suunto, and Cressi use it?

Newer Mares computers have switched to Bülhmann.

 

[tursiops]

All you need is a depth gauge and your watch to do the safety stop.

If he couldn't trust his computer, then he had neither.

 

[johndiver999]

If he couldn't trust his computer, then he had neither.

The dive site has a known depth. If the diver stays with the group, then there should be no question about the depth. If the DM adheres to a max dive time, then there should be no ambiguity about the maximum dive time. I doubt the diver will die, following a dive plan that the operator has run many hundreds of times, even if the computer should give bad data on a single dive.

 

[tursiops]

The dive site has a known depth. If the diver stays with the group, then there should be no question about the depth. If the DM adheres to a max dive time, then there should be no ambiguity about the maximum dive time. I doubt the diver will die, following a dive plan that the operator has run many hundreds of times, even if the computer should give bad data on a single dive.

You are probably right; he probably could follow the crowd and do just fine. In fact, that's what he did, but this does not make it the right decision,
He posted in Basic Scuba, and following the leader is NOT a best practice. He lucked out. That is not a dive plan or thoughtful execution; it is blind luck and total "trust-me" diving.
He should have aborted and surfaced, especially in Basic Scuba.

 

[broncobowsher]

It is still a difficult to use computer being used by someone not highly familiar with it.
Telling them they should have known how to use it better, you got your education from books and not real life. You don't know what you don't know until you find out you didn't know. They thought they had it right, to find out later they didn't do the magic hand shake just right and it was wrong.
I bought a version of this same computer 20 years ago. I still have a reference card to use it. A couple things are user friendly enough, but a good chunk of it requires non-intuitive and not very clear steps and settings. Don't blame the user for a product that is difficult for a beginner to use. I'm sure some of you have mastered this thing, you would be the exception. Most use it as a first computer, on air, then move on to better things later.

 

[scubadada]

It is still a difficult to use computer being used by someone not highly familiar with it.
Telling them they should have known how to use it better, you got your education from books and not real life. You don't know what you don't know until you find out you didn't know. They thought they had it right, to find out later they didn't do the magic hand shake just right and it was wrong.
I bought a version of this same computer 20 years ago. I still have a reference card to use it. A couple things are user friendly enough, but a good chunk of it requires non-intuitive and not very clear steps and settings. Don't blame the user for a product that is difficult for a beginner to use. I'm sure some of you have mastered this thing, you would be the exception. Most use it as a first computer, on air, then move on to better things later.

I have been diving Oceanic computers since 2002, more than 2400 dives. I have never once turned on the FO2 50% default. This function is described in detail on pages 13 and 14 of the Pro Plus 3 manual. Yes, please be familiar with your computer and read the owner's manual.

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There is no excuse for diving on the FO2 50% default by accident. I don't disagree, this is a particularly lame setting that has been in place for a very long time on Oceanic computers. Extremely easy to avoid, permanently

Oceanic has some idiosyncrasies, but they are easy to deal with. The initial nitrox setting will apply for 2 hours and would then require a reset. Once diving, the nitrox remains unchanged as long as the surface interval is less than 24 hours, otherwise would require reset.

Hi @broncobowsher

There is no good excuse for someone diving their computer with incorrect settings or not knowing how it functions. You run through the setup menu and come to the FO2 50% Default. If you do not know what it means, you look it up in the owner's manual before proceeding. Once correctly set, it is good forever.

You seem to have had a negative early experience with an Oceanic computer. I have dived several second computers along with an Oceanic computer, Cochran, other Oceanics, Dive Rite, and now, a Shearwater. All of these computers have taken some time to learn to set and use them correctly. Time everyone should expend.

 

[tarponchik]

You are probably right; he probably could follow the crowd and do just fine. In fact, that's what he did, but this does not make it the right decision,
He posted in Basic Scuba, and following the leader is NOT a best practice. He lucked out. That is not a dive plan or thoughtful execution; it is blind luck and total "trust-me" diving.
He should have aborted and surfaced, especially in Basic Scuba.

You idolize dive computers and overestimate their role in safety. I was certified in 2002 but I got my 1st comp only in 2010. Why? Because before comps there were dive tables which I've used. I know that according to the tables I will be perfectly safe on a dive like this, therefore, a comp failure won't make me abandon the dive.

Sure, comps make planning and watching your N2 way easier and more reliable when you do 3-5 dives a day, but on a 2-tank mostly flat profile dive at Jupiter breathing EAN36 the only convenience a comp gives you is to register the data for your log book.