Nitrox Question

[Majickyl]

My computer does the same, reverts to 21%.

It kind of makes me wonder if computers marketed to the technical community tend to do the 21% default, where computers marketed to the rec community do the 50% default. Tech divers presumably know their MODs, may be diving mixes higher than 50%, and are more concerned with decompression obligation, so conservative in the sense of nitrogen is more important and the revert-to-air makes sense.

Rec divers should be staying within their NDLs and on lower mixes, so the 50% rule would be more appropriate for avoiding ox-tox.

Do all computers that have the 50% fO2 default also have the 79% fN2 default?

Because 50% / 50% is not really a safety in terms of nitrogen loading. Sure, I'd take bent over toxed, but neither is better...

 

[eponym]

Regarding Cave Diver's post,

Thanks good info, and I have no argument with the feature.

Actually, as I posted above, I think that conservative approach is preferable to what my makes do . . .

Although they also assume worst-case N2 loading (79%) unless instructed otherwise, which is good.

-Bryan

PS. . . . And I see Majickyl above has already made this case while I was typing. Well done.

 

[Majickyl]

Just want to thank the SBers for this useful conversation.

I've definitely revised my opinion of these features and think they are actually a really good thing as long as we understand them. I'm actually planning on turning my revert-to-air feature back on. I always plan my mix based on the dive and know my MOD, so in the situation where I forget to set my mix I will be diving EANx on an air profile... nice and conservative.

Thanks for making me a safer diver.

 

[wve]

Some computers also have the annoying habit of resetting to Air if you don't dive before your computer turns off on its own (2 hrs in my case).

Example, up early getting ready to dive. Analyze the tanks, put the mix info into the computers. Ready to go. Buddy turns up late. Delayed dive start. Computer thinks we aren't diving and shuts itself off.

When I turn it back on, everything is back to baseline. Not hard to fix, but on mine, the Air/Nitrox indicator is small and easy to overlook if you don't realize that the darned thing will reset (this is how I learned about this "feature").

So there was at least one occasion where I dived 32% with the computer set to Air. Fortunately, I knew the MOD was well beneath the bottom, so it was a non-issue anyway.

Point: You do have to check those pesky computers before you splash, and read the fine print in the manual.

 

[Jax]

Other Oceanic models like the Atom 2.0 and VT3 have this (IMO stupid) feature as well. You can turn this feature off.

If or when the computer still goes berserk during a dive you realize how vital it is to have the important numbers (MOD, max BT, and later deco schedule) in your head.

Perfect! Exactly where I was going . . .

It bothers me -- am I in the minority? -- that manufacturers are trying to make their product 'fix' us, the diver. I don't want my computer telling me lies. Is it really 'safer' for a computer to adopt its own settings?

I rely in my equipment to report status, period. I count on that piece of equipment to do calculations thousands of times faster than I am able. I do not like the idea that it would make up a number based on some programmer's best guess.

 

[Majickyl]

Perfect! Exactly where I was going . . .
I rely in my equipment to report status, period. I count on that piece of equipment to do calculations thousands of times faster than I am able.

I'm with you on this point. My computer is there because it gives me information quickly that helps me make decisions. It's not there to tell me what I am allowed to do or plan my dive for me. I make the decisions - it helps me maximize my dives.

Actually, besides my tanks, my computer was the last peice of equipment I bought... once I started doing multilevel dives it helped me to maximize my bottom time, and it saved me some math once I started diving nitrox. Though actually, I still do the math anyway... if I'm analyzing a tank I usually have a calculator handy.

But I do like that if I screw up, my computer can help me. I overstay my bottom time, it will help me out and throw me a stop. I forget to program the right mix, it will help me out and pick a really conservative one.

It's not something to be relied upon, and it bugs me to see so many divers dive what their computers tell them to do without an understanding of what's really going on. (In no means directed at the OP - you did the right thing by ascending when your computer was giving you threatening numbers!)

It really irks me when there is discussion about eliminating tables from training because the are "useless" now that we have computers. Tables help illustrate the concept of NDL in a classroom much better than a computer could.

 

[Jax]

Here, here!

Now, let's look at the other side of the equation . . . the diver that looks at the computer and decides, "No way!" and ignores it . . .

In the OP's example, she clearly had the MOD in mind, but chose to take the conservative route. Good call, Laura!


But if manufacturers keep making their computers more and more "foolproof"¹, won't we have more and more divers looking at the computer and saying, "No Way!"? Are we not creating too many opportunities for people to second-guess what the computer is reporting, because of these programming decisions? IS this the right way to go?

How many divers would second-guess an SPG? a depth gauge?


¹ Make something foolproof, and only a fool will want to use it.

 

[Cave Diver]

It bothers me -- am I in the minority? -- that manufacturers are trying to make their product 'fix' us, the diver. I don't want my computer telling me lies. Is it really 'safer' for a computer to adopt its own settings?

No, but it's a CYA for the manufacturers. First time someone goes diving with the wrong mix and has an oxtox episode the family of the deceased will be crying that something should be done to make the computers safer. Right or wrong, it's gonna cost big bucks to defend against the suit and it only costs a few pennies to throw an extra line of code into it.

 

[Cave Diver]

¹ Make something foolproof, and only a fool will want to use it.

Make something foolproof and they build a better fool.

But if manufacturers keep making their computers more and more "foolproof"¹, won't we have more and more divers looking at the computer and saying, "No Way!"? Are we not creating too many opportunities for people to second-guess what the computer is reporting, because of these programming decisions? IS this the right way to go?

Like I said, it's a CYA thing. If you ignore the mod warning on most computers you get a bunch of annoying beeps and flashing lights telling you to ascend. It's much easier for a manufacturer to defend that they've taken every reasonable precaution and the user ignored it than it is for them to admit they could have done something else to make sure the user used proper judgment.

If you need proof of this, look in the accident forum about the family suing the resort because someone got killed ignoring just about every free diving rule there is. It was his own stupidity, but they want someone else to pay for it.

 

[giles45shop]

Just an FYI, if you want a computer that doesn't reset after each dive, spend the $$ and buy a Liquidvision X1.

Mine stays set on whatever I used last, regardless of whether that was the last dive 10 minutes ago, or 2 weeks ago. As others have said, resetting the last mix is a safety feature. If you jumped in the water without checking the settings on your X1, you could be really screwed, depending on what you last dive/mix was.

Of course the X1 does a few other non-conventional things as well. It doesn't give you a 10-20' safety stop time on recreational dives (you have to be smart enough to watch the clock and note those run times if you are doing that), It doesn't beep at you or lock you out if you do something wrong, and if you F-up the mix, you can change it underwater and it just keeps right on ticking.

John