Air/Nitrox?

[MikeS]

I am in the process of buying some new gear. I'm not sure if I need to replace my current computer. If I start using Nitrox blends do I absolutely need a computer that is Nitrox compatable? Is there a formula I can use to make adjustments?

You can use an air computer with Nitrox, there are several options:

1. You can dive with Nitrox using the air computer as you normally would. Since the computer does not “know” you’re diving with Nitrox, you would not get additional NDL time. You will have less nitrogen loading so in theory your risk of DCS will be reduced. Additionally the computer will not track your oxygen exposure.

2. You can dive with the computer in gauge mode and use tables. You will lose the advantage of the computer treating the dive as a massively multilevel dive. And again the computer will not track your oxygen exposure.

Mike

 

[5615mike]

Okay, here we go. There are two parts to the quote you have included in your post, and they talk about two different things... so I'll break up my response into two different though processes.
1) Multi-level credit.
2) O2 displaces N2, less N2 is good.

1. Multi-level credit - this is only extending your NDL and not addressing the safety issue. Tables would be safer since they don't recalculate the same way as a computer does so they don't give you as much credit for depth change and how you make that change.

2. Obviously less N2 is better but you have not addressed the issue of the gas being "safer". You have only said there is less N2 which provides for longer exposure at depth(within MOD). Sure it is, but address the issue when you approach NDL. Again, not addressing the safety issue of using the gas.

You know what I'm talking about Scuba as I assume you have a decent working knowledge of what you are talking about. But for those who are new to scuba, you can't just make such a statement. Nitrox is no "Safer" when it comes to DCS, getting Narc'd and then you have to operate within MOD or you've got to deal with OxTox. I'm not trolling here just trying to make a point for those that are relitively new.

 

[Scubakevdm]

1. Multi-level credit - this is only extending your NDL and not addressing the safety issue. Tables would be safer since they don't recalculate the same way as a computer does so they don't give you as much credit for depth change and how you make that change.

2. Obviously less N2 is better but you have not addressed the issue of the gas being "safer". You have only said there is less N2 which provides for longer exposure at depth(within MOD). Sure it is, but address the issue when you approach NDL. Again, not addressing the safety issue of using the gas.

You know what I'm talking about Scuba as I assume you have a decent working knowledge of what you are talking about. But for those who are new to scuba, you can't just make such a statement. Nitrox is no "Safer" when it comes to DCS, getting Narc'd and then you have to operate within MOD or you've got to deal with OxTox. I'm not trolling here just trying to make a point for those that are relitively new.

Okay, so I'm not trying to cause friction here either, and I'm going to hang it up after this, but I would like to point out that I said a computer lets you dive longer safely not safer, and comparitively, the same dive would be saferon nitrox than on air (assuming it is within MOD).
Is everyone cool with that? I hope so, 'cause I'm tired of it. Peace.

 

[Dan Gibson]

If you are pushing the limits on nitrox, have you not just defeated the extra safety margin the nitrox gave you? It would be correct to say diving air limts on nitrox (within MOD and accounting for length of exposure) is safer.

More O2 and less N2 making the dive less narcotic is not true if you are in the camp that believes O2 is just as or more narcotic than N2. Helium would be the gas needed to reduce narcosis.

Okay, so I'm not trying to cause friction here either, and I'm going to hang it up after this, but I would like to point out that I said a computer lets you dive longer safely not safer, and comparitively, the same dive would be saferon nitrox than on air (assuming it is within MOD).
Is everyone cool with that? I hope so, 'cause I'm tired of it. Peace.

 

[Scubakevdm]

If you are pushing the limits on nitrox, have you not just defeated the extra safety margin the nitrox gave you? It would be correct to say diving air limts on nitrox (within MOD and accounting for length of exposure) is safer.

More O2 and less N2 making the dive less narcotic is not true if you are in the camp that believes O2 is just as or more narcotic than N2. Helium would be the gas needed to reduce narcosis.

...

 

[DiveSpeak]

Sell your old computer on eBay and apply it to a nitrox ready computer! Nitrox places a ceiling above and below you so to speak and you need the right computer to do it safely if you plan to do multi-level diving. Put another way, the Partial Pressure of Oxygen in the mix cannot exceed 1.4 -(1.6/contingency), without increased risk of oxygen toxicity ans associated "Grand Mal" seizures. Oxygen Toxicity is like an "Oxygen Clock" that runs faster the deeper you go due to the higher partial pressure of oxygen. So lets say you had a 38% mix blended for your planed MOD (Maximum Operating Depth), then you spot a Rollex just lying on a ledge over the wall just 40 feet deeper. Checking your "Air" computer you've got 15 min left at this depth and plenty pressure on the guage so you go for it, but since you "Air" computer is only tracking nitrogen loading (incorrectly I might add because there is less nitrogen in Nitrox) it does'nt warn you that your Oxygen partial pressure just went to 2.0, and the rescue divers find you dead with a Rollex clamped tightly in your fist! DONT EVEN THINK IT! NO MATTER WHAT ANYONE SAYS, EITHER DIVE SQUARE PROFILES USING THE NOAA TABLES OR BUY A NITROX COMPUTER! END OF DISCUSSION - SCAREY THINKING MY FRIEND - VERY SCAREY!!!

 

[Snowbear]

Nitrox places a ceiling above and below you so to speak and you need the right computer to do it safely if you plan to do multi-level diving.
...
DONT EVEN THINK IT! NO MATTER WHAT ANYONE SAYS, EITHER DIVE SQUARE PROFILES USING THE NOAA TABLES OR BUY A NITROX COMPUTER! END OF DISCUSSION - SCAREY THINKING MY FRIEND - VERY SCAREY!!!

While your explanation of MOD and N2 loading is pretty much valid, these statements are a bit overzealous, don't you think? You seem to be implying that diving without a Nitrox computer is bad. While a computer can be a useful tool if used wisely, it can't and won't keep a diver above the MOD or below the "ceiling," buoyancy control, a basic understanding of gas laws and physiology and being able to relate it to the dive will.

 

[MikeS]

DONT EVEN THINK IT! NO MATTER WHAT ANYONE SAYS, EITHER DIVE SQUARE PROFILES USING THE NOAA TABLES OR BUY A NITROX COMPUTER! END OF DISCUSSION - SCAREY THINKING MY FRIEND - VERY SCAREY!!!

It’s a good practice to select an O2 percentage that prevents you from reaching an O2 PP of 1.6 without a shovel. For example if you’re diving a wreck where the bottom is 115 fsw use EAN 30. There are some circumstances such as wall dives where this isn’t practical.

Additionally you should know the Maximum Operating Depth (MOD) of your fill; most agencies teach you to clearly mark it on your cylinders. If you have good situational awareness you’ll always know how deep you are. How is monitoring the O2 PP on the computer any easier than monitoring your depth on a depth gauge?

As far as a warning, depending on the audible warning from a computer is a very dangerous practice. What happens when you learn to rely on it and it doesn’t work? Most computers have a maximum depth setting anyway. If you set it to MOD you would get a warning. At least with a depth gauge you watch it change as you descend and ascend so should have a good idea if it’s working or not.

I dive a Cobra, Nitrox Air integrated computer because in my mind anyway, there are advantages But I think that your warning misses the preverbal boat.

Mike