Nitrox vs Air

[dougaldiver]

Personally I wouldn't try to trick the computer. For a single dive it probably won't make much difference but for repetative dives the cumulative effect could be an issue. Bear in mind that your computer doesn't just analyse your max depth and time. It looks at the overall profile including ascent rates, stops and predicts off gassing during surface intervals.

I would also remember that, while people do get bent while diving conservatively, diving conservatively never caused anyone to get bent (at least as far as I know).

If YOU want to dive less conservatively get a different computer. If it's just pressure from the people you dive with be less conservative get different buddies

 

[LavaSurfer]

Wow, this is a new one

My first reaction is YIKES

I wonder how many understand and accept that the Oceanic computers are designed to be safe if you leave the water in the Green - Not the Yellow or Caution Zone. I wonder if they convince themselves they should be okay as long as not Red...?

Interesting point. I have both an ATOM 1 and VT-Pro and if they are in the yellow when I hit 33 feet, its time to thumb the dive. I always do SS until I hit the green even if it means 10 minutes at 15 feet. Several times I did a 5 min 15 feet and a 10 minute 10 foot just to get out of the Yellow zone. Depending on air of course…

Overkill? Maybe. But better safe than sorry.

 

[LavaSurfer]

I hate to use tables because till now I do just recreational dives as the name says, recreational means to enjoy a dive, not do guessing whether you will die or not if you do not use the tables.

Planning a dive means using the tables. Even if its a multilevel dive and you use the wheel or some software package. If your not planning your dive and diving your plan then you are taking un-nessesary risks in my mind. JMHO

Computers are there to support you in your dive not hinder your diving.

 

[Walter]

I hate to use tables because till now I do just recreational dives as the name says, recreational means to enjoy a dive, not do guessing whether you will die or not if you do not use the tables. So I bought a computer which will do every calcs to me, even better than I could, because multilevel dives you will never know how will be.

You're under the mistaken impression that computers are safer than tables.

So after more than a hundred dives you start to compare your computer with others and I find out that Suunto is almost always the more conservative one. If you are like me, always diving with a different buddy, you know this is a pain !!!

In what way is it a pain? Buddies should always agree to surface according to the more conservative computer. It's simply a part of diving.

So I've made some exercises with the simulator and I guess with more less Nitrox 24% O2, my mosquito will be more less equal "liberal" computers using air.

More or less?

Anyway, I would like to hear if somebody here already have done this comparisons or even used this trick. What our dive community think about that?

I think it's a usless comparison.

Since nobody analize the percentage of O2 inside tanks with gas, I could say that is not impossible to have more than 21% O2 (or less) in a tank. Is this 3% more is higly significative?

Yes, it is significant. If you are contemplating using your computer at a higher O2 setting than what is actually in the gas you are using, you're likely to get bent. I'll dive with just about anyone. If I knew someone was going to pull such a stunt, I wouldn't dive with them.

 

[ianr33]

My first reaction is YIKES



Interesting point. I have both an ATOM 1 and VT-Pro and if they are in the yellow when I hit 33 feet, its time to thumb the dive. I always do SS until I hit the green even if it means 10 minutes at 15 feet. Several times I did a 5 min 15 feet and a 10 minute 10 foot just to get out of the Yellow zone. Depending on air of course…

Overkill? Maybe. But better safe than sorry.

No I dont think it is overkill at all.I do exactly the same.

Had an PM conversation once with a board member who had done a 2 tank dive,came up with the computer in the yellow on both dives and got bent.

I use my Aeris computer as a backup on deco dives,it is pretty interesting to see it go into the yellow (and thus "safe" to get out of the water) when the tables we are following need maybe another 10 minutes deco.

I would need a VERY convincing reason to get out of the water with it in the yellow zone (drowning,Great White etc)

 

[mer]

Multilevel profiles where you crawl up the reef, ascending a little bit as your NDL remaining gets low at your current depth, actually is a rather aggressive profile, as you will load a lot more gas than a square profile. Add in repetitive dives on vacation, maybe a little dehydration, and you could be in for a rough time.

I know of several people who have been bent, anywhere from subclinical to chamber needed, even when staying with their computer and other "rules".

Play it safe, use the equipment as intended.

 

[DA Aquamaster]

Multilevel profiles where you crawl up the reef, ascending a little bit as your NDL remaining gets low at your current depth, actually is a rather aggressive profile, as you will load a lot more gas than a square profile. Add in repetitive dives on vacation, maybe a little dehydration, and you could be in for a rough time.

I know of several people who have been bent, anywhere from subclinical to chamber needed, even when staying with their computer and other "rules".

Play it safe, use the equipment as intended.

Well stated. Everyone understands (or should) the concept of a square profile where you push a table to the limits and remove any safety factor. When used this way some tables even have an expected hit rate of 1 to 3%.

However most people don't seem to realize that when you dive a computer to the top of the yellow you are doing exactly the same thing by pushing the computer to it's limit in terms of the tissue loading that is being modeled. All computers compensate for this to varying degrees by using shorter NDL's at a constant depth compared to tables to try to add some fudge factor back in given that many people will do what amounts to a square profile on every computer dive. But it is important to recognize that it's not an exact science and that individual differences in dive profile and in the on and off gassing traits of individual divers introduce a lot of variables that can get you in trouble with this approach. So it is always a good idea to add some conservatism of your own in the form of deepstops, slower ascents and a safety stop at 15-20 ft that is extended until you are back in the green, or at a minimum, well down in the yellow rather than maxing it out.

And I'll repeat myself, if a diver is concerned about being the one who always has to turn the dive due to having the most conservative computer, and you donlt go below 110 ft on most of your dives, go with 32% Nitrox and then you wonlt have to worry about it as it will add more bottom time at depth than even a very liberal computer used with 21%. In most cases it will add more safety as well as you will still be in the green when your air sucking buddies are at the top of the yellow.

 

[halocline]

Why do you load more nitrogen on a profile of slow ascent up a reef as opposed to a square profile? That one does not make sense to me. Please explain.

Regarding the relative safety of liberal vs conservative computer, as far as I know there is absolutely no evidence that in rec diving use of a liberal computer is more likely to result in DCS than use of a conservative one. Although it intuitively makes sense that "more conservative=safer" there simply is no evidence to support this. There are SO many other factors that have a corrolation with DCS; rapid ascents, dehydration, exertion immediately after diving.

While trying to learn more about this, I came across an old thread on SB discussing the differences between the oceanic algorithm and the suunto; one interesting thing was the statement that these two computers display nitrogen loading differently. According to the post, with the suunto, the nitrogen bar display is simply a graphic display of relative NDL, where with the oceanic (aeris, etc) made an attempt to calculate a display of off-gassing separate from the calculated NDL. This explains how on my atmos towards the end of a dive I can show an hour or more (sometimes a lot more) of NDL, but still significant nitrogen loading, like in the yellow.

Getting back to the original question of "fooling" the computer, I would agree with the more experienced divers that it can't be a good idea. As long as you have sufficient gas supply, what's wrong with just following the deco obligation, as it's likely that the required stop will be very similar to a safety stop, and as posted before, could very well clear with proper ascent rate anyway.

 

[DandyDon]

Interesting point. I have both an ATOM 1 and VT-Pro and if they are in the yellow when I hit 33 feet, its time to thumb the dive. I always do SS until I hit the green even if it means 10 minutes at 15 feet. Several times I did a 5 min 15 feet and a 10 minute 10 foot just to get out of the Yellow zone. Depending on air of course…

Overkill? Maybe. But better safe than sorry.

Not at all. That is exactly how they're supposed to be used.

I use my Aeris computer as a backup on deco dives,it is pretty interesting to see it go into the yellow (and thus "safe" to get out of the water) when the tables we are following need maybe another 10 minutes deco.

No, no, no, no, no!! Yellow = caution. Green = Safe.

How long does it take to enter the Green Zone when you have 10 min left on tables? Another 10 min at least, I bet.

Please repeat Drivers Ed course before driving with stop lights.

 

[emelotto]

As for setting it on 24%, wellllllllll.....if you've explored this a lot and find it to be a safe adjustment to make, I suppose it might not hurt you. However, keep in mind that the algorithms are designed to work best when used as intended. If you're really needing an extra few minutes, switch to another computer. Personally, I wouldn't trust 'more or less' for dives. )

Thanks by your answer, but one point botters me...
Let say that I buy another computer, don`t you think that I am doing exactly the same, which means, changing the algorithm in order to get extra bottom time?

Well, changing this in the same computer or in other one to me sounds equal! Don`t you? Off course we need to be coherent, nobody should put 32EAN in the computer and dive air. I agree with most of you that say to not trick the computer, specially if you don`t know how this trick will affect it`s operation, but I won`t expent any money to buy a liberal computer if I could understand and change my own computer.