Nitrox and Regular air

[rivrdiving]

I have my nitrox cert and was wondering about diving with both nitrox and regular air on the same day..
I was talkin about it with my buddy and we both figured that use regular air for the first dives and then use nitrox on the last dives of the day,,
Would this be the right way to dive the tanks? Seems to me from my understanding that it would in theory be the way to go.
What ya`ll think?
Ron

 

[String]

Doesn't make any difference.

If the first dive is the best dive (usually the case) then why not use nitrox on that instead to get longer on it?

The order you use a mix really isnt important.

 

[rivrdiving]

all my dives are my best dives lol and really my first dive I dont see as much,I get to thinking whoa this is cool wish I would been one of the babies that gets bornin a pool,lol
and I try to cover too much ground then in later dives i slow down and really start looking at things longer and paying more attention to detail.

 

[Rhone Man]

Depends upon which depth is more optimal for the Nitrox mix. If your first dive is below 100' there is no point in using Nitrox. If your second dive is shallower than 50' there is not much point in using Nitrox. Otherwise you really have a choice.

I know there is one diver operator in Cayman that pushes doing the deep dive first on air and the second shallower dive on Nitrox. The theory is that using the Nitrox gives you a better wash out of nitrogen on your final dive when your nitrogen absorbtion is highest, and saves the "energy boost" (for those that believe in it) for the last dive of the day.

But that is just one theory.

 

[rstofer]

The correct answer to your question depends entirely on the depths of the dives. For shallow dives, air NDLs are so long that you will run out of gas before you run out of time. For deep dives, Nitrox is of limited value if it can be used at all. The advantages of Nitrox are most apparent in the 60 to 100 fsw range.

Within the limits of MOD, Nitrox allows for increased bottom time and decreased SIT, simple as that. So, any time you use air where Nitrox could be used, you take on more nitrogen and require a longer SIT to get rid of it. Why would you ever use air if Nitrox could be used? Ok, cost... But compared to the total cost of diving, the additional cost of Nitrox is insignificant.

I could almost understand using air for the last dive because you have a long time to get rid of the nitrogen. It makes no sense to use it for any of the earlier dives if Nitrox could be used.

Richard

 

[T-Dog]

Typically the first dives tend to be deeper than successive dives. I'm a strong proponent of nitrox on the first dive: maximizes dive time, minimizes nitrogen loading for the second dive. Run through the tables on what you expect for depths, dive times, surface intervals between dives, and it will help you figure out what is best for your dive profiles.

 

[spectrum]

There have been some lengthy threads in the last year and it really depends and in general didn't matter much.

Using Nitrox on dive one which normally is the deeper can limit some nitrogen absorption.

Using Nitrox on the second makes for something of a deco mix to end the dive day with.

I would probably defer to the best fill or larger cylinder if they vary for dive one.

added.... As T-Dog stated if the nitrox will extend the bottom time of dive one (you are good with air) with the added NDL then it becomes a no brainer.

Pete

 

[rivrdiving]

Its not so much a cost thing but like when we dove the Cooper I took all 4 of my tanks 2 regular air and 2 nitrox,saved me from having to go get fills, My instructor told us to do deep dives first,
and thats what I do, LOL
In the long run it doesnt look like it makes alot of difference what ya use first,lol
Thanks for the replies.
Ron

 

[boulderjohn]

I am not in full agreement with those who say there is little benefit to Nitrox below 100 feet. Let's say you are going to 120 feet on that first dive using, say, 30%. Assuming you have enough air or a good enough SAC rate, you will get extended bottom time, which is one of your goals. Even if you have to ascend earlier because of the amount of gas you have left, you will get a benefit for the rest of the day. You will have shorter surface intervals and/or longer bottom times on the remaining dives for the day.

Whether or not you need to do your deepest dive first is a matter of controversy. To sum it up, there is no known physiological reason for that to be true. There is way more to it than that, but I don't want to hijack the thread. (A search will reveal previous threads on this topic.)

 

[John_B]

Get your tables out or put your computer in planning mode and work out if you'll get more bottom time with one or the other. Personally, I'd do 32% for both dives but that's just me.