Nitrox mixes that you use - 'best mix' or 'what is available'

[macado]

It's an interesting question; for a lot of my shallow dives in New England I don't bother with Nitrox. I guess that's all relative to some people but I generally don't use Nitrox less than 60fsw.

If I am diving stuff in the ~120-130fsw range, I will often ask for a custom 28%-30% blend.

If going deeper (150fsw/45m) I would usually just do it on air since I don't think it's worth it to ask for a nitrox 25% mix. Most of these would not be recreational though and I would probably be using 50% or O2 for a deco gas. I'm not trimix trained yet but beyond this I would be adding helium to my mixes if I had that option.

Otherwise I stick with standard Nitrox mixes when the dives call for it. The alternative is I use whatever left over nitrox mix that I have topped off with air.

 

[shoredivr]

I do both. I use nitrox 32% if is available for the second and third day of a three day dive trip, and 25% for a 140' wreck that is commonly dived up here at a shop that will mix whatever you'd like.

 

[RTee]

Around here, I normally dive EAN 32 as it is readily available, banked and does not cost me more than air. Most dive profile are also above 110 ft. If I go deeper than that, then I will adjust my O2 level accordingly. There will come a point where for the sake of simplicity I will dive solely on air and elect to do a deco dive instead so I can have a decent bottom time over the point or area of interest rather then just doing a quick touch and go.

 

[TSandM]

I long ago decided that my brain doesn't work very well at all below 100 feet without helium. So that's my hard deck for recreational diving, and 32% works just fine. Plus I have the tables for 32% memorized, which makes life very easy. And most everybody I dive with dives 32%, which also makes life easy.

 

[HowardE]

I'm a big fan of getting nitrox. Usually, whatever comes out of the whip is good with me.

Sometimes I can't always get what I want, so I just dive what ends up in my tank.

If I'm requiring a lean mix like something less than 32%, then I must insist upon precision with the mix.

If shops are partial pressure blending, then I expect them to mix what I want.

 

[manni-yunk]

Most (90%) of my dives are from my boat - I mention this because it means I know with pretty good certainty what wreck we will be diving.....since I run the boat there. So - max depth change due to destination change is not a concern to me as it is to many others running on charters.

I am fortunate enough to have an onboard compressor - and Nitrox stick.


Since I know where we are diving - and the depth - I fill my tanks with the best mix for the max depth that we will see. That number can be anywhere from 21-40%.

I usually add 5-10 feet to the known max depth of the wreck - then blend whatever % will equal a 1.4 UNLESS - it is a planned deco dive. Then I often plan it at a 1.3 or 1.35 and also mix up a 50 and/or 80% deco tank.


Im also getting trained now to start using helium - and - I plan on having helium in my tanks for everything deeper than 110'

 

[MichelG]

Around here no dive shop has banked nitrox. So what I normally do is to use air for dives above 40 feet, 36% or richer mixes for wreck diving above 80 feet and usually 32% or 30% for deeper dives. If I'm not sure about where my next dive will be, I'm filling with 32% or I top my leftover nitrox with air. That way I can do about anything. But if I had access to say, 32% banked nitrox that is cheaper than partial pressure blend, I will use it almost all the time.

 

[SeaHawk12]

Since the shop I use does whatever mix you'd like, I always do best mix with a PPO2 of 1.4. However, if I'm diving under 60ft for both dives, I'm usually cheap and stick with air.

 

[mikecotrone]

A series of posts in another thread (Devil's Throat question) caused me to wonder - for diving within recreational (NDL) limits, how often do people actually use any kind of 'best mix'? The question is difficult to articulate, so here is the background.

1. In teaching nitrox, I go through a number of calculations with students, to determine what the maximum percentage O2 would be for a given depth and MOD. I generally use a MOD of 1.4 for these exercises, and point out that problems with oxygen toxicity are quite unlikely to present if you stay at or below a PO2 of 1.4 - not impossible, just very improbable. I go on to say that, while you can use any mix that you determine to be best, you will seldom have a problem with the common banked mixes (32% probably being the most common, with 30% also available in our area) in recreational diving. If the depth you want to reach doesn't work with the banked mix available, either stay shallower or go to air. (Or, ask the fill operation if they can give you a more precise, depth-adjusted mix).

2. Personally, I can think of only one time in the past 10 years when I intentionally blended a mix other than a banked nitrox mix for recreational diving. I was going on a wreck at 136 feet, and diluted some 30% to get a slightly lighter mix. (This may contradict my emphasis on 'recreational' diving, but that is not the point.) And, I have used lighter mixes resulting from topping off partially used nitrox bottles with air. But, that was also a matter of convenience. While I have 'clean for oxygen service' bottles available, and the ability to partial pressure blend whatever I want, I also don't blend richer mixes for shallower depths for recreational dives. The other divers I am usually in the water with do the same.

My question: how frequently do experienced divers tweak their mixes, beyond banked mixes, for recreational diving? And, where you do 'tweak' the oxygen concentration - between 21 and 40% - why? Or, perhaps, the better question is, on what quantitative basis do you do so?

I don't intend the question as a criticism of 'best mix' approaches. (And, I am really not interested in resurrecting another recreational trimix discussion, although that may happen.) Rather, I am now intrigued by what the usual and customary practice is outside of my own little world. Maybe, I just opt for convenience (or am lazy, or cheap), and 30%, 32%, or 21% seem to work for what I want to do.

My answer is very similar to Peter_C and a few others. I bank 32% and I can mix any other mixes including w/ helium on demand. I do alot of quarry diving in between trips and my deepest depth there is 90 feet which 32% suits me well.

 

[Searcaigh]

No EAN banks here unfortunately, so I have to pay extra for blends, although from another thread it is fairly cheap compared to the US

My max depths locally are 30M so I have my doubles and two tanks usually filled with EAN32. Other than that I use EAN36 for specific dives even on one site which is only 16M, I like the long bottom time it gives me at that depth compared to air.

On my overseas dive trips I prefer to use Nitrox and whatever is available, one place I frequently go to has banked EAN32, so that makes it an easy choice.