Nitrox Common Mixes

[Tortuga68]

Simple. Choose a standard nitrox gas that matches the deepest MOD you'd be willing to dive anyway. For me, that works out to 32%. Past 110', I'd want helium locally anyway. 32% covers *any* dive depth I'd be willing to do on nitrox (1-110').

If I bring 40% for a dive planned to 70', but that's blown out and we end up at a site in 100', I'm screwed (been there, done that once, never again).

There are also other benefits to a standard gas choice: teammates are all on the same gas (so similarly NDL-limited), familiarity with allowable NDLs at various depths / profiles, not having to remix for future trips, ease of blending, ease of gas acquisition, etc.

The DIR forum is two doors down to the left

 

[Rainer]

I made the choice to standardize WELL before I'd even heard of DIR. Try missing some dives due to having a too rich gas and you might come around. Best mix sucks when plans change... I'd prefer some flexibility over a few extra minutes of NDL.

The DIR forum is two doors down to the left

 

[Tortuga68]

Good for you. The OP asked what people dived, not why you don't dive what I dive. Standard mix has it's advantages, which you've clearly stated. Best mix also has it's advantages, which you also alluded to. The issues you mentioned have never been relevant for me. YMMV. If Best Mix is 32% then we'd be no different. I don't even know why you mentioned 40%

 

[SandyRobinson]

I dive 32% exclusively for recreational dives. It's pretty widely available, and gives you a reasonable MOD (111) which is deeper than I want to go, because I'm pretty susceptible to narcosis. It gives a substantial advantage in bottom time as compared with air. All my buddies dive it, too, which means that we don't run into problems with people having different NDLs.

Higher Nitrox percentages will give you longer bottom times, but shallower MODs, which decreases your flexibility to change dive plans or sites, if the one you intended can't be done for some reason.

plus 1

 

[Centrals]

I prefer 32% over 36% because:
1. It is cheaper! In multi-level dive the extra 4% of O2 has minimum impact on "extended bottom time".
2. More flexible on depth.
3. I hate long dive, 50 mins max.

But I would use 'best " mix for wreck.

 

[scubadiver888]

In my area all the shops do partial pressure blending. They can mix whatever percentage you want. If I am at a site and know what I'm going to be diving, I get a blend that puts me close to 1.4 ppo2.

If I am filling my tanks just so I have tanks filled and ready for a dive I'll fill with 28%. The MOD for 28% @ 1.4 ppo2 is 132'. Since I'm a recreational diver, this mix is good for any dive I would do. In the places I dive there are many sites which are below 110' and some which have a hard bottom WELL below 132'. So it makes sense to me to use 28%. If I knew the deepest, local dive was 80' or less then I'd fill with 40%.

 

[down4fun]

What percentage mixtures are you commonly using and why? pros and cons?

Just wanting to learn more about certain limits placed on certifications (32 and 40 being common) and if it matters much to me as a rec only diver.

Thanks in advance! I always learn a lot reading here as we get answers that we didn't even ask for as the threads progress.

The local fill shop banks 32%, 36% and 40%. All at the same cost. As a recreational diver most of the charters here are two tank dives with the first being the deeper of the two. The destination of the first dive was known before arrival and one could get the nitrox mix that was appropriate for that depth with out exceeding MOD. I got pretty good at figuring out what to top the remaining gas in my first bottle with to get the best mix for the next weeks dive. The second dive was almost always a 60ft reef and so my second bottle was always 36%. It gave me a better bottom time and if the reef went a little deeper I was still good.

 

[VooDooGasMan]

Instead of missing the dive Why not let some nitrox out and blend with air using a transfill or on board compressor, and o2 sensor.

If the op has a sensor, for the 40% fill you can dive it, then fill with air and, analyze with your o2 sensor and dive. lets say its 29%, a couple of nitrox dives on a 40% fill and a air fill.

Nitrox is a great bottom time blend.

 

[scubajo007]

Most of my dives are on the Philippines where it seems 32% is the standard gas. Saying 32% means that varies between 30 to 34%. All my dives are suitable with this mix so I would say I prefer 32%.

 

[RTee]

I normally opt for 32% for a couple of reasons:
1) it seems to be the mixture that is generally banked locally and other places and in my case, not more expensive than air at my LDS;
2) with a MOD of 110 ft (111.375) it accommodates the vast majority of the local dive sites I use
3) generally similar to what the other divers I normally dive with are using (NDL)
4) is pretty much in line with the max depth my GF has in mind

Having said that, this will not prevent me from getting a tailored mix to accommodate specific dives I may have in mind and if in doubt, I will show up with my doubles filled with 25% (150 ft) ...and one or two stage bottles to complement.