Nitrox Common Mixes

[TSandM]

I understand the rationale for standard mixes and don't argue against anyone using that method but I think it can lead to mental laziness in regards to dive planning if one is not careful. I also think it's a hard sell to nix computers in favor of BT's and ratio deco then insist best mix is too edgy for rec diving.

I don't think anybody is insisting best mix is too "edgy". I think most of us who adopt "standard gases" have also adopted the 100 foot END limit, and once you do that, 32% just makes sense. There is a real advantage to having everybody who shows up for a dive on the same mix, too. I may plead guilty to the laziness part, though . . . I know my MOD is 111, my END limit is 100 feet, and so I can put all my limited mental capacity into figuring out what my gas limits for the dive are

 

[vladimir]

By 'limits' I meant that the local SSI place here offers a nitrox cert that is limited to 32%. It has a through lab and test after the study work. But they also offer a 40% max cert if you include dives. Little more expensive and it is getting colder here. Not sure if this is standard everywhere (I haven't gotten the same answer twice when I call around), but I love this shop and their customer service.

This is an arbitrary and stupid distinction, in my opinion. What increased risk does 32% to 40% entail, and how do those training dives mitigate it? If you are certified to 32% and you get a tank of 33%, what are you supposed to do, not dive it? You're qualified to dive 32% and unsafe with 33%? It's not a hypothetical problem--you will get tanks of 33%.

I'm pretty sure you can do a PADI nitrox certification with no dives. Find a PADI instructor, pay your $99, and get a nitrox certification that doesn't limit you to 32%.

 

[mddolson]

For less than 60 ft : air ,
for 60ft to 110ft : 32%
Deeper= custom mix, & 50% nitrox for ascent deco.

Mike D

 

[Tigerman]

Locally I dive 21% mostly, simply because air is obtainable and nitrox is not. When travelling I use almost exclusively 32% as its the richest blend for the maximum depth I want to go to.

Cant wait for that semi-local dive shop to get their membrane filtering system in place though.


My (PADI) cert is limited to 40% and I coulda gotten it without doing any actual dives with nitrox, but why the hell would I waste a perfectly good day by not diving?
Reason why its limited to 40% is apparently the increasing fire hazards and gear requirements etc. that you get from richer mixes.

 

[CamG]

Greetings conway400 use 32% a lot for most of my diving just because it is very flexible.
When diving deep I like to use best mix because it is available and I can blend my own gas.
When I make my jump to Trimix then I will move to a helium standard mix 21/30-35.

I have had great dives blending gas for specific depths / wrecks.
It has allowed me to extend bottom times far beyond what we needed to achieve the goal of the dive.
For deco gases I stick with 50/50, 100%.
Take your time and train well be conservative and always watch your PO2!

CamG Keep Diving....Keep Training....Keep Learning!

 

[Tortuga68]

Reason why its limited to 40% is apparently the increasing fire hazards and gear requirements etc. that you get from richer mixes

Real reason is that there's not much practical benefit to using >40% for recreational diving

 

[DaleC]

A basic nitrox course should include all the theory and skills needed to use mixes up to 40% and there is nothing more to be learned whether using 32%, 28, 36 or 40%. What difference does doing dives make in regards to using 40% over any other percentage mix?
Basic nitrox is a knowledge based course, not a skills course - with the exception of analyzing your tank. This should be done by you regardless of whether you are recieving a custom order 40% blend or a prebanked 32% mix so the two courses need to cover exactly the same material.
You do not need to do dives in order to learn that skill. Diving with nitrox is no different than diving with air and, unless you know you are doing so, you would never know the difference during the dive. That's why analyzing the tank is neccisary. So the question is: what do the dives offer you? And, why do you not need whatever that is when diving 32%?
The answer would be interesting and I suspect have a lot to do with what I said earlier about mental laziness; only this time sponsored by the dive industry. If you only use one mix, you only need to learn one MOD and only need to learn one table of adjusted NDL's (if you learn that at all).

 

[DaleC]

I don't think anybody is insisting best mix is too "edgy". I think most of us who adopt "standard gases" have also adopted the 100 foot END limit, and once you do that, 32% just makes sense. There is a real advantage to having everybody who shows up for a dive on the same mix, too. I may plead guilty to the laziness part, though . . . I know my MOD is 111, my END limit is 100 feet, and so I can put all my limited mental capacity into figuring out what my gas limits for the dive are

Like I said, I get it and don't knock anyone following the regime... I just find it irksome to combine standardized mixes with arbitrary MOD's when I don't need to. But that reflects my approach to diving which is, more often than not, individually driven.
One could say 32% is standard but for most of my shore diving I just use air. I have no great need to extend my NDL's, and it costs 1/2 as much. So, I could pay twice as much to be standardized but why bother?

If I had a different personality, and dove with the same people all the time, I would probably be more in favor of standardization. I do see its benefit in groups.

 

[Colliam7]

By 'limits' I meant that the local SSI place here offers a nitrox cert that is limited to 32%. It has a through lab and test after the study work. But they also offer a 40% max cert if you include dives. . . . Not sure if this is standard everywhere (I haven't gotten the same answer twice when I call around).

That is certainly not a standard everywhere, at least not in PADI land. Nothing wrong with it, although I confess that I don't see the point of making a distinction between 32% and 40%, given there is already a distinction between 40% and higher concentrations.

I prefer best mix . . . when I use nitrox, which is pretty rare these days. Air, it turns out, is often adequate for my needs.

Interesting comment, very consistent with what I have come to. For recreational diving, I use air 90% of the time. Right after nitrox certification, I consistently used enriched air. But, over time I came to the point of using air for all local quarry dives, and air even for the majority of coastal diving. When I am diving multiple times/day for multiple days, I will use nitrox (which is frequently available at no extra charge in many Caribbean resorts catering to groups staying for 5 or more days). But, for a one day, two tank coastal boat dive, air is fine.

 

[MXGratefulDiver]

Real reason is that there's not much practical benefit to using >40% for recreational diving

While this is true, the historical reason why EAN40 was established as the upper limit for recreational diving was that it's difficult to get yourself in trouble with it. Prior to just a few years ago, EAN40 was considered "safe" to a max depth of about 100 feet. Also, it was established that a mix at 40% or less oxygen didn't require any special regulator servicing ... mixtures above that do.

Gotta keep in mind that just 20 years ago there was a LOT of resistance to any elevated O2 levels in recreational breathing gas ... the 40% limit was established primarily to address the concerns of those who were resisting nitrox usage at all in recreational diving.

... Bob (Grateful Diver)