Best Mix VS Standard Gasses (split from a GUE fundies course report)

[seeker242]

it SEEMS to me like GUE Standard Gases are pretty limiting - not making "it easier" like the GUE people keep telling me. At least, for sport divers anyway.

It's not the standardization of gasses that is limiting. It is the maximum narcotic depth of 100' that is limiting. If the max was 130' and the standard was 28%, this thread probably wouldn't exist. For a GUE rec diver following the standards, 32 works on every single dive, always, because the max depth is always 100'. It's certainly easier to always use the same gas on every dive.

The standard is 32 because of the conservative limits regarding narcosis. It's no secret that GUE is conservative. That is exactly why many people like them. If that narcotic limit is too conservative for you, well then you just don't follow it. The limit is for people who do want that level of conservatism.

 

[TrimixToo]

Let me take a step back for a second.

I was not around when the standard gas list was created, and I'm not cave-certified, but I will speculate freely anyway (grin). @PfcAJ or @JohnnyC can chime in to correct me if I'm off-base here.

Deco theory was no so far advanced when that list of standard gases was originally made. One reason to have standard gases is to reduce the number of variables. If everyone is using the same gases, the deco plans and algorithms can be changed when necessary and everyone benefits in a broader sweep when variability is more limited. There are fewer edge cases to worry about. When I took trimix classes, my instructor pointed out that WKPP probably used more He more often than anyone else, and he saw some logic in using the same mixes to take advantage of that large body of experience. Some years later, and lots of He bubbles later, I agree that he was absolutely right at the time, and much of that "rightness" persists even though we have learned a lot more.

The other thing to consider is that GUE stresses a team diving approach with its roots in cave diving. Everyone is rigged the same. Everyone uses the same procedures. Everyone uses the same cylinder markings. And, everyone breathes the same gases. There are at least two big advantages to the standard gas approach when diving as part of a team. One is that anyone can donate gas at any time, to anyone, and no deco recalculations are needed. This reduces the stress and complexity of gas donation scenarios. The second is that everyone knows the minimum and maximum operating depths for everyone else's gases, because they're the same across the board. So when double-checking gas switches (part of the protocol), nobody needs to think about the MODs. Likewise, everyone has the same deco schedule, so the whole team can act like a school of fish without leaders and laggards.

I think the second part stands, still, as a good idea in that kind of diving.

Further, if you are a GUE-trained diver (I am not), the urge to dive the same way, all the time, regardless of recreational or technical settings (which I share) is likely a strong one. Why change all those procedures that work? No particular reason in favor, and some against.

To me, none of this should necessarily guide a firm choice between "best*" mixes or standard gases for a non-GUE diver on a recreational dive. They're chalk and cheese in that context anyway, and the meaningful differences are negligible most of the time in my view.

* The very definition of "best mix" has changed since my original nitrox cert.

(Edited to fix typo.)

 

[PfcAJ]

@johnkendall dismissed my NC scenario with "I wouldn't do it without helium, so this conversation is pointless" but I guess didn't notice the other scenario I posited - heading out for a 90' dive off Key Largo and diverting to a 40-ish foot dive. Like I said in the preceding paragraph, EAN32 will work. But, EAN36 would work better....

The practical difference between 32% and 36% at 40’ is nonexistent. The NDL time is absurd, longer than you’ll be diving a single tank for anyways. 310mins according to the NAUI table for 32%....

 

[CptTightPants21]

Out of curiosity, what would you say makes a diver a GUE diver?

I would say that too many people take fundies for a variety of reasons for that to be the benchmark for 'GUE Diver'. This is not to say that they are not GUE-like divers, GUE inspired divers, etc or that they have rejected or ignored everything they learned in fundies, but to get the title of GUE diver I would say you need at least a Cave 1 or Tech 1 cert. Even after getting one of those certs a case could be made that adhering to certain protocols might be an additional requirement, but I don't think that is a discussion for the thread. I will say you wont see me diving 30/30 at 120' unless someone else is buying. Does that disqualify me from being a GUE diver--maybe. I think that if you look deep inside yourself you'll know if you have the 'GUE Diver' title.

Stuart--let's get some definitions straight. Your 30% NC example is not a 'best mix'. It's just a variation of a standard gas where 30% is substituted for 32%. Best mix would be similar to your reef example where you put 36% in tanks because the dive site is at 90ft. In that case, going shallower provides minimal benefit and you now have a gas in your tanks too rich for a variety of dive sites---but you will say, I wouldn't have 36% if deeper sites might be available. Then you are not diving best mix, you are diving a version of standard gas, just not GUE's standard gas list.

In the Northeast, 28% is considered the standard gas because a lot of our common everyday wreck sites are in the 65-140 range. I will say that getting blown off one wreck or having to redirect because of fishing boats is not uncommon, the dive depth can absolutely change--some wrecks are great 60-110 because they are intact, others only start at 110-130 because they are more debris field--both would be fair alternatives on any given day. The risk of getting blown out means people don't use the richer best mix and most people have 28%, maybe 30% as the standard gas.

People seem to forget that GUE was originally created as a deep cave diving organization in Florida. While the philosophy is sound, there is some location specific idiosyncrasies that it has trouble incorporating. Where am I supposed to clip off my sledge hammer? It's hard to have a philosophy and then half a dozen bullet points in the footnotes for slight variation. It had been my experience that once a person returns from GUE, they MAY make one or two small modifications depending on the type of diving. In Florida cave diving, 32% works great for a ton of caves and the couple that are a hair deeper are covered under 30/30. Notice how these discussions never venture into the deep end of technical diving--where the standard gas list was really designed to be used and where it excels from a practical standpoint. Instead you are fighting in the shallow end of the pool arguing over shallow depths and single tank dives.

GUE philosophy of 100 END, plus 1.2 are good standards in general and are great for what they were originally designed for--deep cave diving. The price of helium and the grey area of depth,110-150, can cause some wonkiness? Impracticality? You have heard the official statement from instructors and what the standards say. GUE diver would use 30/30 for a dive past 110 feet. In the real world, I have seen some GUE divers do this religiously, but I have seen just as many divers do those dives on 32% or 30%, some will partially refill tanks that previously has 21/35 so there is still some helium. And yes, some have done shallower dives on Helium blend from time to time. To help mitigate this they will usually wait until 2-3 days before the charter is set to go out to get fills when the weather is more certain. I do sometimes wish GUE would amend the standard gas list to include 28% or 30%, but it would run counter to a very standard philosophy of 100 and 1.2.....using that, you can actually guess the standard gases given the depth range so I understand why they don't. In the mean time, GUE is X and I am diving Y because....

 

[rddvet]

The downside to 30/30 for a recreational reef dive at 80' is simply cost. I would feel like it was a good chunk of money spent for no practical benefit.

Agreed it can be costly (unless you own your own compressor and booster, then you put helium in everything like I do). I will say that I have been shocked how much more I've enjoyed dives with a little helium in the 80-90ft range. I used to think I rarely got narced. Now I realize that depending on the dive, even at 60-70 feet I have had unrecognizable narcosis. Do the same dive with a little jesus juice in your tank and you quickly realize you actually had some affects. Of course this isn't every dive though.

 

[Billy Northrup]

Another angle on standard gasses is the shop/mixer/banker. Blending each gas whether standard or custom is labor intensive and SLOW. For allot of reason it's not practical to take the tanks from the AM dive, mix them and have them ready or accurate for the afternoon boat (trimix). I do have banks of standard gasses I can blown in a few minutes. If someone wants a custom mix I can blend a few standard gasses and get the O2 number they are looking for and the helium is what it is. It's less wasteful to cont blend trimix ending with a cheaper/faster product.

 

[PfcAJ]

Another angle on standard gasses is the shop/mixer/banker. Blending each gas whether standard or custom is labor intensive and SLOW. For allot of reason it's not practical to take the tanks from the AM dive, mix them and have them ready or accurate for the afternoon boat (trimix). I do have banks of standard gasses I can blown in a few minutes. If someone wants a custom mix I can blend a few standard gasses and get the O2 number they are looking for and the helium is what it is. It's less wasteful to cont blend trimix ending with a cheaper/faster product.

Helping with your efficiency problem, most standard gases can be blended by mixing helium with 32% nitrox. It’s super easy and convenient.

Exceptions are 100% (duh) 50% (duh) 30/30, and 35/25. The rest are just helium and nitrox.

 

[rjack321]

The other plus is when you go to recycle or top off all those standard mixes 21/35, 18/45, 15/55, 12/65, or 10/70. You can mush them all together into a storage bottle and the resulting mix can be used as a based to make any other standard mix by adding... wait for it! 32% or helium.

 

[leadduck]

Helping with your efficiency problem, most standard gases can be blended by mixing helium with 32% nitrox. It’s super easy and convenient.

The other plus is when you go to recycle or top off all those standard mixes 21/35, 18/45, 15/55, 12/65, or 10/70. You can mush them all together into a storage bottle and the resulting mix can be used as a based to make any other standard mix by adding... wait for it! 32% or helium.

This is all true and convenient, but works with many mixes such as 28/15, 26/20, 24/25, 22/30, 21/35, 19/40, 18/45, ...
Standard gases are a subset of these. Others like 30/30 are not in this set.

 

[leadduck]

P.S. I'd say every best mix is EAN32+He because this gives the right END at any MOD. Standard gases are just a once arbitrarily chosen subset of best mixes.

Regarding the argument of changing dive plans on a boat: say everybody has 18/45 on the boat and you're the only one showing up with 21/35, all standard gas but bad luck. Better know the max.depth first and all have the same gas.