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

[helodriver87]

I did a deco dive a couple of years ago with a buddy. The bottom was something like 135'. We used Air for the bottom gas because neither of us felt like helium was needed for the specific conditions and Nitrox was not needed because we were not concerned with NDLs. Using Air was less expensive and the most convenient. We decided it was the best mix for the planned dive. We used a single deco gas of 80%, because we DID want to be prepared for significant surface surge that would make hanging at 20' more difficult and less pleasant than hanging at 30'.

Couldn't help it.

Edit (because this post needs some actual value):

I don't think arguing edge cases really has any value. One of the foundational assumptions of standard gasses is that they're rarely going to be ideal for a given dive, but that the benefits outweigh that (realistically) small disadvantage. If your dive is right on the edge of the recreational/technical divide, you need to approach it with the right mindset. In my opinion, that mindset isn't "what if I accidentally breathe some helium a few feet shallower than it's absolutely needed." Standard gasses simplify logistics, gas planning, deco, tank marking/gas switches, and team procedures. A few weird edge cases don't invalidate that or really even take much from it.

 

[rjack321]

Woo hoo! It took 12 pages for it to come out that Stewart is making up his own definitions about what best mix is.

Air at 135ft might be someone's gas of choice - but it is not even close to best mix as defined in every nitrox class ever. (@ ppO2 1.4 it's EAN28)

 

[seeker242]

The standardization of gases IS limiting if you want to do a dive and the prescribed Standard Gas is not available...

So then don't use them...problem solved!...

 

[TrimixToo]

The standardization of gases IS limiting if you want to do a dive and the prescribed Standard Gas is not available...



I get where they came from and why. Ratio Deco depends on an assumption of what gas you are using for a certain depth range. There was a time when all that was needed.

It seems to me that that time has passed.

It also seems like requiring people doing (relatively) shallow, warm, clear water drift dives to use specific gases that made sense for the technical cave divers who came up with the list is simply a case of using the wrong tool for the job.

Your other statements seem to carry an implication that if you are not GUE-trained and not diving with Standard Gases that means you are not adhering to good team diving principles like gas matching. I don't know about other training, but my OC tech training has been all TDI and it most certainly included things like everyone on the team having all the same gases. And the same algorithm and parameters. So, everyone also has the same deco profile. None of that requires use of Standard Gases.

<snip>

I neither meant to imply what you inferred, nor was I talking about RD. Had I meant readers to think I meant those things, I'd have said them outright. Having somehow raised hackles twice in this thread without meaning to in any way either time...I am done.

 

[RainPilot]

Make. Sensible. Informed. Choices.

If you occasionally dive different sites and get tanks filled for that, by all means pick the gas for the job.

If, like AJ and others, you may be called at any time to dive to any depth at the drop of a hat (think Edd rescuing the guy the other day) AND you have a bunch of your own filled tanks on standby, then it makes sense to have them filled with an easy-to-mix, flexible gas.

Which also allows permanent marking of the tanks, which gets REALLY important when you are doing widely varied dives and the human factor permits grabbing the wrong tanks etc.

It also means one less thing to discuss beforehand when members of the team are arriving in the dark at some cave entrance with a time pressure.

It means your Perdix can be set on the same gases all the time and you just have to switch some off, but even if you don't its no big deal. You certainly can't accidentally set the gas wrong.

If you leave your tanks at the shop for fill, the markings will let them know exactly what you want in them even if the bit of tape the filler stuck on falls off. You will probably also get your tanks first in some shops because all those gases are banked or can be blended fast.

If none of these advantages are applicable to you, then sure, the disadvantages will not make the standard gasses worth it. I, for one, don't have anybody here where I am banking anything so everything is PP blended, usually at the shop before/between dives. That means that 32% ends up being what I use for everything shallower than 100' or so, and air for anything deeper (recreational).

If I have a tech dive planned, then there is more time to get stuff organised beforehand so I will get a tank of a suitable gas, sometimes ends up being what the other guys have a full tank of, more often than not a standard gas around here with my usual dive buds.

I won't can a dive because a standard gas isn't available, I also won't go deeper than 130' without He just because He is expensive.

 

[NAM001]

The question of best mix or standard gas is not black and white. The meat of the question is BEST for what??? Best for Rec NDL then use the best mix process you learned in nitrox if that is best for your pocket book.. If you are talking best mix for deco and you are a RD person then the mixes are tuned to provide a specific process to work with RD as the priority. If you look at all the standard gases for trimix they are in many aspects the same to the body in their assigned depth bands. By that I mean at their max depths the PPO2 and PPN2 are the same +/-.... Its a key to making RD work. Yes there is much more to it than that but standard gasses are key to making RD WORK. Since Rec diving has no deco,,,,the terms of standard or best change,, and become more a matter of what is convenient and less about what is necessary. An 80 ft dive would call for a 40% nitrox mix but most will dive 32 because it is readily available as a standard shop mix. Which is better depends on what is the most important to you . Max NDL or cost and ease of use. and that may be driven by whether you are doing a single dive or multiple dives in a day or repeated days. So in that regard best is not a text book fixed definition.

 

[Germie]

If I have to use a 30/30 or any triox with >21% oxygen, I would take a nitrox. I really don't see any need in a gas like 30/30. Or 28/25 or whatever kind of triox as bottomgas.

30m as max without helium is for myself too shallow. Somewhere between 40 and 45m I will think about some helium. A lot is depending on where I dive. Cold dark waters vs warm clear waters.
END is a personal thing. In courses it is 36 or 39/40m, but after a course you see people choosing what fit. Some use END of 30m, others use END of 45m. And some do deep air (courses are still teached). I don't teach deep air, as I am responsible, but I don't have problems with people doing this if they want.
The CMAS 3* divemaster cert is a 60m cert on air(or for newer divers a PO2 of 1.4, so 57m cert). This depths are done regularly in the south of Europe (France, Italy) on air without any problems. To teach this depths on air, it is too deep in my eyes, but you see this teached by others without problems.

But what is the advantage for a 55m dive on 18/45, ean50 and 100% over using 18/35, ean50 and 100%? 18/45 costs about 15 euro more for a fill, but there is no difference in 'safety'. First the END at 55m (O2 not narcotic) is 28m with 18/35 and is 20.4 m with 18/45. Both are within the max END of 30m for 'DIR'. If you use ratio deco (even gue moved now to pragmatic deco more and more, what I already do for years), you can still use it. You will with 18/35 1-2 minutes more conservative if you put it in a diveplanner to check your plan. So I don't see any reason not to take 18/35.

The most used reason to fill standardgases is if they are already banked. But other standard poormansmixes are also banked a lot of times. But as soon as you need to start partial blending, there is no advantage in using a standardgas, mixing can be hard, poormansmixes are easiest to fill. The problem with poormansmix is that it sometimes is low on helium. 10/50 vs 10/70. On a 100m dive oc I prefer a 12/60 or so.

I dive with all kind of divers, DIR, non-DIR, ccr, etc. Of course sometimes I take oc also standardgases. My buddies/teammembers must be thinking divers and not only parrots speaking what others told them to do. And then bestmix vs standardgases is no problem and can be discussed with a right outcome for every diver.

And some divers are more sensible for being narcotic than others. Where let's say 90% of the divers still can function at 40m, some can't. And for them it is nice to have the helium/trimixoption/trioxoption. And it is quite popular to do such a course.

The problem with too low on PO2 is too much deco. To high on PO2 is the oxtoxrisk. 1.4 is meaned as 'safe', but you see at 100m more and more 1.2-1.3 used. Some use only 1.0, but then they have more deco with a bottomtime of 20 minutes at 100m, but in a team you have to discuss these things and if it are just marginal differences, the discussion will not be that hard.

On CCR you can choose easier a higher heliumpercent in your diluent. Even for example a poormansmix 6/72 works really well as 100+ diluent. As bailout a 10/70 is then better or 12/60 (at 100m). My bailoutmixes at home and only used for bailouts are 6/72, 10/70, 15/55, 18/45, so all standardmixes (6/72 poormansmix). Further I have then a 100% (already standardmix instead of a widely used ean80 by best mix divers), and then an ean50 (or 50/20). If needed I will get an ali80 with 21/35. With these bailoutgases I can do the whole range of depths on ccr. This is an example of where I prefer to have standardgases.

I still plan my dives and can dive 100m dives on a bottomtimer with wetnotes, but I have a trimixcomputer, so normally I plan, I write it in wetnotes and dive on my computer with still the TTS from the diveplan and max divetime from the plan in my head. So even if I would forget to put in the right gases, I would not have to worry that I don't have a diveplan. I think everydiver should practise diving on a slate with bottomtimer.

 

[Storker]

The CMAS 3* divemaster cert is a 60m cert on air(or for newer divers a PO2 of 1.4, so 57m cert).

National restrictions may apply. In Sweden and Norway, max depth for 3* is 40m, and max depth for 2* is 30m.

 

[kensuf]

Helium - 0.015
Nitrogen - 0.05
Oxygen - 0.11
CO2 - 1.34
Nitrous Oxide - 1.56

The greater the number, the more likely you'll be to get wasted on that particular gas. It's fascinating for me to see how close CO2 is to a whippet compared to the other gases we breathe underwater.

 

[Germie]

National restrictions may apply. In Sweden and Norway, max depth for 3* is 40m, and max depth for 2* is 30m.

Is that a law in your country or just justt standards?
Here we dont have a law, just training standards that say even for 3* max 30 m. BUT we get a ' brevet international' and then it is 60m or the newer po2 of 1.4 ( or national regulation that does not apply in my country as we dont have a law).
So we take the 3* abroad and have a 60m cert. Or go to lets say 50 m after becoming 2* certified in my country as this is within cert limits. ( Mines is older, so it is 60m and not po2 of 1.4, even if this is not stated on a cert). A 2* diver never need a commercial deep diver cert. Just because of the 1.4 rule.
Strange? Yes, but this is cmas and there are not more accidents happen.
And yes, in France 60m on single tank on air is normal.