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

[Storker]

Is that a law in your country or just justt standards?

There's no law. Is there a law about such things in other countries? How should they enforce it?

If you look at their websites, both the Swedish certifying body Svenska Sportdykarförbundet and the Norwegian certifying body Norges Dykkeforbund state explicitly that their 2* cert is good to 30m and their 3* cert is good to 40m:

Efter den här utbildningen anses du vara kompetent att dyka till max 40 meters djup.

"After this education you are seen as competent to dive to max 40 meters' depth"

Dette kurset [...] kvalifiserer for dykking ned til 40 meter.

"This course [...] qualifies for diving down to 40 meters"

If you show up on a dive up here with a 3* cert and no tech certs, and tells the dive leader that your max planned depth is 55m, there's a fair chance that the answer will be "not on my watch, mate".

 

[CAPTAIN SINBAD]

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.

THIS!

Where have you been all this time man?

 

[Germie]

Here 30m. But: brevet international is written and there is no law. This means international standards apply after it. So easy it is. No discussion. They try to say here same, BUT it are the words brevet international and no national regulation ( no law). I have done such deep air dives on my 3* without any problems in France and Spain ( and without any knowledge, so if it is a good choice?) Now I have all tx certs and never a discussion, but if people state 3* is only 30m they are wrong, just read international standards and apply it on laws. If no law, then the 1.4 or the 60m is the rule. Easy.
So trainingstandards can differ from certification limits.
And air is a standardgas?

In France they bring you to 60m wrecks with this cert.
And in my country you can reach 51m and as there is nolaw, everybody can do it, even without any cert and is still insuranced.
Strange? Maybe, but it is the real world.

 

[Storker]

if people state 3* is only 30m they are wrong

Of course they are. I don't think anyone has said 30m. Depending on where and when you got the 3* it's either 60m, 1.4 bar PO2 or 40m. Regardless of that, if I suddenly believed that it's a good idea to dive to 60m (which I, incidentally, don't), who can stop me?

It seems as if you're forgetting that there isn't one single certifying body for CMAS certs. Any national CMAS cert must follow the minimum standards given by CMAS, but there's nothing saying that it can't have stricter standards and/or stricter limitations than CMAS' minimum standards and limitations. In fact, it seems like a pretty good idea since diving in the Nordics is pretty different from diving in e.g. Italy, so you need somewhat different skills.

 

[RainPilot]

Where have you been all this time man?

Diving more, posting less...

Thinking back to the cattle boat ride that @cerich , @ScubaWithTurk and I took to PhiPhi islands, it's sort of reassuring that we are divers for whom "to standard gas or not to standard gas" is a big deal. SB discussions are REALLY not representative of the diving world at large.

 

[Germie]

Really, it is here 30m. But then you get an an internatio 60m cert. With 2* from where in the world you dont need to do a deep diver anymore. And that isso strange with our 2* standards where divers can choose to stay shallower than 20m, or do the on top speciality 'deep' to max 30m. I refuse to sign off without 'deep' as you get a 40m, or inyernational 57 m cert. So only been to 20m, i refuse, you are not worth a 2* cert then.
Cmas is different from other commercial agencies. But at the end the international standards apply, even if you learned different things added different in every country.

But back on topic. There are stilld air certs, and i am not against them. It Is the divers choice. But I dont teach them ( i teach 3* to 30m and adv nitrox to 42, technical diver you do normoxic trimix) There is no proof that standards gases give less dcs than best mix.

 

[helodriver87]

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.

This gets ignored so often in these kinds of discussions. People make a big deal out of a few feet of END, but there's no discussion of gas density and, by extension, CO2 buildup. If I go to 130-140 on air and stay nice and relaxed, I'll probably be fine, but I'm pretty ill equipped to handle any exertion or excitement thanks to the density of my breathing gas. Hell, I've had a few dives shallower than 100' where I found myself wishing I'd brought 30/30. Going deeper on air because "conditions probably don't warrant helium" is like planning for things to go right. You'll probably be fine. Until you're not.

 

[Germie]

Gasdensity is also or a much bigger problem on ccr on deepdives. On 6/72 diluent, at 130m depth, the END is ok. 27 if o2 not narcotic, 32 if o2 is narcotic. But the EADD is getting 46m.
On oc, the process of getting off co2 is only over your lungfilter ( smokers are less efficient in this).
On ccr the scrubber must filter all co2 out of your exhaled gas, and this is getting less efficient at depth.

A higher EADD means higher WOB, on oc, and on ccr.
But at deeper dives the end can be ok, but eadd quite high.

If you have a headache after a 50 m dive on air and no headache if you use trimix then it is CO2. And as with narcoses, some divers are co2 retentioners and others not.
Some divers have a more effective lungfilter than others.
Even with co2 taken into account you cannot say allways trimix needed. It is still a personal thing and can change from person to person and dive to dive. But it it is good to be aware off it and get trimix certified if you want to dive over 40-45m.

 

[leadduck]

maybe time for another thread split ... deep air is not best mix.

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.

^^this. Standard gas vs best mix is ease-of-use vs optimality (deco, cost per fill). A personal situation-dependent choice.

 

[stuartv]

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)

I can only speak to the training I have personally had. Which STARTED with "figure out what FO2 gives you a ppO2 of 1.4 at the max depth you are possibly expecting. And figure out what FHe gives you an END of 100'."

It then went on to (in short), "adjust those numbers as appropriate for the other factors (factors other than depth) that may be relevant to the particular dive you are doing."

One example: Planning a dive that is the nth in a series of deco dives with a lot of O2 exposure? Consider adjusting the mix for a max ppO2 of 1.2, instead of 1.4.

The insistence in equating Best Mix to a very simplistic approach to dive planning that means it is always "ppO2 = 1.4 and END = 100" is not what I have learned. That is just where I would start the process of selecting gases.

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.

No hackles raised here. My apologies if I made it seem that I felt attacked or that I was attacking back. Your post is not the first time I have gotten a vibe (here on SB - not from you specifically) that some people equate non-GUE training with "no team skills".

Re-reading what you wrote there, I took it as somewhat in that vein, but I can see now that maybe you were just saying "GUE has all these team skills at the core of their diving, so Standard Gases makes sense for GUE because of that." Again, my apologies for misinterpreting your intent.

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.

I have NO experience in that arena. But, to my non-cave-educated point of view, it seems like that is a time when you would LEAST want to take shortcuts (like not discussing the details of the gas plan)?