Cheaping out on Trimix - travel gas

[CptTightPants21]

But that's not what allegedly happened and even so your example's still not a great way to do things.

My example is exactly what happened only moving one rung up the standard gas ladder. 32% became 21/35, and the 21/35 became 18/45.

Diving two different bottom mixes isn't ideal and it needs to be planned out on deco software, but nothing about this plan is even remotely outrageous. The PPO2 of gases is still 1.4 or less. All of the gases are breathable at every point in the dive. If this was a situation where gas in the backgas was not breathable at certain points in the dive I would be on board with you, but this is not the case. (Ignore hypoxic mixes <3m)

You talk about multiple stages and dpv task loading, that is a separate issue. That is a number of tanks and gear selection issue combined with experience of using all the equipment together. If there was trimix in the bottom stage and back gas you wouldn't have an issue? Your complaint seems go be too much gear, not necessarily the gas choice.

I have seen ccr divers plan dives using 1.3 and 1.4 set points to save on deco. Have seen divers lie about helium percentage on their computers. I would call these normalization of deviance.

I say this is an example GUE diving interacting and blending with the real world practicalities.

If they had been diving 30% nitrox with no helium, would you call it normalization of deviance? If they did put 21/35 in their back gas and then diluted with air on subsequent shallower dives so that it was no longer 21/35 who that be normalization of deviance?

I see lots of references to these hard-core DIR divers and yet most of the GUE divers I see in the wild are far more practical.

 

[rjack321]

If you are in the 30 to 40m window and nervous about CO2 (maybe swimming hard) or its cold and narc-y and 21/35 seems a bit rich you can consider 25/25. Its not a GUE standard gas (it is for UTD).

Used as -10% EAD it works pretty well in the shoulder zone, keeps your density down, your END modest, makes sense between -20% EAD for 32% and basically neutral EAD for 21/35, easy to mix with 25% helium topped with 32%, not really a huge cost savings but is less painful.

If you go this route I would suggest 100% as a deco gas, coming up from 35m to a 21m 50% switch is a bit wonky. And you end up with 50% N2 in both gases which is not ideal.

Gas choices don't have to be binary but it does help to be intimately familiar with your choices and definitely avoid the best mix trap.

 

[PfcAJ]

There’s nothin wrong with 25/25. It’s got good utility.

GUE standard gases make sense for a lot of areas. WKPP has a different set of standard gases. Your particular environment might lend itself to another set of gases.

No matter what, perpetually chasing the “best” gas for every possible scenario is ridiculous.