Cheaping out on Trimix - travel gas

[Alekseolsen]

That is correct yeah.

IANTD Advanced Rec Trimix - Aquarius Dive Center Tenerife
for those specially interested (I did not take the course there, but thats explained with same limitations we were given)

 

[rjack321]

And thanks a lot to you to - the ease of mixing up comes as a surprise to me, but very happy I asked.

Up until now you just put your long hose 2nd stage in your mouth (usually its on the right side of your doubles). And you are ready to do your final checks and dive.

If you dive with stages and a deco gas you can't do that anymore. You have to verify the "gas switch" before your head is even wet. It not something you are accustomed to or part of your routine or training. So its easy to forget or not really think about. Just pulling out the 2nd stage from the travel gas bottle is doing an unverified gas switch - exactly what not to do. In this case it is harmless on the surface whether you are breathing 32% or 50% or 100%. But you can't descend safely without you and your buddy doing a verified switch.

Here's an example of how even the best divers starting on the wrong gas leads to all sorts of problems.
Fatality at WKP | ScubaBoard
Jim Miller was breathing an RB80 rebreather but that just delayed the eventual oxygen toxicity problems caused by the gas switch issues.

You're new, stick to the exact protocols you were taught and don't add cylinders or gases. Those switch protocols are a reflection of some very painful lessons and fatalities over many decades.

 

[DogDiver]

I’ll add my 2 cents worth on cheeping out. Read the book The Last Dive. The Rouses cheeped out by not using protocol and mix on the U-869. Both died.

 

[ls23]

My advice for saving money would be to get a dedicated trimix twinset, if you haven’t already. Then you just have to pay for the top-up, instead of getting a full 21/35-fill every time.

 

[Wibble]

I do this but I would replace 50 with 100

Don't.

Loads of reasons:

• High pressure O2 needs boosting so is hard to get
• High CNS
• Can't use it below 6m/20'
• High OTU
• Consequences for screwing up are more likely to be serious
• But most of all, for this use case as a bottom gas, it's dangerous.

Lots of far better shallow gasses are available.

 

[Joris Vd]

I didn't know you could do the adv rec trimix without and advanced eanx...
My advanced eanx from IANTD, clearly says 21 to 99% EANX, but I did it without the recreational trimix combo.

I've actually been thinking of doing the adv rec trimix, but the costs are so prohibitive where I live.
It's similar to Norway a fill will cost you + - 150 euros.

 

[Wibble]

Regarding fills. 21/35 is the "standard gas" for use down to 57 metres / 170'. If you're not diving to that depth and aren't GUE person (or other dogmatic agency), you're allowed to use other gas fills that better matches the depth you'll be diving to, i.e. far cheaper mixes given that helium is so expensive.

For example, diving to 40m. You could do this on 28%, but with narcosis. Add enough helium to bring up the END*** (Equivalent Narcotic Depth) to whichever depth you're personally happy with. Lets just say you'll tolerate an END of 30m.

Thus you could use a mix of 28% oxygen (MOD = dose over mix = 1.4 / 0.28 = 5ata = 40m)
Add 20% helium the formula using ATA is
END = (1 − fraction of He) x Depth_in_ATA – 1
= (1 - 0.2) x 5 – 1
= 0.8 x 5 – 1 = 30m

So your "cheap" mix is simply 28/20 for an END of 30m when diving to 40m.


Again, for a 45m dive:
O2 = 1.4 / 5.5 = 25.5%, round to 25%
He at 27%
END = (1 - 0.27) x 5.5 – 1 = 30m

Thus dive with 25/27 mix at 45m.


As most dives the you're diving above the max depth, you could reduce your Helium a tad (don't mess with the O2 MOD!). For 45m, many people consider the right gas is 25/25.

Or, to put it another way, you can dive with expensive mixes. Or you could do more diving! When you do more diving you'll be a lot less bothered about narcosis and expensive gasses; but that's for you to decide based upon your experience and the type of dive; if it's particularly complex (penetration, current, workload) then use more helium. If it's looking at the pretty fish, cheap may be better!


*** END; do or don't you count O2 as narcotic in END calculations. A topic for another thread.

 

[Wibble]

I didn't know you could do the adv rec trimix without and advanced eanx...
My advanced eanx from IANTD, clearly says 21 to 99% EANX, but I did it without the recreational trimix combo.

I've actually been thinking of doing the adv rec trimix, but the costs are so prohibitive where I live.
It's similar to Norway a fill will cost you + - 150 euros.

Rebreather's rule!

That would be €15 for a rebreather diluent gas (once you've paid for your bailouts!) -- you'd consume, say, 300 litres not 5500 litres

 

[jale]

Don't.

Loads of reasons:

• High pressure O2 needs boosting so is hard to get
• High CNS
• Can't use it below 6m/20'
• High OTU
• Consequences for screwing up are more likely to be serious
• But most of all, for this use case as a bottom gas, it's dangerous.

Lots of far better shallow gasses are available.

?? do you never use oxy to deco???

 

[Marie13]

I didn't know you could do the adv rec trimix without and advanced eanx...
My advanced eanx from IANTD, clearly says 21 to 99% EANX, but I did it without the recreational trimix combo.

I've actually been thinking of doing the adv rec trimix, but the costs are so prohibitive where I live.
It's similar to Norway a fill will cost you + - 150 euros.

Midwest US (Chicago area) - last week I paid $372 for 4xLP85 (filled to 3000 psi) for 20/20. $4.60/cft. That’s just the helium.