Tri-mix and the Need for a Helium Analyzer

[Steve Lawson]

Some friends of mine and I are pursuing tech diving using trim-mix. Given the cost and lack of shops that fill the mix, we're considering blending our own.

How cruicial is the need to know exactly how much helium is in the mix? When blending your own by adding a specific amount of O2 and He, is it really necessary to verify the percentage of He in the tank? It seems like simple math that can be partially verified with an O2 analyer and that the only time a helium analyzer would be needed is to verify the percentage and reduce the error when a mix is topped off and/or changed.

What are your opinions and what is the common practice?

Steve

 

[Doc Intrepid]

Steve,

For what its worth, its generally an unsafe practice to dive a mix when you really don't know what mix you're diving.

On one hand, if you're off on the helium content by a bit (say you're actually diving 18/50 instead of 18/45) it isn't likely to ruin your day. Some amount of slack is, while not desirable, at least acceptable. Particularly if you're aware of it in advance.

But - as you noted - if you are taking the remnants of one mix and re-mixing to refill your tanks with the same or a different mix for the next day...using an He analyzer can alert you to other potential issues that are at least possible. If you have no access to an He analyzer, you really don't know what the end result is. You can speculate, but you don't know.

I don't own one myself, only an O2 analyzer, but I use the He analyzer at the shop where I get the He. I'm pretty insistent on knowing the mix and marking the tanks accordingly, before I'll dive it.

YMMV.

 

[francousteau]

How cruicial is the need to know exactly how much helium is in the mix? When blending your own by adding a specific amount of O2 and He, is it really necessary to verify the percentage of He in the tank? . . . . . . .

Steve

Not trying to be a smartarse here Steve, but if ya really need to ask those questions, you're really not ready to use tri-mix and forget about blending your own until you get lots more training.

 

[rjack321]

Plus or minus 1% on O2 and 5% on He are common slop allowances and don't typically require substantive changes in deco. O2 is much more critical than He. Until a few years ago He analyzers were actually pretty rare. But their price has come down so much you'd be penny-wise and pound-foolish to not to use one at your shop or have one at home.

Its pretty hard to reliably change a partial fill of one mix to another mix without an analyzer. Using continuous blending (at home) I can easily change mixes. I monitor both O2 and He at the inlet.

 

[Meng_Tze]

Some friends of mine and I are pursuing tech diving using trim-mix. Given the cost and lack of shops that fill the mix, we're considering blending our own.

How cruicial is the need to know exactly how much helium is in the mix? When blending your own by adding a specific amount of O2 and He, is it really necessary to verify the percentage of He in the tank? It seems like simple math that can be partially verified with an O2 analyer and that the only time a helium analyzer would be needed is to verify the percentage and reduce the error when a mix is topped off and/or changed.

What are your opinions and what is the common practice?

Steve

I would advise to get an analyzer.

 

[karstdvr]

I used trimix for many years before there were analyzers,and the only way to get by was mix your own. If you did the math correctly,and built in a helium fudge factor,then typically your were safe. Oxygen is the critical component,but verifying the oxygen percent will give you an approximation on helium to a +/- 5%. Interestingly when I did have a helium analyzer to check some of my previous mixes,I was pretty darned close.

 

[DA Aquamaster]

If the math is right, if the gauges are accurate and if the fill procedures are both appropriate and consistent, the mix will be correct.

That was the general feeling and practice when HE analyzers were unavailable or prohibitively expensive, but that way of thinking does not make nearly as much sense now as an HE analyser will let you ensure that all of the "ifs" happened the way they were supposed to.

 

[fweber]

Not trying to be a smartarse here Steve, but if ya really need to ask those questions, you're really not ready to use tri-mix and forget about blending your own until you get lots more training.

Really? It's not a bad question if you haven't already read the blending manuals or attended class. And if that is the case, shows that Steve and his buddies are thinking about what they will or won't need in order to do what they want to.

If the math is right, if the gauges are accurate and if the fill procedures are both appropriate and consistent, the mix will be correct.

That was the general feeling and practice when HE analyzers were unavailable or prohibitively expensive, but that way of thinking does not make nearly as much sense now as an HE analyser will let you ensure that all of the "ifs" happened the way they were supposed to.

A very accurate assessment of the situation. IF, IF, IF, IF, then! And that is how it was done by an awful lot of divers for a while. But, with He analyzers available and not that expensive, why not have one? So you "know" what you're mix is.

 

[pir8]

Considering the depths that you will be diving and your experience level doing them, it would be prudent to get the analyzer and be aware of what you really have.