Trimix pros and cons...

[ianr33]

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I'd be interested to hear from the experienced trimix divers on the board whether there is much experience of trimix divers having an "unearned hit" whilst following computers or tables. My exposure is very limited, but I have never heard of this on trimix (as opposed to air, where it is a common enough tale), which makes me feel that calculations on helium are probably pitched quite far inside the lines. I love to hear thoughts on that topic from the trimix gurus on the board.

There was an account on The Decostop recently of someone getting bent on Trimix The Deco Stop
Suspect you dont hear about it much for 2 reasons: 1) In % terms not many trimix dives are done and 2) Much more attention is paid to profiles,hydration,hangovers etc than on your average Caribbean rec dive

I have done mix dives to 300ft and runtimes of 3+ hours (incl deco obviously). Both OC and CC mix dives. No hits, niggles or anything in relation to DCS when diving mix. But then I was in no rush and had ample time to think things through...

Never been that deep and no expert on this , but I get the feeling that profiles to 300 feet are pretty well mapped out,much deeper than that and it gets more,err... interesting.

 

[diverdowndude]

Suspect you dont hear about it much for 2 reasons: 1) In % terms not many trimix dives are done and 2) Much more attention is paid to profiles,hydration,hangovers etc than on your average Caribbean rec dive

Never been that deep and no expert on this , but I get the feeling that profiles to 300 feet are pretty well mapped out,much deeper than that and it gets more,err... interesting.

The only undeserved hit and chamber ride in our group was the result of hydration or more appropriately the lack of Hydration according to the attending physician- Five of us were diving the same profiles at the same time, one of us got hit on day eight the rest of us finished the last of our dives on day nine and canceled our planned dives for the last day padding our no fly time by twenty four hours.

I think the reason that you don't hear of many trained extended range divers getting hit now a days is 1. TRAINING 2. EQUIPMENT. With proper training, extended range divers are diving dive plans that include contingency and then some, and are not diving beyond their comport or training level in the last ten years printed tables, custom computer software and dive computers have become available and affordable for those of us diving beyond recreational limits, along with excellent extended range training offered by TDI, DSAT, and NAUI to name a few. (In the not to far past you took your best guess using the Navy AIR tables or a computer generated program in the works and padded them)

By the way one thing that I notice with mix in the 150+ range is that I remain clear headed and don't get tunnel vision like diving air or nitrox at or beyond those depths.

Remember recreational diving is supposed to be fun, if diving mix sounds like something you want to do- work up to it-take your time and most importantly get proper equipment/training.

 

[rmc77]

Another con of diving with very high helium percentages (like Heliox) is the HPNS (High Pressure Nervous Syndrome), AKA Helium Tremors. It gives you, off course, tremors as well as somnolence, visual disturbance, nausea, dizziness, and decreased mental performance.

 

[ianr33]

Another con of diving with very high helium percentages (like Heliox) is the HPNS (High Pressure Nervous Syndrome), AKA Helium Tremors. It gives you, off course, tremors as well as somnolence, visual disturbance, nausea, dizziness, and decreased mental performance.

And what is the shallowest depth that anybody has ever suffered from HPNS ? 500 feet???? 600??
Not going to be a problem to many divers!

 

[rmc77]

And what is the shallowest depth that anybody has ever suffered from HPNS ? 500 feet???? 600??
Not going to be a problem to many divers!

That depends on the percentage of Helium used and personal factors. Nevertheless, the original question was what are the PROS and CONS of using Helium and nobody mentioned HPNS. Would you deny that HPNS is something you need to be aware of when planning your dive?

 

[TSandM]

I would say that, for 99.9% of OC divers, HPNS is not going to be a consideration. Sheck Exley and Dave Shaw probably had to think about it.

 

[rmc77]

I would say that, for 99.9% of OC divers, HPNS is not going to be a consideration. Sheck Exley and Dave Shaw probably had to think about it.

Despite the fact most of the rec divers will never ever get close to OTU limits, we still teach its risks during Nitrox classes, right? And like I said, HPNS risk increases as helium percentage increases... so, $$$ is not the only factor to consider when attempting a 300ft dive with Heliox: it's a waist of money and an unnecessary exposure to HPNS.
And by the way, as the percentage of Helium on the back gas increases, another issue we need to be aware of is ICD (Isobaric Counter Diffusion)... But someone will say that we shouldn't care, as most of the divers here will never see that, right? So pretend I didn’t mention that…

 

[ianr33]

Funny you should mention that! Unless I was diving deeper than 300 feet at the very least I would not give ICD a second thought either. Maybe I just like living dangerously

 

[Dan Ziegner]

And by the way, as the percentage of Helium on the back gas increases, another issue we need to be aware of is ICD (Isobaric Counter Diffusion)... But someone will say that we shouldn't care, as most of the divers here will never see that, right? So pretend I didn’t mention that…

I consider ICD, as I have made a number of dives deeper than 300 ft on a variety of gasses. ICD will be of greater concern as evolving CCR technology (as well as OC) will allow divers to spend greater time at greater depths.

 

[rmc77]

I consider ICD, as I have made a number of dives deeper than 300 ft on a variety of gasses. ICD will be of greater concern as evolving CCR technology (as well as OC) will allow divers to spend greater time at greater depths.

Thanks! This is exactly my point. The risk is there, and we need to know about it, plan and simple. I agree that for most divers in this board the risk of HPNS or ICD is irrelevant, but even if someone wants to pretend it's not there it won't make it go away...