heliox

[Bob3]

You have an *increased* risk of DCS when using He

Yep.
While He offgasses at a much faster rate, it also loads you up faster, especially the slower offgassing deep tissues.
Consulting the USN Heliox tables, you'll see a slight increase of a deco obligation using heliox at most levels.

Industrial (commercial & USN) use of heliox is more common because it is either pre-mixed in 300cuft deck or bell bottles, or mixed with a manifold & fed to the diver with a hose. Easier to manage 2 gasses than 3.
Being tightwads, the commercial sector doesn't switch to heliox 'till the magic 180' level is reached, when the O2 content of straight air gets unacceptable. They seem to be happy to accept the reduced diver performance from narcosis to increased cost of the He. Heck, some commercial divers work better narked, it's closer to their natural state of mind.
:bonk:

 

[Lost Yooper]

Originally posted by Rick Murchison
Allow me to sum up...
The simple answer to your question has two parts.
1. It's expensive.
2. You have an *increased* risk of DCS when using He.
There are other more complicated things to consider... thermal properties, gas containment, even long-term metal embrittlement among others. But those two are the main reasons Helium just doesn't make sense for dives where narcosis isn't a factor - and why just adding enough Helium to keep Nitrogen exposure at a "no significant narcosis" level makes sense at moderately deep depths.
For example, if you want to keep your oxygen exposure at 1.4 ATM or below, and your equivalent Nitrogen exposure to 80 FSW or less, no Helium is called for for dives of 102 feet or less. (Use EAN34 at 100')

Rick

I don't want to come right out and say that Rick is wrong about number two without a bit of explanation on his part. Physiologically, helium in a mix is a good thing as long as you know how to decompress from it. It's easier to deco from than nitrogen, easier to breath at depth, causes less CO2 build up, and there's evidence that it much easier on your body (in the long term) than nitrogen.
To say that you have an "increased risk" of DCS with a helium mix is a bit off the mark, I think. However, this is a common misconception in the diving industry that still basically makes helium voodoo. I don't want to say that Rick is wrong, but I could easily argue that air divers are at a much greater risk of DCS than a helium diver. Air is very difficult to "properly" deco off of, and it CAN'T be done (properly) using the traditional decompression tables which the mainstream diving industry would lead you to believe.
I would hope that he means that if you don't know what you're doing as far as decompression, then helium mixes have the potential to increase the risk of DCS. Of course, the same can be said about air, nitrox, and everything else involved in diving. You have to know what you're doing.

Take care.

Mike

PS. Rick, you may be potentially right under certain circumstances, but I sure would like to know what you mean by "increased risk of DCS". What are you comparing this to? I'd like to discuss this a bit further if you'd care to elaborate.

 

[monster]

When I first read ID's question, my answers were pretty much the same as Rick's.

1. Cost -- He and O2 are expensive
2. "Increased Risk of DCS"

Just to clarify, by increased risk, I was thinking more along the lines of, since He is a "faster" gas, it is less forgiving of depth variations, sawtoothing, or fast ascents (just my thoughts, based on what I've been studying; I have no experience with actually using He as a breathing gas, other than sucking on balloons at kids' parties).

As for N2 being added back to the mix to help alleviate HPNS... that's news to me. You learn something new everyday...

 

[omar]

How much is your life worth?

O2 $0.14 cuft
He $0.21 cuft

A set of LP104's w/ 17/55 = appx $32.00
A set of LP80's w/ 20/40 = appx $20.00

(tanks pumped up to 3300psig)

very cheap for the amount of increased safety

omar

 

[blacknet]

Hello,

Please omar don't stop there. Run figures for how much extra it will cost for a shop for equipment/training/upkeep to supply that helium mixtures to the clients. Think you'll find that for the slight increase in client cost you'll find alot more expenses for the shop.

As for "increased DCS risk" someone please tell me the conclusions stated in USN research report 7-58. (Yes that's the june 1958 report)


Ed

 

[Lost Yooper]

Cost should be irrelevant to safety when dealing with this type of diving. Trimix is leaps and bounds more safe than air in every regard. If you can't afford to do it right -- DON'T DO IT. Find another hobby. Sorry to be so blunt, but that's how I see it.

As people go out and blow money away on worthless and extremely expensive, but flashy, dive gear ($1200 regs, $800 BC's, $200 fins, $$$ computers, etc), they all too often forget (or more often don't know) about the real issues involved in diving. If people would spend their money wisely, they would find themselves better able to afford safer diving.

I'm not necessarily blaming people here as most are completely ignorant of what's out there. Most are never taught what real decompression is all about, why deep air is bad, and why helium is good (among other things). The greedy dive industry is to blame for this, and fortunately for a few who are willing to listen and to learn, there's a few people out there trying to set the record as straight as possible.

Take care.

Mike

PS. The real trick is knowing what to ask and to whom to get your answers from. Figure that out, and you'll have it made.

PS. PS. I ain't necessarily talking about asking me either .

 

[roakey]

Originally posted by blacknet
As for "increased DCS risk" someone please tell me the conclusions stated in USN research report 7-58. (Yes that's the june 1958 report)

You mean you can't? You need someone to tell you the conclusions? Oh, I get it, you're being flippant.

Ed, if you have something to tell us, tell us. Don't refer to documents and expect us to do your digging. If USN research report 7-58 has something interesting in it, either give us a URL for the document if it's online or transcribe the pertinent information.

Thanks in advance,

Roak

 

[blacknet]

Hello,

Yes I have read that document. Yes I was being sarcastic. I am not expecting anyone to do my research for me, I am more than capable of doing my own.

LY I do agree with you on this one about safety.

Ed

 

[roakey]

Originally posted by blacknet
Yes I have read that document. Yes I was being sarcastic. I am not expecting anyone to do my research for me, I am more than capable of doing my own.

You seem to think there's a rather important conclusion in the document, care to share it? Otherwise I don't see the reason for bringing it up in the first place.

I'm being serious here, Ed. Saying "Go look it up for yourself" sways no one. That's taught in debating 101.

Roak

 

[blacknet]

roakey,

This is not debate 101, nor is then even remotely close to a debate. Plus i'm not attempting to sway anyone. However you do seem to have alot of hostility in your post so care to explain that to me please?

Ed