Requiring shallow helium mixes?

[RyanT]

I met hundreds (rough numbers) of deep air divers, not suprised a few regular this forum. I'm fascinated by the spectrum represented here. Wide variety of the differing training, experience and philosophies backing these numbers.

Hey Cameron, yes, historically there were lots of folks doing deep air dives. Given what we know now, I simply can't fathom why anyone would do those kinds of dives today on air.

 

[stuartv]

No I'm saying there is a downside to helium and suggesting otherwise is disingenuous.

That supports my point. Deco times are artificially lengthend for helium because you'd bend otherwise.

What is the downside (other than needing a separate inflation system for a drysuit)?

You clearly did not actually understand the Helium Penalty article on Shearwater's site. And I'm thinking you don't really "get" what M-values are and how they are used in the Buhlmann ZHL-16B or C algorithm, either.

 

[stuartv]

ps. Let me spoonfeed you a litte bit. The Shearwater Helium Penalty article is specifically making the point that you do NOT need longer deco times for helium than you need without helium.

 

[boulderjohn]

Underwater the disadvantages of shallow helium are low (none exist?) but I think the above water factors keep our 'need' for it deeper.

You are evidently unaware of Shallow Water Helium Narcosis (SWHN), a phenomenon I myself discovered some years ago.

Another diver and I drove across the country in a van filled with diving equipment, including many sets of doubles filled with a mix rich in helium. We arrived in Pensacola where we were met by friends who had flown there. (We had their gear in our van.) We were all planning deep dives on the Oriskany. The weather in Pensacola was warm and sunny, without a breath of wind, but the dive operator assured us things were hairy out on the wreck, and they would not take us. (BTW, that has been my experience every single time I have tried to dive the Oriskany, leading me to believe its existence is a hoax designed to lure people to the area in an elaborate bait and switch scheme.)

Stuck there with nothing to do with all the gas we had brought, we eventually decided to dive in nearby Morrison springs, a much, much, much shallower site. We found we could not concentrate on our dives--we were constantly fighting the hallucinations of dollar signs flying away.

 

[boulderjohn]

That supports my point. Deco times are artificially lengthend for helium because you'd bend otherwise.

ps. Let me spoonfeed you a litte bit. The Shearwater Helium Penalty article is specifically making the point that you do NOT need longer deco times for helium than you need without helium.

We had a recent thread about this. REcent research does say that the old idea of the helium penalty does not appear to be valid; helium itself does not add to the needed length of decompression; HOWEVER, that same research indicated that the extra length that was being added for the presence of helium was beneficial and should probably be done, with or without the helium.

 

[blac86]

What is the downside (other than needing a separate inflation system for a drysuit)?

You clearly did not actually understand the Helium Penalty article on Shearwater's site. And I'm thinking you don't really "get" what M-values are and how they are used in the Buhlmann ZHL-16B or C algorithm, either.

So you'll admit that manufacturers add helium penalties, and that helium penalties are shown to be beneficial, which was my point, then you want to go in on attacking me about what you think I may or may not know. Well buckle up up buckaroo.

M values are mathematical constants presented as coefficient pairs which represent the amount of supersaturation a theoretical body tissue can intake before experiencing dcs symptoms. I think you're trying to call back to the fact that I despise rgbm for artificially altering m values to create a theoretical profile that doesn't reflect the dive actually performed. I'll restate my opinion that creating a profile the isn't reflective of the actual dive and the altering of mathematical constants to alter the total output of the equation is irresponsible and dangerous. Not only do DAN and NEDU confirm that bubble models are busted, but suunto even admits in their own release about fused rgbm that rgbm is unsafe and they altered it to be basically zhl whike still getting to be proprietary.

I don't get your stance here I said "manufacturers artificially increase helium deco" which is true. I said this is a safety precautions, and NEDU agrees. You agree but then go on to try and start an argument from a position of agreeing with me.

 

[Kay Dee]

Depending on the coditions i.e. cold and dark, maybe 25 / 30m, in warm clear Pacific waters 40 to 50m, or maybe a bit more depening on several factors.

 

[northernone]

May I respectfully suggest you change one of your poll 'questions' slightly, as I was left no choice but to tick 200, while my prefered air limit when no He is actually 220.

And while I would / have dived to 240 on air, its not something I'd tick saying I am confortable with doing per se. But 220ft/66m or 1.6bar/ata I would do anytime - and have often back in the day - when/if He was not available - in certain conditions that is.

Anyway I think your jump from 200 to 240, i.e. past the 1.6 bar/ata is a bit of a leap for those trained to respect the 1.6 bar/ata air 'limit.

Just my two cents worth.

You're right. I forgot about the 1.6 crowd and just ballparked.

@boulderjohn in all due respect I think you have severally underestimated the depth where symptoms of SWHN can afflict a diver debilitatingly. For some we even see the face of the wife we haven't met yet crying tears of rage in every exhaust bubble at 150ft.

Cheers,
Cameron

 

[Kay Dee]

Hey Cameron, yes, historically there were lots of folks doing deep air dives. Given what we know now, I simply can't fathom why anyone would do those kinds of dives today on air.

Because, as big as a surprise as it may be to some, helium is not available everywhere in the world, and if / when it is it can be extremely expensive, espcially if diving on OC. So rather than give up a dive because of no He, I would still - and have - today as it were, do a 220ft / 66m air dive in warm clear water.

But thats just me, I am not reccomending anyone else follow or even agree to my fall-back 'no helium' position as it were!

 

[stuartv]

We had a recent thread about this. REcent research does say that the old idea of the helium penalty does not appear to be valid; helium itself does not add to the needed length of decompression; HOWEVER, that same research indicated that the extra length that was being added for the presence of helium was beneficial and should probably be done, with or without the helium.

Right. As I said here:

...current models often produce longer deco times when using helium, but it appears to be the case that that is actually good and lucky for us divers because the same dive on just air/nitrox would result in an unsafely short deco profile.

IOW, (according to recent NEDU data) there is no (practical) difference in off-gassing for helium versus no-helium. But, what we actually need, to be safe, is the longer deco profiles that are produced when you tell the computer you're using helium.

So you'll admit that manufacturers add helium penalties, and that helium penalties are shown to be beneficial, which was my point, then you want to go in on attacking me about what you think I may or may not know. Well buckle up up buckaroo.

M values are mathematical constants presented as coefficient pairs which represent the amount of supersaturation a theoretical body tissue can intake before experiencing dcs symptoms. I think you're trying to call back to the fact that I despise rgbm for artificially altering m values to create a theoretical profile that doesn't reflect the dive actually performed. I'll restate my opinion that creating a profile the isn't reflective of the actual dive and the altering of mathematical constants to alter the total output of the equation is irresponsible and dangerous. Not only do DAN and NEDU confirm that bubble models are busted, but suunto even admits in their own release about fused rgbm that rgbm is unsafe and they altered it to be basically zhl whike still getting to be proprietary.

I don't get your stance here I said "manufacturers artificially increase helium deco" which is true. I said this is a safety precautions, and NEDU agrees. You agree but then go on to try and start an argument from a position of agreeing with me.

No. Manufacturers (using Buhlmann ZHL-16B or C, anyway) are not adding helium penalties. They are using the algorithm as intended and using the M-values for helium and calculating a result. The same way they do it for nitrogen, just with different M-values. The M-values were all determined empirically. So, they are not "cheating" or making some special coding allowance because it's helium.

They are not ARTIFICIALLY increasing helium deco. That would mean they are taking the results of the algorithm and then doing something to those results to increase deco, and they are not.

I had no idea of any of your thoughts on RGBM, so that has nothing to do with anything I have said.

So, again, manufacturers do NOT ARTIFICIALLY increase helium deco time. They calculate the time the same way they do for nitrogen - using M-values that are determined scientifically, not "artificially" inflated or something.

And the point of the Helium Penalty article was that there is no need to allow extra time because of using helium. But that we SHOULD be allowing extra time when we're not using helium. Because the profile generated using helium M-values is safer and the profile for no-helium (on the dives that were used in the study) resulted in an unacceptable incidence of DCS. So, if anything the manufacturers SHOULD "artificially" increase non-helium deco times (to match helium deco times).

In other words, people are generally having safe dives to deep depths because they are using helium, so they get longer deco profiles. If people were doing more deep diving on air, and using those same computers, there would be more incidence of DCS because those non-helium profiles that are calculated are unsafely short.