Helium Fraction and Standardized Gases

[MXGratefulDiver]

AL80's can, generally, only be pumped to 207 bar thus giving you about 4500 litres of available gas - half of which you have used on the bottom and the other half has to last you until you can get onto the 02 at 6m. Doesn't seem to be alot of reserve?

80's aren't necessarily AL80's. Take a pair of PST LP-80's and pump 'em up to 3800 psi (about 260 bar) and you've got a bit more than 230 CF of back gas ...

... Bob (Grateful Diver)

 

[Kevrumbo]

Happy to....
It seems that you are giving your tacit approval to a dive of 280 ft (in my world that's about 85m) with double 80's and a 30 cuft bottle of 02.
Now, i would assume that you guys were at the top of your game physically, even so your breathing rate be somewhere around 15 litres per minute? Without knowing your exact deco profiles it is difficult to make an accurate assumption on gas consumption, but your bottom time alone will have consumed something like 2000 litres. AL80's can, generally, only be pumped to 207 bar thus giving you about 4500 litres of available gas - half of which you have used on the bottom and the other half has to last you until you can get onto the 02 at 6m. Doesn't seem to be alot of reserve?
Obviously it all worked out well for you as you noted that you never even got a suggestion of a hit, however i would question whether modern thinking around minimum gas, team gas and deco theory would have this as a suitable profile?
My initial comment about it being scary was not meant to be detrimental, simply of statement of my response upon reading your post.

No sir . . . there is no insinuation of diving with that bare minimum from Dan's post; contingency gas planning is implied, IMO.

Quick overview on the gas plan for Rock Bottom: Figure 2200 litres needed for 10 min at 90m (300') for a SCR of 22 L/min (0.75 cf/min) --that's equivalent to one ENTIRE 11 litre (AL80) tank; need around 6300 litres to get an Out-of-BackGas Buddy from 90m to the first deco stop at 21m, which would require another aluminium 11 litre stage bottle of bottom mix together with at least double aluminium 11 litre backgas tanks of bottom mix for each teammate. This totals roughly 8800 litres of bottom mix for each of the three-man team.

Better option would be larger capacity doubles (15 to 17 L) and the use of at least one more intermediate deco mix starting at 36m --minimum gas reserve from 90m to 36m would be reduced to roughly 4000 litres.

 

[danvolker]

Does this mean you've never had a DCS hit ever?

Never. Always felt great after every dive.....Well, there were a few days when the seas kicked up, and I could feel a little gren in 8 to 10 foot seas, but that is another story

 

[danvolker]

Dan will have better explanations about the slightly multi-level nature of the dive profiles, etc. but you are also making incorrect assumptions about the fill pressures of George's tanks.

These tanks were waayy overfilled , and 25 minutes would be run time from surface...we would do very fast falling descents, and with scooters it would be "trigger on", all the way down.
This was way before present concepts of Rock bottom, ......but this was "team based DIR diving" ...We had been diving for years together on the same deep 280- foot dives with air before anyone did helium, so we already knew the gas consumption habits of each other, as we did ourselves. When George got everyone on Helium, it made things much easier, as we had considerably more thinking power and awareness at 280 this way
The "George profiles" would not waste a lot of time from 280 to 200, and then we would slow the ascent, and do a few short deep stops. but it would not mirror the assent speeds of GUE today until we were around 100 feet. Then it would be quite similar...but we would have a great deal of back gas left, between the 3 to 5 of us on each of these dives.
I am not going to spell these out exactly, because they worked for our individual physiologies...remember, George was an amazing Masters Swimmer, and became a full Ironman Triathlete in 6 months on a bet....I was one of the faster racing cyclists at cat 3 level in Florida. We had very high VO 2 max levels, and the profiles George had created, were customized to him--and me...Bill was not quite as cardio extreme as we were, but still had a very high natural vo2 max, and did far more cardio than the tech divers of the day....so these worked for us.....There would have been every expectation, that they would have injured an relatively sedentary tech diver, maybe severely.... This was "boundary stuff", which became essential to the theories used by Jarrod in the evolution of the larger and larger pushes by an elite exploration team...each with high VO2 max scores.

The entire ascent proceedures for GUE have changed/evolved quite a bit from WKPP practices back in the 90's, but George was like a test pilot for new theories of deco shapes , and his knowledge and the data sets he helped to provide, certainly figured in to the extreme duration schedules of JJ and the other exploration team members today....
I do not believe that in 1999, to 2002, there were "standardized" gas volumes and mixes that were enforced for 280 foot tech dives in ocean.

Someone in this thread brought up the 1999 extended range information, which is why I decided to add this.

The DIR ideas were clear back then.....as a team, we never had an incident we could not easily handle, and this was with hundreds of dives, in some conditions that most tech divers would consider very severe ( 5 mph+ currents, etc)....Today there are ALSO GUE ideas, and they are NOT aimed at George or me or Bill...they are not aimed at "test pilots" ...the GUE ideas are a compendium of DIR ideas, that were made more conservative by JJ and his inner group,, to be uselful to a much broader range of individuals, and more typical dive environments, I think with more emphaisis on cave environments.

George and Bill and I love most of the GUE evolutions, but we do not use as much gas as GUE standards, on dives we have done many hundreds of times, where we know the greatest challenges will be staying "low drag" in huge currents. I also think we do not stay down as long as many GUE divers would, on a 280 foot wreck in the high currents--Even if we had the gas they had, and could stay down 35 minutes, we would never do this, for the reasons I mentioned earlier.

Last I checked, this was a DIR forum, not a GUE forum..even though most things GUE and DIR mesh nicely, it is not a 100% fitting. Then again, there are only a handful of us that were DIR in the late 90's, and we are barely a spec, in relation to the huge phenomenon, which is now called GUE.

 

[Slamfire]

Never. Always felt great after every dive.....Well, there were a few days when the seas kicked up, and I could feel a little gren in 8 to 10 foot seas, but that is another story

That's good to hear. I've heard that if you dive long enough, it almost unavoidable to get a hit at one time or another. This, through the use of faulty logic, can lead to a conclusion that you don’t have much experience if you haven’t gotten a hit.

I’ve also heard that “you have to listen to your body” and fine tune deco strategies for yourself. I’ve never gotten a hit and I’ve always felt fine after a dive. I try to “listen to my body” but it won’t speak to me. Honestly, I know where the comment is coming from, but I prefer to have a silent body. “Listen to your body” feels like you have to gradually be decreasing conservatism until your body gives you some feedback, otherwise you won’t get a reading. I think it’s perfectly fine to find a certain methodology and conservatism level that works for you consistently and does not make you feel any discomfort after a dive and stick with it. If you never get to ride a chamber or even feel joint pain or skin bends, more power to you.

 

[danvolker]

That's good to hear. I've heard that if you dive long enough, it almost unavoidable to get a hit at one time or another. This, through the use of faulty logic, can lead to a conclusion that you don’t have much experience if you haven’t gotten a hit.

I’ve also heard that “you have to listen to your body” and fine tune deco strategies for yourself. I’ve never gotten a hit and I’ve always felt fine after a dive. I try to “listen to my body” but it won’t speak to me. Honestly, I know where the comment is coming from, but I prefer to have a silent body. “Listen to your body” feels like you have to gradually be decreasing conservatism until your body gives you some feedback, otherwise you won’t get a reading. I think it’s perfectly fine to find a certain methodology and conservatism level that works for you consistently and does not make you feel any discomfort after a dive and stick with it. If you never get to ride a chamber or even feel joint pain or skin bends, more power to you.

I think there is some individualization to this.....high VO2 max, high cardio fitness and cycling muscle fitness, using table still slightly biased for less "well perfused people", even though the tables were customized to us....Staying inside the profiles George used with me, I always felt great.

But I knew people far beyond us in deviation from the DCS expectations..... with way more diving than any of us will ever be likely to get, like still living dive Legend Frank Hammett. Frank would do profiles impossible for George or me to do, and he had done them since the mid 1950's thorugh the 80's and 90"s when I began diving with him...there is clearly a genetic basis for someone like Frank being able to do the Hole in the wall at 150ft for 20 minutes on a steel 72, empty it, hit the J valve, shoot one more fish, empty completely, free ascend, get on the boat, grab another 72, go back down, and repeat everything...and do this for decades with no chamber rides.


The tables are based on a "population" of divers with many different individual fitnesses and genetics.

I think it is wrong to say everyone will be bent, or that there is any such thing as an "undeserved hit"....Each of us has a profile we can stay within, given our normal physical fitness and health/hydration, etc., where we will not be bent if we stay in this... I have since 1972 of personal history saying this..niot that this means much statistically--but statistics means squat to YOU as an individual.

 

[lamont]

No Lamont! It's a simple quantitative arithmetic discrepancy with regards to Decompression Strategy:

The gist of it is --that if you're trying to off-gas Nitrogen loading from your bottom mix, why are you switching to a intermediate "standardized deco gas" with significantly more Nitrogen than your bottom mix??? (i.g. 10/70 bottom mix has fN2 of 20%; and you switch to a 21/35 intermediate deco mix that has a significantly greater fN2 of 44%???)

substituting 21/59 for 21/35 is not "best mix" and is within the parameters of GUE standardized gases. it is acceptable to add more helium.

and i doubt you need to be that precise in holding fN2 constant -- your quantitative arithmetical discrepancy likely needs some physiological reality added to it.

 

[Kevrumbo]

substituting 21/59 for 21/35 is not "best mix" and is within the parameters of GUE standardized gases. it is acceptable to add more helium.

and i doubt you need to be that precise in holding fN2 constant -- your quantitative arithmetical discrepancy likely needs some physiological reality added to it.

The physiologic reality & motivation is all stated --quantitatively & qualitatively-- in post #1.

Quit "dicking'" around with semantics Lamont and call the deco blend what it is: A Best Mix Deco Strategy in this case, over Standardized 21/35.

Precision is not required in holding fN2 constant through all deco gas mixes after such an extreme dive: only a Rule of Thumb of no greater than 0.5 ppN2 ratio change from bottom mix to your first and subsequent deco gases. Depending on the bottom mix chosen in this case (a dive to 90m/300'), you might find that you can use certain Standardized Gases. . .

For example:
Enter a dive in V-planner to a depth of 90m for 20min with a bottom mix of 12/60, and Standard GUE deco gases of 21/35 at 57m; 35/25 at 36m; Eanx50 at 21m; and Oxygen at 6m. There will be a red warning ICD (Isobaric Counter-Diffusion) highlight along the row corresponding to the 21/35 gas switch, signifying a 0.5 or greater change in ppN2 in this instance. Note that you're going from an fN2 of 28 percent from the bottom mix of 12/60, to an fN2 of 44 percent in the intermediate deco mix of 21/35.

Check:
At 60m, your inspired ppN2 on backgas is: 0.28(7.0) = 1.96
Switch at 57m, your ppN2 on 21/35 is now: 0.44(6.7) = 2.94
Your ppN2 change is: 2.94-1.96/1.96 = 0.5 hence an ICD warning.

If you use an intermediate deco gas of 18/45 instead (fN2 of 37percent):
Switch at 57m, your ppN2 would be: 0.37(6.7) = 2.47
Your ppN2 change: (2.47-1.96/1.96) = 0.26 , and the ICD warning clears. . .

 

[PfcAJ]

Is your argument based on anything besides a warning in a computer program? Real experience? Or just something a computer made up?

Genuinely curious here. Despite being called a myriad of names and slurs.

 

[lamont]

you win kevin, JJ promotes "best mix", GUE is a fraud, you've uncovered the big secret... game over...