Helium Fraction and Standardized Gases

[lamont]

The fact remains that counter diffusion of Nitrogen from this "bad practice" still exists and may --or may not elicit signs & symptoms of DCS; and there is no reasonable justification for blindly following such a practice just because "we don't see people regularly getting bent from it".

actually that's a perfect justification.

if you're not decreasing the actual DCS incidence then you're just paying for helium to make a ratio come out right. you're not doing anything physiologically meaningful.

Intuitively, if you can eliminate possible factors that can preclude a DCS hit (even rare but always seriously acute Inner Ear DCS) wouldn't you sensibly do so?

sure, so go run Doolette's model for me and show me what happens when you switch to 21/35 (and how about when you switch to 50%?) and i'll start to care. the rule of thumb you're quoting from over 10 years ago though is on even less solid theoretical footing, it was not handed down from God to Moses to Eric Baker to you.

the principle that you're quoting did get divers away from using 21% as a deco gas and starting to use helium-mixes to deco out on, which was a good thing. you need to *show* that there's really additional improvement to be had by nailing that ratio exactly.

 

[Kevrumbo]

Because you're not going to be on it long enough to significantly load nitrogen into your own compartments, while the helium is going to offgas a great deal faster than the nitrogen is loading? You've quoted two people that have said as much.

Define "long enough" quantitatively using a particular Decompression Model or simple physiological principles --otherwise not an acceptable or rigorous enough answer. . .

actually that's a perfect justification.

if you're not decreasing the actual DCS incidence then you're just paying for helium to make a ratio come out right. you're not doing anything physiologically meaningful.



sure, so go run Doolette's model for me and show me what happens when you switch to 21/35 (and how about when you switch to 50%?) and i'll start to care. the rule of thumb you're quoting from over 10 years ago though is on even less solid theoretical footing, it was not handed down from God to Moses to Eric Baker to you.

the principle that you're quoting did get divers away from using 21% as a deco gas and starting to use helium-mixes to deco out on, which was a good thing. you need to *show* that there's really additional improvement to be had by nailing that ratio exactly.

Fund a study and go run Doolette's model for yourself --if you cannot logically answer the question below without the pointless rhetoric and vague baseless rationalizations above, then the only justification you have for performing this bad practice is "personal choice" and "because every else does it and seems not to get bent". Sorry! Not a good enough excuse !

_______

The fact remains that counter diffusion of Nitrogen from this "bad practice" still exists and may --or may not elicit signs & symptoms of DCS; and there is no reasonable justification for blindly following such a practice just because "we don't see people regularly getting bent from it".

Again, the simple logical means to an end --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???Intuitively, if you can eliminate possible factors that can preclude a DCS hit (even rare but always seriously acute Inner Ear DCS) wouldn't you sensibly do so?

Decompression from an N2-based dive is longer with N2 containing deco mixes because some N2 is continuously diffusing into tissue during deco. Decompression from a He-based dive can be longer with N2 containing deco mixes because N2 is diffusing into tissue as He is diffusing out of tissue. The decompression obligation of a tissue compartment is based on the sum of gas partial pressures in the compartment. This means that if a tissue is loaded with N2 as He is being removed, its tissue has a greater decompression obligation than when no N2 is added to tissue during He off-gassing. . . The gas partial pressure gradient for movement from tissue into blood is not controlled by ambient pressure; it is controlled by the gas partial pressure in the tissue and in arterial blood. As long as the arterial [inert, non-metabolic] gas partial pressure is zero, the gradient for [inert, non-metabolic] gas removal from tissue is maximal . . .It should be intrinsically obvious that removal of a gas from tissue can be speeded by elimination of the gas from the inspired mixture. If the arterial partial pressure of a gas is zero, then no gas will diffuse into tissue while the gas is diffusing out of the tissue. . .Gas Exchange, Partial Pressure Gradients and the Oxygen Window, p.12, J.E. Brian M.D.

 

[PfcAJ]

"My way doesn't get anyone bent"
"Your way might get someone bent!"
"But they arent getting bent..."
"My way is much better and consistent"
"If no one is getting bent, how is it better?"
"It doesn't make a warning pop up on my computer machine"

 

[LiteHedded]

can we all agree to do the opposite of what kev is doing? do they have internet access in chambers now? how's he even posting this?

 

[Kevrumbo]

"My way doesn't get anyone bent"
"Your way might get someone bent!"
"But they arent getting bent..."
"My way is much better and consistent"
"If no one is getting bent, how is it better?"
"It doesn't make a warning pop up on my computer machine"

can we all agree to do the opposite of what kev is doing? do they have internet access in chambers now? how's he even posting this?

All fallacious arguments. . .

Clearly, the popularity of an idea is no guarantee that it's right.

Extreme examples & analogies of these types of fallacious arguments: a common justification for bribery is that "Everybody does it".
And in the past, "Everybody does it", was a justification for slavery.

(Continue drinking your kool-aid boys . . .bottoms up! )

The question still remains:
Again, the simple logical means to an end --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???Intuitively, if you can eliminate possible factors that can preclude a DCS hit (even rare but always seriously acute Inner Ear DCS) wouldn't you sensibly do so?

 

[ScubaFeenD]

All, fallacious arguments from above quotes: Clearly, the popularity of an idea is no guarantee that it's right.

Extreme examples & analogies of fallacious arguments: a common justification for bribery is that "Everybody does it". And in the past, "Everybody does it". was a justification for slavery.



(Continue drinking your kool-aid boys . . .bottoms up! )

There seem to be less inflammatory uses of "it just works" too. For instance in both medicine and science lots of things are done because they work and always have. Knowing exactly why isnt always immediately necessary.

The question still remains:

Indeed it does, but perhaps it is : Why the hell are you beating this dead horse? Or perhaps its: Did you get ICBD using GUE standard gases or something? Or: Do you use GUE standard gases now? Or even: Why are you using so much BOLD?

 

[LiteHedded]

All, fallacious arguments from above quotes: Clearly, the popularity of an idea is no guarantee that it's right.

Extreme examples & analogies of fallacious arguments: a common justification for bribery is that "Everybody does it". And in the past, "Everybody does it". was a justification for slavery.

(Continue drinking your kool-aid boys . . .bottoms up! )

The question still remains:
Again, the simple logical means to an end --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???Intuitively, if you can eliminate possible factors that can preclude a DCS hit (even rare but always seriously acute Inner Ear DCS) wouldn't you sensibly do so?

why don't you go ask your questions on the gue forums directly to jarrod?

 

[PfcAJ]

Didn't we already establish that you're mostly decompressing from the Helium rather than the Nitrogen at that point of the ascent?

 

[Kevrumbo]

There seem to be less inflammatory uses of "it just works" too. For instance in both medicine and science lots of things are done because they work and always have. Knowing exactly why isnt always immediately necessary. . .Why the hell are you beating this dead horse? Or perhaps its: Did you get ICBD using GUE standard gases or something? Or: Do you use GUE standard gases now? Or even: Why are you using so much BOLD?

Because I have yet to receive a reasonable & valid "DIR Practitioners" answer to the question (perhaps I should address it to GUE and Jarrod Jablonski, as well as UTD & Andrew Georgitsis):

Again, the simple logical means to an end --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???Intuitively, if you can eliminate possible factors that can preclude a DCS hit (even rare but always seriously acute Inner Ear DCS) wouldn't you sensibly do so?

Didn't we already establish that you're mostly decompressing from the Helium rather than the Nitrogen at that point of the ascent?

No. . .! To recap again with cited articles for this particular deep dive application:

Decompression from an N2-based dive is longer with N2 containing deco mixes because some N2 is continuously diffusing into tissue during deco. Decompression from a He-based dive can be longer with N2 containing deco mixes because N2 is diffusing into tissue as He is diffusing out of tissue. The decompression obligation of a tissue compartment is based on the sum of gas partial pressures in the compartment. This means that if a tissue is loaded with N2 as He is being removed, its tissue has a greater decompression obligation than when no N2 is added to tissue during He off-gassing. . . The gas partial pressure gradient for movement from tissue into blood is not controlled by ambient pressure; it is controlled by the gas partial pressure in the tissue and in arterial blood. As long as the arterial [inert, non-metabolic] gas partial pressure is zero, the gradient for [inert, non-metabolic] gas removal from tissue is maximal . . .It should be intrinsically obvious that removal of a gas from tissue can be speeded by elimination of the gas from the inspired mixture. If the arterial partial pressure of a gas is zero, then no gas will diffuse into tissue while the gas is diffusing out of the tissue. . .Gas Exchange, Partial Pressure Gradients and the Oxygen Window, p.12, J.E. Brian M.D.

A trimix of 10.5 percent oxygen/ 80 percent helium was selected owing to the average bottom depth of 280'/85m. Considerations in this selection were:

Since many tissue compartments will reach saturation and decompression will take longer than a few hours, the high helium content has advantages for off-gassing effficiently later in the dive. The amount of time helium takes to reduce its partial pressures in tissues by one-half are about 2.7 times faster than the half-times for nitrogen. . .

As decompressions times lengthen to two and a half hours or more, counterdiffusion of excessive amounts of nitrogen can become a real problem. It can have the effect of doing a deep air dive in the middle of decompression. As shallower stops are made near the end of deco, the diver's body can be loaded with enough nitrogen that it offsets any advantages gained in eliminating helium. Because of nitrogen's greater molecular weight, greater solubility in body tissues and slower half-times, it can take longer and be more difficult to eliminate than helium. This is a special concern at the final deco stop where oxygen is used to remove inert gas from the slowest tissue compartments. . .[Non-standard, intermediate] decompression mixes that achieve an acceptable balance of these factors are a trimix of 19 percent oxygen / 50 percent helium at 240'/73m; trimix 25 / 35 at 190'/58m; trimix 35 / 25 at 120'/36m; trimix 50 / 15 at 70'/21m; 100 percent oxygen at 28'/8.6m [in a dry habitat], with periodic breaks using trimix 15 / 45.

This selection allows the fraction of helium to gradually taper off while the fraction of oxygen gradually increases and the fraction of nitrogen remains nearly constant. Helium off-gases efficiently with the reduction in pressure and the increasing oxygen fractions. Nitrogen loading during deco is kept below target limits upon arrival at the [oxygen] dry habitat stop. . .From Erik C. Baker, Decompression Strategies Enable Deep, Long Explorations of Wakulla Springs, Immersed Magazine p.30, Fall 1999.
See also Erik Baker and the Varying Permeability Model: Technical VPM Publications

 

[PfcAJ]

Because I always enjoy a good debate, the gases listed in the very article you site are only a few percentage points off from the GUE standard gases. Below is from your beloved article, sections in italics and parentheses are my words:

"trimix 25 / 35 at 190'/58m (21/35 is 190 deco gas. A whopping 4% less oxygen, but you also are on a 1.6 deep with 25%. Completely unsurvivable if you have a toxic episode); trimix 35 / 25 at 120'/36m (35/25 is 120 gas); trimix 50 / 15 at 70'/21m (yup); 100 percent oxygen at 28'/8.6m [in a dry habitat], with periodic breaks using trimix 15 / 45."

I don't think anyone is using 240 deco gas (18/45) for a 280-300 profile as it doesn't provide much benefit vs the cost/ risk of bringing the bottle.

So what, exactly, are you arguing for? What gases would you use? In one breath you're chastising the gases, and in another you're celebrating an article that advocates what you are so against in the previous breath. Are you arguing for introducing 240 gas on all 280-300' dives? That's old news, and there are a ton of dives that show that its not really needed. If you don't need it, don't take it...