Helium Fraction and Standardized Gases

[Kevrumbo]

If you reduce the depth, you reduce ambient pressure, you also reduce fN2, which reduces the ppN2 in the lungs, which will reduce the dissolved gas tension/pressure of N2 in the blood.

If it didn't, decompression wouldn't work at all.

Yes Lamont! That is very true! The most efficient way of getting rid of inert gasses is in dissolved form in the venous bloodstream returning back to the lungs to be exhaled via respiration; together with prescribed ascent rates, reduction in ambient pressure and deco stops according to whatever particular decompression algorithm in use. But these tactics along with changes in ambient pressure are for later in the deco profile strategy.

First things first --you also gotta get inert gas out of the tissues into the venous blood, which is the point of J.E. Brian's article:

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.

I'm talking about early in the deco profile, after the deep stops to keep the free phase bubbles in check and where you don't want sudden ambient pressure reductions to induce a Boyle Expansion of these free phase bubbles in blood & tissue. Additionally, you don't want to add any more inert gas loading by switching to a deco gas with a greater inert component than your bottom mix --in this case Nitrogen-- that can potentially diffuse back into these free phase bubbles and cause problems later in the deco profile (or worse on the surface post-dive).

So the questions and the thesis still remains:

Why do you use an intermediate deco gas (21/35) that has a higher fN2 than your bottom mix (12/60 or 10/70 trimix in this case, a dive to 90m/300')???
---->(i.g. 12/60 or 10/70 bottom mix have a fN2 of 28% and 20% respectively, while 21/35 intermediate trimix deco gas has an fN2 of 44% --why are you switching to a deco gas that has more Nitrogen percentage wise, than that of your bottom mix???

Coming off a bottom mix of 12/60 or 10/70 to standard intermediate deco trimix 21/35 --look at the fraction of Helium: you have a concentration of either 60% (if using 12/60) or 70% (10/70), and upon switching to 21/35 on deco at 57m you have a Helium fraction now of 35%. You have now a decreasing concentration gradient, going from 60 or 70% Helium in the bottom mix to a lesser inspired gradient of 35% in the intermediate deco mix of 21/35, which is the proper tactic for off-gassing the Helium from tissues. That's a given, noted and understood . . .
By this tactic above for decreasing the gradient of the inert Helium then, --why can't you do the same simultaneously with the inert Nitrogen?

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?

Think about it (and this is exactly what I'm arguing for)! The much better & consistent strategy is to utilize deco gases that titrate down, or at least hold the fraction of Nitrogen nearly constant (i.e. no significant fN2 increases as you ascend through the deco stops); that means using a "best mix" deco blend over standard mix.

 

[limeyx]

Think about it (and this is exactly what I'm arguing for)! The much better & consistent strategy is to utilize deco gases that titrate down, or at least hold the fraction of Nitrogen nearly constant (i.e. no significant fN2 increases as you ascend through the deco stops); that means using a "best mix" deco blend over standard mix.

Kevin,

Go take your "best mix" to a forum/thread where someone actually cares. We (who are posting), Don't.

You repeat the same arguments based on some paper that just doesn't reflect the reality that if you use the standard gases for reasonable ranges of bottom times and increase the He percentage for longer bottom times, the results are very very good and safe.

People (using DIR standard gases) are simply not encountering the issues your theoretical paper bring up.

The reason I am OK switching to a mix with a higher PPN2 on deco is because it works "well enough" and it's totally impractical from logistics to have the "Correct" amount of Helium, as well as occurring extra expense for basically a non-existent benefit

Go tell it to someone that cares. (I believe some people actually do)

 

[boulderjohn]

Go tell it to someone that cares. (I believe some people actually do)

I think the issue and the overall logistics of gas choices would make a very interesting topic in the general tech or the T2T forum. It is problematic here, though, because the issue is pretty much settled.

 

[limeyx]

I think the issue and the overall logistics of gas choices would make a very interesting topic in the general tech or the T2T forum. It is problematic here, though, because the issue is pretty much settled.

I agree, if it was a real discussion. Even here, if it was a discussion, it might not be the worst thing in the world.

However, when it's one guy repeatedly quoting a research paper that supposedly documents an effect that in real life (with good gas choices) never really happens, with no real documented effects except what happens "in theory" (even if the effect is too small to actually notice)

Then said poster gets frustrated and continually adds longer and longer more-important sounding words that it's unclear are even understood, let alone add any weight to the argument.

*Then* ends up advocating "best mix" in the DIR forum as "the ideal way to do deco"

I don't think it's of much use (same in the Tech forum ... you have to have actual discussion to have a discussion)

 

[Rainer]

The fallacy in your argument, Nick, is that you're discounting Kev's extensive experience in these matters. Don't forget, he's taken GUE Fundamentals and UTD Essentials. And while he might not have much (any) practice with 300' dives, he HAS read a paper (so what if it's over a decade old) and has substantial deep air (and chamber) experience. You can't just ignore such burnished credentials.

I agree, if it was a real discussion. Even here, if it was a discussion, it might not be the worst thing in the world.

However, when it's one guy repeatedly quoting a research paper that supposedly documents an effect that in real life (with good gas choices) never really happens, with no real documented effects except what happens "in theory" (even if the effect is too small to actually notice)

Then said poster gets frustrated and continually adds longer and longer more-important sounding words that it's unclear are even understood, let alone add any weight to the argument.

*Then* ends up advocating "best mix" in the DIR forum as "the ideal way to do deco"

I don't think it's of much use (same in the Tech forum ... you have to have actual discussion to have a discussion)

 

[Kevrumbo]

Kevin,

Go take your "best mix" to a forum/thread where someone actually cares. We (who are posting), Don't.

You repeat the same arguments based on some paper that just doesn't reflect the reality that if you use the standard gases for reasonable ranges of bottom times and increase the He percentage for longer bottom times, the results are very very good and safe.

People (using DIR standard gases) are simply not encountering the issues your theoretical paper bring up.

The reason I am OK switching to a mix with a higher PPN2 on deco is because it works "well enough" and it's totally impractical from logistics to have the "Correct" amount of Helium, as well as occurring extra expense for basically a non-existent benefit

Go tell it to someone that cares. (I believe some people actually do)

I agree, if it was a real discussion. Even here, if it was a discussion, it might not be the worst thing in the world.

However, when it's one guy repeatedly quoting a research paper that supposedly documents an effect that in real life (with good gas choices) never really happens, with no real documented effects except what happens "in theory" (even if the effect is too small to actually notice)

Then said poster gets frustrated and continually adds longer and longer more-important sounding words that it's unclear are even understood, let alone add any weight to the argument.

*Then* ends up advocating "best mix" in the DIR forum as "the ideal way to do deco"

I don't think it's of much use (same in the Tech forum ... you have to have actual discussion to have a discussion)

Nick, you always fall back on the same illogical, non-valid and fallacious arguments & rationale: The Group Think DIR Practitioner attitude and "Everybody is doing it and not getting bent. . ." Guess you've to fall back on what you know Nick, and what you offer as an explanation is not good enough. Clearly, you don't have a clue what you're talking about other than blindly justifying your "herd mentality" and a meaningless appeal to authority (GUE). . .

Excuse yourself Nick . . .take your toys and go away now to another sandbox.

 

[Crush]

There have been few threads that I have enjoyed more (as a spectator) than this thread. My ignorance in these matters keeps me from participating. To all you posters - Bravo!

 

[nadwidny]

Our pretzel friend keeps quoting decade old articles and yet he keeps missing the most important quote of all regarding deco

"What works, works." Dr Bill Hamilton

 

[PfcAJ]

If your theory doesn't match your results, something is wrong with your theory.

Yanno, science and stuff.

 

[Kevrumbo]

Kevin,

Go take your "best mix" to a forum/thread where someone actually cares. We (who are posting), Don't.
You repeat the same arguments based on some paper that just doesn't reflect the reality that if you use the standard gases for reasonable ranges of bottom times and increase the He percentage for longer bottom times, the results are very very good and safe.

People (using DIR standard gases) are simply not encountering the issues your theoretical paper bring up.

The reason I am OK switching to a mix with a higher PPN2 on deco is because it works "well enough" and it's totally impractical from logistics to have the "Correct" amount of Helium, as well as occurring extra expense for basically a non-existent benefit

Go tell it to someone that cares. (I believe some people actually do)

I agree, if it was a real discussion. Even here, if it was a discussion, it might not be the worst thing in the world.

However, when it's one guy repeatedly quoting a research paper that supposedly documents an effect that in real life (with good gas choices) never really happens, with no real documented effects except what happens "in theory" (even if the effect is too small to actually notice)

Then said poster gets frustrated and continually adds longer and longer more-important sounding words that it's unclear are even understood, let alone add any weight to the argument.

*Then* ends up advocating "best mix" in the DIR forum as "the ideal way to do deco"

I don't think it's of much use (same in the Tech forum ... you have to have actual discussion to have a discussion)

If your theory doesn't match your results, something is wrong with your theory. Yanno, science and stuff.

Our pretzel friend keeps quoting decade old articles and yet he keeps missing the most important quote of all regarding deco

____
Then y'all numbskulls above have just incriminated yourselves, GUE and everyone who uses DecoPlanner & V-planner software. . .

Thousands of copies of DecoPlanner are used by divers around the world in both recreational and aggressive technical diving situations, including world record cave diving explorations in the Woodville Karst Plain and deep-sea documentation of the Britannic shipwreck. DecoPlanner has been used to calculate a series of progressively more aggressive long and deep dives. Developed by Simon Tranmer, with assistance by Erik Baker and GUE representatives from around the world, DecoPlanner is available through GUE for Windows 95/98/NT 4.0/2000/ME/XP/Vista. DecoPlanner 3.1.4 | Global Underwater Explorers

The same Erik Baker behind the "old" 1999 article (and theories which predate all your present mistaken notions about "DIR Practitioner Standardized Gas" applications); the same Erik Baker, developer of the Gradient Factor Model, and a VPM algorithm that Ross Hemingway applies in V-planner:

Decompression Strategies Enable Deep, Long Explorations of Wakulla Springs
(Jarrod Jablonski in consultation witn Erik C. Baker)

Obviously you don't know the history of decompression modeling; you cannot comprehend basic deco physiological theory & principles; and all you "DIR Practitioners" can't even enunciate valid viable reasons or doctrine to justify a flawed practice in using standardized deco gases for extreme deep dives. Your feigned & flippant contempt for the theories I quote to back my thesis (as well as your ad hominem attacks) clearly shows your continuing ignorance, unwillingness to understand and dismissal in having a meaningful dialogue. . .
_____
So the questions and the thesis still remains:

Why do you use an intermediate deco gas (21/35) that has a higher fN2 than your bottom mix (12/60 or 10/70 trimix in this case, a dive to 90m/300')???
---->(i.g. 12/60 or 10/70 bottom mix have a fN2 of 28% and 20% respectively, while 21/35 intermediate trimix deco gas has an fN2 of 44% --why are you switching to a deco gas that has more Nitrogen percentage wise, than that of your bottom mix???

Coming off a bottom mix of 12/60 or 10/70 to standard intermediate deco trimix 21/35 --look at the fraction of Helium: you have a concentration of either 60% (if using 12/60) or 70% (10/70), and upon switching to 21/35 on deco at 57m you have a Helium fraction now of 35%. You have now a decreasing concentration gradient, going from 60 or 70% Helium in the bottom mix to a lesser inspired gradient of 35% in the intermediate deco mix of 21/35, which is the proper tactic for off-gassing the Helium from tissues. That's a given, noted and understood . . .
---->By this tactic above for decreasing the inspired gradient of the inert Helium then, --why can't you do the same simultaneously with the inspired inert Nitrogen?

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?

Think about it (and this is exactly what I'm arguing for)! The much better & consistent strategy is to utilize deco gases that titrate down, or at least hold the fraction of Nitrogen nearly constant (i.e. no significant fN2 increases as you ascend through the deco stops); that means using a "best mix" deco blend over standard mix.

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

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.