Helium Fraction and Standardized Gases

[limeyx]

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


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.
_____
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.

Almost sure I am going to regret having one more go at this

Quoting from YOUR post

#1 - "As decompressions times lengthen to two and a half hours or more..."
Hmmm, wasn't this exactly what I said about for "reasonable" bottom times there being no problem?
Hoe many dives have you done where you needed more than 2.5 hours of deco Kev ? For me it's zero.....

#2 -
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.


Kevin.

Given the above quote

taking into account the exact example that boulder john presented

Dive 12/60 at 10 ATA.
Switch to 21/35 @ 190 as your first gas.

In your opinion, what is
a- The PPN2 of gas in your tissues at 10 ATA ?
b- The PPN2 of gas in your tissues at 190 *before* the gas switch
c- WHen you switch to the 21/35, "the arterial [inert, non-metabolic] gas partial pressure of N2" (from the article you quoted that never mentions percentage in the section you quote, only PPN2)

Maybe if you list those, I will be able to see the problem you are identifying

 

[PfcAJ]

I just noticed something that I find humorous. Kev keeps copying and pasting an excerpt from that 1999 article, but adds in a little tibit.

"[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."

That's the bit I'm focusing on. It says non-standard, intermediate. Those words are not in the original article. I already listed that those ARE the standard gases (plus or minus a few percentage points here and there, nothing worth getting geeky over).

Kev, do you even know the standard gases? Also, you haven't answered MY question. What gases would you use? Or are you too busy copying and pasting OVER AND OVER to come up with an answer?

btw, oxygen at 60ft in a chamber is not an appropriate answer.

 

[Kevrumbo]

Almost sure I am going to regret having one more go at this

Quoting from YOUR post

#1 - "As decompressions times lengthen to two and a half hours or more..."
Hmmm, wasn't this exactly what I said about for "reasonable" bottom times there being no problem?
Hoe many dives have you done where you needed more than 2.5 hours of deco Kev ? For me it's zero.....

#2 -
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.


Kevin.

Given the above quote

taking into account the exact example that boulder john presented

Dive 12/60 at 10 ATA.
Switch to 21/35 @ 190 as your first gas.

In your opinion, what is
a- The PPN2 of gas in your tissues at 10 ATA ?
b- The PPN2 of gas in your tissues at 190 *before* the gas switch
c- WHen you switch to the 21/35, "the arterial [inert, non-metabolic] gas partial pressure of N2" (from the article you quoted that never mentions percentage in the section you quote, only PPN2)

Maybe if you list those, I will be able to see the problem you are identifying

Nick, thank you for now engaging in respectful dialog instead of immediate outright dismissal as a heretic in the Holy Name of Most High DIR Dogma (I apologize for the personal insults in the posts above ).

My opinion on all above is that some tissues will be M-value saturated at ambient (or potentially super-saturated like blood), and some will be at whatever particular value below M-value --depending on whether it's fast tissue (i.g. neural) or slow tissue (muscle, organs, fat). The article doesn't mention an outright value percentage wise, because if you choose to inspire zero ppN2 in a deco gas (like Oxygen on the final clean-up at 6m; and if you've got $$$ for heliox mixes of 20/80 at 57m, 35/65 at 36m, and 50/50 at 21m, coming off a bottom 10/80 trimix as a hypothetical example:shocked2 --it's assumed that you're breathing 0% Nitrogen in your deco gas. I'm willing to compromise by at least holding the fN2 constant in my deco gas --the same or similar fN2 that was in the bottom mix-- for a "best mix" strategy (see below).

I just noticed something that I find humorous. Kev keeps copying and pasting an excerpt from that 1999 article, but adds in a little tibit.

"[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."

That's the bit I'm focusing on. It says non-standard, intermediate. Those words are not in the original article. I already listed that those ARE the standard gases (plus or minus a few percentage points here and there, nothing worth getting geeky over).

Kev, do you even know the standard gases? Also, you haven't answered MY question. What gases would you use? Or are you too busy copying and pasting OVER AND OVER to come up with an answer?

btw, oxygen at 60ft in a chamber is not an appropriate answer.

I've been considering a similar strategy here locally in SoCal, of using "best mix" deco gas progressions of trimix blends for gradual off-gassing of the helium & nitrogen inerts, coming off a hypoxic trimix bottom mix. (This is assuming of course, you have a gas logistics support source that uses partial pressure blending and can afford using higher helim concentrations for the deco gases).

For instance, from bottom hypoxic mix of 12/60/28 used at 90m, instead of a standard deco mix of 21/35/44 and switch at 57m --use a best mix of 21/51/28 at the initial 57m deco stop. The next switch at 36m, instead of standard deco mix of 35/25/40, use 35/37/28. The next deco gas switch at 21m, use 50/25/25 and finally 100% O2 for the last 6m deco stop before surfacing.

In essence you're providing a decreasing inspired gradient for the helium, and although you still have a constant nitrogen fraction of 28% to 25% until the O2 stop -- it's mitigated by gradual ascent thru the deco stops with successive decreases in ambient absolute pressure (from 6.7ata to 4.6ata and 3.1ata in this example), and you are not significantly ongassing any more amount of nitrogen than you would if you decided to use standard gases as intermediate deco mixes instead (i.g. 21/35; 35/25 and 50% nitrox). And of course finally by the end of the prescribed 6m O2 stop, all inerts should be at a low level to permit ascent to the surface. . .

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 controlled ascending 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).

(see also Ross Hemingway's V-planner website: http://hhssoftware.com/v-planner/decomyths.html#ibcd)

 

[danvolker]

Does anyone here have a photo of Kevin as a young child, reaching into a hornets nest and refusing to let go of it ?

 

[Kevrumbo]

Infidel!
Blasphemer!
There is no god but Allah DIR, and GI3 is his Prophet!
Holy Imam JJ & AG --Help us pass judgment! Prepare for Jihad!
Stone to death Kevrumbo --the Evil Apostate. . .!

 

[MXGratefulDiver]

Stone to death Kevrumbo --the Evil Apostate. . .!

... I think he's already stoned ...

This thread reminds me of some of the conversations I used to get into with my college buddies while enjoying a few hits on the bong ...

... Bob (Grateful Diver)

 

[VooDooGasMan]

Bombay, the answer I can give you is that the commercial diving you do is hard hat, correct. while you are tethered with heavy boots and brought up a line.

Where as, lets call it self contained underwater breathing apparatus, you have to take in account of buoyancy issues, caves, wrecks, current, and hypothermia from long dives, also gas supply.

With your given 2/98 and 4/96 lets say an easy dive to 350' what would your profile be in terms descent time, bottom time, ascent time. and how much CF of gas needed?

kevin is doing what we all are wanting, a safe dive with a mixture that we can handle as a scuba diver.

 

[danvolker]

I understand the cost factor, but none of the DIR type divers sound that hard up for cash. HPNS is a non issue if you are compressed conservatively. All deep commercial dives are now usually on a deep mix comprising 2/98 or 4/96. No N2. Also not introduced into the deco, so the vestibular DCS (Isobaric) is a non issue.
I have never had the twitches and shakes.

Just wanted to understand the DIR stand on it.

One thing that you mentioned is that you dont get the twitches because you go down very slowly.
Where we dive in the ocean, in 300 foot drift current environments, your descent MUST be rapid. I will typically scooter full speed down from the moment the team is all set 10 or 20 feet from the surface--we all go down at maximum speed to assure we actually reach the structure or feature the boat had marked before we jumped in....If we are not using scooters, then we just go in with all air sucked out of the wings, with a comfortable swim /cruise speed straight down. 150 to 200 feet per minute is a nice minimum pace for this.
I do not think this practice would fit the description you gave...though the 300 feet depth may be shallow enough for no HPNS to result.

From my own perspective, using 50% helium always left me sharp down to 300 feet, and i have never had any hint of even the tiniest hit in several decades of deep diving ( using helium since around 96)....So, for me, why would I spend twice as much money on every deep dive, for no apparent benefit? If I experienced ANY percieved benefit, I could consider this, but as of now, I don't see this for me.

If we had a reason to do 450 feet deep, or so, this would be a different conversation...but the types of tech dives I like, are in places with huge masses of marine life, and there tends to be high current issues whereever we find the life we enjoy seeing---this means drag from several extra tanks is a huge problem, and this eliminates the 450 foot dive ( and the pure helium and O2 discussion) unless using a rebreather, and diving with insufficient bailout..so I won't be doing this ...and then there is still goig down fast enough to not miss the structure.

Surface Supply lets you do many things we can't do....but it would be fun to see you guys try this in a 5.5 mph current from Gulf Stream intrusion, over a wreck like the Skyclife or the Andi on as day it is really blowing....This makes it great for us and DIR, but hard to imagine for Surface Supply.

 

[LiteHedded]

One thing that you mentioned is that you dont get the twitches because you go down very slowly.
Where we dive in the ocean, in 300 foot drift current environments, your descent MUST be rapid. I will typically scooter full speed down from the moment the team is all set 10 or 20 feet from the surface--we all go down at maximum speed to assure we actually reach the structure or feature the boat had marked before we jumped in....If we are not using scooters, then we just go in with all air sucked out of the wings, with a comfortable swim /cruise speed straight down. 150 to 200 feet per minute is a nice minimum pace for this.
I do not think this practice would fit the description you gave...though the 300 feet depth may be shallow enough for no HPNS to result.

From my own perspective, using 50% helium always left me sharp down to 300 feet, and i have never had any hint of even the tiniest hit in several decades of deep diving ( using helium since around 96)....So, for me, why would I spend twice as much money on every deep dive, for no apparent benefit? If I experienced ANY percieved benefit, I could consider this, but as of now, I don't see this for me.

If we had a reason to do 450 feet deep, or so, this would be a different conversation...but the types of tech dives I like, are in places with huge masses of marine life, and there tends to be high current issues whereever we find the life we enjoy seeing---this means drag from several extra tanks is a huge problem, and this eliminates the 450 foot dive ( and the pure helium and O2 discussion) unless using a rebreather, and diving with insufficient bailout..so I won't be doing this ...and then there is still goig down fast enough to not miss the structure.

Surface Supply lets you do many things we can't do....but it would be fun to see you guys try this in a 5.5 mph current from Gulf Stream intrusion, over a wreck like the Skyclife or the Andi on as day it is really blowing....This makes it great for us and DIR, but hard to imagine for Surface Supply.

because your buddy might not be the rockstar you are

 

[danvolker]

because your buddy might not be the rockstar you are

What kind of a thing is that to say? George and Bill dove this way when I met them, and so this is the way I dive with them or my other buddies now.....
And of course, your choice of buddies IS your most important gear choice... If someone is pathetic at descending, they will not be allowed to buddy with us.
The rockstar comment??? There is nothing hard or impressive about descending fast. It is as easy as breathing.