Deco Gas Question

[TheDecoStop]

What are the advantages/disadvantages of diving a deco gas of 50% vs 36% when doing a dive around 175 – 190 on 21/35? I generally run a 21/35, then switch to 36 then to 80 on a 190’ dive. By running 36 instead of 50 I get a shorter run time since I am getting off the helium sooner, and moving to a higher % O2. I know that certain agencies advocate nothing but 50 and 100, is this the main reason that people would run a 50 over a 36 or is there another reason? The reason I ask is that some good old dir guys gave me crap about my 36 mix, actually all my mixes… but I will leave that discussion off this board.

Thanks for any input.

Safe diving,

Rick

[WreckWriter]

TheDecoStop once bubbled...
The reason I ask is that some good old dir guys gave me crap about my 36 mix, actually all my mixes… but I will leave that discussion off this board.


You'll get the same thing here, particularly about using 80%. Good luck.

WW

[Doppler]

Hi Rick:

I am going to resist the temptation to give you the gears about your dive and deco mixes <LOL>.

OK this is the very short version... you'll hear more, so take this as a overview or precursor.

Your decompression will be more successful if the partial pressure of oxygen during your ascent is somewhere between 1 and 1.6 ata. By the time you switch to that 80 mix at 30 feet, you're at about 0.75 ata. In effect, you have just executed a couple of stops with marginal efficiency... There's way more to this topic -- mostly vacant partial pressure (the oxygen window) -- but this is the answer to your original question.

Something to think about too is that the dive schedules that we cut on our computers are only mathematical models. Few programs take into account the partial pressure effect and therefore, mostly they will tell you that if you deco on 80/20 and your EAN36 you will get you out of the water sooner. Well, from the perspective of the algorithm... the calculus used to model what's happening inside you... that may be the case.

What the math doesn't tell us is how we actually feel after the dive... basically how close to the edge we are...

There's a whole essay topic here about silent bubbles activating the complement complex (immune system) and the drop in partial pressures from the mouth to the avioli but for the time being, I hope I have answered your question. :)


Take care and dive safe

DD (Hogarthian diver... Doing It Longer)

[TheDecoStop]

I appreciate the answer. Makes plenty of sense. I will rethink my methods after a little more research.

Thanks again.

[AquaTec]

Doppler once bubbled...
Hi Rick:


Your decompression will be more successful if the partial pressure of oxygen during your ascent is somewhere between 1 and 1.6 ata. By the time you switch to that 80 mix at 30 feet, you're at about 0.75 ata. In effect, you have just executed a couple of stops with marginal efficiency... There's way more to this topic -- mostly vacant partial pressure (the oxygen window) -- but this is the answer to your original question.

What the math doesn't tell us is how we actually feel after the dive... basically how close to the edge we are...

DD (Hogarthian diver... Doing It Longer)

If high partial pressure is you answer then what is the difference between 36% at 113 feet and 50% at 72 feet. which ever gas you choose to use double your stop time at the gas switch were the PO2 is the highest

the longer deco time is because he is on helium for the additional 40 feet, if he gets off the helium then his deco is a bit shorter.

yes there are arguments to the contrary, but that may be outside his question.

as for feeling better, I will pressume you are talking about nitrogen loading, perfect reason to get onto the 80% shallower, and flush that out. do the balance of your deco at the 30 foot stop, and just your added safety deco time at the 20 foot stop.
with the 80% there is no back switching required for those longer stop times.

36% and 80% are better choices for deeper diving, until it is time to add in that intermediat trimix, but consideration then is given to added tanks to carry and beyond his question

[TheDecoStop]

Here is some interesting info that I have come accross while doing a little extra research on this subject.

"Furthermore, trying to maintain high partial pressures of oxygen with multiple mixtures results in
vasoconstriction (a reduction in off-gassing potential), increased pulmonary irritation (likely with reduced
diffusion efficiency), and increased CNS toxicity risk."

Just a portion of the story, but interesting. The rest of the story points towards using minimal gases with the best calculated results.

I always like to hear peoples practices and the reasons behind them, so keep them coming.

Rick

[omar]

It is an outdated notion that you need/should get off of helium as soon as possible. If you are basing this statement on running different scenarios on the available models then you need to realize All of the models out there except RGBM do not adequately account for the ongassing/offgassing and bubble formation and growth with respect to helium. Even RGBM does not do a good job for the shallow stops as well.

Selecting the proper deco gases ALSO includes selecting the appropriate bottom gas. It is a symbiotic process, you can not properly do one without the other. For the first dive to 190 the proper gas would be 18/45. I would only take 50% for the first deco gas starting at 70 ft. Subsequent dives would be done with 50% and 100% at 20 ft.

The use of 36% vs 50% and 80% vs 100% are based on the oxygen window and utilizing it to maximum benefit to offgass. To go over the mechanism would take considerable space which would still be inadequate.

I suggest that you check out.

Aksnes, E., and H. Rahn. Measurement of total gas pressure in blood. J. Appl. Physiol. 10: 173-178, 1957.2.

Acott, C. Is 100 % Oxygen Necessary In The Emergency Management Of Decompression Illness, SPUMS, 28(3) Supplement, Sept. 1998, 16-20.

Acott, C. Oxygen Toxicity: A Brief History Of Oxygen In Diving, SPUMS, 29(3), 1999, 150-155.

Anderson, L. & Atikkan, E. Oxygen: Friend Or Foe? in PROCEEDINGS OF THE 1992 IQ, NAUI, Montclair, CA. 1992, 1-3.

Bassett, B. Oxygen: Is It A Miracle Drug For Divers, Ocean Realm, Fall, 1986, 13-16.

Betts, J. In-Water Bends Treatment, NAUI News, Aug/Sept. 1980, 6.

Betts, J. Oxygen Recompression Therapy Underwater, Undersea Journal, Second Quarter, 1981, 20.

Bookspan, J. Is Oxygen A 'Feel Good' Gas For Divers? Underwater USA, Oct. 1992, 35.

Bove, F. Diving Medicine: Oxygen, Skin Diver, June, 1985, 16.

Bove, F. Diving Medicine: Oxygen Toxicity, Skin Diver, Oct., 1992, 24-25.

Cadenas, E. Biochemistry of Oxygen Toxicity, in C. Richardson (Ed.) ANNUAL REVIEW OF BIOCHEMISTRY, V. 58, Annual Reviews Inc. Palo Alto, CA. 1989, 79-110.

Clark, J. Oxygen Poisoning, in J. Davis (Ed.) HYBERBARIC & UNDERSEA MEDICINE, Medical Seminars, San Antonio, TX. 1981, Chapter 17, 12 pages.

Clark, J. Oxygen Toxicity, in Bennett & D. Elliot (Eds.) THE PHYSIOLOGY AND MEDICINE OF DIVING, Best Publishing, San Pedro, CA. 1982, 200-238.

Comroe, J. & Dripps, R. PHYSIOLOGICAL BASIS FOR OXYGEN THERAPY, C.C. Thomas, Springfield, Il. 1950, 85 pages.

Corry, J. Setting The Record Straight: Oxygen Delivery And The Injured Diver, in Bennett & R. Moon (Ed.) DIVING ACCIDENT MANAGEMENT, UHMS, Bethesda, MD. 1990, 323-342.

Corry, J. Setting The Record Straight: Oxygen Delivery And The Injured Diver, in H. Viders & F. Wells (Ed.) IQ 1991 PROCEEDINGS, NAUI, Montclair, CA. 1991, 29-44.

Corry, J. Unique Oxygen Training Course Developed By Diving Community, Response, Winter, 1990, 17-18. Also: Alert Diver, V. 4, #2, 10.

Crea, J. Oxygen: Princess of Gases: Why You Should Use It For Decompression, Aqua Corps, Winter, 1991, 28-32.

Crea, J. Oxygen: The Princess Of Gases, Discover Diving, May/June, 1991, 89-91.

Davis, J. & Hunt, T. (Eds.) HYBERBARIC OXYGEN THERAPY, UMS, Bethesda, MD. 1977, 348 pages.

Daugherty, G. In-Water Bends Treatment, Diver, December, 1986, 12.

DAoust, B. G., H. T. Swanson, R. White, R. Dunford, and J. Mahoney. Central venous bubbles and mixed venous nitrogen in goats following decompression. J. Appl. Physiol. 51: 1238-1244, 1981.3.

Dick, A. Bennett, & Miller, J. Oxygen & Diving Accidents, Undersea Journal, Third Quarter, 1983, 23.

Dick, A. Bennett, & Miller, J. Oxygen & Scuba Diving Accidents, Scuba Times, May/June, 1983, 26-27; Also: Alert Diver, V. 2, # 1, 1985, 1-2.

Edmonds, C. In-Water Recompression: A Potential Field Treatment Option For Technical Divers, Aqua Corps, N5, 1993, 46-49.

Edmonds, C. Oxygen Treatment Of Decompression: A Review. SPUMS, 25(3), Se 1995, 122-128.

Edmonds, C. Underwater Oxygen Treatment For Decompression Sickness, SPUMS, 26(1), March, 1996, 20-23.

Fawcett, T. Vann, R. & Gerth, W. Surface Interval Oxygen,: Rationale and Study Design, in Lang and Vann (Eds.), AAUS Repetitive Diving Workshop, Duke University, NC. 1991, 293-297.

Fischer, B. Jain, K. Braun, E. & Lebel, S. HANDBOOK OF HYPERBARIC OXYGEN THERAPY, Springer-Verlag, New York, NY. 1988, 359 pages.

Gerth, W. Vann, R. & N. Leatherman, Whole-body Nitrogen Elimination During Oxygen Pre-breathing And Altitude Decompression Sickness Risk, in R. Vann (Ed.) THE PHYSIOLOGICAL BASIS OF DECOMPRESSION, UHMS, Bethesda, MD. 1989, 147-152.

Gorman, D. Decompression Sickness And Arterial Gas Embolism In Sports Scuba Divers, Sports Medicine, 8(1), 1989, 32-42.
Greer, H. & Massey, E. Neurologic Injury From Undersea Diving, Neurologic Clinics, (10)4, 1992, 1031-1045.
Groom, A. C., S. H. Song, Y. Ohta, and L. E. Farhi. Effect of anesthesia on rate of N2 washout from body stores. J. Appl. Physiol. 37: 219-223, 1974.4.

Hamilton, R. Kenyon, D. Powell, M. & Freitag, M. Importance Of Oxygen In Mixed-Gas Decompression, in DECOMPRESSION THEORY, UMS, Bethesda, MD. 1978, 133-136.
Hydlegarrd, O. & Madsen, J. Influence Of Helox, Oxygen and N2O-O2 Breathing On N2 Bubbles In Adipose Tissue, Und. Biomed. Res. 16(3), 1989, 183-193.

Hyldegarrd, O. Moller, M. & Madsen, J. Effect of He-O2, O2, and N20-O2 Breathing On Injected Bubbles In Spinal White Matter, Und. Biomed. Res. 18,(5-6), 1991, 361-371.

Hyldegarrd, O. Moller, M. & Madsen, J. Protective Effect Of Oxygen And Heliox Breathing During Development Of Spinal Decompression Sickness, Und. Biomed. Res. 21,(2), 1994, 115-128.

Hydlegarrd, O. & Madsen, J, Effect Of Air, Heliox, And Oxygen Breathing On Air Bubbles In Aqueous Tissues In The Rat, Und. Biomed. Res. 21(4), 1994, 423-424.

Jain, K. & Fischer, B. OXYGEN IN PHYSIOLOGY AND MEDICINE, C.C. Thomas, Springfield, IL. 1989, 376 pages.

Kindwall, E. P. Measurement of helium elemination from man during decompression breathing air or oxygen. Undersea Biomed. Res. 2: 277-284, 1975.5.

Kroos, B. Oxygen Helps Beat DCI Odds, Immersed, Winter, 1998, 49-52.
Lambertsen,C. Bond, G. & Jacobson, J. (Ed.) HYPERBARIC OXYGENATION (ANNALS OF THE NEW YORK ACADEMY OF SCIENCES, 117(2)), 647-890.

LeMatre, F. Meunier, N. & Bedu, M. Effect of AIr Diving Exposure Generally Encountered By Recreational Divers: Oxidative Stress, UHM, 29(1), 2002, 39-49.

Lippmann, J. in DEEPER INTO DIVING, Aqua Quest Publications, Locust Valley, NY. 1990, 499-521.

Loewenherz, J. Pathophysiology And Treatment Of Decompression Sickness And Gas Embolism, J. Florida M.A. 79(9), 1992, 620-624.

G. Rogataky, E. Shifrin, & A. Mayevsky (1999), Physiologic and Biochemical Monitoring During Hyperbaric Oxygenation: A Review, Undersea Hyperbar. Med. 26(20, 111-122.

Rutkowski, D. Physiological Implications Of Oxygen And Oxygen Life Support Ranges, in NITROX MANUAL, IAND, Key Largo, FL. 1989, 39-45.
Rutledge, R. Oxygen Delivery Systems, in B. Bridge (Ed.) IQ 14 PROCEEDINGS, NAUI, Montclair, CA. 1983, 199-203.

Ryan, R. Hyperbaric Oxygen Therapy For Diving Casualties, in PROCEEDINGS OF THE 1992 IQ, NAUI, Montclair, CA. 1992, 181-186.

Samsung, R. Oxygen Toxicity And Its Prevention In The Saturation Diving Associated With Project Flare, in J. Banbury (Ed.) PROCEEDINGS OF THE FIFTH ANNUAL SEMINAR ON CAVE DIVING, NACD, Miami FL. 1972, 97-103.

Schilling, C. & Faiman, M. Physics Of Diving And Physical Effects On Divers, in C. Schilling, C. Carston & R. Mathias (Eds.) THE PHYSICIAN'S GUIDE TO DIVING MEDICINE, Plenum Press, New York, NY. 1984, 39-41.

Sterk, W. The Use of Oxygen In Decompression, in I. Nashimoto & E. Lanphier (Eds.) DECOMPRESSION IN SURFACE-BASED DIVING, UHMS, Bethesda, MD. 1987, 13-19.

Thom, S. & Clark, J. The Toxicity Of Oxygen, Carbon Monoxide And Carbon Dioxide, in A. Bove & J. Davis (Eds.) DIVING MEDICINE, W.B. Saunders, Philadelphia, PA. 1990, 82-94.

Vann, R. The Oxygen Window, Alert Diver, Jan/Feb. 1993, 14-16.

Vann, R. D., and E. D. Thalmann. Decompression Physiology and Practice In P. Bennett and D. Elliott (eds): The Physiology and Medicine of Diving. London, W. B. Saunders Company, Ltd., 1993, pp 376-432

Weatherby, Hart, B. Flynn, T. & Walker, W. Role Of Oxygen In The Production Of Human Decompression Sickness, J. Appl. Phys. (1987) 63(6), 370-374.

Walters, KC, Gould, MT, Bacharach, A. & Butler, FK, Screening foe oxygen sensitivity in U.S. Navy combat swimmers, Undersea Hyper Med 27(1), 2000, 21-26.

Weinke, B. Oxygen Management, Advanced Diver, Issue 7, 45-47.

Wells, F. Report On State Laws And Regulations Concerning The Use And Dispensing Of Oxygen By Providers Of First Aid, Document Furnished To NAUI by author, 1989, 50 pages.

Wendling, J. Normobaric Oxygenation In Dive Accidents: A Challenge For The Developers Of Oxygen Delivery Systems, SPUMS, 27(2), June, 1997, 101-104.

Wilmshurst, P. ABC of oxygen: Diving and oxygen, BMJ, 10 October, 1998, 996-999.

[Divesherpa]

For dives in the 190 range for times between 30-70minutes, I prefer to jump on 32% or 36%, then 100%.
I feel much better after the dives.

[voidware]

Few programs take into account the partial pressure effect and therefore, mostly they will tell you that if you deco on 80/20 and your EAN36 you will get you out of the water sooner.

Doppler,
What is the partial pressure effect? I have never heard that term used before. While I could understand the benefits of using pure O2 to eliminate N2 in the breathing media, I do believe that whatever get's you out of the water fast would be beneficial (which for many dives means using 80).

brandon

[Doppler]

voidware once bubbled...


Doppler,
What is the partial pressure effect? I have never heard that term used before. While I could understand the benefits of using pure O2 to eliminate N2 in the breathing media, I do believe that whatever get's you out of the water fast would be beneficial (which for many dives means using 80).

brandon

Hi Brandon: should have been "VACANT partial pressure effect... also known as Oxygen Window... sorry for the mis-type... gotta start sense-checking this stuff!!! Very, very simply put in the current context... why breathe something that contains 20% of the stuff you are trying to eliminate?

[detroit diver]

TheDecoStop once bubbled...
Here is some interesting info that I have come accross while doing a little extra research on this subject.

"Furthermore, trying to maintain high partial pressures of oxygen with multiple mixtures results in
vasoconstriction (a reduction in off-gassing potential), increased pulmonary irritation (likely with reduced
diffusion efficiency), and increased CNS toxicity risk."

Just a portion of the story, but interesting. The rest of the story points towards using minimal gases with the best calculated results.

I always like to hear peoples practices and the reasons behind them, so keep them coming.

Rick

When using high o2 gasses, many divers break to back gas at set intervals so that the irritation that you mention above does not occur. That gives them full benefit of the high Po2's without the dangers of irritation and it's problems.

[Tampico_ED]

Hi Guys,

Excuse my ignorance. If I understood from other readings...When you go deco TDI 150ft. you can only use EAx21 (Air). Right? ...Also, Am I wrong saying that if you have doubles you put two different Nitrox gases?

I promise to take the TDI courses soon !

[Azza]

If high partial pressure is you answer then what is the difference between 36% at 113 feet and 50% at 72 feet. which ever gas you choose to use double your stop time at the gas switch were the PO2 is the highest

That’s great for the initial gas change but what about your ascent from the first gas switch to the second switch? You start running consistently lower and lower PPo2 and consistently higher and higher PP of inert gasses.
You spend more time between 70ft and 20 ft than you do between 113 ft and 70 ft. Surely it’s better to have the advantage of those higher PPo2 before your second gas switch?




as for feeling better, I will pressume you are talking about nitrogen loading, perfect reason to get onto the 80% shallower, and flush that out. do the balance of your deco at the 30 foot stop, and just your added safety deco time at the 20 foot stop.with the 80% there is no back switching required for those longer stop times.
Well you wont be flushing it out as well as jumping on O2 at 20 ft because you are still taking in 20% of inert gasses, as Doppler stated.
Staying on 02 at 20ft for the remainder of deco you have the added benifits of a higher PPo2 and no inert gasses entering your system.



36% and 80% are better choices for deeper diving, until it is time to add in that intermediat trimix, but consideration then is given to added tanks to carry and beyond his question
I don't believe so for the reasons already stated in this thread. However it is up to you how you want to deco...

[wedivebc]

Hi Brandon: should have been "VACANT partial pressure effect... also known as Oxygen Window... sorry for the mis-type... gotta start sense-checking this stuff!!! Very, very simply put in the current context... why breathe something that contains 20% of the stuff you are trying to eliminate?
I have not read an understandable explaination of oxygen window from a credible source. Steve, could you point me in a direction that will help me understand this. (other than you know who's rant on the subject)

[Lil' Irish Temper]

Just in case,

the last comment from detroit diver was 2 1/2 years ago.

Now back into the secret bat cave I go :D

[wedivebc]

Just in case,

the last comment from detroit diver was 2 1/2 years ago.

Now back into the secret bat cave I go :D
Doh! (again)

[boomx5]

I have not read an understandable explaination of oxygen window from a credible source. Steve, could you point me in a direction that will help me understand this. (other than you know who's rant on the subject)

Boy, I haven't seen this thread in...years. ;) Anyway, Maiken has some good stuff on decompression (http://www.decompression.org/maiken/Bubble_Decompression_Strategies.htm) you might find interesting. I think this the article I'm thinking of. I'll do a bit more searching and see what I can find for you Dave. :)

[Azza]

last comment from detroit diver was 2 1/2 years ago.

Now back into the secret bat cave I go :D

Doh!!!

[BigJetDriver]

Dave,

Try Bennett and Elliot's Diving Medicine for a good explanation.

As for this gas switching nonsense, get a good ECCR and an RGBM wetcomputer, run heliox surface to surface, and forget dragging all these tins of odd mix arround. HA! :D

As Mr. Natural once said: "Get the right tool for the job, kids!"

[eanxgirl]

Wow, Mr. Natural. Talk about a blast from the past!

[BigJetDriver]

My kinda gal! :sappy: :lol3:

[Jason B]

Wow, Mr. Natural. Talk about a blast from the past!
LOL! I had to look at your profile to see your age when I saw that post....it appears we are thinking of the same blast!

[eanxgirl]

Yes, my moniker is not really accurate--but trimixoldlady didn't sound as good!

[DiveGolfSki]

Yes, my moniker is not really accurate--but trimixoldlady didn't sound as good!

Why, you're both too young. :11:

[roturner]

I have not read an understandable explaination of oxygen window from a credible source. Steve, could you point me in a direction that will help me understand this. (other than you know who's rant on the subject)

Well...I'm a bit of neophyte tek diver but to me it all seems like fairly straightforward stuff that somehow gets made mysterious for no good reason.

If you want to eliminate inert gas as efficiently as possible then you have to create the biggest partial pressure difference you can to drive it out at top speed. Oxygen isn't inert so you get the effect of *not* having the inert gas in the mix *plus* the metabolism of the O2, creating a vacant space that gets filled up with what ever is most willing (most concentrated) to come out of solution at that moment.

Driving the pO2 higher and higher and driving the inert gas out by moving shallower and shallower will open the so called "oxygen window". It's not magic. it's just a matter of getting your head wrapped around what they're doing. The most efficient stop, therefore is the 6 metre oxygen stop, at least in theory. No inert gas and pO2 maxed at the shallowest possible depth.

With the caveat that they've discovered that inert gas moves out *faster* when it's still in solution than when it has to come out of bubbles....(read RGBM) which basically means that it can be better to do some stops deeper to avoid bubble formation than to fix it after the fact. Also not magic. This should be old news to you.

The aversion to 80% can be found in the loss of efficiency but the added safety of 80% tilts the scales back a bit in my mind. Denying that these things are in a weigh scale by referencing things like skills and buoyancy control is a bit of peculiar "ostrich politics" typical to tek diving. It all depends on how fast you need/want to be out of the water.

Does that make any sense?

R..