Riding GF99 instead of mandatory/safety stops

[Wallowa]

You are missing the point of the oxygen window. The point is tht the use of 100% O2 means 0% Ne, so the nitrogen gradient between what is in your tissues and what is in your breathing gas is very large, and thus helpful in off-gassing. But the gradient using 40% O2 is much smaller, therfore much less helpful, if helpful at all.

You did it again....."much smaller", certainly 40% is less than 100% but larger than 21%...but "therefore, much less, if helpful at all'....really? Any enhanced reduction in tissue nitrogen tensions is a win. Divers can either subscribe to the belief that the oxygen window can lessen the risk of tissue damage or not....any reduction is win-win for me personally; to each their own. From the "if helpful at all" statement you seem to doubt the probative value of breathing higher concentrations of oxygen at a safety stop. I recognize there are no guarantees but I will take the small improvements. The oxygen window benefit is such an improvement.

 

[Wallowa]

If you're properly trained in gas switching and staged decompression then feel free to do that, it won't hurt. But the fact that you're asking these basic questions online leads me to suspect that you lack this training and might be taking risks that you don't really understand with things like gas switching protocols and oxygen exposure limits. Nitrox 40 would be an odd (non-standard) and rather pointless choice of deco gas at the typical "safety stop" depth of about 15 ft / 5 m.

If you want to get into this type of entry-level technical diving then the GUE Master Diver (Rec 3) course could be a good option. It covers skills pretty similar to what you want to do including switching to a nitrox mix on ascent. And it should get you clear on the basics of modern deco theory. We can't teach you how to do this stuff safely on a ScubaBoard thread.

Nick, Nick...again your training and subscribed to organizational tenets are held up as superior to how others choose to dive....you have no idea of my background, diver training and most importantly dive time; but you still render an opinion that I am lacking knowledge, skills and training...others are not lacking but different.

You are correct in one assumption...the ScubaBoard can't teach anyone how to safely dive.

Oh, and for EAN40 being a "rather pointless choice" says a lot not about the use of 40% at a SS but more about what for you believe constitutes diver safety. There are no first among equals. A "safe diver' need not comport to organized strictures but only need take full responsibility for their competency. One size does not fit or benefit all. The oxygen window is not an all or nothing process; if 40% at any depth washes out inert gas tissue tension then take the improvement of reduced inert gas in the tissues,

 

[tursiops]

You did it again....."much smaller", certainly 40% is less than 100% but larger than 21%...but "therefore, much less, if helpful at all'....really? Any enhanced reduction in tissue nitrogen tensions is a win. Divers can either subscribe to the belief that the oxygen window can lessen the risk of tissue damage or not....any reduction is win-win for me personally; to each their own. From the "if helpful at all" statement you seem to doubt the probative value of breathing higher concentrations of oxygen at a safety stop. I recognize there are no guarantees but I will take the small improvements. The oxygen window benefit is such an improvement.

You clearly do not understand what the oxygen Window means or how off-gassing occurs. Th off-gassing of the excess N2 in your tissues occurs because the N2 partial pressure in the gas you are breathing is lower than the N2 partial pressure in your tissues. It has nothing to do with the O2 partial pressure in either your tissues or your breathing gas. At your safety stop, the PPN2 in your tissues is higher than the PPN2 of air, so you can off gas. The lower the PPN2 in your breathing gas, the better you off-gas. Oxygen thuys helps a lot; 40% nitro, very little.

 

[Wallowa]

You clearly do not understand what the oxygen Window means or how off-gassing occurs. Th off-gassing of the excess N2 in your tissues occurs because the N2 partial pressure in the gas you are breathing is lower than the N2 partial pressure in your tissues. It has nothing to do with the O2 partial pressure in either your tissues or your breathing gas. At your safety stop, the PPN2 in your tissues is higher than the PPN2 of air, so you can off gas. The lower the PPN2 in your breathing gas, the better you off-gas. Oxygen thuys helps a lot; 40% nitro, very little.

Last attempt.....look to your own understanding of the mechanics of the oxygen window mechanisms...."It has nothing to do with the O2 partial pressure in either your tissues or your breathing gas." Ah! The % of oxygen in the breathing gas is what drives the oxygen window washout of nitrogen from the tissues; 100% in chambers remember....re-read the articles I posted...then you say "The lower the PPN2 in your breathing gas, the better you off-gas. Oxygen thuys helps a lot; 40% nitro, very little."....can't have it both ways....oxygen either is beneficial in reducing nitrogen tissue tensions or is not....oxygen functions not just as a dilute but as a metabolic gas.....back to "very little"....oxygen on SS stops enhances the elimination of nitrogen from tissues...

I surrender you folks continue on in the echo chamber.....dive any manner in which you choose....

 

[boulderjohn]

It has nothing to do with the O2 partial pressure in either your tissues or your breathing gas.

Oxygen PPO2 and the Oxygen Window

There was once a belief, chiefly among DIR divers, that a very high PPO2 sped up the off-gassing process because the metabolism of oxygen (changing to CO2) created an "oxygen vacancy" that allowed for faster nitrogen off-gassing by creating more room for it to leave. That is the reason behind what was called the "S-curve" on their decompression ascents, in which divers would spend more time (using 50%) on the 70 foot stop and the 60 foot stop than on the 50 and 40 foot stops. They believed that the high PPO2 was driving decompression. They called it the "oxygen window."

Does my brief description sound like a violation of Dalton's Law? That's because it is indeed a violation of Dalton's Law. In Deco for Divers, Mark Powell described three different definitions used for the term "oxygen window," and he flatly said the one described above as not valid for that reason.

I believe I may still be able to access the email in which Jarrod Jablonski told me that GUE had determined that the science behind their definition of the oxygen window was flawed. He said they were still using the S-curve ascent profile because it had been working for them. They later abandoned it.

When I was with UTD, I argued with Andrew Georgitsis against that definition, and just before I left, he agreed that the science was indeed wrong, but he was keeping the S-curve profile. The UTD version of Ratio Deco was still using the S-curve when it came out so badly in the Spisni study, a comparison with a Buhlmann with GFs profile.

 

[boulderjohn]

Last attempt.....look to your own understanding of the mechanics of the oxygen window mechanisms...."It has nothing to do with the O2 partial pressure in either your tissues or your breathing gas." Ah! The % of oxygen in the breathing gas is what drives the oxygen window washout of nitrogen from the tissues; 100% in chambers remember....re-read the articles I posted...then you say "The lower the PPN2 in your breathing gas, the better you off-gas. Oxygen thuys helps a lot; 40% nitro, very little."....can't have it both ways....oxygen either is beneficial in reducing nitrogen tissue tensions or is not....oxygen functions not just as a dilute but as a metabolic gas.....back to "very little"....oxygen on SS stops enhances the elimination of nitrogen from tissues...

I surrender you folks continue on in the echo chamber.....dive any manner in which you choose....

Ah! You posted this while I was making my post above. So you still believe in the oxygen vacancy theory. Is that right?

 

[Nick_Radov]

The % of oxygen in the breathing gas is what drives the oxygen window washout of nitrogen from the tissues

Not really. The PN2 differential gradient in the lungs (inhaled gas) relative to the bloodstream is what drives the washout from tissues.

oxygen functions not just as a dilute but as a metabolic gas.

True but irrelevant. Rate of oxygen metabolism is independent of PO2 (assuming PO2 is high enough to sustain life).

 

[grantmac]

Open water deep air with stashed deco, not a profile where any sort of efficiency or safety is a priority.

 

[dmaziuk]

I vote we train Maxwell's demon to let N2 molecules out and O2 molecules: in, and call it "the oxygen door" -- much more efficient than a window, no?

 

[Nick_Radov]

Ah! You posted this while I was making my post above. So you still believe in the oxygen vacancy theory. Is that right?

The notorious "oxygen window" was extensively discussed on the old Aquanaut Techdiver list decades ago. For historical reference only, here is one of the typical messages. (I am not claiming this is an accurate description.)

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