nitrox at surface to improve off gassing?

[BrianKon]

I would think that taking an extended safety stop breathing your 32EAN would be more beneficial than breathing at the surface.

Regardless of what your breathing, just floating at the surface for even a few minutes prior to the physical exertion of climbing onboard a boat will help to off-gas and reduce DCS symptoms. This is a safety practice I use after long and deep dives.

 

[Tortuga68]

It's hard to say without knowing what benefit the OP is looking for... I think the main conclusion is that any difference will be pretty marginal

Coventional thinking is excercise after diving can contribute to bubble formation, although some recent studies seem to show that it may actually reduce bubbles. Either way it's not really accurate to say avoiding excercise will help off-gassing

 

[rebelrph]

Thanks for the input. My thinking is that my O2 sat will already be 100%, but with the differing partial pressures I figure a larger percentage of Nitrogen and any CO2 built up will be more easily eliminated compared to breathing 21% for the same time. The "purpose", if I were to come up with one, is to decrease the risk of DCS and prevent the post-dive headaches caused by CO2 build up. During this (now day 15) diving trip I've had no headaches that usually have occurred on a 1 in 4 dive basis in the past.

 

[Tortuga68]

CO2 retention isn't a function of partial pressure, in diving it's more to do with breathing technique and work - I don't think breathing EAN32 at the surface will have any effect on it (positive or negative)

As previously stated, it may have some positive effect on N2 off-gassing but it's going to be pretty minimal IMO. But if it makes you happy, no reason not to do it. The placebo effect might be even more beneficial than the physiological one

 

[rebelrph]

I'm all for effective, whether placebo or real. I was re-thinking my previous post and realized I should have said, "differing concentrations" rather than partial pressures. Logically thinking, to achieve equilibrium there would have to be a shift from blood gases to the "air" in the lungs and with the 32% this difference would be greater therefore the shift would occur quicker. Whether this "quicker" is measurable or not is probably questionable. I just couldn't think of any reason NOT TO and wanted some "second opinions".

Thanks again for the input

TC

 

[craracer]

So, just for giggles, lets change it from 32 to 50%, or even to 80 or 100. Is everyone still of the same opinions? (Just for the sake of .....whatever.....lets say that his dive was on 32).

 

[ianr33]

So, just for giggles, lets change it from 32 to 50%, or even to 80 or 100. Is everyone still of the same opinions? (Just for the sake of .....whatever.....lets say that his dive was on 32).

After any dive with a significant amount of deco I'll breathe O2 on the surface for several minutes. (the reg is in my mouth anyway) . It's cheap insurance.

Breathing air at the surface the pN2 is .78. Breathing 32%, pN2 will be around .68 ,not much difference compared to air. (Remember air is ~1% Argon)

But when breathing o2 on the surface the pN2 is zero. That's a huge advantage and greatly increases the net offgassing of nitrogen.

 

[ianr33]

Regardless of what your breathing, just floating at the surface for even a few minutes prior to the physical exertion of climbing onboard a boat will help to off-gas and reduce DCS symptoms. This is a safety practice I use after long and deep dives.

Totally agree that relaxing on the surface and reducing exertion after a dive is a great way to reduce DCS risk, but that's because its REDUCING the amount of off gassing. It's the old coke can analogy. Rest calmly (don't shake the can) and bubbles come slowly and harmlessly out of solution. Major exertion (shake the can) bubbles erupt violently out of solution and you get bent.

The only DCS case I've ever seen involved a buddy who carried a steel tank uphill almost immediately after a long dive.

 

[Tortuga68]

Definitely breathing 100% would be more beneficial in terms of reducing DCS risk compared to EAN32, although it's a bit of a moot point since you'd then have to take an O2 tank (I know, just for ****s & giggles). It would increase OTU & CNS loading as per an earlier question, but again not by a significant amount following a recreational dive

Regardless of what your breathing, just floating at the surface for even a few minutes prior to the physical exertion of climbing onboard a boat will help to off-gas and reduce DCS symptoms. This is a safety practice I use after long and deep dives.

Thinking about it further, if we change the statement slightly to "...will help to off-gas at a safe rate and reduce [avoid] DCS symptoms" then yeah

Similary eliminating N2 from the breathing gas (eg by breathing 100% O2) doesn't increase the rate (speed) of N2 off-gassing per se, but reduces overall N2 over time