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Hans Petter Roverud wrote:
To much super saturation is a bad thing. Super saturation will
create an off gassing gradient. But its all in how you interput it.
This stuff is difficult to comprehend after learning/reading it one way
here and another way there. But as I see it our off gasing gradient is
created this way.
Furthermore I am not refering to switching to a higher helium mix.
What I am refering to is not jumpimg off the helium so fast.
As in you bottom paragraph, this is what I am talking about but the
helium loading you are refering to has plenty of time to offgas at the
last stops aspecially the O2 stop.
John
> Supersaturation is a bad thing. The M-values try to limit it so it won't
> get excessive and create (too much) bubbles. I think you're confusion
> supersaturation with offgassing gradient (driving pressure). A high
> gradient, accomplished by a productive gas switch does not cause
> supersaturation since the ambient pressure keeps the dissolved gas in
> solution. However, it causes a gradient or "steeper downhill" for washing
> out inert gas. This is what nitrox/ oxygen deco is all about.
>
> Further, you'd want to switch from faster to slower inert gases. Switching
> to more helium during ascent is hardly productive. This means that you
> ongas with helium faster than you offgas what's already dissolved in your
> tissues. This may create a surge of more gas in your body, before it drops
> again. The extra helium rushes in and adds to the nitrogen, which takes
> longer to diffuse out of your body. This is what may cause
> counter-diffusion problems: You carry a high load of a slow gas (as
> nitrogen) and suddenly dump a lot of fast gas (helium) on top of it.
>
> True, the gradient for eliminating nitrogen would be excellent but the
> sluggish gas doesn't leave as fast as the fast gas ongasses -- thus, total
> gas peaks shortly after that switch. That peak may give you a sudden,
> transient bubble trouble before things level off. Conversely, when you go
> from helium on the bottom to less helium/ nitrox you lose the helium faster
> than you ongas with nitrogen. Thus, total gas drops faster. The fast
> offgassing of helium turns into a blessing the moment you discontinue
> breathing helium -- from there on helium rushes out of your tissues fast.
>
> regards,
>
> Hans
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