Nitrox course. What's the point?

[chillyinCanada]

You vastly experienced divers have taken this conversation way out of the realm of "New Diver".

I believe that you should take this conversation "outside" and carry on!

Unfortunately, by participating in this thread, I have eliminated myself from being able to moderate it.

 

[Gareth J]

That must have been quite some time ago?

Page 17

 

[Angelo Farina]

I believe you're correct there on both counts. The inert gas gradient is already maximized when breathing O2 so added pressure from depth doesn't benefit the offgassing much, other than helping reduce bubbles.



Angelo - I learned that offgassing is proportional to the difference in the tissue inert gas tension and inspired inert gas tension. Your ambient pressure doesn't affect the tissue gas tension (i.e. you don't multiply by the pressure). The tissue gas tension is just a pressure value representing the actual pressure of gas absorbed inside that tissue - that is the basis of most decompression models.

You would only multiply by ambient pressure just to determine the partial pressures of a gas when you know its fraction (e.g. 79% N2 at 2 atm = 1.58 atm), but that is not needed in this case.

Because tissue tension is what it is, just a pressure value (e.g. 2.3 atm), then in the special case of breathing pure O2, where the inert gas tension is zero atm regardless of depth, then the rate of offgassing is the same regardless of depth.

There are other biological factors, such as elevated O2 PP being a vasoconstrictor, so the rate of offgassing could be in reality slower at 6m than at 3m.

OK, I see. The problem is using the "pressure" version of the Fick's law. Probably everything is much simpler using the concentration version of the Fick's law, where the difference to be taken into account is the difference between the concentration of the Nitrogen in the tissue (in kmol/m3) and the concentration of oxygen in the lungs. Of course the concentration of Nitrogen in the tissue does not depend on the ambient pressure...

 

[chillyinCanada]

Page 17

I meant the period of time when your club wasn't to use Nitrox for rec dives.

 

[Edward3c]

You vastly experienced divers have taken this conversation way out of the realm of "New Diver".

I believe that you should take this conversation "outside" and carry on!

Unfortunately, by participating in this thread, I have eliminated myself from being able to moderate it.

Go ahead and moderate, the thread needs it.

Mods are always right.

 

[Julius SCHMIDT]

Nitrox prevents me falling asleep as much driving after a strenuous days diving and a long drive home

 

[Neilwood]

Go ahead and moderate, the thread needs it.

Mods are always right.

She can't - it is a mod rule AFAIK that any mod participating in a thread is automatically barred from mod'ing within that thread.

Sensible imho as it prevents anyone with a vested interest in a thread using power inappropriately (not that our mods would).

 

[Dody]

Oh, yes, I am well aware that BSAC teaches deco early on and doesn't call it technical diving. This discussion comes up all the time.

Here's my thinking on that.

This is the new divers forum. Not to be an ugly American, but I would guess that the numerical majority of users of this platform go by the simple rec=NDL / tech=deco dichotomy. Now that may or may not be true, but even if this were a BSAC / CMAS majority site, we shouldn't imply to new divers (most of whom are NOT trained in staged decompression) that if we decide to change the plan during the dive, it's not a problem, we can just do deco.

That's the reason that I'm beating this particular dead horse.

Agree. I am already over my head in this thread now. To fully understand it, I would need to learn the science of deco. I guess that this is next in my training plan.

 

[David Novo]

Agree. I am already over my head in this thread now. To fully understand it, I would need to learn the science of deco. I guess that this is next in my training plan.

You can check "Deco for Divers" by Mark Powell.
When I did the Science of Diving free specialty back in April, the explanation regarding decompression theories was so short that I did not understand anything. The book I mentioned helped a lot.

 

[Jcp2]

Agree. I am already over my head in this thread now. To fully understand it, I would need to learn the science of deco. I guess that this is next in my training plan.

There is no pressing need to fully understand something in order to benefit from its use.