Decompression vs Off-gassing

[PfcAJ]

That's what happens upon decompression from a dive in your blood. There's more nitrogen dissolved than your blood would normally be able to hold. It's a super-saturated solution. Fortunately there's no good nucleation points around, so the nitrogen stays in solution. The only points where it can come out of solution is in your lungs: you exhale it. That's off-gassing. However, if you decompress too quickly, the amount of super-saturation becomes too great and nitrogen starts coming out of solution without proper nucleation points. You've got DCS.

Thats not completely accurate. Asymptomatic microbubbles are very common even in rec profiles. The pulmonary capillary bed filters the bubbles out and you exhale the excess inert gas. This kind of deco is ok, and doesn't cause a problem in most folks. PFOs and bounce dives can allow bubbles to pass around or through (respectfully) the capillary bed and cause DCS symptoms. Of course, overloading the cap bed is bad and can produce the 'chokes', a type 2 DCS symptom.

One of my favorite decompression sayings - Measuring with a micrometer, marking with chalk, and cutting with an axe.

 

[DaleC]

I understand phase changes pretty well but why are you complicating such a simple process? It's the saturation of N and it's potential for future expansion in a gaseous state that concerns us.

I guess I just see myself trying to explain the concept of decompression so someone like the OP can understand why his answer was not out of line. Every time we introduce a different term or level of complexity it makes it that much harder for the basic message to be transmitted. So, are we trying to convey the message to the target audience or what?

This is the basic recreational forum, not the technical forums, and as such, I am trying to keep the discussion (for my part) in terms that basic recreational divers will be able to relate to. I know it's fun for some, but deco theory need not be made uber complicated to be understood at a basic level. And it should be understood at a basic level by all divers as we all, potentially, have the risk of being affected by it.

And, to be completely accurate, the OP's reply should have been:

"I said, "So you switch to the higher mixture to decompress faster"

and the instructors answer should have been:

"To off-gas faster".

But that would be somewhat like the OP's instructor's behavior to point that out