Nitrox course. What's the point?

[tursiops]

There’s quite a difference between basic PADI nitrox certification level understanding to full on tech and beyond understanding.

Yes there is, but there is no need to be at either of those two extremes, most of the time. I think the purely "here is how you set your computer" and "don't go too deep" end of the spectrum is much too little. It does not invite any understanding, nor does it provide the information to allow people to do anything other than follow the rules. And we know how well THAT goes.

 

[Storker]

How is this thread 48 pages?

Scubaboard

 

[Storker]

Correct me if I'm wrong but I'm pretty sure that increasing the ambient pressure while breathing oxygen does NOT increase the rate of nitrogen off gassing because what we care about is the nitrogen partial pressure and that is 0 while breathing oxygen regardless of depth. This is also why some people choose to do a 6m final stop on 100% instead of a 3m stop because the time is the same but you're further underwater and less affected by the swell.
Hyperbaric oxygen treatment increases the depth to crush or recompress any bubbles in your body.

Not quite. The maximum amount of N2 dissolved in your tissues will be higher at 6m than at 3m, so the driving force for offgassing would be smaller at 6m than at 3m. Henry's law and Fick's law. So no matter what you're breathing, you'll offgas slower at 6m than at 3m.

No matter that sometimes it's smarter to deco at 6m than at 3m. Because other things.

 

[Storker]

There’s quite a difference between basic PADI nitrox certification level understanding to full on tech and beyond understanding.

There's also a middle ground.

Law of excluded middle - Wikipedia

 

[Blackcrusader]

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.

Do the Nitrox course first. Rack up the required number of Nitrox dive then look at the TDI Advanced Nitrox and Decompression course. Of course there are other agencies as well like GUE and BSAC PADI etc.

Courses - SDI | TDI | ERDI | PFI

 

[Blackcrusader]

Depending on what you mean with "shallow", I bet this is what would happen in practice most of the time (in the recreational realm, at no more than 30m). But yes, the science behind is rather complex...

PADI nitrox on 32% MOD is 34 meters so not 30m only but a lot of dive centers policy would be lets not exceed 30m on 32% nitrox.
Of course you could get a 26% mix and go deeper.

 

[KenGordon]

And the same goes for a computer if you don’t follow it. It’s as easy to make a 10m/min. assent with a watch and depth gauge as a computer with practice. For me its the same as walking a 10 metre line in a min. Zero the bezel and watch the second hand. Watch and depth gauge on one arm keep buoyancy slightly negative. There’s something wrong with divers training and practice if they can’t maintain a steady assent. The real problem with maintaining deco stops and timing them is thinking you can do them without a station.

Do a slow ascent and the computer will account for it. On a slate all you can do is move to the “longer” plan or course the computer cannot fix the gas situation.

Divers are told not to ascent to quickly over and over, they generally cannot do 10m/minute unless explicitly trying and only then with a bit of encouragement.

 

[Celt]

Do a slow ascent and the computer will account for it.

Do a slow ascent with a watch and you can add the delay to the first stop, but really if a diver can’t control an ascent they have no business going into deco. Being able to tell the time is pretty basic

 

[EFX]

Correct me if I'm wrong but I'm pretty sure that increasing the ambient pressure while breathing oxygen does NOT increase the rate of nitrogen off gassing because what we care about is the nitrogen partial pressure and that is 0 while breathing oxygen regardless of depth. This is also why some people choose to do a 6m final stop on 100% instead of a 3m stop because the time is the same but you're further underwater and less affected by the swell.
Hyperbaric oxygen treatment increases the depth to crush or recompress any bubbles in your body.

Not quite. The maximum amount of N2 dissolved in your tissues will be higher at 6m than at 3m, so the driving force for offgassing would be smaller at 6m than at 3m. Henry's law and Fick's law. So no matter what you're breathing, you'll offgas slower at 6m than at 3m.

I think you have it backwards. If the amount of N2 is higher at 6m than 3m then the partial pressure of N2 in the tissues relative to 0 N2 partial pressure in the oxygen will be greater at 6m than 3m which means higher offgassing not lower offgassing. My understanding is that higher offgassing means higher flow which comes from a higher pressure gradient. Am I misunderstanding something?

 

[dmaziuk]

I think you have it backwards. If the amount of N2 is higher at 6m than 3m then the partial pressure of N2 in the tissues relative to 0 N2 partial pressure in the oxygen will be greater at 6m than 3m which means higher offgassing not lower offgassing. My understanding is that higher offgassing means higher flow which comes from a higher pressure gradient. Am I misunderstanding something?

Nope, as far as the formula is concerned, Pamb N2 is zero at either depth so off-gassing is faster at whichever depth you have more Pinsp N2. I strongly suspect that IRL the difference is only slightly more significant than the difference between 6 and half a dozen -- unless of course you have an actual ceiling at 6 msw. But then you wouldn't be choosing 3 msw for your stop depth.