Nitrox course. What's the point?

[Storker]

Google any of the explanations of interference theory, and you will see that too much information is the enemy of memory.

I'm unsure whether you're arguing my point or if you're adding to it. In any case, I believe we agree pretty well on this topic.

I might be wrong, though. I still remember that time back in '78...

 

[boulderjohn]

I'm unsure whether you're arguing my point or if you're adding to it. In any case, I believe we agree pretty well on this topic.

I might be wrong, though. I still remember that time back in '78...

Sorry I was unclear. I was agreeing with you and adding information.

 

[Celt]

That was certainly not what I said. If it was interpreted as such I apologise.

The whole point, way back early in the thread. It was noted that Nitrox is of particular benefit where repeat diving is being carried out.
This was because less Nitrogen was in the breathing gas, allowing a greater NDL dive time compared with air. This becomes more noticeable as the number of dives increase.
If you have the luxury of breathing optimum mix for each dive this becomes significantly pronounced over a weeks diving.
Recreational facilities may only provide standard gases, which generally means Nx32 or Nx36.
I have certainly done my 'shallow' second dive on a rich / optimum mix to flush Nitrogen so that the following morning I can maximise my dive time. [A typical behaviour in Scapa.] Yes, if I avoided the second dive altogether, I would have had more time available than if I did the second dive on an optimum Nitrox mix. But I am on holiday, with limited time and opportunity, so I am maximising my dives.
Which is back where we started.



[*] This is somewhat academic these days for me. Most of my dives are on CCR, so I am always on optimum mix

Okay, I assumed all deco schedules reduced a critical amount of nitrogen, but you’re say because the gas is enriched it leaves less residual nitrogen and so lessens the surface interval, if that’s true would breathing 100% O2 on the surface also reduces the surface interval?

 

[boulderjohn]

Okay, I assumed all deco schedules reduced a critical amount of nitrogen, but you’re say because the gas is enriched it leaves less residual nitrogen and so lessens the surface interval, if that’s true would breathing 100% O2 on the surface also reduces the surface interval?

Absolutely!

The problem is there is no good way to measure it--and there should be.

When I am done with most of my technical dives, I have a long drive home with significant increases in altitude spread out over time. I take my oxygen bottle from my last dive, put it in the front seat, and breathe it for at least an hour as I drive.

When I reach the surface, my Shearwater computer assumes I am breathing air, and it gives me no other option. It would be a piece of cake for them to add code that allows me to identify a different breathing mix and track my tissue off-gassing accordingly, just as it does under water, but they will not do that, I assume because it has not been studied.

 

[Divin'Papaw]

Okay, I assumed all deco schedules reduced a critical amount of nitrogen, but you’re say because the gas is enriched it leaves less residual nitrogen and so lessens the surface interval, if that’s true would breathing 100% O2 on the surface also reduces the surface interval?

Of course. This is exactly why putting a suspected DCS victim on 100% O2 is an urgent, primary treatment.

 

[Degenerate]

Millions of divers are still being trained this way here in Europe, in Italy, France, Spain, UK, Germany, etc....

I'm going to call massive BS on that one.
There is no way that millions of people are being certified in Europe for backgas deco on air, there is just no way.
I would bet a lot of money on the fact that a very large majority of newer divers go the PADI route or something similar, in the large scheme of things very few divers get their certifications from a club with CMAS or something similar.

 

[Gareth J]

Okay, I assumed all deco schedules reduced a critical amount of nitrogen, but you’re say because the gas is enriched it leaves less residual nitrogen and so lessens the surface interval, if that’s true would breathing 100% O2 on the surface also reduces the surface interval?

I do not understand your question.

I am trying to say, the lower the amount of Nitrogen in the breathing gas, the longer it takes for the diver to reach the saturation level that stops him/her ascending directly to the surface. (for a given depth)

Your second point. If you where to breath oxygen after a dive on the surface, it would flush the nitrogen quicker from the body, than if you where breathing air is correct.
This technique is used by pilots and NASA (as mentioned previously by both myself and @boulderjohn ).
So, yes, you could reduce your surface intervals by breathing 100% oxygen at the surface. (If you had a computer or software that would allow this) .

 

[Storker]

Sorry I as unclear

No worries

 

[Celt]

Of course. This is exactly why putting a suspected DCS victim on 100% O2 is an urgent, primary treatment.

I always assumed surface oxygen was given to prevent further damage from DCS and it wasn’t until recompression on O2 could DCS be treated

 

[boulderjohn]

I'm going to call massive BS on that one.
There is no way that millions of people are being certified in Europe for backgas deco on air, there is just no way.
I would bet a lot of money on the fact that a very large majority of newer divers go the PADI route or something similar, in the large scheme of things very few divers get their certifications from a club with CMAS or something similar.

According to the last PADI statistics I saw a few years ago, for the last decade, they had been averaging a little over 900,000 certifications a year world-wide for about a decade. That's all certifications at all levels.

I have seen statistics suggesting that PADI accounts for something like 80% of all certifications. I have also heard "behind the scenes" that PADI thinks the number might be higher but does not want it to be anywhere near that high because of fears of anti-trust legislations in certain areas. They would actually prefer to have more competition.

All the truly major agencies in terms of OW certification numbers are members of the WRSTC; PADI is only one of them. None of the WRSTC members teach decompression as a part of OW training.

So, without seeing the actual numbers (which are not published to my knowledge), I, too, find it hard to believe that CMAS and BSAC are together certifying millions of divers to do decompression at the basic level.