Nitrox course. What's the point?

[Gareth J]

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

100% O2 has a number of benefits.

1. It improves the pressure gradient, between the Nitrogen in the tissues, and the Nitrogen gradient in the surrounding tissues and blood, encouraging Nitrogen to diffuse faster into the surrounding tissues and blood and be expired.

So it helps you get rid of the Nitrogen quicker and reduce the bubble size quicker. Potentially returning circulation to areas impeded by the bubble(s)

2. It saturates the blood and surrounding tissues with 100% oxygen. This allows oxygen to perfuse past the restriction and oxygenate (some) of the surrounding tissue. Reducing tissue oxygen starvation down stream of the restriction.

3. It compensates for limited efficiency of the lungs and circulation system, where the lungs or circulation system have been damaged.

I am sure someone else will add to this.

NOTE
There is often an apparent worsening of the situation when a diver suffering from DCI is put on 100% O2. Ignore this.
Gas them Hard and gas them quick.
Do not ration O2.

Never forget Administering O2 is ONLY A FIRST AID TREATMENT, you still need to evacuate them to a hyperbaric facility and medical care.

Remember if you are out of O2 use the next richest Nitrox.

 

[boulderjohn]

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

Oxygen therapy under pressure is much better for treating DCS than oxygen therapy without pressure, but in either case the oxygen therapy is doing the job of eliminating nitrogen from the system.

 

[tursiops]

I always assumed surface oxygen was given to prevent further damage from DCS

Yes, but not only. The surface O2 also helps eliminate excess N2 from the tissues.

 

[Angelo Farina]

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.

Ok, "millions" is of course just a rhetoric figure.
But CMAS or BSAC affiliated clubs make diving courses in almost every european city, all the year around, at prices which are roughy half of PADI, and borrowing you the equipment for free for the course. People interested into diving usually choose the cheapest option.
PADI is strong only in diving resorts, when people are on holidays and find that in their hotel or resort there is a diving center, and they want to try it. When back at home, usually people understand how poor was the training, and if they did like the experience, they continue with a longer, serious course in the local diving club. So yes, PADI makes a good business on holidays location, not in European towns.
I have no figures comparing the number of OW certifications released every year in Europe, but I suppose that the two numbers are not very different.
In UK I am told that BSAC is well ahead of PADI in the number of divers trained each year...

 

[EFX]

Will the computer not tell both divers to slow if there ascending to quickly, in other words control the assent so they are both offgasing enough

Yes, the computer will alert the diver if ascending too fast but that does not come from anything built into the algorithms to determine NDL or deco stops. Ascent rates are set constants programmed in by the manufacturer to inform and alert the diver should ascent rates be too fast. The computer will calculate tissue loading and in turn the proper deco stop depth and time regardless of ascent rate. The consensus of 30 fpm (or slower at shallower depths) comes from the dive science to prevent AGE and possible DCS should the fast tissues become overwhelmed.

 

[Blackcrusader]

As someone already stated, diving is in general very safe (that is, very low risk calculated as a ratio between accidents and dives). And most dives are made by vacation divers, so they are in theory very safe according to that definition of risk.

So what exactly do you mean with safe?

Yes and my post mentions that when I do vacation dives I do not do gas planning. Some people will say this is not safe and we must all gas plan our dives and stick to the dive plan regardless of it being a recreational dive. There is no real dive plan except don't exceed NDL run out of air follow the guide or do your own dive and enjoy yourselves on vacation dives. For me diving has been a pretty safe activity.

 

[David Novo]

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.

Ok, "millions" is of course just a rhetoric figure.
But CMAS or BSAC affiliated clubs make diving courses in almost every european city, all the year around, at prices which are roughy half of PADI, and borrowing you the equipment for free for the course. People interested into diving usually choose the cheapest option.
PADI is strong only in diving resorts, when people are on holidays and find that in their hotel or resort there is a diving center, and they want to try it. When back at home, usually people understand how poor was the training, and if they did like the experience, they continue with a longer, serious course in the local diving club. So yes, PADI makes a good business on holidays location, not in European towns.
I have no figures comparing the number of OW certifications released every year in Europe, but I suppose that the two numbers are not very different.
In UK I am told that BSAC is well ahead of PADI in the number of divers trained each year...

I may be wrong, but, regarding new certifications, CMAS share seems to be residual in Portugal.

 

[EFX]

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.

I don't think the issue is lack of knowledge but a legal issue that's stopping them. The computer doesn't care you are on the surface. (The Shearwater Perdix stores the pre-dive surface pressure). For all practical purposes when you are back on the surface the computer continues to calculate tissue loading. You are essentially "still diving" but on the surface. The slowest tissue compartments are still off-gassing and may still be off-gassing days later. So, using 100% O2 on the surface is essentially accelerated deco for the surface dive. The problem comes from making sure divers select air once they're done with the surface O2. Neglecting to reset the gas back to air will cause the computer to calculate all tissue compartments to zero inert gas load which screws things up for the next dive. It will assume you have less inert gas loading than you actually have, highly increasing the probability of a DCS hit. In contrast, a diver on 100% O2 decompressing in the water, the computer will automatically select air after surfacing because it "knows" the in-water dive has ended.

 

[boulderjohn]

I don't think the issue is lack of knowledge but a legal issue that's stopping them. The computer doesn't care you are on the surface. (The Shearwater Perdix stores the pre-dive surface pressure). For all practical purposes when you are back on the surface the computer continues to calculate tissue loading. You are essentially "still diving" but on the surface. The slowest tissue compartments are still off-gassing and may still be off-gassing days later. So, using 100% O2 on the surface is essentially accelerated deco for the surface dive. The problem comes from making sure divers select air once they're done with the surface O2. Neglecting to reset the gas back to air will cause the computer to calculate all tissue compartments to zero inert gas load which screws things up for the next dive. It will assume you have less inert gas loading than you actually have, highly increasing the probability of a DCS hit. In contrast, a diver on 100% O2 decompressing in the water, the computer will automatically select air after surfacing because it "knows" the in-water dive has ended.

I have no idea how to tell my Shearwater computers that I am breathing O2 at the surface. Please tell me how to do that.

 

[Gareth J]

100% O2 has a number of benefits.

1. It improves the pressure gradient, between the Nitrogen in the tissues, and the Nitrogen gradient in the surrounding tissues and blood, encouraging Nitrogen to diffuse faster into the surrounding tissues and blood and be expired.

So it helps you get rid of the Nitrogen quicker and reduce the bubble size quicker. Potentially returning circulation to areas impeded by the bubble(s)

2. It saturates the blood and surrounding tissues with 100% oxygen. This allows oxygen to perfuse past the restriction and oxygenate (some) of the surrounding tissue. Reducing tissue oxygen starvation down stream of the restriction.

3. It compensates for limited efficiency of the lungs and circulation system, where the lungs or circulation system have been damaged.

I am sure someone else will add to this.

NOTE
There is often an apparent worsening of the situation when a diver suffering from DCI is put on 100% O2. Ignore this.
Gas them Hard and gas them quick.
Do not ration O2.

Never forget Administering O2 is ONLY A FIRST AID TREATMENT, you still need to evacuate them to a hyperbaric facility and medical care.

Remember if you are out of O2 use the next richest Nitrox.

Sorry for quoting myself. I added a bit to the bottom, which is important and relevant.
I would strongly recommend, if you have the opportunity, attend an O2 administrating course.