Nitrox - Is it "worth it"?

[Bigbella]

And how much do you remember from those dives?

60 meters is >1.6 bar pPO2, above currently recommended max pPO2 for deco and significantly above currently recommended max pPO2 for the working phase of a dive. Just throwing out that tidbit of information. Not to mention the effect of >7 barA on gas density and the ability to vent CO2.

I recall them quite clearly. At the time, we were seeking a particular species of sea star (Patiria sp.) that some Canadian clients required for their experiments. When I had asked them about their knowledge of the animal, they said that the reference for their then current intertidal distribution was Between Pacific Tides by Ed Ricketts (of Steinbeck and Cannery Row fame) and Jack Calvin, whose original publication was in the 1930s. Their edition was far more recent: 1947. It was a challenge, at the time, to find sufficient quantities in the shallows.

We did, as I recall, ten or more dives, over sixty meters, during that period. Ironically enough, the only time that I felt the more common symptoms of nitrogen narcosis, was during a shallow twenty meter dive, while using antihistamines, in the 1980s -- a couple of martinis worth, in effect. At no time, during those deeper dives, did we have any confusion or inability to read our gauges; nor did we skip any required stops or experience any discomfort, along the way, save for the 10˚ water.

Diving to those depths, off Carmel, California, was fairly common at that time, regardless of the PO2 consequences; or any other statistical modeling.

The record for diving on air happens to be over 150 meters; just throwing that out . . .

 

[PBcatfish]

.... I've also been told that diving EAN is a good option if you get headaches. I got a nasty headache after my first dive one morning in Cozumel back in August and decided to not make the second dive. That headache was pretty debilitating and even made me a bit nauseous. I was told later that I'd have felt better had I switched to EAN. Not sure how much truth there is to that but increased oxygen intake to curb a headache sort of seems like it makes sense.....

The main benefit there may be that the extra O2 thins out the CO that got sucked into the compressor from the gas motor that was running it or from the local traffic. The last time I went to Mexico with the intent of diving, I got one look at the compressor they were using to fill the tanks & changed my game plan from SCUBA to free diving.

That paragraph has a bit of wise crack in it, but it also holds some truth. I do not know if nitrox benefits those who would have gotten a headache on regular air or not & I don't really believe that adding O2 to a CO contaminated tank would make things OK.

My real comment here is that I did not trust the air quality at the place I went to in Mexico. Even a little bit of contamination can give you a headache. A little more contamination can cause much bigger problems. Since you said that you got a headache in Cozumel, my next question would be - did you take a look at the compressor they were using & if so, what did you see? It would be nice to have had an analysis of the gas in that tank, but since it is not common practice to test every tank, even in well-developed & highly-regulated areas, I would not expect to have access to that kind of data

 

[1atm]

Adding extra O2 to counter the effect of CO contamination does NOT work.

The affinity of CO for hemoglobin is about 230 times higher than O2, and 60 times higher than O2 for myoglobin. What then happens - in a simplified manner - in the case of hemoglobin, once that CO is bound to it, hemoglobin cannot deliver the O2 anymore. To be more precise, if CO binds to one of the four available sites in a hemoglobin molecule, it changes the dissociation constant for the other three sites, ie it alters the property of the hemoglobin. The CO-poisoned hemoglobin can still bind O2 in its other three sites, but it will not release this O2 anymore. Consequently, that hemoglobin molecule is now “out of order”, and it will not deliver the O2 to the cells where it is needed.

If your thinking is that since hyperbaric oxygen is used to treat CO poisoning, then bear in mind that with this treatment the PO2 of the inspired gas goes up, while it contains no CO. When breathing from a contaminated tank, the pCO also goes up, so that would cancel out, Besides CO has also other adverse effects.

Long story short, you cannot compensate CO poisoned tanks with more oxygen/EAN. If there’s any indication of CO contamination, get fills elsewhere / stay away.

 

[Bert van den Berg]

Nitrox is not worth the effort or expense for me. This is a personal observation based on hundreds of dives over three years. The limitations on depth outweigh the advantages for me.

 

[BlueTrin]

Nitrox is not worth the effort or expense for me. This is a personal observation based on hundreds of dives over three years. The limitations on depth outweigh the advantages for me.

Nitrox (certification) is (often) a pre-requisite to Trimix classes, so that would limit you to air.

 

[Angelo Farina]

Nitrox (certification) is (often) a pre-requisite to Trimix classes, so that would limit you to air.

Trimix provides great benefits for going deep, below 50 meters.
Air is pretty fine for me, in the range of 35-50 meters.
I really do not see any reason for going down more than 50m, evaluating my age and my general fitness.
So Nitrox could be of some utility for extending the NDL just for medium-depth dives, in the 20-30 meters range.
Where indeed I can do well also with air: the NDL is shorter, but still long enough for most situation.
And even when there is need to exceed it, then you plan for some deco. I always considered that diving with a deco plan (and equipment) at 25-35 meters is safer than planning a NDL dive at the same depth.

 

[KenGordon]

Trimix provides great benefits for going deep, below 50 meters.
Air is pretty fine for me, in the range of 35-50 meters.
I really do not see any reason for going down more than 50m, evaluating my age and my general fitness.
So Nitrox could be of some utility for extending the NDL just for medium-depth dives, in the 20-30 meters range.
Where indeed I can do well also with air: the NDL is shorter, but still long enough for most situation.
And even when there is need to exceed it, then you plan for some deco. I always considered that diving with a deco plan (and equipment) at 25-35 meters is safer than planning a NDL dive at the same depth.

The trouble is that most divers are not adequately trained to do deco. Indeed if what they are going to do is largely shallower than 30 then nitrox will be a great help, especially if doing more than a couple of dives a day. Even if trained for deco, doing four dives a day on air is going make for some avoidable stops.

 

[Angelo Farina]

The trouble is that most divers are not adequately trained to do deco. Indeed if what they are going to do is largely shallower than 30 then nitrox will be a great help, especially if doing more than a couple of dives a day. Even if trained for deco, doing four dives a day on air is going make for some avoidable stops.

Four dives a day???
I barely can make one!
If I exceed in bottom time, I will make, say, 10 minutes deco, which is nothing really hard.
When young I did sometimes two dives per day, but I do not think this is good anymore, at my age. Not only for Nitrogen accumulation, but simply because I would be too tired. And during the day at the sea, I prefer to spend some hours doing some other nice things, like swimming/snorkeling, exploring around some new site with the zodiac, or having a good lunch and then sleeping on the beach, under a shadow.
Or pulling my sons doing "undwerater wing" or water-ski...
I did never understand those packages where you are on a boat for two days and half, doing 10-11 dives, and nothing else.
I did this just once in Cairns (Australia) in 2007, I will never do this again.
I prefer to rent a zodiac, and manage myself the whole day with my wife and my sons.
If they give me cylinders filled with Nitrox-32, I perceive it as an advantage only if the dive is in the 25-34m range, as this allows some more minutes on the bottom. But if the dive is shallower, there is no advantage.
And if it is deeper, then Nitrox suddenly becomes a strong limitation. So I can still enjoy the day with a cylinder of Nitrox-32, but if they give me air, instead, I am still happy, or perhaps even happier...
Also consider that usually we get 15-liters cylinders at 232 bars with double valves (and we use double regs), and we always stay together (usually diving just in 2, with the other two staying on boat, ready to help - then we swap, but on boat there are always two more cylinders with some air reserve). So a moderate deco is nothing alarming.

 

[1atm]

Four dives a day???
I barely can make one!

I did never understand those packages where you are on a boat for two days and half, doing 10-11 dives, and nothing else.
I did this just once in Cairns (Australia) in 2007, I will never do this again.

Well, some people like to make several dives a day, maybe even on consecutive days. On a liveaboard that would be quite common. In these cases, Nitrox is a huge benefit, because at the end of the week, the folks on air have NDLs of 10ish minutes while the Nitrox folk have 20s.

Fair that liveaboards or consecutive diving aren’t everyone’s cup of tea - to each their own. For single dives, Nitrox would give more NDL for those not deco trained, or add safety margin, as elaborated earlier in this thread.

 

[Angelo Farina]

For single dives, Nitrox would give more NDL for those not deco trained, or add safety margin, as elaborated earlier in this thread.

True, but just when depth is between 25 and 34 meters, which is a very shallow window. Probably just one dive ever 3 falls within it. I know people who never exceed 25m, while others always reach at least 40.
So, no one discussed the advantages of Nitrox, but they are effective just within that small window of depths.
And that is Nitrox 32. Nitrox 36 or higher has an even smaller window...