While we're at it, I don't understand what happens to all the oxygen I don't metabolize, either. When you listen to nitrox as commonly explained, the nitrogen isn't there to dissolve in your tissues to bubble out later. While the oxygen it's replaced with just... isn't.
Dangerous lies?
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While we're at it, I don't understand what happens to all the oxygen I don't metabolize, either. When you listen to nitrox as commonly explained, the nitrogen isn't there to dissolve in your tissues to bubble out later. While the oxygen it's replaced with just... isn't.
The general thinking on nitrox and narcosis is that it makes no difference. According to the prevailing theory on the causes of narcosis, oxygen should be more narcotic than nitrogen. The fact that some of it is metabolized makes it hard to predict, and you can't easily test high O2 levels for narcotic potential because of the danger of toxicity. All courses I know of teach that nitrox is just as narcotic as air.
I did hear of a recent study that suggests otherwise, but I don't have a link for it.
A treatise on the theory that you can extend your bottom time with nitrox OR dive more safely with nitrrox, but not both.
It is obvious that you can extend your bottom time with nitrox.
The theory behind the safety benefit always says to dive with nitrox but to air limits. For example, let's say I did 2 dives with a 1 hour surface interval, with the first one to 110 feet and the second one to 60 feet. I use nitrox 32 for the first one and nitrox 36 for the second, but I dive both using the PADI air tables. Diving on air, my first dive time limit would be 16 minutes, and I would be in pressure group M. After one hour, I would be in pressure group D. My maximum bottom time for the second dive would be 39 minutes, after which I would be in pressure group W. If I did those dives for the same lengths of time using those nitrox mixes, I would end the first dive in pressure group K. After 1 hour, I would be in pressure group C. After the second dive, I would be in pressure group O, which is quite a bit farther from limits than the air dives.
The reason people say that you can't get more bottom time AND more safety assumes that the diver on nitrox will dive to the limits of the NDL nitrox, too. If that were true, there would indeed be no safety advantage. But there is no requirement that people dive to those limits on nitrox; in fact, I would say they usually don't.
Let's do the above dives using the nitrox but doing the dives for the lengths of time we see on typical single tank dives.
The NDL for the first dive on EANx 32 is 25 minutes, but most people don't have the breathing capacity to last that long on a single tank dive, so let's say the diver ascends after 20 minutes--adding 25% more bottom time compared to the air limits. This puts the diver in pressure group M--the same as the air diver. After 1 hour, the diver would be in pressure group D, again the same as the air diver. For the second dive, the nitrox diver has a maximum time of 92 minutes, but he isn't going to last that long on a single tank at that depth. He ascends instead after 50 minutes.He is now in pressure group R.
In summary, the air diver got a total of 16 + 39 = 55 minutes of bottom time, and ended in pressure group W. The nitrox diver got a total of 20 + 50 = 70 minutes, more than 25% more bottom time. That diver ended in pressure group R. He would have had to stay in the water another 25 minutes on the second dive to get to the same level as the air diver.
It seems to me you can indeed get both extended bottom times and greater safety.
It is obvious that you can extend your bottom time with nitrox.
The theory behind the safety benefit always says to dive with nitrox but to air limits. For example, let's say I did 2 dives with a 1 hour surface interval, with the first one to 110 feet and the second one to 60 feet. I use nitrox 32 for the first one and nitrox 36 for the second, but I dive both using the PADI air tables. Diving on air, my first dive time limit would be 16 minutes, and I would be in pressure group M. After one hour, I would be in pressure group D. My maximum bottom time for the second dive would be 39 minutes, after which I would be in pressure group W. If I did those dives for the same lengths of time using those nitrox mixes, I would end the first dive in pressure group K. After 1 hour, I would be in pressure group C. After the second dive, I would be in pressure group O, which is quite a bit farther from limits than the air dives.
The reason people say that you can't get more bottom time AND more safety assumes that the diver on nitrox will dive to the limits of the NDL nitrox, too. If that were true, there would indeed be no safety advantage. But there is no requirement that people dive to those limits on nitrox; in fact, I would say they usually don't.
Let's do the above dives using the nitrox but doing the dives for the lengths of time we see on typical single tank dives.
The NDL for the first dive on EANx 32 is 25 minutes, but most people don't have the breathing capacity to last that long on a single tank dive, so let's say the diver ascends after 20 minutes--adding 25% more bottom time compared to the air limits. This puts the diver in pressure group M--the same as the air diver. After 1 hour, the diver would be in pressure group D, again the same as the air diver. For the second dive, the nitrox diver has a maximum time of 92 minutes, but he isn't going to last that long on a single tank at that depth. He ascends instead after 50 minutes.He is now in pressure group R.
In summary, the air diver got a total of 16 + 39 = 55 minutes of bottom time, and ended in pressure group W. The nitrox diver got a total of 20 + 50 = 70 minutes, more than 25% more bottom time. That diver ended in pressure group R. He would have had to stay in the water another 25 minutes on the second dive to get to the same level as the air diver.
It seems to me you can indeed get both extended bottom times and greater safety.
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They both have the same mass, but which is more comfortable to stuff your pillow with? For the same depth and bottom time, nitrox will leave you further from your NDLs. Ergo, safer. Regardless of the table used, for the same depth and bottom time, diving nitrox will result in less uptake of nitrogen in your tissues.
First, understand that we don't have lots of experience, so no judgements please. So we are doing 4 days of diving next week. I bought a Nitrox package that covers all the dives. But I noticed that one of the dives is 130 fsw - a wreck. The MOD of Nitrox 32 according to my computer is 110. So, I am thinking that we will opt for air during this dive. Does this make sense? It seems like a no-brainer but looking to my more experienced forum members to confirm.
kafkaland
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Not dangerous, just fun: having a full cave card doesn't mean you're OW certified. Happened to me a few weeks ago on a dive boat. They asked for my c-card, and as usual, I produced my highest, Full Cave. And the DM checking the cards insisted on an OW or AOW cards - nothing "funky" like what I had. Now, it was an IANTD card, but not an instructor card or I would understand his problem given what's currently going on with that agency (just being snarky here).
gfaith
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An advantage, not often considered, when ascending on Nitrox vs air we have reduced the partial pressure of nitrogen during the ascent. Thus off-gassing slightly faster.
"Deco for Divers" Mark Powell page 99
"Deco for Divers" Mark Powell page 99
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I personally still adhere to the 1.6 MOD theory, but only because I'm a fossil and I've been happily diving 1.6 since I discovered nitrox. If I were your instructor, I would tell you not to exceed 1.4 PO2 because..... I don't know, the certification agencies tell me to tell you that. That's why I don't teach nitrox. But what I'd really tell you is don't go deeper than 100 feet on 32, you don't have lots of experience.
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