Not so, and the science is beginning to understand why there might be less fatigue.
Alternating Nitrox and Air dives ok on ProPlus 3?
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Thanks--if you quote the item to which you are referring, it helps. I thought you were responding to what I wrote.
As for what Freewillow wrote....
The "official" nitrox instructor response is that diving nitrox with an air profile does not make you safer. Actually, it does make you safer, but only so slightly that it is not statistically significant. Although it is impossible to estimate precisely the risk of DCS on a NDL dive, it is extremely low--I have seen the number 0.002% used with some frequency. If you improve your safety by 50%, then you have improved it to 0.001%. Congratulations!
The real reasons to dive with nitrox are to increase bottom times and decrease surface intervals. A couple of recent articles in Dive Training magazine inaccurately said that you cannot have both the added safety mentioned above and added bottom time--it is either one or the other. That is silly, as the following two dive profiles to the same depths with the same surface intervals using the PADI tables illustrate.
AIR DIVES:
Dive #1: 80 feet for 30 minutes--Finish in pressure group R
Surface Interval: 1 hour--Finish in pressure group F
Dive #2: 60 feet for 36 minutes--Finish in Pressure Group W
Total dive time = 66 minutes
Final Pressure group = W
EANx 36 dives:
Dive #1: 80 feet for 41 minutes--Finish in pressure group P
Surface Interval: 1 hour--Finish in pressure group E
Dive #2: 60 feet for 47 minutes--Finish in Pressure Group T
Total dive time = 88 minutes
Final Pressure group = W
The nitrox dives give you 22 more minutes of bottom time and finish you 3 pressure groups lower.
tarponchik
Contributor
Thank you!
Sure. We did this several times while shore diving cause you can plan your own dive, and will do again. With boats and liveaboards this can be questionable.
tarponchik
Contributor
Any references you can share? I can understand less fatigue while climbing Everest but underwater you already get more oxygen than your body needs. Also, the only fatigue I feel when diving comes from boat rides, long road drives or long surface swims. Diving from liveaboard gives me no more fatigue than watching TV, my butt on the sofa.
I'll look for some of the threads, but the essence of the argument is NOT about the O2, it is about more efficient off-gassing of N2 if the gas in your lungs has a lower percentage of N2, i.e. nitrox. Most of the technical discussion about nitrox is about the on-gassing phase...descent and bottom time. In this case the argument is about how you take up less N2 than you would on an equivalent air dive, because the PPN2 is less. If you stay to NDL on nitrox, then you've got the same amount of N2 in your tissues as you would on a shorter-NDL air dive, so it seems like there are no advantages other than the additional BT. However, while breathing nitrox, you are off-gassing more efficiently to get that N2 out of your body, because the N2-gradient into your lungs is more favorable for off-gassing. Less N2 in the body, less fatigue. it is the subclinical DCS argument...N2 makes you tired, so you are less tired if you can get rid of the N2 more efficiently. Not everybody feels tired after an air dive, or a series of air dives over several days; I do. Nitrox lets me do 4-6 dives a day on a liveaboard or a Bonaire-type place, which I can't do on air. I've tried it.
never heard on "undeserved" DCS hit. ? Every dive bears a statistical chance of getting a DCS hit. To dive Nitrox and follow a dive computor on air is just lowering your chances of getting a hit. You say 50% less chances. I know the chances are low, but no one can say that there is no difference.
Now Nitrox of gazing compared to air makes a very small difference if you are not doing long deco's. Then there is a clear advantage of doing deco with 50% or 100% 02. But now we start to enter into Tec diving
Now Nitrox of gazing compared to air makes a very small difference if you are not doing long deco's. Then there is a clear advantage of doing deco with 50% or 100% 02. But now we start to enter into Tec diving
I did say there was a difference, but it is not much. The wording was probably not clear, but I did not say it was 50%. I said IF it were 50%, then you would have reduced it from 0.002% to 0.001%, a pretty negligible difference. In reality, that difference will be nowhere near 50%, so the difference will be far less.
But it will be safer, just as it will be safer to wait until crossing a one lane road until there are no approaching cars with 150 yards than it would be to cross when they are no approaching cars within 125 yards. Your call.
In the standard instruction you find in the courses I know, they say that insignificant difference is not reason enough to pay for and use nitrox. It makes more sense to use it for the significantly increased bottom times and decreased surface intervals. (Yes, it can be one, the other, or both.) You are free to disagree and do what you want.
I never disagreed with you on anything. I know and understand that nitrox is used in order to increase bottom time. I simply said that you increase the "safety factor". You do not know by how much , so why would you want to start an argument?
Having said that, I have an issue with this statement of yours, giving the impression that what I wrote was wrong.:
"The "official" nitrox instructor response is that diving nitrox with an air profile does not make you safer. Actually, it does make you safer, but only so slightly that it is not statistically significant. Although it is impossible to estimate precisely the risk of DCS on a NDL dive, it is extremely low--I have seen the number 0.002% used with some frequency. If you improve your safety by 50%, then you have improved it to 0.001%. Congratulations!"
The deco procedures have been established on statistical occurences of DCS hits. I am not an instructor at your level, but the scientist that I am has a problem with the above statement. You just cannot say that it does not make you safer, then it does make you safer, then there is no statistical difference.
tarponchik
Contributor
This whole safer/safe/negligible/significant discussion is hardly worth pursuing, because it is totally wrapped in liability concerns and the statistics of very small sample.
It is similar to how fast can you safely ascend? PADI once upon a time said 60 fpm, then said, not not exceed 60, then said slower is better. As we learn more, we often change our rules-of-engagement. We now know that 60 was a SWAG by the USN as a compromise between 25 (favored by hard-hat divers being hand-cranked up on platforms) and 100 (favored by scuba divers); the compromise was necessary because ascent rate is a factor in calculating tables, which at the time were all done my hand on electric (not electronic!) calculators, and the USN did not want to make two sets of tables. We now know that 60 may be OK if deep, but 30 is better as you get nearer the surface, and 10-15 might be even better near the surface (anybody take one minute to surface from their safety stop?). But PADI can't now publish that 30 is the safe ascent rate....because what about the liability from all those years they said 60? So we've now got, 60 is a maximum, or slower if that is what your computer says (and of course, they all do say slower!).
So if using air within the NDLs is safe, how can you be safer than safe? If nitrox is published as safer, what about all those people trained on air? If the incidence of DCS is primarily dependent on things like ascent rate and hydration (c.f. DAN), then why worry about the less important things like air vs nitrox? Neal Pollock, in his lectures on Decompression safety, Lists 25 factors that are involved; one of them is the gas used.
It is similar to how fast can you safely ascend? PADI once upon a time said 60 fpm, then said, not not exceed 60, then said slower is better. As we learn more, we often change our rules-of-engagement. We now know that 60 was a SWAG by the USN as a compromise between 25 (favored by hard-hat divers being hand-cranked up on platforms) and 100 (favored by scuba divers); the compromise was necessary because ascent rate is a factor in calculating tables, which at the time were all done my hand on electric (not electronic!) calculators, and the USN did not want to make two sets of tables. We now know that 60 may be OK if deep, but 30 is better as you get nearer the surface, and 10-15 might be even better near the surface (anybody take one minute to surface from their safety stop?). But PADI can't now publish that 30 is the safe ascent rate....because what about the liability from all those years they said 60? So we've now got, 60 is a maximum, or slower if that is what your computer says (and of course, they all do say slower!).
So if using air within the NDLs is safe, how can you be safer than safe? If nitrox is published as safer, what about all those people trained on air? If the incidence of DCS is primarily dependent on things like ascent rate and hydration (c.f. DAN), then why worry about the less important things like air vs nitrox? Neal Pollock, in his lectures on Decompression safety, Lists 25 factors that are involved; one of them is the gas used.
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