It is neither more or less safe.... it just poses different risks.
1. It reduces your nitrogen uptake.
2. If planned as air dives, provides a large amount of conservatism.
3. It has a max operating depth, that it is extremely unsafe to exceed.
4. Ox-Tox can occur within the MOD.
5. There is a cumulative %CNS loading that increases chance of Ox-Tox.
6. Most people forget the %CNS loading calculation, because it only figures on repetitive diving where you have higher PP02.
7. There are dangers with filling, storing and handling the tanks,
8. There is fire danger.
9. Some equipment (such as my Scubapro S600 Titanium regs) cannot be used with Nitrox because of fire/degredation risk.
Andy, you've given some reasonably good information in this thread ... but some of the above are, at best, misleading.
1. Is only true if you are talking about comparable dive profiles. And even then the partial pressure difference between 21% and 28% isn't significant enough to be a real concern for most no-decompression dives.
2. I think it would be more accurate to say it provides a "larger" amount of conservatism ... but on most recreational dives, that consideration isn't significant enough to make any real difference. But there is already so much "safety padding" in the algorithms used by dive tables and computers that it really wouldn't make any practical difference.
3. Since the max operating depth is at the limit of recreational diving, exceeding it on air is also unsafe, albeit for different reasons. But to be honest, if you're exceeding MOD on EAN28 as a recreational diver, you've got bigger issues than the gas that you're breathing ... especially for the typical recreational diver on an AL80.
4. Yes, ox-tox can occur within MOD ... but with hundreds of thousands of dives done on nitrox each year, you can count on one hand the incidences of it happening.
5. %CNS limits on EAN28 shouldn't be an issue, since you'll reach NDL long before that happens. And if a diver is exceeding NDL, a little extra oxygen in the gas they're breathing is hardly their biggest concern.
6. See #5. If you stay within NDL and recreational limits, it's extremely unlikely you will come anywhere close to your %CNS, either for a single dive or for the 24-hour limits.
7. That depends entirely on the method used to create the mix. Only in a partial-pressure blending method, where one is handling 100% O2, will this be a concern.
8. See #7. EAN28 is barely more combustible than air, and certainly not sufficient to be a concern under anything less than extreme conditions.
9. I don't use titanium regs (and consider them a total waste of money), but I do not believe that breathing EAN28 through a titanium reg causes any significant reaction to the metal. You need richer mixtures (above the 40% mandated as "safe" for recreational use) for it to be a concern.
I do not advocate people diving a mix they aren't trained to use ... ESPECIALLY since by implication they won't be analyzing it (which any nitrox diver should always do). But I don't think, under the correct conditions, allowing people to use a "slightrox" mix is going to create a bunch of dead divers either.
... Bob (Grateful Diver)
