But what about the people who dive with nitrox but dive to air limits? Aren't they safer? In theory, yes they are. If you tell your computer you are on air, but you are really on nitrox, you are somewhat safer in terms of DCS. How much? Well, the likelihood of getting DCS on an air dive is something like 0.002%. (I am making that number up--don't quote it.) If you dive on nitrox but on air standards, you may well be able to cut that risk to 0.0017. Congratulations! Yes, it is safer, but to a statistically insignificant degree.
If you dive recreational nitrox (<40%), do it for the extra bottom time. If you want to be safer, it is a whole lot easier (and cheaper) to keep your dive time farther away from the NDLs.
Actually, statistically there is no difference. There also isn't any statistical difference in safety from keeping your dive time further away from the NDLs. That's why the statistics are meaningless. According to the statistics, if you stay within the NDLs, ascend at the recommended ascent rate, maybe or maybe not do an optional "safety" stop, and stay hydrated, you will never get bent. Unless you're one of the statistical anomalies.
As you say, DCS within the NDLs is pretty rare. It's usually chalked up to dehydration, simply because the hyperbaric doc needs to tell his patient something and "I dunno why" doesn't sound very professional.
If, and that's a big if, dehydration is the cause of these otherwise "undeserved" hits, doesn't it make sense that less nitrogen in one's tissues would make one less prone to DCS because of dehydration? Physiologically, that's a big yes.
It has not been proven and it will likely never be proven, but I firmly believe that less nitrogen in one's tissues (and a higher PPO2 for offgassing during ascent and safety stop) can only help mitigate why might otherwise be factors leading to "undeserved" DCS hits such as dehydration, alcohol consumption, being fat and out of shape, and exercising and hot showers/tubs after diving. Just having 50% more oxygen with each breath (the difference between 32% and 21%) at the safety stop acts in a similar manner to using a tech diver's deco mix of 50% or 70% or 80% or 100%.
Being fat and out of shape, consuming lots of alcohol which tends to dehydrate one the next morning, exercising by being out of shape and carrying my heavy camera back and forth to the dock, and jumping into a hot shower or hot tub soon after the dive, I totally believe a tank or two a day of nitrox is well worth the expense for me to stay unbent. YMMV.
Now if you'd like me to prove my theory, please find me 1,000 fat and out of shape divers and the money to get them drunk every night, exercise and hot tub them, and dive half of them on nitrox using air tables and half on air for a week, four dives a day, I promise at least twice as many DCS hits among the air divers.
Otherwise, that's my theory and I'm sticking to it.
Besides, everyone knows nitrox tastes better.
