Posted by Ken Kurtis on October 28, 2000 at 21:33:06:
I took the liberty of moving this up as I thought it was an interesting point and it was getting awfully far down in the thread. We'll see if this discussion has any oomph left to it.
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(Eins posted) Ken Kurtis "The problem with this whole argument in general is that we're trying to show a reason for something that didn't happen (the bends) and there's simply no way to prove someone didn't get bent on a dive because they used nitrox, or that they would have been bent if they'd used air, or if they did get bent on air that they wouldn't have been bent if they'd dove on nitrox."
Ken,
I considered you as being a knowledgeable diver. But your statement surprises me. Are you saying that, following NDLs, the risk to get an undeserved (or unexpected) hit is the same, whether diving 100fsw or 75fsw (or even 81, for that matter)?
These are the EADs for a dive to 100 fsw with 36% or 32% Nitrox respectively. If you consider this not a significant safety margin, than I think I've got to adjust my image of you.
Eins
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The short answer is, yes, I know what I'm saying. Let me try to explain it to you in language that might make more sense.
Simply put, it's impossible to show a cause-and-effect for something that DIDN'T happen. If someone DOESN'T get bent on nitrox, that doesn't mean they WOULD have gotten bent on air. Conversely, if someone DOES get bent on air, there's no way to prove that they WOULDN'T have gotten bent on nitrox since there's no data (facts) to prove it one way or the other.
What you quoted is theory. "If you have less N2 in your body, you should be at a lesser risk of getting a hit." No argument. I never said that wasn't true. But what I AM saying is there's simply no way to take your theory and actually prove it to show what's right and what's wrong.
Let me try an analgoy. I just drove from our store in Beverly Hills to my home in Westwood without incident. Why wasn't I involved in a traffic accident? Was it because I took Wilshire instead of Olympic? Was it because I left at 7:45PM instead of 6PM? Was it because I put saline drops in my contacts and could see better so avoided problem situations? Was it because I had some stuff rattling around in the back of my car and slowed down to lessen the noise?
Can you PROVE to me why I wasn't involved in an accident? I think the answer is, no. Too many variables. To me, it's the same thing as trying to "proving" the nitrox argument one way or the other.
As far as the "statistically insignificant" statement, I think you're looking at the wrong end of the problem.
Karl Shreeves wrote an excellent (IMHO) article in the PADI Journal about a year and a half ago concerning nitrox and bends risk.
In round numbers, there are roughly 1000 bends cases reported to DAN yearly. It is assumed that there are 2 million "active" divers doing an average of 10 dives per year. So we have 20 million dives producing 1000 bends hits. That's a statistical rate of 0.0050%, or 1 hit per 20,000 dives. The number STARTS out statistically small. That's not to minimize the very real problem of a bends hit should it happen to you, but I think the numbers underscore that most people (somehow) manage to dive safely. And even if you look at this on a hits-per-diver basis, it's still only 0.05%. (And if you factor out the morons diving without tables or computers, the rate becomes even smaller.)
If we presume (and I'm making this number up) that nitrox gives you a 10% advantage, if everyone dove nitrox, we'd see 900 hits instead of 1000 for a rate of 0.0045% or 1 hit per 22,222 dives. In the world of numbers, gaining an extra 0.0005% edge is considered statisically insignificant.
Now I grant you, though, that if you're one of those 100 who doesn't get bent because you dove nitrox instead of air, then you'll be singing the praises of nitrox to all who will listen.
The marketing goal of the dive industry when we try to sell you nitrox (from a safety standpoint - and this is why I feel the "safety" issue is somewhat bogus) is to covince ALL of you that you're going to be one of the 100 and that you'd better start diving this stuff lest you get an undeserved hit.
It's sort of like diving's equivalent of a Ponzi scheme.
Ironically, there's a very easy way to get ALL the presumed "safety" benefits of nitrox without taking a class, without buying an extra gear, with using nitrox.
All you have to do is dive shallower &/or dive shorter. My air dive to 75 is the same (based on your statement and numbers) as your nitrox dive to 100. Should be the same relative risk, n'est pa?
But it seems that divers don't want to put limits on themsevles. We want to stay longer and go deeper with the same relative risk. And that's where I think the nitrox argument starts to lose a little steam.
Enough said. Time for dinner and then head for San Pedro. Lots more fun to actually go diving than to sit around and debate the merits of going diving. To quote Woody Allen from "Annie Hall", "Those that can - do, those that can't - teach, and those that can't teach - teach gym."
Ken Kurtis
NAUI Instr. #5936 (never a gym teacher)
Co-owner, Reef Seekers Dive Co.
Beverly Hills, Ca.