And what does Random House have to say about "margin of safety"?

And what you don't seem to understand is that you do NOT reduce risk by
increasing "margin of safety".

You can make, or call, your margin of safety whatever you want. Call it
8343478135987567.233575 increase it to 2332157243467284690819158.2

Your risk remains the constant risk of diving within the tables, the sum
of undeserved hits plus heart attacks plus giant octopus plus rogue
submarines plus whatever other risks there are underwater. And that
number has been published by DAN.

There is NO margin of safety until risk has stabilized, right?

Once risk has stabilized, what is the advantage of increasing "margin of
safety"??????

esg

Man, has this thread ever gone on a long time. Try this, and perhaps it'll
clear up a bit. Your statement is like all of the following. They are all
true, but they all are conditioned specifically on dealing with the risk
they address. There's never any risk if you always avoid all risks.
There is no risk of DCS as long as you don't go deep enough for long enough
for nitrogen in your system to be a problem.
There is no risk of Narcosis as long as you don't go deep enough for the
nitrogen in your system to be a problem.
There is no risk of oxygen toxicity as long as you don't go deep enough for
long enough for the oxygen in your system to be a problem.

Using nitrox adds a toxicity risk within the range normally considered to be
recreational.  You can tox at less than 130 feet, and die. That risk does
not exist, in the recreational range, if you're breathing air. Nobody said
the risk is not manageable. We only said that you can't manage it if diving
like you're on air. If you observe the mod for the gas you're breathing,
you're not diving like you're on air,  you're diving like you are on nitrox.
Hopefully, that's enough to end the toxicity debate.

Let's try the DCS risk issue.

There is no safety advantage at all to limiting yourself to no deco limits
for air while using nitrox if you add a bit of conservativeness to your
nitrox profile and nobody I know that is not specifically planning a deco
dive, recommends pushing your depth and times right to the maximum, on
nitrox or otherwise. If you leave yourself a reasonable margin, you are just
as safe diving nitrox as nitrox as you are diving nitrox as air, maybe
safer. Don't believe it, here's the evidence:

My Oceanic Computer, for which I have a simulator, gives a no deco limit at
100 feet on air, of 19 minutes. In a simulated dive, it enters the caution
zone after about 10 minutes. That's a 9 minute, or 47% margin to account for
conditions and mistakes, a pretty significant number.

The same computer allows me 31 minutes at 100 feet on 32% and enters the
caution zone after about 15 minutes. That's a a 16 minute or 51% margin to
account for conditions and mistakes, an even more significant number.

Diving on nitrox, to the same limits as though you were using air, you're
diving 9 minutes on a gas good for 31, providing a 22 minute or 71% margin.

Air limits on air - 10 minute dive - 47% margin - safe enough for me.
Nitrox limits on Nitrox - 15 minute dive - 51% margin - safe enough for me &
a 50% increase in dive time for a small cost increase.
Air limits on nitrox - 10 minute dive - 71% margin - safe enough for me, but
no benefit for the higher cost.

Let's look one more time. Assuming that, since your're not really at your
caution zone limit on nitrox after 10 minutes, you decide to push air limits
to the max. After all, you still have a margin, you're breathing nitrox. Are
you as safe as you would be breathing nitrox as nitrox and leaving a
reasonable margin? Nope. Here's the math. The max for air at 100 feet is 19
minutes. The caution zone for nitrox is 15 minutes. Breathing air to the max
provides a smaller margin for error than breathing nitrox to a reasonable
limit.

Mike and I are arguing about how many angels can dance on the head of a pin.
We like to argue about such things, and do so without getting mad.  Everyone
else is arguing on a much broader, much more realistic basis, and,
practically speaking, Mike's right.

1. Diving on air, to air limits, with a reasonable margin for error, is
safe.
2. Diving on nitrox, to nitrox limits, with a reasonable margin for error,
is almost exactly as safe.
3. Diving on nitrox, to air limits, with a reasonable margin for error
relative to the air limits, adds no safety, but does add expense.
4. Diving on nitrox, to maximum air limits, with no margin for error
relative to the air limits, nets a smaller margin of safety than diving on
nitrox to reasonable nitox limits.

Is this registering with anyone yet?

Is it time to talk about guns, religion or politics yet?

Lee

<snip>

Actually, one must also observe the CNS clock, which most of us have
been ignoring during this discussion but which is nonetheless important.
 (I forget who posted something about it, but it's a pertinent point.)

What's the mod for 32%? Is it 111 fsw, 122 fsw, 132 fsw, 173 fsw, or
something else?

. . . and time, and mix, and acceptable PPO2, and how much margin is enough
relative to each.

"Sheldon" <sheldon@XXXXXXXXsopris.net> wrote in message

 What risks?

 Isn't diving nitrox safer than diving air...?

That's correct:  what you "hit" is a higher risk of OxTox.

FYI, we had three divers yesterday hit 125fsw while on 32.6%.

Not my point.  My point is that it is irresponsible to try to wave a
magic wand and assume that certain risks can magically be ignored.

Controlling depth to keep to within one's planned MOD is a risk
*management* strategy.  And that's all that it is.

The fallacy of "dive Nitrox as if it were air" is that the Rec Limit
for Air is 130fsw, which at the concentration limit for recreational
nitrox of 40% results in a dangerously high PPO2.   As such, the
reality is that you can't safely dive Nitrox as if it were air, but
have to impose additional constraints.

Thus, you're spending more money for a smaller dive envelope, so where
are the objective benefits of doing so?  Nowhere, since undeserved
hits are constant.  This is why diving Nitrox on air limits is
illogical.

-hh

Obviously, you've never been in a bar fight.

Ummm, if I'm in the bar, the chances of my getting into a bar fight
approximate the chances that Popeye will get into one. Actually, they're
slightly lower. Over the years, I've had all the bar fights I desire. Popeye
is unlikely to get in one and even if he does, I'm unlikely to participate
unless it looks like he's about to get an ass-whooping. It's always a good
idea if someone stays out of jail and available to arrange bail.

Being in another room of the bar, reduces the odds of my being in a fight.
Being in the bathroom reduces them further. Being outside the front door
reduces them even more. Being miles away makes the odds negligible, unless
Popeye, or someone else in the bar calls for help. Enough miles, makes it
pretty certain that I won't enter into the fight if I can't get there before
it's done. On the other hand, it may increase the odds that I'll get in some
other bar fight. Ya never know.   Now, what were we talking about?

I recommend against it. If you're going to do it though, may I suggest
something more substantial than a mallet?

Lee

Maybe in the racing you guys did. In drag racing, a win was a win. Of
course, when the difference between a win and a loss is never more than a
few seconds and is often measured in thousandths of a second, it's hard to
build a point system to separate the easy win from the close call.

Lee

Over the years, he's made a few, but not enough to be worth remembering. The
bigger potential problem is information taken from his resource library out
of context. Most of what is in his library is not his work, it's a
collection of the work of others. Much of it, while still of significant
interest, is also dated and it's not like Greg never deceived by misquote,
out of context quotes or deliberate misdiretion.

Lee