When to use different EANx Mixes?

[Michael Kazma]

Except that's not what you yourself said:



which implies that if you don't "know what Dalton's diamond is" then you can't do the rest.

You sound like my wife

To clarify.......To dive nitrox you need to know the 3 equations (which are simplified in dalotons diamond/triangle (TDI uses the triangle and IANTD uses the diamond)). Thank you and good night.

 

[disbelief]

Forgive the hijack, but I figure we're done on the entry-level nitrox issue. (No doubt someone will prove me wrong!)

O2 is for all practical purposes narcotic. The day to day differences in perceptions of narcosis far and away exceed the trival metabolism of O2 which might reduce the ppO2. The Myers_overton solubility rule actually suggests that O2 would be more narcotic than N2 but that seems to be a wash with metabolism.

This is a bit too definitive for my taste.
My current view (though I'm very open to persuasion!) is: the jury is out on O2 narcosis

Here's why:
The Myers-Overton hypothesis is just that, an hypothesis. It turns out that it's extremely difficult to test within the realms that affect us as divers. But to the extent that solubility in lipids is correlated to efficacy of binding to intracellular enzymes (which more recent evidence fingers as a candidate for better understanding breathing gas narcosis), MO might be a useful proxy.

This is a pretty good, and short, layman's summary of the evidence to date:
Diving Doctor - Diver Magazine

And here's a thread on one of the rebreather forums I found quite interesting, particularly with respect to us divers (including me) trying to be physicochemists:
How Narcotic Is Oxygen? - Rebreather World

What I would say is that while I've never experienced (or heard of) narcosis at 1.6 ata PO2 on rich FO2 mixes (i.e., low PN2), I don't discount the possibility of high PO2 potentiating high PN2 narcosis).

In other words, O2 narcosis at recreational depths/mixes? I'm prepared to discount the possibility.
O2 potentially increasing the narcotic effect of high PN2 on mix? Unproven, but maybe. Certainly enough doubt for caution to suggest including O2 in END calcs and upping the He.

 

[MauiScubaSteve]

You sound like my wife

To clarify.......To dive nitrox you need to know the 3 equations (which are simplified in dalotons diamond/triangle (TDI uses the triangle and IANTD uses the diamond)). Thank you and good night.

Your posting style is still a work in progress.

I did my IANDT Instructor crossover in the spring of '01. My Instructor Trainer was Dick Rutkowski.

My IANTD Nitrox Manual; Complete Guide to Nitrox Diving (rev 10/96) uses a T, with Pg on top of the T, Fg in shall we say the "left arm pit" and P in the "right pit."

My IANDT Enriched Air Nitrox Diver; Student Manual and Workbook (rev 8/97) uses a Circled T.

My hand written notes from the lectures by the agency founder, author of both above manuals, IT #001, only include one equation; Pg = Fg x P; no geometric shapes on that page. Perhaps that is because Hyper Dick knew I understood algebra?

My IANDT Sport Diving Instructor Manual, written by Bill Nadeau & Don Townsend, is a 10/99 1st edition. The text with regards to Dalton's Law in the Nitrox section says "using the T illustrated above" and the Illustration is a "circled T" (slide 28) just like the Student Manual and Workbook listed above. Interestingly, I now see that in the Advanced Nitrox section, slide 19 looks to be a typo, with P on top.

Anyway, I no longer have the extra money for multiple Instructor Memberships and have not renewed my IANDT Advanced Nitrox Instructor rating in a few years. You may be right that IANTD now mandates using a diamond, but that does not mean all experienced IANTD Nitrox divers have heard or care about Dalton's Diamond.

 

[Michael Kazma]

Your posting style is still a work in progress.

I did my IANDT Instructor crossover in the spring of '01. My Instructor Trainer was Dick Rutkowski.

My IANTD Nitrox Manual; Complete Guide to Nitrox Diving (rev 10/96) uses a T, with Pg on top of the T, Fg in shall we say the "left arm pit" and P in the "right pit."

My IANDT Enriched Air Nitrox Diver; Student Manual and Workbook (rev 8/97) uses a Circled T.

My hand written notes from the lectures by the agency founder, author of both above manuals, IT #001, only include one equation; Pg = Fg x P; no geometric shapes on that page. Perhaps that is because Hyper Dick knew I understood algebra?

My IANDT Sport Diving Instructor Manual, written by Bill Nadeau & Don Townsend, is a 10/99 1st edition. The text with regards to Dalton's Law in the Nitrox section says "using the T illustrated above" and the Illustration is a "circled T" (slide 28) just like the Student Manual and Workbook listed above. Interestingly, I now see that in the Advanced Nitrox section, slide 19 looks to be a typo, with P on top.

Anyway, I no longer have the extra money for multiple Instructor Memberships and have not renewed my IANDT Advanced Nitrox Instructor rating in a few years. You may be right that IANTD now mandates using a diamond, but that does not mean all experienced IANTD Nitrox divers have heard or care about Dalton's Diamond.

Wow, you are all being so picky!
Let me rewrite my DIAMOND post. Know the ******* equations! I teach IANTD through trimix courses and the slides include all equations and I LIKE the diamond
My whole point was that a nitrox diver needs to know the 3 equations some how. If anyone disagrees on this then please post on this belief and not on the way divers should be taught them.

I still believe that if a diver is not taught how to calculate MOD, "Perfect mix" and PO2 in a nitrox course then they have not been taught what the NEED to learn.

 

[Rainer]

My whole point was that a nitrox diver needs to know the 3 equations some how.

If you've had a middle school math class, you just need to know one equation.

 

[rjack321]

Certainly enough doubt for caution to suggest including O2 in END calcs

Very long winded way of agreeing with me (I think, its hard to tell what you personally recommend). EAN32 is for all practical purposes just as narcotic as air. Trying to measure a 11% reduction in "narcosis" at 4ata is impractical and there's too much variability to really know so you might as well skip the nitrox ENDs and just call it equal to air.

 

[TSandM]

grammatical, if you are still reading this, I just want to say that your insight is correct . . . as your dives get deeper, the gas you can use must be less and less enriched, and the additional no deco time you get from using it is shorter and shorter. Nitrox is most useful, in terms of payoff in bottom time for money invested, in about the 80 to 110 foot range -- which just happens to be where 32% is really your best mix.

There are a lot of arguments about calculating "best mix" versus using a standardized gas for a depth range, but to me, the benefits of standardizing on 32% outweight the disadvantages. It's a gas that's good to 110 feet, gives you substantial improvement in bottom time in the 75 - 100 foot range, is banked by quite a few dive shops or operators -- and those who don't bank it, are used to mixing it. If I don't use today's tank for some reason, the gas will be good for a wide range of sites on another day.

 

[Hepcat62]

Here is an example: A diver plans a 95fsw (29m) dive.

Best mix would be 28% which gives a pO2 of 1.4 ata, END = 150fsw

You might want to check your formula for END again. Of the two common variants I'm aware of (depending on whether you consider O2 narcotic or not), neither should produce an END that is deeper than the actual depth.

 

[disbelief]

Very long winded way of agreeing with me (I think, its hard to tell what you personally recommend). EAN32 is for all practical purposes just as narcotic as air. Trying to measure a 11% reduction in "narcosis" at 4ata is impractical and there's too much variability to really know so you might as well skip the nitrox ENDs and just call it equal to air.

Actually, it's more a long-winded way of disagreeing with you

I do not agree with your earlier statement that 'O2 is for all practical purposes narcotic'. I believe it is at best unproven; and I think the thread I linked to previously
(How Narcotic Is Oxygen? - Rebreather World) gives a great summary of why.

What do I personally recommend? Avoiding definitive statements on the narcotic properties of oxygen.

 

[ianr33]

UPDATE: I passed the PADI test, but as most of you said, it seems that the instruction was not there. The PADI test was way too simple, all of it multiple choice. I would rather have the exam like the section reviews which require you to write the answer, or not have choices to choose from, especially when you are dealing with mathematical equations. Anyway, I will probably take the ANDI course next summer, or sooner if I find someone in my area teaching it.

I don't really see why you would need to do another course. Do some reading to fill in any gaps in knowledge .

Nitrox is not rocket science.

My suggestions: (How I use nitrox in practice)
Use 32% and a computer.
Do not go deeper than 111 feet. Do not go into deco.
Do that and you can forget about O2 toxicity (and your computer will track it anyway)

Anything deeper than 111 I generally just use air. If you do want to use nitrox at 130 then 28% will do just fine.