When to use different EANx Mixes?

[MXGratefulDiver]

Not explained. They just said that I should just read the book and if I have questions the instructor will discuss them with me. I should just take the exam then off I go. Good thing I told them that I want to do the dives!!!

... so in other words you didn't pay for a class ... you paid for a book and a c-card.

I don't care much for classes like that. EAN is a pretty easy class ... but an instructor is supposed to be providing instruction. That's why they call 'em that ... and why you pay them money.

Whether for this class or any subsequent ones, I'd find a different instructor ... in fact, a different shop since this one apparently feels that telling a student to "read the book" constitutes instruction ...

... Bob (Grateful Diver)

 

[muddiver]

I am almost finished with the PADI nitrox course, but I am wondering if people on this forum can give me some information about when to use different nitrox mixes. I don't think that the PADI course explains this issue very well.

Thanx.

Here is another twist on the answer to you question:

I think everyone is assuming you are only certified/trained to scuba dive with one cylinder and one breathing gas mix.

Another use for diferent gas mixes would be if you dive with a second cylinder for safety reasons, but on ascent you use it as a decompression mix.

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

Now assuming that the diver figured his gas consumption and has enough main gas supply for the dive with a bottom time of 30 min. but a plans to only spend 12 minutes at 95'.

To add safety to the dive a mix with a higher oxygen content can be used on ascent to speed up off gassing of Nitrogen (in theory).

For 100' and shallower a good ascent gas is 40%. The way it is used is that the diver leaves surface on the bottom mix (28% in this example), proceeds with the dive at the planned depth (95') and starts his ascent on the bottom mix until reaching the predetermined safe depth for the second mix of 40% (40% at 80' is a pO2 of around 1.4 ata).

The second mix has a pO2 of 1.6 at 99 fsw, so it can double as an emergency reserve as well as a decompression gas.

This example is within the limits of recognized recreational diving and No-Decompression diving limits, with the exception of the switch between gasses and is an example of when to use different Nitrox mixes.

I am typing this up from my office so there my be some errors because I don't have my diving library to reference right now.

 

[muddiver]

I am not aware of the narcotic equation, unless it is something different in the PADI book.

END = 10 meters X [(ppN2/fN2)-1] ppN2 = 4.0 maximum

What I did to calculate the depths is use the equations and use the DSAT table provided by PADI. I also used the RDP table for air and for the Nx32 and Nx36. Best mix, what I mean is that, for example, if you go 60ft for x number of minutes and are well within the NDL, how would you chose either x32 or x36. I know about the o2 levels, etc. to take into consideration, but at 60ft, for instance, if two people went to a depth of 60ft for the same amount of time (1 dive) why would one chose x32 over x36, and vice versa.

I'm sorry if I didn't explain this very well.

Breathing any gas in a hyperbaric environment (i.e. breathing Nitrox underwater) has a number of physiological effects. Oxygen toxicity is only one of those effects. Nitrogen Narcosis is another that should be considered.

My advice here is loosly based on the ANDI training for the Complete SafeAir certification (Advanced Nitrox). In the training it is noted that diving research has found that a pN2 of 4.0 ata is the optimal limit of narcotic effects of Nitrogen for scuba diving. Yes this is totally debatable and any tri mix diver will denounce the premis, but it is a published guideline for pN2 exposure. This is also the reasoning behind the newer 100 fsw depth limit for recreational scuba diving as mentioned by rjack321.

The decision to use 32% or 36% should be based on 1) are there other dives planned for the day, if so go with the 32% or you will reduce the bottom time available for the repetative dives, or 2) or will the planned dives for the day be decresingly shallower from 60 fsw. Then I would go with the 36% to reduce the amount of Nitrogen loading for the day, also 3) are you diving the Nitrox tables or using the air tables.

 

[rjack321]

I am not aware of the narcotic equation, unless it is something different in the PADI book.

END = 10 meters X [(ppN2/fN2)-1] ppN2 = 4.0 maximum

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.

 

[Michael Kazma]

As said, you did not may for the course but just the book and c-card. You need to report the instructor to the dive training organization through which they teach (which one was it by the way?) and demand a refund from the instructor.

Dalton's diamond is the core to the nitrox course and will be the core of any more advanced class from here. YOU NEED TO KNOW IT.

 

[ZenDiver.3D]

Not explained. They just said that I should just read the book and if I have questions the instructor will discuss them with me. I should just take the exam then off I go. Good thing I told them that I want to do the dives!!!

That is not acceptable. Go take a TDI nitrox course. When you are done, you will understand Maxim um Operating Depth MOD, Equivalent Air Depth EAD, partial pressure of oxygen, how to calculate PPO FFO EAD MOD, and what and why. I am sorry that you have not been taught these basics for enriched air diving. Dalton's Diamond is key adn should have been taught not read about.

The PADI manual/class does not cover the Dalton's Diamond. Honstly it was not covered in my ANDI class either.
If not, I would never suggest PADI teach a nitrox course then. Or ANDI, if they didn't cover it.


32% is a standard NOAA mix that was the first used to create a table to dive EAN. 36% came later and is the only other authorized NOAA mix. The NOAA was the first organization to publish a Nitrox dive table and most of todays theory/tables/math came from the NOAA program.

grammaticus, the PADI course and manual came with a Equivilant Air Depth (EAD) table. Why are you not using that along with the basic equations to figure the Best Mix for the dive problems you are working?

Best Mix is based on the Maximum Operating Depth (MOD) equation and the Equivilant Narcosis Depth (END) equations. You have to work both to find your limit, or your best percentace of gas mox for the depth you plan to dive.

MOD = 10 meters X [(ppO2/fO2)-1] ppO2 should not exceed 1.4

END = 10 meters X [(ppN2/fN2)-1] ppN2 = 4.0 maximum

Most courses either ignore or forget that you have to take into account the narcotic effect of Nitrogen in the mix as well as the oxygen partial pressure.

As said, you did not pay for the course but just the book and c-card. You need to report the instructor to the dive training organization through which they teach (which one was it by the way?) and demand a refund from the instructor.

Dalton's diamond is the core to the nitrox course and will be the core of any more advanced class from here. YOU NEED TO KNOW IT.

I completely agree.

 

[muddiver]

So what is Dalton's Diamond?

 

[rjack321]

So what is Dalton's Diamond?

I think Kazma means ppO2, ATAs, and fO2. Knowing 2 solve for the third. Commonly oriented in a pie or diamond to make remembering to divide or multiply a little easier.

 

[muddiver]

Thanks, we used the "pie" or tri-forcated circle in the ANDI class. It does make the calculations easier to derive.

Sorry ZenDiver.3D, but bashing an agency because they don't use the same term for a derivation tool is uncalled for. If I were to base my opinion of SDI on the Solo Diver manual for teh only SDI course I have taken, then I would say SDI is the worst, crackpot certification agency out there. But I am above that, and I know that there is a lot of other important information in the other SDI/TDI courses that are available.

 

[Quero]

So what is Dalton's Diamond?

Nothing but a cutesy way of referring to the formula for Dalton's Law.
See this post.