Ean Mod Po2 Wth?

[doghouse]

Ok, so I am writing myself a little log book while waiting for the winter to finish up.

I do not use nitrox, but what the heck might as well write code for that section anyways.

Please correct any mistakes in my understanding of the subject. Examples and formulas are from scubatoys. Thanks for the clear explanation

EAN is the O2% in the tanks
PO2 is the partial pressure of oxygen, at a given depth. PO2 = ATM * FO2
MOD is the Maxium Operatng Depth you want to dive

-----Example: with PO2 of 1.4 and 36% in your tank: 1.4 / .36 = 3.89ATM
(3.89 ATM – 1 is 2.89 ATM * 33 = 95.3 feet)
BUT if you have regular air you get 187.

I repeat that I don't understand Nitrox and have not been trained on it yet so don't beat me up over this question.

If with enriched air, you can only dive to 95.3' how does it give you this "greater depth and longer bottom time?"

There has to be some facts I am missing somewhere.

sorry for the color, it is from the comments in my code I coppied and pasted.

 

[KMD]

If with enriched air, you can only dive to 95.3' how does it give you this "greater depth and longer bottom time?"

There has to be some facts I am missing somewhere.
[/COLOR][/SIZE]

It doesn't. Its a common misconception on nitrox. It gives you lesser maximum depth but with a greater duration.

 

[Crazy Fingers]

This is true, but to be fair, most divers are fine breathing EAN36 up to 115'. Which is just a rabbit's hair over the recommended 1.6 atm O2. EAN32 is basically no problem within the limits of recreational diving. So nitrox doesn't really limit your depth too much if you are willing to accept 1.6 atm O2.

I consider the 1.6 atm recommendation enough of a built in safety factor that I don't need to add another one. I believe the Belgian Navy let's their divers hit 2.0 or 2.1 or something crazy like that. I think that's definitely pushing it but if you got a war to fight, you gotta get it done.

 

[Gene_Hobbs]

It gives you lesser maximum depth but with a greater duration.

Moving from your question to an explanation of the comment above is here:

AN EVALUATION OF THE EQUIVALENT AIR DEPTH THEORY
Logan, JA 1961
RRR ID: 3835
NEDU technical report AD0242325

If you need help getting started with the Rubicon Research Repository, please visit our FAQ page.

 

[ianr33]

This is true, but to be fair, most divers are fine breathing EAN36 up to 115'.

Except of course for those that Tox and die doing so.

I see NO reason to push O2 limits just for the sake of it.What do you gain? 2 minutes of NDL??

 

[Blackwood]

I consider the 1.6 atm recommendation enough of a built in safety factor that I don't need to add another one. I believe the Belgian Navy let's their divers hit 2.0 or 2.1 or something crazy like that. I think that's definitely pushing it but if you got a war to fight, you gotta get it done.

Last I heard the US Navy cuts divers who can't handle PO2=2.0 for something like 45 minutes.

 

[scubafool]

Maybe so, but I don't dive for the Navy.

 

[Gene_Hobbs]

Last I heard the US Navy cuts divers who can't handle PO2=2.0 for something like 45 minutes.

Not anymore...
http://www.scubaboard.com/showpost.php?p=2683594&postcount=13

 

[Meng_Tze]

Ok, so I am writing myself a little log book while waiting for the winter to finish up.

I do not use nitrox, but what the heck might as well write code for that section anyways.

Please correct any mistakes in my understanding of the subject. Examples and formulas are from scubatoys. Thanks for the clear explanation

EAN is the O2% in the tanks
PO2 is the partial pressure of oxygen, at a given depth. PO2 = ATM * FO2
MOD is the Maxium Operatng Depth you want to dive

-----Example: with PO2 of 1.4 and 36% in your tank: 1.4 / .36 = 3.89ATM
(3.89 ATM – 1 is 2.89 ATM * 33 = 95.3 feet)
BUT if you have regular air you get 187.

I repeat that I don't understand Nitrox and have not been trained on it yet so don't beat me up over this question.

If with enriched air, you can only dive to 95.3' how does it give you this "greater depth and longer bottom time?"

There has to be some facts I am missing somewhere.

Your calculations look okay to me. The thing is that the higher content of O2, lowers the content of Nitrogen, thus the 'equivalent air depth becomes shallower..... It is as if you are diving air at a shallower depth. So in your example. 36% at 95 ft (1.4 AT of PO2) the dive can be planned as if diving air at around 70ft.

But the higher content of O2 also has shorter O2 Exposure times. PO2 at 1.4 is 150mins, at 1.6=45 mins, at 1.5=120 mins. So EAN (with higher than 21% O2 - there is another thread that argues that 21% and less is also EAN, but that to me is nitpicking) allows you to stay down longer at that depth due to less exposure to, and related absorption of Nitrogen. But there is also a limit closing in in terms of Oxygen exposure.


Accepted limits are PO2=1.4 ( some highly exerting dives are recommended at 0.9 even)for the working part of the dive and 1.6 for deco. Some books and schools vary to 1.5, but recreational diving pretty much is set at 1.4
Hope this helps

 

[Crazy Fingers]

Except of course for those that Tox and die doing so.

I see NO reason to push O2 limits just for the sake of it.What do you gain? 2 minutes of NDL??

Jeez, it's not like I told the dude to dive 1.8 or 2.0.

If you tox at 1.6, then you are a walking epileptic seizure and are ready to die at any minute anyways.