Diving Nitrox -- pros & cons

[Cave Diver]

Large Diver,

I just wrote a brief "What is Nitrox?" article to answer some basic questions for a class of BOW divers at my LDS.

If you would like it to see if it answers any of your questions, PM me with your email address and I will gladly send you a copy.

 

[BigJetDriver]

large_diver once bubbled...
I am pretty much in the dark when it comes to Nitrox...so a few questions...

SOME OF THESE QUESTIONS HAVE BEEN ANSWERED, BUT FOR THE SAKE OF CLARITY, I WILL TAKE THEM IN ORDER.

Roman -- when you say that they bank EAN40....I assume the filling method is that they partially fill your tanks with the EAN40 and then add air to get to the O2% you want -- correct?

CORRECT! THE SHOP WILL BANK (OR STORE) THE EAN40, AND THAT MAKES IT EASY TO GET TO THE TWO STANDARD MIXES OF NN32 OR NN36 WITH JUST A LITTLE AIR FROM THE COMPRESSOR.

Big-T....when you say "alot of people PP fill".....are you are talking about adding 100% O2 and then adding air.....?

CORRECT! THIS IS THE STANDARD METHOD FOR THOSE WHO, LIKE MYSELF AND OTHERS, DO NOT WISH TO GO THROUGH THE EXPENSE OF SETTING UP A STORAGE BANK, OR WHOSE MIX NEEDS VARY WIDELY FROM THE STANDARD MIXES. ALSO, WE MAKE OTHER MIXES, SUCH AS HELIUM AND OXYGEN.

All -- please explain the following (1) why the need for O2 cleaning at higher 02 %s and not at lower %s; and (2) the % when O2 cleaning is required.

PLEASE SEE MY NOTE (ABOVE), AND THAT OF NOTABOB, ABOUT OXYGEN HANDLING.

Charlie -- it may be that I mis-remembered this. Can anyone else confirm the differences between air and Nitrox in terms of breathing effort and breathing capacity?

THE DENSITY OF AIR AND THAT OF NITROX AT NORMAL DIVING DEPTHS IS NOT SUFFICIENTLY DIFFERENT FOR IT TO BE NOTICEABLE. WHAT YOU WILL FIND IS THAT, WITH SO MANY MORE OXYGEN MOLECULES AVAILABLE, WHATEVER THE EFFICIENCY RATING OF YOUR LUNGS FOR GAS EXCHANGE UNDER NORMAL CONDITIONS, THE AMOUNT OF OXYGEN IN TRANSPORT IN YOUR SYSTEM WILL INCREASE. MORE WILL BE AVAILABLE FOR YOUR METABOLIC PROCESSES, ALL THINGS BEING EQUAL.

Thanks.

AS A FINAL NOTE, AS HAS BEEN POINTED OUT BY VARIOUS STUDIES, YOU CAN DIVE NITROX ON AIR TABLES OR METERS AND GET A VERY SMALL FRACTIONAL INCREASE IN THE STATISTICAL SAFETY OF YOUR DIVE IN REGARD TO DCS.

IF YOU DIVE NITROX ON NITROX TABLES OR METER SETTINGS, HOWEVER, YOU GET TWO THINGS. YOU GET MORE BOTTOM TIME, WHICH IS WHAT WE ARE ALL HERE FOR, WITH THE SAME STATISTICAL SAFETY RATING AS THE STANDARD TABLES AND METERS.

YOU ALSO, (ALTHOUGH THIS IS ANECDOTAL IN NATURE), FEEL BETTER AT THE END OF A LONG DIVING DAY!!!:wacko:

 

[notabob]

BigJetDriver69 once bubbled...


A minor correction if I may. It is not the oxygen that will spontaneously combust. What happens is that, in the presence of so much available oxidizer, the required ignition temperature of a whole lot of materials, such as ordinary o-rings, or ordinary lubricants, is much lower than normal. It can get so low that adiabatic compression and molecular friction will be enough to reach ignition temperature.

The rest is quite correct, and a very good point to be made!

You're absolutely right, of course... I should've said "oxygen, when combined with various contaminants &/or materials (rubber, oils, etc.), may result in a spontaneous combustion." Thanks for giving the details behind the process, I wasn't thinking semantics when I typed my response.

-Roman.

 

[Big-t-2538]

large_diver once bubbled...

Big-T....when you say "alot of people PP fill".....are you are talking about adding 100% O2 and then adding air.....?

YEs, for those shops that don't bank something, some places pump 100% O2 in the tank to psi XXX, then top with air to get EANx ZZ. There is also the method of using a blending stick (but I'm not 100% sure how that works), and yet another method with a membrane filter.

Reasons to clean a tank that is going to see a % of O2 higher than 40 have been discussed. So if your local shop banks EANx of less than 40, or membrane fills tanks, you do not need to worry about O2 cleaning.

 

[H2OHead]

large_diver once bubbled...
I have been diving strictly air up to this point and am considering the conversion to Nitrox.

Most of my diving is in the 20-80 foot, range, with occasional dives to 100 ft (nothing deeper than 100).

The pros & cons of using Nitrox as I see them are as follows:

Pros:
- Physical benefits -- reduced nitrogen levels
- Decreased gas density = decreased breathing effort
- Additonal protection against DCS (asuming following air NDLs)
- Additional bottom time (assuming following Nitrox NDLs)
- Potential increase in breathing capacity at depth vs. air

Cons:
- Oxtox risk
- More expensive
- Complexity -- need to analyze breathing gas carefully before using

Also, I have mild allergen-induced asthma -- not sure if there are any issues regarding Nitrox and asthma.

Any feedback is greatly appreciated -- thanks.

The depth ranges you mention include the exact depths that the EAN 32 and 36 mixes were developed for. Just thought I’d mention it since everyone got stuck on how to fill a tank.

 

[Gr8fldiver]

is cost. Here in FLL we pay between $6 and $12 for a nitrox fill compared to $2 to $4 for air. Those weeks when you do 15-20 tanks it can get pretty pricey. Sure is worth it though.