NITROX and Luxfer tanks

[knotical]

All of our new Luxfer cylinders are being shipped with Luxfer's green warning label which states the cylinder is oxygen clean.

But from:
http://www.luxfercylinders.com/support/faq/aluminumoxygen.shtml

8. Question: Are Luxfer scuba cylinders ready for oxygen service when they leave the Luxfer factory?
Answer: New Luxfer scuba cylinders manufactured from January 1, 2000 , until December 31, 2004 , will have been cleaned for oxygen service at the factory and sealed with an oxygen-compatible cap before being shipped. However, starting on January 1, 2005 , Luxfer will provide oxygen-clean scuba cylinders only by special order. Unless specifically ordered “oxygen clean,” all new Luxfer scuba cylinders will be cleaned for gas mixtures containing only up to 23.5% oxygen. (Of course, it will still be possible to have these cylinders cleaned for use with higher concentrations of oxygen by following the DOT-specified procedures cited above.)

 

[Leadking]

I totally agree. Oxygen clean, unless properly maintained, is but a single point in time.

That is the reason most cylinder and valve manufacturers will not state oxygen clean.

 

[wedivebc]

The issue is how the tank will be filled.

There are still plenty of shops filling nitrox using partial pressure blending. Doing so, you hit the valve and tank with high-pressure 100% oxygen, then top off with oxygen compatible air. You can be well below 40% when you finish a nitrox fill, but still expose the valve and tank to high-concentration conditions. Luxfer's advice will cover you for this filling method, and of course also for banked nitrox.

However, bear in mind that if you fill the tank with grade "E" air (most common) or banked nitrox that is not made from de-nitrogenating hyper-clean (Oxygen compatible) air,

What does de-nitrogening have to do with O2 compatability?

 

[Henryville]

What does de-nitrogening have to do with O2 compatability?

It's a method (membrane separation) of getting oxygen-enriched air without having to partial-pressure blend. Essentially you pull nitrogen out of air and what is left behind is nitrox of your desired oxygen concentration. The denitrogenation itself doesn't impact the O2 compatibility, it's the purity of the air that you start with or the filtration you do after separation.

If you are just running grade E air through a membrane to get your nitrox, what you produce is not oxygen compatible - meaning the tolerance for contaminants (chiefly in this context concerned with hydrocarbons but other contaminants as well) is too high. The risk is you lay down some minute but nonetheless significant "fuel" in the valve and/or tank that, when hit with high-pressure O2 in a subsequent partial-pressure blending exercise, goes "boom."

NOAA and the CGA are coming at the issue from two different perspectives. NOAA is looking at what concentration starts presenting a hazard for combustion of contaminants, o-rings, grease, etc. The CGA is looking at how the tank gets filled and assumes the possibility that partial pressure blending will be used meaning 100% O2.

But now that I look at your profile, I think you know all that so maybe I misunderstood your question.

 

[Leadking]

You got it, Dave.
Show me a 40% O2 clean standard and I'll eat it. It is either O2 clean or it's not.

 

[wedivebc]

It's a method (membrane separation) of getting oxygen-enriched air without having to partial-pressure blend. Essentially you pull nitrogen out of air and what is left behind is nitrox of your desired oxygen concentration. The denitrogenation itself doesn't impact the O2 compatibility, it's the purity of the air that you start with or the filtration you do after separation.

If you are just running grade E air through a membrane to get your nitrox, what you produce is not oxygen compatible - meaning the tolerance for contaminants (chiefly in this context concerned with hydrocarbons but other contaminants as well) is too high. The risk is you lay down some minute but nonetheless significant "fuel" in the valve and/or tank that, when hit with high-pressure O2 in a subsequent partial-pressure blending exercise, goes "boom."

NOAA and the CGA are coming at the issue from two different perspectives. NOAA is looking at what concentration starts presenting a hazard for combustion of contaminants, o-rings, grease, etc. The CGA is looking at how the tank gets filled and assumes the possibility that partial pressure blending will be used meaning 100% O2.

But now that I look at your profile, I think you know all that so maybe I misunderstood your question.

Where does it say in my profile that I know all that? :06:
Actually I know little about the de-nitrogenation other than it probably works on a very small particle level such as reverse osmosis for desalinating water. If that were the case I would assume the hydocarbon particles would be removed during the de-nitrogening process, but like I say, I don't know that to be true.
I do know that NOAA does not set the industry standards when it comes to handling O2 and other gasses. That is the job of CGA and I think that anyone who says to "ignore CGA and do it anyway" is akin to someone saying "I don't need training I will dive this cave". If we ignore the standards and accidents happen regulations will come down and dictate how we do things. The scuba industry has been pretty good about maintaining it's own standards but if we get complacent with gas regulations we will see enforcement like never before.

 

[Henryville]

I figured as an LDS owner maybe you had pumped some nitrox.

Actually, N2 is the smaller molecule (than O2 anyway.) Excess N2 goes through the membrane, bigger stuff stays with the nitrox.

After cleaning, the tank is O2 clean until it gets contaminated, then it isn't. With the potential consequences, you're absolutely right. We need to police ourselves and particularly so when dealing with high pressure gases.