Why O2 Clean with a membrane Nitrox filler?

[charlesml3]

Gang,

Bear with me for a minute here before you fire off a response. I recently bought a pony tank that came with an integrated tank valve with a first stage and a dedicated 2nd stage. It's a little self-contained bailout system. At any rate, the pony came O2 cleaned for Nitrox with the usual disclaimer about requiring another O2 cleaning if it ever got filled with air. Yada, yada, yada.

The difference is, this pony is filled with a transfiller. It's an adapter that attaches to a full tank and then some of the gas is transferred over to the pony. So this got me thinking about this whole O2 clean thing. Since I'm never going to do a PP02 fill by pumping in pure O2 and then topping it off with air, why does this tank need to be O2 cleaned?

The way I see it, this is no different than me taking my Mares reg and diving one tank of Nitrox and the next on regular air. All of my class material indicates this is just fine. If that reg is safe to be exposed to air, 32% and 36% without cleaning, then so should this pony.

So that takes me to my last point. If I know my LDS only uses a membrane style Nitrox filler, then why would I need any of my tanks to be O2 cleaned? With a membrane style filler, the tank would never be exposed to 100% O2. Yes, I know, I could take the tank to a different lDS that does PPO2 fills and be SOL, but let's stick to the point here.

Thanks!

-Charles

 

[PhilEllis]

Gang,

Bear with me for a minute here before you fire off a response. I recently bought a pony tank that came with an integrated tank valve with a first stage and a dedicated 2nd stage. It's a little self-contained bailout system. At any rate, the pony came O2 cleaned for Nitrox with the usual disclaimer about requiring another O2 cleaning if it ever got filled with air. Yada, yada, yada.

The difference is, this pony is filled with a transfiller. It's an adapter that attaches to a full tank and then some of the gas is transferred over to the pony. So this got me thinking about this whole O2 clean thing. Since I'm never going to do a PP02 fill by pumping in pure O2 and then topping it off with air, why does this tank need to be O2 cleaned?

The way I see it, this is no different than me taking my Mares reg and diving one tank of Nitrox and the next on regular air. All of my class material indicates this is just fine. If that reg is safe to be exposed to air, 32% and 36% without cleaning, then so should this pony.

So that takes me to my last point. If I know my LDS only uses a membrane style Nitrox filler, then why would I need any of my tanks to be O2 cleaned? With a membrane style filler, the tank would never be exposed to 100% O2. Yes, I know, I could take the tank to a different lDS that does PPO2 fills and be SOL, but let's stick to the point here.

Thanks!

-Charles

You would not need anything cleaned if you are of that camp that believes that "anything less than 40% O2 is ok". Of course, you would not be in the camp with the Compressed Gas Association, the United States Navy, the Environmental Protection Agency, and many other groups with more knowledge about O2 related manners than I. In the end, absent some local or state law to the contrary, it is a personal decision. YOU decide with your cylinders and regulators are "clean enough". Thanks.

Phil Ellis

 

[fisheyeview]

If you want to fill it with more than 40% O2 then it needs to be clean.

 

[fisheyeview]

If you want to fill it with more than 40% O2 then it needs to be clean.

Beat to the answer.

 

[charlesml3]

Phil,

All of that is very interesting, but still doesn't address the point. What's the difference between these two practices:

1) Filling a tank that isn't O2 cleaned with a membrane style filler.

2) Moving my plain old Mares reg from air to Nitrox and back without having it O2 cleaned.

If my reg isn't in any danger because it isn't exposed to 100% O2, then the tank shouldn't be either since a membrane style Nitrox filler doesn't do a partial pressure fill with 100% O2. According to all of my Nitrox courseware, moving that reg back and forth is perfectly fine.

-Charles

 

[charlesml3]

If you want to fill it with more than 40% O2 then it needs to be clean.

Now that's an answer I can understand. Since I only use EAN 32 and EAN 36, I intend to fill my pony with a transfiller off of whatever is in my tank.

Thanks!

-Charles

 

[ClayJar]

Let me first chime in about this:

Since I only use EAN 32 and EAN 36, I intend to fill my pony with a transfiller off of whatever is in my tank.

Be sure you think about what you're doing if you're going to fill a bailout bottle with nitrox. If you regularly breathe from it (to keep your skills in order, should you ever *really* need it), it'll end up with the mix you're diving. This can be a problem if you then go on a deeper dive past the MOD of the mix in your bailout.

From all the materials I've read, stress and exertion seem to increase your susceptibility to CNS oxtox, and if you've just lost your primary gas, you're likely to be in a bit more stress than usual (and you may have had to exert yourself to get the situation back under control). Personally, I wouldn't want to choose that moment to switch to another gas while deeper than its MOD. Obviously, it's all exposures and timing and durations, but if the fish hits the propeller, I don't want to be pushing anything.

In my ponies, which are only used for facilitating normal ascents in the case of equipment failure, I use air and air alone. I don't consider narcosis to be of primary importance, since if I'm on the pony, I'm ascending (with stops, of course). The consequences of oxygen toxicity, on the other hand, cannot be overlooked. You can analyze your bailout gas before any dive deeper than the MOD of the richest mix you've transfilled with, but is the nitrogen loading you'll save compared to making the ascent on air worth the increased potential for an oxtox mistake? (It's your call, of course, but it's good to think about it from all angles.)



Now, as to oxygen clean and all that. According to lots of scuba people, you can treat mixes up to 40% O₂ as if they were air (with respect to oxygen cleaning and such). Outside dive shops and scuba manufacturers, however, 23.5% O₂ is the cutoff. Gases with greater than 23.5% O₂ require special procedures and handling (basically, treating them as if they were pure O₂).

Whatever term you choose, the main thing to remember concerning Luxfer scuba cylinders is that when you fill a cylinder with an oxygen concentration of 23.5% or more, that cylinder must be specially cleaned for oxygen service as though it contained 100% oxygen.

Proper shipping name: Compressed gas, n.o.s. (>50 Nitrogen, 0.1-23.5 Oxygen, 0.1-30 Carbon Dioxide)

Oxygen levels over 23.5 percent create a serious fire or explosion risk.

Oxygen levels over 23.5 percent create a serious fire or explosion risk.

Above 23.5% O₂, oxygen-nitrogen mixtures are categorized as an "oxidizer" by the NFPA. *Technically*, then, anything you use with nitrox should be O₂ clean, but there are many, many divers diving nitrox up to 40% O₂ without oxygen-clean handling and gear. Just make informed decisions.

 

[charlesml3]

Hey Clayjar,

Excellent points. I've been thinking about that a lot and wondering what I should have in my pony. Like you said, it's only there if I experience some kind of catastrophic failure. First stage quits, hose bursts, something like that. It's a small pony and I only intend to use it to get to the surface.

I usually use EAN 32 on my deep dive and EAN 36 on my shallow. When I say "deep" I mean 100 feet or so. I rarely dive any deeper than that. I'll probably fill the pony with EAN 32 or air. I'm not worried about MOD or OxTox given my profiles. The computer is tracking all of that for me.

I'm still wondering if all the fear surrounding Nitrox isn't rooted in the somewhat older practice of PPO2 fills. I fail to see how a membrane filler is all that more dangerous than an air filler.

Thanks for the input!

-Charles

 

[PhilEllis]

.........I'm still wondering if all the fear surrounding Nitrox isn't rooted in the somewhat older practice of PPO2 fills. I fail to see how a membrane filler is all that more dangerous than an air filler.

Thanks for the input!

-Charles

Hi Charles. I don't think there is any "fear" surrounding Nitrox filling. It is simply that almost EVERY organization that is involved in gases and gas packaging views the increased danger as being somewhere below 40%....in fact, far below 40%. As to partial pressure filling being the "somewhat older practice", it is not that at all. It still remains the dominant method of creating enriched air nitrox; probably used by well over 80% of all stations that make that product.

When using enriched oxygen mixes AT ANY LEVEL, clean is a good practice. Use common sense with your equipment and all will work out well.

Phil Ellis

 

[charlesml3]

Very well. I understand the issue surrounding O2. I use to work as a steam fitter in a factory.

I'm not so sure about the "well over 80%" part. All of my local LDS' use a membrane filler. The only one in Cozumel does as well. Don't liveaboards also pretty much use membrane fillers as well?

-Charles