Nitrox Info

[Scuba446]

I am seeking to take my Nitrox course but am attempting to clarify what I would need to do to be able to use my regs and tanks for BOTH air and Nitrox.

My concern is that once tanks and regs are 'O2' cleaned won't they get 'contaminated' by pure air fills instead of Nitrox?

This is what my LDS has said on this topic, but I'm kind of confused on all this. Can someone help?

"As far as equipment considerations, you can use most regulators up to 40% O2 without concern.

As far as tanks go, if you are having your tank filled by shops that do partial pressure blending, then your tank and valve need to be O2 cleaned. After that, you can fill the tank with O2 compatible Air or "hyper air" without concern of fire/explosion. All the shops in the area sell "hyper" air so there is no risk of "contaminating" your tank. Some charge more and some don't. All the air I sell is "hyper" air and don't necessarily chargemore. That way, a customer can have a Nitrox tank and use it with just air."

So, it sounds like I can switch back and forth in between air and Nitrox fills?

 

[Drew Sailbum]

Whether your tank and valve should be subjected to special cleaning should be covered in your nitrox class.

To keep it simple for now, it is possible to "switch" back and forth between nitrox and air. You simply get air fills that are filtered to a higher level of purity in order to prevent hydrocarbon recontamination of your tank.

If any area shops bank nitrox, or use methods other than partial pressure blending, then you may not need any special cleaning of the tank or valve.

The fine print.
When using nitrox, follow all manufacturer recomendations with regard to use of scuba equipment in an oxygen enriched environment.

 

[Genesis]

and let me expand on it a bit...

(This will be covered in the class - but there are some LDSs that are b******* about this, and if yours is you need to find another one, because the facts aren't quite what some people make them out to be)

Ok, first things first.

1. Enriched Air Nitrox (EAN), in recreational use, is any mix between 21% (normoxic) and 40% (enriched). The most common two mixes are 32% (or "Nitrox I") and 36% (or "Nitrox II"), although any shop worth a hill of beans CAN fill a tank with any mix BETWEEN what they bank and 21%. Many shops, however, will refuse to do so because the tank monkey doesn't understand how - it is trivial for them to do so using only their banked Nitrox and banked Air, but that doesn't stop some people from being unable to perform basic algebra!

2. ANY shop that BANKS Nitrox should be filling AIR tanks with hydrocarbon-free air, as it is a near-certainty that they DO NOT own two compressors. If a shop partial-pressure fills they MUST have air that is hydrocarbon-free - no exceptions - or they risk an explosion that is THEIR fault. Therefore, any shop that SELLS Nitrox AND Air absolutely should NOT garf about filling your Nitrox tank with Air, and labelling it 21%. If they do, you need a new shop.

3. MOST regulators today are perfectly fine up to 40% O2. This is a somewhat-arbitrary number, but was, in no small part, developed after NASA attempted to INTENTIONALLY cause explosions in regulators that were NOT cleaned with 40% EANx and failed to do so, despite what later proved to be fairly gross-level hyrdocarbon contamination. However, there are manufacturers who say "no Nitrox", and the "rule" is that you must follow not only common sense and convention but also manufactuer's statements - of course if you disregard them they are your tailfeathers, PROVIDED its a reg (this is NOT true for a tank as blowing up your shop and/or tank monkey is not considered to be kosher!)

4. For partial-pressure blending the greatest risk is on the INITIAL burst of O2 going into the tank and again if the tank monkey incorrectly manages the valves when adding the air. The reason for this has to do with adiabatic heating - when a gas is compressed it heats up. When you blast O2 into an empty tank to partial-pressure blend any restriction to the flow (like, for instance, the VALVE!) creates a localized high-pressure spot. If there is contamination there it can ignite. High O2 percentages increase the risk of this by lowering the flash point dramatically and grossly increasing the rate of combustion once it is initiated. The solution is to (1) have clean gear, (2) add the O2 to the tank S.L.O.W.L.Y., and (3) have the proper equipment on the filler's side. The reason for the stricture about O2 cleaning valves and tanks has to do with the POSSIBILITY of a fire or explosion if there is contamination in them, not the certainty thereof. The worse news is that a flash fire may not blow the tank up or melt the valve, but rather could just produce a nice bunch of CO in the tank, which would be very un-good for you when you breathe it!

Short answer - yes, you can switch back and forth in 90+% of the cases, provided you get air from a shop that also sells Nitrox and is aware that you need Hydrocarbon clean air in the tank - they should REFUSE to fill your Nitrox tank with air otherwise (it will be banded, so there's no excuse for them not knowing your intended use for the tank!)

 

[Scuba446]

Thanks,
My LDS keeps referring to 'Hyper Air.' What IS Hyper Air?

Ok, so sounds like as long as I have the proper Nitrox sticker on my tank and am at a reputable LDS worth its beans, I should be able to go back-and-forth between both Nitrox and air fills.

 

[Genesis]

just their way of saying "hydrocarbon-free air".

 

[MikeFerrara]

They are refering to hyper filtered air. It is called that because, in most cases we run the air from the compressor through an addirional filter called a hyper filter. I would expect most shops to charge extra for this because the unit is expensive and the filters are expensive.

 

[Genesis]

They already have to have hydrocarbon-free air to put in their bank once they put in the O2!

If they're turning around and claiming that they should get MORE money for "regular air" that has no hydrocarbons in it, then I'd turn around and show them the back of my head - immediately.

 

[MikeFerrara]

I don't know about others but we don't bank hyper-filtered air. Our hyper-filtered air is not regular air. We run air from the bank through the hyper-filter to get hyper-filtered air when we need it. Anyone buying a fill of hyper filtered air from us would see us connect the whip to the hyperfilter and the whip from the hyper-filter to their tank.

Air streight from my compressor meets modified grade e but we still don't pump that on top of O2. that is because there are no garantees. The hyperfilter takes care of things even if the air quality of the compressor degrades.

As a side note there are many shops pp blending using standard air streight from their bank. It's all a crap shoot.

 

[roakey]

Genesis once bubbled...
2. ANY shop that BANKS Nitrox should be filling AIR tanks with hydrocarbon-free air, as it is a near-certainty that they DO NOT own two compressors.

I agreed with your response except for this.

If they’re banking Nitrox they’re either doing continuous blending or using a membrane system. Neither requires hyper filtered air.

So if a shop banks Nitrox it’s a good bet that DON’T have hyper filtered air, unless they have a hyperfilter for PP mixing on the side (as Mike states)

Roak

 

[roakey]

Genesis once bubbled...
They already have to have hydrocarbon-free air to put in their bank once they put in the O2

I know of no shop that PP mixes a bank.

Roak