Nitrox - O2 Clean/Refilling

nv · Mar 19, 2014

As some of you may know I am looking into getting my nitrox card, see post "Nitrox a Certification", but have a couple questions for those that are familiar with shop compressors and the knowledge behind a higher concentration of oxygen in the cyclinder.

Based onto e preliminary research I have done I have found the following:

1) nitrox labeled gas comes in two forms
A) Premixed/Banked
B) Partial Pressure or mixed inside your cyclinder, 100% O2 then topped off with O2 compatible air

2) gas that is banked, but does not exceed 40% does not require O2 cleaning of your cylinders

3) gas that is NOT banked requires O2 cleaning

I am not sure how accurate this is, but from about 4 articles that I have read this is the consensus.

Given the information above I have the following questions:

1) what exactly goes into an O2 cleaning of your cyclinder and regardless of filling with banked gas or not should I get my cylinders O2 cleaned? (Regardless requirement from shop)

2) what exactly should I be looking for from a shop that claims to fill nitrox gas? I read that if the air is not banked that the shop should have an O2 compatible compressor, but how am I supposed to know whether it is or it isn't.

3) is nitrox going to cost more?

4) if I happen to not want or unable to get nitrox and choose to dive air can I still do that with my cylinders?

Thanks in advance.

Nick

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Montana Diver · Mar 19, 2014

I just completed having my cylinder and valve cleaned for nitrox...partial pressure blended. The tank was close to needing Hydro, so it was sent their first. Upon return, we tumbled the tank to remove any flash rust and then completed VIP. The valve was rebuilt using viton O-rings to make it O2 clean. All parts were washed in an O2 safe cleaning solution and then rinsed and dried. Cleanliness during the rebuild was set at the level to reduce contaminants introduced, from foreign matter to oil from skin.
New cylinders with a O2 safe valves, viton O-rings, meet the requirements.

My LDS use an additional filter on the compressor system to insure that the initial O2 and the air fill to complete are clean. Depending on the LDS and their compressor you might find a variance from place to place. Having the extra filter protects my valve from having any foreign matter introduced. Hopefully that answered the first question.

2. If the tank and valve are O2 clean, all additional fills, nitrox or air are should be done with extra filtered air.
Shops can have their air tested to provide you a gauge of the cleanliness grade of the air they supply.
If you will only dive at shops that use premixed air or have the ability to remove the nitrogen and not have to partial pressure blend then you can use any air.
The O2 clean safety factor is for partial pressure blending.

3. Nitrox will cost more, however I like the safety factor of less nitrogen loading. Voodoo gas stickers on the tank are kinda cool also. :rolleyes:

4. I will always choose to use the O2 cleaned air. Your LDS might provide this level of clean air all the time. My shop chooses to use the extra filter for all nitrox tanks. This may be way to cautious, however a tank explosion would be catastrophic. Loss of limb or life for my friends at my shop would be devastating.

nv · Mar 19, 2014

Thanks! How do you verify with the shop whether their air grade is o2 compatible?

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AfterDark · Mar 19, 2014

nv:
Thanks! How do you verify with the shop whether their air grade is o2 compatible?

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A good LDS will only fill O2 cleaned tanks from the nitrox whip (hose), you can get any %O2 you're certified for with O2 blending.

If they don't have nitrox, then a talk would be in order.

Scared Silly · Mar 19, 2014

nv:
2) gas that is banked, but does not exceed 40% does not require O2 cleaning of your cylinders

The above is not correct. A scuba industry convenience but does not follow DOT rules that requires O2 cleaning for any cylinders with greater than 23.5% O2. This point gets argued ad nauseum - do a search.

nv:
1) what exactly goes into an O2 cleaning of your cyclinder and regardless of filling with banked gas or not should I get my cylinders O2 cleaned?

Yes, get them cleaned. O2 clean cylinders are cleaned to remove hydrocarbons. There are different solutions such Simple Green and Dawn that will do the job.

nv:
2) what exactly should I be looking for from a shop that claims to fill nitrox gas? I read that if the air is not banked that the shop should have an O2 compatible compressor, but how am I supposed to know whether it is or it isn't.

The best is to ask if the air produced is Mod Grade E (O2 compatible).

nv:
3) is nitrox going to cost more?

Not always - but usually yes.

nv:
4) if I happen to not want or unable to get nitrox and choose to dive air can I still do that with my cylinders?

Always fill with Mod Grade E (O2 compatible) air. If you can not get Mod Grade E (O2 compatible) air then technically your cylinders are no long O2 clean and they should be cleaned again or at least be inspected. That does not always happen ...

nv · Mar 19, 2014

Scared Silly:
The above is not correct. A scuba industry convenience but does not follow DOT rules that requires O2 cleaning for any cylinders with greater than 23.5% O2. This point gets argued ad nauseum - do a search.

Yes, get them cleaned. O2 clean cylinders are cleaned to remove hydrocarbons. There are different solutions such Simple Green and Dawn that will do the job.

The best is to ask if the air produced is Mod Grade E (O2 compatible).

Not always - but usually yes.

Always fill with Mod Grade E (O2 compatible) air. If you can not get Mod Grade E (O2 compatible) air then technically your cylinders are no long O2 clean and they should be cleaned again or at least be inspected. That does not always happen ...

Thanks for the corrections. At least I gathered the concept..

One question: after having nitrox in my cylinder and needing to get a full where nitrox isn't available is there any damage that arises from filling with normal air? Non-grade e? Other than it not being o2 clean anymore

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KD8NPB · Mar 19, 2014

nv:
1) what exactly goes into an O2 cleaning of your cyclinder and regardless of filling with banked gas or not should I get my cylinders O2 cleaned? (Regardless requirement from shop)

2) what exactly should I be looking for from a shop that claims to fill nitrox gas? I read that if the air is not banked that the shop should have an O2 compatible compressor, but how am I supposed to know whether it is or it isn't.

3) is nitrox going to cost more?

4) if I happen to not want or unable to get nitrox and choose to dive air can I still do that with my cylinders?

1.)
The widget (tank or valve) is inspected as normal.
A gross pre-clean takes place to remove gross contaminants (rust in steel tanks, crusty old silicone/MCG/tribolube on around the neck of the cylinder, or excessive deposits in an aluminum tank)
The cylinder is rinsed
A detergent wash takes place using an oxygen compatible soap. Crystal simple green is a popular choice. For cleaning the valve, some shops may use an aggressive detergent such as trisodium phosphate. Glass bead is tumbled with the detergent inside the cylinder in order to knock free any ionically bonded contaminants...as an added bonus, this also usually eliminates all odors.
The cylinder / valve is rinsed. To confirm rinse, a shake test of the rinse water is done. If shaking a clean vial of the rinse water causes bubbles, then the rinse must continue. If detergent remains, then so does the suspended contaminants.
Steel tanks are then treated with oxy-safe rust inhibitor
Tanks are blown dry using clean compressed air (Grade E is fine), or sometimes nitrogen.
Tanks / valves are reassembled using oxygen compatible seats, orings, and lube.

It might be good to get your cylinder O2 cleaned once in a while. It ensures absolute cleanliness of the cylinder. However, it is not necessarily a value added process. If you can get banked cheaper and easier, then go banked.

2.) If the shop has a continuous blender, then it is probably the cheapest option for nitrox. If they offer banked, continuously blended custom fills, or partial pressure custom fills AND they have an oxygen booster, as well as helium...you're probably in a fairly competent shop that is ran by a true dive enthusiast.

3.) More than likely. Anywhere from a few dollars more, to maybe even triple the cost.

4.) If the cylinder is O2 clean and is then filled with Grade E air, then the cylinder is no longer considered O2 clean. Is this really the case? Does one, two, or ten Grade E air fills push enough contaminants in to your cylinder to cause it to lose its O2 clean status? Probably not. Dick @ Global estimates that greater than 70% of dive shops produce compressed air that meets or exceeds oxygen compatible air requirements...they might not even know it.

nv · Mar 19, 2014

KD8NPB:
1.)
The widget (tank or valve) is inspected as normal.
A gross pre-clean takes place to remove gross contaminants (rust in steel tanks, crusty old silicone/MCG/tribolube on around the neck of the cylinder, or excessive deposits in an aluminum tank)
The cylinder is rinsed
A detergent wash takes place using an oxygen compatible soap. Crystal simple green is a popular choice. For cleaning the valve, some shops may use an aggressive detergent such as trisodium phosphate. Glass bead is tumbled with the detergent inside the cylinder in order to knock free any ionically bonded contaminants...as an added bonus, this also usually eliminates all odors.
The cylinder / valve is rinsed. To confirm rinse, a shake test of the rinse water is done. If shaking a clean vial of the rinse water causes bubbles, then the rinse must continue. If detergent remains, then so does the suspended contaminants.
Steel tanks are then treated with oxy-safe rust inhibitor
Tanks are blown dry using clean compressed air (Grade E is fine), or sometimes nitrogen.
Tanks / valves are reassembled using oxygen compatible seats, orings, and lube.

It might be good to get your cylinder O2 cleaned once in a while. It ensures absolute cleanliness of the cylinder. However, it is not necessarily a value added process. If you can get banked cheaper and easier, then go banked.

2.) If the shop has a continuous blender, then it is probably the cheapest option for nitrox. If they offer banked, continuously blended custom fills, or partial pressure custom fills AND they have an oxygen booster, as well as helium...you're probably in a fairly competent shop that is ran by a true dive enthusiast.

3.) More than likely. Anywhere from a few dollars more, to maybe even triple the cost.

4.) If the cylinder is O2 clean and is then filled with Grade E air, then the cylinder is no longer considered O2 clean. Is this really the case? Does one, two, or ten Grade E air fills push enough contaminants in to your cylinder to cause it to lose its O2 clean status? Probably not. Dick @ Global estimates that greater than 70% of dive shops produce compressed air that meets or exceeds oxygen compatible air requirements...they might not even know it.

For number 4 you said that filling an o2 clean cylinder with grade e air deems the cylinder no longer o2 clean. Is that a typo? I thought that as long as you put grade e you were okay.

Also does my reg need to be cleaned?

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KD8NPB · Mar 19, 2014

nv:
For number 4 you said that filling an o2 clean cylinder with grade e air deems the cylinder no longer o2 clean. Is that a typo? I thought that as long as you put grade e you were okay.

Also does my reg need to be cleaned?

There are two grades:
Grade E
Modified Grade E (also called oxygen clean air, or oxygen compatible air)

Grade E can have up to 5 mg/m3 hydrocarbons
Modified Grade E can have up to 0.1 mg/m3 hydrocarbons

Regulator O2 cleaning is not required unless the regulator sees mixes hotter than EAN40. So basically, if it is an EAN50 or O2 deco regulator, it needs to be cleaned.

kwinter · Mar 19, 2014

If you are only going to get your fills from a place that banks their nitrox and never, ever have the possibility of needing a partial pressure blend, then you can save yourself the cost of O2 cleaning. Otherwise, get it O2 cleaned. A decent shop won't charge that much and you will be better off. But beware of ripoffs.

Nitrox - O2 Clean/Refilling

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