"Clean Air" for Nitrox Tanks

[gxsr_sarge]

I understand that there are different types of "air" that a LDS could use for tank fills depending upon their fill station system/certification. For purposes of when I just want to use “air” in my O2 cleaned tanks, I'd like to know the following:

1- What is the correct nomenclature for the air that one would use for "Nitrox 21" (i.e., the air that should be used for partial pressure Nitrox fills) and what "other" types of air are there (I've heard “Grade E” and “Modified Grade E”, etc.)?;
2- Can a LDS in fact offer "clean air" when they use the membrane system for Nitrox fills?;
3- Are there any certificates, plaques, stickers, or whatever that the LDS might be displaying that I could look out for to verify "clean air"?; and,
4- What could I look out for in terms of harware, tubing, gauges in the area of the fill station itself?

Long story short, I ask this because this past weekend, I wanted a "clean air" fill and went to a random area dive shop. They went to hook up my O2 cleaned doubles to a nasty looking whip along side a bank of their other rental/dive boat tanks (not otherwise O2 cleaned) and represented that it was “clean air”. No need to bore you with the ensuing “back a forth” but I took my tank elsewhere but would have liked to have asked the right questions or looked for the right certification, hardware, etc.

Knowledge would be greatly appreciated!

 

[Blackwood]

At the end of the day, unless you analyze their product, you either trust the shop or you don't. That decision may be primarily superficial.

I'd probably go take a gander at their filters, and look for the change dates. Hyperclean air/grade E or better generally requires a lot of filtration. Comparing my "tech" shop to my local shop, the difference between the fill stations is night and day (and I'm talking more than banked helium and oxygen).

Ask to see test results. I'm not sure if there is any sort of requirement for them to get their output tested in order to sell it as clean, but I wouldn't trust a shop that wouldn't get it done. Trace Analytics is a big nationwide lab used by many LDSs.

 

[oly5050user]

Grade E or modified is not necessarily o2 clean air..What you want is hydrocarbon free air..Yes it is also known as hyperfiltered ..At our lds we use hydro carbon free clean air for nitrox/air to nitrox tank/trimix fills.The fill hoses are marked as such because the air coming out of it goes through an additional filter system.
ANDI facilities have hydrocarbon free air.

 

[gxsr_sarge]

Thanks to both of you for the above responses.

Let me see if this rings a bell to anyone: I was able to retrieve a note that I found from a conversation that I had with a LDS in Orlando (very helpful guy is who is tech). He told me that (from less to more "clean") - you had "CGA Grade E", "CGA Modified" and then O.C.A (Oxygen Consumption Air) which is for partial pressure EAN fills. I guess that that is consistent with Oly5050user's comment above. Before this, I had never heard of "OCA". Has anyone else?

 

[Jimmer]

OCA which is actually Oxygen Clean Air, is a pretty common term when you're discussing gas blending. It pops up a lot. If you want to learn more about it, you should pick up the Oxy Hacker's handbook from airspeedpress.com.

 

[Blackwood]

I've always heard it as Oxygen Compatible Air.

 

[texdiveguy]

Around my area we refer to it as simply 'hyper filtered air'.

 

[Blackwood]

depending on where I am, it's sometimes called "regular unleaded"

 

[gxsr_sarge]

OCA which is actually Oxygen Clean Air, is a pretty common term when you're discussing gas blending. It pops up a lot. If you want to learn more about it, you should pick up the Oxy Hacker's handbook from airspeedpress.com.

Thanks. That seems to be THE guide.

 

[SDAnderson]

1- What is the correct nomenclature for the air that one would use for "Nitrox 21" (i.e., the air that should be used for partial pressure Nitrox fills) and what "other" types of air are there (I've heard “Grade E” and “Modified Grade E”, etc.)?;

“Grade E” air is a Compressed Gas Association (CGA) standard that is used in scuba. The air is clean enough to breathe but not clean enough for use in high-pressure high-oxygen mixing.

• Oxygen: 20% to 22% (balance of gas predominantly nitrogen)
• Water vapor: May vary depending on intended use
• Condensed hydrocarbons: 5 mg/m 3
• Gaseous hydrocarbons (methane): 25 ppm
• Carbon monoxide: 10 ppm
• Carbon dioxide: 1000 ppm
• Odor: none
• Sampling Frequency: Quarterly
• Lab Analysis: Recommended

“Modified Grade E” air is a NAUI standard used by many in the scuba industry. Usually, Grade E air is run through an additional filtration process (a/k/a “hyperfiltered) to reduce the hydrocarbon content, making it more suitable for use in partial pressure blending.

• Oxygen: 20% to 22% (balance of gas predominantly nitrogen)
• Water vapor:128 ppm (v/v) -40 ºF Dew Point
• Condensed hydrocarbons: 0.1mg/m3
• Gaseous hydrocarbons (methane): 25 ppm
• Solid particulate: less than 2 microns
• Carbon monoxide: 2 ppm
• Carbon dioxide: 500 ppm
• Odor: none
• Sampling Frequency: Quarterly
• Lab Analysis: Recommended

“SafeAir” is an ANDI standard and involves not just the gas quality but a lengthy protocol for mixing, handling and storing scuba breathing gases. The term “Oxygen Compatible Air” or “OCA” refers to the gas quality standard used by ANDI but does not include the entire ANDI protocol. Compared to Modified Grade E air, there is less moisture in OCA and the O2 content isn’t specified. OCA is the “cleanest” standard used for scuba breathing gases that I am aware of.

• Oxygen: not specified (it can be any percentage, including 20.9%)
• Water vapor: -50 ºC Dew Point
• Condensed hydrocarbons: 0.1mg/m3
• Gaseous hydrocarbons (methane): 25 ppm
• Solid particulate: less than 2 microns
• Carbon monoxide: 2 ppm
• Carbon dioxide: 500 ppm
• Odor: none
• Sampling Frequency: Quarterly
• Lab Analysis: Required

2- Can a LDS in fact offer "clean air" when they use the membrane system for Nitrox fills?

Yes, though it isn’t required. The the additional filtration required for ModE or OCA often isn't used when membranes or sticks are being used to bank EANx. Ask how clean the gas is and ask for the test results to prove it.

3- Are there any certificates, plaques, stickers, or whatever that the LDS might be displaying that I could look out for to verify "clean air"? and,

EVERY fill station should test their air at least quarterly and post the results in a prominent place where everyone can see it and most LDS do. It never ceases to amaze me how many people who have spent the money to set up a fill station in their garage but never test their air. If you’re getting a fill from a bank (air or otherwise), you decide if ModE or OCA standards are important to you – they are to me and I try to avoid CGAE fills whenever possible. If you're getting a partial pressure fill and you aren't getting ModE or OCA quality air, you should run for the exit. The simplest rule of thumb for insuring your gas is clean is to look for the analysis (and to ask for it if you don’t see it) and READ the thing – it should tell you exactly what standard was employed in the test and, at the very least, whether or not the gas met that standard. If they can’t show you results from a test conducted within the past 3 months, skeedaddle.

4- What could I look out for in terms of hardware, tubing, gauges in the area of the fill station itself?

The fill station should be well maintained and clean but it isn’t necessary for it to be all shiny and new – most of this stuff is pretty heavy duty equipment and it isn’t uncommon for parts of it to be old. What matters most is the result which is why reading the test report is so important, though I personally avoid places that still wet-fill, no matter what their test reports say. If they don't check your C-card and look for hydro dates and VIP EOI stickers, you know they are sloppy with protocols and you should be nervous about what they're going to put inside your cylinder. Likewise, if they sell anything other than plain old air they should use a fill log, have a suitable analyzer available and insist that you use it when you pick up your fills.

If you're interested in this stuff, I recommend the previously mentioned Oxygen Hacker's Companion book and the ANDI Oxygen Handling and Gas Blending course student manual.