Switching between standard and enriched air

[rescuediver009]

I'll add one more vote to not bothering switching your regs over. since they will never encounter the 100% O2 used in partial pressure filling, and now that almost every manufacturer says that their regs are up to 40% compatable you're ok. As far as tanks go, not too many places use the membrane system so you are better off cleaning them.

 

[Spectre]

Most (if any at all) of the shops will not fill your tank with nitrox without the proper markings which usually entails O2 cleaning.

Never had a problem with shops that banked nitrox with my non-clean tanks. Nor have I had issues with my cleaned tanks that don't have nitrox stickers [just the o2 clean VIP sticker].

If they did, I would inquire as to what their concern was, and most likely not frequent them if they didn't understand the risks and reasons for O2 cleaning.

 

[Zaphod]

FWIW, I just attended a PSI Fill-Station and Hazmat course yesterday and they are currently promoting the idea (in their class) that air should NEVER be introduced into a Nitrox cylinder, regardless of the quality/grade of the air, etc., etc. If it is, then they say that the cylinder is no longer suitable for nitrox. Unfortunately, the instructor I had claims only to be the messenger and couldn't answer the tough questions (like, what about using NITROX21). So, here I am relaying what I was told - so don't shoot me either. According to PSI, there is currently some federal politicians (that PSI is involved with) that want to change the laws to reflect this thinking.

 

[Genesis]

FWIW, I just attended a PSI Fill-Station and Hazmat course yesterday and they are currently promoting the idea (in their class) that air should NEVER be introduced into a Nitrox cylinder, regardless of the quality/grade of the air, etc., etc. If it is, then they say that the cylinder is no longer suitable for nitrox. Unfortunately, the instructor I had claims only to be the messenger and couldn't answer the tough questions (like, what about using NITROX21). So, here I am relaying what I was told - so don't shoot me either. According to PSI, there is currently some federal politicians (that PSI is involved with) that want to change the laws to reflect this thinking.

Buy your own compressors folks.

I'm going to call PSI on this one. If they are truly promoting this then its time to consider their "certifications" worthless.

Air IS Nitrox 21, provided it meets hydrocarbon cleanliness standards. If they're promoting the idea that it is otherwise, they're lying for profit and its time for people to change their attitude on this agency.

 

[SDAnderson]

FWIW, I just attended a PSI Fill-Station and Hazmat course yesterday and they are currently promoting the idea (in their class) that air should NEVER be introduced into a Nitrox cylinder, regardless of the quality/grade of the air, etc., etc. If it is, then they say that the cylinder is no longer suitable for nitrox. Unfortunately, the instructor I had claims only to be the messenger and couldn't answer the tough questions (like, what about using NITROX21). So, here I am relaying what I was told - so don't shoot me either. According to PSI, there is currently some federal politicians (that PSI is involved with) that want to change the laws to reflect this thinking.

If true, this is a big change from what I learned when I last took the course from Bill High a couple of years back. I suppose there could be a semantics argument here - is it air or is it EAN21, but hyperfiltered air is hyperfiltered air, whether you cut it with O2 or He shouldn't be relevant.

No offense, but since there was an issue with the instructor being able to explain why to your class, I think a check with PSI is in order before we start accepting this as gospel. It don't make no sense to me.

 

[Zaphod]

The statement was on a PSI-supplied PowerPoint presentation written by Bill himself. So, I'm kinda accepting it as gospel. I'll try to get the presentation.

If true, this is a big change from what I learned when I last took the course from Bill High a couple of years back. I suppose there could be a semantics argument here - is it air or is it EAN21, but hyperfiltered air is hyperfiltered air, whether you cut it with O2 or He shouldn't be relevant.

No offense, but since there was an issue with the instructor being able to explain why to your class, I think a check with PSI is in order before we start accepting this as gospel. It don't make no sense to me.

 

[SDAnderson]

The statement was on a PSI-supplied PowerPoint presentation written by Bill himself. So, I'm kinda accepting it as gospel. I'll try to get the presentation.

Since you just took the course, would you help us all out by giving him a call or email and asking him for a further explanation or clarification? He was good about answering a couple of questions that I had post-class and seems to like hearing from people. I'd call, but I wasn't there and then it would be one of those, "I heard from a guy..." things.

 

[Zaphod]

Will do.

 

[Zaphod]

As suggested, I contacted Bill @ PSI and he confirmed the statement in the presentation I saw for the FSO course. The presentation says to not switch between air and nitrox in the same cylinder, regardless of the quality of the air. It seems, like myself, he is the messenger for another party. In this case, he's relaying the thoughts of the Compressed Gas Association who state that a cylinder must be re-qualified (hydrotested and remarked) if the gas type is changed. The CGA and DOT consider air to be 19% - 23% O2 content. So switching back-and-forth between gasses makes the cylinder mis-labelled and illegal. Apparently, these two regulatory bodies are also concerned about having a little remaining gas in a cylinder and then filling with another mixture (and presumably not measuring the O2 content). I guess they don't assume that we measure our O2 content when we pick up the cylinder.

Aside from the legalities, he, of course, acknowledges that switching between standard SCUBA air (with some hydrocarbons) and nitrox is poor practice.

The grey area, which he couldn't clarify, is one where you mark your cylinder as Nitrox and simply label it as EAN21 (assuming you're getting "nitrox compatible air"). It's possible that since EAN21 is not actually enriched in any way, it really isn't EAN (a.k.a Nitrox), but now falls back into the category of "air" and is, again, mislabelled. Bill says that there probably won't be an examination of this issue until there's an accident of some sort.

He summed up the conversation by saying: "So, bottom line is that nitrox cylinders should stay nitrox and air cylinders stay air."

BTW, he says that these rules have been in place for quite a while - LONG before we started using Nitrox. I guess only recently have they started to sorta tow the company line.

 

[Genesis]

Actually, "Nitrox" is ANY Nitrogen/Oxygen mixture. It is entirely possible (although I can't come up with a particularly good reason to do so) to mix up some EANx15 or somesuch, albiet that would require either de-oxygenated air for the top or a tank full of nitrogen as the "PP" component.

So don't call it an "enriched" air tank. Call it "oxygen compatible Nitrox." That can be anything from 0.1% to 99% oxygen, the balance nitrogen, with a low enough contaminent (hydrocarbon, etc) count to remain safe in an enriched atmosphere.

Now you break no CGA or DOT rules; your tank is properly labelled, and it contains what it says it contains.