Nitrox Question

[windapp]

The reason a nitrox tank has to be labelled is so that nobody accidentally uses nitrox thinking it is air.

My question is, if I have a nitrox tank, and I get air in it, do I need to analyze the tank, or is there a good way to ensure that it has been filled with air, and not inadvertantly filled with nitrox?

I was thinking that maybe, I always use nitrox in the tank for dives of 25 m or more, and only use air if the dive is less that 25 m. That way, even in the unlikely event the cylinder was accidentally filled with 40% nitrox, I would still be safe.

[Mustang29]

If the tank has the possibility of anything other than air (21% nitrox) you MUST test the gas so you know what you are breathing.

[emoreira]

A tank filled with Nitrox should be labeled because it should not be filled with AIR.
A tank to be filled with Nitrox requires to be clean for oxigen and apt for oxigen, depending on the blending system.
If a tank that was used for Nitrox is filled with air, all the Nitrox labels should be removed immediatelly. If this tank is going to be filled again with nitrox, it should be cleaned for use with oxigen.
Nitrox is a gas suitable for longer NDL, but has depth limitations. Air has deeper limits than Nitrox. EAN32 has a depth limit of 33 meters, and EAN 36 has a depth limit od 29 meters.
AIR can go up to 40 meters.
I would recommend to review your Nitrox concepts.

[chrpai]

Yes, it's labeled nitrox so therefore you need to test it. You'll also find that it probably isn't air. If it had some form of nitrox when you topped it off with air it'll still have a higher O2 content.

For example, if I bring back a tank with 500-1000psi of say 32 or 36 and fill it with air, it won't be unusal to have an FO2 of say 24% or 26%. I don't do blending so I'm not going to calculate it exactly but the point is it won't be "air" so I test it and label it.

[Teamcasa]

My question is, if I have a nitrox tank, and I get air in it, do I need to analyze the tank, or is there a good way to ensure that it has been filled with air, and not inadvertantly filled with

Yes. Get it tested or emptied and refilled.

[TSandM]

A tank filled with Nitrox should be labeled because it should not be filled with AIR.
A tank to be filled with Nitrox requires to be clean for oxigen and apt for oxigen, depending on the blending system.
If a tank that was used for Nitrox is filled with air, all the Nitrox labels should be removed immediatelly. If this tank is going to be filled again with nitrox, it should be cleaned for use with oxigen.

This actually is not true. If the shop that fills with air uses filtration that is O2 compatible, there is no problem with putting 21% Nitrox in a Nitrox tank, and then reusing that tank for enriched gas. After all, what do you think they put in the tank after they put the O2 in it? O2-clean air!

In practice, if you are filling tanks at a place that is filling Nitrox or any other gas than air, it is a good idea to analyze all your tanks, no matter what you asked to have in them. You never know when someone will make a mistake. Analyzing doesn't take much time. All tanks should be analyzed and have their contents and the MOD on a label which is easily visible.

[Mustang29]

I was thinking that maybe, I always use nitrox in the tank for dives of 25 m or more, and only use air if the dive is less that 25 m. That way, even in the unlikely event the cylinder was accidentally filled with 40% nitrox, I would still be safe.

Still be safe with 40% EANX at 25m or more??? 40% EANX is PO2 1.48 at 27 meters, depths beyond that are NOT safe!
I think you should spend some time reviewing your manual.

[emoreira]

This actually is not true. If the shop that fills with air uses filtration that is O2 compatible, there is no problem with putting 21% Nitrox in a Nitrox tank, and then reusing that tank for enriched gas. After all, what do you think they put in the tank after they put the O2 in it? O2-clean air!

In practice, if you are filling tanks at a place that is filling Nitrox or any other gas than air, it is a good idea to analyze all your tanks, no matter what you asked to have in them. You never know when someone will make a mistake. Analyzing doesn't take much time. All tanks should be analyzed and have their contents and the MOD on a label which is easily visible.

Though I agree with you, a tank labelled for Nitrox that was filled with air, makes me think that it was filled in an installation that has no Nitrox capabilities, therefore that installation would not be apt for oxigen or clean for oxigen. Why would you fill a tank with air in an installation that is nitrox capable ? Why would you mix rabbits with pigs ? If you want to dive air, use another tank.

[windapp]

Still be safe with 40% EANX at 25m or more??? 40% EANX is PO2 1.48 at 27 meters, depths beyond that are NOT safe!
I think you should spend some time reviewing your manual.

I may not have been clear. What I am saying, is use 40% Oxygen, and 79% nitrogen, if I am assuming air. That would make my MOD for unanalyzed air in my Nitrox tank 25m. If I am diving more than 25m, I would use Nitrox, and analyze the mix.

[rongoodman]

Though I agree with you, a tank labelled for Nitrox that was filled with air, makes me think that it was filled in an installation that has no Nitrox capabilities, therefore that installation would not be apt for oxigen or clean for oxigen. Why would you fill a tank with air in an installation that is nitrox capable ? Why would you mix rabbits with pigs ? If you want to dive air, use another tank.

One solution is just to avoid buying nitrox fills in shops that fill by partial pressure blending--I only know of one in a 150 mile radius. Gas should still be analyzed before breathing, though. The only labels I see a need for is a contents label with the current analysis(since on any given day it could hold air, nitrox, or trimix) and MOD labels on deco bottles.