nitrox/air fills switcheroo

[L_A_S]

I'm planning to get a steel tank clean for nitrox for offshore dives, but I was wondering if I can just get a 21% fill in it when I'm just in the quarry. I heard somewhere along the line that you always have to put more than 21% oxygen in a nitrox only tank, so would I have to pay extra for 22% or higher nitrox every time even at a quarry? Isn't 21% (air) technically nitrox?

 

[Miller64]

Some things to me dont sink in real quick,and this is one of them,,,It's my understanding you can use UP to 40 percent nitrox in a tank,,after that, it has to be O2 cleaned for higher percentages.Hoping I learned something in the class,,so ,you could use 21 percent in a quarry and up to the 40 percent for shore dives before O2 cleaned...Correct?

 

[halocline]

It's amazing how much confusion there is about nitrox and tanks. There is no "nitrox" clean, there is an industry standard O2 clean which refers to equipment that will be used for greater than 40% O2. The only reason a tank used for nitrox needs to be O2 cleaned is if it is filled by the partial pressure method, which uses 100% O2 as part of the fill. Partial pressure fills used to be very common, but are now not nearly as common, having been replaced by banked nitrox and continuous blending systems.

Once a tank is O2 clean, it cannot be filled with air or a compressor that does not meet O2 clean standards, or technically the tank must be O2 cleaned again. Many scuba fill stations these days use equipment that produces O2 clean air fills.

So unless you're getting nitrox by partial pressure fills, just use your regular tank and don't worry about it. The only problem you might face is ignorance at a dive shop/fill station that won't fill a tank that's not "nitrox clean." I've heard it before....

 

[Miller64]

oops..worded it wrong,,,,thanks,,it will sink in soon...

 

[masterof0]

mattboy hit the nail on the head.
Basically you need to ask your fill station a single question.
Do you do partial pressure fills?
If the answer is yes, then you will need an O2 clean tank. If the answer is no, then they use banked EANx, and you will not need an O2 clean tank for percentages up to 40%.

Now the catch is that if you travel with your tank and do not know who will be filling your tank. If this is the case, then you will want an O2 clean tank and want to fill it with "safe" air. Safe air is a 21% mix that meets the same requirements as EANx and the elimination of hydrocarbons. By doing this, you can use banked EANx or do partial pressure fills.

 

[awdemeo]

I'm planning to get a steel tank clean for nitrox for offshore dives, but I was wondering if I can just get a 21% fill in it when I'm just in the quarry. I heard somewhere along the line that you always have to put more than 21% oxygen in a nitrox only tank, so would I have to pay extra for 22% or higher nitrox every time even at a quarry? Isn't 21% (air) technically nitrox?

hey their i am nitrox certified and switch back and forth between nitrox and air all the time. the onlything is make shure the air is filtered aka Nitrox compatibale air. many dive shops that have nitrox have filtered air so no worries their. places that dont have nitrox is where you need to do some checking in about how they filter their air. other then that you can go back and forth no prob

 

[SubMariner]

mattboy and masterofO have nailed it! Anything else just clouds the issue.

Well done, you two.