Measuring O2 in enriched air

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I never stated there was a standard for this and was speaking strictly about the center I have worked at the ones I have been diving with. I fully agree with having a MOD label on the cylinder. I also never said to NOT analyze.

I always analyze my own cylinders. It is my responsibility to make sure that I know the gas I am about to dive with.



I stated some DCs have green and yellow labels on Nitrox cylinder. These labels do not state the percentage but state that it is for nitrox. Now lets say a blender fills the cylinder, measures it and determines it is 32.4% and labels it as such. Two days later I come to dive and get that cylinder. No way in hell I am trusting that it is 32.4% without verifying it for myself. Often times I have seen a cylinder labeled one way and be off at dive time by 2%.

Now what could be the cause of this? Could be it was not analyzed properly to begin with or it was analyzed too soon and had not yet homogenized properly. It could be the blender was doing multiple cylinders and put the sticker on the wrong cylinder. Humans are prone to error and if you do not check a cylinder prior to diving, it is a trust me dive.
And that is why I don't calibrate off "air" tanks and always check my O2 level.
 
Can you trust two cylinders? Say you calibrate on a cylinder thought to be air...then you analyze another cylinder that is supposed to be air. If you get 21% is that not evidence that you are in fact diving air? I always calibrate on an air cylinder and have never once had an issue with that air cylinder not being air
Fairly often I have had multiple cylinders of 32% that we breathed down and then had a shop fill with air. I don't analyze those and breathe them as air because we are never diving below 130. I also take the 32% labels off, because they are not 32%. Certainly in the realm of possibility to get two of them with very similar mixtures. The big air tank is always 21%.
 
Fairly often I have had multiple cylinders of 32% that we breathed down and then had a shop fill with air. I don't analyze those and breathe them as air because we are never diving below 130. I also take the 32% labels off, because they are not 32%. Certainly in the realm of possibility to get two of them with very similar mixtures. The big air tank is always 21%.
How long would it take to analyse the tank and labelled it?
 
Can you trust two cylinders? Say you calibrate on a cylinder thought to be air...then you analyze another cylinder that is supposed to be air. If you get 21% is that not evidence that you are in fact diving air? I always calibrate on an air cylinder and have never once had an issue with that air cylinder not being air
If they weren't filled by the same fill station, and both tested 0% CO and 21% oxygen then I think it's safe enough to assume the nitrogen content. Of course you'll want to use some certified gas to calibrate that meter you're using to analyze it. Otherwise, it's a gamble. Some like to gamble, some don't.
 
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