Scuba Diving Anti-Stress Kit
Rejecting the Cylinders for Nitrox
By now you are probably asking, why would they reject a tank for recreational Nitrox? Here are the reasons that the kid behind the counter told my friend.
- Hydrocarbons – Over time, hydrocarbons may build up and possibly contaminate their system. This reason was troublesome for me for a couple reasons. First, my friend’s tanks are only two years old. I doubt that there could be that much build up of hydrocarbons to worry about contamination, unless he was getting fills from a questionable source. Second, if a fill station is designed properly, there should be no worries about bank bottle contamination from destination tanks. There should be check valves in place to prevent gas from going into their system.
- Losing O2 Cleaning – The repair “technician” had said that after a couple of years, tanks lose their O2 clean rating from the factory. Thus the tank needs to be O2 cleaned again to keep in order to fill with pre-mixed Nitrox. [Start Banging Head]
The 40% Rule
If you take a Nitrox class, you’ll learn that any Nitrox mixture with an oxygen content of 40% or less can be treated the same as air. This means that your tanks and valves do not need to be O2 cleaned if the Nitrox has been pre-blended prior to entering your tanks. So, if we keep this in mind when thinking about item #2 above, do we really need to O2 clean a cylinder for pre-mixed Nitrox? Not really. Let’s not forget that if you are going to O2 clean a tank, and want to keep it O2 cleaned, you should be doing it once a year at it’s visual inspection date.
The truth to all of the O2/Nitrox voodoo is that you do not need an O2 cleaned tank for pre-mixed, recreational Nitrox fills. Certainly it doesn’t hurt, but it isn’t required. If the dive shop in question has this policy just to be extra conservative, then fine. Just admit it and state that it is the store policy. Don’t lead customers to believe it is the industry standard when it’s not.
Dive Safe,
Duane
Precision Diving
About Duane Johnson
Does this shop do PP blending?
If the do, that’s probably why they’re claiming that, that and to try to get an $80 O2 cleaning fee out of the guy.
Another one I hate is people trying to say regulators won’t work with recreational nitrox if they don’t explicitly say “nitrox compatible”.
Like you said, any beginner’s nitrox class teaches that <= 40% oxygen is treated as air. This isn't a scuba thing, but a more general gas handler's credo.
My guess is that reg manufacturers choose not to include it to upsell customers to more expensive regulators that "work with nitrox". Or maybe I'm just a pessimist.
I’ve found that for some reason talking with shops (even quarries!) about gas mixing procedures and regulations is like taboo. Everyone has there own theory and no one really knows what they’re talking about. The information is out there but no one appears to care to take the time to read it, instead it seems they come up with their own theories that would be hysterical if it weren’t my tanks they were rejecting.