boulderjohn:
That 23.5% rule is relatively new, and it comes from the regulations of the Compressed Gs Association (CGA). It is not law. It has not only not been uniformly adopted by the scuba industry, it is rarely adopted by the scuba industry.
Sadly, not true. At least some of the CGA is incorporated by reference by the DOT as enforceable parts of the CFR.
Actually, I would argue that the second half of John's statement IS true. The 23.5% threshold has NOT been adopted by the scuba industry.
Wetlens:
This is exactly my point. Either it is O2 clean or it is not. Combine all the noted reading in the past few posts and it seems clear to me that all Nitrox tanks need to be O2 clean. Can't be half pregnant.
This (pregnancy) is probably not the best analogy, even if it is somehow viscerally appealing. And, if you choose to believe that 'all Nitrox tanks need to be O2 clean' that is your choice, and I wouldn't argue with you.
In general, most in the scuba industry would agree that, if a cylinder is going to have 100% O2 (or anything greater than 40% O2 infused into it, it should be cleaned for oxygen service. Generally what that means is that if partial pressure blending, e.g. with 100% O2, is to be used the cylinder - AND VALVE - should be 'cleaned for oxygen service'. In general, most of the scuba industry would also agree that, if a cylinder is going to have 40% (or less) enriched air infused into it, it does not need to be cleaned for oxygen service. Whether that remains a valid position in view of the CGS guidelines, is another matter, altogether.
WetLens:
The NC shop that I used previously would not apply an O2 clean label unless they cleaned on inspection. They did not require O2 clean for Nitrox 40% and below. The NC shop I currently use just punched out O2 clean on my Nitrox tanks after VIP - with inspection only (no cleaning).
I have worked in two shops that fall into the former category (O2 clean above 40%). It is common practice. With regard to the third shop, the practice raises an interesting, and challenging issue. Because cleaning for oxygen service is a time-consuming, and not altogether inexpensive, process, some shops have taken the approach that, once a cylinder has been cleaned for oxygen service, it can be re-qualified by visual inspection, with appropriate methods (e.g ultraviolet light examination). That has become an attractive middle ground, which allows shops to avoid the effort and expense of cleaning equipment for oxygen service, and passing that expense along to the customer. Unfortunately, that inspection does not apply to the valve, as there is not way to inspect the valve without disassembling it. If the shop you referred to did such an inspection (with UV light), then I can understand why they 'just punched out O2 clean on my Nitrox tanks after VIP - with inspection only (no cleaning)'. If they simply looked in a cylinder with a normal wavelength light, and did nothing else, I think they are foolish to have put a 'cleaned for oxygen service' sticker on that cylinder. Personally, i have not adopted this abbreviated process at all. If someone wants me to put a 'Oxygen Clean' VIP sticker on a cylinder, I have to clean it AND the valve. And, that is time consuming, and materials intensive. And, I expect to be paid to do it.
