Uncle Pug once bubbled...
...you are one of those DIR dudes who thinks air is only for tires and that only an idiot would use air for diving! 
Actually I know folks who are nitrox certified but chose to dive air on occassion using their nitrox wrapped tanks.
Steven... a nitrox wrap doesn't mean the tank contains nitrox... it only means that the tank might contain other than air. The fill analysis label tells you what the contents of the tank are.
Why do you think that it is idiotic or dangerous to put air in a tank with a nitrox wrap?
Mom! Uncle Pug called me a DIR dude! Make him stop!!!
Sheesh, UP, first time anyone has ever called me a clonediver and I don't know whether to take it as a compliment or an insult. Besides, I think that you're a lot closer to sucking the Kool-Aid than I am...
Just because my days of 200ft on air are done doesn't mean I've been assimilated. Does it?
Sorry if this is a kind of disjointed and rambling post, but I'm on the fly and don't have time to run it by the editorial board...
I dive nitrox pretty regularly, but, since most of my diving is in the southern basin of Lake Michigan (where depths rarely exceed 60ft, let alone 100ft), I don't use the geezer gas as often as some divers in other areas. Around here a nitrox fill costs around $15, another disincentive. I'll take a guess that I had 40 or 50 dives with nitrox last year, so I'm not completely unfamiliar with the stuff, however. Some of my tanks are set up for nitrox and some are not - and I don't cross them, ever.
I agree that the tank analysis sticker/tape tells you what the
oxygen content of the tank is - but that's all, unless you want to add trimix labeling to the discussion. I disagree about the meaning of the nitrox tank wrap, however. I'm also inclined to say that the nitrox tank wrap is unnecessary braggadoccio, but around here you have a hard time getting a tank filled without one. Nitrox markings (tank wrap and inspection sticker and MOD labels) should mean that the tank and valve have been prepped, cleaned and inspected for O2 service and that only CGA Type J air (modified to include higher oxygen levels) is used in the tank. The example given stipulated both a tank wrap and nitrox inspection stickers, the basis for my response.
Many, if not most, divers don't get our nitrox fills from banks of premix. In all of Chicago, I know of one place that banks premix, the rest (of those that fill nitrox, and many don't or send nitrox fills out) use partial pressure blending, starting with 100% O2. I don't know of any local pp blenders that start with 40% and I don't know of any local shops that continuous blend. I also don't know of any local shops that hyper-filter their air fills. (Help me out if I'm wrong, Chicago divers - I'd love to find someplace nearby that was cheaper/faster/better) These shops are, rightly or wrongly, pretty crabby when it comes to issues about O2 prepped and cleaned. Some of them won't accept a sticker from any shop but their own, which is aggravating as all heck. The reason they get so crabby is because there are a bunch of divers in this world that think all this standards nonsense is, well, nonsense.
Fill a tank with air hyper-filtered to GCA Type J standards and you've just filled it with EAN21, even if you didn't have to mix it. Fill a tank marked nitrox with CGA Type E air (in any O2 concentration) and you've just voided the O2 clean status. Voiding the O2 status means that the stickers come off before the fill. Since a fill station will presumably never fill a tank without a valid inspection sticker, a new inspection is in order. An inspection will cost you $15, unless you're going to suggest that a new sticker should be applied without an inspection? Returning the tank to nitrox service once the nitrox stickers have been removed will cost you $50 in my neighborhood for a tumble and a peek and is a pretty high price to pay to save a couple of bucks on the fill. Unless you want to cheat and tell the guy with the fill whip in his hand that your tank is still clean and let him take the risk of losing that hand and the shop that employs it. I'll stick by my earlier statement - at the worst this is a stupid tax. If a diver can't figure a way around this without jeapordizing the fill operator, he should spend the afternoon on the beach.
There's them that argues that all this standards stuff is paranoid foolishness. They might be correct. I'm not a physicist and couldn't tell you, but I will say that when the argument becomes a statistics battle that I have an automatic reaction involving a serious tightening in my gluteal region. Number crunching and tall tales and all that...so I'm inclined to take the most conservative approach in the interest of not hurting anybody and staying out of the newspapers and courts.
A couple of questions for you folks that see it otherwise:
- How does a +40% fill impact your thinking? If you'd fill an EAN tank with normal air, would you then use that tank for a 50% or 100% mix without cleaning it?
- If you don't need nitrox markings to get nitrox fills, why do you get nitrox markings?
- Anybody know how to jam a fill station into a small high-rise apartment? I'd love to be doing my own...
Steven
