Nitrox cylinder bands

[The Chairman]

If a tank only sees one shop, then PP blending is fine. However, once you start traveling, that O2 compatible air that unfamiliar LDS is giving you, just may not be, leaving an oily residue. Back to your home LDS and once they put the O2 in that not-so-clean tank, you now have poison in a bottle.

I have to admit that this baffles me. Why should PP blending increase the risk of CO poisoning?

I had explained it earlier (see quote). I've been poisoned twice and both were after PP blending. I'm not looking for a third time.
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[uncfnp]

TDI issue a sticker which clearly just says oxygen clean. It appears a LDS issues a sticker which states clearly "cleaned for Nitrox to 40% or oxygen clean to 100%. It is on this basis I would ask ONLY for oxygen clean as clearly both methods are the same. One however limits you to 40% which is really a con if you ask me. If you want your tank clean then its oxygen cleaned, how you use it after that is up to you, <40% or oxygen, its clean for either.

It would appear in OZ anyway in many of the LDS, they clean for Nitrox on the basis of PP fills, rather than pre-blended or Nx stick.

[View attachment 366541

The TDI sticker is dual-purpose, and you can punch the lower 'star' (as in your picture), or the upper star if the cylinder is not cleaned for oxygen service. We use a similar sticker (although not agency-labelled) at the shop where I currently do the VIPs. For the majority of enriched air cylinders, I punch out the upper 'star' as the cylinder is NOT cleaned for oxygen service. PADI offers two separate stickers, one of which is labelled 'NOT OXYGEN CLEAN' and the other is labelled 'OXYGEN CLEAN'. BUT (and this is a big 'but' which doesn't adequately cover my 'butt' as the VIP person, from my perspective), even though the upper 'star' on the dual purpose sticker, and the small print on the PADI 'NOT OXYGEN CLEAN' sticker both imply some 'cleaning', there is none done.

Interesting. I took another look at my VIP stickers just to confirm and they have the dual option to pinch as well but for either 21 to 40 or O2 clean greater then 40. I know nothing special was done beyond inspection for 21 to 40 and there doesn't seem to be an air only option. So it seems from this that there is no difference in tanks, at least here, between an air only tank and a nitrox tank.

So based on this, the fact that there are competing recommendations and that there seems to be a long safety record with the common practice of filling tanks not labeled O2 clean with nitrox not pp filled that the "standard" of O2 clean for nitrox seems poorly supported. Unsure how this would playout in court but seems to be another case of antiquated or outdated regulations.

My other thought is who would be libel. I assume it would be the individual doing the fills, and they are the ones theortically at risk. And for a dive shop, I would think the OSHA standards would be the most applible.

 

[The Chairman]

Doesn't really make sense to blend/bank a "standard" mix when the standard is to dive nonstandard mixes.

Not true. You can create most any 'nonstandard' mix from banked 32 and any non-standard mix from banked 40 without the problems associated with putting pure O2 into an unclean tank.

 

[MXGratefulDiver]

We only have one shop in our area that requires nitrox banners ... and although I like the shop owners and think they run a good business I rarely use them. However, for those occasions when I do stop by, I "humored" them by adding some tank banners to some of my cylinders. I use these ...

 

[Colliam7]

Interesting. I took another look at my VIP stickers just to confirm and they have the dual option to pinch as well but for either 21 to 40 or O2 clean greater then 40. I know nothing special was done beyond inspection for 21 to 40 and there doesn't seem to be an air only option. So it seems from this that there is no difference in tanks, at least here, between an air only tank and a nitrox tank.

Yep. That is the 'usual and customary', it would seem.

So based on this, the fact that there are competing recommendations and that there seems to be a long safety record with the common practice of filling tanks not labeled O2 clean with nitrox not pp filled that the "standard" of O2 clean for nitrox seems poorly supported.

I agree. Now, I don't think it is a 'conspiracy' to add a level of bureaucracy to the process. But, the 23.5% threshold is a CGA standard - again, not a 'regulation' - and it is a PSI - PCI standard. So, the issue (unfortunately) isn't going to go away anytime soon. In fact, the 'standard' is relatively new, so it really isn't a matter of outdated regulation, it is a matter of a growing body of activity which may end up in regulation in the future.

You can create most any 'nonstandard' mix from banked 32 and any non-standard mix from banked 40 without the problems associated with putting pure O2 into an unclean tank.

Also a very good point. I have long thought that maintaining a bank of 40% would give a fill operation considerable flexibility in filling enriched air cylinders for recreational divers.

 

[uncfnp]

I have to admit that this baffles me. Why should PP blending increase the risk of CO poisoning?

This confused me too but my understanding from his reply is that his tanks were being contaminated with fills from other then his usual LDS causing CO when the tanks were then pp filled with 100% O2?

 

[archer1960]

Do any local FL shops still do this Partial Pressure blending? Or is it mostly a foreign thing?

I'm not in FL, but my shop in RI does PP blending.

 

[Peter69_56]

This confused me too but my understanding from his reply is that his tanks were being contaminated with fills from other then his usual LDS causing CO when the tanks were then pp filled with 100% O2?

Yes perhaps the OP could provide more information on this?

 

[2airishuman]

I avoid Partial Pressure blending whenever possible. I've been poisoned twice with CO due to this.

I have to admit that this baffles me. Why should PP blending increase the risk of CO poisoning?

I believe that NetDoc concluded that a flash explosion occurred in these two incidents when the accumulated hydrocarbon residue in the tank (caused by previous fills of low purity) was in the presence of hyperbaric pure oxygen (during the oxygen-fill step of the partial pressure blending process). I don't understand the chemistry well enough to explain why, but apparently the carbon chains don't always oxidize all the way to CO2 when this occurs, and the CO is stable at room temperature even in the presence of hyperbaric oxygen. It doesn't take much CO to be toxic, 20 milligrams in 10 pounds of air (one 120 cf cylinder, more or less) would lead to a concentration of 5 ppm, enough to cause onset of some symptoms depending on depth, duration, activity, personal physiology, and previous exposure.

 

[Storker]

I use these ...

I use the "This is not your tank!" sticker.