Tank still clean?

[pengwe]

I got some new tanks, with Nitrox stickers on them, because at that point they were O2 clean. Since them I have regularly had air fills from a place that doesn't do Nitrox, and I don't think they have O2 clean equipment. Is it still OK to get Nitrox fills in these tanks at a shop that does partial pressure blending? Some people are saying yes, and some say no - what do Scubaboarders say?

 

[Colliam7]

I got some new tanks, with Nitrox stickers on them, because at that point they were O2 clean. Since them I have regularly had air fills from a place that doesn't do Nitrox, and I don't think they have O2 clean equipment. Is it still OK to get Nitrox fills in these tanks at a shop that does partial pressure blending? Some people are saying yes, and some say no - what do Scubaboarders say?

If the air being put in your tanks was not oxygen clean air, then the tanks are no longer O2 clean, irrespective of what the stickers on them may say. The condensed hydrocarbon standards for Grade E air, and 'modified' Grade E (OCA) are different. However, many shops will perform partial pressure blending on tanks that are not O2 clean. I personally won't but many others do. And, that doesn't necessarily mean that the shops are reckless, or 'bad'. It is a matter of shop policy, and willingness to accept risk.

 

[h2odragon1]

The shop that didn't do nitrox should not have touched those tanks, or at least pulled the nitrox stickers off. If you want nitrox, take the to a shop that can fill nitrox, tell them what had happened to the tanks so they can O2 clean them before using them for nitrox.

 

[Buoyant1]

You can't do partial pressure blending, but you CAN have them filled at a shop that does continuous blending....I would take the O2 clean stickers off so they don't get confused with "clean" cylinders. But yeah....the shop that filled with with air probably should have pulled the stickers!!!

 

[DA Aquamaster]

The shop that didn't do nitrox should not have touched those tanks, or at least pulled the nitrox stickers off. If you want nitrox, take them to a shop that can fill nitrox, tell them what had happened to the tanks so they can O2 clean them before using them for nitrox.

You can't do partial pressure blending, but you CAN have them filled at a shop that does continuous blending....I would take the O2 clean stickers off so they don't get confused with "clean" cylinders. But yeah....the shop that filled with with air probably should have pulled the stickers!!!

It's a good example of why Nitrox bumper stickers are totally worthless - they have no impact on what happens to the tank after it is cleaned and mean absolutely nothing.

That said some shops require them before they will do a nitrox fill and if a shop selling non-O2 compatible air filled my nitrox marked tanks and then pulled my $7.50 each nitrox bumper stickers off, I'd get crabby with them as I'd not only have to get the tank recleaned before getting a partial blended fill, but also would have to buy new bumper stickers before getting any nitrox fill.

Better for me and them if they just tell me up front their air does not meet the lower hydrocarbon standards needed to be O2 compatible. If Nitrox Bumper stickers mean anything at all it is to the fill operator who needs to respect the O2 clean status of the tank and not fill it with anything other than O2 compatible gasses (more on this later) .

More importantly, you need to determine the quality of the air used for the fill. If it met the lower hydrocarbon standards required to be O2 compbatible, the tank is still "clean".

Less obvious but just as important, if the shop mixes nitrox with a membrane or stick, the fact that it is nitrox does NOT guarentee the compressed air used in the blending process is any more O2 compatible than regular grade E air so that nitrox fill you just got may have equally violated the precious "O2 clean" status of your tank - the only difference being you do not even realize it because it was a Nitrox mix that you assumed met O2 compatible standards.

Now...you need to mark the tank as containing nitrox with appropriate mix and MOD markings and all a Nitrox bumper sticker really does is clue the diver in to the fact the tank may not contain air and that the the diver needs to look for the smaller mix/mod tag to see what is in the tank. The O2 clean sticker is what the fill staff need to respect as if the tank is O2 clean, it only stays that way if they heed the O2 clean VIP sticker and decline to introduce any gasses into the tank that are not fully O2 compatible - including in some cases nitrox produced with a membrane or stick.

So in short and as a review, a nitrox bumper sticker means absolutely nothing with regards to the "O2 clean" status of the tank, and the "O2 Clean" notation on the VIP sticker is just about as worthless unless you are religious about what goes into your tank and excercise total control over what goes into your tank.

More and more shops are either moving away from partial pressure blending entirely or are partial pressure blending into a bank and then filling tanks out of the bank to avoid having to trust the O2 clean status of tanks owned by customers who often are not real sure of the actual status themselves. It's just safer that way.

To make it more confusing consider this...

I own tank A and I fill it 100 times with gas that has half maximum the hydrocarbon content allowed in oxygen compatible air.

I also own tank B and fill it 50 times with gas that has the maximum hydrocarbon content allowed in oxygen compatible air.

Finally I own tank C and fill it 25 times with gas that has twice the maxium hydrocarbon content allowed in O2 compatible air.

Which tank is "cleaner" and more importantly, are your O2 clean tanks really "O2 Clean" after several fills even with O2 compabitble gases?

 

[littlejohn]

So what I am reading is, there is no DOT Reg's as to what air is put into a O2 cleaned tank?
They have regs for everything else

 

[oxyhacker]

Correct. The whole nitrox-sticker and O2-cleaned thing exists totally apart from the DOT regulations, and has no legal force. You could argue that its an industry standard, but there's too much disagreement within the diver community to make a really strong case for that. So each diver decides what he or she is going to try and get away with, and each shop decides for itself what they are going to let their customers get away with.

Just about all the ceritifcation agencies doing tech and mix courses will tell you that just one tank of non-OCA will contaminate your O2-clean tanks, and you must either reclean them or remove the O2 clean stickers (but not necessarily the wraps, they don't make any promises regarding the O2-clean status of the tank).

On the other hand there are many very knowledgeable people in the dive industry who will tell you, some publically but many more only privately, that Grade E air is just fine for PP mixing.

Others will say that whatever danger there is happens only over time, if one was to receive multiple, contaminated fills, and that if your tanks are cleaned annually you'll be fine with even if they do see some fills of Grade E air.

And then there are a lot of people who make a distinction between how clean a tank has to be to receive that 400-500 psi of 100% it will see in PP mixing, compared to a full pressure fill of 100%.

So there really is no simple answer. But more divers I know would not get too upset over a few fills of non-OCA air into an tank marked O2-clean.



.

So what I am reading is, there is no DOT Reg's as to what air is put into a O2 cleaned tank?
They have regs for everything else

 

[ppo2_diver]

Correct. The whole nitrox-sticker and O2-cleaned thing exists totally apart from the DOT regulations, and has no legal force. You could argue that its an industry standard, but there's too much disagreement within the diver community to make a really strong case for that.

What about OSHA regulations? I have heard that OSHA states that cylinders (including SCUBA tanks) must be permanently marked with their contents. I haven't seen the regulation specifically, just heard it in passing. Anybody know anything specific?

 

[oxyhacker]

There is some stuff in 1910.253(b) about marking tanks for contents in a "not readily removable" way, but it seems to apply specifically to welding tanks. I have never seen an OSHA requirement for scuba tanks (which is a long way from saying there's no such thing).

However, OSHA jurisdiction is only workplace safety, so any such regulation, even if they exist, would not apply to privately owned tanks.

What about OSHA regulations? I have heard that OSHA states that cylinders (including SCUBA tanks) must be permanently marked with their contents. I haven't seen the regulation specifically, just heard it in passing. Anybody know anything specific?

 

[pengwe]

Guess I will ask the dive shop that does the partial pressure blending if they are happy to fill them or not. If not, there is another shop that uses a membrane that shouldn't have any problems.