Topping off Tri-Mix with air

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Sigh. You just aren't getting this. It's simple, so I'll try again.

There's nothing the store is currently doing that keeps someone from getting an air fill there (just regular, good old air, into an empty cylinder), THEN LATER going and mixing O2 into the same cylinder (for trimix, nitrox, airgon, whatever).

This typically isn't done in this order because it's easier to get the O2 (and I assume the helium) into the tank when it's empty.

They'd face the SAME liability under your scenario where something happens and someone goes looking to blame another. Even in this case where no trimix is implicated, you could still try claiming they contaminated your cylinder for future O2 blending purposes.

Absolutely

Of course, the defense is simple: I gave them an air fill, what they did later is none of my concern.

Actually what you did is introduce non-O2-clean air into a cylinder that had an "O2 Clean" sticker on it, rendering it no longer O2 clean.

I'm not trying to be dense here, AFAIK, but the OP doesn't have air that's certified for use in PP blending, which makes filling an O2 clean tank a problem, regardless of what it currently contains or will contain.

Now if the customer's tank isn't O2 clean (maybe he's blending trimix using banked Nitrox?) then it doesn't matter if the op fills it or not.

Terry
 
If the OP is that worried about it, then have the customers sign some waiver of liability forms.

There are no governmental rules and regulations (self policing isn't law) that prevent the shop from filling air into trimix bottles or whatever. As long as the shop doesn't have cause to worry about the tanks "blowing up" while being filled, it's all good.

I would assume that trimix/adviced nitrox/heliox divers by now would know a bit more about their equipment configuration, gas mixing and containment, etc. instead of just being nod-your-head-pay-DM-once-a-year-Cozumel divers.
 
Actually what you did is introduce non-O2-clean air into a cylinder that had an "O2 Clean" sticker on it, rendering it no longer O2 clean.

Where was it established that the tanks in question are O2 clean? Trimix fills don't require clean cylinders, if that's what you're thinking.
 
LOL.

Again, if your air is so dirty to pose combustion issues in the presence of pure O2, then really, you shouldn't be letting people breathe it. It's that simple.

True, my point was that sometimes, when there are no other options for topping off a tank, I know I've had to get an air top off from a shop that did not do nitrox fills so they did not have that magical e grade air so topping off my tank at this shop TECHNICALLY disqualified it from being filled by partial pressure. The air was still good to breath, it met all current standards for recreational scuba diving but was not good for using in partial pressure blending. I knew this, because I was properly trained and I had the tank cleaned shortly after. If the shop you're trying to get the fill from can't tell you what grade air they're pumping then I wouldn't breath it either.
 
Where was it established that the tanks in question are O2 clean? Trimix fills don't require clean cylinders, if that's what you're thinking.

That's exactly what I was thinking. I've never seen it made except by PP blending.

Terry
 
This typically isn't done in this order because it's easier to get the O2 (and I assume the helium) into the tank when it's empty.

Again, not what I'm saying. Let's do this slowly. First, an air fill into an empty cylinder from the shop in question. Now it's "contaminated" according to you. Next, the diver leaves the shop and drains the cylinder completely. He fills it at his own house with O2. If there's a problem, his heirs (according to you) sue the shop for having contaminated it. Again, NO trimix is implicated (there's not even any helium in this story).

You see, your problem is only with a shop that sells "non-O2-clean air" since it could later be used with O2. Since the shop currently isn't doing anything to prevent this, why worry about trimix. Get it?



Actually what you did is introduce non-O2-clean air into a cylinder that had an "O2 Clean" sticker on it, rendering it no longer O2 clean.

I'm not trying to be dense here, AFAIK, but the OP doesn't have air that's certified for use in PP blending, which makes filling an O2 clean tank a problem, regardless of what it currently contains or will contain.

Now if the customer's tank isn't O2 clean (maybe he's blending trimix using banked Nitrox?) then it doesn't matter if the op fills it or not.

Terry

I actually make a lot of my trimix from He and banked nitrox (32 tops), so yeah, plenty of people do do this. In this case, since the divers in question are asking for air tops, it's pretty clear that they are blending O2 and He. The point is, most air is already clean enough not to worry (regardless of whether it's "O2-clean"). Again, if the air fills were so bad to actually pose a combustion issue, I wouldn't want to breathe the air in the first place. Personally, I'd find out just how clean the air is (any decent shop will share with you their test results).
 
Greetings - I teach at a dive shop in San Diego. We only do air fills (no Nitrox or Tri-mix). Recently a couple of Tec Divers came into the shop with these massive doubles filled with Tri-mix, and wanted us to top them off with air.

The question came up on our side about liability, whether it's safe, etc. I'm sure you could have them sign some kind of waiver, but I'm curious what other's thoughts might be on this in terms of risks or liabilities? Do other shops do this?

Thanks in advance,

Marcus Gee
PADI MSDT #235938

Marcus,

You may want to suggest to the dive shop owner and staff that because the use of nitrox and trimix is growing among rereational divers and not just technical divers with rebreathers or double tanks, that those providing air fills take a nitrox and trimix gas blender course. Even though you don't blend those gases, the staff will understand how the process works and you may even be able to assist nitrox and trimix divers by having gas blending software on your shop's computer to help verify what mix should result after an air top-off. This way, you'll be able to build your customer base by providing friendly service to divers who have been well-trained to dive the mixtures they wish to have topped-off rather than fearing liability. Even if you don't get too many technical divers, you never know who will walk through the door and how a friendly can-do dive center could impress the right person on the right day that could bring you more business or help you expand to meet the need for a growing interest in triox and trimix.
 
That's exactly what I was thinking. I've never seen it made except by PP blending.

Terry

There's no rule that the O2 has to go in before the He.
 
There's no rule that the O2 has to go in before the He.

I make a lot of trimix. None of my doubles are O2 clean, and I would NEVER put O2 in first. Always put in Helium, and top with 32 (if available and possible). Otherwise, depending on the mix, put O2 in, but never to exceed a mix greater than 40%. If the mid mix will be more than 40, put some air (grade E at a minimum, Oxygen clean is preferred), then O2, then air top. I put check valves on all whips to prevent back flow (I really screwed up someones mix that way, cost me a lot of money) and cross contamination.

Make mixing easy. Common mixes are 10/50 for rebreathers (50% helium with air), 16/50 for open circuit to 250 (50% helium with 32% top), 21/35 for shallow OC (35% helium with a 32% top), and others. Don't make gas blending harder than it has to be.
 

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