Topping off Tri-Mix with air

[marcus0453]

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

 

[Rainer]

If the O2% is <40%, really there's no risk from a filling safety standpoint. I assume you'd top up someone who had left over 40% nitrox in his cylinders, so there's really no difference. Depending on how you feel about the cleanliness of your fill station, you'd probably also be just fine topping off pure O2, but that does come at increased liability. Again, if the divers in question have already mixed Helium and O2 so that what they are bringing you for top off is a mixture that contains less than 40% O2, fill away happily. If they want to bring you pure O2 to top off, it's worth a further discussion.

Edit:
Forgot to add, but all the shop's I've had a long term relationship with have been fine topping air on to both He+O2 mixes and pure O2. I was never asked to sign a waiver.

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

 

[walke121]

I would think its the diver's responsibility to check the mix just like it is with nitrox. If they were trained they had the proper analyzers I'm sure that topping off a trimix with air could save some $$$ if the mix fits the profile they are diving. You said you don't pump nitrox, so my question is, is the air pumped through some sort of membrane system? That is the only issue I could see.

 

[Wookie]

Which safe? Whether their gas is safe to dive? Whether your air is safe enough to breath? Whether or not they are safe to dive the gas they are asking for? You are not the scuba police. If they want air tops in their doubles, and they show cards for the resultant mixture, charge them double and get on with the fill. If you don't want to do it, tell them you don't have a certified gas blender at the facility, and since the resultant mixture is a blend, you can't do it. Take a class ald learn that, while tech diving may not be attractive to you, or may not fit in with your shops idea of a good time, people do accomplish the task and live to tell about it. Become a blender and learn how to make trimix yourself.

The short non-snarky answer to your question is that air tops are common, and not unsafe. Be sure to bleed the whips out after a fill to absolutely make sure any helium that might have seeped back into the whips at the end of the fill is purged.

Frank

 

[Web Monkey]

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?

I'd just say "sorry".

Everything would probably be OK, but if the guy with the O2 tank in his garage manages to blow himself up, you'll be the first place his heirs attorney will look to for tank contamination problems.

Terry

 

[Blackwood]

Personally, if I think your shop will give me grief, I won't tell you what's in my tank.

That said, I see no reason for the shop to give me grief. I'm asking for air, and you're giving me air. Period, end of story. In my opinion, what another shop sold them is outside your realm of responsibility.

If they want air tops in their doubles, and they show cards for the resultant mixture, charge them double and get on with the fill.

Seriously?

 

[Jim Lapenta]

We have one tech diver in my area that does not have a compressor but has haskel and T bottles of O2 and Helium. He just mixes the proper He and O2 and goes to the local shop to top off with air. There really is no issue with putting air in tanks unless your air has too many hydrocarbons in it. That and O2 is not a good combination. The question is did the tanks contain mix or just O2 and He? If they were indeed already mixed and all they wanted were top offs what would be the issue and why would you even need a waiver? It;s up to them to reanalyze and set a profile based on the new mix. No different than topping off a nitrox bottle that has 1500 psi of 32%. Reanalyze, plan profile, and go. As an MSDT you should know what is safe and is not when mixing gasses.

 

[Rainer]

That's silly, since it has *nothing* to do with topping off trimix. What if the same guy who occasionally also blends O2 in his cylinders came into this guy's store for an air fill (no O2 added), then went diving, and the next day while mixing some O2, blew himself up. According to you, his heirs would still seek out this shop for contamination, but in this case, only an air fill was given. By your logic, every shop that fills air should refuse to give fills to anyone who might some day put pure O2 in his cylinders for fear of prosecution. Since the shop in question probably doesn't have such a policy now, it doesn't really make sense to extend it just to the cases of trimix top-offs.

I'd just say "sorry".

Everything would probably be OK, but if the guy with the O2 tank in his garage manages to blow himself up, you'll be the first place his heirs attorney will look to for tank contamination problems.

Terry

 

[Wookie]

Personally, if I thought your shop would give me grief, I wouldn't tell you what's in my tank.

That said, I see no reason for the shop to give me grief. I'm asking for air. Period.



Seriously?

I don't charge anybody for air fills, it comes with the trip, but if I did, yeah, I'd charge them double to fill doubles. Do you get your doubles filled for a single tank price?

 

[Blackwood]

I don't charge anybody for air fills, it comes with the trip, but if I did, yeah, I'd charge them double to fill doubles. Do you get your doubles filled for a single tank price?

My mistake, I thought you were suggesting to charge them more because you were filling on top of helium.