Topping off Tri-Mix with air

[Gilldiver]

Up here in New England I know of no shop with banked NITROX. There may be some in NY or NJ, but none in CT, RI, MA, NH, or ME. In fact, I know of only one shop with a boster, all other are PP blend with air top off's

I do my own in my garage and put the O2 ontop of the Helium, why? Because O2 is cheap compared to He, so I'll keep more cylindars of O2 to get the 1500-2400 psi needed to top onto the He and use all the He down to a about 100 psi.

 

[Rainer]

Up here in New England I know of no shop with banked NITROX. There may be some in NY or NJ, but none in CT, RI, MA, NH, or ME.

None in MA? Really?

Hmmm, the following all have pre-banked nitrox (or did when I lived in MA two years ago):

Mass Diving (MASS Diving, Inc. - scuba equipment, scuba diving, dive, massachusetts, diving, new england, ma, boston, Natick, Framingham, metrowest, worcester, south shore, north shore)
Atlantic Divers (Atlantic Divers | 978-774-9997)
North East Scuba (Northeast Scuba in Chelmsford, MA offers PADI courses, diving gear, tank rentals, diving trips and dive instruction.)
South Shore Divers (Welcome to South Shore Divers)
East Coast Divers (East Coast Divers: Scuba Diving Instruction, Professional, Instructor, Courses, Lessons, Training, MA, Massachusetts, Boston, Framingham, Brookline, Travel, Equipment, Sales, and Service.)

I can also think of a few shops with boosters in NE.

Your general point, that many more shops PP blend in NE than elsewhere, however, is probably correct. Definitely the case as compared to SoCal, that's for sure.

Oh, and yeah, always He before O2! One costs A LOT more than the other.

 

[Colliam7]

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 curious what other's thoughts might be on this in terms of risks or liabilities? Do other shops do this?

Marcus, your post has generated some spirited discussion. But, I am curious about the exact basis of the questions that were raised in your shop, about liability, safety, etc. I am NOT in any way saying the questions were not valid, only trying to understand the specific background of the questions. And, rather than assume, and react on that basis, I thought it wiser to ask first.

In our shop, we routinely top off cylinders, already containing trimix, with air. We do the top off with OCA, so contamination isn't (or shouldn't be) a problem. And, as we do with nitrox fills, we require the customer to analyze the gas and verify what is in them, when they pick up the tanks, before we let them go.

 

[Gilldiver]

None in MA? Really?

Hmmm, the following all have pre-banked nitrox (or did when I lived in MA two years ago):

Mass Diving (MASS Diving, Inc. - scuba equipment, scuba diving, dive, massachusetts, diving, new england, ma, boston, Natick, Framingham, metrowest, worcester, south shore, north shore)
Atlantic Divers (Atlantic Divers | 978-774-9997)
North East Scuba (Northeast Scuba in Chelmsford, MA offers PADI courses, diving gear, tank rentals, diving trips and dive instruction.)
South Shore Divers (Welcome to South Shore Divers)
East Coast Divers (East Coast Divers: Scuba Diving Instruction, Professional, Instructor, Courses, Lessons, Training, MA, Massachusetts, Boston, Framingham, Brookline, Travel, Equipment, Sales, and Service.)

I can also think of a few shops with boosters in NE.

Your general point, that many more shops PP blend in NE than elsewhere, however, is probably correct. Definitely the case as compared to SoCal, that's for sure.

Oh, and yeah, always He before O2! One costs A LOT more than the other.

OK, you made your point. That us what I get for being shop independent for the past 5 years or so. But in CT I know of only New England Divers of CT with a Booster.

Any shops on the Cape with Nitrox or a booster now?

 

[200 Bar]

nother question, just what do you consider "massive doubles" to be?

44ddd ....:d

 

[Capt Scotty]

44ddd ....:d

Now that's what I call a big set of doubles....

 

[Rainer]

It's all good. Trust me, I had to look hard and long to find the fills I wanted.

Doesn't Scuba Shack in CT (Scuba Shack) also have a booster? I know they fill air, nitrox, trimix, and argon.

Cape Ann or Cape Cod? I really only ever dived the former (where you had to bring your own nitrox; Atlantic Divers in Danvers was the closest bet otherwise; they *might* have a booster now). For Cape Cod, the only shop I know that pumps nitrox is the Dive Locker in Hyannis (http://capedivelocker.com/). Doubt they have a booster, though.

OK, you made your point. That us what I get for being shop independent for the past 5 years or so. But in CT I know of only New England Divers of CT with a Booster.

Any shops on the Cape with Nitrox or a booster now?

 

[Bretagus]

If you're filling from a bank of compressed air, then attaching a trimix tank to it will cause helium to diffuse into your banked air. I guess depending on the volume of the bank, this could be a negligable amount. Regardless, I wouldn't do risk it, especially if you're running a commercial operation.

 

[IDS_Bill]

Isn't trimix made with O2?

Terry

We usually do mixes that allow us to fill with He and top with air.

Examples: 10/50, 14/33, etc...

Makes it simpler is you don't have to put in O2.

I hate how paranoid some shops are about topping with air. If you are worried, make them sign your standard nitrox waver (you do have one right?). It's trimix, not high explosives.....

 

[Jim Lapenta]

If you're filling from a bank of compressed air, then attaching a trimix tank to it will cause helium to diffuse into your banked air. I guess depending on the volume of the bank, this could be a negligable amount. Regardless, I wouldn't do risk it, especially if you're running a commercial operation.

How do you figure this? The fill stations I have seen and used have a valve at the bank, another for the fill whip, one on the whip, and the tank itself. If you charge the whip and attach it to the tank, then open the whip followed by the tank valve it's pretty hard for 1500 psi of mix to push back 3500-4500 of air. When the tank is full at 3000 you close the feed from the bank. Close the whip, then the tank valve. You then bleed off the excess in the whip itself to relieve the pressure so you can get the whip off the tank. A lot of isolation there. Pretty hard to get mix back into the banks. Unless there is more pressure in the tank than in the air bank. In which case it would be stupid to try to fill from them anyway. There is no risk in topping off tanks. As long as reasonable care is used by someone with some sense and intelligence.