Topping off Tri-Mix with air

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E nomine patre, et spiritu, sanctu. You are forgiven. Go in peace and sin no more. And don't start crap either or God'll kick your ass! I love it when the priest says that.

snort!
 
I know many shops where when a whip goes on a tank, its a fill no matter if they started at 100 SPI or 2500. They also charge more for a tank above 80 cubic feet. One shop near by is asking for $12 to fill any single tank above a 100 with air.

As for top offs, if you were doing something like a 21/30 mix at 3000 psi you would add 240 psi O2 and 930 psi He and top off to 3000 with air. The mix in the tank at the time that you start the air fill is 20% O2 or just a little under air. In other words there is no explosion problem.

In the North East we will many times make up a rich mix like 17/70 with the intention of diving them by strict thirds, then top off with air to get a lighter mix of 21/25 or so for a shallower 2nd dive with the same tanks.

There is a potential for contamination, so did they ask for Grade E air?

At least they told you what they were doing, many will just ask for a fill and analyze down the street.
 
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.

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

If the OP was setup to do partial pressure blending, he woudl already be pumping Grade E modified air, wouldn't be asking the question, and it wouldn't be an issue. I'd say "feel free!."

However, since he did ask the question, I'm going to assume he's not setup for partial pressure blending and is not pumping hyperfiltered air.

This means that he may be contaminating the tank, which could become a problem when the tank owner goes to dump in the O2, or even if he isn't contaminating the tank, when the owner burns his house down while filling O2, the first place anybody will look is to the SCUBA shop that filled his tanks with air that wasn't certified to the necessary standards.

You can feel free to fill whatever you please, however from my perspective, it's a ton of liability to accept for a few bucks.

Terry
 
This means that he may be contaminating the tank, which could become a problem when the tank owner goes to dump in the O2,

Sort of, but this has nothing to do with topping up He mixes. It only has to do with those that also use their cylinders with pure O2. Since the shop hasn't cared to date about this possibility, why worry about the trimix?

In any case, if your gas is so bad that it can cause a spontaneous fire when introduced to pure O2, I don't want to be breathing that ***** in the first place!
 
I've run into the same problem before in the Keys and it all came down to the guy filling the tank having no clue what he was doing. For some reason he thought Trimix was some kind high O2, nitrox mix with Helium thrown in for an unknown reason and that pumping air on top of it would somehow cause a thermo nuclear reaction. :nuke:

Once we got the shop owner involved and explaned to them both exactly what Trimix was and why there was no issue with topping up the tanks with air they were more then happy to do it. Trimix typically has no more then 21% O2 and, depending on the depth of the planned dive, could have as little 8 to 10% O2 so topping off that kind of mix with plain air would pose absolutely no risk of any kind of explosion, unless you put a cave fill in a set of AL tanks but I won't go there. :D

If these guys were certified to dive with mix then they should be smart enough to know that filling their tanks with J grade air will render them "unclean" and unfit for O2. They should also be smart enough to analyze the tanks after the fill and plan their dive accordingly.

Check their C cards for the proper mix cert and if they have it top off the tanks.
 
Sort of, but this has nothing to do with topping up He mixes. It only has to do with those that also use their cylinders with pure O2. Since the shop hasn't cared to date about this possibility, why worry about the trimix?

In any case, if your gas is so bad that it can cause a spontaneous fire when introduced to pure O2, I don't want to be breathing that ***** in the first place!

Isn't trimix made with O2?

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

Isn't trimix made with O2?

Terry
 
If these guys were certified to dive with mix then they should be smart enough to know that filling their tanks with J grade air will render them "unclean" and unfit for O2.

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.
 
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