Not sure if I'm going mad but....

Buddha Boy

.....can anyone confirm whether or not bottles that are used exclusively for hypoxic Trimix blends needs to be O2 cleaned? Is it an HSE requirement?

My bud has a problem at the mo with a dive shop (to remain anonymous (for now!)) who says they won't fill his Trimix labelled 3l dil bottle with 18/48 as it doesn't have an O2 clean sticker or certificate.

I haven't had my Trimix dil or offboard bottles O2 cleaned and have had no probs having them filled (even at the same shop). I'm sure you don't need to O2 clean if you're using 21% or less, but for the sake of my sanity, I thought I'd ask!

Cheers,
Pete

Beanie

Probably due to partcial pressure blending - still going to be putting O2 into the cylinder.

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JPJones

If they are partial pressure blending then the bottle needs to be O2 cleaned.

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lizardland

Hypoxic mix or heliair?

Heliair wouldn't need O2 cleaning as it is just helium and air, and the mix would be hypoxic.

What the others said if it is a true trimix with pure O2 (or a rich EAN) going in.

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nigelh

As others have said:
18/48
Start at 1 bar.
Add 18 bar of oxygen
Then 109 bar of Helium
Air top to 230bar

If youre putting pure O2 in at any stage of the operation it wants to be oxygen service and oxygen clean even if the final mix is hypoxic.

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nigelh

diverklondike

There is a way around it depending on what kind of premix nitrox your shop carries. It will eliminate the need to have your tanks 02 cleaned.... It's an old trick that I used in the OC days...

Start with 118 bar of He in the tank.

Add 100 bar of Nitrox 36 - Must be premixed

Top with 12 bar of air

The gas mixer in V-Planner supports playing with the numbers like this. You simply say that you want to do a trimix top off and start with 0% He in the mix. You could start with the nitrox in the bottle and top with He. It's just a bit harder on your booster.

Good Luck and Dive Safe


Mark

Mixaddict

Why not just O2 clean the bottles and not have the problems with dive shops filling them? That way, regardless of the process that the shop uses to fill, you will be able to get them filled.

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Buddha Boy

Dear All,

Many thanks for the responses; they're really appreciated.

Very good point made - of course, add the 100% O2 first, then top off; my mind had fixated on the heliair mix method.

Mixaddict - I promise you we are religious about O2 cleaning and testing, Gold Card members at G-Squared in Burgess hill in fact!!! Clearly we need to double check though.

Thanks again to all and have a great (safe diving) weekend.

Pete

diverklondike

Pete,

As a quick aside... "HighJack" A lot of Rebreather divers here in the US dive with 10/52 as a standard dil. for dives in the 120 fsw - 270 fsw.

1) Very easy to mix... fill bottle half with He and top with air.

2) Very simple to calculate expected FO2 with for a full dil. flush.

3) The O2% is low enough to make a real difference when flushing at depth to address a high PP02

Dive Safe

Mark