Ad-Hoc Tank Blending Risk

[gmerick]

Topic came up in after-dive conversation. I was complaining about the lack of banked Nitrox anywhere in the local area. The few dive shops that do offer nitrox all use a booster pump and blend directly to the customer's cylinders. Of course they all insist on current 2 clean certification. Some around the table described their personal work-around. They rent a 250cf Oxygen tank, and bought a transfer whip with O2 / DIN fittings. Prior to bringing the tank to the local (non-Nitrox) dive shop, these divers would connect the O2 transfer whip, and bring the tank pressure up to 1000psi. I gathered that the 1000 number was only approximate, and they would actually do the math for the desired EAN blend. These cylinders, now way in excess of 40% O2 would be brought to the unsuspecting LDS for filling.

I am looking for a concise risk statement to support just how bad this process really is. I've downloaded the Oxygen Hackers Companion, and the manual from Eco Diving.

I guess my biggest concern is if the high O2 content of the cylinder rapidly back-feeds the LDS fill whip. Of course there are numerous risks the divers are taking on themselves transferring 100% O2 to their own tanks,

 

[Lorenzoid]

I don't know the risk, but I recall reading in a tech diving history about this workaround being used by outlaws, er, pioneers in the very early days of Nitrox, when it was considered voodoo gas by many.

 

[runsongas]

depends on the fill system setup. fully automated system is basically zero risk, low risk for manual cascade and experienced/careful operator, inexperienced or sloppy operator + fully manual system is where the problem lies.

 

[happy-diver]

Of course there are numerous risks the divers are taking on themselves

Those things you talk about I do at home, it would be good to have a relationship
with the pumping guy which you should anyway so he knows what he is pumping

I thought a while back, that rather than trying to control life, I should let life control me
and I've found that generally if you respect stuff, even when you're dealing with people
you should get some respect back certainly when dealing with mechanical and physical
things like when we started learning about petrol, oxygen which isn't scary, even diving

The thing is that you still have to steer the ship, so if it's mostly through troubled waters
is where you shall be where the difference between a good day and bad is state of mind

Unless you win the lottery which many blow away anyway


What is not a state of mind is how many millions of drive gas gallons you use boosting
in order to steer the ship out I am currently bringing this electric beauty into O2 service

We will see how I go but I already know, please don't blow

With experience maybe comes learning, and some change

 

[Lostdiver71]

As someone who dealt with that problem back in the early 1990’s working at a dive shop, there are several problems that you can have. One of the most common was that if you hooked up multiple tanks up and opened the valves before pressurizing the system, the O2 could get distributed between all of the tanks causing them all to be at the wrong O2 percentage.

 

[Learner Diver]

I guess my biggest concern is if the high O2 content of the cylinder rapidly back-feeds the LDS fill whip. Of course there are numerous risks the divers are taking on themselves transferring 100% O2 to their own tanks,

Wouldn't you check your cylinders before diving anyway?

 

[happy-diver]

his concern is oxygen entering a depressurised whip quickly not what's left in the bottle

 

[Learner Diver]

his concern is oxygen entering a depressurised whip quickly not what's left in the bottle

...and the quick answer is?

 

[Lostdiver71]

Wouldn't you check your cylinders before diving anyway?

Not if you think that you are getting air fills and get Nitrox instead.