Oxygen clean?

[Marcosis]

I'm nitrox certified for about 2 years and have a really silly question I've wondered about but never asked as to not seem like an idiot!

Why does a nitrox tank have to be oxygen cleaned and what would happen if it were "contaminated" by a regular air fill?

I understand the flamibiltiy of oxygen but I don't understand the reason of the importance of dedicated nitrox tanks.

Thanks for the help. Marc

 

[The Kraken]

If a nitrox dedicated tank were to be "contaminated" by filling from a station not rated to do O2 compatible air fill, technically it would have to be "O2 cleaned" again.

What would "happen"? Probably nothing.

Oxygen, in and of itself, is not flammable, it only supports combustion of a flammable substance.

Hydrogen on the other hand . . . well, remember the Hindenburg????

Special greases and materials are used in nitrox dedicated tanks that greatly reduce the possibility of flash combustion when pure O2 is being pumped into a tank. The filling process generates great pressures and significant heat.

It is the heat element in the filling process that creates the hazardous situation.

That said, there are other situations wherein some petrochemical materials may react, with some volatility, to the presence of 100% O2.

the K

 

[gypsyjim]

First understand, I am not an expert. Only did my EANX earlier this year, but I work with Oxygen every day. I think the problem is that pure Oxygen is used in some methods of filling, where the mix is not done up stream. The risk of filling pure Oxygen into a tank that might be contaminated with substances that could be combustable in that environment is risking some one's life and health. Not worth killing someone!

 

[rongoodman]

Unless your shop is providing partial pressure fills, it won't be an issue. Just be sure to ask.

 

[dannobee]

Yup, as stated above, it's only an issue if the shop is filling using the partial pressure method. They'll usually say they "blend" your gas. If they "bank" nitrox, it doesn't need to be oxygen cleaned.

FWIW, oxygen cleaning includes cleaning not only the tank, but the valve should be taken apart and cleaned, along with O2 compatible parts installed.

If a previously oxygen clean tank is filled with "regular" air, there's a chance (albeit small) that hydrocarbons from the oil used in the compressor gets passed the piston rings and gets into the tank unfiltered. Then the next time someone adds oxygen, the tank goes boom.

 

[cummings66]

Not to disagree, but an O2 cleaned tank can go boom as well. The issue is one of how it's filled, i.e. how quickly they fill it as much as how clean it is. With proper procedures you might get away with filling a dirty tank, and with improper procedures you might cause problems in a clean tank.

Of course, a EAN diver should be well aware of the safety aspects of diving this mix and the do's and don'ts, if not then it's not a bad idea to reread the books or ask questions. Better to ask and be safe than sorry.

 

[Marcosis]

Thanks for the info everyone. The more I know about what can kill me ,the better.
Have a great day!!

 

[steveann]

The O2 cleaning is for partial pressure filling and for FO2's above 40%. Of course, those are just guidelines, and you can fill a non-O2 clean tank just as easily as an O2 clean one. Of course, you're dealing with a situation that can kill you faster than you can think if you screw it up, so why not play it safe and get the O2 cleaning when you're going to do things like PP fills and >40%?

And yes, it's about the hydrocarbons and impurities non-O2 clean air puts in the tank. Those impurities can have a reaction with high FO2 concentrations, causing a spontaneous combustion effect, which in turns leads to a high O2 fire. Of course, you as a diver really don't need to worry about it, unless you're filling your own tanks. It's the guy who does the fills who better be on the ball.