Nitrox Fill - Is This Cool??

[LakeStevensCatDiver]

I don't remember this being covered in my nitrox class...so I'm posting to see if some experts will chime in.

I got my last nitrox fill in a small town with one LDS. When I did the analysis, one tank was close to 80% oxygen. The LDS dude tells me that they forgot to mix the regular air. Turns out that they don't have nitrox fill capabilities in the shop, so they contract with someone that does a partial fill with pure O2, then the tank comes back the shop, and they top it off with regular air to get the percentage down the normal Nitrox range.

I am wondering if this is cool, because I looked into just going back to regular air (because I couldn't always find a nitrox fill on the weekend). I was told by a few folks that as long as I stayed in the 32-36% range, I could switch back and forth between nitrox and air without loosing the O2 certification on my tanks/reg.

See where I'm going with this? If the LDS is putting pure O2 in the tank BEFORE mixing in the regular air....does this now mean that I can't use an occasional regular fill without risking problems during the pure O2 fill process?

This may be a totally normal process, but I'd like to get some input from some DM's or LDS operators. My goal is end every dive breathing...I'm kinda funny that way...

 

[Uncle Pug]

My goal is end every dive breathing...I'm kinda funny that way...

EAN80 fill when you expected EAN32?

That was unacceptable. And if you are having your tanks filled by PP blending then the only air the tanks should see is O2 compatible air.

It amazes me how hard it is to get decent nitrox fills around here.

Please PM me with the name of the dive shop.

 

[bug]

It is my understanding that the only way a tank can be enriched air certified is if it is always filled by a compressor that can handle enriched air. So if a nitrox tank is ever filled by a normal air compressor then it is no longer enriched air certified.

To get 21% gas in an enriched air bottle the compressor is dialed in or using by partial by only enriched air compressors.

With that in mind an enriched air bottle that has gas in it should never be filled by a normal air compressor.

 

[stratboy]

EAN80 fill when you expected EAN32?

That was unacceptable. And if you are having your tanks filled by PP blending then the only air the tanks should see is O2 compatible air.

It amazes me how hard it is to get decent nitrox fills around here.

Please PM me with the name of the dive shop.

Define "PP blending"?? Thanks.

 

[emtdan]

Please disreguard my previous post, I realize I didnt completely understand the situation, thats what you get for not completely reading the initial post. And no, I didnt need 3 replies to tell me that.

 

[Uncle Pug]

Partial Pressure blending is where extra oxygen is added to the cylinder and then it is topped with air to get the final desired fraction of O2.

Continuous Blending is enriching the oxygen content of the gas entering the compressor either through the direct addition of O2 into the intake stream (what I do) or though the use of a de-nitrogenating membrane system.

 

[Uncle Pug]

dsaxe01
Obviously there was a major screw up.

 

[LakeStevensCatDiver]

Are you saying that the contractor fills every tank with 80%, bleads it, then fills with air? I have a few problems with that:

1) Isnt that a HUGE waste of 02? to drain your tank from 80% to 30%? then refill with air?

Not quite what happened...no bleeding of O2 involved. When it was 80%, the pressure was way low because the plan was to complete the fill with regular fill air.

 

[SeanQ]

Good thing you analyzed your tank. If you didn't analyze it, you could have easily died from O2 toxicity. This is not cool.

 

[jbd]

I got my last nitrox fill in a small town with one LDS. When I did the analysis, one tank was close to 80% oxygen. The LDS dude tells me that they forgot to mix the regular air. Turns out that they don't have nitrox fill capabilities in the shop, so they contract with someone that does a partial fill with pure O2, then the tank comes back the shop, and they top it off with regular air to get the percentage down the normal Nitrox range.

I read through dozens of documents from DOT and OSHA the last couple of days and it seems like I read something that would indicate that this practice is in violation of DOT or OSHA regulations. What I am referring to is the O2 fill being done at one place and then the tank being transported to another place and topped off with another gas.

I am wondering if this is cool, because I looked into just going back to regular air (because I couldn't always find a nitrox fill on the weekend). I was told by a few folks that as long as I stayed in the 32-36% range, I could switch back and forth between nitrox and air without loosing the O2 certification on my tanks/reg.

If you go back to regular air any markings or labels that indicate that the cylinder is O2 clean should be removed. If you decide to go back to Nitrox fills via the partial paressure blending method the cylinders would need to be re-cleaned. Thats the way it should be done, however, its not always done that way.

See where I'm going with this? If the LDS is putting pure O2 in the tank BEFORE mixing in the regular air....does this now mean that I can't use an occasional regular fill without risking problems during the pure O2 fill process?

Indeed there would be an increased risk. Just how much would be anyones guess, but when you consider the consequences when there is an O2 fire/explosion not much of increase would acceptable