Gettiing to 32%

[billt4sf]

They are not my tanks. I am renting them from the shop that is mixing the gas. I was wondering whether the low O2 % might be due to them using them for air, then Nitrox, and if so, is that bad? IIRC, during my Nitrox training they said that should not be done.

- Bill

 

[Chugwhump]

Billt4sf;
here is my two pieces of copper that are really just zinc discs that are coated with a thin layer of copper.

I am assuming that these are "partial pressure fills" that they are preparing for you.

I am FULLY in the "roll 'em around before you test them" camp on this one.
I have had my tanks filled MANY times in this PP fashion, and have seen as much as a 4% variance from initial reading to final reading in my gigantic steel lp120's, and hp 130 and 149's after having kicked them around for a minute or so.
I would under no circumstances ever write a number on the label that was not what I personally had read on the tank from an analyzer.

Chug
Like sticks and membranes but hates green nitrox bands.

 

[tomfcrist]

It's nessecarily bad. I do it all the time with my tanks. I consider it partial pressure filling to 21% nitrox.

 

[Superlyte27]

I am not nearly as experienced as the others that have posted on this subject but I have never heard of 32% mix starting out at 28% and ending up at 32% later. That's a new one to me and a bit suspicious IMO. When my LDS fills 32% or 36% and we analyze the tank it is as stated above +/- ~1%.

Completely normal minutes after filling. 4 hours later, if it was filled right, it'll settle out to 32%.

With that said, I won't dive anything without first analyzing it's final mix. This is the reason why everyone should own their own analyzers.

 

[boulderjohn]

They are not my tanks. I am renting them from the shop that is mixing the gas. I was wondering whether the low O2 % might be due to them using them for air, then Nitrox, and if so, is that bad? IIRC, during my Nitrox training they said that should not be done.

Going back and forth between air and nitrox has no impact whatsoever on the ability to come up with the correct nitrox percentage.

The reason you were told not to do that in your nitrox tank was a fear that putting in air that is not properly filtered into the tank could introduce contaminants that could ignite when pure oxygen is added to the tank during a partial pressure nitrox fill. But when a tank is filled with nitrox using tje partial pressure method, air is added to the tank after the oxygen. So any tank that has been partial pressure filled with nitrox has also had air added to it, so it makes not sense to forbid air fills. You just have to make sure the air is filtered enough. If the air being added to a partial pressure nitrox fill is clean enough for that purpose, then it is clean enough for an air fill.

 

[Dr. Lecter]

Recently did a PP blend for 80%, added the calculated pressure of O2, topped with air to 3000, and analyzed maybe 5 minutes later...came in at 58% or something. Checked the math, checked what was added, and it should have been 80%. Checked again the next morning and it was 81%.

Tell your shop that mixing it 10 minutes before you pick it up is no longer acceptable and that you'll reject any tank that doesn't analyze right before you leave the shop.

 

[Superlyte27]

Tell your shop that mixing it 10 minutes before you pick it up is no longer acceptable and that you'll reject any tank that doesn't analyze right before you leave the shop.

Everyone diving Nitrox should own their own analyzer.
It's only a matter of time before you end up at a dive site and realize you forgot to check at the shop. Your choices are dive with an unknown gas or call the dive. Both of those options really friggin suck, and the first option might kill you. That's simply not acceptable.

 

[Dr. Lecter]

Everyone diving Nitrox should own their own analyzer.
It's only a matter of time before you end up at a dive site and realize you forgot to check at the shop. Your choices are dive with an unknown gas or call the dive. Both of those options really friggin suck, and the first option might kill you. That's simply not acceptable.

Duh. The point is that you can't know WTF you're taking if you can't accurately test it before leaving. Analyzing just before the dive will save your ass but not your dive.

After more than one 'make multiple drives out to the shop to get the O2 % right' experience, my rule is that if I can't read it accurately before I leave, I'm not accepting it.


Sent from my Shearwater Petrel using Tapatalk

 

[Superlyte27]

Duh. The point is that you can't know WTF you're taking if you can't accurately test it before leaving. Analyzing just before the dive will save your ass but not your dive.

After more than one 'make multiple drives out to the shop to get the O2 % right' experience, my rule is that if I can't read it accurately before I leave, I'm not accepting it.


Sent from my Shearwater Petrel using Tapatalk

First of all, if your shop can't consistently get it right, get another shop. Secondly, it might kill the plan, but probably won't kill the dive. You wanted 30% but got 32%... don't go as deep. You wanted 32% but got 28%... don't stay at max depth for quite as long. Neither of these issues is life threatening. However, picking up a tank that is labeled 28% when it left the shop but is really 34% when the tank stabilizes could possibly kill you.

 

[PfcAJ]

As moronic as this sounds, turn the tank over, then turn it right side up. Analyze. It might just read what you expected it to if it was recently blended.

Sounds ridiculous, and I used to clown on people who talked about this before I saw it myself.