Visual Inspection and O2 Wash

[eweingarden]

I'm putting my steel tank in for it's first visual since buying it. I use it for both Nitrox and air. The dive shop tells me I need an O2 wash in addition to the vis. Does that sound correct? Thanks.

 

[Tug]

Are you using the tank for partial pressure nitrox blends? If so, the tank should be kept O2 clean. If you're just using premix nitrox blends, then keeping the tank O2 clean is unnecessary.

 

[Scared Silly]

Perhaps, was the air used always Mod Grade E (i.e. O2 compatible air) or plain ole air? If plain ole air and the inspection for hydrocarbons is positive then following DOT standards yes it needs to be O2 cleaned for use with O2 percentages above 23.5%. Even if you used Mod Grade E air and NITROX you still might need to have the cylinder O2 clean because of hydrocarbon contaminants. Regardless I would test for hydrocarbons and decide based on the test results. So is it absolutely required no.

Now, some will come along (like the post above) and say no you do not need to have your cylinder O2 cleaned if using less than 40% NITROX. However, that is not following DOT standards when filling above 23.5%. That is an ad-hoc process that some fill operators have adopted and is not recommended.

 

[eweingarden]

Thanks for the detailed replys. Since I get both Nitrox and air fills at different shops, depending on where I'm diving, I'm not sure of the Nitrox method, nor the grade of the air. Since I don't know what's involved in testing for hydrocarbons, nor the cost, I suppose it's best to just get it O2 cleaned.

 

[redacted]

The problem is there are different standards. Some set 40% and others set 23.5%. From a safety standpoint, there does not appear to be any data supporting one standard over the other. It is my impression that most shops follow the standard that makes them the most $$$. Providers that bank Nitox usually go with the 40% standard. Those that PP blend use the 23.5% standard.

I believe scuba training agencies are still using the 40% standard in their training.

I don't believe the banked providers care much about the grade of the air whereas the PP blenders (who are supposed to be using the higher grade of air) also tend to be the ones saying you must repeat the O2 cleaning if you used regular breathing air in your tank. They make more $$ that way.

 

[eweingarden]

The cost differential is substantial. Is the risk of not getting an O2 wash real...have cases been reported in dive journals and/or forums of adverse events with a presumed cause to be the lack of O2 cleaning?

 

[redacted]

The cost differential is substantial. Is the risk of not getting an O2 wash real...have cases been reported in dive journals and/or forums of adverse events with a presumed cause to be the lack of O2 cleaning?

PP blending in a tank that is not O2 cleaned is just asking for trouble. If your tank is not O2 cleaned, you should not be able to get gas from PP blenders.

So the difference is not really safety but the limitation of where you can buy nitrox. As long as you have a banked nitrox supplier, you should have no problem with your "unclean" tank.

 

[eweingarden]

Safety is always my number one priority, so the cost differential although significant, is inconsequential.

 

[MB]

So far, nobody has addressed the valves... O2 cleaning the cylinder without also cleaning the valves makes me wonder whether:

1. the cylinder didn't actually need it but it was a good way to increase some coin;
2. the dive store can't manage cleaning valves so they didn't require it;
3. the folks at the dive store aren't smart enough to think about the valves...

Don't let the mystery of the filling method confuse you. Go back to your nitrox text and review the fill methods. If you aren't clear, just ask. Its far better to gain that knowledge than to let the dive store salesperson confuse you into buying un-needed stuff.

 

[JohnnyC]

If there is ever the potential to get a fill where there will be pure O2 introduced into the tank at any point, you need to have the tank and valve O2 cleaned. Period. Full stop. If you are unsure if this will be the case, you need to have the tank and valve O2 cleaned. Period. Full stop.

The cost is marginal in the grand scheme of things, and could prevent a serious incident.