Switching from Air to Nitrox in the same tank?

[RonFrank]

If your tank is O2 clean, you can use a 21% O2 clean fill in place of air.

If you tank is not O2 clean, this is a mute point.

If you want an O2 certification on the tank, it needs to be O2 cleaned. Prices vary, so if you are finding it expensive to get a tank O2 cleaned, than review your options before making a decision.

IMO, if you are not diving over 60', O2 clean may not be necessary. I'm about to kill my O2 clean as diving locally, my max depth is 85', and while Nitrox WOULD be nice, it's also not available at a lot of places, and not all that necessary.

 

[Graeme Tolton]

I can be wrong but the above statement only valid for shops using partial pressure method

The compressor is going to still have to have the same filtration no matter what method is used... Can't be pumping non 02 clean nitrox from a continuous blend system into a Nitrox tank. The shop is more than likely using 1 compressor for everything.

 

[Web Monkey]

I am getting my Nitrox cert once I get back from the desert. However, my buddy is going to come dive with me for a week while we're on leave and he will be diving air and I'd prefer to dive air as well so we have roughly identical NDLs. Then once I head back I'd like to switch my tanks over to Nitrox only. Any problem going this way?

As long as nobody that fills your tanks will be doing Partial Pressure Blending (where 100% O2 is dumped in to the tank, the topped off with air), you can switch between air and Nitrox as often as you want and get fills anywhere you want.

As soon as you start getting fills from anyplace that does PPB, you'll need to have your tank(s) O2 cleaned and keep them that way. This means only getting fills from shops that use hyper-filtered (O2 compatible) air when mixing their gasses.

A "Nitrox" sticker on your tank is meaningless. An "O2 Clean" sticker will be required by anybody doing PPB, but it's only valid until you get a non-hyper-filtered fill. This is pretty much an honor system since they have no way of knowing, however if you get a bad fill somewhere and lie about it, you could be responsible for burning down/blowing up your LDS and/or killing or maiming the employees.

Terry

 

[RonFrank]

To summarize, there are two methods for blending Nitrox.

1) PPB - Partial pressure blending. This involves putting 100% O2 into a tank, and then topping it off to obtain either mixes beyond 36%, or odd mixes. This method can also be used to obtain any Nitrox blend, and if the shop uses this, your tanks are required to be O2 clean.

2) Bank blending - In this case the blending is done in large banks of tanks. Fill Express for example has banks for common blends. Many bank systems only bank one common blend like 32%. In this case the O2 content is not generally high, and pure O2 is never introduced into the individual tank. Shops may still require O2 clean tanks to provide this fill, but most agree that is not necessary.

Depending on your shop, and their requirements you may or may not need O2 clean tanks to get a Nitrox fill.

 

[mkutyna]

Something not directly mentioned is that if you are going to be diving tables, you may not be able to switch back and forth between Nitrox and Air depending on which tables you use. Some computers do not allow you to switch back and forth either without waiting for 24 hours. Sometimes you can trick them and tell them that you have a 21% nitrox mix though.

 

[SteveAD]

Something not directly mentioned is that if you are going to be diving tables, you may not be able to switch back and forth between Nitrox and Air depending on which tables you use. Some computers do not allow you to switch back and forth either without waiting for 24 hours. Sometimes you can trick them and tell them that you have a 21% nitrox mix though.

I am not aware of any circumstances under which any of this is true.

 

[Teamcasa]

It seems none of the so-called rules are followed by all of the different shops with any degree of consistency. Some will demand O2 cleaning (regardless of filling method) and some don't know or care as long as it has a Nitrox sticker and still some just fill it and call it a day. The hard part is trying to convince them to do something different.

Personally, I would not bother. Different NDL's won't matter much unless you are diving doubles or going really deep.