Nitrox on Dive Boats Question

[runway1]

Am told by a LDS manager that local dive boats don't have "clean" nitrox. He said that I would have to reclean my tank if got EAN on the boat.

Anybody have info on this? Thanks.

 

[mselenaous]

Nitrox tanks are cleaned to be O2 compatible. From that point forward whether diving on an enriched O2 mix or a 21% air mix, that air must be O2 compatible - in otherwords, that air that is used to mix Nitrox has been through extra filtration systems. If you fill a Nitrox cylinder with standard air rather than O2 clean air, then that tank must be recleaned for future nitrox fills or be retired from Nitrox service. Fill stations are required to have their air tested quarterly to meet required standards. The standards for O2 compatible air are more stringent. Producing O2 compatible air is also more expensive because of the additional filtration. In many LDS you will still pay more for a %21 air fill of Nitrox compatible air for your Nitrox tank, than you will for a standard air only fill.

To answer your questions regarding Nitrox on dive boats. Most day charter dive boats do not have nitrox/O2 cleaned fill capabilities. Hence, if you want to dive nitrox on these boats, you have to take all of your nitrox tanks with you. Those that do have compressors for refilling tanks will only refill standard air tanks as they do not have the extra systems in place to provide O2 clean/nitrox compatible air. Some liveaboards on the other hand do have full on Nitrox systems. These liveaboards usually provide you with their own cylinders which they maintain to meet nitrox standards. Some of the liveaboards, to avoid having 2 systems aboard - one for nitrox and one for air - will fill all tanks with the same more expensive O2 compatible/nitrox clean air for the air divers as they use for their nitrox fills.

And one more issue with nitrox fills. Once initially filled, many tanks are just topped off using the partial pressure method. Read the existing amount of nitrox and its PO2, then calculate the top off mix - how many psi of O2 to add and then the psi of air to add. We as blenders are trained that if we did not mix the existing remaining nitrox blend (ie the source of that O2 and air), that we must drain that cylinder and start with a new mix rather than top it off. That is more time consuming and costs the LDS more for each fill. And if we can not for certain verify that the cylinder & valve have remained O2 cleaned internally, that we can refuse to refill it until it has been re-O2 cleaned.

I recommend to you, that you check with the dive boat you are planning to go out on and ask them about their capabilities. If you own your own Nitrox tanks, use your LDS for all your fills and follow their recommendations.

Diving with nitrox can greatly enhance your dive profiles, but it does require a little more diligence with the safety issues. The basic nitrox diver classes teach you the basics of using nitrox (ie. check your blend then reset your computer) and IMO don't place sufficient on these issues. I also recommend the Gas Blender class to learn the science and techniques involved in gas blending (whether you decide to fill your own tanks or not) so you will be able to judge for yourself the fill station operation upon which your life underwater depends upon.

Just my 2psi.

 

[Teamcasa]

Am told by a LDS manager that local dive boats don't have "clean" nitrox. He said that I would have to reclean my tank if got EAN on the boat.

Anybody have info on this? Thanks.

What boats?

 

[runway1]

Magician fills NEA during a single day trip. Says on their website:
The Magician now provides 32% NITROX fills for NITROX certified divers for an extra charge. You can use any tank with our membrane system, O2 clean tanks are not required.

Then, upon hearing, the LDS fellow said "It's not clean! You'll have to reclean your tank if you got NEA from the boat.".

 

[Teamcasa]

The Magician uses a Membrane system and fills at 32%, therefore O2 cleaned tanks are not required. Nitrox filling makes some people crazy. Does filling an O2 clean tank with Nitrox render it unsafe for re-filling Nitrox? To me, not a chance. But one thing is certain, it does not matter what I think or what the facts or truth is. Some shops will not fill a tank with Nitrox unless it is O2 clean and has never had 21% air or been filled on any boat. I found it’s just not worth arguing with them.

That said, many boat fills, regardless of whether they are pumping Nitrox or air can be wet. This should not matter but you should have your tanks vis’d a little more often if you dive off boats frequently.

 

[Web Monkey]

Magician fills NEA during a single day trip. Says on their website:
The Magician now provides 32% NITROX fills for NITROX certified divers for an extra charge. You can use any tank with our membrane system, O2 clean tanks are not required.

Then, upon hearing, the LDS fellow said "It's not clean! You'll have to reclean your tank if you got NEA from the boat.".

The reason it's confusing is because they're using irrelevant and misleading terms.

Tanks need to be O2 cleaned if they will be filled using a method called "Partial Pressure Blending". This involves adding 100% O2, then topping off with "hyperfiltered air", which is also known as "Grade E Modified".

Tanks do not need to be O2 Clean if they will be filled using any type of continuous blending, where the nitrox is already at the desired percentage (32%, 36%, etc.) when it is added to the tank. This type of nitrox does not have to meet the standards required for Partial Pressure Blending. This is what they are using on the boat, and is why you don't need O2 clean tanks to get a nitrox fill on the boat.

However this also means that if your shop does Partial Pressure Blending, and requires an O2 clean tank, and you get a fill from someplace that does not meet the "Grade E Modified" standards (the boat), your tank needs to be re-cleaned before the shop that does PPB can fill it again.

The reason for this is because tank contaminants can cause a fire or explosion when filling using PPB.

While the boat says that you do not need an O2 tank, what they're not telling you is whether or not it will still be O2 clean after you get a fill. It's possible but unlikely that their air meets the Grade E Modified requirements. In fact, a lot of boats have a hard time even meeting the standard requirements.

Terry

 

[scjoe]

The shops don't know what you have had put in your tank, so it is an honor system. The person at risk when filling a tank that is no longer O2 clean is the shop employee, not the customer.

The likelihood of a fire occurring when putting 100% O2 under high pressure into a tank that is no longer O2 clean may be quite low for any single fill, but if a fire does result it will be catastrophic. The average dive shop does not have the capacity to handle an O2 fire.

 

[runway1]

The reason it's confusing is because they're using irrelevant and misleading terms.

Tanks need to be O2 cleaned if they will be filled using a method called "Partial Pressure Blending". This involves adding 100% O2, then topping off with "hyperfiltered air", which is also known as "Grade E Modified".

Tanks do not need to be O2 Clean if they will be filled using any type of continuous blending, where the nitrox is already at the desired percentage (32%, 36%, etc.) when it is added to the tank. This type of nitrox does not have to meet the standards required for Partial Pressure Blending. This is what they are using on the boat, and is why you don't need O2 clean tanks to get a nitrox fill on the boat.

However this also means that if your shop does Partial Pressure Blending, and requires an O2 clean tank, and you get a fill from someplace that does not meet the "Grade E modified" standards (the boat), your tank needs to be re-cleaned before the shop that does PPB can fill it again.

The reason for this is because tank contaminants can cause a fire or explosion when filling using PPB.

While the boat says that you do not need an O2 tank, what they're not telling you is whether or not it will still be O2 clean after you get a fill. It's possible but unlikely that their air meets the Grade E Modified requirements. In fact, a lot of boats have a hard time even meeting the standard requirements.

Terry

The shops don't know what you have had put in your tank, so it is an honor system. The person at risk when filling a tank that is no longer O2 clean is the shop employee, not the customer.

The likelihood of a fire occurring when putting 100% O2 under high pressure into a tank that is no longer O2 clean may be quite low for any single fill, but if a fire does result it will be catastrophic. The average dive shop does not have the capacity to handle an O2 fire.

Now that's good info. Much more clear now. Thanks!

 

[runway1]

Which begs the question; Then why nitrox? Wouldn't you want to use it for multiple dives? Don't multiple dives usually occur from a boat?

How often does someone go multi-diving while returning to the LDS for a NEA fill?

 

[Web Monkey]

Which begs the question; Then why nitrox? Wouldn't you want to use it for multiple dives? Don't multiple dives usually occur from a boat?

How often does someone go multi-diving while returning to the LDS for a NEA fill?

We just bring more tanks.

Two tanks is usually plenty of air for a deep dive and a couple of shallower dives. I'm generally happier doing that anyway, since the percentage of contaminated tanks that we see during O2 cleaning is a lot higher than you would expect.

Terry