converting air tanks to EAN

[NAM001]

Just how do you know,,, REALLY KNOW,,, that you are getting E+ air short of testing each and every tank fill in a lab? So this statement is mostly moot. There are too many threads about O2 cleaning that if all was taken to heart one woould never get ouit of bed in the morning. I have talked to people who do gas analysis and they say most samples meet or far exceed the oca requirements. The cluge in this is that sampales are often taken with new filters fresh oil and a number of aspects to insure a good if not better lab result to cvover their liability. The real test owuld be what is the gas content 1/2 through the filter life. And that is cost prohibitative. So i guess that if you want to ge a warm fuzzy on the air quality would be to look at how many filter stages is used, what they are and hope that they are maintained properly. No matter what,,,, you dont have any idea what you are getting,, so integrity becomes the major factor. If you could regulate integrity it would be done by a body that knows nothing about it and would have to govern by the 'WHAT IF" process.

As far as the new tank is concerned mine have come plugged and labeled saying cleaned for up to 40% o2. They also say that they have been vis'd by the maker and their vis is good for one year from the born date or the first service date, I dont recall. The fillers do not accept that either as proof of a vis.

O2 cleaning does not make the tank sterile. all it does is the hazardous levels of IE oil that if under the right condition could cause a problem are removed. There are those who have posted regulation sections that say that O2 cleaning must be done on any any tanks with mixes of >23.5 and that the cleaning MUST be done prior to each use. All i can say is that those who beleive that a cleaning is required for each fill are living in that world whre they are afraid to come out of the house.

I don't think this is correct. The room air isn't really relevant to the O2 cleaning standard (barring suspended oil mists, which cause you other problems).

If the manufacturer claims the tank is O2 clean, it will come with a shipping plug that protects the threads and interior. If an O2 clean valve and O2 compatible O-ring are installed, the tank is O2 clean and ready for PP blending. If a tank has been O2 cleaned, and is unused, it's still O2 clean.

What pollutes the tank is substandard (less than E+) air fills. It only takes one such fill and your tank is no longer O2 clean. This is common in the middle east.

 

[SOFDiver]

KWS makes some good points. I think the answer is how the shop you are working with is set up, and who they service. For example: In our shop we PP fill nitrox, but we also do lots of air fills for customers and our charter boat (often more than 100 a day). We have two seperate fill stations. Our nitrox station air is filtered 3 times, giving us the cleanest air we can possible produce and suitable for Trimix as well as nitrox. Our "air only" station product exceeds grade E standards. When we fill a tanks that are O2 cleaned they are filled at the "nitrox" station even if only being filled with air, ensuring against any risk of contamination. To ensure quality of air we change filters on a very conservative schedule, which does add a good deal of extra expense. We welcome our customers to examine how we do things, and our set up was designed with technical/cave divers in mind. Most shops I have been associated with put a viz sticker on a brand new tank and fill it before it goes out the door (no charge for the first vip and fill), and the sticker reflects if the tank is O2 clean or not. If you buy on line, you won't have a sticker, and KWS is correct "no vip sticker no fill". In my opinion, recleaning tanks after each fill is crazy, but the owner of the tanks must ensure that he/she is having them filled at a place where the air quality is grade E or better. If you have any doubt about this you had better find someone else to fill your tanks. As a side note, the only tanks that I have ever seen that came from the factory O2 cleaned with O2 ready valves have been Faber/Blue Steel tanks, all others I have seen of late have factory stickers that cite the 23.5 restriction. A annual vip inspection if done carefully does not require a tank to be recleaned for O2 service, again owner of the tank should, again be aware of the shops process. KWS has a point, one can become overly concerned, but if you are supported by a shop/other who is following all the rules/regs you should have no concern. Unfortunatly, many divers care only how fast they can get their tanks filled, and want it done as cheeply as they can get.

 

[nitroxfox]

You shouldn't have to clean your cylinder before each fill. If it is clean and you keep it that way it should remain clean. If you read the regulations, per RRC901-d, certain levels of hydrocarbons are permitted. We are not working on microchips!! Learn how to clean a cylinder correctly and maintain it that way and you should be safe. There is not a requirement to remove absolute contamination.

Per the DOT Official Interpretation:

"Gas mixtures with Oxygen concentrations greater than 23.5% by volume should be considered to cause or contribute to combustion of other material to a greater extent than air. These gas mixtures must be described as "Compressed gas, oxidizing, n.o.s." and must be classified and labeled with a Division 2.2 (nonflammable gas) primary hazard and a Division 5.1 (oxidizer) subsidiary hazard. If the Oxygen concentration is greater than 23.5%, the conditions specified in § 173.302(b) must be met. Each DOT Aluminum cylinder, including a 3AL cylinder, must be cleaned in accordance with the requirements of General Services Administration (GSA) Federal Specification RR¿C¿901D, paragraphs 3.3.1 and 3.3.2 (IBR, see §171.7 of this subchapter). Cleaning agents equivalent to those specified in Federal Specification RR¿C¿901D may be used provided they do not react with Oxygen. One cylinder selected at random from a group of 200 or fewer and cleaned at the same time must be tested for oil contamination in accordance with Federal Specification RR¿C¿901D, paragraph 4.3.2, and meet the specified standard of cleanliness."

From RR-C-901-D:

3.3.1 Preconditioning and internal preservation. After hydrostatic and any other testing, the
cylinder internal surface shall be cleaned and dried to be free of moisture, oil, grease, grit,
machining products, loose scale, slag, or other foreign materials. Rust bloom or particulate
matter (approximately 1.0 to 1.5 grams) generated subsequent to inspection as a result of
handling and shipping is acceptable. Cleaning agents used shall be compatible with the cylinder
materials and the intended gas service.
3.3.2 Oil and hydrocarbon residue. Residual oil and other hydrocarbons resulting from the
manufacture of the cylinder shall be removed to a level not greater than 2.5 milligrams (mg) per
square foot of internal surface area, but shall not exceed 20 mg per cylinder regardless of the size
of the cylinder. Trailer tubes shall not contain more than 40 mg of oil or residual hydrocarbons.
Verification of cleanliness shall be measured by gravimetric or infrared analysis or any
equivalent chemical analysis method."



The regulations are law and in place here in the USA. If you don't like them, petition for a change to the law. Good luck with that though. You will be fighting with members of the gas community which includes many more aspects than recreational scuba and they are adamant about cleaning at 23.5%.

Luxfer and Catalina both state that cylinders have been O2 cleaned at the factory. Unless you get an O2 clean valve, the system is only rated for 40% as it may not have the proper seats and o-rings. If you are PP filling, get the O2 clean valve and keep components clean.