Disadvantage of Worthington Steel 100s with Nitrox?

[Mike Boswell]

There is some info about this issue on the Luxfer website Luxfer: SCUBA oxygen-enriched and oxygen service FAQ

Note that the language specifies ALUMINUM cylinders. I don't know if the rule also applies to steel cylinders.

Excerpts:

"For pure oxygen, DOT mandates strict pressure limits: Gas pressure in an aluminum cylinder containing pure oxygen must never exceed 3,000 psi (even if the cylinder is stamped for a pressure above 3,000 psi)."

"4. Question: I’ve read in some scuba manuals, including those published by well-known scuba organizations, that it’s only necessary to clean cylinders and other scuba equipment for oxygen service when the oxygen concentration exceeds 40%. Why does Luxfer require cleaning for oxygen concentrations above 23.5%?

Answer: Few concepts have caused more confusion and controversy in the recreational diving industry than the so-called “40% rule.” While there seems to be general agreement that special cleaning is required when a pressurized oxygen concentration reaches a particular “threshold” percentage, there is disagreement about exactly what that threshold should be and at what pressure it becomes important. Some say 40%; others say 23.5%; still others say anything more than 21% when a gas mixture is pressurized more than 100 psig. It would be helpful to explore the background of this confusion briefly before discussing Luxfer’s position on this vital subject.

The 40% threshold is cited in a single Federal CFR published by the Occupational Safety and Health Administration (OSHA) of the U.S. Department of Labor: 29CFR910.430, which applies to “Commercial Diving Operations” and states in the section titled “Oxygen safety” on page 854: “(1) Equipment used with oxygen or mixtures containing over forty percent (40%) by volume oxygen shall be designed for oxygen service. (2) Components (except umbilicals) exposed to oxygen or mixtures containing over forty percent (40%) by volume oxygen shall be cleaned of flammable materials before use.”

Please note that OSHA also provides a very specific definition about who should—and should not—be considered a “commercial diver” to whom the 40% threshold applies: “Commercial diver means a diver engaged in underwater work for hire excluding sport and recreational diving and the instruction thereof” (46CFR197, page 409; italics added for emphasis).

Even though OSHA clearly excludes sport and recreational divers from the CFR that specifies a 40% threshold, some professionals in the recreational diving industry have nonetheless been citing the OSHA “rule” for many years and maintaining that special cleaning of recreational diving equipment is not necessary with oxygen concentrations of 40% or less. These advocates of the “40% rule” have often stated that the U.S. Navy supports their position, which at one time was true—but no more. In the current applicable military specification (Mil-Std-1330D), the Navy specifies a 25% threshold for oxygen cleaning. Compounding the confusion is the fact that two other OSHA documents, 29CFR1910.146 and 29CFR1910.134, specify an oxygen threshold of 23.5%.

For the sake of clarity, here’s a summary of the oxygen threshold percentages at which various key U.S. agencies and organizations require special cleaning of oxygen-handling equipment and systems:

Organization Oxygen threshold Reference
U.S. Navy >25% Mil-Std-1330D
U.S. Compressed Gas Association (CGA) >23.5% CGA Pamphlet 4.4
National Fire Prevention Association (NFPA) >21 – 25% NFPA standards
American Society for Testing & Materials (ASTM) >25% G126, G128, G63, G94
National Aeronautical & Space Administration (NASA) >21%/>100 psig Various KSC & JSC
Occupational Safety & Health Administration (OSHA) >23.5% 29CFR1910.146
OSHA >23.5% 29CFR1910.134
OSHA >40% 29CFR1910.430

The reasons for Luxfer’s position: Luxfer supports an oxygen-cleaning threshold of 23.5% and does not support the alleged “40% rule.” This means that when a pressurized oxygen concentration used in a Luxfer cylinder exceeds 23.5%, the cylinder must have been cleaned to the same cleanliness standard mandated for a cylinder containing 100% oxygen. Luxfer’s reasons for this position are:

All key U.S. regulatory and gas industry references except one advocate an oxygen threshold of 21% to 25%.
Luxfer is a member of the Compressed Gas Association and therefore supports the CGA-specified threshold of 23.5%. Furthermore, Luxfer defers to CGA on all safety matters related to oxygen handling and containment, as do OSHA and DOT.
As an international manufacturer, Luxfer works with regulatory authorities and industry associations around the world—the overwhelming majority of which support a threshold value from 21% to 25% (for example, this is true in the United Kingdom, Australia, France, Germany and Japan).
United Nations compressed air packaging guidelines (see UN 1002) indicate that when compressed air contains oxygen as the only oxidizing gas and the oxygen concentration exceeds 23.5%, then the entire gas mixture must be listed as an oxidizing gas."

 

[fppf]

So there are actual rules and regulations with fill pressures and oxygen mixtures in cylinders.

However, the shop has there facts mixed up a little.
DOT 3AL type cylinders are limited to a fill pressure of 3000 PSI for oxygen service. And "oxygen service" is any gas that contains more then 23.5% oxygen. To put any gas in a cylinder that has more then 23.5% oxygen in it, the cylinder and valve must be O2 cleaned, it must have straight threads, and the valve must be brass or stainless.

There are no pressure limits listed for an oxygen mixture for any of the 3AA cylinders. And worthington's special permit required to make the HP cylinders does not list a pressure limit as well. The cylinders standard fill pressure limit still applies of course.

Here is a link to the DOT regulations regarding this issue, its CFR 49 section 173.302 paragraph (b) sub paragraph (4)
Electronic Code of Federal Regulations:

Here is a link to the special permit filed for Worthington cylinders SP14157
http://www.phmsa.dot.gov/staticfiles/PHMSA/SPA_App/OfferDocuments/SP14157_2009070249.pdf


Looks like Mike beat me to it, nice post Mike. I posted the actual links to the actual laws that are current and up to date as of this posting for the na sayer's that will now jump out of the wood work.

 

[deepstops]

My advice - Get rid of your lame dive shop.

I'd seriously like to know what shop is advocating this nonsense.

 

[Mike Boswell]

So there are actual rules and regulations with fill pressures and oxygen mixtures in cylinders.

However, the shop has there facts mixed up a little.
DOT 3AL type cylinders are limited to a fill pressure of 3000 PSI for oxygen service. And "oxygen service" is any gas that contains more then 23.5% oxygen. To put any gas in a cylinder that has more then 23.5% oxygen in it, the cylinder and valve must be O2 cleaned, it must have straight threads, and the valve must be brass or stainless.

There are no pressure limits listed for an oxygen mixture for any of the 3AA cylinders. And worthington's special permit required to make the HP cylinders does not list a pressure limit as well. The cylinders standard fill pressure limit still applies of course.

Here is a link to the DOT regulations regarding this issue, its CFR 49 section 173.302 paragraph (b) sub paragraph (4)
Electronic Code of Federal Regulations:

Here is a link to the special permit filed for Worthington cylinders SP14157
http://www.phmsa.dot.gov/staticfiles/PHMSA/SPA_App/OfferDocuments/SP14157_2009070249.pdf


Looks like Mike beat me to it, nice post Mike. I posted the actual links to the actual laws that are current and up to date as of this posting for the na sayer's that will now jump out of the wood work.

Thanks fppf. Don't you just LOVE Google?

Here is a dive shop that seems to have their act together - they publish their filling rules and policies.

Looks to me like regular Nitrox can be filled to the rated tank pressure, but there is a limit of 3,000 psi on pure O2.

Scuba Equipment - Gas Fills - Aqua Immersion, Columbus Ohio

 

[JahJahwarrior]

It is curious to me that they require mixes of higher than 74% o2 to be labeled as "oxygen." While it might be 3/4 oxygen, I'd still be more comfortable with a correctly labeled tank.

 

[rjack321]

Historically, the 23.5% = an oxidizer biz comes from firefighting. You don't want extra O2 around a fire (duh). AL and steel tanks with EAN32 in them are not burning up their valves or orings (although they may if the shop partial pressure blends with pure O2 to make said 32%).

Don't bother trying to get a proper nitrox fill from that shop - get a new shop.

 

[fppf]

This law does not matter much for the run of the mill AL80, there service pressure is 3000 PSI.

But, for the new Neutral AL80 and the AL100 that have 3300 PSI service pressures, this law does apply. I would bet most shops don't even know about this, and if they do they chose to ignore it.

And lets be clear, this is a LAW and not some dive industry thing.

 

[Sonic04GT]

From what I've gathered in the past, the owner is a very knowledgeable guy and the lead instructor, but I won't argue on his side where the information came from.

However, I am stationed at Fort Hood in Central Texas, Killeen and C&J Divers (a very tiny shop) is the only one in the area so I have no choice. Good people there though.

 

[fppf]

I would ask for the exact CGA or DOT article, section, paragraph, and sub paragraph this rule is referring too. Would be nice to hear what they site as there source.

 

[H2O 70]

Like fppf challenge them. If it is some new rule, It may be good for all of us to know and if not, it would behoove your LDS there to know what they are talking about.