Cleaning and Cleanliness Verification of Aluminum Oxygen Cylinders
Questioning the Applicability of RR-C-901D
Recently we contemplated the applicability of the RR-C-901D cleaning and testing requirement found in 49 CFR 173.302(b) for filling aluminum oxygen cylinders. For years, hundreds (perhaps thousands?) of companies in the US have been hydrostatically testing and refilling aluminum oxygen cylinders without non-volatile residue (NVR) testing equipment or even heptafluorocyclopentane (or equivalent) for that matter. Many small organizations may not even clean the cylinders at all. We read the regulations a little closer and we’re interested to know what you think of our findings. Read below and send us your comments!
Industry Interpretation vs. Legal Requirements
The industry-at-large has interpreted this rule to be applicable only to cylinder manufacturers. However, any facility that merely fills oxygen cylinders (like aviation fixed based operators or FBO) may have hidden responsibilities under the law. Reading the plan language of the law indicates that anyone filling aluminum oxygen cylinders would have to ensure that a cylinder was cleaned and verified as clean before filling! Is this true?
Understanding the Regulatory Requirements
If you’re confused already, let’s recap the requirements:
49 CFR 173.302(b) states that “each aluminum cylinder filled with oxygen must meet all of the following conditions” with 49 CFR 173.302(b)(3) specifically explaining:
Each DOT cylinder must be cleaned in accordance with the requirements of 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.
Frequency of Cleaning and Testing
What’s not clear here is how often the cylinder needs to be cleaned and batch tested for contamination. Only once? After every hydro test? Any time before filling? Some airframe manufacturers like Gulfstream Aerospace have rules in aircraft manuals regarding fully depleted oxygen cylinders so perhaps it’s only when a cylinder is depleted to zero pressure?
RR-C-901D Section 3.3.1: Cylinder Processing
To answer these questions we reviewed RR-C-901D section 3.3.1 (the “cylinder processing” section) which states:
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.
Visual Inspection and Contamination Control
What is clear from this statement is that cylinders must be cleaned before filling after hydrostatic testing. What is not clear is if this refers to the cylinder’s initial hydrostatic test or a requalification test or both (although “any other testing” stands out to us). It also describes an inherent visual inspection requirement for contamination. Both rules make sense to perform after a cylinder requalification since contamination can easily be introduced during testing, a thorough visual inspection is already required under the law, and visual inspection can be an acceptable way to verify cleanliness per applicable Compressed Gas Association (CGA) Pamphlets.
RR-C-901D Section 3.3.2: Residual Oil and Hydrocarbons
Let’s move to RR-C-901D section 3.3.2 which states:
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.
Scientific Cleaning Verification
What’s clear here is that a specific level of cleaning is required after manufacturing and more “scientific” cleaning verification must be performed (i.e. not visual) after manufacturing. This would lead requalifiers and fillers to not bother with the analyses explained in RR-C-901D section 4.3.2 which discusses both gravimetric (evaporation method) and infrared analysis (infrared spectrophotometer) described in the rule.
Mandatory Oil Residue Testing
Unfortunately, 49 CFR 173.302(b)(3) specifically states the cylinders must meet the level of cleanliness via oil residue testing without regard to the cleaning procedure used. Further, the regulation states cleaning performed to 3.3.1 and 3.3.2, not 3.3.1 or 3.3.2.
Complex Testing Procedures
Now the big problem:
RR-C-901D section 4.3.2 explains the testing process for “oil and hydrocarbon residue” based on a process of rolling the cylinder with heptafluorocyclopentane for 10 minutes, extracting the solvent to a beaker, and analyzing for residue using an infrared spectrophotometer or more commonly the “evaporation method.” The more common method can take several hours in addition to the “15 minutes” oven drying time called for in the section. Also unwritten are the various standards for non-volatile residue (NVR) testing such as verification of cleanliness of the solvent and beaker itself. This is a very complicated procedure for the layman and certainly not economically feasible for small repair stations and cylinder requalifiers to perform at the prices currently being charged in the aviation, medical, and welding industry (those who commonly use oxygen gas).
Challenges for Small Facilities
It gets worse:
The regulation requires this test to be performed on one cylinder out of a batch of 200 or fewer cleaned at the same time. That is, if you are a facility that hydrostatically tests and cleans a cylinder one at a time, very common in practice, suddenly you’re faced with the fact that every cylinder is a batch of one. That means every single cylinder will potentially require hours of cleaning verification testing if the regulation is to be read plainly.
Confusion and Clarification Attempts
“Wait! What?” (I hope you’re shouting). There must be an explanation!
To answer that question, we reviewed some well-intentioned but confusing DOT PHMSA letters of interpretation. Specifically, Reference No. 06-0064, 11-0175, and 11-0238 which are a series of clarifications based on an initial request by Catalina Cylinders, a prominent aluminum cylinder manufacturer, to clarify the cleaning requirement for oxygen gas mixtures.
DOT’s Stance on Cleaning and Verification
Long story short: The DOT just restates the requirement for cleaning and verification in 173.302(b) with no relief.
Common sense tells us that if you’re not engaged in manufacturing cylinders, it would stand to reason that you don’t need to conform to RR-C-901D 3.3.2 and therefore have no need to perform the “scientific” testing. It also stands to reason that 4.3.2 relates to the “scientific” testing requirements of 3.3.2 not the visual requirements of 3.3.1. However, the DOT isn’t always reasonable in their interpretations or enforcement. For example, almost every portable halon fire extinguisher installed on aircraft has been illegal to ship for decades (more on that here: solving the shipping dilemma for aircraft fire extinguishers over 900ml) and that has just recently come to light.
Industry Implications and Future Audits
Is this just another detail that has been missed by the entire industry, or will common sense prevail during your next PHMSA or FAA audit? Will the new inspectors at the FAA Office of Hazardous Materials Safety have the same opinion on this matter as DOT PHMSA? Our experience tells us they sometimes do not.
How Tym’s Can Help
If this problem affects your company or if you have a similar regulatory conundrum, solving complex problems like this is at the heart of what we do at Tym’s. We can solve problems preemptively using a variety of tools like Letters of Interpretation, Letters of Variation, and Special Permits created for your unique situation. We can even connect you with one of the top regulatory attorneys in the country for a thorough legal review.
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