As we waited for almost a month for our compressor repairs, we developed quite a bit of backlog on cylinder fills and service. We manufacture enriched air nitrox though the partial-pressure blending method, so one of the services that became pretty backlogged was the cleaning of cylinders in preparation for use with enriched air nitrox. As I watched the guys go through this backlog, it started me to thinking about an issue that comes up quite often….what does it mean to have a cylinder “oxygen cleaned”?

Any local scuba store works quite different from a large laboratory or industrial setting where items and components are prepared for exposure and use in an oxygen environment. There is considerable misunderstanding about what scuba stores mean when they use the term “oxygen clean” and how this same term might be used in industry, science, and medical applications. As Harry Avril stated in his April 20o0 article written for Dive Rite, the issue is one of semantics. In that article, Mr. Avril quoted on old story about three blind men and an elephant to describe the misunderstanding many people have about the issue of “oxygen cleaning” cylinders and valves….

Three blind men came upon an elephant. The first, feeling the animal’s leg, proclaimed that an elephant must be much like a tree trunk. The second, finding the animals trunk, said that a more apt comparison would be a snake. The third, holding on to the elephant’s tail, was puzzled by the first two’s misinterpretation of the facts. To him, an elephant felt exactly like a rope.

Quoted from “What Exactly is Oxygen Clean” by Harry Avril April 2000

Differences in the meaning of the terms “oxygen clean” and “oxygen ready” are as open to misunderstanding in the scuba industry as is the description of an elephant in the story above.

In industrial and medical settings, items prepared for oxygen service are properly cleaned, tested, and assembled in special clean rooms, designed to prevent any sort of contamination that might damage the results of the cleaning and assembly. Items are then tested using millipore weight tests, or other scientific test methods, to MAKE SURE that no material lingers that might make the components unsafe in the presence of pure oxygen. In the scuba store, we lack clean rooms and the sophisticated tests necessary to do it they way it is done in industry. So, we resort to more basic ways of preparation.

“Oxygen cleaning” for a scuba cylinder and valve, in a local scuba store, is more about the business of making the scuba items “as clean as possible” by following a defined and tested cleaning process. Given the inability to perform cleanliness tests after the cleaning, the importance of following a defined process, step by step, cannot be understated. Cylinders and valve components are repeatedly washed in special solutions designed for removing hydrocarbons; solutions that don’t leave drying residue that creates more damage than good. They are rinsed thoroughly with clean water and are assembled using o-rings and other components made from materials known to be less effective as fuels in the event of an oxygen fire. All lubricants used in assembly are special lubricants known to be “oxygen safe”. Of course, all of this is done in an area that is as clean as possible, so environmental contamination is limited. The result is an assembly that is as “clean as possible” and provides reduced risk when exposed to pure oxygen. However, we should clearly remember that it IS NOT the same as a clean-room assembly and we don’t have the cleanliness testing capability used in industry and medicine.

While most manufacturers ( out of fear of legal liability) will never say that their components are “oxygen ready”, we all know and accept that pure oxygen is used in diving and that we must apply our best abilities to make sure that cleanliness and attention are used in our cylinders and valves. When processes are applied in the local scuba store, they are done to get the cylinders “nitrox ready”, a step below real industrial cleaning.

If you have scuba cylinders that are used for enriched air or oxygen service, you can follow a couple of simple rules to greatly improve the safety of their use…..

1. Clean them OFTEN using a proper process DESIGNED to remove hydrocarbons.

2. ONLY use gases from sources known to be as clean as possible.

3. NEVER take the importance of cleanliness and common sense for granted.

Phil Ellis

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