Hello Thomas-
I worked for a gas company for over 20 years, retiring in 2019. Your question has come up many times and the answer to your questions can vary. There are several "Food Act" legislative bills that have been approved since the original in 1938. Let me explain the intention of the FDA guidelines, as I remember them. I would encourage you to contact the company that actually fills the cylinders you use for more detail (the company name will be on the cylinder label located on the shoulder of the cylinder).
First, the "grades" of gases are important to the end user, because the gas cylinders are only used in that industry to prevent any chance of cross contamination. Food grade, medical grade and industrial grade have their own environments that may be detrimental to the others. Example: Medical cylinders could have blood borne pathogens on them. Or worse, someone could have left a valve open on an empty cylinder, and some impurity found its way into the cylinder. Normal cylinder filling practices include a cylinder vacuum to remove any residue. This FDA rule helps prevent any cross contamination of the cylinders from different end user types. Also, Food Grade, Medical grade and other specific grades, like UHP, have lot numbers on the cylinders for tracking and analysis. Each lot has test results for that particular grouping of cylinders filled with that particular gas, from that particular cylinder filling manifold. Those results are available from the gas cylinder filling location, sometimes for an additional cost.
Then there are the gas purification standards. These standards detail what purity minimums are needed of the gas and what the maximum amount of any impurities that can be in the gas. These standards must be proved through testing at the gas cylinder filling site where the purification standards are available to the end user, sometimes at an added cost. I do not have any updated details on the purification of Oxygen, but my past notes show that the minimum standard in 2017 was 99.0% for Medical Grade and 99.2% for Food Grade. And yes, the gas is likely to come from the same bulk storage tank at the gas filling location and filled into different grades of cylinders. That is common practice and usually results in better purity of the gas in all grades filled at that gas filling location.
Regarding Ultra High Purity Oxygen (UHP) Gas being certified as Food Grade- not likely. Refer back to the cylinder standards and the gas cylinder filling company most likely is not allowed to put UHP gas into a Food Grade Cylinder. I am not certain that there are restrictions for you using UHP in your application. That answer would come from the gas cylinder filling company.
Your best source for the answers to your questions is the company that actually fills the gas cylinders. They are responsible to use the correct cylinder and prove the purity and impurities of each lot of cylinders that are filled. I hope my limited insight helps you make the best decision for you.
Best Regards,
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Bob Bernier
Retired from Matheson Gas
Auburn, ME
207-740-8256
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