CRG is correct and giving you the right path. I was involved in producing,distributing, and installing the facilities for these gases in the Caribbean and in South America for some years. My recommendations (if you are going to be in the business) is to become a member of the CGA and purchase their flagship book: "Handbook of Compressed Gases". In it, you'll quickly be oriented with the criteria and the subject matter involved in applying medical gases.
You're going to need background preparation to get into the meat of the subject. For example, you'll need a complete understanding of cryogenics and the methods used to distribute and apply the cryogens safely. You'll also need some detailed background in compressible gas flow and measurement. I don't think you can afford to be without this book throroughly read and understood if you are going to be associated with Medical Gases.