Quote Originally Posted by Airmutt View Post
Welding oxygen is used in certain types of welding techniques, either to aid in the production of heat or as an additive to aid in stability of the process. While in use, other contaminants may enter the oxygen cylinder, such as acetylene. When a cylinder must be filled with oxygen, the fill station operator will detect whether there is a presence of acetylene. If there is, the cylinder is cleaned and later filled with oxygen. If the cylinder is labeled for medical oxygen, the cylinder must be evacuated before being refilled.
Aviation breathing oxygen (ABO) is strictly regulated, and neither medical nor industrial grade oxygen can be substituted because of these standards. The CGA’s Grade E is commonly also called aviator’s grade, and this oxygen must also go through additional drying steps before it goes into a cylinder.
Research grade oxygen is 99.999% pure (“five nines,” also called grade 5) and is used in both chemical research facilities and specialty welding applications in the aerospace industry.
Medical oxygen is used for oxygen therapy and hospitals, is designated as a drug and therefore must satisfy FDA requirements for compressed medical gas. One of the requirements is that cylinders containing oxygen must always be completed evacuated to minimize the risk of contamination.
The Airgas facility in Flagstaff, 2004. Saw their servicing facility. One tank of LOX fed a manifold. On the manifold, takeoff fittings labeled "welding", "medical", and "aviator breathing" along with the appropriate warnings, hazmat labels, regulatory gobbledegook. One LOX tank, one manifold. I'll believe what the reference said. I'll also believe what I saw in practice by one of the biggest and most reputable companies in the business, a subsidiary of one of the largest companies in the business worldwide, to meet those standards. Of course, the world has changed a lot since 2004.