Many people may think that getting oxygen is easy since it’s in the air we breathe. Our ambient air (i.e., the natural air around us) comprises of only 20% oxygen; the rest is a mixture of nitrogen, argon, carbon dioxide and other gases. To get pure oxygen, oxygen plants must employ a specialized technique to separate the oxygen from the air, often by collecting air in its gaseous form and liquefying it at cold temperatures.
Once it’s collected, it must be inspected and packaged into different grades.
The Oxygen Grades: From Aviation to Welding
There are several ways that industry professionals refer to oxygen grades. The Compression Gas Association (CGA) has identified seven grades of oxygen, A through G, which determine how pure the oxygen is. Oxygen may also be designated as USP, which means that it has been certified by the eponymous organization, the United States Pharmacopeia (USP).
Almost all oxygen produced in plants now meets USP requirements, mainly due to economic reasons of storing oxygen in separate facilities, but it is the purity of the oxygen (i.e., how much of any other gases are still present) and the way the oxygen cylinders are filled that separate oxygen grades. There are four accepted “grades” of oxygen used in various industries: welding, research, aviation and medical.
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, which is used during one type of welding. 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. According to Dr. Larry Taylor from the University of Michigan, the FDA has prosecuted facilities for improperly filling medical grade oxygen cylinders.
Prescription for Medical Grade Oxygen:
Because the FDA classifies medical grade oxygen as a drug, you must have a prescription to purchase it as well as other oxygen-related medical devices, such as oxygen concentrators. It may seem like an unnecessary step since the production and fulfillment of medical grade oxygen is already regulated, but a prescription is an extra step to ensure that the oxygen you are getting is safe to use.
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