A colorless, odorless, tasteless elemental gas that supports life and combustion, constitutes about a fifth of the atmosphere. At temperatures ranging below -300°F, it is a transparent, pale blue liquid that is slightly heavier than water. All elements except the inert gases combine directly with oxygen to form oxides. Oxygen is non flammable but it readily supports combustion. All materials that are flammable in air burn much more vigorously in oxygen. Some combustibles, such as oil and grease, burn with nearly explosive violence in oxygen if ignited.
The major uses of oxygen stem from its life-sustaining and combustion-supporting properties. It is used extensively in medicine for therapeutic purposes, for resuscitation in asphyxia, and with other gases in anesthesia. It is also used in high-altitude flying, deep sea diving, and as both an inhalant and a power source in the United States space program.
Industrial applications include its very wide utilization with acetylene, propane, hydrogen, and other fuel gases for such purposes as metal cutting, welding, hardening and scarfing. In the steel industry, oxygen helps increase the capacity and efficiency of production in steel and iron furnaces. One of its major uses is in the production of synthesis gas (a hydrogen-carbon monoxide mixture) from coal, natural gas or liquid fuels. Synthesis gas is in turne used to make gasoline, methanol and ammonia. Oxygen in similarly employed in manufacturing some acetylene through partial oxidation of the hydrocarbons in methane-rich feedstocks such as natural gas. It is also used in the production of nitric acid, ethylene, and other compounds.
Commercial oxygen is produced at air separation plants by liquefaction of atmoshperic air and separation of the oxygen by fractionation. Very small quantities are produced by the electrolysis of water.
Oxygen ranging in purity between 90% and 97% is produced by pressure swing absorption (PSA) techniques. PSA oxygen is used chiefly in steel making, but there are also many small units in homes producing therapeutic oxygen. Recent innovations in membrane technology are also being used for production of oxygen from the air.
High pressure cylinders, tube trailers and tank cars often serve as the storage supply for gaseous oxygen. Larger amounts of oxygen are frequently stored more economically in liquid form at the users' site.