Oxygen is one of the components of air, colorless, odorless, tasteless. Oxygen density than air, in the standard conditions (0 ℃ and atmospheric pressure 101325 mpa) density of 1.429 g/l. Oxygen method for large scale production is fractional distillation of liquid air, will first compressed air, after waiting for the expansion of oxygen and frozen in liquid air, due to gases and the boiling point of nitrogen is lower than the oxygen after fractionation, liquid oxygen, is what is left of can be stored in high-pressure cylinders. All of oxidation and combustion process need oxygen, such as steel in addition to the impurities such as sulfur, phosphorus, oxygen and acetylene mixture combustion temperature as high as 3500 ℃, used for welding and cutting steel. Glass manufacturing, cement, minerals, roasting and hydrocarbon processing requires oxygen. Liquid oxygen is also used for rocket fuel, it is more cheaper than other fuels. In hypoxia or anoxia environment, such as a diver, astronaut, oxygen is necessary to sustain life.