Oxygen saturation (medicine)
Oxygen saturation is the fraction of oxygen-saturated hemoglobin relative to total hemoglobin (unsaturated + saturated) in the blood. The human body requires and regulates a very precise and specific balance of oxygen in the blood. Normal blood oxygen levels in humans are considered 95–100 percent. If the level is below 90 percent, it is considered low resulting in hypoxemia. Blood oxygen levels below 80 percent may compromise organ function, such as the brain and heart, and should be promptly addressed. Continued low oxygen levels may lead to respiratory or cardiac arrest. Oxygen therapy may be used to assist in raising blood oxygen levels. Oxygenation occurs when oxygen molecules () enter the tissues of the body. For example, blood is oxygenated in the lungs, where oxygen molecules travel from the air and into the blood. Oxygenation is commonly used to refer to medical oxygen saturation.
Liquid oxygen
Liquid oxygen has a pale blue color and is strongly paramagnetic: it can be suspended between the poles of a powerful horseshoe magnet. Liquid oxygen has a density of 1.141 g/cm (1.141 kg/L or 1141 kg/m), slightly denser than liquid water, and is cryogenic with a freezing point of and a boiling point of at 101.325 kPa (760 mmHg). Liquid oxygen has an expansion ratio of 1:861 under and , and because of this, it is used in some commercial and military aircraft as transportable source of breathing oxygen.