section_path: Safety and precautions/Toxicity
section_name: Toxicity
paragraph_text: Toxicity
  
  Oxygen gas (O) can be toxic at elevated partial pressures, leading to convulsions and other health problems. Oxygen toxicity usually begins to occur at partial pressures more than 50 kilo pascals (kPa), equal to about 50% oxygen composition at standard pressure or 2.5 times the normal sea-level O partial pressure of about 21 kPa. This is not a problem except for patients on mechanical ventilators, since gas supplied through oxygen masks in medical applications is typically composed of only 30–50% O by volume (about 30 kPa at standard pressure).
  
  At one time, premature babies were placed in incubators containing O -rich air, but this practice was discontinued after some babies were blinded by the oxygen content being too high.
  
  Breathing pure O in space applications, such as in some modern space suits, or in early spacecraft such as Apollo, causes no damage due to the low total pressures used. In the case of spacesuits, the O partial pressure in the breathing gas is, in general, about 30 kPa (1.4 times normal), and the resulting O partial pressure in the astronaut's arterial blood is only marginally more than normal sea-level O partial pressure.
  
  Oxygen toxicity to the lungs and central nervous system can also occur in deep scuba diving and surface-supplied diving. Prolonged breathing of an air mixture with an O partial pressure more than 60 kPa can eventually lead to permanent pulmonary fibrosis. Exposure to an O partial pressure greater than 160 kPa (about 1.6 atm) may lead to convulsions (normally fatal for divers). Acute oxygen toxicity (causing seizures, its most feared effect for divers) can occur by breathing an air mixture with 21% O at 66 m (217 ft) or more of depth; the same thing can occur by breathing 100% O at only 6 m (20 ft).