is it toxic?
Can be Toxic at elevated partial pressures, leading to convulsions and other health problems.
Oxygen
Oxygen gas () 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 kilopascals (kPa), equal to about 50% oxygen composition at standard pressure or 2.5 times the normal sea-level 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% by volume (about 30 kPa at standard pressure).

where does most of the oxygen come from on earth The most amount of Oxygen comes from photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. when was it discovered? In the year 1773. by whom? It was discovered independently by Carl Wilhelm Scheele, in Uppsala, in 1773 what are it's uses? Low Pressure Breathing gas in Modern Space Suits, Scuba Divers rely on artificially delivered Oxygen & Medically for Oxygen Masks among many other uses.
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Oxygen [SEP] Toxicity
Oxygen gas () 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 kilopascals (kPa), equal to about 50% oxygen composition at standard pressure or 2.5 times the normal sea-level 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% by volume (about 30 kPa at standard pressure). At one time, premature babies were placed in incubators containing -rich air, but this practice was discontinued after some babies were blinded by the oxygen content being too high.