Precautions of oxygen - Toxicity
Oxygen gas (O³01³) can be toxic at elevated partial pressures, leading to convulsions and other health problems. (Since O2's partial pressure is the fraction of O³45³ times the total pressure, elevated partial pressures can occur either from high O³67³ fraction in breathing gas or from high breathing gas pressure, or a combination of both.) (Cook & Lauer 1968, p.511) Oxygen toxicity usually begins to occur at partial pressures more than 50 kilopascals (kPa), or 2.5 times the normal sea-level O³89³ partial pressure of about 21 kPa. Therefore, air supplied through Oxygen masks in medical applications is typically composed of 30% O³1011³ by volume (about 30 kPa at standard pressure). At one time, premature babies were placed in incubators containing O³1213³-rich air, but this practice was discontinued after some babies were blinded by it.Breathing pure O³1415³ 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. (
(#14) ) In the case of spacesuits, the O³1617³ partial pressure in the breathing gas is, in general, about 30 kPa (1.4 times normal), and the resulting O³1819³ partial pressure in the astronaut's arterial blood is only marginally more than normal sea-level O³2021³ partial pressure (see arterial blood gas).
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 O³2223³ partial pressure more than 60 kPa can eventually Lead to permanent pulmonary fibrosis. ( (#15) ) Exposure to a O³2425³ partial pressures greater than 160 kPa may Lead to convulsions (normally fatal for divers). Acute Oxygen toxicity can occur by breathing an air mixture with 21% O³2627³ at 66 m or more of depth while the same thing can occur by breathing 100% O³2829³ at only 6 m. (Donald 1992)
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11/23/2008 4:19 AM v0.61.106 ADBEFEED