Breathing in too much pure oxygen can cause oxygen toxicity, resulting in symptoms such as nausea and airway inflammation. Central nervous system damage occurs at high pressure, while long-term exposure at normal pressure can lead to lung or eye problems. Divers are particularly at risk. High oxygen levels produce highly reactive byproducts that can damage cells.
Oxygen toxicity is a condition that occurs when you breathe in too much pure oxygen. Breathing air contains about 21% oxygen; the rest is made up of nitrogen and a variety of other substances. When molecular oxygen, or O2, is inhaled at a higher ratio, a variety of symptoms can occur including tunnel vision, nausea, and airway inflammation. Different forms of oxygen toxicity can result from different forms of exposure to high levels of oxygen. Central nervous system damage tends to result from high-pressure, short-term exposure to high oxygen levels, while long-term exposure to high oxygen levels at normal atmospheric pressure tends to lead to lung or eye problems .
Central nervous system oxygen toxicity tends to occur only at high pressure, so it is primarily a problem for divers and others who spend time in conditions above atmospheric pressure. As a diver progresses deeper into the water, the partial pressure of any gas in his tank increases in proportion to his depth. Central nervous system oxygen toxicity, therefore, is possible at sufficient depths as the diver breathes oxygen at significantly higher than normal atmospheric pressure. This can lead to a variety of symptoms, including nausea; dizziness; spasms; and in severe cases, seizures and possible death.
Oxygen toxicity is still possible at normal atmospheric pressure; this occurs when the fraction of oxygen in the air is significantly higher than normal at about 21 percent. Toxicity can occur with 50 percent oxygen or more, although it generally takes some time, usually more than 24 hours, for symptoms to appear. At an oxygen level closer to 100%, symptoms can come on much more quickly, usually after 14 hours, but sometimes after as little as four hours. Oxygen toxicity that occurs from prolonged exposure to high levels of oxygen at normal atmospheric pressure generally leads to pulmonary symptoms rather than central nervous system symptoms. These symptoms include inflammation of the airways and lungs, cough, difficulty breathing and fever.
A variety of chemical mechanisms related to cellular respiration and metabolism are responsible for the symptoms associated with oxygen toxicity. While oxygen is required for cellular respiration, higher than normal concentrations lead to the production of highly reactive byproducts that can cause significant damage to cells. Similar highly reactive chemical species enter or are produced by the body on a regular basis, but the body has many systems capable of preventing or repairing the damage that may be caused. The body systems are unable to keep up with the production of these destructive elements under high oxygen conditions hence oxygen toxicity in the form of cellular damage occurs.
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