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As every schoolchild knows, you cannot live without oxygen. Oxygen makes up one-fifth of the Earth's atmosphere – the air we breathe contains 21 percent – and it is the third most abundant element in the universe by mass. However, even a small increase in the oxygen level is hazardous. Increase the oxygen level to 24 percent and fires start faster and burn hotter than in normal air. Breathing higher concentrations of oxygen can cause oxygen toxicity – symptoms may include nausea, dizziness, muscle twitching, loss of vision, convulsions, and loss of consciousness.

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