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At sea-level, 0.5 bar is exceeded by gas mixtures having oxygen fractions greater than 50%. Lung oxygen toxicity damage-rates at sea-level pressure rise non-linearly between the 50% threshold of toxicity, and the rate of damage on 100% oxygen. For this reason, intensive care patients requiring more than 60% oxygen, and especially patients at fractions near 100% oxygen, are considered to be at especially high risk, since if the situation is not corrected, the treatment may begin to cause lung damage which contributes to need for the high-oxygen mixture.