Carbon monoxide is a highly poisonous gas. Because of its molecular similarity to oxygen, hemoglobin can bind to carbon monoxide instead of oxygen, which subsequently disrupts hemoglobin’s efficiency as an oxygen carrier. Carbon monoxide actually has a much greater affinity (about 300 times more!) for hemoglobin than oxygen. When carbon monoxide replaces oxygen, this causes cell respiration to stop, leading to death. The particular danger of carbon monoxide poisoning lies in the fact that a person exposed to high levels of this toxin cannot be saved by being transported to an environment free of the poison and rich with oxygen. Since the hemoglobin remains blocked, artificial respiration with overpressurized, pure oxygen must first be performed to return the hemoglobin to its original function and the body to normal cell respiration.