The
toxicity of carbon monoxide (CO) is related to the high
affinity of
hemoglobin for CO. The affinity of hemoglobin to CO is about 200-300 times than its affinity of
oxygen. The result is the formation of a stable
carboxyhemoglobin complex instead of the formation of oxyhemoglobin. The
carboxyhemoglobin will not accept any more oxygen, and thus oxygen transport will be severely hindered. Even low concentrations of CO can be extremely dangerous upon prolonged exposure.
Carbon monoxide is also an explosive gas. The lower explosive limit in air is 12.5%, and the upper explosive limit is 74%.