Why is carbon monoxide (CO) poisonous?

CO is poisonous because it blocks the ability of the blood to absorb oxygen. It is called the “silent killer” because it is colourless and has no smell. CO results from the burning of all fossil fuels – not just gas and it is given off most when things smoulder rather than burn fiercely.

CO is poisonous because it combines with haemoglobin in red blood cells, about 240 times more tightly than oxygen. Haemoglobin is the substance that carries oxygen from the lungs to all organs of the body. The compound formed, called carboxyhaemoglobin, effectively reduces the ability of the blood to transfer oxygen.

CO arises from the partial combustion of carbon bearing compounds and so it is when a barbecue is smouldering, for example, that the danger is greatest.

Date Updated/Created: 22/06/2012

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