Incomplete oxidation during combustion may cause high concentrations of carbon monoxide in indoor air. Clogged chimneys, wood-burning fireplaces, decorative fireplaces, gas burners and supplementary heaters without properly working safety features could vent carbon monoxide into indoor spaces. In homes in developing countries, the burning of biomass fuels and tobacco smoke are the most important sources of exposure to carbon monoxide. In developed countries, the most important source of exposure to carbon monoxide in indoor air is emissions from faulty, incorrectly installed, poorly maintained or poorly ventilated cooking or heating appliances that burn fossil fuels. Parking areas can also be a source of carbon monoxide ( 6).Ĭarbon monoxide is produced indoors by combustion sources (cooking and heating) and is also introduced through the infiltration of carbon monoxide from outdoor air into the indoor environment ( 7). Exposure to low levels of carbon monoxide can occur outdoors near roads, as it is also produced by the exhaust of petrol- and diesel-powered motor vehicles. Small amounts are also produced endogenously in the human body ( 4, 5). Anthropogenic emissions are responsible for about two thirds of the carbon monoxide in the atmosphere and natural emissions account for the remaining one third. Inhalation is the only exogenous exposure route for carbon monoxide. The relationship of carbon monoxide exposure and the COHb concentration in blood can be modelled using the differential Coburn-Forster-Kane equation ( 3), which provides a good approximation to the COHb level at a steady level of inhaled exogenous carbon monoxide. It is only slightly soluble in water, blood serum and plasma in the human body, it reacts with haemoglobin to form carboxyhaemoglobin (COHb). Carbon monoxide is not detectible by humans either by sight, taste or smell. It reacts vigorously with oxygen, acetylene, chlorine, fluorine and nitrous oxide. It is combustible, may serve as a fuel source and can form explosive mixtures with air. It mixes freely with air in any proportion and moves with air via bulk transport. The molecular weight of carbon monoxide is similar to that of air (28.01 vs approximately 29). It is produced by the incomplete combustion of carbonaceous fuels such as wood, petrol, coal, natural gas and kerosene. Carbon monoxide (CO) is a colourless, non-irritant, odourless and tasteless toxic gas.
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