It cannot be seen or smelt . Faulty gas fires or boilers may produce carbon monoxide and poison the air in a room without anyone knowing . Every year, people die from carbon monoxide poisoning . Carbon monoxide acts as a poison by combining with haemoglobin in the blood . Haemoglobin normally reacts with oxygen from the air and transports the oxygen to the parts of the body which need it.
Carbon monoxide is much more reactive with haemoglobin than oxygen is.
It combines to form a stable compound with haemoglobin , preventing the transport of oxygen around the body . Combustion of hydrocarbons , whether complete or incomplete , have environmental and health concerns , see Environmental Issues .