 Carbon monoxide is a product of combustion of organic matter under conditions of restricted oxygen supply , which prevents complete oxidation to carbon dioxide ( CO2 ) . Sources of carbon monoxide include cigarette smoke , house fires , faulty furnaces , heaters , wood @-@ burning stoves , internal combustion vehicle exhaust , electrical generators , propane @-@ fueled equipment such as portable stoves , and gasoline @-@ powered tools such as leaf blowers , lawn mowers , high @-@ pressure washers , concrete cutting saws , power trowels , and welders . Exposure typically occurs when equipment is used in buildings or semi @-@ enclosed spaces . 
