Ore, limestone and carbon in the form of coke are put into the top of the blast furnace in layers. At the same time, hot air called "wind" is blown inside the furnace. Special nozzles called "tuyeres" are used to put the air in the furnace. The nozzles are at the bottom of the furnace. This process is called "blasting". It is why it is called a "blast furnace". The coke ignites (lights on fire) and burns. This creates carbon monoxide because there is not enough oxygen to make carbon dioxide. The carbon monoxide then reduces the metal oxide to the metal and makes carbon dioxide. This process is used to make iron. The limestone forms a substance called slag with the rock of the iron ore.