A blast furnace is a tall cylinder of steel lined with firebrick, some reaching 35 metres tall. In a blast furnace iron is extracted from iron ore. Iron ore, coke (carbon) and limestone are placed in the top of the furnace. Hot air (between 760°C and 1150°C) is introduced lower into the furnace which burns the coke and melts the iron. The iron runs down and forms a pool at the bottom of the furnace where it can be tapped off. Impurities in the iron are melted using limestone as a flux. The impurities then float to the top of the metal forming slag.

The pig iron produced in a blast furnace contains about 93% iron, 3-4% carbon and other elements in small quantities.

There were three furnaces on blast and one being realigned on that plan. It was a three year campaign. When one furnace was lit it didn't go out again for three years so it was quite a long period before one was put out and the other that was realigned was put on blast again. (Mervyn Hammond)

There were three furnaces and each furnace cast at six hour intervals, throughout the day so each furnace had four casts a day. Three furnaces, twelve casts a day. And so one furnace was casting every two hours. (Mervyn Hammond)