Steelworks blast furnace at night. A blast furnace is where iron is produced from iron ore. The iron ore is heated in the presence of coke (carbon) and limestone. As these raw materials pass through the furnace they react with hot air blown in from the bottom of the furnace. The air passes upwards in a few seconds, but the raw materials take 6-8 hours to reach the bottom. The final products are liquid slag and iron. Further refinement is needed to produce steel. Once a blast furnace is started, it will run for up to 10 years with only brief halts for maintenance. Photographed at the Corus Redcar Steelworks, Cleveland, UK.