The step from bloomery to true blast furnace is not big. Corus announced partial mothballing of the Teesside blast furnace. There were problems with the operation of the blast furnace itself. This was a particular concern in smelting iron using a blast furnace. One design was the shaft kiln, similar in design to a blast furnace. In the century after the Old Blast Furnace closed, it became buried. The Scrantons focused instead on manufacturing pig iron using a blast furnace. Currently only one out of two blast furnace are in operation. Some chemicals are deliberately added such as flux which makes a blast furnace more efficient. The Boudouard reaction is an important process inside a blast furnace. East Granite is north of the blast furnace at US Steel. Nozzles used for feeding hot blast into a blast furnace or forge are called tuyeres. Examples are the bloomery furnace and the blast furnace. Coke is used as fuel in a blast furnace. The third powerhouse was built in 1941 as part of the No.1 Blast furnace.