The platform directly above the slag cars supports the main blast furnace structure. Certain areas of the raised platform contain openings, allowing impurities and by-products which float to the top of steel during its molten stage, known as slag, to be skimmed off and dumped into the ladle of the slag cars below. The topped off railcars would then be hauled off and the slag dumped into a contained area known as a heap, where it remained to safely cool. The cooled slag by-produced was then sold to be used in various cement blends.