Fuel injection into the blast furnace as a substitute for expensive coke has become an accepted asset in the art of ironmaking. In a short span of seven years, fuel injection has been expanded to 50% of the furnaces in the United States and Canada and the types of fuels now include gas, fuel oils, tar, coal, and slurries on a trial basis. This technological innovation brought about the emphasis on hot blast temperature operations which in turn led to numerous other developments in the ironmaking industry. Fuel injection is necessary because more iron is being produced, therefore, more fuel is required. It is possible to replace as much as 20% or more of the coke with fuel injection, but to do this it is extremely important that the injection system is soundly designed to give reliable performance.