This presentation will focus on how PI is being used to help monitor Dofasco's #4 Blast Furnace thereby providing an improved degree of certainty in extending the life of the furnace by several years. Dofasco is one of the major integrated steel producers in Canada. The #4 Blast Furnace is the largest of the blast furnaces producing an average of 4800 tons of molten iron per day, approximately 70% of the total daily iron production. In May 1994 a major breakout of molten iron through the hearth wall of the furnace caused major damage. Extensive repairs to the hearth were made over the next 30 days, in an effort to extend the life of the furnace for the next 6 à 12 months until a major reline could be planned and scheduled. During the repairs to the hearth, PI was installed as part of the extended monitoring system. This presentation will focus on how PI and PI-ProcessBook have helped to raise the confidence in extending the life of the furnace. Currently the reline of #4 Blast Furnace is planned for sometime during 1998.