Operator procedures are documents telling operators what to do in various situations. They are widely used in process industries including the nuclear power industry. The correctness of such procedures is of great importance. We describe how model checking can be used to detect potential errors and to verify properties of operator procedures. As there could be problems with modelling and model checking large systems, incremental modelling and verification is proposed as a strategy to help overcome these problems. A case study is presented to show how model checking (with the model checker Spin [5]) and the incremental strategy work in practise.