Installations in process industries such as chemical and petrochemical industries, especially when they are subject to German Major Accident Regulation are considered in this guideline. Practical recommendations for engineering, realization and operation of safety instrumented systems (SIS), with special emphasis on the subsystem sensors, actuators and logic systems are given. Basic considerations for the selection of devices of SIS, measures against systematic and spurious faults, measures related to fault tolerance as well as the operation of SIS and operational realization and documentation are given. The examples and checklists offer users advice for pactical use, serve as a mnemonic and for verification management.