The propagation of faults in process plants: 8, control systems in fault tree synthesis

Abstract An interactive, computer-based facility has been developed for the investigation of fault propagation in process plants, including fault tree synthesis, which is embodied in the FAULTFINDER code. The general development and status of the work and the modelling are described in an overview paper and work on dividers and headers, on trip systems and on fault tree synthesis in further companion papers. This paper describes the treatment of control systems in the methodology. Control loops are integral to the whole pattern of operation of the plant. They tend to be a central feature of, and to dictate the form of, manually constructed fault trees. It is desirable that this feature be reflected in automatically synthesised trees also. Further, it is found in practice that it is necessary to treat control loops as a special feature in order to obtain correct trees. Characteristic features of the methodology developed include systematic decomposition of the control system; special features of the modelling of the control loop units; use of control loop templates; and additional rules for handling hierarchial and other complex control systems.