Hazard Identification in Batch and Continuous Computer-Controlled Plants

Abstract

It has been recognized that due to increasing use of computers in chemical processes some incidents have occurred not because of equipment faults but because of errors in control software. A qualitative, functional model-based approach to hazard identification for general computer-controlled plants is presented in this paper. A functional model, the Process Control Event Diagram (PCED), is proposed. It can be used to represent discrete or continuous control systems. The PCED developed for a computer-controlled plant is used as the basis for hazard identification. State transitions are generated manually by applying the PCED and process information in order to identify whether an undesirable state can be reached. Hazard and operability analysis is carried out by introducing deviations for each control action in the PCED. Case studies are presented to illustrate the methodology.