PROGRAMMABLE ELECTRONIC SYSTEMS APPLIED FOR RISK CONTROL IN PETROCHEMICAL PLANTS

The chemical industry today is in transition, with increasing emphasis on total quality control along with needs to meet even more stringent levels of health, safety and environmental management. Fortunately, t hese needs are being paralleled by major developments in process monit oring and control instrumentation. Microprocessor-based process sensor s, programmable electronic systems (PESs), and precision throttling va lves make possible the implementation of complex process control strat egies in DCSs where operators interact with the process through video display human/machine interfaces. The automation of past, manual opera ting tasks is justified under the umbrella of reducing the likelihood of human errors. Although automation does reduce the sources of human error in plant operations, these programmable control systems and soft ware introduce new and different potential sources of error, leading t o new implementation considerations. Many of the hazard identification and risk assessment methodologies used today treat the process contro l system as a 'black box'. Furthermore these methodologies are based o n techniques that assume independence of failures. However, when PESs are used for both regulatory and safety interlock controls, the possib ilities for common mode failures and covert faults are greatly increas ed over that demonstrated by older technologies. Data highways, common software, central supervisory control computers and subtle deficienci es in design all introduce new potential sources of shared failures. T oday, achievement of plant safety is a systems issue [1]. Process haza rd assessment and control requires an integrated analysis with inputs from each of the disciplines involved in process design and plant oper ation, as well as the guidance of safety and risk specialists. This pa per presents an approach to total process safety assessment in which i nstrumentation is applied as one means for risk mitigation. A methodol ogy for reduction of hazardous event likelihood by using modern progra mmable electronic monitoring and control systems is described, and app lications of the methodology to industrial examples are presented. The methodology applied is that documented in [2].