Software Based Systems Dependability Requirements in the Process Industries

Abstract

Following the Flixborough (1974) and Seveso (1976) disasters the 1982 European Community Directive (EC-501/82), imposed basic safety regulations on those process industries (chemical, petrochemical, refineries) handling dangerous substances. Successive national amendments highlighted the relevance of reliability assessment as a quality measure for the safe management of plant. Despite experiencing continuous reliability growth the process industries realised that careful attention had to be paid to the safety issues arising from the use of computer-based systems in hazardous applications, where human injury¹ or economic loss might be involved. Historical information on accidents arising within petrochemical plants can be used to identify the causes and the measures needed to avoid these dangerous conditions arising, or to mitigate their consequences. Electronic command and control systems are extensively used for military, air, ground transport, space and ship control. Similar systems are applied in nuclear power plants and in the process industries. It is recognised that there is a great variety of Electrical/Electronic and Programmable Electronic Systems (E/E/PESs) in a variety of application sectors covering a wide range of complexity, hazard and potential risk. In any specific application domain the safety measures required are dependent upon many factors specific to the application itself. At the same time, there are increased pressures to improve plant productivity. All these factors have led to the evolution of new requirements for safety systems. Reliability, and in a more general context dependability², relies on the use of appropriate design procedures to ensure that automatic control and protection systems are safe.