Method for Selecting the Safety Integrity Level for the Control-Command and Signaling Functions

Abstract

The purpose of the article is to present selected method of risk assessment of railway control and signaling systems, including current normative and legal bases, such as directives and regulations that regulate the interoperability and safety of the railway system. Selected methods used at the initial stage of creating safety requirements and referring to the initial definition of the system defined at a high level of abstraction are considered. Issues of holistic approach and residual risk management are also discussed. Risk models are presented as well as individual steps of risk analysis, evaluation, and assessment, including hazard identification, impact analysis, and selection of the risk acceptance principle. Selected model based on hazard and operability studies (HAZOP) and an adapted risk graph was applied to the real signalling equipment. The key aspect undertaken in the article is the proposal to set quantitative safety objectives based on the safety integrity level/tolerable hazard rate (SIL/THR) indicator, as an important parameter in further analysis of the system, especially in computer applications. The result of study showed that application of proposed combination HAZOP and adapted risk graph method are efficient and suitable for a railway signalling application. The results and conclusion are presented in Chapters 4 and 6 of the article.