Methodological issues of functional safety and reliability assessment of critical systems in industrial hazardous plants

The aim of this article is to identify and discuss some methodological issues that are of interest among functional safety specialists and experts after publication of the second edition of international standards IEC 61508 and IEC 61511, including the design and implementing the safety-related functions of higher safety integrity levels and protection layers. The basic role of safety-related systems is to reduce effectively and to control in time the individual and/or societal risk with regard to its tolerable levels. These issues include: risk criteria, reliability data, probabilistic models of systems operating in high and/or low mode, dependent failures, human reliability analysis, security of programmable safety-related systems, and reducing uncertainty issues in decision making process applying the cost-benefit analysis. Selected aspects of these issues are discussed and some challenges requiring further research are indicated.