Inclusion of Human Failure in Risk Assessment

Management of chemical sites and facilities has an obligation to conduct the operations on the site in such a way as to ensure the safety of people and the environment. In many countries this obligation is a legal requirement. Within recent years a new standard IEC 61508 has been published. This standard and its derivative standards are providing clear guidelines for the use of electrical, electronic and programmable systems for functional safety. These standards are risk-based standards and they require the user of the standards to undertake some form of risk assessment. This risk assessment is to justify the choice of any instrumented protective functions and their required performance or safety integrity level. Within such risk assessment it is important to ensure that there is proper consideration of human factors and particularly the impact of human failures. This paper will address some of the aspects in which human factors impact upon the application of instrumented functional safety systems. It will specifically consider the hazard and risk analysis of event sequences leading to hazardous events and the ways for inclusion of human factors elements within such analysis. It will help users of IEC 61508 and related standards with the incorporation of human factors into their assessments and will conclude with some illustrative cases to show ways in which this can be done.