Estimation and Evaluation of Common Cause Failures

Success of many modern applications is highly dependent on the correct functioning of complex computer based systems. In some cases, failures in these systems may cause serious consequences in terms of loss of human life. Systems in which failure could endanger human life are termed safety-critical. The SIS (safety instrumented system) should be designed to meet the required safety integrity level as defined in the safety requirement specification (safety requirement allocation). Moreover, the SIS design should be performed in a way that minimizes the potential for common mode or common cause failures (CCF). A CCF occurs when a single fault result in the corresponding failure of multiple components. Thus, CCFs can result in the SIS failing to function when there is a process demand. Consequently, CCFs have to be identified during the design process and the potential impact on the SIS functionality have to be understood. This paper gives details about the estimation and evaluation of common failures and assesses a loo2 system. It is a survey paper that presents the newest developments in common cause failure analysis.