An extension to the Alpha Factor method for enhanced common cause failure analysis

Abstract

Common cause failures occur when multiple components fail simultaneously due to a shared cause, and can significantly increase the overall probability of system failure. Therefore, it is essential to consider them in reliability and safety assessments, particularly for redundant systems in which components often share design, operational, or maintenance characteristics. The main objective of this work is to develop an advanced Alpha Factor method to enhance the assessment of common cause failures. One of the main drawbacks of the existing Alpha Factor method is that each component is limited to a single common cause failure group. The proposed method overcomes this limitation by allowing components to be assigned to multiple groups. The new method is applied to a simplified, yet representative, redundant safety system, and the corresponding results highlight the significant impact of common cause failures on system failure probability when analyzed through the proposed approach.