Abstract
Due to increasing complexity of operational systems it is becoming necessary to make use of rational techniques to quantify risks and to measure influence of component failures on system risks. Reliability theory and fault tree analysis can be used to provide tools for safety decisions in ship operation and marine traffic. Computer aids for modelling and graphic representation of logical structures are described as well as methods for structural and quantitative analysis of risk models. Importance measures to judge influence of component risks on system risk are discussed. Methods are exemplified using subsystem models of ship operation. (A)