A modelling approach based on a mixed structural/functional graph that allows the simultaneous representation of the structural and the functional aspects of a system is presented. This model provides a framework to formalize risk analysis while being as simple as possible. The focus of the proposed approach is to achieve in a common analysis a functional failure analysis and the identification of physical damage, these being the two complementary parts of a full risk analysis. The resulting failure propagation graph is useful for model-based reasoning for fault diagnosis, the detection of dangerous situations, and the prediction of critical events. In addition, the approach is modular and reusable. The approach is illustrated by its use on an example.