A Generic Method for a Bottom-Up ASIL Decomposition

Automotive Safety Integrity Level (ASIL) decomposition is a technique presented in the ISO 26262: Road Vehicles - Functional Safety standard. Its purpose is to satisfy safety-critical requirements by decomposing them into less critical ones. This procedure requires a system-level validation, and the elements of the architecture to which the decomposed requirements are allocated must be analyzed in terms of Common-Cause Faults (CCF). In this work, we present a generic method for a bottom-up ASIL decomposition, which can be used during the development of a new product. The system architecture is described in a three-layer model, from which fault trees are generated, formed by the application, resource, and physical layers and their mappings. A CCF analysis is performed on the fault trees to verify the absence of possible common faults between the redundant elements and to validate the ASIL decomposition.