As our society becomes more and more dependent on IT systems, failures of these systems can harm more and more people and organizations both public and private. Diligently performing risk and hazard analysis helps to minimize the societal harms of IT system failures. In this paper we present experiences gained by applying the System Theoretic Process Analysis (STPA) method for hazard analysis on a forward collision avoidance system. Our main objectives are to investigate effectiveness in terms of the number and quality of identified hazards, and time efficiency in terms of required efforts of the studied method. Based on the findings of this study STPA has proved to be an effective and efficient hazard analysis method for assessing the safety of a safety-critical system and it requires a moderate level of effort
