Safety & Security Engineering, due to its special nature, represents an interdisciplinary area of research and applications that brings together, in a systemic view, many disciplines of engineering, from the most traditional to the most advanced and novel. Safety & Security Engineering is characterized by a totally new approach since it first analyzes the hazard context not only by means of traditional tools but also by means of risk analysis techniques and then manages the above mentioned context through technical solutions, installations, systems, human resources and procedures to prevent and face incidental events, natural and voluntary, that could damage people or goods. The purpose of the fourth International Conference on Safety and Security Engineering (SAFE 2011) was to continue to provide a forum for the presentation and discussion of the most recent developments in the theoretical and practical aspects of Safety and Security Engineering.The papers in this volume cover the following topics: Infrastructure Protection; Risk Analysis, Assessment and Management; Public Safety and Security; Modelling and Experiments; Construction Safety and Security; Transportation and Road Safety; Safety of Users in Road Evacuation; Emergency and Disaster Management; Process Safety and Security; Emerging Issues in Safety.