The utilization of stpa techniques for system design safety enhancement

The widely used safety analysis techniques usually assume that accidents mainly occur by the failures of system components. That’s why the classical techniques focus on either preventing the failures of the critical components or adding redundancy to back them up. Such techniques suffer from various limitations; most importantly is the main focus is in enhancing the defined system-by redundancy for example-without approaching a safer design from the beginning. In the previous years, a new technique is introduced called STPA (System-Theoretic Process Analysis) which is based upon a new accident model called STAMP (Systems-Theoretic Accident Model and Processes)[1]. One of the advantages of this technique is that it focuses in defining earliest design decisions upon safety considerations. The output of such technique consists of the unsafe scenarios and safety constraints to be taken in consideration during early design steps. Recently, various developers tried to adapt the new STPA technique in a software tool. The tools focus in defining a control process of the system and providing a general solution of safety considerations. Our work in the past years has been targeting the improvement of MBSA (Model-Based Safety analysis) tools to provide more accurate, cohesive failure analysis automatically [2]. Our developed methods based upon using component models of failure modes along with a system structure and systematically capturing the critical single components or combinations causing a system failure. In this paper we are trying to utilize the STPA techniques in our methods. The STPA method shall not be only used to define safety constraints of a system but also rectify a system hierarchy by providing design modifications that will handle any captured unsafe scenarios. These unsafe scenarios usually are not captured using the classical safety analysis methods utilized in most of the MBSA tools. Our approach is intended to be used in the early design steps in which the designer can know what modifications should be applied to handle the captured unsafe scenarios by STPA methods. In short, we are aiming to bridge between MBSA tools and STPA tools.