Tool-assisted hazard analysis and requirement generation based on STPA

Abstract

The automotive industry has been observing a trend of integrating new features into old vehicle designs to provide more convenience and flexibility to customers. However, it can be challenging to ensure safety without the support of appropriate techniques and tools for hazard analysis and requirement engineering. Systems Theoretic Process Analysis (STPA) is a hazard analysis technique that has been developed at MIT. It is based on systems and control theory and aims at capturing more causal factors leading to accidents, including component interactions. So far, STPA has been successfully applied to various industries. While there are tools that allow engineers to document the results of hazard analysis based on STPA, there are no tools that provide guidance during the analysis. Also, although a method is proposed to generate requirements from an STPA analysis, no tools have been developed to support that process. This thesis illustrates how tools can provide support for hazard analysis and requirement generation based on STPA, based on the proof of concept of a software tool that was developed at MIT. This STPA tool assists STPA Step I analysis by applying logical simplification to the original Step I results and automatically generating the simplified requirement in formal and executable forms. The simplified requirements are easily understandable and address all of the unsafe control actions identified in the original STPA analysis. The use of the STPA tool is illustrated through a case study of automotive systems that include multiple features. The STPA tool generates simplified and formal requirements for each individual feature based on STPA Step I results. In addition, it is also used to check whether conflicts between features have been resolved and to identify exactly what decisions should be made jointly between multiple design teams.