An extraction method of STPA variable based on four-variable model

Abstract

STPA is a hazard analysis technique based on systems thinking and a new model of accident causation based on systems theory rather than reliability theory [1]. However, STPA is a relatively new approach and its application has so far been without strict procedures, formal mathematical definitions, or model-based design tools to assist in the analysis of complex systems. A key step in the STPA research method is how to identify unsafe control actions. It’s unable to judge the control action itself is safe or unsafe. To determine whether a control action is unsafe, it is necessary to consider the controller in what circumstances to issue control actions. The environment in which a system is located is very complex. Analysts need to understand which environmental factors affect the operation of the system. These variables cannot rely on brainstorming by domain experts, but rather should give a methodology. Therefore, this article will give a more formal and standardized variable extraction method. Through the example of the train door system, the specific method steps will be presented, and the final extraction results will be given.