Virtual Button and Graphical Interface System Safety Evaluation using System Theoretic Process Analysis (STPA)

System Theoretic Process Analysis (STPA) is an extremely valuable methodology, especially when used early in a system’s concept phase, for effective and efficient development of safety requirements that address potential safety issues associated with human machine interactions. This paper outlines how STPA can be used to explore potential safety concerns associated with interactions between human operators and virtual buttons within graphical interfaces across the planned operational scenarios and expected system behaviors. Appropriately validated system safety requirements can be developed based on this exploratory effort. The paper shows how STPA includes drivers and operators as system elements within the control structure where these humans are expected to interact with a “system/feature of interest” by means of virtual buttons presented in a graphical interface. The inclusion of humans as elements of the control structure enables a representation of the human as a “human controller” and, as such, enables STPA evaluation techniques to be applied to them just as these techniques would be applied to any “control” element in a control structure.