Integrating STPA into ISO 26262 Process for Requirement Development

Paper #:
  • 2017-01-0058

  • 2017-03-28
Developing requirements for automotive electric/electronic systems is challenging as they are becoming increasingly software-intensive. Increasingly, designs must account for unintended interactions among software features, combined with unforeseen environmental factors. In addition, engineers have to make architectural tradeoff and assign responsibilities to each component in the system before developing safety requirements. ISO 26262 is an industry standard for the functional safety of automotive electric/electronic systems. It specifies various processes and procedures for ensuring functional safety, but does not limit the methods that can be used for hazard and safety analysis. System Theoretic Process Analysis (STPA) is a new technique for hazard analysis in the sense that hazards are caused by unsafe interactions between components (including humans) as well as component failures and faults. Otherwise stated, STPA covers analyzing the safety of the intended function (SOTIF) as well as functional safety. This paper introduces a process map for integrating STPA into the functional safety process based on ISO 26262. In particular, it illustrates how STPA can help evaluate safety and other system-level goals with ASIL classification from Hazard Analysis and Risk Assessment (HARA). The process map also provides guidance on making architectural decisions in order to create functional safety requirements. To make the process map applicable to different functional safety processes adopted by OEMs, modeling and tool support are developed based on Systems Model Language (SysML). Guidelines on how to develop a meta-model that supports STPA and the model interoperation are given.
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