Introducing a system theoretic framework for safety in the rail sector: supplementing CSM-RA with STPA

To meet the ever-growing challenge to improve the capacity and performance of the UK's rail network, the industry continues to deliver technical, operational and organisational change projects. The safety risk associated with such change is controlled through a risk management framework known as the Common Safety Method for Risk Evaluation and Assessment (CSM-RA). But as we continue to deliver extremely complex mega-projects, with the use of new and novel technology and systems to support safety-critical functions, new modes of both machine failures and human errors arise. This paper discusses how System-Theoretic Process Analysis (STPA), a relatively new hazard analysis technique based on systems theory, can be used in the application of CSM-RA. This paper discusses how we can use STPA to supplement our current 'toolbox', promoting a 'systems-thinking' approach to safety in the rail sector to help us to answer that crucial question: How can we be confident that we understand what our safety requirements should be, and are we really sure that all reasonably foreseeable hazards have been identified?