Ahmad Dehghan Nejad - Department of Safety Engineering, Faculty of Health, Safety and Environment, Shahid Beheshti University of MedicalScience (SBMU), Tehran, Iran
Reza Gholamniya - Department of Safety Engineering, Faculty of Health, Safety and Environment, Shahid Beheshti University of MedicalScience (SBMU), Tehran, Iran
Ahmad Alibabaee - Department of Safety Engineering, Faculty of Health, Safety and Environment, Shahid Beheshti University of MedicalScience (SBMU), Tehran, Iran
Sara Ghanbari - Department of Civil Engineering Technology, Environmental Management & Safety, Rochester Institute ofTechnology, Rochester, NY, USA

Following the principles of the systemic accidentmodels and in particular, based on the STAMP(Systems-Theoretic Accident Modeling and Processes)causal model and STPA (System Theoretic ProcessAnalysis) risk analysis method, this paper focused onorganizational aspect of hierarchical safety controlstructure in complex socio-technical systems. In thisregard, a new framework was offered and tested tomodel organizational Feedback Control Loops. In fact,the STPA risk analysis method has been accommodatedfor deficiency analysis of organizational aspect ofhierarchical safety control structure.Accordingly, a new framework together with anexplicit guideline has been introduced and presentedthat can model the Organizational Feedback ControlLoops and their particular Process Models. With respectto this framework and procedure, the STPA has beenapplicable for analysis of Organizational ControlMechanisms that participate in control structure ofcomplex socio-technical systems.The presented framework was applied in a samplesystem that is utilized for civil helicopter maintenance.By applying this framework and its customized ProcessModel, the Organizational Control Mechanisms of thissample system was modeled and analyzed with respectto STPA method.In conclusion, in this paper have been shown that anaccommodated version of STPA can apply accurately toanalyze organizational mechanisms that may havedetrimental effect on safety of Complex Socio-TechnicalSystems.

Complex Socio-Technical Systems, Hierarchical Safety Control Structure, Organizational Control Mechanism, Feedback Control Loop, Systemic Accident Models