Work within sociotechnical systems involves inherent performance variability, which can lead to undesirable outcomes. In this study, a framework has been developed to model this variability and identify critical activities within sociotechnical systems. To this purpose, we propose integrating Ergonomic Work Analysis (EWA), the Functional Resonance Analysis Method (FRAM), and Fuzzy Set Theory. A case study in the healthcare sector is presented to demonstrate the model's applicability. The results indicate that improvements such as updating the hospital's internal system, formalizing procedures, and enhancing information flow coordination across departments could benefit the process. Although the model is still in an intermediary development phase, it has demonstrated promising results, particularly in its potential for prospective investigations to understand how interventions could impact the system’s behavior. By using work analysis, the model can account for contextual factors that influence a system-oriented analysis. Therefore, the model could be valuable in managing sociotechnical systems, particularly those with a higher level of complexity and numerous functions.