Beyond SHELL: the SSHELL framework for advancing Human Factors theory

The SHELL model has remained one of the most widely used conceptual tools in Human Factors since its introduction, shaping training, safety research, and system analysis across aviation, medicine, and defence. Its representation of human interaction within complex systems has been influential; however, the model’s architecture is predominantly external, focusing on the relationships between Software, Hardware, Environment, and Liveware components, while neglecting the intrapersonal dimension that regulates these interactions. Over the past two decades, interdisciplinary research in psychology, cognitive science, and neuroscience has highlighted the critical role of self-consciousness in performance regulation, resilience, and error prevention, indicating a limitation in the explanatory and predictive capacity of the traditional SHELL framework. In response, this paper employs a conceptual synthesis and cross-sectoral analytical methodology to examine the limitations of existing Human Factors models and proposes an extension, SSHELL, which integrates Self-consciousness as a new central element. SSHELL reframes the human operator as a self-regulating, conscious system that actively manages both internal states and external system interactions. By reintroducing the self into system thinking, the SSHELL framework advances Human Factors theory by offering a domain-neutral model applicable across aviation, healthcare, military, and educational systems, while highlighting the need for future empirical validation.