## 2 Research Methodology  
This research adopts a three-stage methodological approach aimed at consolidating and systematising current knowledge on XR applications for safety in construction and translating it into a structured and practical framework. This is a conceptual and methodological study focused on the design and theoretical validation of a framework. The methodology combines a systematic literature review, analytical categorisation of implementation requirements, and framework development supported by illustrative implementation examples. This approach was chosen to bridge the current fragmentation in XR-based safety tools and to ensure that the proposed solution is grounded in both academic research and practical considerations relevant to the Construction 4.0 context. Figure 1 shows the research methodology used. It shows the stages, research tools, activities and deliverables of each activity. The methodology has three stages: Stage I: Background of XR frameworks for safety management in construction; Stage II: Requirements and considerations for the implementation of XR in safety management; and Stage III: Design of a proposed framework for an extended reality solution for holistic safety management in construction, and examples of implementation of this proposed framework. In Stage I, a state-of-the-art review was conducted to identify background information on frameworks or workflows that show how to implement extended reality for construction safety management. For this purpose, the Web of Science and Scopus databases were reviewed. The search strings included combinations of the following keywords: (\"construction safety\" OR \"occupational safety\" OR \"hazards\" OR \"risk management\") AND (\"virtual reality\" OR \"augmented reality\" OR \"mixed reality\" OR \"extended reality\" OR \"XR\"). Publications between 2010 and 2025 (April) were reviewed. The inclusion criteria were: (a) studies addressing XR applications in the context of construction safety, and (b) publications proposing frameworks, workflows, or implementation strategies. Exclusion criteria included: (a) studies not related to construction or infrastructure projects, and (b) papers focusing solely on unrelated uses of XR (e.g., gaming, healthcare). A total of 32 articles met these inclusion criteria and were analysed in detail, and overall, 85 articles were included in the review. The search in Stage II was based on the same search as in Stage I, and the requirements and considerations for the deployment of XR for integrated construction safety management were identified according to three main aspects: (a) a holistic vision of construction safety management; (b) approaches from Construction 4.0 and methodological trends in the sector; and (c) extended reality as a paradigm for human-machine interactions in new virtual work environments. Considering these requirements, a framework for an extended reality solution for holistic safety management in construction was proposed in Stage III. It considers the deployment of construction safety management tasks in XR environments linked to BIM models and the project life cycle in the construction sector. Additionally, examples of the implementation of the proposed framework are shown to demonstrate the proposal's reliability. These illustrative examples serve to demonstrate the technical feasibility and internal consistency of the proposed XR framework in simulated scenarios. Although they do not involve data collection from real participants, they allow for a conceptual validation of the framework's structure and potential applications. The analytical categorization of the selected literature was carried out using a thematic coding approach, guided by the objectives defined for each stage of the methodology. For Stage I, studies were categorized based on whether they proposed frameworks, workflows, or case applications involving XR for construction safety.