## 6 Conclusions  
This paper proposes a simplified and practical approach to evaluating the Classroom Indoor Air Quality (CIAQ) Risk Index. The primary objective of the developed tool is to assess the potential of a classroom, originally designed for specific activity levels and occupancy, to maintain CO\({}_{2}\) levels within the established acceptable limits. Achieving this can lead to a reduction in health issues, an enhancement of well-being, and an improvement in overall performance and quality of life for educational communities. * The proposed approach is then applied to a case study. Additionally, a sensitivity analysis is conducted by varying the following parameters: (1) classroom volume, (2) students' age, (3) session duration, (4) maximum permitted occupancy, (5) activity level, (6) location and proximity to traffic, and (7) ventilation system. The following conclusions can be drawn:
* The proposed framework (considering the three vectors of hazard, vulnerability, and exposure) proved to be an effective approach for considering the main IAQ factors affecting classroom risk assessment. * The three-vector framework yielded highly satisfactory results, demonstrating repeatable, logical, coherent, and consistent evaluations that align with experience. * The results reveal that potential occupancy, occupants' activities, and the operational ventilation rate of the classroom are key factors influencing the developed risk index, consistent with previous studies. * The approach effectively identifies the influence of each parameter on the overall CIAQ Risk Index, allowing educators and facility managers to analyse different combinations of measures to create a safe and conducive learning environment for students and staff. Although the research study demonstrated the potential of the developed method to evaluate the CIAQ Risk Index and analyse potential measures to maintain appropriate air quality conditions in classrooms, certain aspects require further investigation. First, the CO\({}_{2}\) generation rates used in the model are based on literature-derived estimates rather than experimental measurements. While these values are sourced from well-regarded studies, the absence of empirical validation--particularly across different age groups and activity levels--may introduce a degree of uncertainty. Second, the model focuses solely on CO\({}_{2}\) concentration as a proxy for indoor air quality, without accounting for other relevant factors such as humidity, volatile organic compounds (VOCs), and particulate matter. While this simplification supports broader applicability and ease of use, it may overlook other important IAQ risks in certain contexts. Third, the case study and sensitivity analysis are grounded in data representative of Spanish educational environments within a Mediter  
Figure 9: Computed CIAQ Risk Indexes along with the hazard indexes for the studied cases. ranean climate. To enhance the robustness and applicability of the index, future work should explore the development of experimental campaigns to validate CO\({}_{2}\) generation rates in real-world classroom settings. Further efforts are also needed to test and adapt the model for use in diverse geographic and climatic contexts. Expanding the index to incorporate additional IAQ parameters--such as temperature, humidity, and particulate concentrations--would also improve its comprehensiveness. Finally, the index holds potential as a decision-support tool for prioritizing investments in retrofitting and ventilation upgrades, and its integration into multi-criteria decision-making frameworks for budgeting and planning should be explored further. Conceptualization, S.A., D.B.-C. and P.P. ; methodology, S.A. and R.D.L.C. ; validation, S.A., D.B.-C. and F.P.-B. ; formal analysis, S.A. and R.D.L.C. ; investigation, S.A., D.B.-C., F.P.-B. and P.P. ; resources, P.P. ; data curation, S.A.; writing--original draft preparation, S.A., D.B.-C., F.P.-B. and P.P. ; writing--review and editing, P.P. ; visualization, P.P. and F.P.-B. ; supervision, P.P.