This study presents a proof-of-concept method for ventilation-informed workplace-layout assessment. Measured carbon dioxide decay was combined with a computational fluid dynamics model of an occupied indoor room during one natural cross-ventilation event. After validation against measurements at a central monitoring point, the simulated CO2 field was evaluated within the breathing zone and local volumes around each seated operator. Mean concentration, percentile concentration, and the fraction of local volume above a comparative threshold characterized spatial and temporal dilution. Cross-ventilation reduced average CO2 concentration, but the improvement was spatially non-uniform. At the end of the analyzed period, op7 and op4 retained the highest local fractions above the threshold. The method identifies positions where layout or ventilation interventions should be prioritized. It serves as a screening and decision-support procedure rather than a completed layout optimization; comparison of alternative configurations is reserved for future work.