## 3 Results and Analysis  
### Predictive Performance of Fire Detectors Based on Fire Models  
Figure 5 presents the activation times of the smoke and heat detectors based on fire growth rate variations obtained using FDS and CFAST, as part of prior research on diverse fire scenarios. The calculation domain adopted in this study featured a corridor-shaped compartment divided into compartment widths (Comp.) for both the FDS and CFAST analyses. As indicated by the smoke detector activation time results in Figure 5a, CFAST tended to overpredict the activation time as the fire grew rapidly and the detector moved farther from the fire source. However, overall, the smoke detector activation times obtained  
Figure 4: Comparison of the ceiling jet flow calculation results for changes in the maximum HRR.  
via CFAST were similar to those obtained using FDS. Compared with the relatively complex FDS, which considers characteristic lengths, delay times, and the time taken for smoke to enter the chamber, CFAST only considers \(O_{u}\) yet exhibited similar activation times. In Figure 5b, the results obtained via CFAST exhibit a large discrepancy compared with the FDS predictions for the heat detector. This result can be fully expected from the empirical correlation in CFAST to predict the activation time of the heat detectors, as previously mentioned. This is because a fixed velocity of 0.1 m/s was applied, rather than the exact velocity considered in the empirical correlation, as the fire room and the area of interest were separated.  
Figure 6 presents a comparison of the smoke and heat detector activation times in FDS based on different compartmentalization methods concerning the calculation domain settings in CFAST. As indicated by the predicted smoke detector activation times in Figure 6a, under the slow fire conditions, the 'Comp.' condition aligned closely with the FDS predictions. However, for 'Comp.+5W', the fire room and smoke detector were located in the same zone and exhibited identical smoke concentration values, indicating that the detectors were simultaneously activated. Smoke detectors situated in spaces adjacent to the fire room exhibited a maximum overprediction of 23 s. Furthermore, at a distance of 7.8 m from the fire, a minimum underprediction of 10 s was observed, and it was anticipated that this difference would increase with the distance from the fire. This implies that for accurate calculation of RSET, the calculation area must be properly partitioned when the smoke detector is a sufficient distance from the fire source.  
For the slow fire condition, as shown in Figure 6b, CFAST overpredicted the heat detector activation time for 'Comp.' by 59-100 s depending on the distance. The reason for this large difference from the FDS results is that CFAST assumed that the space separated from the fire room had a \(v_{cj}\) of 0.1 m/s, even if it was adjacent to the fire room. For 'Comp.+5W', the predictions from FDS and CFAST were similar, because CFAST used a built-in empirical correlation to calculate the temperature as the fire and detector were set in the same fire room even though they were far apart. To appropriately predict the temperature, which is significantly affected by velocity, close attention must be paid to the division between the fire room and the areas of interest. Ultimately, for smoke detectors, a suitable division from the fire room is necessary if they are a sufficient distance from the fire. For the prediction of the heat detectors, they must be within the same calculation area as the fire.  
Figure 5: Comparison of activation times for smoke and heat detectors according to the design of the computational domain in CFAST.