1. Introduction
In recent times, buildings have been becoming increasingly taller. As casualties may occur due to smoke propagation during building fires, measures are required to prevent smoke from spreading into evacuation routes in the event of a fire. Accordingly, in Korea, regulations related to smoke control systems were established under the Fire Services Act in 1973, and measures to prevent smoke propagation have been implemented, including the installation of pressurization smoke control systems in accordance with the Fire Safety Standards for Smoke Control Systems in Special Evacuation Staircases and Ancillary Rooms of High-rise Buildings [1]. However, various issues have been raised regarding pressurization smoke control systems, such as system malfunction and discrepancies between the actual airflow rate and design airflow rate [2].
In Korea, the supply airflow rate and damper capacity of pressurization smoke control systems are determined based on the leakage area of buildings and pressure differentials through NFSC 501A and its commentary, which reference the British BS EN 5588 and NFPA 92 standards. However, factors such as building occupancy and scenarios involving firefighting activities are not sufficiently considered in the current approach. In contrast, the British BS 12101-6 standard is similar to the Korean standard in that it secures supply airflow rates based on leakage area and pressure differentials. However, it classifies buildings into Classes A to F by considering evacuation and firefighting activities and accordingly establishes different pressure differential and smoke containment airflow velocity requirements. Furthermore, it provides experimentally derived data considering fire and non-fire rooms, as well as door open and closed conditions, and specifies methods for applying these data in calculations [3]. In the United States, methods have been established to determine minimum and maximum pressure differentials according to sprinkler installation conditions and ceiling height and to calculate smoke containment airflow velocity based on smoke temperature and opening height [4]. In Japan, as shown in Figure 1, calculations are performed based on fire safety engineering principles by considering heat release rates and temperatures generated during fires, which differs from the Korean design approach [5]. Furthermore, previous studies using CONTAMW confirmed that when the temperature of the fire source was set higher than typical conditions, a significant deviation from the designed pressure differential occurred [6].
As such, improving pressurization smoke control systems in Korea requires consideration of fire scenarios that may occur during actual fire events. Because maintaining a higher pressure in ancillary rooms is essential for smoke containment, the analysis of pressure differentials is particularly important. However, in Korea, a uniform criterion of 50 Pa is currently applied, while fundamental data related to pressure calculation methods under fire conditions remain insufficient [7]. Therefore, this study aimed to establish a foundational basis for the design of pressurization smoke control systems considering fire scenarios by analyzing pressure differentials and smoke flow characteristics while accounting for temperature rise in vertical spaces.
2. Overview of the Reduced-Scale Experiment for Pressure Differential Analysis in Vertical Spaces
2.1. Overview of the experimental model
In this study, an experimental model was constructed by reducing an actual six-story building to 1/6 scale. Each space consisted of a room, lobby, and shaft, and because the fundamental characteristics of the actual building had to be preserved, the dimensions of each room and opening were reduced in similar proportions. An overview of the entire experimental model is presented in Table 1, and the schematic and dimensions of the experimental model are illustrated in Figure 1.
2.2. Overview of the fire source and thermocouples
In this experiment, heptane was used as the fire source, and containers with diameters of 10, 20, and 24 cm were used to vary the heat release rate. The heat release rate was calculated as the product of the fuel mass loss rate, m ˙
Furthermore, to estimate the heat release rate corresponding to an actual building, the equivalent heat release rate was derived using the Froude scaling model, as expressed by Eq. (2), and the results are presented in Table 2 [10].
K-type thermocouples were used to measure temperature as an experimental parameter. To measure smoke and flame temperatures, a thin steel column penetrating the entire shaft space was installed, and six thermocouples were placed at one point on each floor within the shaft space. In addition, six thermocouples were installed at the openings connecting the corridor to the shaft, with one thermocouple positioned on each floor at a point 50 mm below the ceiling surface, resulting in a total of 12 thermocouples. Furthermore, the front wall was constructed using heat-resistant glass to enable observation of fire conditions inside the experimental model. An overview of the fire source and thermocouple locations is shown in Figure 2.
3. Results of the Reduced-Scale Experiment for Pressure Differential Analysis in Vertical Spaces
3.1. Temperature distribution in the shaft and room spaces
In this experiment, temperatures were recorded at each measurement point, and the temperature distributions were analyzed according to container size (i.e., variations in heat release rate). Experiments were conducted five times for each container size of 10, 20, and 24 cm. Figure 3 presents the time-dependent temperature distributions in the shaft space (Figure 3(a)) and the room spaces on each floor (Figure 3(b)) for the 20 and 24 cm container cases. Here, the temperature distributions in the shaft and room spaces on the first floor, where the fire source was located, were excluded from the analysis because they were strongly affected by thermal plumes generated by the fire source, making pressure differential calculations difficult.
From the temperature trend analysis, it was found that in the shaft space, S-2 exhibited the highest temperature, and the temperatures at S-4, S-5, and S-6 were higher than that at S-3 on the third floor. In addition, for the room spaces on each floor, R-4 showed the highest temperature, followed by R-2, R-3, R-6, and R-5 in descending order. These characteristics are considered to have resulted from the upward movement of thermal plumes in the shaft space, causing temperatures in the upper region to become higher than those at the intermediate level (S-3). In the room spaces, similar characteristics appeared because thermal plumes entered each room space from the lower floors upward. Furthermore, it was confirmed that similar temperature distribution trends were observed regardless of the heat release rate (i.e., fire source size).
3.2. Pressure differential between the shaft and room spaces
In this study, the pressure differential between the shaft and room spaces was calculated based on the temperature data measured at each location. The pressure differential calculations were performed using Japanese smoke flow and pressure differential calculation equations. To determine the pressure differential, the mass flow rate was first calculated using Eq. (3), one of the parameters required for pressure differential estimation. Then, density was calculated using Eq. (4), which is based on the ideal gas relationship. Finally, the pressure differential was obtained by substituting the derived parameters into Eq. (5) [11].
As described above, pressure calculations require determination of the average temperature of each room based on the previously measured temperature data. Accordingly, the temperature value for each floor was defined as the average value over the 240-300 s interval, which included the peak temperature data for each condition. The average temperatures of the shaft space for each condition are presented in Table 3, and the average temperatures of the room spaces on each floor are shown in Table 4.
Based on the temperature differences presented in Tables 3 and 4, the calculated pressure differentials according to container size (variation in heat release rate) are presented in Figure 4.
In addition, the mass flux within the shaft space flows into the fire room, while all flow is discharged through the upper floors because they remain open. Therefore, based on the characteristics shown in Figure 4, the total mass flux within the shaft was calculated using Eq. (6).
The results of the pressure differential calculations derived from this relationship are shown in Figure 5.
The calculation results showed that, for the 10 cm container case, the pressure differential decreased from the second floor to the third and fourth floors but increased again on the fifth floor. In the 20 cm container case, relatively high pressure differentials were observed on the second and fourth floors, while decreasing trends were identified on the remaining floors. In addition, for the 24 cm container case, a large pressure differential was observed on the second floor, whereas relatively small pressure differentials were observed on the third, fourth, and fifth floors. These results indicate that smaller container sizes (lower heat release rates) tend to produce larger pressure differentials in the upper floors, whereas larger container sizes (higher heat release rates) result in higher pressure differentials in the lower floors but lower pressure differentials in the upper floors. As the fire size, represented by factors such as container size (heat release rate), influences the pressure differential within the shaft space, pressure differential calculations considering fire scenarios are necessary during the design of pressurization smoke control systems to effectively control smoke propagation during fires.
Furthermore, this study was conducted to obtain fundamental data; therefore, opening conditions were maintained identically throughout the experiments. In addition, considering the potential risk of measurement errors associated with temperature-based analysis, direct pressure differential measurements were not performed. Instead, only theoretical pressure differentials calculated using Japanese design equations, representing the relationship between actual temperature and pressure differential, were presented. Therefore, for further validation, it is necessary to compare measured pressure differentials obtained using pressure measurement instruments with calculated values and to secure data considering different opening and closing conditions of openings. In addition, this paper presented results based on temperature data obtained within the reduced-scale experimental space, and verification using actual buildings remains insufficient. Therefore, validation through comparison with simulation results is necessary, which remains a subject for future study.
4. Conclusion
In this study, experiments were conducted on a 1/6-scale vertical building model by varying the container size, thereby changing the heat release rate, and analyzing the resulting temperature distribution within the vertical space. In addition, pressure differentials at each floor were derived by applying existing theoretical equations. The results are summarized as follows:
1. Analysis of the temperature distribution showed that temperatures in the shaft space tended to be higher in the upper floors than in the lower floors, whereas temperatures in the rooms on each floor tended to be higher in the lower floors than in the upper floors.
2. Regarding pressure distribution, it was confirmed that as the container size (heat release rate) increased, the pressure differential in the lower floors increased, while the pressure differential in the upper floors decreased. These findings indicate the necessity of calculating pressure differential distributions considering fire size and fire scenarios.
3. It was confirmed that different fire scenarios influence pressure differentials in the upper floors, which in turn influence the stack effect within the shaft space, and the location of the neutral plane is expected to change according to temperature variations. However, the current design approach for pressurization smoke control systems does not consider pressure differential distributions resulting from fire scenarios. Therefore, additional investigations are required to obtain supporting data for future pressurization smoke control system designs considering fire scenarios.
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