## 3 Experimental Results
### Effect of the Volume of Firestop Material  
Figures 8-10 show the peak temperature as a function of the firestop-material cross-sectional area under three criteria: opening area, net fill ratio (firestop area minus penetrant area), and firestop-to-opening area ratio. Although nominal diameter combinations such as 50-100 mm, and 75-125 mm defined the test conditions, all area values in the graphs and analysis were calculated from measured outer diameters to reflect actual cross-sectional areas. Each graph entails a red line representing data excluding the 125-150 mm condition and a black line representing all data. For nonmetallic pipes, the red line includes the 50-75, 75-100, and 100-125 mm conditions; meanwhile, for metallic pipes, it includes the 50-100, 75-125, and 100-150 mm conditions. This comparison helps visualize the influence of the 125-150 mm condition in both material types. To visually distinguish the two trendlines, data points used for the red line are marked in red outline, while all data points are denoted as black-filled circles. Figure 8: Peak temperature as a function of firestop cross-sectional area: (**a**) nonmetallic pipe; and (**b**) metallic pipe. Figure 7: Post-test condition of metallic-pipe specimens. Figure 8 shows the peak temperature as a function of the absolute firestop-material area. For nonmetallic pipes, both lines excluding and including the 125-150 mm condition, exhibit a strong positive correlation: the peak temperature increases as the firestop material volume increases. This indicates that the firestop material volume is a critical determinant of fire-resistance performance in nonmetallic systems. In contrast, for metallic pipes, the correlation coefficient drops sharply. Even though the firestop volume is larger relative to the available space, the peak temperature rises, confirming that the pipe's thermal conductivity and structural role outweigh the firestop volume in influencing fire resistance. Figure 9 analyzes the peak temperature as a function of the net fill ratio. For nonmetallic pipes, the correlation coefficient collapses when the 125-150 mm condition is included, revealing low to near-zero correlation. This is because nonmetallic pipes soften and collapse at high temperatures, so that the pipe opens before it becomes sealed by expanded intumescent material; thus, the initial annular gap is not a critical factor in fire-resistance performance. By contrast, metallic pipes retain their structural continuity and conduct heat directly. The net fill ratio remains influential. Figure 10 shows the peak temperature as a function of the firestop-to-opening area ratio. For nonmetallic pipes, both lines show strong negative correlations indicating that the extent of opening coverage directly influences fire resistance. For metallic pipes, correlations are weaker as heat is conducted through the pipe, which limits the explanatory power of firestop ratios based solely on opening size. The trendline slope for metallic systems  
Figure 10: Peak temperature as a function of the ratio of firestop cross-sectional area to opening area: (**a**) nonmetallic pipe; and (**b**) metallic pipe. Figure 9: Peak temperature as a function of the ratio of firestop cross-sectional area to annular space area: (**a**) nonmetallic pipe; and (**b**) metallic pipe. also shifts considerably with the inclusion of the 125-150 mm condition, indicating the amplified heat-transfer effect of larger pipe diameters. In summary, nonmetallic pipes exhibit a direct relationship between the extent of firestop application and fire resistance, owing to pipe collapse at high temperatures, requiring complete sealing by intumescent materials. Meanwhile, metallic pipes maintain their structure and conduct heat directly; thus, firestop material alone cannot ensure sufficient fire resistance--dedicated thermal insulation design is essential.