## 3 Results and Discussion
### Classification Discussion Based on Overall Results
#### 3.3.3 Different Thickness  
After comparing the data for case 3, case 4, case 5, and case 6 in Figure 8, it was found that the thicker the coatings were, the better the fire protection effect was. After observing the coatings of these four cases, the expansion effect for each case of coatings was found to be good, and there was essentially no shedding phenomenon. The coatings of these four cases after the fire test were taken for thickness measurements, and the data were recorded in Table 7.  
From the table, we could find two phenomenon:  
1. The expansion ratio of the coatings decrease with the increase of the coating thickness. 2. The final coating thickness of case 4 after expansion was similar to that of case 3, but the failure time was very different. According to the principle of IFC in Section 2.4, shielded by the upper char layer (closer to fire), the lower layer might be in the last three stages without full expansion, so it seemed unreasonable to take it as a conclusion directly. We took the upper char layer and the lower char layer after the experiment, and found that the color of the lower char layer was lighter, as shown in Figure 14, which further indicated that the lower char might not fully expand. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Case Number** & \
\begin{tabular}{c} **Coating Thickness** \\ **before Test (mm)** \\ \end{tabular} &
\begin{tabular}{c} **Coating Thickness** \\ **after Test (mm)** \\ \end{tabular} & **Expansion Ratio** \\ \hline
3 & 4.4 & 94 & 21.36 \\
7 & 4.5 & 52 & 11.55 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Thickness statistics of IFC before and after the test. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Case Number** & \
\begin{tabular}{c} **Coating Thickness** \\ **before Test (mm)** \\ \end{tabular} &
\begin{tabular}{c} **Coating Thickness** \\ **after Test (mm)** \\ \end{tabular} & **Expansion Ratio** \\ \hline
3 & 4.4 & 94 & 21.36 \\
4 & 3.5 & 83 & 23.71 \\
5 & 2.5 & 62 & 24.80 \\
6 & 1.5 & 39 & 26.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Thickness statistics of IFC before and after the test. From Table 8 and Figure 16, we could see that the expansion ratio of the same kind of coating had nothing to do with the initial coating thickness. After the complete expansion, the expansion ratio was basically the same, and the expansion speed gradually slowed down with time. However, the coating with thicker initial thickness always had thicker thickness in the whole process of expansion, so this might be the reason why the temperature rise of 2.5 mm specimen was slower than that of 1.5 mm specimen in Figure 9.  
Further observation of the temperature curve displayed in Figure 9 showed that the initial stage of the temperature curve of case 3 was a downward convex curve, while the initial stage of the temperature curve of case 4, case 5, and case 6 was an upward convex curve, which indicated that the initial temperature rises of the latter three cases were faster. According to the analysis of the supplementary experiment, it was speculated that this might have been because the coating thickness was thinner during the heating process due to the thinner initial thickness, and when the coating were expanding, a large amount of heat was transferred to the tray at early stage. Even after the coating completely expanded, the temperature rise rate decreased, but because the temperature in the tray had reached a high value, the cable still failed quickly. Therefore, when IFC were used to protect the cables in the trays, a certain initial thickness of the coatings was necessary. For case 8, case 9, and case 10, brand C NFC were used, and the thicker the coating was, the better the fire protection effect was. The initial temperature rises for these three cases were relatively slow, and the temperature rise rate slowly increased with time. For case 11 and case 12 using brand D FC, the thicker the material was, the better the fire protection effect was.