## 2 Materials and Methods  
### Materials and Instruments  
In the investigation of the oil storage company mentioned above, it was found that the power cable and the control cable used for the emergency shut-off valve of the company were RVV 3*1.5 mm\({}^{2}\) and ZA-KVVP 14*1.5 mm\({}^{2}\), respectively. In this experiment, the above two kinds of cables were selected for testing. The two kinds of cables were composed of 3 and 14 copper wires, each copper wire was separated by insulating skin, and the cross-sectional area of each copper wire was 1.5 mm\({}^{2}\). The two types of cables are shown in Figure 1.  
According to the test standard, the cross-section size of the tray was 200 \(\times\) 100 mm, and the length was 1800 mm [29; 30]. Five kinds of fire-retardant coatings were used in this experiment, namely, brand A intumescent fire-retardant coatings for steel structures (water-based), brand B intumescent fire-retardant coatings for steel structures (water-based), brand B intumescent fire-retardant coatings for steel structures (oil-based), and brand C non-intumescent fire-retardant coatings for steel structures. In order to compare with other common fireproof materials, two kinds of fire-resistant cotton with thicknesses of 30 mm and 50 mm were selected. For the convenience of writing, the above materials' names will be abbreviated according to Table 1.  
The parameters of the above materials are shown in Table 2. \begin{table}
\begin{tabular}{c c} \hline \hline
**Types of Material** & **Abbreviation** \\ \hline Intumescent fire-retardant coatings for steel structures & IFC \\ Intumescent fire-retardant coatings for steel structures & IFC (W) \\ (water-based) & Intumescent fire-retardant coatings for steel structures (oil-based) & IFC (O) \\ Non-intumescent fire-retardant coatings for steel structures & NFC \\ Fire-resistant cotton & FC \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Abbreviation comparison of the materials’ names. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Types of Material** & **Component** & **Other Parameters** \\ \hline Brand A IFC (W) & APP, MEL, PER, EVA & adhesive strength: 0.73 Mpa \\ Brand B IFC (W) & APP, MEL, PER, EVA & adhesive strength: 1.29 Mpa \\ Brand B IFC (O) & APP, MEL, PER, AR & adhesive strength: 1.32 Mpa \\ Brand C NFC & PC, EP, EV & thermal conductivity: \\ Brand D FC & & \(\leq\)0.0117 W/(m\text{-}K) \\  & CF & thermal conductivity: \\  & & 0.03 W/(m\text{-}K) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Parameters of the materials. Figure 1: Photos of cables: (**a**) RVV 3*1.5 mm\({}^{2}\); (**b**) ZA-KVVP 14*1.5 mm\({}^{2}\). The coating thickness was measured with a Kedian MC-2000 coating thickness gauge. The temperature and the insulation resistance were collected with an Agilent keysight 34970A data acquisition instrument that was set to collect every 10 s. The temperature measurement range of the instrument was 0.000 \({}^{\circ}\)C-1200.000 \({}^{\circ}\)C, and the insulation resistance measurement range was 1-999,999,999 \(\Omega\). The test furnace that was used was a vertical fire-resistant test furnace with liquefied petroleum gas (LPG) as fuel. The opening size was 4.5 \(\times\) 3.0 m. The appearance is shown in Figure 2a. Open fire heating was adopted for the fire resistance test. In order to make the specimen subject to the flame act similar to the actual fire, the temperature change in the test furnace referred to the ISO 834 standard fire condition, and the change law met the following functional relationship [31]:  
\[\text{T}=\text{T}_{0}+345\log_{10}\left(8\text{t}+1\right), \tag{1}\]  
where T is the average furnace temperature at the time of t in (\({}^{\circ}\)C), T\({}_{0}\) is the initial temperature in the furnace in [\({}^{\circ}\)C], which needed to be in the range of 5 \({}^{\circ}\)C-40 \({}^{\circ}\)C, and t is the time of the test in [min].