# Temperature Distribution Characteristics of Concrete during Fire Occurrence in a Tunnel
## 3 Tunnel Fire Simulation
### Analysis of Fire by Combustion Material Type  
Comparative analyses were carried out on the changes in the fire characteristics according to the duration of ignition sources that were used to simulate fires for different materials in the FDS. The simulations were conducted by modelling for materials with different properties (e.g., combustion heat, density, and ignition point). Based on the results, the appropriate duration of the ignition source was determined and applied to the fire simulation.  
Diesel and octane (C\({}_{8}\)H\({}_{18}\)), which are the commonly used gasoline types, as well as heptane (C\({}_{7}\)H\({}_{16}\)) and ethanol (C\({}_{2}\)H\({}_{6}\)O), were the hazardous materials applied to the fire simulation analysis. The values of the heat of combustion for these hazardous materials are 44.80 MJ/kg, 47.89 MJ/kg, 48.07 MJ/kg, and 29.65 MJ/kg, respectively. To analyze the changes in fire intensity with respect to the types of hazardous materials, specific analysis conditions were set to verify the fire intensity inside the tunnel when the fire occurred due to a hazardous material with a similar or lower heat of combustion. Table 1 outlines the model and conditions used for the analysis. Table 2 lists the material properties of the combustion materials.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Input Data** \\ \hline Space size (m) & 45 \(\times\) 8 \(\times\) 5.5 \\ Grid size (m) & 0.5 \(\times\) 0.5 \(\times\) 0.5 \\ Conductivity of concrete (W/m\(\cdot\)K) & 1.28 \\ Specific heat of concrete (KJ/kg\(\cdot\)K) & 0.75 \\ Density of concrete (kg/m\({}^{3}\)) & 2400 \\ Vehicle location & Middle of the tunnel \\  & 27,000 L capacity \\ Combustion material type & Diesel, ethanol, octane, and heptane \\ Simulation time (s) & 3600 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Analysis conditions by hazardous material type.  
Figure 1: Dimension of tunnel and position of fire in tunnel modelling.  
Figure 2 shows the analysis results for different combustion materials. Except for ethanol, whose heat of combustion is 29.65 MJ/kg, diesel, octane, and heptane have similar values for heat of combustion, i.e., 44.80 MJ/kg, 48.07 MJ/kg, and 47.89 MJ/kg, respectively. These three fuels had a similar fire intensity level of approximately 160 MW. However, the results for diesel showed a longer fire duration by approximately 500 s. In comparison to these three fuels, the heat of combustion of ethanol is approximately 60%, and this fuel also resulted in a lower fire intensity. However, the duration of its fire was longer than 1 h, much longer than the fire durations of the other combustion materials.  
The above analysis revealed that different types of hazardous materials on a highway can cause fires with different characteristics (i.e., the fire intensity and duration are likely to differ depending on the material type). The analysis of the simulation results showed that a fire caused by dangerous-goods vehicles carrying diesel results in the most serious conditions of fire intensity and fire duration.