## 3 Analysis of the EV Thermal Runaway Fire Scenarios
### Analysis of Thermal Radiation from an EV Fire and the Damage Caused  
The main hazard of an EV fire comes from the uncontrolled \"energy\" released during the vehicle combustion and the damage and loss caused to people, objects and the environment. The damage caused by uncontrolled \"energy\" can be classified into two categories: (i) flame damage and the thermal radiation released by the combustion and (ii) the pollution and chemical damage caused by the toxic and harmful smoke. Owing to the openness of the roadside parking, the impact of hot smoke and the thermal convection on the surrounding environment near the ground is reduced. Therefore, in this study, the risk impact of the combustion flame heat was considered without considering the damage caused by the harmful substances, such as smoke, generated by the combustion and the impact of the violent combustion explosions. Combustion thermal hazards are mainly caused by contact with the flame front through heat conduction and the flame thermal radiation. For the objects outside the flame range in the open region, the mode of the flame propagation and damage was mainly thermal radiation. Therefore, the damage analysis of an EV fire is mainly used to determine and analyze the factors influencing the thermal radiation from the fire. Calculation of the flame radiation intensity based on the HRR  
The HRR is an important index for assessing fire hazards. It provides information about the intensity of the energy released by the fire in the form of heat [33] and the HRR can more accurately describe the energy released by a flame [17,34]. The HRR of the battery is directly related to its state of charge (SOC) and [PERSON] [35] pointed out that the SOC mainly affects the reaction intensity of the battery combustion. The higher the SOC, the more intense the combustion reaction and the lower the residual mass after combustion. Considering the most disadvantageous situation, the PHRR of each stage was selected as the parameter to calculate the risk-accident threshold range. According to a statistical study on the PHRR of power batteries [9], there is a linear relationship between the PHRR, \(Q_{Lib}\) (kW), and the power battery capacity, \(E_{B}\) (Wh), with an applicable range of approximately 10 Wh to \(10^{7}\) Wh. This relationship is as follows:  
\[Q_{Lib}=2E_{B}{}^{0.6} \tag{1}\]  
With the \"battery energy\" parameters listed in Section 3.2, we can obtain that \(Q_{Lib}=1728.3\) kW. Other combustibles in EVs are mainly plastics, leather and textile fibers and these different materials have different combustion PHRRs. Considering the worst-case scenario, the highest HRR of the material (leather nonwoven felt) [36] was selected as the PHRR when the EV combusted the other combustibles. For the convenience of calculation, the PHRR per unit area was taken as 0.5 MW/m\({}^{2}\). The formula for estimating the PHRR of the other combustibles in EVs is as follows:  
\[Q_{O}=\eta A_{p}Q^{\prime\prime} \tag{2}\]  
We assumed that the PHRR per unit area was \(Q^{\prime\prime}=500\) kW/m\({}^{2}\); the combustion efficiency was \(\eta=\)1; and the combustion projected area was \(A_{p}\), with the unit: m\({}^{2}\), estimated from the projected area of the vehicle. Therefore, the PHRR of the flame in the burning EV in the thermal runaway combustion stage was \(Q_{1}=Q_{Lib}\) and in the vehicle combustion stage was \(Q_{2}=Q_{Lib}+Q_{O}\). With the parameters in Section 3.2, the vehicle combustion stage was \(Q_{2}=5468\) kW. The flame surfaces of the burning vehicle transfer heat to the acceptor through the thermal radiation. The thermal radiation received by the receptor is expressed as:  
\[q=\tau_{air}FE \tag{3}\]  
where \(q\) is the incident thermal radiation flux at a certain point (\(\mathrm{kW/m^{2}}\)), \(\tau_{air}\) represents the air transmissivity and \(F\) is the view factor, which represents the proportion of the energy radiated from the flame surface to the target surface.