Effect of Fire-Source Location on Flame Behavior and Temperature Distribution in Subway Carriages with Multiple Lateral Openings

Urban rail transit has been widely adopted to alleviate surface traffic congestion. However, subway fire safety remains a critical concern because of the confined carriage space, high occupant density, and complex ventilation conditions. Most previous studies have focused on fires located at a single or central position, whereas actual fire events may originate from various locations within a carriage. In this study, reduced-scale experiments and full-scale simulations were conducted to investigate the effects of fire-source location and heat release rate (HRR) on flame behavior and temperature distribution in subway carriages. The results demonstrate that flame inclination and plume structures are strongly governed by the fire-source location due to asymmetric air entrainment induced by side door openings and wall boundaries. Quantitatively, for end carriage scenarios (A1–A4), only 25% of fire locations (A1) exhibit a symmetric flame structure. For middle carriage scenarios (B1–B6), only 16.7% of fire locations (B5) display a symmetric flame structure. In end carriages, door-facing flames tend to deflect toward the end wall, resulting in localized heat accumulation. Fires near the end wall produce higher maximum temperatures than those near the side wall, indicating that stronger confinement enhances local heat accumulation and increases the peak ceiling temperature. As HRR increases, the temperature difference between the two regions gradually decreases. Based on the experimental and simulation results, predictive models for the maximum ceiling temperature rise were developed. Moreover, fire-source location has little effect on longitudinal temperature attenuation but significantly affects transverse and near-source vertical temperature distributions. These findings provide guidance for temperature prediction, fire detection, and fire protection design in subway carriages.