Can heavy rainfall affect the burning and smoke spreading characteristics of fire in tunnels?

Extreme rainfall events are increasingly common under the current trend of global warming. This work investigates how a heavy rainfall on one exit affects the fire burning and the smoke spread in tunnels. Several reduced-scale tests are designed with various rainfall intensities (up to 60 mm/h, equivalent to 232 mm/h in nature), raindrop sizes (1.0-1.5 mm, equivalent to 4-6 mm in nature), and tunnel fire heat release rates (2.1-6.7 kW, equivalent to 2-6 MW in real scale). Experiments show that heavy rainfall on one exit can induce a longitudinal airflow inside the tunnel, and the induced airflow is caused by the increased pressure at the rainfall exit. The airflow pushes the flame tilting towards the no-rainfall portal, and the correlation models of the flame length and flame inclination are characterized by considering the induced airflow and rainfall. The rainfall-induced airflow has a limited effect on the burning rate of pool fires, but it can change the ceiling temperature and limit the smoke back-layering toward the rainfall portal. In contrast, the ceiling temperature distribution towards the no-rainfall portal is found not sensitive to rainfall, which can be well described by an empirical model. (c) 2023 Published by Elsevier Ltd.

Automated summary

Extreme rainfall events due to global warming have been investigated for their impact on tunnel fires and smoke spread. Reduced-scale experiments with varying rainfall intensities, raindrop sizes, and fire heat release rates were conducted. It was found that heavy rainfall induced a longitudinal airflow inside the tunnel, causing the flame to tilt towards the no-rainfall portal. This induced airflow had a limited effect on the burning rate of pool fires, but it affected the ceiling temperature and prevented smoke back-layering towards the rainfall portal. The distribution of ceiling temperature towards the no-rainfall portal was not sensitive to rainfall and could be described by an empirical model.