Risk Assessment of Toxic Pollutant Dispersion after a Methane Pool Fire Accident in a Street Canyon ^†

A fire accident in an urban environment can result in injuries or death, as well as environmental and property damages. The ‘street canyon’, which is defined as an urban street with tall buildings on both sides, is an important geometric element covering an urban area. The interaction of wind with the street canyon can create complicated flow patterns and areas of large pollutant concentrations. This study focuses on the airflow characteristics and pollutant dispersion following a pool fire accident involving methane in an urban street canyon. Large eddy simulations (LES) are performed using the FireFoam solver with the PISO algorithm for the pressure correction equation and a simplified one-step combustion model. Flow and fire characteristics, such as, flame height, heat transfer, combustion chemistry and pollutant dispersion are computed and used to define the toxic areas inside the street canyon and subsequently identify the various risk zones, based on temperature, vertical velocity and CO₂ mass fraction fields. This study shows that a methane pool fire is transformed into a jet fire, which is influenced by the wind velocity and the heat transfer rate between the wind and the pool fire. The temperatures inside the street canyon create very dangerous and fatal conditions for pedestrians and rescue crews, whereas on the roof of the buildings the range of temperatures encountered cannot be lethal.