Application of computational fluid dynamics: Fire safety awareness for gas station in dense urban areas with wind effects

Consequent to a big gas station fire in Macau and another recent one affected by a nearby explosion in a fireworks factory in China, there are concerns on the fire safety issues of gas stations in urban areas. Those two incidents were not too terrible but the situation would be much worse if there was strong wind, especially in a dense urban area where buildings are closely built together. There are many gas stations built within residential areas in Hong Kong. Wind-induced air movement is a transient phenomenon which depends not only on the wind speeds measured at some designated sites, but is also strongly affected by the surrounding environment. For a gas station located adjacent to a taller building, turbulent effects due to incident wind fields would be important. This is not just a safety problem of the gas station, nor for any single building. A risk management system should be worked out by the Authority in the estate district, suburb, or even the whole city. The problem must be considered carefully for cities with dense population and numerous highrise buildings. Computational fluid dynamics (CFD) is a suitable tool for hazard assessment on the spreading of smoke and heat. In this paper, the wind-induced air flow in a gas station fire next to a building was studied by CFD. The CFD simulator selected is the Fire Dynamics Simulator (FDS) version 3.01. Acoustic filtering technique was applied to remove the flow with high Mach number and large-eddy simulations (LES) were applied to model smaller turbulent scales. Different scenarios on the gas station position, building height and distance away from a vertical wall of the building were simulated. Wind effect was simulated by taking the incident air flow as a parabolic boundary layer. The results are very useful for working out risk management in case of accidents. Note that smoke or even flame will spread by following the wind-induced air motion.