Expanded polystyrene (EPS), which is widely used in outer shell insulation systems due to its excellent thermal insulation, waterproofing and low density, poses significant fire risks due to its flammability, high heat output and thermoplastic droplet behaviour. In recent years, there have been numerous reports of building fires related to EPS. Therefore, this study focuses on EPS as an insulation material for outdoor applications. This thesis combines experimental analyses and numerical simulations on micro, small and medium scales, with the aim of investigating the droplet and flow behaviour of EPS during fire accidents. The thesis analyzes the fundamental thermal properties during combustion and flame spread, such as thermal degradation and thermal shrinkage at the microscale level. Small-scale experiments, conducted with the structure of exterior walls of buildings and under exposure to radiant heat fluxes, have been conducted to explore the ignition and combustion properties of molten droplets of the burning EPS material. Based on small- and medium-scale experiments, the behavior of flowing fires caused by non-continuous EPS panels was investigated. Finally, the mechanical and heat transfer models were coupled to theoretically analyze the dynamic evolution and dispersion behavior of burning currents using OpenFOAM software.