The explosion and fire events on offshore platforms are major accidents. They makes most serious damage to human, structure, and environment. Definition of explosion and fire loads is key task to perform the structural analysis to predict the damage. The Korea Ship and Research Institute (KOSORI) at Pusan National University is preparing the large scale explosion test facility for definition of explosion loads. This study is first step for the design of the explosion test facility at KOSORI. The aim of this study is to investigate the explosion loads associated with the effects of congestion and confinement by using FLACS computational fluid dynamics (CFD) program.