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BACKGROUND AND OBJECTIVEWhen a fire occurs in a building, there becomes a risk of fire spreading to upper floors through openings such as windows and doors. A fire plume ejected from an opening is an important factor to consider in order to prevent damage from a spreading fire. It is possible that the behavior of the fire plume and/or flame ejected from an opening varies depending on the spatial structure of the building. As the modern spatial structure of a building becomes taller, more overcrowded and more complicated, the dangers associated with a fire become greater. According to the assorted data per building structure with respect to the path of the fire spreading to other rooms, in most fire resistive buildings 40% of the paths involve "spreading through an opening". The "fire spreading path to other rooms" can be identified as the most vulnerable area that causes human injury and property damage.In general, the flame behavior can be determined by the shape of the compartment and the openings, and the total heat release rate of the flammable materials in the compartment. It is presumable that the fire plume is ejected from an opening as a result of the reaction of the unconsumed flammable gas inside the compartment with the oxygen outside the compartment. Therefore, in order to understand the behavior of the fire plume ejected from an opening, it is necessary to determine the heat release rate (threshold limit) of the fire source when the flame was ejected. It is very important for fire safety design to determine the ejected threshold conditions of the heat release rate in order to understand the risks of the fire spreading and to minimize damage.In the past research [1-5], the ejected threshold condition of the heat release rate is considered to be dependent on the size of the compartment and/or the opening factor. However, even with Yokoi's experiment [6] conducted in the past, the influence of external factors such as the adjacent wall of the opening (e.g. wing wall and opposed wall) has not been taken into account.Therefore, from the perspective of fire spreading prevention, by focusing on the wall in the vicinity of the opening, which is a common condition in areas where buildings are overcrowded, an experiment was conducted to determine the ejected threshold condition of the heat release rate when the opposed wall and wing wall were installed in the vicinity of an opening. Additionally, this experiment used a small-sized compartment model to quantitatively understand how the position of the walls and opening factor would affect the ejected threshold condition of the heat release rate.

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