1 Study on Flame Merging Behavior in Group Fires W.G. Weng 1, 3 D. Kamikawa 1 K. Kagiya 2 Y. Fukuda 1 Y. Hasemi 1 1 School of Science and Engineering, Waseda University, Okubo 3-4-1, Shinjuku-ku, Tokyo, 169-8555, Japan 2 National Institute for Land and Infrastructure Management, Ministry of Land, Infrastructure and Transport, Kasumigaseki 2-1-3, Chiyoda, Tokyo, 100-8918, Japan 3 State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui, P.R. China, 230026 ABSTRACT In this paper, numerical and experimental study on flame merging behavior in group fires were carried out. The porous 15cm-square burner was used as a unit burner and propane was employed as a fuel. The burners with various numbers and heat release rates were placed in square configuration with various separation distances. Flame height using video images and temperature distribution with height using thermocouples were measured. The validity of numerical model of FDS (Fire Dynamics Simulator) from NIST (National Institute of Standards and Technology) was confirmed from the comparison with the experimental data. The comparison results show that FDS correctly simulate flame merging behavior in group fire. In addition, the transitional separation distance with frequent flame merging was determined by way of numerical simulation. Key words: Flame merging behavior, separation distance, group fire, FDS INTRODUCTION There are many areas inhabited densely and disorderedly by small buildings in lots of big cities all over the world. Once fires occur in these areas, it is easy to appear group fires. In the city fires emerged after the Great Hansin Earthquake (1995) in Japan, the developments of merged flames or flames affected by nearby flames in the firing zone were observed during the propagation of the city fire, and these flames propagated outward from some fire origins [1] . In fact, these flames in firing zone usually extended to nearby unburned areas through the paths and alleys between many houses, due to the thermal radiation and convection. And then flame merging behavior occurred, which is believed to make the fire more destructive, cause difficulties in fire fighting and often lead to fire whirls. Copyright © International Association for Fire Safety Science