Model Experiment of Hazardous Forest Fire Whirl RICHARD I. EMORI and KOZO SAITO The fluid dynamical scaling laws of forest fires are derived by dimen- sional analysis and a scale model is constructed to investigate a forest fire which seriously injured several fire fighters. The result of the small-scale experiment indicate that a fire whirl could be generated in such a fire. B ECAUSE OF safety hazards, economical aspects, and the difficulties of controlling boundary conditions, a full-scale experiment is not always practical. A laboratory scale model experiment is sometimes performed in place of a full-scale experiment. In a scale model experiment, the develop- ment of the scaling laws is especially important as suggested by Williams in his review. ~ The objectives of this paper are to derive scaling laws of forest fires and design a scale model similar to a real forest fire. The forest fire being modeled herein, called the prototype, caused serious injuries to several fire fighters. The report 2 regarding the forest fire states that the injuries oc- curred at the mid-point of the valley's slope. The fire suddenly changed its spreading direction at that point and increased both its spreading velocity and its flame height. Because of this rapid change, fire fighters lost their escape routes and received serious injuries. To simulate the conditions of this accident in a scale model, the scaling laws were derived by dimensional analysis. All of,the significant parameters had to be collected. In collecting the significant parameters among many ex- isting parameters, the concept of partial modeling 3 was introduced, and our interest was focused on the fluid dynamical aspects. Some previous works 4-6 were also used to make this job easier. The designed scale model is geometrically similar to the real forest fire with the scale ratio of 1/2500. The mean air velocity and the fluctuating NOTE:Mr. Richard I. Emori is with the Mechanical Engineering Department, Seikei Uni- versity, 3-Kichijoji Kitamachi, Musashino, Tokyo, Japan. Mr. Kozo Saito is a Research Asso- ciate with the Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey. 319