Canyons or ridges are associated with a large number of fatal accidents produced during forest fires all over the world. A contribution to the understanding of fire behaviour in these terrain conditions is given in this paper. The basic geometrical parameters of the canyon configuration are described. An analytical model assuming elliptical growth of point ignition fires and constant values of rate of spread is proposed. A non-dimensional formulation to transfer results from analytical, numerical, laboratory or field simulations to other situations is proposed. An experimental study at laboratory scale on a special test rig is described. A wide set of canyon configurations were covered in the experimental program. In spite of the relatively small scale of the experiments they were able to put in evidence some of the main features found in fires spreading in this type of terrain. They show that in practically all cases the rate of spread of the fire front is non-constant. On the contrary, the fire has a dynamic behaviour and its properties depend not only on the canyon geometry but on the history of fire development as well. The convection induced by the fire is enhanced by terrain curvature and the fire accelerates causing the well-known blow-up that is associated with canyon fires. The rate of spread of the head fire increases continuously even in the absence of wind or any other special feature or change of boundary conditions that are sometimes invoked to justify such fire behaviour. The results of the present study confirm the predictions of a previous numerical study of the flow and fire spread in canyons that showed the important feedback effect of the fire on the atmospheric flow and how this affects fire behaviour in canyons. Results from a field experiment carried out in a canyon-shaped plot covered by tall shrubs were used to validate the laboratory scale experiments. Case studies related to fatal accidents that occurred in canyon-shaped configurations are analysed and recommendations to deal with this problem are made. It is shown that these accidents may occur even in the absence of special fuel or atmospheric conditions as they are intrinsically related to terrain configuration.
The biggest fire fighting accident in the history of Croatia happened on August 30, 2007. The routine fire fighting operation ended with 12 dead and 1 badly injured fire-fighter. That was the biggest human loss in the history of fire fighting in Croatia. In order to understand the Kornati accident a research team was formed and independent scientific investigation performed. The accident was analyzed from meteorological, vegetation, thermodynamics and aerodynamic points of view, and several simulation models of fire propagation were used. This paper describes in detail one possible explanation connected with eruptive fire behavior. Eruptive fire behavior has been reported in many fire accidents in the past causing a lot of causalities. Based on the real Kornati accident data, the eruptive fire model was conceived and appropriate results derived. The paper describes them in detail. Our aim in studying this and other accidents is not to find who is guilty or to blame anyone but rather to find what happened and to extract lessons, to avoid future accidents.
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