L.P.C. Pita

Fire spread in canyons

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.

Impacts of Fire on Society: Extreme Fire Propagation Issues

Human activities namely forest management interact with natural conditions to determine fire occurrence and fire impact in a complex form. Climate change tends to facilitate even larger and more dangerous fires. The wildland urban interface is an emerging problem derived from the expansion of urban areas associated to high risk fire conditions. Extreme fire behaviour in the form of eruptive fires, crown fires and spot fires are associated to great damage to the environment and to loss of human lives. Some cases of fatal accidents that occurred recently in Europe are presented to illustrate the proposed concepts.

Monitoring fire-fighters' smoke exposure and related health effects during Gestosa experimental fires

The main objective of this study is to contribute to the scientific knowledge regarding fire-fighters’ exposure to smoke and its related health effects. Forest fire experiments were developed with an extensive number of measurements of individual exposure to smoke pollutants and of medical parameters for a group of fire-fighters. For the smoke exposure monitoring, ten fire-fighters from four different fire brigades were selected. The fire-fighters’ individual exposure to toxic gases and particulate matter was monitored with portable devices, and their location in time was registered with GPS equipment. For all the monitored fire-fighters, air pollutant concentration values acquired during the fire experiments were beyond the limits recommended by the World Health Organization (WHO), namely for PM2.5, CO and NO2. Daily averages of PM2.5 concentration values as high as 738 µg.m -3 were obtained, well above the recommended limit of 25 µg.m -3 . In terms of CO, hourly averaged values higher than 73,000 µg.m -3 were monitored, clearly above the 30,000 µg.m -3