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Coimbra, Portugal

Lopes S.,Polytechnic Institute of Viseu | Viegas D.X.,ADAI LAETA | Viegas D.X.,University of Coimbra | De Lemos L.T.,Polytechnic Institute of Viseu | Viegas M.T.,ADAI LAETA
International Journal of Wildland Fire | Year: 2014

Modelling adsorption and desorption processes and equilibrium moisture content of dead fine fuels below fibre saturation is required to provide an accurate prediction of their drying and wetting processes within the range where flammability increases rapidly with decreasing moisture content. Data from laboratory tests on sorption processes and equilibrium moisture content isotherms of dead Pinus pinaster (Ait.) needles were used to evaluate several models applicable to fine forest fuels and agricultural and food products. Laboratory and field data were used to assess model accuracy in predicting drying and wetting curves and equilibrium moisture content isotherms showing a medium to high predictive ability for almost all cases. The best fitting combinations were obtained with the application of agricultural and food products models for drying and wetting phases and fine forest fuel models for equilibrium moisture content determination. © IAWF 2014. Source


Viegas D.X.,ADAI LAETA | Viegas D.X.,University of Coimbra | Almeida M.,ADAI LAETA | Raposo J.,ADAI LAETA | And 2 more authors.
Fire Technology | Year: 2014

An experimental laboratory study on the probability of ignition and ignition time delay of new fires for 11 pairs of burning embers and fuel beds of species common in Mediterranean forests is presented. For the no wind conditions of the present tests it was found that positive ignition was achieved only for embers with flaming combustion. Fuel bed moisture content was identified as a very important parameter to assess probability of ignition and ignition time delay. In the range of the present tests it was found that ignition depended more on fuel bed properties than on ember characteristics. © 2012 Springer Science+Business Media, LLC. Source


Almeida M.,ADAI LAETA | Viegas D.X.,ADAI LAETA | Viegas D.X.,University of Coimbra | Miranda A.I.,University of Aveiro | Reva V.,ADAI LAETA
International Journal of Wildland Fire | Year: 2011

Spotting is a very important mechanism of forest fire spread. Its negative effect increases in extreme fire danger conditions. In order to predict the maximum spotting distance, the duration of the combustion reaction of potential firebrands should be evaluated. This paper reports the results of an experimental laboratory study of the combustibility of firebrand material (pine cones and scales and pieces of bark of eucalypt) of two representative species in Portugal, Pinus pinaster Ait. and Eucalyptus globulus Labill. The main purpose was to assess the role on the burning conditions of the firebrand particle orientation angle θ in relation to the airflow and of the flow velocity (U) around the particle. Tests were made varying the angle of orientation of the main axis of the particle in relation to incident flow in the range of ±90°; flow velocities were tested from 0 to 6.5ms -1. After ignition, particle mass loss owing to flaming or glowing combustion of the particle was continuously measured. Residual mass, duration of the flaming phase and the burnout times are reported for each case. Empirical models to estimate the trends of variation of some of these parameters with θ and U are proposed to illustrate their importance for the range of test conditions. © IAWF 2011. Source


Almeida M.,ADAI LAETA | Viegas D.X.,ADAI LAETA | Viegas D.X.,University of Coimbra | Miranda A.I.,University of Aveiro
International Journal of Wildland Fire | Year: 2013

To validate the use of the combustion laws of embers that can be potential sources of spot fires, namely mass loss prediction laws determined in fixed or pure static conditions to changing flow or particle orientation properties, a series of tests in which these parameters were changed during particle combustion were performed. Hollow cylindrical pieces of bark of eucalyptus trees (Eucalyptus globulus Labill.) burning from one extremity to the other in a vertical flow were tested. It was found that ember combustion in varying conditions of flow velocity or incident flow direction (dynamic or quasistatic conditions) was quite different from that observed in pure static tests for the same values of the reference parameters, indicating that the combustion laws for pure static conditions are not applicable in cases where an ember is immersed in a varying flow. It was found that mass loss coefficients depend not only on the flow velocity and flow particle incidence, but also on the sign and magnitude of variation of these parameters. Mass loss coefficients obtained in pure static conditions were usually a lower limit of the corresponding parameter for dynamic and quasistatic conditions. It was concluded that significant errors can be committed when using common experimental static-condition parameters to predict maximum spotting distance in real situations in which the flow conditions vary continuously. © IAWF 2013. Source


Viegas D.X.,ADAI LAETA | Viegas D.X.,University of Coimbra | Soares J.,University of Coimbra | Almeida M.,ADAI LAETA
International Journal of Wildland Fire | Year: 2013

The problem of predicting the rate of spread of a linear fire front in a fuel bed composed of one live and one dead fuel component in no-slope and no-wind conditions is addressed. Two linear models based on the mass fraction of each fuel component are proposed to predict the rate of spread of a fire front as a function of the mass fraction of the dead or dry fuel component. Experimental results obtained with two different mixtures show that for each fuel mixture there is a threshold value of mass concentration of the dead fuel below which the fire front does not spread. The rate of spread results compare favourably with the proposed models. A composite fuel moisture content of the fuel bed is shown to be a good descriptor of the rate of spread of the mixture. An exponential model using composite fuel moisture content of the fuel bed is proposed to estimate the rate of spread of the mixture and a comparison is made with the concept of fuel curing that is used to characterise live fuels. © IAWF 2013. Source

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