Alvarez, C., Moreno, G., Valenzuela, F., Rivera, J. I., Ebensperger, F., Reszka, P., et al. (2023). Use of an electric heater as an idealized firebrand to determine ignition delay time of Eucalyptus globulus leaves. Fire Saf. J., 141, 103923.
Abstract: The Idealized-Firebrand Ignition Test (I-FIT) protocol was used to evaluate the piloted ignition delay times of fuel beds composed of leaves of Eucalyptus globulus (Labill.). The amount of fuel layer used for evaluation ranged between the fraction volume (������) of 0.03 to 0.07 which are values expected to be found in forest bed fuels. A theoretical model was developed to describe the heating and ignition of the fuel beds, based on the thermal ignition theory. The model, which was originally developed for pine needle beds, considers the penetration of radiation to the porous matrix. The model is able to accurately predict the ignition delay time for different values of ������, but shows a poorer accuracy for the temperature evolution. This is explained by the large variability observed for the Eucalyptus leaves.
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Correa, N., Cuevas, J., Fuentes, A., Torero, J. L., & Reszka, P. (2024). Understanding the effect of char oxidation on wood temperature profiles for varying heating and oxygen conditions. Fire Saf. J., 142, 104049.
Abstract: The use of mass timber framing as a sustainable material, particularly in high-rise buildings, requires detailed structural fire performance calculations. Thermal models describing only the solid phase are cost-effective alternatives to provide information to structural behavior models. Their accuracy depends on an adequate description of drying, pyrolysis, charring and eventually flaming phenomena. While in recent years there have been considerable contributions to the development of such models, there are still open questions. This work proposes a thermal model which incorporates char oxidation, describing both the kinetic-and diffusion controlled regimes. The model was used to replicate two sets of experimental results which used standard fire calorimeters to study the ignition of thick wood specimens within a range of incident heat fluxes and oxygen concentrations, respectively. The model yields adequate temperature predictions in the early heating stages, but fails to replicate the behavior at later stages, when the effect of the surface combustion is noticeable. In terms of mass loss rates, a poorer performance is observed. To change from one oxidation regime to another, a Damkohler number is proposed, based on char oxidation reaction rates. It is found that for compartment fire conditions, char oxidation will mostly occur develop under diffusion-controlled conditions.
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Manzello, S. L., Blanchi, R., Gollner, M. J., Gorham, D., McAllister, S., Pastor, E., et al. (2018). Summary of workshop large outdoor fires and the built environment. Fire Saf. J., 100, 76–92.
Abstract: Large outdoor fires present a risk to the built environment. Wildfires that spread into communities, referred to as Wildland-Urban Interface (WUI) fires, have destroyed communities throughout the world, and are an emerging problem in fire safety science. Other examples are large urban fires including those that have occurred after earthquakes. Research into large outdoor fires, and how to potentially mitigate the loss of structures in such fires, lags other areas of fire safety science research. At the same time, common characteristics between fire spread in WUI fires and urban fires have not been fully exploited. In this paper, an overview of the large outdoor fire risk to the built environment from each region is presented. Critical research needs for this problem in the context of fire safety science are provided. The present paper seeks to develop the foundation for an international research needs roadmap to reduce the risk of large outdoor fires to the built environment.
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Reszka, P., Cruz, J. J., Valdivia, J., Gonzalez, F., Rivera, J., Carvajal, C., et al. (2020). Ignition delay times of live and dead pinus radiata needles. Fire Saf. J., 112, 7 pp.
Abstract: There are still many open questions related to the fire behavior of live and dead wildland fuels and their senescence process. We have physically and biochemically studied live and dead pinus radiata needles, their aging process, and their fire behavior using a systematic aging procedure which allows to characterize the evolution of the fuel moisture content and the photosynthetic pigments over time, and to determine the period of time after sample collection in which specimens can be considered to be alive. Results show that pine needles stay alive for up to 12 h after collection if they remain attached to the twigs. The influence of senescence on spontaneous ignition was tested on two bench-scale devices, the I-FIT and the SCALA, under discontinuous and continuous configurations, respectively. Live pine needles showed larger critical heat fluxes than dead needles, while dead and re-hydrated samples have increased critical heat fluxes for greater moisture contents. Experimental results were interpreted with thermal models based on a two-phase description of the fuel layer. We established a correlation of the form 1/t(ig)proportional to q(inc)" for both ignition configurations, which is adequate for engineering applications and allows the estimation of effective properties for wildland fuel beds.
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Rivera, J., Hernandez, N., Consalvi, J. L., Reszka, P., Contreras, J., & Fuentes, A. (2021). Ignition of wildland fuels by idealized firebrands. Fire Saf. J., 120, 103036.
Abstract: Experiments were carried out in the Idealized-Firebrand Ignition Test (I-FIT), a bench scale apparatus specifically designed to test the ignition of forest fuel layers from a representative firebrand. A cylindrical heater was used to model the firebrand, which allowed to control the incident radiative heat flux on the specimen, from the critical heat flux up to 25 kW/m2, for five different porosities of the fuel layer. Experimental ignition delay times were interpreted based on a theoretical model of the radiative heating of the fuel layer. Radiative heat transfer within the fuel layer was modeled by using the P1 approximation. In the limit of small ignition delay times an analytical expression was derived to correlate the inverse of the ignition time to the incident heat flux. This analytical expression is used to obtain the ignition temperature and effective properties for the forest fuel layers, namely the product of the fuel volume fraction by solid fuel density and solid heat capacity. Analytical solutions were found to be consistent with experimental data and a correlation relating the inverse of the non-dimensional time-toignition to the non-dimensional heat flux is provided.
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Thomsen, M., Cruz, J. J., Escudero, F., Fernandez-Pello, C., & Fuentes, A. (2023). Sooting behavior on a spreading flame over PMMA rods under different oxygen concentrations. Fire Saf. J., 141, 103967.
Abstract: The flame spread process over the surface of a solid combustible material is highly influenced by the radiative feedback from the flame, and the conditions under which the process takes place. Soot particles generated during the burn are a big contributor to flame radiation and can play a critical role in the radiative exchange between the flame and the solid. Thus, increased knowledge of the soot production processes involved in the spread of a flame can further promote the understanding of growth and development of fires. The main purpose of this work is to study the effect of oxygen concentration on the sooting behavior of cylindrical samples of polymethyl-methacrylate (PMMA) in an opposed flow configuration. Measured data shows that during downward/opposed flame spread the mass burning rate and soot volume fractions increase with higher oxygen concentrations. The data presented is correlated using a scaling analysis that provides correlations for the maximum soot volume fraction, and the maximum integrated soot volume fraction as a function of the oxygen concentration using similar residence times to establish comparable conditions. The data shows the correlations introduced here provide useful information of the sooting behavior of spreading flames in environments of varied oxygen concentrations that could be used to guide potential fire safety applications.
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