Title: Complexities of the Thermal Boundary Conditions when Testing Timber using the Fire Propagation Apparatus // Proceedings of the Ninth International Seminar on Fire and Explosion Hazards. Vol. 2: 21-26 April 2019, Saint Petersburg, Russia
Creators: Cuevas J. I.; Hidalgo J. P.; Torero J. L.; Maluk C.
Organization: University of Queensland; University of Maryland
Imprint: Saint Petersburg, 2019
Collection: Общая коллекция
Document type: Article, report
File type: PDF
Language: English
DOI: 10.18720/SPBPU/2/k19-88
Rights: Свободный доступ из сети Интернет (чтение, печать, копирование)

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The potential for Engineered Timber Products to self-extinguish is the focus of study of numerous researchers worldwide, but regardless of scientific efforts, a relatively high discrepancy still exists on the definition of the critical threshold for self-extinguish. This discrepancy can be attributed to the variability in the test sample material, testing conditions, and/or test methodologies executed. The work presented herein analyses the impact of the thermal boundary conditions imposed by the experimental setup, analysing the divergence of the thermal response from the idealized scenario usually proposed in theoretical frameworks. In particular, the impact of two key assumptions, a semi-infinite solid behaviour and the existence of one-dimensional heat transfer within the solid, are evaluated by means of a case study corresponding to a series of bench-mark experiments conducted in the Fire Propagation Apparatus. By means of a simple one-dimensional heat transfer model, it was found that in order to guarantee a semiinfinite solid behaviour for a thermal exposure of 50kW/m2 during one hour, a minimum sample thickness of 150 mm is needed. Furthermore, the results of this numerical model have shown that imposing an adiabatic boundary condition in the back face of the sample decreases the time during which this assumption can be sustained, whereas having an exposed or heat sink boundary condition at the back face generates the opposite effect. Following, in order to assess the validity of assuming a onedimensional heat transfer regime during the tests, the radiative heat transfer between the heating elements and the sample was simulated. The results show the presence of additional heat fluxes through the lateral faces of the sample. The effectiveness of insulating the lateral faces of the sample, to minimize this undesired effect, was analysed by means of a set of experimental tests. The results show that the effect of the lateral incident heat flux over the sample can be minimized, but not discarded. Thus, it is not valid to assume a one-dimensional heat transfer regime within the solid. It is proposed that neglecting these effects can, therefore, cause an inaccurate determination of the thermal conditions imposed during testing.

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