A series of numerical experiments have been carried out through a CFD code, namely Fire Dynamics Simulator (FDS), to analyze the influence of the fire heat source location (transversal, longitudinal and vertical positions) on the hot gas layer temperature (HGLT) in pre-flashover compartment fires. Knowing the HGLT helps engineers to predict the onset of flashover and to design fire safety systems, which give more time for evacuation procedures. Using these numerical data, and based on an energy balance on the upper layer, new semi-empirical correlations were developed to predict the HGLT in pre-flashover compartment fires, as a function of the fire source location, heat release rate, ventilation factor, surface area, effective heat transfer coefficient and ambient thermal properties. As an external validation of the newly developed correlations, their outcomes were tested against several sets of experimental data available in the literature, showing a good agreement. So, it is concluded that these improved correlations are capable to predict the HGLT for different pre-flashover fire scenarios, accounting to the position where the fire started.
There is a persistent risk of large-scale fire conflagrations in informal settlements, which can threaten hundreds of people simultaneously. Although the literature implies that wind conditions have a significant impact on these fires, little is known about how wind conditions affect the dynamics and spread of flames in informal settlements. In order to comprehend the impact of wind conditions (speed and direction) on the time to flashover and fire severity in informal settlement dwellings with different wall thermal characteristics, a numerical study was conducted utilizing the Fire Dynamics Simulator (FDS), a Computational Fluid Dynamics (CFD) code. For six different wind speeds (1 m/s, 5 m/s, 10 m/s, 15 m/s, 20 m/s and 25 m/s) and two wind directions (side and back wind). Simulations were conducted with full-scale informal settlement dwellings burning wood cribs, analyzing the fuel mass loss rate, hot gas temperature, global equivalence ratio, radiative heat flux outside the door, and time to flashover. In addition, the influence of wall thermal properties was examined for thermally-thin steel-clad and asbestos cement-clad dwellings (thermally-thick). Regardless of wind direction, it was noticed that an increase in wind speed significantly shortened the time required to attain flashover. This was shown to be the result of the wind accelerating the burning rate of the wood cribs and, as a result, the faster temperature rise of the hot gas. Radiative heat fluxes observed outside the door increased with the wind speeds. The direction of the wind had a small effect on the investigated fire characteristics, with the side wind scenarios exhibiting somewhat longer timeframes to flashover. Thermally-thin walled informal settlement dwellings exhibited a greater fire severity, with higher fuel mass loss rates, hot gas layer temperatures, and higher external radiant heat fluxes, as well as shorter timeframes to flashover. These findings indicate that both wind speed and thermal wall characteristics have a substantial impact on the severity of fires in informal settlements and can enhance the risk of fire spread.
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