Fire and Materials最新文献

Bushfires pose a significant threat to numerous countries, often causing vast property damages and loss of lives. Efforts to combat and manage these fires heavily rely on predicting the fires' rate of spread and intensity. A significant component of these predictions involves understanding the thermophysical characteristics of vegetative fuels. The accuracy of predictive models (especially physical models) also depends on obtaining precise thermophysical and combustion parameters. This research aims to provide a comprehensive set of thermal degradation and combustion parameters for surface and near-surface fuel samples collected during prescribed fire experiment conducted in April 2022 in Little Desert National Park, Victoria, Australia. Firstly, fuel properties like fuel height, moisture content, bulk density, fuel load and heat of combustion were meticulously characterized for both surface and near-surface samples. Then activation energies for degradation reactions were determined using the Flynn–Wall–Ozawa method and for the determination of pre-exponential factors, in most cases these reactions closely aligned with a Second order model. This was followed by determination of other parameters such as heat of reaction, specific heat and conductivity. It was found that the density, activation energy and heat of combustion did not vary significantly across the six samples under question. The comprehensive set of obtained parameters will likely help to facilitate better predictions in fire propagation modelling.

The properties and structure of flexible PVC by incorporating zinc borate (ZB)-modified diantimony trioxide (Sb₂O₃) were investigated. The results of flame retardancy and smoke suppression testing indicate that there was an obvious maximum Limited oxygen index (LOI) value of PVC/20 wt.% ZB–Sb₂O₃ composites reached 37.5% and passed the UL 94 V-0 rating. An obvious synergistic effect between ZB and Sb₂O₃ was observed by LOI, SDR, and TG. Moreover, remarkable decreases in the smoke density were observed when ZB–Sb₂O₃ was incorporated into PVC. In addition, the tensile strength and elongation at break of PVC/ZB–Sb₂O₃ composites was higher than PVC/Sb₂O₃ composites, and this ameliorative effect was mainly arising from the ZB–Sb₂O₃ nanoparticles, which reduced the degree of fatal defects on PVC. The addition of ZB and Sb₂O₃ greatly increased the amount of residual char and apparently improved the mechanical properties of PVC composites. According to scanning electron microscopy photographs of residual char, after thermal decomposition, there were many fragments linked to the condensed phase and the compact char layer. Fourier transform infrared spectroscopy shows the residues char was composed of benzene ring, the flame retardants occurred and the condensed phase with significant interactions.

The available theories of evacuation movements are primarily founded on data gathered from adults, making them potentially unsuitable for children, especially in schools. Consequently, it is necessary to undertake further research to collect data on how children move during evacuations to understand their unique characteristics and disparities compared to adults. In this context, this paper aimed to explore the movement of school children and adolescents as they moved over stairs and through exit doorways during evacuations. The evacuation drill involved 295 school children and adolescents, whose behavior was closely monitored using a series of cameras. During the drill, their movement patterns, including flow and speed, were analyzed over stairs and through doorways. The observations revealed that children exhibited frequent interactions and contact with one another, unlike adults, who tend to maintain personal space. The findings of this study indicated that the average traveling speed over stairs was comparable to previous research, although female adolescents had a lower average speed compared to other groups. The speed and flow of participants passing through doorways were found to vary depending on their age and differed from estimates based on adult data. This study highlights that existing evacuation models fall short of adequately accounting for the dynamics of children, indicating the need for further research to improve the generalizability of evacuation models.

To investigate the improvement induced by horizontal smoke baffles during lateral smoke exhaust, an immersed road tunnel with various horizontal smoke baffles positioned below the lateral exhaust vent was studied numerically. Together with the velocity field characteristics, the temperature distribution was investigated near the lateral smoke exhaust vent, followed by the analysis of lateral smoke exhaust efficiency under different horizontal smoke baffles. Results showed that after installing the horizontal smoke baffle, there was a significant decrease in the extracted cold air, while the high-temperature smoke in the exhaust vent increases, indicating the plug-holing is effectively suppressed. It is known that the efficiency of smoke exhaust increases when the length exceedance ratio of the horizontal smoke baffle is smaller than 100%, while it changes slightly when the baffle length continues to increase. When the width ratio of horizontal baffle is smaller than 40%, the efficiency of smoke exhaust increases with the baffle width and then changes slightly with a wider smoke baffle. With a larger aspect ratio, the wider and shorter lateral exhaust vent is beneficial for improving the lateral smoke exhaust. Under the current conditions, the case shows the optimal smoke exhaust performance with a horizontal baffle length exceedance ratio of 100%, a baffle width ratio of 40%, and exhaust vent aspect ratio of 3:1. Finally, an empirical model is developed to describe the improvement of smoke exhaust efficiency caused by horizontal smoke baffle. These outcomes are helpful to the design of lateral smoke extraction system in road tunnels.

In this work, different kinds of silane coupling agents modified expanded graphite (MEG) fillers were successfully prepared and then incorporated into silicon rubber matrix to fabricate flame-retardant composite materials (SR/MEG). The inserted MEG fillers with siloxane chains exhibited good compatibility with the silicon rubber matrix, which cannot only reduce the negative impact of adding fillers on mechanical properties but also endow the silicon rubber composites with ideal flame retardancy. Subsequently, platinum (Pt) catalyst was incorporated into the SR/MEG composites to prepare SR/MEG/Pt composites, and the synergistic effects of MEG and Pt catalyst on the thermal stability, flame retardancy, and combustion behavior of silicon rubber composites were systematically investigated. The target SR/MEG/Pt composite with appropriate addition of MEG and Pt catalyst can obtain relatively high char residue of 41.9% and limiting oxygen index value of 29.6%, as well as achieve V-0 rating in the vertical combustion test, owing to the formation of expanded and dense silicon–carbon protective layer under the catalysis of Pt catalyst. Moreover, the cone calorimeter test results showed that the peak of heat release rate and total heat release of SR/MEG composites were further reduced after the addition of an appropriate amount of Pt catalyst, manifesting the good synergistic effect of MEG and Pt catalyst on the flame retardancy performance of silicon rubber. The method proposed herein may provide a promising way for fabricating high-performance flame-retardant silicone rubber materials.

The management of end-of-life tyres faces challenges due to insufficient recycling infrastructure and technologies, as well as limited markets for the materials recovered from them. To mitigate this, waste rubber can be upcycled and used as filler material for polymer matrix composites. Before rubber-reinforced composites can be certified for fire-prone applications, their thermal and flammability properties must be understood. This research investigates the effect of rubber fillers on the thermal stability, flammability and flame spread characteristics of epoxy matrix syntactic foam. Thermogravimetric analysis, Fourier Transform Infrared spectrometry (FTIR), scanning electron microscopy and attenuated total reflection FTIR spectrometry were employed to elucidate changes in thermal degradation behaviours. The influence of rubber fillers on the flammability of syntactic foam was assessed using the cone calorimeter. The fire reaction properties of rubber-reinforced foam were affected by the intensity of the incident heat flux. Regardless of the incident heat flux, an increase in rubber content led to higher total heat release. At the lower heat flux of 35 kW/m², the fire growth rate increased with rubber content, but at the higher heat flux of 50 kW/m², the fire growth rate decreased as the rubber content increased. Importantly, all rubber-reinforced syntactic foams achieved a UL94 HB ranking and exhibited reduced flame spread rates compared to the unmodified foam. This study demonstrated the potential for upcycling waste rubber into sustainable engineering products and expanded the knowledge base on fire reaction properties and flame spread characteristics of such hybrid composite materials.

Previous studies have mainly focused on the situation that the tunnel's continuous flame region was lower than the ceiling height. For tunnels with longitudinal ventilation, the temperature characteristics of strong fire plumes are still unclear. In this paper, the maximum temperature rise beneath the ceiling for strong fire plume conditions in a small-scale tunnel is studied using fire dynamics simulator. Results show that when the effective height (the distance from the burner surface to the ceiling of the tunnel) is 0.65 m, the maximum temperature rise beneath the ceiling in this work shows a good correlation with Li's model and Kurioka's model. However, as the effective height decreases to 0.55 and 0.50 m, the maximum temperature rise would be significantly lower than the previous model. Therefore, a dimensionless coefficient is introduced to modify the maximum temperature rise model for a strong fire plume, which involves the effective height coefficient, heat release rate, and longitudinal ventilation. A calculation model for the maximum temperature rise beneath the tunnel ceiling in the condition of strong fire plumes is established. The temperature attenuation data along the tunnel are given by statistics. The relationship between the dimensionless temperature rise and the dimensionless position parameter is established, and a unified model under various heat release rates is obtained.

The pyrolysis by-products of five common wood-based construction materials (low-density wood fiberboard, oriented strand board, pine, particle board, and plywood) were studied using pyrolysis-gas chromatography/mass spectrometry. Samples of wood-based materials were pyrolyzed under helium from 300 to 800°C to further understand the production of compounds that may become airborne and available for respiratory and dermal exposure. Benzene, toluene, ethylbenzene, p-xylene, styrene, and naphthalene were specifically targeted since these compounds are common by-products of pyrolysis. These compounds have been measured in previous live fire scenarios and are associated with human health concerns. The generated pyrolysates were separated and identified with a gas chromatography/mass spectrometry instrument. The results from total ion chromatograms and selected ion monitoring chromatograms were analyzed to compare the abundance of chemicals of interest generated during pyrolysis. Oriented strand board and plywood generated the greatest total concentration of the targeted volatile organic compounds. Plywood and particle boards generated the largest variety in results. Samples from solid pine boards generated the smallest number of volatile compounds, followed by low-density wood fiberboard that is manufactured with wood fibers, starch, and wax. Notably, pyrolysis by-products are not the sole compounds generated during the combustion of biomass and these products evolve when they are exposed to the conditions of combustion. Our future work plans to study the combustion by-products of these materials.