Fire and Materials最新文献

This paper has analyzed the longitudinal ventilation on the effect of the efficiency of the smoke evolution mechanism in a metro tunnel of multi-window carriage fires. These were simulated by Large Eddy Simulation (LES) with Fire Dynamics Simulator (FDS). In the past, analyses of smoke temperature under the tunnel ceiling and smoke overflow characteristics have been conducted. However, longitudinal ventilation has a different impact on temperature than natural ventilation, especially in a subway tunnel with a multi-door carriage fire. Consequently, several simulations were run in a subway tunnel (360-m long, 6.0-m wide, and 4.8-m high). The longitudinal ventilation velocity is set by 0–10 m/s with the heat release rate of 1–10 MW. The results show that there is a linear relationship between the maximum temperature and the longitudinal ventilation velocity. An empirical model considering various longitudinal ventilation velocities was developed to predict the maximum smoke temperature underneath the subway tunnel ceiling. The effects of the longitudinal ventilation velocity, the heat release rate, and the distance of the fire source on the characteristics of longitudinal temperature distribution were analyzed. What's more, smoke overflow characteristics under different longitudinal ventilation velocities have been described. The findings and results can also provide a reference for the fire risk assessment of a metro tunnel of multi-window carriage fires.

Currently, rural fire protection issues in China loom large, resulting in frequent fire incidents due to an inadequate rural fire infrastructure and insufficient firefighting resources. Consequently, prompt fire suppression becomes challenging, leading to significant casualties and economic losses. To address these challenges and align with the national rural revitalization strategy, our research team dedicated 5 years to meticulously scrutinizing fire incident data in China spanning from 2012 to 2022, alongside an extensive review of international documents. We conducted on-site investigations in rural areas across 63 cities in 11 provinces, including Anhui and Jiangsu. By analyzing fire data and field investigation results, we identified the causes and percentages of 11 types of rural fires, as well as summarized five types of rural fire hazards and six types of rural fires. Drawing from insights gleaned from the experiences of countries such as the United States, Australia, Canada, and South America, we have formulated eight policy recommendations for rural fire protection, encompassing aspects like organization, responsibility, planning, construction, operation, and maintenance, as well as public awareness. Therefore, we anticipate that this study will catalyze enhancing rural fire protection efforts in China and other developing nations.

This paper reports an experimental campaign to evaluate the residual mechanical resistance after high temperatures of two structural masonry components: block and mortar. Residual compressive strength and deformation modulus of four different hollow concrete blocks and two different mortar mixes after heating at high temperatures are investigated. The test method used was the one recommended by RILEM TC 200 for mortars and an adaptation of the same method proposed by Medeiros et al. suitable for the geometry of hollow blocks. Despite the sharp drop in the deformation modulus after heating blocks and mortar, no different behaviours are observed in the deformability of the materials caused by the variables studied. The same cannot be said in relation to the variation of the residual compressive strength of the blocks, which is affected by the variables: initial nominal compressive strength and width of the concrete block. Regarding laying mortars, the results confirmed the small influence of compressive strength on the evolution of residual mechanical strength. The data and analyses reported here on the residual mechanical properties of hollow concrete blocks produced from a concrete mixture of very dry consistency, vibro-pressed and with normal weight aggregates are relevant, since the data found in the literature generally refer to the wet cast concrete material and in cylindrical bodies.

Polyamide 11 (PA) blends based on char-forming industrial lignin and aluminum phosphinate (AlP) were prepared to improve flame retardant (FR) properties using a green and eco-friendly approach. This study investigates the thermal degradation and combustion behavior of PA blends prepared by using AlP in combination with two different types of industrial lignins (i.e., kraft lignin (DL) and lignosulphonate lignin (LL). Thermogravimetric (TG) analysis showed that ternary blends containing LL and AlP developed higher char residue up to 10.7 wt% upon decomposition in inert atmospheres. The combination of lignin and AlP increases the thermal stability by shifting the initial decomposition temperature (T_5%) and temperature at maximum decomposition (T_max) to a higher temperature range, attributed to the stabilization of decomposition products. Furthermore, combustion behavior studied by cone calorimeter (forced combustion) and pyrolysis combustion flow calorimeter (PCFC) tests presented a significant reduction in the peak of heat release rate (PHRR) and total heat release (THR). It was found that LL and AlP-containing blends more effectively decreased fire parameters like PHRR and THR than that of DL and AlP-containing blends. The best interaction with reduced fire-retardant properties was obtained when 10 wt% loading of lignin (DL/LL) and AlP was used. The reduction in heat release parameters was mainly ascribed to the condensed phase mechanism by forming an efficient protective char layer, which acts as a barrier against heat and mass transfer between the condensed and the gas phases. Raman spectroscopy analysis also confirmed the formation of the protective graphitic layer in the condensed phase.

Foam extinguishing agents are crucial for the suppression of flammable liquid fires. Their thermal stability performance and heat insulation characteristics are critical indicators to evaluate the efficiency of the fire-fighting foam. There have been some studies focused on exploring the behavior of fire-fighting foams exposed to radiant heating. However, the decay mechanisms and heat transfer behaviors of the foam at the micro-scale are still unclear and require further clarification. Therefore, in this study, the volume reduction coefficient, falling time of foam column height, and the temperature profiles of the foam layer under the thermal radiation environment of different conditions are discussed. The results indicate that the high temperature generated by the radiative heat flux will accelerate the collapse rate of the foam layer. The stability of the foam structure will be seriously damaged. There is a relationship between heat radiation intensity and foam attenuation coefficient. The empirical model for reflecting the fire-fighting foam collapse process under the fire environment with high heat radiation flux is modified. Moreover, the average collapse rate and temperature difference gradient are used to characterize the thermal stability performance and heat insulation characteristics of the foam. Analysis of the micro-scale foam structure parameters from the foam scans has revealed that the thermal stability performance and heat insulation characteristics of the foam are stronger when the surface tension of the foam is within the range of 17.4–20.4 mN/m.

Residual strength tests are commonly used to characterize the high-temperature mechanical properties of concrete materials. In these tests, the specimens are heated to a target temperature in a furnace and then cooled down to room temperature, followed by mechanical testing at room temperature. This research investigates the influence of the cooling method on the residual strength of Strain Hardening Cementitious Composites (SHCC) after exposure to 400°C and 600°C. Two types of cooling methods — furnace-cooling (within a closed furnace) and water-cooling (immersed in a water tank) — were adopted. Four different SHCC previously investigated by the authors for high-temperature residual mechanical and bond behavior with steel were studied. Two different specimen sizes were tested under uniaxial compression and flexure to characterize the residual compressive strength and modulus of rupture. The effect of the cooling method was prominent for the normalized residual modulus of rupture at 400°C, but not at 600°C. The cooling method had no effect on the normalized residual compressive strength of any material at either of the two temperatures, except one of the SHCC (PVA-SC) at 400°C. Specimen size also had no effect on the normalized residual compressive strength and modulus of rupture irrespective of the cooling method.

The objective of this study was to investigate the effect of adding flame-retardant melamine and five different dispersants on the precipitation, foaming, mechanical, and thermal properties of flexible polyurethane foam (FPUF). Precipitation experiments were conducted to analyze the effect of dispersant on the separation of flame retardant and polyol, and the foaming characteristics of polyurethane (PU) foam after adding dispersant were analyzed. The effect of adding a dispersant on mechanical strength was characterized by measuring tensile strength, tearing strength, and hardness, and scanning electron microscopy analysis was performed to analyze morphological characteristics. Thermogravimetric analysis (TGA) was performed to analyze the thermal properties of PU foam. A horizontal flame test, limiting oxygen index test, and cone calorimeter tests were conducted to examine the flame retardancy of PU foam with flame retardant melamine and dispersant added. The dispersant ANTI-TERRA-U is a solution of a salt of unsaturated polyamine amides and low-molecular acidic polyesters. And, the dispersant BYK-220S is a solution of a low molecular weight, unsaturated acidic polycarboxylic acid polyester with a polysiloxane copolymer. The dispersants ANTI-TERRA-U and BYK-220S improved the density, tensile strength, tear strength, and hardness of FPUF. TGA of the top and bottom portions of the foam showed less weight difference for samples containing dispersants, indicating better homogeneity due to improved dispersibility. Therefore, we conclude that dispersants are beneficial additives to improve the mechanical properties and dispersibility of PU foam.

This study investigated the efficacy of the full transverse exhaust method for smoke extraction in tunnel fires. It examines factors such as the number and layout of air supply and exhaust outlets, analyzing their impact on smoke spread, tunnel temperature, visibility, and airflow. The results demonstrate that the full transverse exhaust method effectively controls smoke emissions in raised highway tunnels. It limits smoke spread, reduces tunnel temperature, and effectively controls the fire-affected area. The number and layout of outlets significantly influence smoke dispersion, with fewer exhaust outlets providing better smoke control and optimizing the tunnel environment. However, insufficient outlets disrupt gas flow stability. The position of exhaust outlets affects smoke distribution, and caution is advised to prevent directing fresh air flow toward the fire. Opening an equal number of exhaust outlets on one side of the fire source yields superior smoke extraction results, reducing tunnel ceiling temperatures and minimizing risks to personnel and structures. Though stabilization may take longer, this configuration proves advantageous. The study offers valuable insights and practical guidelines for implementing the full transverse smoke control method in real-world scenarios.

Exhaust flow measurements are a significant source of uncertainty for measurements of heat release rate in large-scale fire experiments. Irregular flow distributions are often present in the exhaust ducts making it difficult to measure flow accurately. Tracer gas dilution (TGD), a measurement method for volume flow, is not sensitive to flow distribution and has been applied to calibrate flow measurement devices at the exhaust ducts of a large-scale open calorimetry system. The in-line calibration reduced the bias in the exhaust flow measurement by as much as 6% improving the overall measurement accuracy of the heat release rate. Experimental results provide evidence that the flow calibration is an improvement over the accepted practice of developing a flow correction from the comparison of oxygen consumption calorimetry with the heat output from a gas burner. The flow calibration is valid for a wide range of flow conditions and decouples the oxygen consumption calorimetry measurement from any error in determining the heat release rate from the gas burner.

Wood–plastic composites (WPCs) are facing fire hazard when they are used in construction and furniture and need to be treated with fire protection. In this work, polyurethane (PU) was applied to derive simultaneously flame-retardancy-improved and mechanically strengthened wood-polyurethane composites (WPUCs). It was constructed with ammonium polyphosphate (APP) and PU by a simple way. The results showed that a decrease in smoke production in the Cone Calorimeter Test was measured. When the mass of APP is 18% of PU, limiting oxygen index can reach 31.2%. In the combustion test, the peak of heat release rate and total smoke production for WPUCs were, respectively, decreased by 42.1% and 89.7% in the presence of the above ratio of APP and PU. In addition, the results of the functional group test show that PU contains highly reactive -NCO which is bonded to the -OH and moisture in the wood fiber, resulting in improvement of physical and mechanical properties. The mechanism for the flame retardancy of WPUCs revealed that polyphosphoric acid produced by APP pyrolysis catalyzed PU into the char, and PU was arched by the resulting gases such as NH₃ to form the tiny spherical structure, which worked in blocking heat and the exchange of substances. WPUCs with APP prepared by this method are shown to have improved results, and, therefore, it is expected to provide a new strategy for the preparation of flame-retardant WPCs.