Fire and Materials最新文献

Compartments with ceiling vents find application in commercial buildings, ship cabins and nuclear facilities. Fire development in such compartments is characterised by the accumulation of hot gases at the ceiling level. Flow through the vent is complex in nature, wherein the effects of both buoyancy and pressure-driven flow become important. In the present work, a set of dimensionless groups is developed by the systematic application of the Buckingham Pi theorem for analysing quasi-steady-state fire in a ceiling-vented compartment. The dimensionless groups are then used to develop a procedure for estimating heat release rate (HRR) and heat losses through the compartment boundaries and vent. A sample calculation is presented to show the application of the dimensionless groups. It is shown that heat losses through the compartment boundaries can be estimated without explicit knowledge of the convection and radiation heat transfer coefficients. The overall heat transfer coefficient for heat flow through the solid boundaries of the compartment is obtained as part of the calculation procedure. The estimated HRRs are compared with CFD predictions for heptane and ethanol pool fires in compartments of volume 0.75 and 17 m³ having ceiling vents of different sizes. The results are found to agree within ±20%.

In recent years, wildfires have escalated into a global crisis, with the United States witnessing a particularly alarming increase in both frequency and severity. Wildfires generate substantial amounts of smoke containing a wide range of toxic and carcinogenic substances, posing significant exposure risks to firefighters during suppression operations. While previous studies have explored individual aspects of smoke toxicity, firefighter exposure and the performance of wildland firefighters' personal protective clothing (PPC), comprehensive reviews integrating toxicological insights with PPC material-specific factors are notably lacking. This review critically examines the exposure risks of wildland firefighters to smoke particles and their toxic components, including polycyclic aromatic hydrocarbons (PAHs), which are generated from the incomplete combustion of biomass during wildfires. A significant public health concern arises from the elevated cancer risk among wildland firefighters, attributed to their recurrent exposure to these hazardous substances during fire suppression activities. An analysis of potential carcinogenic exposure pathways reveals that dermal absorption plays a predominant role, with PAHs and other substances accumulating on and penetrating protective gear. Furthermore, the factors affecting the efficacy of firefighter protective clothing in mitigating carcinogenic exposure are evaluated. The filtration efficiency of toxic particles correlates with the pore size of the fabric, while the accumulation of these particles is affected by the surface texture. The findings of this study underscore the critical need to optimize the properties of the materials and to develop advanced fabrics with self-cleaning or decontaminating surfaces to reduce exposure to hazardous substances during wildfire response efforts.

Concrete structures are inevitably exposed to fire, and the resulting waste is typically recycled in the same manner as ordinary concrete debris. Therefore, evaluating the performance of post-fire concrete waste and its derived materials is essential for promoting the broader use of recycled aggregates. In this study, intact concrete specimens were heated to 600°C, 800°C, and 1000°C to simulate the fire damage. The fire-exposed concrete was crushed into fine aggregates and incorporated into cement mortar to evaluate their effects on drying shrinkage and mechanical strength. The results indicated that the drying shrinkage of the mortar increased to different extents, depending on the replacement ratio and heating temperature of the recycled fine aggregates. Meanwhile, the loss of mechanical strength increased with higher replacement ratios and heating temperatures. Overall, this study provided evaluations of post-fire concrete waste for engineering applications, contributing to sustainable construction material management.

To promote the application of fly ash (FA) in UHPC at elevated temperatures and achieve green development in the construction industry. In this study, the effects of curing regimes and FA on the evolution of compressive properties, hydrates, and microstructure of ultra-high performance cementitious materials (UHPCM) at elevated temperatures were systematically investigated by macroscopic mechanical performance testing and microscopic analysis. The results indicated that the combination of steam curing and dry-hot air curing could accelerate the secondary hydration to significantly enhance the compressive strength of UHPCM. As the FA content increased from 0% to 15%, the residual compressive strength at elevated temperatures was improved, the specimen cracks reduced in size, and the mass loss rate decreased after elevated temperatures. The mechanism of FA improving the fire resistance of UHPCM is that the secondary hydration reaction of FA was intensified by thermal curing, especially the suitable dry-hot air curing, to generate more stable calcium silicate hydrates, which filled the internal defects. This process had been well verified by analyzing the samples through X-ray diffractometer (XRD) and scanning electron microscope (SEM). Furthermore, as the exposure temperature increased, the residual strength of UHPCM initially increased and then decreased, reaching a maximum of 217.4 MPa at 400°C. Finally, based on the analysis of the test results, a compressive strength model of UHPCM at elevated temperatures was established considering the influence of FA content.

Earthen construction materials offer environmental benefits and strong thermal, hygric, and mechanical properties, but their fire behavior is not well understood, limiting their use. This study examines how external load and water content affect, simultaneously, the fire behavior of compressed earth bricks. Three types of bricks were tested: unstabilized bricks compacted at 5 and 50 MPa, and cement-stabilized bricks with 3.5% cement compacted to Proctor level (the compaction necessary to achieve the material's maximum dry density at its optimum water content). These bricks were equalized at 0%, 75%, and 100% relative humidity, then exposed to the time–temperature curve defined in ISO 834-1 while subjected to loads from 0 to 2.5 MPa. Results showed that at 0% and 100% RH, all materials were thermally stable regardless of load. At 75% RH, SW50 and SWC3.5 became thermally unstable with increased load, at different intensities, while SW5 remained stable. Increased loading affected crack opening/closure, internal pore pressure, and vapor permeation in SW50 and SWC3.5. In contrast, SW5's stability was unaffected by load or crack behavior. Further load-bearing capacity tests conducted on the thermal stable samples confirmed prior hypotheses about the interrelated thermo-hydro-mechanical coupling in the behavior of earthen materials at high temperatures.

The primary purpose of student residential colleges is to serve as a secure and well-equipped place to reside while adhering to established safety standards and regulations. Fire safety ought to incorporate a comprehensive and harmonized array of measures, encompassing continuous fire safety education and awareness initiatives. This study aims to investigate the correlation between individuals' educational background and their perception of fire safety, encompassing their awareness and understanding of fire safety measures. The study focuses specifically on the residents of a college dormitory. The present study employed a quantitative methodology. Data collection is conducted using a closed-ended questionnaire. The quantitative methodology comprises four primary components: Section A pertains to demographic information, Section B focuses on educational background, Section C assesses the level of fire safety awareness, and Section D assesses the level of fire safety knowledge. The results of the hypothesis testing indicate a statistically significant inverse relationship between individuals' perception of fire safety and their participation in fire safety educational activities. The aggregate score regarding the perception of fire safety is relatively high. This study holds significance for professionals engaged in the field of fire safety engineering and regulations, as it will assist them in enhancing their preparedness for conducting effective fire hazard and risk assessments.

Tunnel fire is one of the major challenges that cannot be ignored in the safe operation of tunnels. Considering the structural characteristics of tunnel fires, it is feasible to use longitudinal ventilation coupled with multi-point centralized smoke exhaust in subway tunnel engineering. Combining common slope tunnels, it is of great significance to investigate the ceiling temperature characteristics of such tunnels. Experimental testing was conducted. The results indicate that there is a strong linear relationship between the ceiling maximum temperature and the tunnel slope. A prediction formula for the ceiling maximum temperature of a sloping subway ventilation tunnel with a multi-point centralized smoke exhaust mode has been proposed. Based on the double exponential addition temperature decay model, the decay trend upstream and downstream of the exhaust vent was discussed. The constant coefficient remains basically unchanged; the decay index coefficient is linearly related to the tunnel slope, and the reduction coefficient is linearly related to the smoke exhaust volume. A tunnel ceiling temperature decay model with a multi-point centralized smoke exhaust mode affected by tunnel slope was proposed.

Highway tunnel fires caused by traffic accidents can lead to multiple simultaneous fires, which are more destructive and difficult to control compared to single fires. This study conducts a series of experimental tests to examine the smoke backlayering length, maximum gas temperature rise beneath the tunnel ceiling, and other critical parameters of dual source fires. The experiments were carried out in a 1:10 reduced-scale model tunnel with longitudinal ventilation, varying burner separation distances and burner dimensions. The results indicate that the smoke backlayering length in dual source fires is influenced by the longitudinal ventilation speed, heat release rate, and burner separation distances, while the maximum temperature rise beneath the ceiling decreases with increasing burner separation distances. A function incorporating burner separation distance and burner dimensions was proposed to predict the smoke backlayering length, based on the prediction model for a single fire source and the experimental data for dual fire sources. Additionally, based on the single fire source theory, a prediction model for the maximum temperature rise beneath the ceiling with dual fire sources was established. These findings provide a theoretical basis for risk prevention in tunnel fires involving multiple fire sources.