Fire Safety Journal最新文献

Evaluation of the temperature profile induced by tunnel fire is of great significance for fire detection and structural damage assessment. In this work, a special plume model, namely, the “plume bifurcation” is introduced, and its impact on the temperature distribution is analysed theoretically. Full-scale tunnel fire experiments and numerical simulations are conducted to investigate the plume evolution under various heat release rates and ventilation conditions. Results show that the plume will sperate into two sub-streams under strong ventilation condition, resulting in the multi-dimensional plume movement pattern when rising. The sub-plume impingement point location, quantified by the longitudinal vertical deflection angle ${\theta }_v$ and horizontal bifurcation angle ${\theta }_h$, is correlated with the fire heat release rate and ventilation condition. The plume bifurcation angle is 0 when the dimensionless ventilation velocity $V^{\prime }\le 0.33$, marking a single-stream plume; and rapidly increase and then slowly decrease with $V^{\prime }$ when $V^{\prime }>0.33$, representing the sudden occurrence and decay trend of plume bifurcation with the ventilation velocity. Finally, a novel bifurcated plume-based model to estimate the maximum ceiling temperature is proposed. This study reveals the role of multi-dimensional smoke movement in reshaping the temperature field, providing new perspectives for a deeper understanding of the smoke transport behaviour in longitudinally ventilated tunnel fires.

Forest fires produce many different pollutants, including soot formation and aerosol emissions. Air pollution from wildfires leads to cardiopulmonary disease and impacts on the environment and carbon cycle. Emissions of soot and aerosols from forest fires need to be assessed. The following methods exist for estimating aerosol emissions: numerical, experimental and empirical. The purpose of the review is to summarize and analyze various numerical models for simulating forest fires to estimate aerosol emissions. This review provides information on various physical, geometric, artificial intelligence, empirical, cellular automation and graph models. These models are summarized and analyzed in terms of various parameters. The review also provides some discussions and suggestions for future research. Conclusions are drawn to highlight the advantages and disadvantages of various mathematical models.

Car fire tests were conducted on fiber reinforced polymer (FRP) reinforced columns to evaluate the fire effects on piloti structures. The study involved a mid-size car (1,998 cc) with fuel and tire air pressure removed to reduce the risk of explosion. The objectives were to measure the heat release rate (HRR) and temperature distributions during the fire and to evaluate the fire behavior of the columns in the piloti structure. Results from the car combustion test showed a total heat release of 5,210 MJ, with a maximum temperature of 455.0 °C at 2.5m height above the car ceiling and an internal temperature of 1025.7 °C near the ignition point at the car seat. In the piloti structure fire test, consisting of four reinforced concrete (RC) columns with and without FRP reinforcement and a roof slab, the maximum temperature reached 728.5 °C under the slab. Thicker FRP reinforcement resulted in lower temperatures on the column surface. Fire Dynamics Simulator (FDS) software was used to validate the test results and showed accurate predicted temperatures at 3m (within 10 % error). However, discrepancies were observed at 2.5m (24 % error) and below, although the simulated fire behavior agreed well with the test results for heights of 2.0m and above.

Densified wood (DW) is a novel structural material with promissing application potential in construction industry due to its excellent mechanical performance. However, it could also be a disastrous fuel contributing to the development of fires. This work experimentally and numerically investigated the combustion behavior of DW. The differences among wood species (fir, pine and oak) and their char oxidation impacts are emphasized. The experimental results indicate that DW has a 44.7 K lower pyrolysis peak temperature on average, a 32.2 % lower peak mass loss rate, and a 8 % higher residual mass ratio than natural wood (NW) in N₂ due to the delignification process. The hemicellulose and cellulose pyrolysis are endothermic in N₂ but exothermic in air. Wood pyrolysis has an additional char oxidation reaction in air. The higher density of DW leads to longer times for ignition and flaming combustion. DW presents a higher heat release rate and average 4.7 MJ kg⁻¹ higher effective heat of combustion of char. Two parallel pyrolysis reaction schemes based on ambiance are proposed, which well-predict the microscale characterizations but fail to represent the combustion behavior. An optimized mode was developed by adding a continuous char oxidation reaction to the N₂ reaction scheme, which best predicts the combustion behaviors.

Jet fire including process pipeline/tank leakage, oil exploitation industry of tail gas treatment flare or other industrial combustors as a common phenomenon can be found at high altitude areas. This work characterizes the flame trajectory evolution of horizontal jet fires under reduced pressures, which is rarely studied. The experimental results show that the horizontal flame projection distance increases monotonously, but the vertical flame length first increases and afterward decreases with the increase of heat release rate and the decrease of ambient pressure. Meanwhile, flame trajectory length increases significantly and then slowly with increasing heat release rate, but first increases to a maximum value and afterward declines with decreasing ambient pressure. Meanwhile, the turning point of vertical flame length appears earlier than that of flame trajectory length with increasing heat release rate (or jet velocity at source) and decreasing ambient pressure. Then, a mathematical model based on the flame arc hypothesis and a dimensionless model were proposed to describe the flame trajectory length, the momentum-buoyancy length scale $L_m={\left(M_0/g^{\prime }\right)}^{1/3}$ was used to normalize the flame trajectory length. The measured flame trajectory length in terms of the nozzle diameter, heat release rate, and ambient pressure was satisfactorily correlated by the proposed models.

The study investigates a coal dust explosion accident within a confined space in Shanxi. The accident was caused by coal dust coming into contact with a high-temperature heat source under the influence of the stack effect. Based on the investigation of the coal dust explosion accident, the study uses computational fluid dynamics (CFD) simulation to reconstruct the accident scenario. The simulation results provide a detailed depiction of coal dust movement within subsurface semi-enclosed confined spaces during the ventilation diffusion stage, influenced by the stack effect, and confirm the formation of a coal dust layer at the heat source due to coal dust deposition. The simulation results of the two explosion processes indicate that excessively high coal dust concentrations within confined spaces have a negative correlation with the development of explosion flames and the peak overpressure. It resulted in a secondary explosion with a relatively low concentration of coal dust, where the peak overpressure was five times that of the primary explosion. Comparative analysis between simulation results and actual investigations the accuracy of the CFD simulation in capturing the accident process and its characteristics, providing valuable insights for preventing and controlling coal dust explosion accidents.

Fire testing is and will remain of paramount importance in helping industry, regulators and all other fire safety stakeholders to achieve a safer world. For this to happen, test data must be stable and reliable, regardless of the test facility that produced the data, its various operators, the measurement equipment used, and so on. The instruments and sensors used to measure heat release, smoke production and mass loss rate are susceptible to mechanical and/or electrical disturbances and all have their own dynamic behaviour. This leads to a variation in the test results. A scatter that is only due to the measurement.

This paper examines the time and frequency domain behaviour of various measurement components and hardware & software filters in use today. It proposes an instrument-independent method of eliminating noise and other interference, describes a method of adjusting the response time of the various input signals to a common value applicable to all test institutes, and proposes a method of accurately synchronising these signals in time.

The result is unambiguous qualitative measurement data that can be confidently compared with data from other sample sets or between different laboratories and researchers. It improves the stability and reproducibility of test results leading to a more stable classification of materials.

A pressurized inhibition method is proposed based on the pre-inhibition process to study the inhibition law and mechanism of the pre-inhibition pressure on the coal spontaneous combustion, with a purpose of enhancing the inhibiting effect of chloride salt inhibitors. In this work, inhibited coal samples were prepared by immersing raw coal in high-temperature and high-pressure reactor at 1 MPa, 2 MPa, 3 MPa, 4 MPa, and 5 MPa, respectively, using MgCl₂ solution with a mass concentration of 20 %. The variation rules of the characteristic parameters, such as the indicator gas concentration, inhibition rate, surface microscopic morphology, and reactive groups, of various coal samples with the elevation of the pre-inhibition pressure were investigated using the programmed temperature-raising oxidation system, infrared spectroscopy, and SEM. It was found that the pre-inhibition pressure was in the range of 1–4 MPa, and with the increase of pre-inhibition pressure, the gas-producing concentration and the content of active groups of coal decreased, and the inhibition rate increased significantly. Increasing the pre-inhibition pressure can significantly improve the inhibition effect, and the optimum pre-inhibition pressure is 4 MPa. Continuing to increase the pre-inhibition pressure will destroy the pore structure of the coal and reduce the inhibition effect.

The objective of this study was to investigate the parameters controlling auto-ignition, degradation and auto-extinction of wood. For this purpose an extensive set of experiments was conducted varying extrinsic parameters such as external heat-flux but also the type of wood. Varying the wood species allowed to explore the role of thermal properties and wood composition. Seven wood samples were tested, some light and some heavy, both hardwood and softwood. The experimental setup was based on a double-cone calorimeter, which allowed to accurately change the imposed heat flux at a predefined moment. More than 600 tests were carried out in a vertical orientation, allowing a statistical analysis. For each test, mass loss, surface temperature and in-depth temperature of the samples were measured using a precision scale, an infrared camera and thin wire thermocouples embedded using a special machining, respectively. The auto-ignition study showed that the time to auto-ignition increases linearly with density. Despite a wide range of these times to ignition, the surface temperatures at ignition were in the same order of magnitude for all species considered: between 450 and 700 °C for auto-ignition before 2 min and between 700 and 800 °C for auto-ignition after 2 min. The onset of char oxidation was observed at low heat fluxes. It occurs at different times depending on the wood species, but at similar surface temperatures, between 380 and 400 °C. The sliding double heating cone made it possible to identify the criteria for auto-extinction: the heat flux for auto-extinction can vary from 40 to 55 kW.m⁻² depending on the wood species, and a linear correlation was found between the mass loss rate at extinction and the initial density of each sample studied. The study highlights the dominant role of density for auto-ignition and auto-extinction.

In recent wildfire prediction research, data assimilation (DA) methods like Ensemble Kalman filtering have gained traction for integrating observation data to enhance prediction accuracy. Most previous studies trusted that the observation data were accurate, and set a small observation error, which causes unreliable predicted results for scenarios with large observation error. To tackle this, our study introduced a method that iteratively adjusted the potential range of observation errors by comparing observation and simulation data over time. We conducted a 30-m experiment and kilometer-scale numerical simulations. Unlike prior research, we adopted larger error ranges (the similarity index with true data ranges from 0.6 to 1) for both real and synthetic observation data. In the experiment, to increase the complexity of fire spread, a heterogeneous fuel arrangement was employed. Irregular flame fronts appeared due to incomplete combustion and were difficult to replicate in simulations. Better accuracy was achieved using real observation data to revise predictions. Furthermore, to improve the applicability of the algorithm, numerical simulations were designed to consider observation error changing over time or not. The Root Mean Square Errors for the fire front prediction using the proposed method remained lower than that of the traditional DA approach.