Fire Technology最新文献

There is a need to revisit movement dataset(s) currently used as egress determinants to assess whether they are truly representative of the current diverse occupant base. This is particularly important with our aging population as these sets contain very limited amounts of recent, age-specific data for older adults. This study provides data on walking speeds of older adults, obtained during standardized tests of walking, and compares those to default walking speeds used in current egress models. From experimental, short-distance walking trials (n = 451), it was seen that sex, increasing age, use of walking aids, those who have previously experienced a stroke (n = 116) and walking under cognitive load all resulted in decreases in walking speed. First iteration Pathfinder simulations showed that more realistic inputs for population walking speed resulted in simulated egress times that were on average 8 s slower compared to use of the current default range of walking speeds. Results suggest that the assumption of a uniform population in egress modelling, and consequently the standard practice of using a default walking speed for older adult occupants, should be reconsidered since, in reality the older adult population is extremely heterogeneous with regards to mobility, as reflected in the variability in walking speeds in this study.

As the complexity and the cost of infrastructures have risen, the need for a fast, reliable, cost-effective and clean fire extinguishing system has become important. Water mist is a clean and effective technology to deal with most types of fires. Over the years, chemicals have been added to the water to improve the performance of the mist and deal with new types of fires. This review presents an exhaustive state of the art on additives for water mist technology over the last fifty years. Eleven publishers were reviewed to form the corpus of almost one hundred articles. A systematic review of the articles highlighted that alkali metal compounds have been the main focus of research. Metal-based compounds have also proved to be effective. Surfactants remain an additive of choice in the formulation of fire-fighting foams and as additives for water mist but hydrocarbon surfactants should be preferred to fluor-based ones for environmental reasons. Solvents have proved to be a new, clean and potent class of water mist additives worthy of further investigation. Overall, the toxicology and environmental impacts of most additives have not been addressed or are often overlooked as an important criterion for a water mist additive.

Connections are the most vulnerable parts of a structure under fire conditions. A novel steel connection with high axial and rotational ductility has been proposed with the objective to improve the performance of steel-framed buildings in fire. Analytical model has been developed to determine the axial displacement of the top and bottom flanges of the beam end at high temperatures. A series of sub-frame models with this ductile connection have been built using Abaqus to study the influence of the characteristics of the connection part between the fin-plate part and face-plate part on the overall connection behaviour. The current critical failure mode of the ductile connection is bolt pull-out from the face-plate zone, and the tensile deformation capacity of the connection is not fully utilized. Therefore, measures to improve the bolt pull-out failure mode of the connection have been tested using the Abaqus sub-frame models, including adding a strengthening plate to the face-plate part of the connection and increasing the connection plate thickness. The simulation results show that the bearing failure of the beam web will become another critical failure mode of the connection, once the bolt pull-out failure is eliminated. To further optimize the high-temperature performance of the connection, the Abaqus steel frame models have also been used to test some measures to delay the occurrence of the beam web bearing failure, including adding strengthening plates to the part of the beam web in contact with the connection, and improving the material properties of the part of the beam web around the bolt holes at high temperatures.

Cone calorimeter tests were conducted to investigate the moisture transfer, burning and charring behavior of timber under fire heating. 99 × 99 × 50 mm glue laminated larch specimens were made in cross grain and straight grain directions. The initial average moisture contents were 15.1 wt. % (cross grain specimens) and 13.5 wt.% (straight grain specimens). Twenty specimens were heated at 50 kW/m² of irradiance. Heating duration was varied between 10 to 50 min. Internal temperatures, surface temperature, heat release rate, and moisture contents were measured during heating. Charred depth, colored depth and burnt-out depth was measured after cooling. Heat release rate was measured by oxygen consumption method. Temperature was measured by an IR camera and thermocouples. Moisture content was measured by the electrical resistance method. Charring and coloring temperatures were estimated by using the measured charred or colored depth data and temperature histories. Burnt-out depth, charred depth and colored depth were slightly larger in case of straight grain specimens than that in cross grain specimens. Heat release rates were almost constant after reaching the first peak values. Temperature creep was observed in each location at about 100°C, according to evaporation of water. Maximum internal temperature of each specimen at each location increased while heating duration increased. Peak value of moisture content varied by each specimen, but the temperatures corresponding with peak moisture content were almost the same, i.e., around 100°C to 120°C. Moving speed of moisture peak is about 1.30 mm/min. Charring and coloring temperature were about 380 and 260°C, respectively.

Closed ro-ro spaces on maritime vehicle carriers are usually protected by a total-flooding carbon dioxide system. Such systems have many benefits, for example that there are no residues that can adversely affect the protected objects (in this case thousands of vehicles) and the agent is electrically non-conductive. However, there could be a considerable time delay from the start of a fire until the carbon dioxide system is discharged. Experience has shown that this delay time can cause significant fire damage and jeopardize the performance of the system. Within the EU funded LASH FIRE project, design and installation guidelines for supplementary automatic water-based fire sprinkler systems were developed. An important design feature is that the system automatically activates at an early stage of a fire. This would allow more time to fight the fire manually or to safely evacuate the space and discharge the CO₂ system when the fire is controlled to one or a few vehicles instead of at a time when it has escalated in size. The work was partly based on a comprehensive literature review that identified relevant standards and information applicable to the design of automatic fire sprinkler and deluge water spray systems. Large-scale fire tests verified that the suggested system designs were able to provide control of realistic vehicle fires, including fires in passenger cars and a freight truck.

In the frame of a research project, the structural behaviour in fire of cross-laminated timber rib panels were studied based on numerical investigations. The floor system consists of cross-laminated timber plates rigidly bonded to glued-laminated timber ribs. The numerical investigations comprised uncoupled thermo-mechanical simulations of two types of finite element models, a beam system and a flexible-in-shear multi-layered part, to investigate the influence of the effective width in fire. All models were validated against the experimental results of previously tested full-scale fire resistance tests. A parametric study analysed the composite cross‐sections’ effective width in fire for a parameter range expected in practice and gave proposals depending on the thickness of the CLT layers. For the conservative case of thin CLT layers, a limit value of 60% of the effective width at normal temperature is proposed as effective width in fire.

Fires can lead to costly building damage as well as loss of lives and injuries. Installed to protect buildings from fire, or to limit the damage from such outbreaks, fire protection measures are a common feature in buildings. However, these features come at a cost. Although quite ubiquitous in buildings, the value of these features to private individuals and to society is not fully understood. To understand their value, a cost benefit analysis detailing the costs and benefits of fire protection measures is needed. Carrying out such an analysis requires methods for computing both the cost of these fire protection measures, and losses from fires (including both direct and indirect losses). This study outlines methodologies for evaluating those costs and losses. An exhaustive collection of available data necessary for estimating both costs and losses is presented. Several limitations in current methodologies and data constraints were identified, with recommendations proposed to address these shortcomings. Relevant sections of a study by the authors that refines fire protection cost estimation at national and sub-national levels are emphasized, including updated building categories, guidance on computing multipliers, and detailed cost calculation methods for installation and maintenance costs. The calculation uses regularly updated U.S. Census Bureau construction data, ensuring timely multiplier updates. The insights and suggestions presented in this study will ultimately refine the process of selecting fire protection strategies that maximize the net benefit of fire protection measures for both private stakeholders and society at large.

Exploring fire resistance of high strength steel end-plate connections is one of the key technical bases for fire resistance design and fire safety assessment of high strength steel structures. Numerical simulation and parameter analyses of high strength Q690 steel flush end-plates will contribute to a reasonable design of high strength flush end-plate connections. In this paper, a finite element model of high strength steel flush end-plate connection considering thermal creep effect was established and validated by experimental results. The thermal creep finite element model can simulate accurately heat performance, failure modes and deformations of high strength flush end-plate connections at elevated temperatures. The increase of axial compression ratio has little effect on rotation, deflection, failure time, critical temperature, and critical rotation with elevated temperatures. The increase of bending moment ratio has little effect on the development trend of rotation and deflection. Proper increase of thickness of the end-plate can improve failure time and critical rotation, and the increase range is within 7% and 36% respectively. Proper increase of diameter of bolt can improve failure time, critical temperature, and critical rotation to a certain extent, and the increase range is within 10%, 6% and 27% respectively. Proper increases of thickness of the end-plate and diameter of bolt will improve the fire resistance of flush end-plate connection.

Model-scale experimental tests and numerical simulations were conducted to investigate the characteristics of the smoke overflow at the lateral carriage doors and the smoke temperature below the tunnel ceiling of a carriage fire in a longitudinally ventilated tunnel. Results indicates that the smoke overflows from the carriage into the tunnel through the lateral doors downstream of the fire source under the impact of longitudinal ventilation. Depending on the fire location, the amount of the overflow smoke exhibited either an inverted V-shaped variation or a monotonical increase with the door position. Multiple peaks in the smoke temperature below the tunnel ceiling is attributed to the uneven distribution of the overflow smoke. A dimensional analysis revealed a quantifiable relationship between the heat flow of the overflow smoke and the peak temperatures below the tunnel ceiling. Consequently, an empirical model was developed to predict the maximum smoke temperature below the tunnel ceiling under different heat release rates and longitudinal ventilation velocities. These findings are excepted to enhance the understanding of carriage fires and provide a theoretical guidance for future ventilation and safety designs in subway systems.

This paper is aimed at studying the down-reaching flame behaviors of tank fires with large ullage heights. Experiments were first conducted using a gas burner in a transparent quartz glass cylinder to simulate the large ullage and the experimental data was used to validate the computational fluid dynamics (CFD) model. Subsequently the effects of ullage height, fuel velocity and burner diameter on the flame behaviors were examined systematically. Both experimental and numerical results showed that, for lower fuel velocities, the down-reaching flame height (h_down) is restricted by the ullage height. As the fuel velocity continues to increase exceeding a critical value, independent of the ullage height, h_down starts to decrease. For a given fuel velocity, h_down increases with an increase of the burner diameter owing to enhanced air entrainment. A detailed analysis of the flow field and oxygen concentration inside the tank at the steady burning stage was also carried out. Based on the numerical results and dimensionless analysis, a piecewise function was proposed to predict the down-reaching flame height and validated against the experimental data.