Fire Technology最新文献

The interaction of multiple fires is a common phenomenon of combustion in forest fires. However, few available literatures examined the dual line fires on a slope. This paper constructs an experimental setup to first study the flame merging probability and flame geometry of dual parallel line fires under different slope angles (θ), heat release rates ((dot {Q})), and spacings (S). The flame merging probability (P_m) was found to first increase and then decrease with the increase in slope angle, which could result from the effect of upslope-induced wind. A dimensionless parameter coupling the θ, S and (dot {Q}) was proposed to successfully fit the P_m. Experimental observations and analyses reveal that when P_m is large, the flame tilt angle depends on the spacing and heat release rate. Conversely, when P_m is little, the flame tilt angle is dependent on the slope angle. Accordingly, correlations of flame tilt angle were developed for P_m ≥ 0.5 and P_m < 0.5, respectively. In addition, an effective perimeter (P) coupling the burner spacing and size was proposed as the characteristic scale in the dimensionless parameter of (dot {Q}_{P}^{{*2/3}}{(cos theta )^{3/2}}), by which the correlation of flame height was developed for the dual parallel line fires on a slope.

In a practical tunnel adopting the semi-transverse system, the actual pressure and flow rate are the essential parameters to assess the performance of the semi-transverse system. Nonetheless, the influence of air leakage and thermal effect on the flow rate and pressure distribution within the semi-transverse system remains unclear. This study delves into the modelling and the solution of air pressure and flow rate within a semi-transverse system coupling the air leakage and the thermal effect induced by tunnel fires. The pressure and flow rate in the semi-transverse system were theoretically analyzed to establish a calculation model, where the effect of air leakage was summarized as the proposed parameter of air leakage coefficient, and the thermal effect was represented by the proposed temperature factor. A 1:20 scale experiment was conducted employing various exhaust flow rates (140 to 240 m³/s in full-scale). The numerical simulation was also conducted, considering different heat release rates (HRR, 20 MW to 50 MW), exhaust flow rates (160 to 240 m³/s), and different configurations for the exhaust vents. A consistent result was obtained, which showed that the temperature was prominent only in the opened exhaust vent region, while it was not significant in that with the closed exhaust vent. A step-by-step solution method for the proposed calculation model of the semi-transverse system was proposed, which can solve the pressure and flow rate distribution within the system. The test data was used to verify the accuracy of the model, which shows good consistency, with a maximum error of less than 8% in the calculated flow rate. The present result provides a method for verifying the design of the semi-transverse ventilation system, it also provides a guideline for assessing the actual flow rate and pressure of ventilation systems in practical tunnels.

This study conducted experimental and finite element analyses on the distortional buckling behavior of cold-formed steel back-to-back built-up columns (CFS-BBC) after exposure to high temperatures. Experimental research included exposure of CFS-BBC to high temperatures, measuring initial geometric imperfections, shearing tests of screw fasteners after exposure to high temperatures, and axial compression tests of CFS-BBC after exposure to high temperatures. The shearing tests on screw fasteners after exposure to high temperatures show that increased temperature would reduce the initial shearing stiffness and shearing capacity by up to 78% and 48%, respectively. However, the ductility of the fasteners connecting 1.5 mm steel was significantly improved after exposure to high temperatures. The CFS-BBC specimens failed in distortional buckling, with the ultimate load-bearing capacity increased (up to 7%) after exposure to 600 °C, followed by a decrease (up to 20%) after exposure to 800 °C. Subsequently, finite element models were developed and calibrated, followed by parametric analysis to investigate the behavior of CFS-BBC after exposure to high temperatures with varied distortional buckling slenderness ratio (λ_d). Results show that the load-bearing capacity after exposure to high temperatures will decrease by up to 29% after exposure to 800 °C. Based on the experimental and parametric analysis results, a predictive formula for the reduction factor of the load-bearing capacity after exposure to high temperatures was proposed. Finally, the coefficients in the Direct Strength Method were modified to improve its accuracy.

This paper presents an engineering approach to modeling pyrolysis. Instead of attempting to define detailed solid phase reactions, this method dynamically scales data from cone calorimeter tests of a material performed for different cone fluxes and/or sample thicknesses. The method can utilize data from multiple cone exposures and/or multiple sample thicknesses. The method compares the model predicted heat flux to a burning surface to the reference heat flux for a cone calorimeter test. The reference heat flux is the flame heat flux plus that portion of the cone heat flux that reaches the sample. In this method the reference heat flux is determined by table lookup of FDS simulations of a range of fuels and fuel burning rates in a cone geometry. The paper provides verification and validation of the approach. Validation is performed at multiple scales including a large series of 1D simulations for 141 materials, a cone calorimeter geometry for PMMA, a single burning item geometry for PMMA, a stack of wood pallets in a corner, and a room corner test at three length scales using plywood or fiber reinforced polymer. The method performs best for polymer and wood based materials. Specifically, it performed best when data from multiple cone exposures was self similar with a monotonic progression in peak burning rate as a function of exposure. The method showed a high degree of grid independence. The method also showed similar or improved performance to simulations using the detailed solid phase kinetics.

In underwater shield tunnel fire emergencies, the evacuation staircase area is prone to creating a significant bottleneck, severely restricting personnel movement and compromising overall evacuation safety. Accordingly, this paper conducted a full-scale tunnel evacuation experiment involving 186 participants. The results showed that participants exhibited hesitation after disembarking from the vehicle, which led to a circuitous evacuation route, taking up approximately 31.4% of the time during the driveway evacuation phase. Based on the maximum capacity (0.65 person/s) and general capacity (0.56 person/s) obtained from the experiment, a predictive model for the passage time of individuals at the evacuation stairs was proposed to quantify the exit passage time. Participants generally tended to choose the escape exit that appeared first in view or the one that was most physically accessible, and external guidance helped reduce their reliance on inertia when selecting a path. The zoning evacuation strategy of “evacuation exit zoning + evacuation direction limitation” significantly altered the personnel evacuation paths, improved the utilization efficiency of evacuation stairs, and reduced the overall evacuation time by 11.7%. The results of this study provide valuable insights for improving evacuation efficiency and designing escape plans.

During the past 20 years, the fire protection of ancient churches in Sweden has been improved with the installation of fire detection, fire sprinkler and water mist systems. The project identified 52 churches with either traditional sprinkler or high-pressure water mist systems. The operating experiences of these systems were documented by interviews with the end users, fire protection inspectors, system installers and by study visits. Problems associated with the use of antifreeze for water mist systems were identified. Systems have experienced leakage, high system pressures during warm days and corresponding unintentional activations due to breakage of nozzles or nozzle glass bulbs. For both sprinkler and water mist systems designed as dry-pipe systems, unintentional activations have occurred during wintertime due to freezing. Testing of dry-pipe systems also revealed unacceptably long water delivery times and residual water in piping. Many of the smaller rural churches are using a high-pressure gas- (nitrogen) driven pump because the public grid is unreliable. Three suffocation incidents were documented when nitrogen was unintentionally released into the confined technical space. Two of the incidents can be described as profoundly serious. For traditional dry-pipe systems galvanized pipes are often used but cases of internal pipe corrosion and leakage from pipes were documented. The church facility managers have a key role in the daily supervision of these installations. But it requires effort, technical competence and not least a substantial deal of self-interest. For some churches, high staff turnover has contributed to a lack of competence and supervision and maintenance has been neglected. High frequency of fault alarms (operating alarms) was also perceived as a burden and is also costly. Overall, the occurrence of technical problems and excessive costs have contributed to the shutdown or even dismantling of water mist systems in ten documented cases.

This paper acknowledges the influence of Dr Rita Fahy’s life’s work on a research project to evaluate fire evacuation guidance from high-rise residential buildings. It compares the application of agent-based simulations with Rita’s publications into pre-evacuation delay times. Her observed bi-modal distribution shape aligns with an approach to modelling pre-evacuation time as a series of component elements. The paper shows where Rita’s work on discrediting the notion of ‘panic’ is further supported by recent surveys and interviews of high-rise residential building residents. Similar to Rita’s findings in which an average of 61% of those in the 1993 World Trade Center bombing would seek information as one of their actions, a key finding is that around 50% of the survey respondents indicated they would likely or very likely seek information from others. The paper describes Rita’s advancement of the EXIT89 network modelling tool and where her work has been used to assess the capability of an alternative model. A comparison is made between EXIT89 simulations with two other tools. A focus on wheelchair users examines Rita’s findings on expected population proportions and movement speeds. Simulation of total evacuation time with varying wheelchair user ratios shows EXIT89 generally predicts shorter times.

Steel structures are vulnerable to fire and need protection. On the other hand, in earthquake-prone areas, seismically resistant steel structures are generally designed with high ductility, which causes them to undergo significant deformations during earthquakes and, subsequently, damage to the applied fire protection coating. Considering the possibility of a fire incident after an earthquake event, understanding the fire resistance performance of seismically damaged fire protection coatings requires conducting research that is considered in this paper. In this research, a series of seismic tests (a total of seven quasi-static cyclic lateral loading tests) and a series of fire resistance tests (a total of 11 tests) have been performed on protected steel elements. The fire protection coatings considered in this research are cementitious spray-applied fire resistive materials that are widely used in the world. The parameters studied here include the type and thickness of the fire protection coating, the type of fire protection coating reinforcement system, and the intensity of the earthquake. According to the results of these tests, complete and accurate information on the fire resistance performance of spray-applied fire resistive materials against post-earthquake fire has been obtained and the effect of various parameters has been determined. In this regard, it has been found that the mechanical properties of the fire protection coating, the reinforcing system of the fire protection coating and the characteristics of the steel section are important parameters and factors.

Informal settlements, where over 1 billion people live globally, are extremely vulnerable to fire events. Thermally thin steel-clad timber-framed homes found in South African informal settlements are a prime example of this. In this paper, we explore, through six full-scale laboratory experiments and modelling, the influence of opening locations, areas, and aspect ratios, on the fire dynamics of thermally thin and leaky compartments. It was found that having the window on the same wall as the door produced the highest heat fluxes opposite the door (13 kW/m²). Having the window opposite the door on the back wall, created a crossflow scenario which produced slightly higher fluxes opposite the door (10–11 kW/m²) compared to when the windows were on a side wall (7–9 kW/m²). Increasing the opening area by including another equally sized window, or by doubling the window width or height, slightly reduced the heat fluxes opposite the door and window, in general slightly increased the time to flashover, and significantly increased the heat release rate required for flashover. The work presented within this paper adds to the growing body of knowledge around informal settlement dwelling fire dynamics which can be used by engineers and urban planners in understanding and mitigating urban conflagrations within these communities.