Fire Technology最新文献

This study utilizes numerical simulations to investigate the maximum ceiling temperature in inclined tunnel fires under natural ventilation, focusing on the impacts of the slope and the cross-sectional geometry of the tunnel. The findings demonstrate that the chimney effect induces longitudinal airflow along the tunnel slope, facilitating smoke exhaust through the upper tunnel opening and causing upward flame tilting. As the tunnel slope increases or the cross-sectional area decreases, the intensified chimney effect results in a substantial decline in maximum ceiling temperature. Furthermore, the Coanda effect, whose strength varies with the aspect ratio of the tunnel, modulates flame behavior and smoke flow. In narrow tunnels with an aspect ratio of 1 or less, the enhanced Coanda effect encourages longitudinal flow and strengthens the chimney effect. In contrast, in wide tunnels where the aspect ratio exceeds 1, lateral smoke diffusion diminishes this effect. Piecewise empirical models are proposed to predict the induced airflow velocity and maximum ceiling temperature under the condition of bidirectional smoke overflow. These research outcomes offer essential guidance for optimizing fire safety designs, refining smoke control strategies, and improving emergency response protocols in tunnel engineers.

A critical research area regarding wildfire modelling often overlooked is the task of finding where a wildfire started and how long that wildfire burned. A literature review revealed that there are no automated methods with the goal of estimating the location of ignition points and propagation duration of a wildfire from a burn scar. This paper describes a novel method called the Wildfire Source Genetic Algorithm (WSGA) which can estimate the ignition points and the propagation duration of a wildfire, given the wildfire’s burn scar and environmental conditions used as input for a forward running wildfire simulator. This paper uses twenty input burn scars generated from a wildfire simulator to validate the WSGA, as their ignition points and propagation durations are known. The WSGA generates sets of ignition points and propagation durations, which are then simulated and compared to the input burn scar. The ignition points and propagation durations of the WSGA seeded burn scars that most closely resemble the input burn scar are iteratively modified using a genetic algorithm to seed wildfires that more closely resemble the input burn scar. The ignition points and propagation duration of the best fitting WSGA seeded burn scar is compared to the inputted burn scar by evaluating two measures of error developed in this paper called the relative distance error and relative simulation duration error. The WSGA had a relative distance error of 0 to 1.25 times the diameter of the inputted burn scar. Lower errors were associated with larger wildfires. The WSGA had a relative simulation duration error of 0.0006 to 0.49 times the propagation duration of the input burn scar.

The mechanical properties of corroded reinforced concrete (RC) beams after exposure to fire serve as one of the critical bases for post-disaster structural restoration. To evaluate the bending performance of corroded RC beams after fire exposure, a calculation program was devised. This program was based on section theory analysis and aimed to analyze the mechanical properties throughout the bending process of corroded RC beams. The section theory analysis method specifically accounts for the strain incompatibility between corroded steel bars and concrete caused by bond-slip. Firstly, a compatibility coefficient and finite element model were introduced to quantify the incompatible strain. The effect of corrosion degree and fire exposure time on the coefficient was investigated in detail. Subsequently, a sectional analysis of corroded RC beams was conducted. The entire bending process was divided into two stages based on the concrete stress of the tension zone: before and after cracking. According to the stress state of the steel, the failure mode of corroded RC beams was divided into brittle and ductile failure. The theoretical analysis process was then programmed using Python. The results showed that the error between the program’s calculation and experimental values of the program was less than 5.62%. Finally, the influence of corrosion ratio, thickness of concrete cover, and fire exposure time on the residual flexural capacity and flexural stiffness was discussed. And simplified formulas for each were established. The calculation values obtained from this simplified calculation method are within a 10% error compared to the experimental values. This research can provide a theoretical basis for the reinforcement and repair of corroded RC beams after fire exposure.

Graphical Abstract

The load capacity of screw fixings supporting building services, such as sprinklers in Cross Laminated Timber (CLT) ceilings was tested before, during and after exposure to fire, to investigate the risk of detachment. The pull-out strength of screw fixing in ambient conditions, during and post-fire were investigated in relation to pull-out strength versus embedment depth. The relationships between pull-out strength have been reported as functions of screw fixing embedment depth, screw dimensions, and char formation. In the experimental study, samples of standard industrial CLT were tested with two distinct types of adhesives with typical construction industry screw fixings used for the suspension of Mechanical and Electrical (M&E) services. A purpose built fire-test rig was designed to expose screw fixings embedded into CLT to a fire in a ceiling mounted configuration. A series of eight fires were conducted, and the pull-out strength of each screw fixing was assessed during or after the fire. The reduction of load capacity can be conceptualised into two factors: The charring across the whole timber surface which was deeper close to the fixings leaving a fragile char which could be scraped off; and the weakening of the timber along the length of the screw thread, resulting from the higher thermal conductivity of the screw fixing. Both these effects increased as a function of the shank width of the screw. The outcome of this study is to inform guidance on the ability of screw fixings to support M&E services beneath timber ceilings in the event of fire.

The effects of heating rate on heat and mass transfer, as well as damage mechanism of lining concrete, were investigated using a coupled thermal-hydro-vapor finite difference model. The results showed that during a steady thermal state, the surface temperature depended solely on the peak temperature, and was independent of the heating rate. Vapor pressure exhibited pronounced nonlinearity. At low heating rates, its peak increased monotonically with depth. Whereas at higher heating rates, peaks appeared earlier and followed a two-stage distribution-initially increasing and then decreasing with depth. Within the first 20 mm of depth, the heating rate had a substantial influence on heat transfer, moisture migration, and phase changes. However, beyond 50 mm, its effect was negligible. Concrete damage was predominantly governed by thermo-mechanical processes, which accounted for more than 80% of the total damage. At higher heating rates, this proportion increased to approximately 90%, underscoring the growing dominance of thermo-mechanical effects. To maintain the structural integrity of tunnel linings, the heating rate should be limited to below 50 °C/min.

Flame-retardant (FR) formula of composite insulators is the key to the fire safety of high-voltage (HV) switchgear when arcing occurs. In this study, a series of experiments was conducted on the ignition and self-sustained burning behavior of five insulators by HV arcing (18 kV). The results show that a strong jet flame came out immediately from the hole when the initial arcing happened in all samples. In the first arcing events, intense burning near the hole quickly stopped after the arc was quenched. Successful ignition occurred after 7–8 times of 0.1 s arcing for all samples, which indicates the little dependence of the insulator ignition on their FR formula due to the high temperature of the arc and the impact of pyrolysis gases. Additionally, at t = 41.5 s, the surface temperature measured 10 mm above the hole varied by up to 32 °C among the five samples, ranging from 380 °C to 412 °C. However, in the self-sustained burning stage, upward flame spread on the samples with higher red phosphorus (RP) content was effectively suppressed. The flame duration dropped from 101 s in FR-EP-1 to 16 s in FR-EP-5 as RP content increased, with reduction as large as 84.2%.

Determining the feasibility of reusing fire-exposed hollow steel sections poses challenges for designers and structural engineers due to a lack of reliable data, as existing guidelines focus on the behavior of steel tubes at elevated temperatures during a fire but lack sufficient research on their post-fire mechanical properties. The paper details an investigation of the post-fire mechanical behavior of YST-240 (mild steel) Square Hollow Steel Tubes (HST), a material widely used in construction. A systematic experimental program was conducted in this regard on the HST stub column and tensile coupon (extracted from HST stub columns) specimens having a thickness of 3 mm. All the HST stub column and tensile coupon specimens were exposed to a range of temperatures (ambient to 1000 °C) with exposure conditions ranging from mild, moderate, and severe (i.e., 30 min, 60 min, and 90 min, respectively). The research introduces novel temperature-dependent equations to quantify the percentage degradation in both material strength and the load-bearing capacity of HST stub columns following fire exposure. Further, predictive equations are proposed for evaluating the residual mechanical properties of YST-240 steel at various temperatures and compared with the existing equations given in IS 800:2007 and AISC360-16. The findings provide critical insights into the fire-induced deterioration of structural steel, offering enhanced predictive capabilities for post-fire structural assessments and design modifications.

Fire poses a continuous threat to human life, and minimizing the number of building residents who may become trapped in a fire is a central concern in fire safety. At-risk groups are particularly susceptible to fire-related perils. This study underscores the need to address fire-related risks faced by building occupants, especially vulnerable groups with mobility or cognitive impairments. A probabilistic risk analysis is used to establish the observed Expected Risk to Life (ERL) for the research’s focus groups. By integrating the observed ERL with reliability considerations, criteria for life safety are defined, including target failure probabilities for safe evacuation, which inform reliability-based design for fire evacuation. A sensitivity analysis identifies the most influential factors affecting evacuation model outcomes. Minimizing the risk of occupants becoming trapped a in fire drives this research’s focus on Reliability-Based Design Optimization (RBDO) principles. By applying RBDO to fire evacuation design, values for impactful design factors are recommended to enhance evacuation reliability by decreasing the failure probability of safe evacuation. The results demonstrate the considerable impact of at-risk group characteristics and building geometry design variables on fire evacuation safety levels, emphasizing the need for reliability-driven design strategies.

With the rapid progress of global urbanization, enhancing the fire safety of power transformers has become increasingly crucial. A primary cause of transformer fires and explosions is the ignition of insulating oil due to transformer leakage, short circuit, high temperature and other failures. To reduce fire risks, transformers typically use high fire point insulating oils or non-flammable oils instead of conventional mineral oils. However, comprehensive research on high fire safety insulating oils for power transformers remains in its early stages globally. From an energy security perspective, this paper conducts an in-depth analysis of the fire characteristics of oil-immersed transformers, demonstrating that substituting conventional mineral oil with high fire-safety insulating oils can significantly mitigate transformer fire risks. From an energy security perspective, this paper analyzes the fire characteristics of oil-immersed transformers in depth, demonstrating that the replacement of conventional mineral oil by high fire-safety insulating oil can effectively reduce the risk of transformer fires. Furthermore, a systematic review of global advances was conducted by analyzing recent publications, focusing on high fire-safety insulating oils for transformers, specifically synthetic esters, natural esters, and flame-retardant transformer oils. Based on a systematic review of the performance of various high fire-safety insulating oils, this paper summarizes their respective advantages and limitations. Synthetic and natural ester insulating oils exhibit excellent insulation properties and high fire points. However, their relatively high viscosity and insufficient stability somewhat impair heat dissipation efficiency and long-term service life. In contrast, flame-retardant mineral oils retain the favorable physicochemical properties of conventional mineral oils, yet face the challenge of balancing flame retardancy with insulation performance. Finally, prospective research directions and critical priorities are proposed for each category of high fire-safety insulating oils, offering actionable recommendations to guide future investigation and development efforts.

This study investigates high-temperature resistance of galvanized steel corrugated panel partitions in the inclined shafts of extra-long road tunnels under tunnel fire conditions. Numerical simulations and laboratory experiments were conducted to evaluate the thermal behavior of galvanized steel and to analyze the influence of fire scenarios on the temperature distribution within tunnel ventilation shafts. The experimental results show that at 400 °C, the galvanized coating deteriorates and loses its protective function. Below this temperature, the coating largely remains intact and continues to protect the base material. However, mass loss increases significantly once the temperature exceeds 250 °C, indicating potential concerns for long-term durability. The simulation results show that temperatures near the shaft partition increase with higher heat release rates (HRR), lower exhaust velocity, and shorter connecting duct lengths, but the maximum temperature does not exceed 250 °C. Temperatures along the shaft height remain nearly uniform, while near the shaft entrance they decrease rapidly with distance from the fire source. Compared with reinforced concrete partitions, galvanized steel corrugated panels are lighter, easier to install, and require less material. This study provides a systematic assessment of their high-temperature performance in inclined shafts, supplying evidence for their application in tunnel fire protection design.