Fire Technology最新文献

As the critical structural member in cable-supported bridges, cables must be safeguarded when subjected to vehicle fires due to their vulnerability at high temperatures. Previous studies broadly adopted a uniform radiative thermal boundary layer on the cable surface, leading to inaccurate predictions of the performance of bridge cables in fire. This paper proposes a novel theoretical method for computing the spatial heterogeneous radiant heat flux on the external surface of bridge cables in vehicle fires. The scheme geometrically discretized the flame and cable surface and then derived a closed-form view factor from an arbitrary position on cylindrical surfaces to the radiating flame face that was geometrized into multiple quadrilaterals. Validated by complex cases, this method is effective in appraising the heterogeneous radiation distribution on the fire-exposed bridge cable surface. Case studies were then performed on a cable-stayed bridge wherein a truck fire occurred near the stay cables and on a suspension bridge whose cable system was exposed to tanker pool fires. The calculated high-resolution radiant heat flux demonstrates that its heterogeneity is prominent axially and circumferentially. Superficial locations facing the flame receive the peak radiation, and the back heat exposure is zero. The resulting thermal boundary conditions for bridge cables more accurately represent real-world conditions, enabling more precise investigations of their thermomechanical response in the future.

In order to improve the effect of traditional water mist on blocking high temperature flue gas and toxic gas in long and narrow space buildings. In this study, an environmentally friendly EMI dust suppressant with a main component of Sophorolipid was added to the water source to carry out a reduced-size fire smoke suppression experiment. Research revealed that at a wind speed of 1.5 m/s, the maximum smoke suppression efficiency for fire sources of 7.5 kW and 15.7 kW was 67.4% and 46.8%, respectively. The lowest CO concentrations recorded were 45.0 mg/m³ and 87.0 mg/m³, respectively. And the decrease of 83.3% in SO² concentration was observed under the 7.5 kW fire source. With the increase of EMI addition concentration, the concentration of soot particles decreased gradually, and then the rate of decline slowed down. The single-row nozzle water mist curtain is easily affected by the longitudinal exhaust air. When the double-row nozzle is used, the highest smoke suppression efficiency of the two fire sources is 65.0% and 74.2%, respectively. Small particle size droplets will be vaporized by the high temperature of the fire source, reducing the droplet sedimentation rate, and the environmental droplet density should be appropriately increased.

This study introduces an innovative approach to improve the fire resistance of reinforced concrete (RC) structures based on the heat-induced prestress of iron-based shape memory alloys (Fe-SMA). The Fe-SMA embedded in concrete can automatically activate its shape memory effect under fire to generate tensile stress called recovery stress to apply prestress to the parent structure. The process of generating recovery stress is also called self-prestressing. The Fe-SMA can enable traditional concrete structures to respond to fire actively and automatically through the self-prestressing effect, improving the fire resistance of the RC structures. Fire tests were performed to examine the fire resistance of concrete beams hybrid reinforced with steel and Fe-SMA rebars. The recovery stress reduces beam deflection under fire while increasing the fire resistance. The fire resistance of the beams in which 2 and 4 of the 6 longitudinal reinforcements were replaced with Fe-SMA bars increased from 112 to 141 min and 152 min, respectively, when compared to the control beam. In addition, the deflection rate of the hybrid reinforced beam is also decreased. The residual deflection of hybrid reinforced beams does not increase when cooled to room temperature. With the reasonable arrangement of Fe-SMA rebar, the recovery stress can last throughout the fire exposure time to improve the fire resistance of concrete structures.

Wildfire’s destruction of homes is an increasingly serious global problem. Research indicates that characterizing home hardening and defensible space at the individual structure level may reduce loss through enriched understanding of structure susceptibility in the built environment. However, improved data and methods are required to accurately characterize these features at scale. This paper does three things: (1) Identifies features correlated with structure loss. (2) Compares methods of characterizing structure susceptibility, including home assessments and emerging fire spread models. (3) Evaluates methods and open data sources used to measure these features. We find that relative feature importance varies widely among studies due to data limitations and scale issues. Built-environment fire spread models show limited inclusion of structure-level features. Additional research, model validation, improved data, and improved data collection methods are needed to bridge the gaps between primary research, susceptibility indices, and built-environment fire spread models. Advancing scalable methods for characterizing built-environment fuels and susceptibility will refine risk mitigation efforts globally.

The safety research of thermal runaway propagation (TRP) has become the current focus with the wide application of lithium-ion batteries (LIBs). It is crucial to design and utilize different combinations of thermal insulation materials to prevent TRP. In this study, an independent experimental platform for investigating TRP behavior in 26,650 LIB modules were established, considering various electrical connections and aerogel insulation placement. The collected and analyzed data include TRP behavior, temperature, mass loss, and heat release rate, aiming to explore the influence of aerogel felt positioning on TRP characteristics. The findings reveal that parallel modules not only exhibit an earlier onset of TRP than other battery systems but also pose a higher risk under various electrical connections. The positioning of the aerogel felt significantly influences the speed of TRP. Placing an aerogel felt between batteries postpones the onset of TRP in the battery module regardless of the electrical connection. Furthermore, situating an aerogel felt between batteries notably diminishes overall heat release during TRP for both series and non-electrically connected batteries. Combining the placement of aerogel felts at the top and middle positions can mitigate harm from TRP in a parallel battery system. This study proposes targeted preventive strategies for diverse electrically connected battery systems and identifies specific aerogel configurations capable of effectively suppressing TRP in the battery module.

This study investigates the influence of a kerosene flame aggression (characterized by a 116 kW/m² heat flux and an 1150 °C flame temperature) and a tensile loading (monotonic or creep) on the deformation and damage mechanisms of quasi-isotropic carbon fibers reinforced laminates consisting of different thermosetting matrix systems (epoxy and bismaldeide). The influence of the carbon fibers reinforcement (unidirectional and woven fibers) along matrix nature were examined on both the fire and mechanical responses of the laminates. A specific fire bench was used to conduct such tests while monitoring the changes in the axial stress and strain as well as temperature along flame exposure time. First, from monotonic testing conducted under fire conditions, the axial strength is about 50 and 30% lower than woven ply C/BMI laminates, in unidirectional (UD) and woven ply C/Epoxy laminates, respectively. These results agree with the tendency observed in virgin specimens. After a 300 s exposure, the axial strength decreases by 40 to 60% of their initial values for studied materials with respect to their virgin state. After a 900 s exposure, the drop has almost stabilized at about 30 to 40% of their initial values. Woven ply laminates being characterized by matrix-rich areas at the crimp, the thermal decomposition primarily occurs in these areas. As a result, the thermally-induced damages (porosities formation and extensive delamination) in these areas contribute the thermal transfers to be modified within the laminates Second, creep testing under fire conditions were performed to comply with the fire certification standards. The underlying idea of these tests is to identify the axial creep stress to be applied to ensure that the loading bearing capabilities of the composite part are preserved for 900 s. With respect to C/BMI laminates, under the same fire conditions, the maximum applied stress is 30 and 20% lower in UD and woven ply C/Epoxy laminates, respectively. Based on the changes in the time-to-failure as a function of the creep tensile force, it is possible to get analytical expressions, which are the first step towards the definition of simple design rules useful to engineers willing to meet safety requirements.

This paper presents results of an experimental study about developing a lightweight and loadbearing masonry block with enhanced bushfire-resistant characteristics by using pumice fine aggregate. First, the chemical, physical and thermal properties of the pumice aggregate were examined. Then, cement mixes for masonry blocks consisting of one cement—sand mix, taken as the control mix and three different cement—pumice mixes that replace sand in the control mix with pumice fine aggregate at varying percentages of 100%, 80% and 60%, were developed by using absolute volume method. Slump and fresh density of these cement mixes and hardened properties such as density, compressive strength and water absorption were measured while bushfire resistance and building fire resistance were examined using the developed masonry blocks against standard fire exposure for 30 and 180 min, respectively. The results from this study showed that the highest density and compressive strength were obtained by the control mix, but masonry blocks made of the control mix showed the lowest bushfire and building fire resistances. In contrast, the bushfire and building fire resistances of masonry blocks made of the cement—pumice mixes were relatively higher, and they satisfied required density and compressive strength for lightweight loadbearing masonry units. Further, the obtained results were compared with a previously developed lightweight masonry block using expanded perlite fine aggregate and the new masonry blocks made with 80% of pumice fine aggregate have shown to be the most suitable for use in the walls of bushfire shelters and other buildings in bushfire prone areas.

A better knowledge of the characteristics of both fire and non-fire particles is crucial for improving the performance of existing detectors. Numerical simulations are important methods for unveiling the scattering behavior of particles. However, previous numerical studies have poor agreements with the experimental results owing to their single-particle assumptions. In this study, morphology models of water droplets, n-heptane soot, and loess dust particles were constructed based on SEM analysis. The light scattering matrices of these three particle populations were then calculated using the discretization-integration method. Furthermore, an orthogonal design was used to quantitatively analyze the effects of particle diameter, morphology, and refractive index on light scattering. The result showed that the discretization-integration method can successfully simulate the bulk scattering matrices for different particle populations. A monomer-particle model with log-normal distribution was proposed, which can better simulate the bulk scattering matrix of n-heptane soot particles. The influence of physical parameters on the light scattering at a certain wavelength decreased in the following order: particle radius > refractive index (imaginary part) > refractive index (real part) > particle morphology. This work is helpful for improving light scattering simulations and thus the detection of smoke from fires.

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.