Fire Technology最新文献

With the wide application of electric vehicles (EVs) in cold areas, low temperature heating of battery is becoming more and more mature, and the way of battery bottom heating is also widely used in EVs. Nevertheless, the battery is not completely safe during the heating process, and there may be a risk that the heating plate trigger the battery to overheat. Firstly, a thermal runaway (TR) model of the battery is built, and the simulation results are compared with the experimental results to verify the accuracy. Subsequently, a bottom heating module is added to the TR model to simulate and analyze. Results show, when the heat flux exceeds 1500 J (m² s)⁻¹ and heating continuously for over 26,787 s, TR is triggered. As the heat flux increases, the TR is triggered nearly half the time earlier, and the maximum temperature reached also increases by 7.62°C. Additionally, the ambient temperature has a great effect on the time of continuous heating to TR at low temperature, and has little effect on the maximum temperature. This work provides a reference for the model study of TR in the case of low temperature heating.

The “Emmons Problem” is a foundation of fire science and gives a mathematical boundary layer solution to the burning of a vaporizing fuel from the surface of a flat plate immersed in a uniform flow of oxidizing gas. It approximates the Navier–Stokes equations assuming infinitely fast chemistry and ignores differential diffusion and thermal radiation. This allows “similarity” solutions to be developed and expressed in terms of the classic Blasius function. The current paper extends the solution, in mathematical form, to the entire domain far from the boundary layer and upstream of the leading edge. The introduction of conformal parabolic coordinates and use of the Howarth transformation allows the solution for the stream function to be expressed in exactly the same form as that found by Emmons and furnishes an explicit recipe for the pressure perturbation. The same coordinate transformations allow the exact solution of the full elliptic mixture fraction equation to be obtained, and the representation of the velocity components in terms of the stream function guarantees that the continuity equation is also satisfied exactly. Further, an exact solution to the transverse momentum equation is also displayed permitting the introduction of a crossflow into the spectrum of results obtained. In short, an analytic solution is found for the Emmons problem in the entire elliptic domain - upstream and in the far field.

The hot and toxic smoke is a major reason for deaths and injuries in tunnel fire hazards, therefore, it is of vital importance for safe evacuation to effectively control the smoke. This paper proposed a smoke control strategy, i.e., completing smoke extraction, and developed the design criterion of exhaust rate based on small-scale experiments and theoretical analysis. The heat release rate (HRR), damper length, and interval were considered. Experimental results showed the critical exhaust rate for completing smoke extraction rose with the increase in HRR and declined with a growing damper interval. Besides, it first rapidly decreased and then turned to be smooth with rising damper length. Subsequently, the ratio of the suction force, F_d to the force, F_s was adopted to determine the completing smoke extraction using force analysis. The results illustrated that the HRR and damper interval barely affect the relative magnitude between the suction force, F_d, and the force, F_s. It was linearly dependent on the dimensionless damper length and then exponentially grew. The critical length of the damper was 0.1 m. Finally, a prediction model was established, and the evaluated results deviated from the experimental data within 15%.

This article proposes an empirical expression to describe the pyrolysis and charring of spruce wood in bench-scale experiments for a wide range of incident heat fluxes. Spruce wood samples were exposed to a cone radiant heater oriented vertically with varying intensities, ranging from (dot{q}_{text {cone}}^{''}) = 22 kW m(^{-2}) to 93.5 kW m(^{-2}) over 53 test samples. The mass loss rate (MLR), the position of the char front and a preliminary additional heat source from smoldering or flaming combustion were experimentally determined. The experimental data were processed to express the burning rate as a function of heat flux and char front position. A grouping of the experimental curves was obtained, allowing to predict the MLR outcome over time regardless of the incident heat flux. A linear regression at the quasi-steady state regime allowed the determination of the fitting coefficients of the correlation, which ultimately correspond to the mass of volatiles produced per unit of energy input into the material. A comparison was made with theoretical analysis of the pyrolysis of charring materials from the literature, and the discrepancies with the proposed approach and its limitations were finally discussed. The main advantage of this approach is that it provides a generalized expression, requiring minimal input of material properties, which predicts the MLR change over time for any heat flux within engineering accuracy.

How to effectively guide occupants to use different evacuation routes under fire situations is the key to improving fire safety and ensuring successful evacuation. Evacuation analysis for fire safety in surveillance videos plays a crucial role in understanding and mitigating risks. The fundamental diagram of pedestrian flow, which illustrates the relationship between pedestrian velocity and crowd density, is a valuable tool for analyzing evacuation dynamics and enhancing fire safety measures. Traditional methods rely on trajectory files obtained from manually tracking each pedestrian in video recordings to construct fundamental diagrams. However, these methods have limitations in accurately representing crowd density and cannot provide real-time analysis, making them unsuitable for surveillance camera analysis in fire safety scenarios. To address this challenge, we propose a novel convolutional neural network-based framework called the deep fundamental diagram network, which is specifically designed for fire safety applications. This framework consists of two modules: the multi-level dilated convolutional neural network (MLD-Net) and the optical flow module. The MLD-Net learns the mapping relationship between input images and density maps, enabling accurate estimation of pedestrian density. Simultaneously, the optical flow module calculates pedestrian movement speed, providing crucial information for evacuation planning. By aligning the density map with the speed map, the fundamental diagram is derived, which aids in understanding evacuation dynamics. The experimental results demonstrate that our method achieves good consistency with traditional approaches while significantly reducing the computational time. Additionally, our framework enables anomaly detection and pedestrian line counting, further enhancing fire safety measures. This work is expected to have good prospects in the fields of fire safety, evacuation dynamics analysis, and real-time crowd analysis systems for fire situations.

Traditional smoke detection sensors are characterized by low sensitivity, poor stability, etc. In this study, we propose a coal mine smoke detection technique based on multi-feature fusion analysis. Detection of smoke on belt conveyors is realized by machine vision technology. Firstly, the inter-frame difference method is used to capture the motion region of the smoke. And the suspected smoke region is obtained. Then, the color features of smoke are obtained by RGB color histogram. The motion direction features of smoke are obtained by smoke optical flow vector extraction. The irregular contour features of smoke are obtained by smoke contour irregularity criterion statistics. Based on obtaining the suspected smoke area, the above three features are used to determine whether the belt conveyor produces smoke. This study collected four video images of the belt surface smoke, stand smoke, light samples, and dust samples. The final combined diagnostic rate was 94.19% by testing the above detection models. This study proposes a stable and effective smoke detection technique for coal mine safety production.

The possibility to subdivide a deck of a ro-ro ship to contain heat and smoke by means of a fabric curtain descending from the ceiling (i.e., the deckhead) is studied experimentally using a reduced-scale experimental setup. As an important part of the study, the requirements of the international convention of Safety of Life at Sea (SOLAS) are investigated for so-called ‘open ro-ro decks’ in comparison with ‘closed ro-ro decks’. To analyse the experiments, sensors are used to measure the opacity levels as well as the gas temperatures and concentrations. These measurements helped quantify the degree of stratification of the smoke, its concentration of soot, and carbon monoxide levels, making it possible to analyze the effects of containment induced by the fabric curtain. The results show that the fabric curtain considerably reduces the gas temperatures and the soot concentration upstream of the curtain if it descends completely (i.e., to the floor level), while it does not disturb the stratification of smoke. The containment of smoke is more enhanced when multiple fabric curtains are used, and a comparison with a water curtain shows that the fabric curtain offers better smoke containment. Finally, the most optimal containment effect is achieved using a system that combines a fabric curtain with a water curtain.

The main objective of this research is to establish a quantitative risk assessment method for fire spread in enclosed building scenarios. The enclosed building fire spread process is divided into three stages: fire fully developed in the fire compartment, failure of weak barrier, and combustibles ignited in the target compartment. The calculation method for fire spread is established, where the time for fire fully developed is calculated based on the t² fire, the barrier failure time is calculated based on the finite difference method, and the combustible ignition time is calculated based on the zone model. The linear regression model is formulated to ensure computational efficiency for fire spread time prediction. The enclosed building fire spread quantitative risk assessment method is proposed based on the Probit model. The effectiveness of the risk assessment method is validated through the enclosed building fire spread experiment, and the method is applied to assess the risk of fire spread in an office. The results demonstrate that the method could quantitatively assess fire spread risk under different conditions with high computational efficiency and excellent versatility, and it could provide guidance for fire prevention, building fire design, and fire rescue.

In this paper, a new gram scale experiment with well characterised boundary conditions is proposed for pyrolysis experiments. The set-up consists of a tube furnace, based on ISO19700, with a newly designed concept for a balance within the oven, allowing for online mass loss measurements. Samples with a length up to 50 cm can be investigated in this apparatus. The oven allows for experiments at fixed temperatures or at fixed heating rates, under controlled atmosphere, w.r.t. gas composition and flow rate. A thorough characterisation of the set-up is presented, including aspects like reproducibility of the heating rate or the precision of the balance. The functionality of the balance has been demonstrated with calcium carbonate (CaCO(_{3})) experiments. This material was chosen because it decomposes in a single reaction, which only releases CO(_{2}). This allows for comparison between the mass loss rate of the balance and the CO(_{2}) production rate, measured by a gas analyser. Results for two different heating rates: 3 K/min and 5 K/min and for different masses (25 g and 8.5 g) are presented. The two measurement methods are in excellent agreement. Finally, the data obtained from the new experimental set-up is compared to results from thermogravimetric analyser (TGA) experiments.