Fire Source Location Research Articles

Two-dimensional inverse problem of fire location in the closed goaf of coal mine based on optical fiber sensors.

Monitoring the temperature to determine the fire source locations is essential for controlling the spontaneous combustion in the goaf. Optical fiber sensors are employed to measure the temperature distribution in the goaf. However, due to changes in the geological conditions and the influence of the falling rocks in the goaf, only sensors on the upper side of the uncompacted goaf, due to inclination and coal pillar, may remain. Unilateral sensors are located on the upper side of the goaf, while fire occurs in the center. To investigate the issue with linear unilateral sensors, a two-dimensional inverse method has been developed to determine the location of fire sources by considering heat transfer after a fire inside the goaf. The equations were theoretically solved using Green's function method to obtain the internal temperature distribution of the physical model of the goaf. Sensitivity analysis identified the most crucial parameters in the process of spontaneous heating at different temperature. The fire source location can be determined using a loop method based on the model calculations. We considered a case to validate the model. Accurately identifying the fire source location in the goaf using the unilateral sensors has an essential theoretical and practical significance for fire prevention and fighting.

Optimal ventilation mode for double fires in a typical interchange subway station

This paper investigates the optimal ventilation mode for double fires in a typical interchange subway station. Numerical simulations were carried out in a full-scale subway station with different heat release rates, ventilation modes, and fire source locations. Results demonstrate that when double fires occur, activating ventilation systems in one line may affect the smoke spread in other lines due to the existence of transfer channels. For the platform-tunnel mixed exhaust mode, when the fire size is small, the optimal TVF exhaust volume range exists. There is no optimal smoke exhaust volume for double fires with the large fire size or near the ends of the platform. Under such circumstances, the subway staff should take some measures to hinder the unwanted smoke flow path.

A physics-informed artificial fish swarm algorithm for multiple tunnel fire source locations prediction

To address multiple tunnel fire source locations prediction for better firefighting, this work aims to establish a model-driven and data-driven fusion algorithm, which is named as the physics-informed artificial fish swarm algorithm. In the algorithm, the artificial fish swarm algorithm is utilized to avoid complex fire mechanisms modelling, which makes the algorithm owns the advantage of the data-driven methods. Meanwhile, a physical model of the longitudinal ceiling temperature distribution relative to fire source locations and some physical mechanisms are utilized to guide the data-driven artificial fish swarm algorithm for converging to the reasonable prediction, which makes the algorithm owns the advantage of the model-driven methods. Two full-scale tunnel fire experiments with two pool fire sources and three pool fire sources as well as one full-scale cable fire experiment in the tunnel are utilized to support and verify the algorithm, which can be utilized to achieve multiple tunnel fire sources prediction and ceiling temperature distribution prediction in tunnel fires.

Study on Temperature Distribution and Smoke Spreading Behavior of Different Fire Source Locations in the Underwater W-Shaped Island-Crossing Tunnel

Study on Temperature Distribution and Smoke Spreading Behavior of Different Fire Source Locations in the Underwater W-Shaped Island-Crossing Tunnel

Simple model combined with data assimilation to forecast buoyancy-driven ceiling jet propagation in tunnel fires

Faster-than-real-time forecast for the ceiling jet head propagation is crucial for evacuation guidance and rescue operation in the early stages of tunnel fires. The ceiling jet head propagation is driven by buoyancy and thus significantly dominated by the heat transfer process in the head region. Simplified models have been established but proved challenging in forecasting complex dynamic processes. The cumulative deviations induced by the model limitations and the input parameter uncertainties lead to distorted forecast during the ceiling jet dynamic propagation process, thereby constraining the applicability of such models in practical scenarios. In this study, an assimilation method, the ensemble Kalman filter (EnKF), was combined with a simple theoretical model to forecast the ceiling jet propagation. Using the EnKF to assimilate the monitored local data, the key input parameters such as mass flow rate m˙ and the temperature of the ceiling jet head Ts are corrected in real time, thus alleviating model prediction deviation. Meanwhile, a heat loss rate correction coefficient λα, introduced to correct the heat loss rate during the ceiling jet propagation process, is dynamically estimated as well. This enables the model to characterize the heat transfer process more accurately, consequently ensuring faster-than-real-time forecasts of the subsequent propagation stage. Finally, the forecasting effectiveness of the proposed combined method was examined in a 1:6 reduced-size experimental tunnel fire scenario and full-scale simulated tunnel fire scenarios with various fire source locations, tunnel geometries, and suddenly changing HRR. In response to the demand of minimizing both the type and quantity of sensors in practical applications, a factor analysis was also performed to examine the robustness of this method. The results exhibited good adaptability to different fire scenarios with very limited monitored data.

Experimental study on the descent distance of fire smoke at the corridor corner

In this paper, a series of experimental studies were conducted in a L-shape scaled corridor to investigate the fire induced smoke descent behavior at the corridor corner. The effects of fire source location and fuel pool size on the smoke descent distance were studied. The variation of the thickness of smoke layer in the L-shaped corridor and the temperature attenuation under the ceiling were elucidated. Results showed that the smoke layer height decreased significantly at the corner. The descent distance increased with the increase of fuel pool size. The temperature of the incoming smoke decreased as the distance between the fire source and the corner increased, the Ri number of smoke layer also decreased. The effects of gas temperature, velocity and thickness on smoke settling distance were analyzed by experiments. A prediction model for the smoke descent distance at the corridor corner was proposed.

Experimental study on the effects of branch tunnel ventilation on the smoke movement and temperature characteristics in bifurcated tunnel fires

A series of fire tests were conducted in a bifurcated tunnel model with branch tunnel ventilation. Three fire locations were considered. The characteristics of smoke movement and temperature profile under various fire source location scenarios were analyzed. The results indicate that when the fire source is not at the intersection, the ventilation airflow in the branch tunnel is diverted at the intersection before it is imposed on the fire source, which results in the actual velocity of ventilation air imposed on the fire source being less than the velocity of ventilation air in the branch tunnel. A new parameter, named the diversion coefficient, was introduced for convenient analysis. By substituting the diversion coefficient values into a classic maximum temperature rise prediction model for the single-line tunnel fires, good prediction results were observed. Moreover, a new dimensionless smoke temperature decay model was developed. The applicability of the model was validated using full-scale fire test data from previous research. The dimensionless temperature decay law of smoke was analyzed based on the newly established model. Results show that when the fire is positioned at the intersection, the decay coefficient of the smoke downstream of the fire decreases linearly as the ventilation rate increases, while decay coefficient of the smoke upstream of the fire decreases slowly at first and then increases with the increase of ventilation rate. When the fire source is not at the intersection, the branch tunnel ventilation conditions could be classified into three categories: sub-critical, critical, and super-critical velocity. Changes in the ventilation velocity within the branch tunnel have little influence on temperature decay process of smoke in the main tunnel under critical and sub-critical velocity conditions. However, under super-critical velocity conditions, the smoke temperature decreases rapidly after reaching the intersection. Furthermore, predictive models for the critical velocity of the branch tunnel under various fire locations were established based on theoretical analysis and experimental data. Within a specific range of heat release rate, the critical velocity is proportional to the cube root of the heat release rate. Compared to when the fire is located at the intersection, the critical velocity is reduced significantly when the fire is not in the intersection.

Study on flame height and temperature distribution of double-deck bridge fire based on large-scale fire experiments

Vehicle fire is one of the important causes of bridge fires. This study conducted large-scale actual fire experiments by simulating heat release rates (HRR) of oil tank truck fires with 50 MW, 100 MW, and 200 MW in rectangular oil pans of varying sizes. The flame shape and spatial temperature distribution at different HRRs were studied bycontrollingvariables such as wind speed,firesource location, andlayer spacing. The results indicated that the actual HRR of the large-scale fire exceeded the anticipated value. In large-scale fire experiments, flame splitting into two main peaks was observed along the long side of the rectangular oil pan due to the coupling effect of ambient wind, long side, and sidewall effect of the diagonal web member. The average flame height was determined through image processing, and subsequently, a formula for predicting flame height during bridge fires under varying heat release rates was developed through the use of dimensionless analysis and feature length analysis. The spatial temperature distribution in the vertical direction of the axis of the center of the fire source, the temperature distribution of the diagonal web member and the bottom of the dense crossbeams, which are critical components of the bridge, were also analyzed. Furthermore, the conclusion that the flame in the lower bridge space which split into two main peaks is validated by the results. The results of this study can provide important theoretical support for investigating bridge fire resistance strategies.

Fire Hazard Analysis on Different Fire Source Locations in Multi-Segment Converging Tunnel with Structural Beams

To investigate the fire risk in a complex tunnel with varying cross-sections, sloped structures, and dense upper cover beams, this study considered four fire source positions: the immersed tube section, confluence section, highway auxiliary road section, and four-lane sections of the main line. It also considered four beam spacings: 1 m, 1.8 m, 3.6 m, and 7.2 m. The Fire Dynamics Simulation Software FDS was utilized to create a comprehensive tunnel model. The analysis focused on temperature and visibility changes at a 2 m height under a 20 MW fire condition for different fire source positions. These changes were then compared with critical danger values to assess the safety of evacuating personnel within the tunnel. Subsequently, this study proposed corresponding emergency rescue strategies. The findings indicated that when the beam grid spacing exceeded 3.6 m, the upper dense beam gap showed a robust smoke storage capacity, leading to a reduced distance of high-temperature smoke spread. However, this increased smoke storage disrupted the stability of the smoke layer, resulting in a heightened smoke thickness. The location of the ventilation vent at the entrance of the immersed tunnel section caused a non-uniform ventilation flow under the girder, deflecting the smoke front towards the unventilated side and decreasing visibility in the road auxiliary area. In comparison to scenarios without a beam lattice, the presence of a beam lattice in the tunnel amplified fire hazards. When the beam lattice spacing was 3.6 m or greater, the extent of the hazardous environment, which is unfavorable for personnel evacuation, expanded. With the exception of the scenario where the fire source was located in the highway auxiliary roadway, all other conditions surpassed 150 m, which is roughly one-third of the tunnel length. Consequently, more targeted strategies are necessary for effective evacuation and rescue efforts.

Experimental study on the fire control and smoke transportation using sealing strategy in tunnel

Sealing tunnel portals is a favorable approach to controlling tunnel fires. This paper experimentally studied the influence of portals-sealing on fire behavior in a small-scale tunnel. A series of characteristic parameters, including fuel burning rate, O2 and CO2 volume fraction, and ceiling smoke temperature in the tunnel were measured. Besides, the flame self-extinguishment time, smoke transportation characteristics and gas temperature field at different fire source locations and sealing conditions were systematically investigated. Results indicated that the critical equivalence ratio for methanol fuel converted to ventilation-controlled tunnel fires is within 0.783–0.923. The combustion state is influenced by fire location. Fires occurring near the tunnel entrance are more prone to self-extinguishment than those away from the tunnel entrance. The critical volume fraction of O2 for flame self-extinguishment ranges from 13.5% to 15.3% and decreases with increasing gas temperature. Moreover, tunnel sealing significantly impacts peak gas temperature values, but hardly changes the longitudinal distribution pattern of temperature. The longitudinal distribution model of gas temperature under the action of the strong plume in a confined space is developed. This study provides guidance for fire risk assessment during the tunnel sealing process and contributes to the scientific development of sealing strategies.

Intelligent fire location detection approach for extrawide immersed tunnels

The confined spaces of extrawide immersed tunnels presents a significant challenge to the effective implementation of firefighting strategies in the event of a fire. In such an event, it is crucial to accurately and promptly identify the fire source location, choose the optimal smoke exhaust scheme, and closely monitor the smoke exhaust conditions. Existing methods rely on human experience to predict the location of a fire source, and few utilize neural network models with self-learning capabilities. In response, we propose a deep-learning-based fire location detection model that provides intelligent and timely smoke extraction schemes for application in extrawide immersed tunnels. Numerical simulation tools were used to create a proprietary database of immersed tunnel fires. We have compiled a comprehensive dataset for fire location detection tasks in extrawide immersed tunnels, integrating soot concentration and temperature data through expert knowledge. This dataset has been publicly released at (https://github.com/zhang-zhen-project/immersed-tunnel-fire-location-detection-data). To the best of our knowledge, this is the first dataset of its kind in the field of extrawide immersed tunnel fires. We compared six existing fire-location detection models: backpropagation neural network (BPNN) using multilayer perceptron (MLP), convolutional neural network (CNN), long short-term memory (LSTM), CNN-LSTM, bidirectional long short-term memory (BiLSTM), and CNN-BiLSTM. Our proposed CNN-BiLSTM-based approach achieved an exceptional detection performance and a remarkable robustness, with an F1 score of over 99% in the fire source location detection task, optimal exhaust damper combination task, and the detection task with different heat release rates (HRRs), even with sensors spaced at over 40-m intervals inside the tunnel.

Comparative Study of Numerical Simulation and Experiment on Temperature Distribution and Central Vent Flow Velocity in Ceiling-vented Compartment Fire

In this study, we conducted numerical simulations to analyze fire phenomena in a compartment with a ceiling vent and compared these numerical simulation results with previous experimental data. Based on the previous experimental conditions, under the heat release rate of 1.5 kW, the vent areas of 1% and 10% of the floor area and the fire sources both at the center and side of the floor were tested. Overall trends of temperature distribution and central vent flow velocity in the present numerical simulations were consistent with those in the previous experiments. The temperature within the compartment was observed to be higher when the vent area was smaller. For compartment with a smaller vent area, the temperature distribution showed minor variations with the fire source location. However, with a larger vent area, temperatures were notably higher when the fire source was at the side than at the center. The present numerical simulations slightly overestimated the temperatures from the previous experimental results, resulting in a bias factor of 1.07 and a model's relative standard deviation of 0.07 for temperature. Regarding the flow velocity at the center of ceiling vent, the fluctuations over time were more pronounced when the fire source was centrally located. When the fire source was at the center, the average central vent outflow velocity was higher for compartment with a larger vent area. When the fire source was positioned to the side, the vent area appeared to have minimal impact on the average central vent outflow velocity. It was also observed that the average central vent outflow velocity was higher when the fire source was centrally placed when compared to a side location. The present numerical simulations underestimated the previous experimental results for the average central vent outflow velocity, and the bias factor and the model’s relative standard deviation for the average central vent outflow velocity were 0.63 and 0.39, respectively.

Experimental investigation and numerical simulation of transverse heat flux attenuation during fire in utility tunnel

To analyze transverse fire protection, the distribution law and evolution mechanism of transverse heat transfer during fire in utility tunnels is required urgently. In this study, the experiment and numerical simulation were employed to investigate the evolution of transverse heat transfer under the curved ceiling. After validation, the fire dynamics simulation models with unstructured geometry were established to predict the transverse heat flux. Through the experiment and simulation, the fire source and target location under the curved ceiling were considered, and the prediction models of heat flux provided by the flame body before the impingement point and the heat flux provided by the extension flame body and thermal environment were proposed. Based on the proposed models, the shift relationship (competition mechanism) between the components provided by flame body before the impingement point and the extension flame body (including the thermal environment) under the curved ceiling was illustrated. The transverse heat flux attenuation of each component in different fire scenarios with different fire sources and target point locations was compared to reveal the competition mechanism among the components in the heat flux. This work provides a reference for the transverse fire protection design and risk assessment in utility tunnels.

Study on the Location Determination of Building Fire Points Based on Acoustic CT Temperature Measurement

Rapid perception of the location of the fire point is crucial to building fire emergency response in the process of building fire emergency response, which can help firefighters direct fire-fighting operations, effectively control fire sources, and provide strong evidence for the analysis and investigation of fire causes. This paper uses acoustic CT temperature measurement technology to determine the fire source location of a building fire and verifies its validity and applicability as follows: we construct various fire point numerical models based on the fire dynamics simulator (FDS) and obtain temperature data at different times; neural network means were used to obtain the time-of-flight (TOF) of an acoustic wave traveling; the large ill-conditioned matrix equation of acoustic flight under different meshing schemes was constructed and solved based on the simultaneous algebraic reconstruction technique (SART) and least squares QR-decomposition (LSQR), and then reconstruction temperature data under each scheme were obtained. Through the error analysis, the reconstruction effect of each reconstruction scheme is evaluated, and then the applicability of the location coordinate determination of the fire point is analyzed. The results show that the determination of the fire location under the conditions of various fire points in the building space can be realized by acoustic CT temperature measurement technology.

Study on moving fire smoke characteristics and mechanical ventilation system of tunnel

Limited by the narrow space of the tunnel, fire has become one of the important factors threatening the safe operation of subway especially the fire on a moving vehicle. Researches on moving fire through the large length-width ratio of tunnels are extremely lacking at present. This study investigates the characteristics of moving fire and the influence of mechanical ventilation under different conditions. First, a three-dimensional model of the tunnel with the moving train is established, and the dynamic mesh simulation is conducted and validated by the experiments. Then, the variation of smoke temperature distribution under different fire source intensities, train speeds, and blocking ratios are studied. Based on the smoke flow characteristics, the mechanical ventilation with different layouts of draught fans is investigated. It is found that the maximum growth rate of smoke spread is 70.90% with an increase of two fans. Finally, the influence of the tunnel shaft on the smoke characteristics under different fire source locations is discussed. When the fire source is under the shaft, the smoke discharge efficiency reaches the highest, almost 5.89% and 21.91% higher than other conditions. This study provides the basis and reference for the research and control of the tunnel moving fire.

Fire scenario-based damage assessment of ductile reinforced concrete buildings using computational fluid dynamics models

This study aims to develop a computational fluid dynamics (CFD)-based framework to assess the thermal behavior of reinforced concrete (RC) structures with non-uniformly distributed fire damage. To achieve this, a CFD model that can predict fire-induced temperature was validated using experimental data of an RC column specimen obtained from an existing study. It was then extended to develop the CFD model of an RC building frame to investigate the extent and pattern of damage to its columns and beams under various fire scenarios, combinations of fire intensity, ventilation coefficient, and fire source locations. The non-uniform temperature distributions of the columns and beams were used to modify the stress–strain curve of concrete and rebar and to perform a moment–curvature analysis to evaluate their residual flexural strength. The computed flexural strengths were compared with those obtained from existing design guidelines. The guidelines were determined to be extremely cautious compared to the results of the proposed method.

Long-distance migration law of radon in overburden of abandoned goaf during coal spontaneous combustion

The surface isotope radon measurement method (SIRMM) is widely used in fire source detection in abandoned mines. However, studies on the long-distance migration of radon during coal spontaneous combustion are lacking, which hinders the further popularization of this technology in coal fire prevention and control. For this reason, the migration law of radon in overlying strata in fire areas was studied through experiments and numerical simulation. The radon exhalation concentration of coal was found to increase at first and then decrease in the range of 30–350 °C through experiments. The radon concentration reaches the maximum value (557.1 Bq/m3) at 150 °C, which is 6.3 times higher than that at 30 °C. Based on the radon source term obtained by fitting the experimental data, the radon migration model of coal spontaneous combustion in abandoned goaf was constructed, and the dynamic distribution characteristics of the airflow, temperature, and radon concentration fields in the overlying strata area were analyzed. The internal relationship between surface radon and underground fire source was discussed. The simulation results revealed the sharp change in the porosity of the overlying rock causes radon concentration at the interface between the caving and fissure zones to increase continually with the process of spontaneous combustion, providing material and energy support for the long-distance radon migration. When the maximum temperature of the coal pile reaches 70 °C, the concentration of radon released from the coal pile increases rapidly to 13696 Bq/m3, and the radon from the underground space appears on the surface at this temperature. In the range of 70–150 °C, with rapid increase in radon released from coal piles, the surface concentration of radon also increased rapidly to 225 Bq/m3. At the high-temperature stage exceeding 150 °C, the concentration of radon released from coal piles exhibited a downward trend, resulting in a decrease in the rate of increase of radon concentration on the surface. A close relationship between the surface radon concentration and underground fire source temperature in the process of coal spontaneous combustion was observed. In the spatial position, the peak position of radon on the surface was highly consistent with that of the fire source longitudinally, which ensures the accuracy of the SIRMM to determine the location of the hidden fire source. This suggests that the SIRMM can accurately evaluate the fire source's temperature and fire area's development trend.

Experimental study on fire characteristics in a double long-narrow confined space connected by multiple lateral doors

A series of experiments were carried out within a scaled-down, elongated, and narrow space featuring multiple lateral doors. These experiments aimed to thoroughly examine the fire characteristics both inside the enclosed compartment and within the connected tunnel, which were induced by the fire occurring in the compartment. It shows that the classic maximum temperature model obtained from a single confined space underestimates or overestimates the values in the carriage and tunnel, and the three-region plume law cannot effectively cover the temperature values inside the carriage, the prediction relations for the double confined space scenario are proposed. The rate of temperature decrease beneath the ceiling in the double long-narrow confined space is greater than in a single confined space, with a significantly reduced impact of HRR on the decay rate. The study also provides a segmented characterization of the influence of HRR on temperature attenuation. Additionally, distinct flame extension and spillover patterns are observed at different fire source locations. These include ceiling jet flame overflow primarily from the upper part of the lateral door and direct overflow from the entire door height. The study's findings offer valuable insights for fire assessment and control in complex confined rail systems.

Enabling fire source localization in building fire emergencies with a machine learning-based inverse modeling approach

During building fire emergency response (ER), one of the most important tasks for firefighting is to locate the fire source. Currently, incident commanders on the fire ground determine the origin of fire sources, relying mostly on the reports of firefighters entering the building or the information from on-site witnesses. This inevitably requires firefighters to approach the fire origin and observe, causing significant dangers and risks. To overcome this issue, an inverse model for building fire source localization is developed. A machine learning (ML)-based inverse modeling approach is used to build the complex relationship between the fire source location and on-site temperature sensor measurements, so that an inversion of the fire source based on the temperature observations can be enabled. By taking fire in an actual building floor as a case study, the inverse model for fire source localization using simulated fire temperature data is established. ML methods of feed-forward neural networks (FFNNs) and long short-term memory (LSTM) are respectively employed. Results indicate that LSTM in stateless mode is more appropriate to establish the relative models because more accurate recognition of the fire source room can be achieved during the initial and growth stages of fire development. Besides, by considering different means of on-site data acquisition in building fire emergencies, fire source localization via stationary temperature sensor arrays and portable temperature measuring devices is realized. The formulated models achieve recognition accuracy of 99.5% (direct recognition) and 92.1% (in top-3 candidates) in the first 15 min of the fires, respectively. The effectiveness of using the ML-based inverse modeling technique for fire source localization in building fire emergencies is demonstrated.

Experimental investigation on effect of fire source location on compartment fire phenomena with a single natural ceiling vent

ABSTRACT The effect of fire source location (FSL) on compartment fire phenomena with a single natural ceiling vent was experimentally investigated under various vent area (VA) and heat release rate (HRR) conditions. Two FSL cases, where the fire source was located at the centre (FSLC) and on the side (FSLS) of the floor, were tested. In the bidirectional vent flow patterns of FSLC and FSLS, the detailed locations where the smoke outflow and the fresh air inflow occurred were different. Empirical correlations were proposed for predicting the smoke outflow areas. FSLC exhibited a higher central velocity of the outflow, larger estimated mass flow rate of the outflow, and lower temperatures inside the compartment than FSLS. The estimated mass flow rate of the outflow depended more on VA than on HRR. A previous correlation was more suitable for FSLS than FSLC in predicting the mass flow rate of the outflow.