Fire Characteristics Research Articles

Ship Fire Detection Based on an Improved YOLO Algorithm with a Lightweight Convolutional Neural Network Model.

Ship fire is one of the greatest dangers to ship navigation safety. Nevertheless, typical detection methods have limited detection effectiveness and accuracy due to distance restrictions and ship motion. Although the issue can be addressed by image recognition algorithms based on deep learning, the computational complexity and efficiency for ship detection are tough. This paper proposes a lightweight target identification technique based on the modified YOLOv4-tiny algorithm for the precise and efficient detection of ship fires, taking into account the distinctive characteristics of ship fires and the marine environment. Initially, a multi-scale detection technique is applied to broaden the detection range and integrate deep semantic information, thereby enhancing the feature information of small targets and obscured objects and improving the detection precision. Then, the proposed algorithm employs the SE attention mechanism for inter-channel feature fusion to improve the capability of feature extraction and the precision of ship fire detection. Last but not least, picture transformation and migration learning are added to the small ship fire dataset to accelerate the convergence pace, improve the convergence effect, and reduce dataset dependence. The simulation experiments reveal that the proposed I-YOLOv4-tiny + SE model outperforms the benchmark algorithm in terms of ship fire detection accuracy and detection efficiency and that it satisfies the real-time ship fire warning criteria in demanding maritime environments.

Experimental investigation and modeling of the spread and burning behaviors of continuous spill fires on a water surface

Spill fires caused by oil leakage from tankers may pose a threat to the liquid transportation safety. In this paper, a series of large-scale gasoline continuous spill fire experiments were conducted on a water surface. The spread area, flame height, burning rate and the temperatures in the water layer were measured for different fuel discharge rates and ignition delays. The findings showed that the spread process can be well predicted by an existing spread model without ignition. For ignited conditions, four burning phases were identified, namely (i) spread burning phase, (ii) shrinking burning phase, (iii) quasi-steady burning phase, and (iv) extinguishment phase. The burning rate at the quasi-steady phase was found to be approximately 45–62 % that of pool fires with the same burning area. Subsequently, a model was developed for predicting the quasi-steady burning rate of spill fires. The flame height at the quasi-steady burning phase was also analyzed and correlated with the fuel discharge rate. Finally, a model was proposed to predict the maximum burning area at the spread burning phase and validated against the experimental data. The present results are of practical importance in understanding the spread and burning characteristics of continuous spill fires and the associated risk assessment.

Flame geometric characteristics of large-scale pool fires under controlled wind conditions

This paper presents an experimental study on the flame geometric characteristics of large-scale open pool fires under well-controlled wind conditions. Square fuel pools with combustion areas of 50 m2, 100 m2, 200 m2, 380 m2, and 400 m2 were used to burn RP-5 aviation fuel and diesel oil. A large-scale open jet wind tunnel generated a well-controlled and regulated horizontal wind field with wind speed (U) of up to 17 m/s. It was found that the evolution of large-scale pool fires under wind conditions involved four regimes, namely free vertical pool fire, tilted pool fire without flame drag, tilted pool fire with stable flame drag, and tilted pool fire close to the ground. The wind significantly affected the flame shape, the vortex structures, and the smoke layer characteristics around the flame. Five quantities of flame geometry were measured, including the flame base drag (ld), the flame length (L), the vertical flame height (H), and two flame tilt angles of θ1 (defined by the fuel pool center) and θ2 (defined by the flame base center). The critical wind speeds for flame base drag were obtained for the first time, and it showed a steady increase with the fuel pool size. With increasing U, the vertical flame height (H) decreased steadily, while the flame length (L) increased slightly, and the flame base drag (ld) and the flame tilt angles (θ1, θ2) increased steadily and leveled off for U>7–8 m/s. By introducing the buoyancy length scale and integrating the mixture fraction equation, the correlations for the five flame geometric characteristics were derived, which agreed well with the data of large-scale pool fires in this work and literature. The correlation for flame base drag also successfully predicted the critical wind speed for the occurrence of the flame drag.

Analysis of the Influence of Organophosphorus Compounds and of Aluminium and Magnesium Hydroxides on Combustion Properties of Epoxy Materials

This paper presents the influence of selected flame retardant additives on heat release rate and thermokinetics properties of epoxy materials made of epoxy resin—Epidian 5. The epoxy resin underwent flame retardant modification with the use of organophosphorus compounds (Roflam F5, Roflam B7) and Al(OH)3, Mg(OH)2. The fire characteristics of the analysed epoxy resin were determined using the cone calorimeter method, and thermal analysis of epoxy resin and the surface morphology of the analysed epoxy materials was with the use of an SEM microscope with an EDS attachment. The lowest value of the heat release rate was recorded for hardened epoxy resin containing one component additive 5% by weight of Mg(OH)2, as well as two component additive 10% by weight of Roflam F5 and 5% by weight of Al(OH)3. Moreover, the initial temperature of thermal decomposition of phase I of the modified epoxy resin samples with Mg(OH)2 (sample 5M) or organophosphorus compounds and Mg(OH)2 (samples 5B + 10M and 5F + 10M) were higher compared to the unmodified epoxy resin for these samples. Considering the surface morphology of the samples with Mg(OH)2, it can be concluded that the additives cause a homogeneous charred layer.

Lip height effects on pool fire: An experimental investigation

This work studies lip height effects on the heat transfer and combustion characteristics of pool fire. Fire experiments of n-heptane and ethanol with pool diameters (D) of 0.1 m, 0.15 m and 0.2 m were carried out, in which the lip height (h) was increased from 0 until the burning could not be sustained. Results show that for both fuels, as the lip height increases, the flame enters the pool and the flame sheet becomes wrinkled and deformed. The n-heptane fire shows two distinct burning behaviors inside and outside the pool, and the burning rate decreases with the lip height due to heat feedback attenuation and air entrainment restriction. The conductive feedback rate remains almost unchanged with different lip heights for both fuels. For n-heptane, the radiative and convective heat feedback rates generally decrease with the lip height, and the convective heat feedback fraction increases as the flame enters into the pool, suggesting intensified turbulence motion. For ethanol, the radiative heat feedback rate decreases monotonically with the lip height, and the convective heat feedback rate increases slightly, followed by a decrease with h/D. A mass flux correlation based on the modified stagnant film theory is developed for the convection-dominated pool fires, which is in good agreement with the experimental data.

Smoke propagation characteristics and influencing factors of high-temperature spiral tunnel fire

Abstract A tunnel fire may cause great damage to people, vehicles, facilities and tunnel structures if it is not effectively controlled. Therefore, it is very important to clarify the smoke propagation characteristics and influencing factors that can help to accelerate the removal of fire smoke and reduce casualties and property losses. In order to study the influence of slope, curvature radius and ambient temperature on smoke propagation during the tunnel operation period, based on the high-temperature spiral tunnel in Midi village, Yunnan Province, the internal and external environmental parameters of the tunnel were measured on site and the numerical simulation model was established by using the simulation software FDS, and the control variable method was used to study the fire smoke propagation characteristics of the tunnel with different characteristics. The results show that: the influence of slope on smoke migration velocity is non-linear, the greater the slope is, the greater the change of smoke spreading speed is; the smaller the curvature radius is, the greater the obstruction to smoke migration is, and the slower the smoke migration speed is; high temperature speeds up the smoke exhaust rate in the tunnel but has less promotion of the fire smoke migration.

Influence of growth rates, microstructural properties and biochemical composition on the thermal stability of mycelia fungi

Mycelium fungal species exhibit fire retardant characteristics. The influence of the growth media on the fungal growth rates, biochemical composition, and microstructural characteristics and their relationship to thermal properties is poorly understood. In this paper, we demonstrate that molasses can support the growth of non-pathogenic Basidiomycota phylum fungal species producing bio-derived materials with potential fire retardation characteristics. Scanning electron microscopy and Fourier transform infrared (FTIR) spectrometry were used to interrogate the microstructural and biochemical properties of the molasses-grown mycelia species. Thermal decomposition of molasses-fed mycelia was evaluated via thermogravimetric analysis interfaced with FTIR for real-time evolved gas analysis. The morphological and microstructural characteristics of the residual char post-thermal exposure were also evaluated. The material characterization enabled the establishment of a relationship between the microstructural, biochemical properties, and thermal properties of molasses-fed mycelia. This paper presents a comprehensive exploration of the mechanisms governing the thermal degradation of three mycelial species grown in molasses. These research findings advance the knowledge of critical parameters controlling fungal growth rates and yields as well as how the microstructural and biochemical properties influence the thermal response of mycelia.

Experimental and simulation study on the combustion fire spreading characteristics of aluminum composite panels with different thicknesses

AbstractTo study the effect of thickness on the fire spreading characteristics of aluminum composite panels, a reduced‐scale test bench was built to simulate the development of an overflow fire in a high‐rise building. Analysis of the fire spreading characteristics was performed in terms of the flame shape, flame height, fire spread rate, and temperature change. Then, an Fire Dynamics Simulatior model was established to verify the accuracy of the experiment using numerical simulations. The results showed that the flame shape of the 3 and 4 mm aluminum composite panels was a triangular cone, while the flame shape of the 5 and 6 mm aluminum composite panels was approximately rectangular. By establishing the dimensionless flame height, the flame height increased with the panel thickness. The fire spread rate of the aluminum composite panels increased first and then decreased upon increasing the thickness, which was consistent with the simulation results. The temperature change curves all showed a rapid initial increase and then a stable temperature in the later period. The simulation results conformed well to the experimental results.

Investigation and numerical reconstruction of a full-scale electric bicycle fire experiment in high-rise residential building

Electric bicycle (E-bike) fires have attracted more concerns recently in the field of fire safety science since several fatal fires occurred especially in residential buildings. This paper conducts a full-scale experiment of E-bike fire in a typical high-rise residential building of China. Fire and smoke characteristics as well as their influences on the residents’ safety and evacuation are studied. It was found that E-bike fire grows quite rapidly once ignited. Less smoke could spread into these residential rooms with closed door. Sealing the entrance door gap could effectively help to prevent the smoke. At the very first stage of the fire (around 4.5min from igniting), the residents could choose to evacuate downstairs. However, it is a better option to stay at home waiting for help during most of the fire period. Smoke from this fire did not exceed the height of the 10th floor in the staircase. Thus, for the residents on the 10th floor and above, to escape through the staircase upward to the building roof is another safe option. Fire Dynamics Simulator (FDS) was used to numerically reconstruct this fire. The numerical results show good agreement with the experiments. Based on accurate parameters and boundary conditions, FDS is verified to be feasible to conduct numerical reconstruction of E-bike fires for the purpose of assisting fire investigation.

Study on the effect of pressure on fire whirl combustion characteristics with different air-inlet widths

Study on the effect of pressure on fire whirl combustion characteristics with different air-inlet widths

Fire severity and post‐fire mulching effects on N transformation rates of temperate soils during the first critical winter–spring period

AbstractWildfires are increasing worldwide and, therefore, the extents of their on‐ and off‐site impacts are particularly important on soil erosion and nutrient cycles. To mitigate post‐fire erosion, mulching is increasingly being used, but its effects on the nitrogen (N) cycle are poorly known. To fill this gap of knowledge, gross N fluxes were modelled with Ntrace to compare with unburnt soils (US) the effects of intermediate (BI) and high severity (BH) burning, and post‐fire straw mulching (BIM and BHM). Two wildfires, two‐time points after the fire and 20 soil‐treatment combinations were studied. The mineralization of soil organic N to NH4+ (MSON) increased in BI (1.9–6.9×) with respect to US, with no clear trends observed in BH and mulched treatments. In most soils, NH4+ immobilisation in labile () and recalcitrant soil organic matter (SOM) () was more important than abiotic NH4+ fixation () and together were larger (3.5–11×) in BI than in US, while contrasting results were found depending on time after a fire (BH, BHM, BIM) and wildfire characteristics (BHM, BIM). Autotrophic nitrification () was included in the best model for all soils, whereas heterotrophic nitrification (OSON) was undetectable in most BH soils. Total nitrification ( + OSON) decreased with time after the fire in BH, increased in US and BI, and was differently affected by mulching depending on fire severity and time from the fire. While NO3− immobilisation () was frequently modelled only for BI soils, the dissimilatory NO3− reduction to NH4+ (DNRA) was retained in the best models for all soils and it was reduced by soil burning, whereas a short‐lived increase was induced by mulching. Denitrification (), modelled for most soils, was negatively affected by burning and positively by mulching. In summary, wildfires tended to increase MSON and , decrease DNRA and and had no clear influence on and nitrification. These effects are usually mitigated by mulching which, however, tended to enhance nitrification.Highlights Direction and magnitude of changes in soil gross N fluxes depend on fire severity. Usually, wildfires increased MSON and , and decreased DNRA and . No clear post‐fire trend was found for and nitrification. Fire effects on gross N fluxes are (partially) counterbalanced by mulching.

Numerical Study on Heat Radiation Attenuation and Flow Characteristics by Water Mist Curtains

A numerical study was conducted to investigate the attenuation effect of fire radiative heat and flow characteristics by water mist curtains. To shield a fire room with a diesel fire source with a maximum heat release rate of 1.8 MW, two mist curtain nozzles that operated at 1.0∼3.0 MPa were installed. The injection flow rate and mean diameter of droplets ranged from 9.1 to 15.8 lpm and from 87 to 58 μm, respectively. The radiative heat flux through the mist curtain was μ attenuated by 50%∼76% based on the given injection pressure range and appropriately followed the trends of previous experimental results. Comparing the flow characteristics with and without mist curtain activation, the effect of smoke shielding using the mist curtain was partially evident at the early stage of the fire; however, the shielding effect decreased, as the speed of the smoke flow increased during the peak period.

Experimental study on combustion characteristics of fire in data room

Through the combustion experiments on the cables and servers in a data room, the combustion characteristic parameters of the materials were obtained, and the materials were analyzed and evaluated from the aspects of heat release rate, gas concentration, flue gas temperature, and so on. The results show that network cable and electric cable can be ignited during the cable combustion test. In the overall fire combustion experiment of single server and the server group with three cabinets, the fire process is divided into three stages: initial growth stage, stable combustion stage, and combustion attenuation stage. The heat release rate, flue gas temperature, and CO2 concentration of the overall experiment have three peaks, respectively, 58, 98, and 134 kW; 100°C, 152°C, and 232°C; 1314, 2514, and 2988 ppm. The research results can provide some reference for design of fire protection system in data rooms.

Characterization and assessment of fire evolution process of electric vehicles placed in parallel

Electric vehicle (EV) fire accidents induced by the thermal runaway of li-ion batteries are increasingly frequent, and the fire dynamics of EVs parked in rows are still unclear. Hence the fire evolution process and characteristics of two parallel placed EVs were studied by analyzing the burning behaviors and thermal fields. The fire source was the battery pack of a battery electric vehicle (BEV). Results showed that the precursor to the BEV fire was the emission of white smoke from the chassis. Flames did not appear until the accumulated smoke exploded, and they engulfed both the EVs. The flame switched between momentum and buoyancy control on the vehicle scale. The maximums of the length and duration of the jet fires were determined. The maximum temperature of the EV fire was consistent with that of internal combustion engine vehicle (ICEV) fires, but the flame spread faster between the EVs compared to ICEVs. Pragmatic methods were proposed to quantify the fire evolution rate. The heat effect of the EV fire on humans was also quantitatively evaluated. These results provide a fundamental understanding of fire rules in a high EV concentration scenario.

Effect of pressure and stacking method on combustion characteristics of paper stacks

The experimental study on the combustion characteristics of paper stack fires was carried out in a low-pressure chamber. The variability of which with different environmental pressures and stacking methods were investigated. The mass of each group of experimental paper strips was 107 g. Three iron frames had the same volume, but different lengths and widths, and the strips were placed evenly in the frames to simulate different ways of paper stacking. The combustion tests of the paper stack were conducted at four ambient pressures of 101 kPa, 80 kPa, 60 kPa, and 40 kPa, respectively. The parameters measured during the experiments included mass loss, heat release rate (HRR), and flame temperature. The experimental results showed that the stacking type and pressure significantly affected the properties of the paper stack fire. For instance, the burning rate was influenced by the cross-sectional combustion area, pressure, and load height. There was a linear relationship between the ratio of the peak burning rate to the characteristic length of the bottom surface and the pressure-load height. The intensity factor of the paper stack fire was closely related to the environmental pressure: the paper stack fire under atmospheric pressure was generally a fast-growing one, which was a medium-growing fire under about 80 kPa. In comparison, that was a slow-growing fire when the pressure was 60 kPa.

Late Holocene fire regime reconstruction and vegetation dynamics of southern Monte desert region

This work presents the first Monte desert palaeofire record from an ephemeral northern Patagonia pond called Bajo de la Quinta (40° 55′ 42″S; 64° 20′ 19″W). The aims of this study are (1) to reconstruct past fire regime changes related to vegetation variability during the last 4000 cal yrs BP for the southern Monte region; (2) to discuss the importance of climatic versus anthropogenic control of fire regime at different periods; and (3) to integrate these results with other fossil pollen sequences located in North Patagonia (between 39° and 43°S), to infer centennial to millennial-scale changes in vegetation, linked to major palaeoclimatic variability. Long-scale fire-vegetation changes have characterised the southern Monte desert modifying vegetation intra-community patches distribution. The heterogeneous two-phase mosaic shrubland distribution is more resilient to fire at centennial to millennial scales than homogeneous high vegetation coverage. Southern Monte desert presents current fire regime characteristics since the last two centuries, which may be related to livestock introduction and the subsequent increase in human-induced- fires and changes in biomass availability. Also, the use of the composite Nothofagus pollen abundance index and the comparison between sequences located along the west-east precipitation gradient of North Patagonia (between 39° and 43°S), suggests synchronous but in opposite direction humidity availability long term changes affecting vegetation and fire behavior in Northern Patagonia during the Late Holocene.

Analysis of wildfires and associated emissions during the recent strong ENSO phases in Southern Africa using multi-source remotely-derived products

In southern Africa, drier conditions are more pronounced during the El Niño Southern Oscillation (ENSO) years, triggering wildfire activity and extreme drought conditions which, individually or together, lead to loss of crop productivity, deaths of livestock and wildlife, famine, degraded ecosystems, water quality and quantity. However, the fire characteristics in relation to the emissions from biomass burning and surface properties are only examined to a limited extent in the literature, especially in Africa, where anthropogenic activities largely determine the fire activity. This study uses the available data from multi-source remote sensing platforms to (1) analyse the spatial distribution of wildfires and associated emissions during strong El Niño (2015/2016) and La Niña (2010/2011) phases in southern Africa, and (2) examine the effects of the severe El Niño and La Niña years on the relationship between the emission parameters, vegetation parameters and climatic parameters. Generally, the results suggest more emissions from the wildfire in the El Niño phase than that of the La Niña. Overall, the Pearson’s correlation clearly shows the influence and the relationship between the climate parameters themselves and also with emission parameters.

Experimental Study of the Effect of Slope on the Spread and Burning Characteristics of a Continuous Oil Spill Fire

Elucidating the characteristics of continuous oil spill fires for different slope conditions can provide important theoretical support for the prevention of, and rescue strategies during, oil spill fire accidents. For this research, we conducted experiments to observe the spread and burning process of continuous oil spill fires under different slope conditions. The changes in physical attributes, such as flame spread rate, burning rate, heat convection at the bottom surface, and flame feedback radiation, were analyzed for the different slope conditions. The results showed that the shrinking phase becomes difficult to see, and the steady phase disappears when the slope increases in the spread and burning process. When the slope increases, the spread speed and spread area increase, and burning rate decreases. Compared with a non-burning process, the resistance to spread decreases in the burning process. We show that the slope directly affects the spreading process, and indirectly affects the burning process.

Status quo and challenges and future development of fire emergency evacuation research and application in built environment

Fire emergency evacuation study has been conducted for decades. In recent two decades, the fire emergency evacuation studies have been incorporating new technologies due to the high demands on efficient and safe evacuation for occupants who have various needs. The proposed fire emergency evacuation system from academic research and solutions from industry practices adopt different technologies to serve various evacuees. Therefore, this study conducts literature review to understand the status quo of current fire emergency evacuation research and practice. It shows that fire emergency evacuation studies mainly focus on the facility operation stage instead of design and construction stages. The facilities include residential buildings, education buildings, subways, shopping centers, etc. Three critical factors affect efficient and safe fire emergency evacuation in a built environment – facility physical features, fire characteristics, and human behavior. This study categories these new technologies, which are incorporated into the fire emergency evacuation research and practices within the recent two decades, into four groups: (1) Facility geometrical analysis, which includes the technologies such as BIM, GIS, VR and the combination of BIM/GIS/VR (2) Fire and smoke simulation, e.g. FDS and Pyrosim. The simulation output such as fire and smoke dynamics is incorporated into intelligent fire evacuation system (3) Crowd evacuation simulation software, e.g. Pathfinder, Massmotion; the output of simulation is used to develop personalized evacuation system (4) Indoor positioning system and mobile device/IoT technology to track and evacuate occupants intelligently. This study presents these new technologies used in the fire emergency evacuation systems and indicates that the development of an intelligent and personalized emergency evacuation system, which may track the evacuees in real time, is the future research trend.

Effect of fire spread, flame characteristic, fire intensity on particulate matter 2.5 released from surface fuel combustion of Pinus koraiensis plantation- A laboratory simulation study.

PM2.5 is one of major pollutants emitted from forest fires. High PM2.5 concentration not only affects short-term human respiration health, but also poses a long-term threat to human cardiopulmonary functionality. Therefore, it is of great importance to quantitatively assess the PM2.5 released by forest combustion in forest fire studies. In this study we examine relationships between the PM2.5 concentration and environment and fuel characteristics laboratory experiments. In the experiments, fuel beds with controlled moisture contents and loads were first built; then 144 ignition experiments were conducted for various combinations of wind speeds using a wind tunnel device. Fire behavior characteristics and PM2.5 concentrations released from fuel combustion were measured and analyzed. The experimental results show that the relationship between fire characteristics, fire intensity and the influencing factors of wind speed, fuel moisture content, and fuel load can be explained by the fundamental theory of forest combustion. Although PM2.5 concentration rises with the increase of wind speed, the decrease of fuel moisture content, and the increase of fuel load, there appears to be a fuel load threshold for a given combination of wind speed and fuel moisture content that the increase of PM2.5 concentration decelerates quickly after the load passes the threshold value. After screening fire behavior characteristics that affect PM2.5 concentration, we found that fire line intensity and flame width are the ones with the strongest association with the concentration. With flame width as independent variable, we have built two regression models to predict PM2.5 and fire line intensity which are treated as dependent variable; the models have high accuracy with R2=0.92 for predicting PM2.5 and R2=0.97 for predicting fire line intensity. Study results can be used as reference to protect the health of forest fire fighters, and can be helpful for forest fire smoke management.