Forest fire smoke recognition based on convolutional neural network

Traditional fire smoke detection methods mostly rely on manual algorithm extraction and sensor detection;however,these methods are slow and expensive to achieve discrimination.We proposed an improved convolutional neural network(CNN)to achieve fast analysis.The improved CNN can be used to liberate manpower.The network does not require complicated manual feature extraction to identify forest fire smoke.First,to alleviate the computational pressure and speed up the discrimination efficiency,kernel principal component analysis was performed on the experimental data set.To improve the robustness of the CNN and to avoid overfitting,optimization strategies were applied in multi-convolution kernels and batch normalization to improve loss functions.The experimental analysis shows that the CNN proposed in this study can learn the feature information automatically for smoke images in the early stages of fire automatically with a high recognition rate.As a result,the improved CNN enriches the theory of smoke discrimination in the early stages of a forest fire.

An attention-based prototypical network for forest fire smoke few-shot detection

Existing almost deep learning methods rely on a large amount of annotated data, so they are inappropriate for forest fire smoke detection with limited data. In this paper, a novel hybrid attention-based few-shot learning method, named Attention-Based Prototypical Network, is proposed for forest fire smoke detection. Specifically, feature extraction network, which consists of convolutional block attention module, could extract high-level and discriminative features and further decrease the false alarm rate resulting from suspected smoke areas. Moreover, we design a metalearning module to alleviate the overfitting issue caused by limited smoke images, and the meta-learning network enables achieving effective detection via comparing the distance between the class prototype of support images and the features of query images. A series of experiments on forest fire smoke datasets and miniImageNet dataset testify that the proposed method is superior to state-of-the-art few-shot learning approaches.

Forest Fire Smoke Detection Method Based on MoAm-YOLOv4 Algorithm

To improve the performance of the forest fire smoke detection model and achieve a better balance between detection accuracy and speed, an improved YOLOv4 detection model (MoAm-YOLOv4) that combines a lightweight network and attention mechanism was proposed. Based on the YOLOv4 algorithm, the backbone network CSPDarknet53 was replaced with a lightweight network MobilenetV1 to reduce the model’s size. An attention mechanism was added to the three channels before the output to increase its ability to extract forest fire smoke effectively. The algorithm used the K-means clustering algorithm to cluster the smoke dataset, and obtained candidate frames that were close to the smoke images;the dataset was expanded to 2000 images by the random flip expansion method to avoid overfitting in training. The experimental results show that the improved YOLOv4 algorithm has excellent detection effect. Its mAP can reach 93.45%, precision can get 93.28%, and the model size is only 45.58 MB. Compared with YOLOv4 algorithm, MoAm-YOLOv4 improves the accuracy by 1.3% and reduces the model size by 80% while sacrificing only 0.27% mAP, showing reasonable practicability.

Evaluation of fire smoke control in underground space

The main goal of the fire management strategy is to avoid people interaction with fire hazards,therefore several studies are carried out for optimal escape route planning as well as smoke management and mechanical ventilation design.Underground spaces are a special case of study due to their technical characteristics that create different fire spread conditions compared to conventional buildings.In this paper,a comparative study on the fire smoke propagation is carried out taking into account the use and performance of smoke mitiga-tion techniques.The Underground Hazardous Waste Management Repository of Lavrion Technological and Cultural Park in Greece,is selected as a case study to achieve the paper objectives.A Computer Fluid Dynamic software is used to simulate various fire scenarios based on the specific characteristics of the underground space.Parameters that have significant impact on evacuation procedure and human health such as visibility and carbon monoxide concentration are monitored.Finally,the results are presented and an evaluation method is proposed based on evacuation simulation results,in order to predict the impact of the smoke control design on the conditions inside the underground space.The results reveal that the ventilation shaft(passive system)offers an effective smoke control without any other combined control system and that the installation of smoke curtains,which are activated on time,offers significant improvement on smoke spread control extending the available egress time(ASET)in case of fire.

Simulation of smoke flow and longitudinal ventilation in tunnel fire

Understanding the characteristics of smoke flow in tunnel fire is very important for tunnel safety. The characteristics of tunnel fire were analyzed. The smoke development in different situations of an engineering example was simulated using commercial CFD software PHOENICS 3.5 by field modeling method. The spreading rules and characteristics of concentration field and temperature field of smoke flow with different longitudinal ventilation speeds were studied, which may provide the theoretical background for evacuation design in tunnel fire. The effective measures of fire rescue and crowd evacuation were also described.

Experimental study on fire smoke movement in a multi-floor and multi-room building

Fire smoke movement of multi-floor and multi-room (MFMR) fire was studied at the model test building in State Key Laboratory of Fire Science (SKLFS). The ingredient, temperature, air pressure difference and air velocity of smoke were measured and analyzed. Meanwhile, the hazard of smoke ingredient to exposed occupants was analyzed based on the national standard, Occupational Exposure Limit for Hazardous Agents in the Workplace (GBZ2-2002). The experimental results showed that the maximum temperature difference in MFMR fire was located along the vertical height from the fire source. With the spreading and diffusion of smoke, the temperature of smoke layer would tend to be no difference. In the fire of woodpile and kerosene, the main smoke ingredients such as SO 2 , CO and CO 2 would first exceed human’s average physiological limit, while smoke ingredients such as NO and NO 2 would come behind. Because of the higher fluctuation range and frequency of air pressure difference of smoke in multi-layer building fire, the fire smoke would spread around everywhere of the passageway and made the human evacuation more difficult.

Numerical Investigation of Fire Smoke Transport in the Tsinghua University Sports Center

Fire Dynamics Simulator v3.0 was used to investigate and management in a realistic indoor sports center. An atrium fire test case assess fire smoke transport and ustrated the code＇s superiority over code-type empirical models for both accuracy and capability. Four fire scenarios in the Tsinghua University Sports Center were then simulated. The smoke layer＇s descent speed was predicted for each case. The importance of the door effect was revealed and an additional mechanical ventilation system for the building was proved to be of no help. The door effect must be carefully considered in future fire safety designs.

隧道内非对称双火源火焰特性及顶棚烟气最高温度研究

针对自然通风下隧道火灾非对称双火源协同作用下火焰特性和顶棚射流烟气最高温度开展研究。在缩尺寸隧道火灾模拟试验平台开展试验,结果表明,随着火源间距的增大,非对称双火源由完全融合到间歇融合,最后完全分离。火焰完全融合且火源热释放速率不同时,火焰呈现非对称形态,存在一个火焰高度,火焰高度主要由较大热释放速率火源决定。随着火源间距的增大,存在两个火焰高度,火焰高度最大值均大于对应工况火焰完全融合时的火焰高度。双火源一侧接收到的辐射热流随离开火源距离的增大而减小,固定水平位置处接收到的热辐射随着火源间距的变化会有波动,但整体变化不大。非对称双火源火羽流顶棚射流烟气最高温度整体随火源间距的增大而减小。当S/D<0.5时,烟气最高温度主要受两个火源热释放速率的影响,火源间距对烟气最高温度的影响较小;而当S/D≥0.5时,烟气最高温度主要受对应侧火源热释放速率的影响,而受临近火源热释放速率的影响较小。在此基础上,建立了非对称双火源顶棚射流烟气最高温度分段预测模型。

通风管道作用下烟气跨舱室蔓延规律研究

船舶舱室通风依赖通风系统,但通风管道极有可能成为火灾中烟气蔓延的隐蔽路径,从而造成火灾烟气的大面积扩散.本文针对船舶双舱室火灾中烟气跨舱室蔓延问题,考虑通风管道和走廊两种烟气蔓延路径,结合1/2尺度实验和数值模拟,通过分析火源舱室和毗邻舱室内温度和烟气流动的基本特征,重点探究了通风管道在烟气跨舱室蔓延过程中的作用.结果表明,在热浮力作用下,烟气将经通风管道更早进入毗邻舱室,流入的高温烟气主导毗邻舱室环境的同时限制走廊内烟气的流入.同时,通风管道内的烟气质量流率随两舱室间压力差增加而显著增加,且呈负指数关系.经计算,经通风管道蔓延的烟气质量流率约占实验平台流出烟气总流率的30%.

基于YOLOv5s的火灾烟雾场景检测改进算法研究

针对多种环境下早期火灾烟雾小导致的目标检测精度不足,以及特征表达能力不充分等问题,提出了一种基于YOLOv5s的火灾烟雾检测改进算法。首先,对火灾烟雾图像数据集的结构进行了详细分析;然后,根据数据集结构特点,在主干网引入了通道注意力机制与空间注意力机制;最后,增加了小目标检测层,以更加有效地关注小目标的检测。实验结果表明,改进后的YOLOv5s算法精确率达到了89.9%,其平均准确率均值PmA相较于原YOLOv5s的提高了5.0%。该模型在火灾烟雾检测方面表现出优异效果,对火灾烟雾的早期预警具有指导意义。

分岔隧道排烟策略下火灾烟气输运特性研究

以某分岔隧道为例,对发生火灾时不同通风方案下隧道内的温度场及烟气的蔓延规律进行了模拟研究,分析了匝道风压、主隧道出口段风压、主隧道加宽段风压对火灾烟气输运特性的影响。工况1与工况2分别采用提高匝道风压与提高主隧道出口段风压的通风方案,对比2种工况下温度场变化得知主隧道出口段通风效果优于匝道。工况3采用提高主隧道加宽段风压的通风方案,随着主隧道加宽段风压的增大,主隧道内高于60℃的高温区域不断缩小,主隧道出口段与匝道2 m高度内温度逐渐降低,主隧道加宽段风压的增大对隧道排烟有利,但并不显著。工况4采用增大匝道风压的通风方案,主隧道2 m高度内温度降低,匝道2 m高度内温度升高,增大匝道风压,匝道的排烟效果明显,由于匝道断面小,可考虑作为排烟通道。

建筑走廊内相邻防烟分区不同排烟方式相互影响研究

同一防火分区内相邻防烟分区采用不同排烟方式可能会对排烟造成不利影响。以某一医院走廊为例,采用FDS软件对同一防火分区采用不同排烟方式时的排烟效率进行分析。结果表明:机械排烟对自然排烟的排烟效果会产生影响;自然排烟会对机械排烟的启动时间有影响;对于本建筑排烟系统,自然排烟窗与机械排烟口正对设置情况下的整体控烟效果更好。相邻防烟分区采用不同排烟方式时,建议采用性能化方式进行优化设计。

通风方式对非对称隧道火灾烟气蔓延的影响

为研究非对称隧道内不同通风方式对火灾烟气蔓延的影响,利用PyroSim数值模拟软件构建非对称隧道模型,对隧道内烟气流速、温度分布和烟气运动进行研究,并分析了不同风速对人员疏散的影响。结果表明:上坡隧道内诱导气流与补充气流存在竞争关系,随着坡度差增大,烟气流速增加,烟气从上坡隧道排出,新鲜空气从平坡段隧道进入补充燃烧消耗;自然通风下隧道充满烟气,在纵向风速1.5 m/s下隧道环境得以改善;随着风速继续增大,隧道烟气流速紊乱,烟气层被扰乱。在实际非对称隧道中,建议火灾初期以1.5 m/s的纵向风速进行通风,待人员疏散后再增加风速加速排烟。

纵向风下大间距排烟阀集中排烟模式温度及烟气蔓延研究

为研究盾构隧道组合排烟模式下火灾时烟气流动特性,采用数值模拟方法研究了盾构隧道在纵向通风与集中排烟协同作用下的隧道温度分布和烟气蔓延长度。选取火源功率50 MW,分析不同纵向风速、排烟口间距及排烟量作用下隧道内温度分布和烟气蔓延长度。结果表明:大间距排烟阀组合排烟隧道火源下游的顶板下方纵向温度分布符合双指数衰减模型,隧道内温度分布情况主要受纵向风速和火源热释放速率主导,集中排烟量对隧道纵向温度分布影响不大;大间距排烟阀组合排烟模式下,火源下游的烟气蔓延长度随热释放速率的增大而增大,随排烟量的增大而减小,随纵向风速的增大而增大。对于大间距排烟阀集中排烟模式,具体设计应考虑三项原则:(1)纵向风速达到临界风速来抑制烟气向火源上游回流;(2)兼顾人员安全和漏风量的设计标准,在满足漏风量的设计前提下尽量缩短排烟阀间距;(3)排烟量达到一定量来控制烟气在两个排烟阀范围内。通过量纲分析,得到大间距排烟阀组合排烟模式下火源下游烟气蔓延长度预测模型。

A review on research of fire dynamics in high-rise buildings

Since serious fire occurred frequently in recent years, fire safety of high-rise building has attracted extensive attention. A National Basic Research Program （973 program） of China has been set up by Ministry of Science and Technology （MOST） of China in 2012 to meet the research requirements of fire safety in high-rise buildings. This paper reviews the current state of art of research on fire dynamics of high-rise buildings, including the up-to-date progress of this project. The following three subjects on fire dynamics of high-rise buildings are addressed in this review： the ejected flame and fire plume behavior over facade out of the compartment window, the flame spread behavior over facade thermal insulation materiMs, and the buoyancy-driven smoke transportation characteristics along long vertical channels in high-rise buildings. Prospective future works are discussed and summarized.

Experimental Simulation Study of Smoke Flowing Properties in Running Train

Tbe experimental simulation has been performed to investigate the smoke flowing properties within the 1/5 reduced-scale model of a sleeping carriage. The velocity field of the running train on fire is simulated in a wind tunnel of the State Key Lab of Fire Science, USTC (University of Science & Technology of China). In this paper, the fire-smoking properties and the variation of the temperature field in the sleeping carriage are analyzed. This paper introduces the simulation method of reducedscale experiment about the running train and the analysis or the experimental data. It provides the basis of experiment for the running train’s fire-safety and full-scale experiment in the future study.

矿井带式输送机火灾烟流特性及其预警防控综述

为有效防控煤矿井下带式输送机火灾事故,保障煤矿工作人员的生命财产安全,系统分析矿井带式输送机火灾的起火原因、燃烧特性、烟流特性、监测预警技术及防治措施,并基于当前研究现状提出展望。结果表明:引发带式输送机火灾的主要原因是摩擦温升、电气设备故障及明火;研究带式输送机火灾燃烧和烟流特性采用的巷道火灾模型及数值模拟相关参数具有一定局限性,需综合考虑运输巷道实际工况及环境等参数;国内虽有针对带式输送机火灾的监测预警系统,但其尚有不足,需引入5G、大数据及人工智能等新兴技术予以完善,并结合硬件探测及人员管理等方面,健全煤矿带式输送机火灾防治体系,进而全面推动煤矿安全智能化建设。

城市轨道交通超长隧道双车追踪模式下火灾烟气控制与人员安全疏散研究

[目的]城市轨道交通发车间隔一般较短,在超长隧道内会出现同方向行驶两列列车的情况,一旦发生火灾容易造成重大财产损失和人员伤亡,因此需对超长隧道双车追踪模式下的火灾烟气蔓延规律和人员安全疏散策略进行研究。[方法]采用FDS(火灾动力学模拟)软件和Path-finder软件,建立超长隧道火灾模型和人员安全疏散模型,对双车追踪模式下的火灾烟气蔓延规律,以及人员疏散进行仿真分析。[结果及结论]双车追踪模式下,前车尾部着火,通过临界风速纵向通风可保证前车火灾安全;火源下游烟气前锋的蔓延速度为3.20 m/s,至600 s时烟气蔓延至后车,620 s时烟气可完全覆盖后车;烟气温度沿隧道纵向衰减很快,且温度衰减符合双指数模型规律。双车追踪模式下,减小联络通道间距可减少人员疏散总时间,对人员疏散时离开列车的时间影响不大;开启列车端门和疏散平台一侧车门,可显著减少人员疏散时间。在超长隧道双车追踪的最不利火灾场景下,人员疏散存在困难,可通过减小联络通道间距保障人员疏散安全。

火源深度对深井立式空间火灾烟气流动特性及火灾探测方式的影响分析

为掌握深井立式车库、深地矿井等深井立式空间内火灾烟气运动规律,进而对此类火灾进行预警,以某深井地下车库为原型,构建深井立式空间模型,通过数值模拟分析火源深度和热释放速率对深井立式空间火灾烟气流动特性的影响,并掌握温度场和速度场的变化规律。研究结果表明:当火源深度足够大时,由于向上的浮力和速度减小,烟气可能无法到达井口,火源位置越深,其上方热烟气温度越高;并且火源深度对烟气流动的影响存在临界值,即临界深度,当火源高于临界深度时,火源可以从深井出口外卷吸空气,当火源低于临界深度时,火源仅能从深井内部卷吸空气。研究结果可为深井立式空间火灾的预测预警提供科学参考。

一种改进YOLOv5s的森林火灾烟雾检测算法

提出一种基于改进YOLOv5s的森林火灾烟雾检测算法。构建包含16573幅图片的火焰烟雾数据集,解决训练数据不足的问题,提高训练模型的泛化能力。设计一种轻量化的GC-C3模块替换原有的C3模块,减少模型参数量和计算量;将加权双向特征金字塔网络结构融合到Neck结构中,增强网络对于中小目标的检测能力;修改网络空间金字塔池化结构,使用SimSPPF结构替换SPPF,提高了网络的计算效率和检测准确度;将边界框回归损失函数CIOU替换为Focal-EIOU,加快模型的收敛速度,解决正负样本不匹配的问题。实验结果表明:改进之后的网络平均检测准确度提高2.3%,模型参数数量下降46.7%,模型计算量下降47.5%。