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.

Smoke movement in a tunnel of a running metro train on fire

Research on the distribution of smoke in tunnels is significant for the fire emergency rescue after an operating metro train catches fire. A dynamic grid technique was adopted to research the law of smoke flow diffusion inside the tunnel when the bottom of a metro train was on fire and to compare the effect of longitudinal ventilation modes on the smoke motion when the burning train stopped. Research results show that the slipstream curves around the train obtained by numerical simulation are consistent with experimental data. When the train decelerates, the smoke flow first extends to the tail of the train. With the decrease of the train's speed, the smoke flow diffuses to the head of the train. After the train stops, the slipstream around the train formed in the process of train operation plays a leading role in the smoke diffusion in the tunnel. The smoke flow quickly diffuses to the domain in front of the train. After forward mechanical ventilation is provided, the smoke flow inside the tunnel continues to diffuse downstream. When reverse mechanical ventilation operates, the smoke in front of the train flows back rapidly and diffuses to the rear of the train.

Wave Motion of Smoke in Subway Fire Environment

Wave motion in subway or tunnel fire is an intrinsic property of smoke.As the pressure of smoke changes with mass of certain power,a kind of linear wave equation for smoke can be derived from the conservation equations of its mass and momentum,under nearly homogeneous zone assumption.The smoke movement of 4 subway fires was simulated with Airpak.By fitting the pressure-mass functions to the simulated data,wave equations of the smoke were derived,and wave motions of smoke were thus validated.It can be seen that smoke wave is a kind of mass wave,whose velocity is inversely proportional to smoke mass,and wave of a bigger fire propagates slower.

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.

A study on the characterization of smoke movement in shafts with different fire source positions

In this study,experimental and numerical simulation methods were combined to simulate the changing course of the temperature and velocity fields in nine different fire scenes. The characteristics of smoke movement in shafts with different fire source position factors(h/H) were quantitatively investigated,and the non-dimensional fitting function between the fire source position factors and the maximum temperature was deduced. The results showed that the location of the neutral plane moved upward as the fire source rose,and all the generated smoke spread to the upper areas;however,there was barely any smoke in the lower areas. The maximum temperature was inversely proportional to the fire source position factor;the higher the source position is,i.e. the higher the ratio factor is,the lower the maximum temperature is in the shaft. The experimental verification of the fire dynamics simulator(FDS) showed good results.

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。

扁平大空间船舶火灾烟气控制试验研究

为有效控制扁平大空间船舶火灾烟气蔓延,研究大尺度火灾过程中的油池质量损失速率、舱室温度分布、隔热效率和烟气控制效果。利用尺寸为30 m×24 m×2.3 m的模拟舱,在0.35、0.55和0.70 m等3种不同挡烟垂壁高度和机械通风条件下开展试验。结果表明:挡烟垂壁高度增加,油池质量损失速率峰值减小;挡烟垂壁高度对舱室上层烟气温度的影响比对下层气体温度的影响更明显,1.4 m以上空间温度峰值明显下降,而1.4 m以下空间温度峰值无明显变化。顶棚平均温度和隔热效率随挡烟垂壁高度增加而下降。随挡烟垂壁高度增加,火源区与非火源区同时控烟模式隔热效率从28.2%提升至50.8%,火源区单独控烟模式隔热效率从29.4%提升至54.7%。

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。

基于区段的地下空间环路通风排烟设计方法

为实现多匝道、多地块、内部空间复杂的地下空间环路烟气控制,提出一种区段式排烟方法:将地下空间环路与地块通过防火门分隔,形成独立的构筑物,结合隧道结构,确定风机房位置,划分区段,使烟气在一定区域内排出。以滨江地下环路为例,在隧道主线上均匀布置6个排烟风机房,并以此为节点,将隧道划分为8个区段。当火灾发生时,开启所在区段两端的风机进行排烟。由于各区段不设置固定分隔,整个风道是贯通的,因而各个风机房里的风机可互相作为备用排烟风机,以降低成本。采用数值模拟软件建立模型,对排烟口开启数量和间距进行模拟,确定排烟量为90 m^(3)/s、排烟口间距为30 m、开启8个排烟口的排烟方案。从人员疏散环境以及排烟效率对典型区段进行分析,结果表明:烟气控制在一定的范围内,人员疏散环境安全,排烟效率达到90%,证明方案合理可行。

环境压力对隧道竖井排烟影响的数值模拟研究

通过FDS数值模拟,研究环境压力对隧道火灾的烟气蔓延规律、烟气分层特性和竖井排烟效果的影响。研究表明:低压环境下隧道顶棚的烟气具有更高的温度,火源-竖井和竖井下游区域顶棚温度的纵向衰减曲线均符合指数分布,温度衰减系数随着环境压力的增加而减小;火源-竖井区域的烟气运动由热浮力主导,层化曲线变化趋势不明显,竖井下游区域层化曲线受环境压力的影响较大,随着环境压力的降低,层化曲线出现顺时针旋转的趋势,层化强度降低,烟气层稳定性下降;低压环境中竖井的排烟效果要优于常压状态下的竖井,且竖井底部产生吸穿现象的临界高度也有所增加。因此,与一般海拔地区相比,海拔较高地区的隧道发生火灾时,较高竖井的排烟效果更好,吸穿临界高度更高,对下游烟气层稳定性的影响更小,更利于疏散排烟。

某核电厂电气仪控房间火灾排烟温度分析

对某核电厂电气厂房的2个电气仪控房间进行了火灾排烟温度模拟分析。模拟计算了排烟系统不同时刻启动时,这2个防火空间室内空气温度的变化情况。结果表明:排烟系统启动后房间空气温度迅速降低,然后逐渐升高,最后随着火灾热释放速率的降低而逐渐降低;对于手动启动的排烟系统,需及时启动才能有效排除火灾中的烟气;需合理设置排烟防火阀,以保护排烟风机等。

海拔对隧道救援站列车火灾烟气蔓延特性的影响

采用三维非定常N-S方程和完全浮力修正的RNG k-ε湍流模型,基于滑移网格技术实现列车在隧道内的运动过程模拟,构建高海拔隧道紧急救援站列车火灾数值模拟方法,并利用现有动模型试验和隧道静止火灾试验数据验证数值模拟方法的可靠性和正确性,研究海拔对事故隧道、紧急救援站和列车中部车厢附近横通道内的烟气流速和温度分布的影响规律。研究结果表明:当着火列车驶入隧道紧急救援站时,活塞风主导了火灾烟气的蔓延趋势;在列车停车瞬间,随着海拔增大,事故隧道拱顶处和列车中部车厢附近横通道拱顶处的烟气流速峰值及温度峰值逐渐增大;列车停车后,活塞风逐渐衰减,烟气开始在隧道拱顶处向火源上游逆流;随着海拔增大,紧急救援站下游高温区域蔓延范围逐渐扩大,事故隧道拱顶处温度峰值随之升高;随着时间推移,高海拔与低海拔隧道拱顶处的温度峰值差异逐渐增大,可能对更高海拔隧道救援站内的人员安全造成更大的威胁;不同海拔处列车中部车厢附近横通道内人眼高度处的温度均超过330 K(对人体有危害),且在同一时刻,海拔越高,横通道内高温烟气层高度越低,烟气沉降速度明显加快。

高海拔铁路隧道紧急救援站排烟结构尺寸参数及排烟效果

为明确高海拔铁路隧道紧急救援站排烟结构合理的尺寸参数,以某高海拔铁路特长隧道为工程依托,数值模拟并分析救援站联络排烟道数量、直径以及平行排烟道尺寸对排烟效率、站内温度和能见度的影响。结果表明:总体上距火源越近,排烟效率、拱顶及疏散站台温度越高,且火源前端能见度显著高于后端,但不同排烟结构参数下的具体分布规律差异显著;随着联络排烟道数量增加,救援站排烟效率略有增加,救援站后端拱顶温度显著降低,部分联络排烟道会出现烟气倒流,救援站疏散站台特征高度能见度低于10 m的范围显著增加;随着联络排烟道直径增加,救援站排烟效率及救援站两端拱顶温度均降低,救援站能见度显著下降;平行排烟道尺寸对救援站排烟效率及站内温度分布影响较小,但随着尺寸增加,救援站疏散站台特征高度能见度低于10 m的范围呈“先增后减”的变化趋势,紧急救援站内联络排烟道数量设置不宜过多,推荐联络排烟道直径为3 m,平行排烟道断面宽度为5 m。