棉垛早期阴燃火灾特性及棉花仓库主动吸气式复合探测研究

以棉花仓库消防安全为背景,在火灾探测标准燃烧室内开展了棉花垛早期阴燃特性试验和吸气式复合探测试验研究。分析棉花垛早期阴燃过程中的质量损失、烟气浓度以及图像特征变化,以棉花垛顶部着火为例,归纳了阴燃过程大致包括水平蔓延及竖直蔓延两个阶段,并分析了各阶段特性。利用吸气式复合烟气诊断,分别记录了吸气管道出口的CO体积分数变化以及吸气式探测器的输出信号。结果表明,CO的响应时间明显快于吸气式探测器且几乎不受采样孔位置的影响。由于阴燃温度低,羽流湍浮力相对较弱,而CO气体密度远小于烟颗粒密度,在吸气管道中表现出更好的迁移性。因此,针对大空间棉储仓库,可以采用吸气式感烟火灾探测器与CO气体探测器相结合的复合探测手段,也可以考虑在传统吸气式探测器内部整合CO探测部件以提高探测报警速度,同时有效降低误报、漏报率。

Early smoldering characteristics of cotton block and correlative compound aspirating smoke detection

By setting the background of study as fire protection of cotton warehouse,the goals of this research are to experimentally investigate the smoldering characteristics of cotton blocks at the very early stage,to compare the change of CO concentration which is a major smoldering product and the response of conventional aspirating smoke detector and finally to provide engineering suggestions on early fire detection in a typical cotton warehouse.Two different series of experiments were designed and conducted respectively.One of them was the study of smoldering characteristics of cotton blocks with different sizes conducted in an ISO standardized combustion room.The smoldering rate,ionization smoke concentration on the ceiling and image information were recorded and analyzed by electronic balance,measurement ionization chamber(MIC) and CCD camera,respectively.It was observed that both horizontal and vertical smoldering spreads occurred if the cotton block was ignited from the top.After ignition,the smoldering first spread over the horizontal surface of cotton block at a relatively slow rate;when the burning area has reached to some extent,it spread vertically at a significant faster rate.Another experiment was carried out to study the responses of fire detectors to typical smoke or gas signal.It has shown that the CO response time of MRU was 1 2.3 times faster than the aspirating detector due to different air entry points.The reason of better transportation of CO in the aspirating pipelines lies on a relatively low smoldering temperature which causes weak turbulent buoyancy of smoldering plume.Furthermore,the density of CO is much smaller than that of smoke particle.The study suggested that a combined technology of aspirating smoke detection and CO gas detection should be adopted in large space especially in a cotton warehouse.The fire detection sensitivity at early stage of smoldering could be greatly improved.Besides,lower false and failure rate of fire alarm could be expected as well.