【作者】 王蔚；

【导师】 张和平；

【作者基本信息】 中国科学技术大学 ， 安全技术及工程， 2008， 博士

【摘要】 随着社会的发展,电缆在大型企业和民用建筑中的使用量大幅增长。电缆在给人们带来方便的同时也带来了火灾危险性。一旦电缆被引燃,所释放的大量有毒气体和腐蚀性气体对人员会造成危害,对环境物体会造成腐蚀,燃烧产生的大量烟雾,会降低能见度,妨碍人员逃生以及灭火救援,此外,在良好通风条件下,被引燃的电线电缆的燃烧火焰很容易沿着电缆的铺设方向快速蔓延,从而扩大火势,增大危害。聚氯乙烯电缆是目前电线电缆行业中用量最大且应用最广泛的一类电缆,这主要是因为聚氯乙烯具有低廉的价格和较高的阻燃性。因此本文以聚氯乙烯电缆作为研究对象,从微观分析入手,结合宏观实验,对其火灾特性及影响因素进行全面研究。本文首先从微观的角度对电缆可燃的外覆材料聚氯乙烯电缆料进行实验研究。利用热重-差热(TG-DTA)联用分析仪研究了PVC电缆料的热解行为,分析了材料在受热过程中结构和成分的变化,考虑了升温速率以及加热气氛对电缆料热解过程的影响,并与PVC树脂的热解过程进行了比较,采用不同方法对聚氯乙烯电缆料的热解动力学进行研究,为研究PVC电缆的火灾行为提供最基础的数据支持。由于传统的热分析方法不能提供火灾燃烧的真实条件,且PVC材料的热解性能与PVC电缆的燃烧性能还存在一定差异,因此利用锥形量热仪对成品PVC电缆的点燃、热释放速率、质量损失速率、烟气产生速率等火灾特性参数进行研究,重点考察了电缆的结构、电缆护套的厚度、外加热辐射强度等对这些火灾特性参数的影响。基于锥形量热仪初步建立了带有线芯层的简化电缆点燃模型,对电缆点燃性能的影响因素进行了分析,同时采用积分方法对电缆表面温度进行了推导,显式的反映了各有关参量对解的影响。全尺寸实验是研究电缆火灾特性的重要手段。电缆能否发生火蔓延,是评价电缆火灾危险性的一个重要指标。为了研究电缆的火蔓延过程,必须开展全尺寸的实验研究。因此,在原有全尺寸多功能热释放速率实验台的基础上,研制并建设了成束电缆火灾特性实验台,利用该实验台对成束PVC电缆的火蔓延炭化长度、热释放速率、烟气产生速率等火灾特性参数进行测量,分析成束PVC电缆的火灾行为,研究各参数之间的关系,考察了电缆护套厚度、电缆可燃体积、电缆排布方式、引火源功率等因素对成束PVC电缆火蔓延过程的影响。研究表明,若电缆能够蔓延至项部,则热释放速率在火蔓延过程中存在两个峰值,火蔓延速率存在一个先减速后加速的过程。引入热烟比的概念,即热释放速率峰值与烟气释放速率峰值之比,表征PVC的燃烧程度及反应方向,结果显示,在火蔓延的不同阶段,热烟比存在很大差距。此外通过理论推导,给出了PVC电缆维持向上火蔓延的两个临界判据,并用实验数据进行了验证。更多还原

【Abstract】 With the development of the society, large amount of cables are being used in power plants and civil buildings. They bring us great convenience and fire hazard at the same time. Once ignited, they will release large amount of toxic gases and corrosive gases, which can lead to great damage to human beings and surrounding objects. Moreover, the heavy smoke will reduce the visibility and it’s hard for people to evacuate and to put out a fire. In well-ventilated conditions, the flame of burning cables is easy to spread along the laying direction, which will enlarge the fire extent and increase the fire hazard.Polyvinyl chloride (PVC) cables are the most popular cables in wire and cable industry at present. This is mainly because of its low price and great fire performance. So in this paper, PVC cables were selected and tested on different scale experiments to explore their fire behavior and impact factors.First of all, PVC cable materials were tested in micro-scale experiments. Thermal decomposition characteristics were analysed with TG-DTA analyser instrucment. The structure and component change were studied. The effects of heat-up rate and atmosphere were analysed. The difference between PVC resin and PVC cable materials was compared. The kinetics of thermal decomposition was discussed, which provided foundermental support for fire performance research on PVC cables.Since the way of tradational themal analysis can’t provide burning conditions of real fire and there’s a little difference between the burning behavior of PVC material and that of PVC cable, small scale experiments on PVC cables were carried out with cone calorimeter. Many fire performance parameters were discussed, such as time to ignition, heat release rate, mass loss rate, smoke production rate etc.. The effects of cable structure, thickness of cable jacket and irradiance level were studied. A simplified cable ignition model was established based on the cone calorimeter. The effects of different impact factors were analysed. Surface temperature of cable was deduced using integral method, it can reflect the effects of impact factors explicitly.Full-scale experiment is an important way to study the fire performance of cables. Whether or not flame spread happens will effect the evalution of cables’ fire hazard . So a full-scale platform for fire performance of bundled cables based on the ISO 9705 heat release rate measurement platform has been established at USTC. The parameters such as char length, heat release rate, smoke production rate etc. were obtained. The fire performance of bundled PVC cables were analysed and the relationship among these parameters were studied. The effect of jacket thickness, combustible volume, installation type and burner output to the flame spread of PVC bundled cables were discussed. The results show that if flame spread happens, there are two peaks of heat release rate during the spread process. The spread rate decelerated first and then accelerated. The ratio of peak heat release rate and peak smoke release rate was used to reflect the burning extent and reaction direction. Two critical conditions were deduced to judge if the fire propogation could occur.更多还原