Study On Fire Performance Of Typical Cables

The cable is widely used in various fields with the rapid development of modern society. The application of cable causes a lot of fire safety problems although it does bring a great deal of convenience. Cable is a combustible material not only enhancing the fire but also paving the way for the spread of fire along the direction it lays as soon as a fire occurs. What makes the situation worse is the cable made of polymer produces plentiful smoke during the combustion including toxic gas and corrosive one which threatens to people in a fire and impedes the rescue work.Polyvinyl chlorides (PVC), polyethylene (PE) as well as natural rubber are widely used cable materials in cable industry nowadays. Along the development of the nuclear power cable with flame retardant properties is increasingly demanded and the flame retardant cable materials like cross-linked polyolefin, inorganic applications are commonly put into use. In this paper, several types of commonly used cable materials are comprehensively studied for their combustion characteristic and impact in a fire by analyzing their chemical composition and conducting experiment.This paper begins with testifying several commonly used cable’s combustible sheath and insulative chemical composition through experiments and then studies their pyrolysis behavior by using thermo gravimetric-differential thermal (TG-DSC).The changes in the structure and composition of the heated material are analyzed, which takes into account the influence of heating rate and heating atmosphere on the pyrolysis of cable material.Because fire characteristics of materials in real conditions are not accurately revealed in traditional thermal analysis and the combustibility of homogenous material differs from the combustibility of cable with composite material, in this paper a cone calorimeter (CONE) is used to study the ignition time, heat release rate, formation rate of CO and CO2and other combustion characteristic with emphasis on the influence of cable structure and the external heating radiation intensity. Moreover, a micro-combustion analyzer (MCC) is utilized to study ignition temperature, heat release rate and other combustion characteristic of those cable materials and experimental results from cone calorimeter were compared. A simplified model of cable with multilayer materials and core is built to analyze influences on cable combustibility and explicit formulation of cable surface temperature is derived by using integral and reveals each relevant parameter on the solution.With the progress of the fluid calculation methods, as well as the rapid development of computer, CFD (Computational Fluid Dynamics) is commonly used in studies of fire and computer numerical simulation studies carried out in studying the cable combustion characteristics is necessary. Utilizing the cone calorimeter is considered as the common approach to test combustion characteristics in Small Scales Experiment and its numerical simulation is worth carrying out. Cone calorimeter of PVC cable is simulated in this paper and ignition time, heat release rate, CO and CO2and other data were compared with the experiment to test its feasibility. The simulation of large-scale fire scenario is widely carried out in present numerical simulation for fire. Experimented cable burned in a vertical bundle (IEC60662-3) simulates cable’s firing behavior in vertical space and the results have a good correlations with the real fire, which has a great significance in this filed. The numerical simulation used in this paper simulates the burring of PVC cable in a vertical bundle and the spread of flame and numerical calculation is carried out for combustion process, flame radiation, component of gas in smoke and different temperature of point set in the test-bed.Traditional cable fire hazard performance assessment standards are mostly simple cable retardant performance evaluation indicators (such as IEC60332series of standards); the evaluation results cannot be a true reflection of the cable flame retardant properties. Combustion characteristics are seldom used as evaluation index or combustion characteristics under different combustion conditions with different test methods to get the poor correlation between the parameters. The analytic hierarchy process was used to calculate the index weight, establish the index system of evaluation methods, which can effectively evaluate different types of cables flame retardant performance.