夹层内PVC电缆燃烧特性分析

Study on burning characteristics of PVC plenum cables

通过建立现代建筑夹层模型,研究铺设大量电缆可能引发的火灾效应,探索夹层内电缆火灾特性,找到电缆在夹层内的合理铺设方式,为制定科学合理的防火对策提供依据。本文主要讨论了不同因素对火焰蔓延速度,烟气温度和有害物质生成浓度的影响,并评价了有害物质的毒害作用。结果表明,夹层内铺设电缆的数量、铺设角度和距离夹层底层远近对电缆的燃烧特性有明显影响。1根电缆时火焰蔓延速度为3.17×10^(-3)m/s,两根时为3.96×10^(-3)m/s;1根电缆情况下,铺设角度由45°到垂直状态时,蔓延速度由4.01×10^(-3)m/s增加到26.09×10^(-3)m/s,产生烟气温度和烟气中有害成分浓度也随之增高;垂直条件下,烟气质量浓度在230 s时达到最高值12.50 g/m^3,产物CO的质量浓度远远超出OSHA标准(1.88 g/m^3)。因此,电缆在夹层内垂直燃烧时发生火灾的危险性更大。

The present paper is aimed to find out the mechanism leading to the plenum cable fire so as to establish a realistic and practical way for in-laid cable in hope to prevent building fire. In addition, probable cable fires in plenum were also simulated in our paper. To make clear the effects of different factors, such as the gas temperature and the hazardous substance concentration, at the flamespreading speed, evaluations have also been done of the damaging power of hazardous substances. The results of our study demonstrate that, the quantity and the slanting angles of the laid-in cables and the distance between the inlaid cables, as well as the plenum bottom, may all have significant effects on the cable combustion characteristics. For example, when there was one single cable in the plenum, the spreading speed of the flame would be 3.17× 10^-3 m/s, while two for the cable 3.96 × 10^-3 m/s. The more cables there were laidin, the faster the fire spreading speed and the higher the smoke tem- perature would be. In the case of a single cable, when the slanting angle increased from 45° to 90°, the spreading speed of flame would grow from 4.01 × 10^-3 m/s to 2.609 × 10^-4 m/s. The raise of slant angle resulted in an increase of the spreading speed of cable fire and the concentration of hazardous substance, but in a decrease of smoke temperature. The fire spreading speed, however, tends to increase when the smoke temperature goes up with the increase in the distance from the plenum bottom. Moreover, under the vertical condition, the concentration of smoke gas would get to the highest level, that is, 12.50 g/m^3 at the 230 seconds. In that case, the amount of CO generated would come far beyond the OSHA standard of 1.88 g/m^3. Meanwhile, if we intend to rack the cables, the way of their layout would play a more significant effect on the fire risks.