Characteristics of smoke generated during thermal decomposition of non-flame-propagating electrical cables

Introduction. Experimental identification of the properties of smoke generated during the thermal decomposition of insulation from non-flame-propagating (NG) cables is an important research problem.

Goals and objectives. This study experimentally evaluates specific smoke-generation coefficient of NG cables and sizes of solid smoke particles formed during their thermal decomposition.

Materials and methods. Experimental methods were used to measure the number, size, and mass of suspended solid smoke particles and the specific smoke-generation coefficient of substances and materials in a small-scale experimental setup. The study was conducted using samples of a control NG cable, KVVGng(A) 4 × 1.5, designed for fixed connections to electrical devices rated at up to 660 V AC and frequencies of up to 100 Hz.

Results and discussion. Fine solid smoke particles smaller than 2.5 μm, which pose the greatest hazard to evacuees during a fire, were found to form throughout the entire period of thermal decomposition. 
At the initial stage of thermal decomposition, the specific smoke-generation coefficient reached maximum values of 772–982 Np·m2/kg. After reaching its maximum, this coefficient decreased sharply and then reached a quasi-­steady level of 314–471 Np·m2/kg. 
Thus, thermal decomposition of NG cables produces an extremely hazardous gaseous environment containing fine smoke particles smaller than 2.5 μm, which can adsorb highly toxic gases generated during the process (carbon monoxide, hydrogen cyanide, hydrogen chloride, phosgene, and acrolein). The results can be used to determine the time until escape routes become untenable due to visibility loss and to assess the effects of exposure to smoke particles on the human body.

Conclusions. When the time until escape routes are blocked by hazardous fire factors is calculated in accordance with fire-safety regulations, failure to account for fine smoke particles may lead to underestimation of toxic exposure among evacuees.

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