# Application Assessment of Electrical Cables during Smoldering and Flaming Combustion
## 3 Results and Discussion
(**b**) Smoldering combustion process initiated by electric current flow through the copper wires. (**c**) Flaming combustion. The changes in the average concentration of smoke (Y) as a function of time for all cable samples in the smoldering combustion process initiated by a heating field or electrical current flowing through the wires and for flaming combustion are shown in Figure 4a-c.  
Figure 4: _Cont._  
Based on the results obtained for the smoldering combustion process initiated by a heating field, it can be stated that, after heating the heating plate, i.e., from about 150 s, the smoke particles began to reach the ionization chamber. In this phase of the fires, the smoke was invisible to the human eye. It should be emphasized that there was a clear difference between the results obtained for cable F and those obtained for the other cables. Particles formed in the combustion process of this cable reached the ionization chamber after a longer time, after 350 s of testing. The maximum smoke concentration value for this cable was the smallest value out of all those obtained for the cables tested and accounted for about 50% of the smoke concentration values of the other cables. For the extinction modulus, the difference was much greater, as the value of the cable F extinction modulus constituted 5% of the average value of the remaining cables. This confirms the observation that the smoke particles emitted during the combustion of the cable were only small (there were no large particles that would have scattered the light of the densitometer). This clear difference was due to the use of silicone rubber, which burns with the release of other products of combustion, and the process usually occurs at higher temperatures. Meanwhile, cables C and H achieved their maximum smoke concentrations 250 s earlier than the others. During the smoldering combustion initiated by electric current flow through the copper wires of the cable samples, it was found that the insulation of cable F was cracked due to its internal heating. Cracks appeared on the surface of the cable, from which smoke emitted from the burned internal insulation was observed. For all cables, an increase in the smoke concentration parameter (Y) to the value of approx. 1 was observed, whereas sample F, after the heating and cracking of the insulation, burned without a flame over the entire surface, and in 850 s the measured value of Y was 2.65. Based on the results obtained for flaming combustion, it can be concluded that, for all cables, the smoke concentration parameter Y increased. Cables C and F did not have a sharp maximum. As expected, the smoke emitted by cable F was detected by the ionization chamber. It should be emphasized that the combustion of cable A in the course of the test started from the beginning of the test, while the increase to the maximum value was  
Figure 4: Changes in smoke concentration (Y) as a function of time for all cable samples in smoldering and flaming combustion processes. (**a**) Smoldering combustion process initiated by a heating field. (**b**) Smoldering combustion process initiated by electric current flow through the copper wires. (**c**) Flaming combustion. slower (similar to the increase in the extinction modulus) and differed from those of the other cables. It can be concluded that the largest extinction modulus (m) values were achieved in the course of the smoldering cable combustion tests initiated with the use of a heating field, while the smallest values were measured in the course of the flaming combustion tests. Moreover, the smallest values of smoke concentration (Y) were measured during the smoldering combustion initiated by electric current flow through the copper wires (exception: cable F). The highest values of smoke concentration (Y) were measured for the smoldering combustion cables initiated by a heating field.