# Application Assessment of Electrical Cables during Smoldering and Flaming Combustion
## 1 Introduction
Based on tests of upward flame spread over 35 commercial electrical cables with a copper or aluminum core, [PERSON] and [PERSON] [18] found that the metal core acted like a heat sink and slowed down flamespread. [PERSON] et al. [19], based on small-scale experiments (TG, FTIR and MCC) with new and aged PVC cable sheaths, found that aging has a strong effect on the heat release rate and toxic gas emissions. Polyvinyl chloride (PVC) is one of the most versatile thermoplastic materials and is widely used in electrical cables due to its processability in the form of flexible PVC produced by adding 30-40 wt.% additives, especially plasticizers, to lower the glass transition temperature. Flexible PVC ignites more easily and burns at a higher rate than rigid PVC because the plasticizers are usually combustible [20]. For this reason, most of the publication concerns the fire behavior of flame-retardant PVC cables, including their decomposition, swelling and spontaneous ignition [21]. The results of the PVC cable tests also allowed the modeling of these cables fires. The numerical simulation of the PVC cable fires required the modelling of cable pyrolysis, which was extremely challenging due to the geometrical complexity and the wide range of different PVC compositions and plasticizers. The different approaches for modelling the kinetics of PVC degradation have been studied by [PERSON] and [PERSON] [22], who concluded that two parallel reactions are needed to describe the first stage of PVC degradation, while a single reaction is required for the second. There are two main typical operating principles for smoke detectors--ionization and optical (photoelectric) detection [23]. Sensitive detectors are used in areas where even smoking is prohibited, such as toilets and schools. Smoke detectors in large commercial and industrial buildings are powered by a central fire alarm system [24]. It has been accepted that a properly functioning smoke alarm reduces the risk of fire death in residential buildings by 50% to 70% [25; 26]. The US Fire Administration reports that over 85% of homes in the United States have at least one smoke alarm installed and that 60% of residential fire deaths occur in homes without a working alarm. An analysis of data from the US Fire Administration's National Fire Incident Reporting System (NFIRS) and the NFPA's Fire Service Survey found that, between 2003 and 2006, 31% of reported home fires and 40% of home fire deaths occurred in the absence of smoke alarms [27]. Ionization and photoelectric alarm ionization and photoelectric alarms work by different mechanisms to detect invisible/fine and visible products of combustion, respectively [28]. Photoelectric alarms use optical sensors and are more likely to respond to slow, smoldering conditions. The principle of operation of ionization detectors is based on a modified theory that considers the functionality of the soot particle charge fraction in addition to the generally accepted dependence on particle size and density [29]. Smoke detectors of the ionization or photoelectric type are designed to activate rapidly and thus provide time for alarmed occupants to escape from most residential fires, although in some cases the escape time may be short [30; 31]. Smoke detectors enable the detection of a fire at an early stage of its development. Smoke extinction measurements are used in assessing smoke detector characteristics. Ionization detectors tend to have higher sensitivities at high concentrations of small particles (e.g., when burning wood), while smaller ones have higher sensitivities at low particle concentrations (e.g., large particles of smoke generated during smoldering combustion). Optical detectors have the highest sensitivity to smoke particles with a diameter equal to the wavelength of light and low sensitivity to smoke particles with a diameter much smaller than the wavelength of the light [32].