# Application Assessment of Electrical Cables during Smoldering and Flaming Combustion
## 1 Introduction  
The fire safety of buildings depends on the introduction of fire-fighting equipment in these buildings, which is responsible for detecting fires in their initial phases. As a result of detection, the building's occupants are alerted to the danger, evacuation routes are identified, roads are smoked, smoke is prevented, and the fire is finally extinguished [1]. However, for this to be possible, the speed of activation of safety systems is crucial, which depends primarily on the speed and reliability of the activation of smoke detectors [2]. The fire risk of electrical cables and wires is significantly determined by the combustible properties (fire characteristics) of the coating and insulation materials that make up their structures, together with the operating conditions and the environments in which they are used [3, 4]. Electric cables and wires are integral parts of buildings and are exposed to the effects of flames, just like other elements of equipment, and, in many cases, they are also a source of ignition, resulting from, inter alia, short circuits, accidental sparks and electric arcs [5, 6]. Fires in buildings represent the greatest danger to human life and health. According to data published by the National Fire Protection Association (NFPA) in 2019 showing statistics from 2012 to 2018, 10% of fires in residential construction were caused by failures of electric cables [7]. In addition, cable failures that caused fires were responsible for 19% of deaths and 10% of injuries to inhabitants [8]. Fires in the interiors of buildings are characterized by high dynamics which reduce the time for safe evacuation. Data published in the literature clearly indicate that only 3-4% of people die as a direct result of flames, while about 80% die as a result of toxic fire gases. Based on an analysis of demographic data and morbidity, it is estimated that between 310,000 and 670,000 people (excluding firefighters) in the US are exposed to fire in residential fires each year [9]. The vast majority of fires in buildings include organic-origin materials in the isolations and sheaths of electric cables. The thermal decomposition products of these materials are mainly [10; 11]:  
Nitrogen oxides (NOx: nitrogen oxide (NO) and nitrogen dioxide (NO\({}_{2}\)));  
Carbon oxide (CO) and carbon dioxide (CO\({}_{2}\));  
Hydrocarbons, mainly polycyclic aromatic hydrocarbons (PAHs);  
Oxygen, hydrogen, fluorine, chlorine, sulfur, nitrogen, and bromine compounds, such as aldehydes, acrolein and benzopyrene, determined as volatile organic compounds;  
Sulfur oxides, mainly SO\({}_{2}\); and  
Solid particles (PM) containing carbon black and a lot of toxic carbon, hydrogen and oxygen compounds, as well as isocyanates, as products of burning PUR foams. The composition of thermal degradation products depends mainly on the type of combustible materials and the type of combustion process--flaming [12] or smoldering [13; 14]. Characteristic products of flame combustion are carbon dioxide and nitrogen oxides. The emission of these compounds is strongly dependent on reaction kinetics, flame temperature and oxygen diffusion to the combustion zone. Smoldering processes occur with organic combustible materials that form charred layers when heated. The phenomenon occurs with oxygen deficiency, resulting in the separation of incomplete combustion products, among which carbon monoxide and polycyclic hydrocarbons predominate [15]. Electric cables have a complex construction; wire insulation and cable sheaths can be made of different materials. This greatly impedes the identification of the products of the combustion of cables, such that only a few studies have examined basic combustion in real cable fires [16; 17]. Piloted ignition time and flame spread rate were studied for several commercial cables under various externally applied radiant fluxes, showing the similarity between the pyrolysis temperature of cable insulation and the ignition temperature [5].