FACTORS OF THE FIRE HAZARD OF CABLE PRODUCTS

Abstract

Formulation of the problem. In modern society, no citizen can do without electricity. Electrical devices greatly improve and facilitate our capabilities, but despite all the positive aspects of electricity, there is one aspect that negatively affects people's daily life - it is its danger. The analysis of the state of electrical devices showed that the most firehazardous of them are electric cables, wires and cords, which, having a significant combustible load, support combustion and contribute to the spread of fire over a considerable distance. The biggest cause of cable products catching fire is short circuits and overloading of the power grid. Overloading the network accelerates the ageing process of the insulation. The intensity of heating depends on the amount and time of the electric current on the conductor and its cross-sectional area. An increase in temperature significantly shortens the service life of conductors. The ageing of insulation is accompanied by a change in its protective and mechanical qualities. It becomes fragile, able to break and crack, which can lead to its breakdown or short circuit. In this regard, the main task is to carry out preventive measures that ensure the normal operation of the network, starting already during its design, installation and operation.
The purpose and objectives of the research. The purpose of the work is to determine the effectiveness of fire protection of cable products based on the analysis of fire hazard factors during the operation of household electrical networks. To achieve the specified goal, it was necessary to assess the impact of emergency modes of operation on the fire safety of cable products to increase their fire resistance and safety of use in electrical networks.
Research methods. To achieve the goal and implement the set tasks, the analytical method was applied. The methods of assessing fire hazard factors during the operation of household electrical networks are analysed. 
Research results. The article highlights the problems of fire hazards in electrical networks and preventive measures for their safe operation. The analysis of the fire situation showed that electrical products, which are widely used by the population and are in almost every home, turned out to be the most fire-hazardous. Electrical cables, wires and cords are considered extremely fire-hazardous parts of these electrical products. The high level of fire danger of electric cables is because they, having a significant combustible load and length, can not only support burning, but also contribute to the spread of fire to a considerable distance from the place of fire, and the products of their combustion are extremely  dangerous due to their high toxicity and corrosive activity for the health of people and material values. 
The correct choice of the cross-sectional area of the conductor, brand, type and method of laying electrical wiring makes it possible to ensure fire safety during the operation of electrical networks.
To simulate the occurrence of cable fires in underground tunnels, warehouses and basements, which pose a great fire threat to people, the FDS software was created, which analyses the change in the temperature field of the corridor and the temperature of the ceiling in underground objects when the firepower of cable passages changes.
The results of studies of the flame retardant properties of the PVC sheath of old and new cables using TG, FTIR and MCC experiments showed that the sheath of the old cable burns more strongly than the sheath of the new one. At the same time, gaseous products of cable pyrolysis are toxic and pose a danger to personnel and the environment. 
The main fire characteristics (time to ignition, peak heat release rate, and time to peak heat release rate) are considered, which quantify the effect of various conditions on the properties of the cable. The study of the influence of the cable sheath on the delay in the onset of the main peak of the rate of heat release, which corresponds to the schedule of non-combustible insulation, was analysed.
Conclusions. The analysed results of studies of the flame-retardant properties of cable sheaths showed that the sheath of the old cable pyrolyses and burns more strongly and more fully than the sheath of the new one. The gaseous products of pyrolysis of cables have certain toxicity and corrosiveness and therefore have certain risks for the safety of personnel and the environment. The main fire characteristics (time to ignition, peak heat release rate, and time to peak heat release rate) are considered, which quantify the effect of various conditions on the properties of the cable. The study of the influence of the cable sheath on the delay in the onset of the main peak of the rate of heat release, which corresponds to the schedule of non-combustible insulation, was analysed. Based on the analysis of the research results, it was found that to prevent the rapid spread of fire from the ignition source, it is best to use the developed new types of nanometre flame retardant coating and the intermediate protective box of the cable.