The collision of conductors of overhead lines under voltage in most cases results in the creation of sparks which, falling on a flammable substance on the ground, can cause it to ignite. Depending on the vegetation and meteorological conditions, this can later turn into a large-scale fire with extensive property damage. There are few research papers in this area and little available literature describing this phenomenon. In this activity, the problem of collision of conductors with the corresponding mathematical modeling is dealt with. In order to explain this phenomenon, it is necessary to know the flammability properties of certain substances (biomass) on which sparks fall after their formation. In addition, the conditions at the place of collision are important, such as: type of conductor, coordinates of the place where the conductor collided, weather conditions and the amount of current flowing at the point of contact. The way sparks are created, their movement in space and the change in temperature and amount of heat over time are described. Based on this, the critical diameter of the spark is determined from the aspect of igniting the biomass on which it falls. In order to confirm the presented theory, conductor collision experiments were performed in a real low-voltage power network and in the laboratory. The location and circumstances of a live conductor collision are random variables, so the number and size (diameter) of sparks (particles) are also random variables. Accordingly, it is important to determine which probability density function best describes the diameter distribution. Based on the critical diameter and the function The probability distribution of the diameter determines the probability of biomass ignition on the ground. From the aspect of protecting an element of the power grid from overload and short circuit, in addition to the existing criteria for selecting the type, and then the setting of the protective device, a new, additional one is introduced, which refers to protection against biomass ignition. on the ground due to the collision of conductors. The scientific contribution of this dissertation is reflected in the statistical approach to defining the number and diameter of electric sparks, and thus the probability of biomass ignition on the ground and the occurrence of a fire. An original algorithm was created for determining the critical spark diameter from the aspect of biomass ignition (critical temperature and the required amount of heat). A new criterion has been formed for the selection of time-current characteristics of protective devices in the power grid for the purpose of fire protection in the event of conductor collision. The results of this doctoral dissertation have practical applications, as they can provide answers to questions such as the probability of a fire occurring due to conductor collision. Based on this, the owner of the line can proceed with the design of its protection.