In this paper for exploring the mechanisms of formation of traumatic situations, the conditions and circumstances that contribute to them, and the study of the course of events leading to dangers in mechanized processes in agriculture the mathematical apparatus was used developed by the probability theory for Markov random processes with discrete states and continuous time, when the transition of a system from one state to another is possible at any unknown random time. It has been established that the processes of traumatic situations and their consequences can be represented by graph structures, using four states of the "man-machineindustrial environment" system: working and defective conditions of the tractor (machinery), hit of the machine operator into a dangerous and emergency condition (situation). A system of Kolmogorov differential equations was made, in which unknown functions are the probabilities of states of the system as functions of time with the normative condition that the sum of these probabilities will be equal to 1. Introducing the matrix of the intensity of events, the Laplace transform was used to solve the system of differential equations, which allowed the system to be transformed into a linear algebraic system. Elements of the matrix of intensities of the flows of events that bind separate states of the graph were given taking into account the probabilities of accidents with mechanics, established on the basis of the statistics of occupational injuries and data of accumulation of cracks in the array of tractor parts, were determined as a result of defectoscopic control. The results of the research allow in the medium and long term perspective to predict the probable states of the "human-machine-industrial environment" system in the risks of professional injury of agricultural machine operators.

The influence of the presence of fatigue cracks detected in the array of operational defects of typical parts of individual units on the condition of safety of tractors has been analyzed. In the work with the help of a specialized portable vibration current flow defectoscope the presence of cracks in the details of the units of tractors with different operating periods was estimated. The defectoscopic control of more than 500 parts of various applications was carried out in 50 tractors that were in service until 17 years since the date of issue in agricultural enterprises of Ukraine. Defectoscopic inspection was carried out during the defect of the details of these tractors received for repair. Based on statistically valid data, the kinetic dependences of the probability distribution of the accumulation of operational fractures of parts of tractor units in time were constructed. The cracks analyzed in the work were detected using a high-sensitivity pulsed vibration current flaw detector, which allowed us to quantify the size of the cracks that correspond to certain operating lifetime terms. It is established that the process of accumulation of a certain type of cracks has exponential kinetics. The regularities considered in the work reflect the consequences of the statistical process of accumulation of an array of fatigue cracks in the details (knots) of tractors within the limits of the studied range of service life. Exceeding the maximum period of operation of aggregates affects the change in the probability of accidents in mechanized and transport works. It is determined that the deadline for the researched tractor types is 13-14 years.

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An analysis of literary sources has shown that the methods used to evaluate occupational risk are mostly attempted to take into account the risk of erroneous actions by workers (operators), neglecting the technical condition of machines and the criticality of accumulation of defects during prolonged operation, which could lead to emergencies and accidents. In the given work the complex method of estimation of occupational risk is offered taking into account the influence of "organizational" and "technical" factors as the basis for forecasting the residual, safe for employees of the resource of machines, in particular method of calculating occupational risks for various types of mechanized work in agriculture using wheeled tractors. The basic events considered the organizational causes of occupational injuries, in particular violation of the requirements of occupational safety and health by mechanics and job managers, and technical malfunctions of tractor units due to the emergence and spread of operational fractures in responsible parts. The total probability of the basic events should be equal to one. Probabilities of basic events for organizational reasons were asked according to the known statistical indicators of occupational injuries in the agro-industrial complex, and probability of occurrence of technical malfunctions depending on the duration of operation of the tractor in accordance with an increase in the relative number of cracks in the total mass of the research parts of the tractor. An example of using the developed method in this paper is the calculation of the probability of a traumatic situation occurring on mechanized works in the agricultureas a result of the sudden lowering of tractor hinged implements, the details of which may cause and spread operational cracks. The calculation is made for cases of subcritical and critical accumulation of operational cracks in the array of investigated critical parts of the tractor.

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