The aim of the dissertation thesis was to identify and assess the risks of major industrial accidents using the example of a technological node of the existing cellulose-paper production company Mondi SCP, a.s. using progressive methods of computer-aided modelling. The dissertation thesis consists of four basic chapters. In the theoretical part, there is a basic overview of the history of the occurrence of major industrial accidents in the world and at national level. The knowledge and experience obtained during coping with these accidents was the basis for the design and implementation of legislation in the area of the prevention of major industrial accidents at the level of the European Union and at the national level. A part of the theoretical part of the dissertation thesis is also the description of the issue of risk management of major industrial accidents and especially the methods of risk assessment. In the practical part, the thesis deals with computer-aided modelling of physical effects and impacts of modelled scenarios of release of hazardous substance from a stationary source. Eleven scenarios of four types of hazardous substances release (hydrogen sulphide, methyl mercaptan, dimethyl sulphide, dimethyl disulphide) were identified at the technological node, i.e. CNCG pipe connected to the recovery boiler, which was identified as the object with the highest risk of a major industrial accident in the risk assessment. Three programme tools were used for modelling: ALOHA, ADAM and GIS. While the application of ADAM and GIS programme resources can be described as innovative approaches to the assessment of major industrial accident risk. Comparison of modelling results in individual programmes showed great differences in the resulting physical effects and impacts of the considered scenarios of release of hazardous substance to the environment, exceeding the predicted deviation of ± 15% of the resulting values of physical effects and the impacts of accidents obtained from modelling. Modelling results pointed to the need for identifying critical points in modelling using ALOHA, ADAM, and GIS software tools resources, as well as suggesting possible solutions to these problems in the future. The benefit of the dissertation thesis is the verification of the possibilities and suitability of application of the ALOHA, ADAM and GIS programme tools to the safety/security practice as well as the identification of critical points limiting their current practical application.