We consider a class of complex systems, such as socio-technical systems on the example of the elemental sulfur producing by Claus process. Its operation takes place in different types of uncertainty and requires the development of specific approaches to the analysis and evaluation of many factors that affect the system operation and aren't giving in to the quantitative and qualitative description. The paper formulates the problem of multifactor risk analysis of emergency situations at hazardous production facilities using the methods of system analysis. The main groups of factors, parameters, and communication of human operator with the technical subsystem are identified. A method is proposed for assessing the level of selected factors influence on the emergency situations risk in system. Introduced the terminological basis for constructing patterns of socio-technical systems state indicators. According to the expert survey an example of the impact assessment diagram of each parameter to the "weight" of one of the indicators was made.

Keywords: socio-technical system, Claus process, multifactor risk analysis of accident, expert survey, system analysis