Abstract. Aim. To show a method of overcoming the uncertainty in the requirements for the quality of data in non-standard situations and ways of formalizing the decision-making process aimed at ensuring safe operation of structurally complex systems. The paper proposes a method of axiomatic construction of integrated indicators that describe the properties of a system and its operational environment through the synthesis of the risk function. Methods . Methods of system analysis of the objective, Russman’s methods of the difficulty in achieving the objectives and the Shewhart charts theory. Results. The author proposed methods of qualitative estimation of two types of safety state, i.e. “better than” (for the purpose of defining a certain target level that characterizes the safety state that is to be ideally achieved) or “not worse than” (for the purpose of defining a certain maximum allowable level that characterizes the safety state, below which it is not allowed to go), that imply certain ranges of deviation from the specified target or, respectively, the minimal allowable levels, within which the safety state evaluated with an integrated index is deemed to be acceptable. Conclusions . It is shown that, in respect to problems of safety and risk assessment of structurally complex systems, one should not try to work with specific safety-related events only. All such events are characterized by a set of properties and contributing factors with associated characteristics. One should try to identify each property and each characteristic of such property, which would later allow defining proactive and reactive control actions in response to changes in such characteristics and properties. Having worked out a property of a situation or an event, we work out a property of a risk, and it is of no significance in which specific risk this property manifests itself. Combinations of risk properties can be extremely numerous, therefore it is very difficult to predict specific situations. That causes the requirement for a proactive decision support system that ensures high-quality managerial decisions short before a critical event.