The comprehensive system of fire safety becomes more and more important for projects in building construction. The system complexity rises along with increasing demands for technical development, safety and security. Associated with the complexity increase of technical building systems there is as well an increase of requirements for fundamental understanding of nature of fire safety. The main objective of the paper is to apply the General Systems Theory of Urmantsev (OTSU) to the field of fire safety, to understand better the fundamental relationships in fire safety. To achieve this objective, the task was set to apply the known algorithm of OTSU to the new field. The paper first presents the fundamentals and basic concepts of OTSU. Based on the OTSU an introduction into systems theory for fire safety as well as elements of the system and illustrative examples in this field are given. Important properties of primary fire safety system elements and their relationship are presented in figures. The discussion of fire safety system elements explains their character and interrelationships between them. In particular, a matrix of all, in principle, possible relationships between basic elements of the system is presented. This allows to identify and describe in general terms the main functional blocks that make up the subject of fire safety. It is also important that this set is complete and no other relationships are possible. This gives full confidence in the completeness of the description of an object that cannot be guaranteed by any other approaches. The advantages of the proposed systems approach for understanding and management of fire safety are presented. Further steps in the development of the approach are indicated.