This paper evaluates fire resistance of principal girders and frame parts of a steel skeleton structural system, considering both constant and variable actions. The fire resistance of steel beams and columns was evaluated according to the exposure to the ISO 834-1 fire curve and using the critical temperature approach in compliance with Eurocode 3 requirements. The research uses qualitative research techniques and depends on empirical investigation of various beams and columns that have different geometric properties. Steel has a major disadvantage in that it has a limited ability to resist fire, despite being famous for having great mechanical properties at ambient temperature. However, several methods exist to improve the fire resistance of steel structures and their members. Furthermore, the fire resistance of all structures can be significantly increased by combining active and passive fire protection measures and enforcing them. Results found in this research show that members of steel skeleton systems, without any fire-resistant materials, can withstand short periods of fire duration before losing their load bearing function. From the perspective of human life and safety, this is not satisfactory, and special attention must be paid to fire prevention and the application of active, but also passive fire protection measures.