For the purpose of determination of technical safety, and additional safety necessitated by public an social reasons, this paper considers methods of relations, probability and combined relation and probability. Also considered are functional failure and collapse failure, as well as the concept of designed service life of the structure. The ultimate safety degree is composed o the part for security regarding the technical and social consequences of collapse. The safety determination method, in technical terms too, strives to avoid the damage which would exceed the bearing capacity of the structure. The relation methods apply the safety degree which was obtained in cases when the similar structures of various dimensions were built, so it is necessary to determine the required dimensions to avoid the structural failure. The Probability method is widely applied using statistical data in the load and strength analysis. The combination of relation and probability methods provides the minimum safety degree as a reliable factor.