Companies contact the University only after the incidents have occurred. The causes must be anticipated with appropriate studies and with the preparation given by universities and research centers. Companies often do not consider the potential of some modern tools (companies no longer have alibis) that would increase the reliability of mechanical components and systems. Accidents due to structural failures, which in the past were often unavoidable due to poor technical knowledge, can now find no justification in the light of the technical knowledge achieved in the structural field. It is more likely that today the damage is caused by insufficient preparation of the designer or improper use of the machine. After all, inadequate maintenance can introduce defects as well as aggressive environment and misuse: all these aspects contribute to unpredictable failure during the design phase. Objective of this paper if to give a critical analysis of the state of art definition and utilization of safety factor in engineering applications.