VDI-EE 4020 Berichtigung:2022-07

Functional safety is one part of the overall safety of a technical facility. Functional safety here refers to control-related measures for risk reduction. Basically, it is about controlling random hardware failures and avoiding or controlling systematic failures. The higher the risk to be safeguarded, the higher the required level of safety integrity. The level of safety integrity is a measure of the reliability with which the safety function under consideration is performed. Basically, error prevention can be achieved via appropriate quality management (project management, documentation, review of all development steps, etc.) and error control via proven safety principles, hardware redundancies and (automatic) diagnostic tests. In this context, it must be taken into account how the technical equipment can be transferred to a safe state after a dangerous failure has been detected. For the hardware, certain values must be observed with regard to the proportion of safe failures and the probability of failure, depending on the desired level of safety integrity and the selected architecture. For different application sectors, in addition to the basic standard IEC 61508, there are other standards that define functional safety requirements adapted to the respective sector. These requirements attempt to take into account boundary conditions relevant to practice (such as costs) and to enable the user to implement the requirements more easily. However, the basic strategies and objectives are the same or at least very similar in all functional safety standards. The expert recommendation provides an introduction to the topic of "functional safety" in accordance with the basic standard IEC 61508. To this end, basic legal requirements are explained, as is all the important normative terminology. Furthermore, the basic strategy for fulfilling the normative requirements for functional safety is explained in detail. In addition, common misunderstandings in the application of functional safety standards as well as specific characteristics of different sector standards are addressed. This publication is intended to close the existing gap between very brief and superficial introductions and very comprehensive publications on the subject of "functional safety". The expert recommendation is aimed at engineers and managers in industrial areas such as safety, planning, quality and risk assessment.