Safety-related requirements are defined in application dependant and independent standards, which determine the definitive test principles of type approvals. The requirements result from the risk analysis of the applications. In consequence, applications generally refer to different categories or levels of safety-related requirements.

Concerning those applications, where such levels or categories are not binding, the independent international application standard IEC 61508 offers methods and support to determine the risk and the requirements referring to the risk of the safety or protection equipment.

The determination of risk is basically made by inspecting the combination of effect and occurence probability of damage of the process including the automation devices without safety or protection devices. The result is a safety integrity level (SIL). The safety and protection devices have to apply to the SIL requirements, which reduce the risk of the application to a tolerable risk.

Automation, Software and Information Technology (ASI) carries out risk analysis to clarify the requirements of safety and protection systems.

Apart from the compliance with safety-related requirements, the reliability resp. availability of a plant or process is of importance to the user. These parameters can be determined by analyzing the structure as well as the failure rates and failure types of the involved components, including the automation devices (equipment).

The influences of the safety devices also have to be examined. Generally the reliability and availability of a plant is highly determined by type and operational mode of safety and protection devices. For instance all detected failures, which result in the shut-down of a plant, lead to a reduction of reliability and availability. In case of redundant structures this influence is less relevant, whereas 2oo3 structures have advantage over 1oo2 structures.

TÜV Rheinland, ASI carries out reliability and availability analysis as well as consulting services to increase the reliablity and availability of systems. A combination with necessary safety analyses is favorable, as partly the same parameters (like failure rates) are reverted to.