Documented evidence with regard to the adherence to the required safety integrity level (SIL) within the scope of the safety life cycle has to be delivered in order to proof that the imple-mentation of safety systems (Safety Instrumented Systems SIS) in the process industry has been executed according to professional standards. When carrying out the hazard analysis and the risk assessment, safety functions (Safety Instrumented Function SIF) will be estab-lished and evaluated against a required SIL. The achievable SIL both for systematic defaults and for random failures can be established for each safety function being carried out by means of a safety system. The established SIL has to be in conformity with or better than the required SIL. The engineers of the weyer group will establish the respective SIL-level of the plant, taking the data delivered by the manufacturers as the calculation base.