The safety integrity level ( SIL) is a procedure for determining the potential risk to people, systems, equipment and processes in the event of a malfunction. The basis for the specifications, design and operation of safety instrumented systems( SIS) is the International Electrotechnical Commission( IEC) IEC 61508 standard.
IEC 61508 provides a coherent framework in which all previous safety regulations are taken into account. These include the safety standards DIN/VDE 19250, DIN/VDE 19251 and DIN/VDE 801, which are well known in Germany. The 61508 standard defines safety in terms of the degree of damage and the probability that a particular application has with regard to a risk-relevant situation. 61508 has its own risk assessment with which the safety integrity levels (SIL) for the devices and systems with safety tasks are determined. The IEC standard recognizes the four SIL levels SIL1 to SIL4, which are defined as safety designs of electrical and electronic equipment. The SIL value expresses the specified safety function in the event of a fault: With what probability does the system operate in the requested fault case, the Probability to Fail on Demand( PFD)?
At SIL level 1, the hazard or economic risk is relatively low and the availability of the safety-related systems is acceptable at 90% or 10% probability of failure. SIL level 3 is fulfilled, for example, if only one fault is likely to occur in 10 million operating hours. The risk potential is determined in technical equipment, process engineering systems, automotive technology, machines, elevators, programmable controllers, IT equipment and systems.