Safety Integrity Level))
SIL stands for Safety Integrity Level. Before defining SIL, you need to first consider the term SIF (Safety Instrumented Function). In fact, SIF is a set of actions to guide a process to a safe state. SIF performance is measured by the “Safety Integrity Level” or SIL. SIL is a reliability measure that is defined in terms of the probability of failure in the performance of an SIF when the process is in abnormal conditions and its existence is required. This is called “Probability of Failure on Demand” (PFD).
Based on IEC61508 international standard, SILs are divided into 4 levels. These SIL levels include SIL1, SIL2, SIL3, SIL4. The higher the SIL level, the lower the probability of failure at the required time (PFD) for an SIF and indicates the greater availability of that SIF, which, of course, should be more expensive. The table below illustrates SIL in simple and understandable speech.
The table above shows that for a system or equipment that has SIL 1 approval, the probability of failure occurring within 11 years is at most once.