Safety Integrity Level (SIL),
SIL defined and explained in standard IEC 61511. Generally speaking this is a safety performance measuring system / methodology and used for safety instrumented functions. The standard IEC 61511 describes several methods for SIL determination.
When it comes to a plant design with the large number and scale of safety functions, the need to integrate multidisciplinary design and operation knowledge is the necessary to achieve effective risk reduction.