[1][2] An SIS is intended to perform specific control functions to prevent unsafe process operations when unacceptable or dangerous conditions occur.
The essential characteristic of an SIS is that it must include instruments, which detect that process variables (flow, temperature, pressure etc.
Support systems, such as power, instrument air, and communications, are generally required for SIS operation.
SIFs are implemented as part of an overall risk reduction strategy which is intended to minimize the likelihood of a previously identified accident that could range from minor equipment damage up to the uncontrolled catastrophic release of energy or materials.
[1][2] International standard IEC 61511 was published in 2003 to provide guidance to end-users on the application of Safety Instrumented Systems in the process industries.