Basics of SIS SIF SIL (Safety Instrumented system Safety Instrumented Functions Safety Integrity level)


Basic overview of what SIL(Safety Integrity Level) is ?

SIL is handled under IEC 61508. SIL is kind of umbrella standard for function safety across all industries.Compliance IEC 61508 ensures with compliance with industry specific safety standard such as

IEC 61511 Process Industry
IEC 61513 Nuclear Industry
IEC 62061 Machinery Industry

These standards are address the entire safety life cycle and are based on performance analysis
Compliance to this standards will reduce risk

I C 61508 late defines three successive tears of safety assessment
it’s composed of

safety instrumented systems SIS
safety instrumented functions SIF
safety integrity level SIL

First level is safety instrumented system

Safety Instrumented System is defined as instruments system used to implement one
or more safety instrumented is made up of any combination of
things like sensors logic solvers so basically this is the
overarching system

The SIS is an instrumented control system that detects “out of control” conditions and automatically returns the process to a safe state

A safety Instrumented function is defined as a function to be implemented by a SIS which is intended to automatically achieve or maintain a safe state for the process with respect to a specific hazardous event (IEC 61511)

The SIF (safety instrumented function) is an independent safety loop or interlock that automatically brings process to a safe state in response to specific initiating events

SIL is the safety integrity level of a specific safety instrumented function which is being implemented by a safety instrumented system

SIL is a measure of risk reduction provided by a specific SIF

SIL is expressed as a number from 1-4
SIL 4 provides the greatest risk reduction
SIL 1 provides the lowest risk reduction


Very helpful for risk reduction.

Thanks :slight_smile: