What is a Safety Instrumented System?
A Safety Instrumented System SIS is a new term used in standards like IEC 61511 or IEC 61508 for what used to be called Emergency Shutdown System ESD, Safety Shutdown System, Interlock System, Permissive Systems, etc. ...
A Safety Instrumented System SIS consists of one or more Safety Instrumented Functions SIF.
What is a Safety Instrumented Function SIF?
A Safety Instrumented Function SIF is defined as a „Function to be implemented by a SIS, which is intended to achieve or maintain a safety state for the process with respect to a specific hazardous event"
What is a Safety Integrity Level SIL?
Safety Integrity Level SIL is a measure of risk reduction provided by a SIF based on four levels. Each level represents an order of magnitude of risk reduction. Every SIF has a SIL assigned to it, the SIS and equipment does not have a SIL assigned to it.
