What is Safe state ? Safety Instrumented System


What is Safe state ?

The safe state is defined as “state of the process when safety is achieved” [IEC 61511 -1:2003]. In order to set a process to a safe state the knowledge of the process is very important.

In some cases the safe state exists only if the process is continuously running, in other cases the process may have to go through a number of states before the process enters the final safe state.

Actions necessary to achieve or maintain a safe state in the event of detected fault(s) shall be described [10.3.1 IEC 61511-1:2003]. The relevant human factors that can affect the safe state shall be taken in account.

The description shall address safe state details regarding process actions needed e.g.:

  • sequential shutdown
  • which process valve(s) is needed to perform a specific action during the safe state. Shall the* valve open or close?
  • which flows should be started or stopped
  • stop, start or continue operation of rotating elements (motors, pumps etc)