Safety First

The conversation around Safety Integrity Level (SIL) has picked up among the industrial community; but what exactly is everyone saying and how does it apply to YOUR process? 

Let’s attempt to break down this often-misunderstood concept and learn how it can be implemented properly. To fully understand a complex concept like SIL, there are a few other aspects to consider, we've looked at Functional Safety and Safety Instrumented Systems (SIS), this week let's focus on Safety Instrumented Function (SIF). 

Safety Instrumented Function (SIF)

The Safety Instrumented Function (SIF), is a protection layer whose objective is to achieve or maintain a safe state of the process when a specific dangerous event occurs. The SIF is implemented in the SIS (Safety Instrumented System) which is normally composed of several Safety Functions. Each SIF has a different assigned SIL level.

Each SIF consists of:

  • SENSOR subsystem 
  • LOGIC SOLVER subsystem
  • ACTUATOR subsystem

According to Exida, its purpose is to Automatically take an industrial process to a safe state when specified conditions are violated; Permit a process to move forward in a safe manner when specified conditions allow (permissive functions); or Take action to mitigate the consequences of an industrial hazard. 

The Safety Instrumented Function is composed of a set of equipment, any combination of sensor, logic solver (PLC), final element and all necessary interfaces, intended to reduce the risk due to a specific hazard safety loop.

It is designed to:

  1. IDENTIFY the need 
  2. ACT to bring the system to a safe state for each hazard scenario

These elements should detect an accident is imminent, decide to take action, and then carry out the action necessary to achieve a safe state. Its ability to detect, decide, and act is designated by the safety integrity level (SIL) of the function. 

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