Safety Instrumented Systems (SIS) are used in many systems for the prevention and mitigation of safety-related hazards.  An SIS may be made up of one or more Safety-Instrumented Function (SIF).  The target Safety Integrity Level (SIL) of each safety-instrumented function (SIF) dictates the required performance of each SIF.  That performance criterion is determined via a SIL assessment.

A SIL assessment may be performed for:

• Existing systems; or
• The design and implementation of new systems.

The benefits of a SIL assessment include:

• Optimization of SIS safety performance
• Improvement in SIS reliability
• Reduced downtime due to spurious trips
• Compliance with the requirements of IEC 61508 and 61511
• Development of a best practice approach to process safety management.

The SIL determination for a particular SIF is based on the expected likelihood and consequence for the hazardous event that the SIF is protecting against and the applicable risk criteria.

AS/IEC 61511-3 describes different methods for the SIL determination.  The method of SIL determination for a specific case would be selected considering what best suits the needs and specifications of that system and the organisation.  Industry-recognized quantitative analytical techniques are used to assess the safety performance of the SIS.  This ensures that the target SIL requirements are met and therefore, the intended risk reduction is achieved.

R4Risk’s SIL practitioners are qualified risk analysts who are also TÜV-certified Functional Safety Engineers.  TÜV-certified Functional Safety Engineers have demonstrated their knowledge of SIS functional safety and satisfy the competency requirements of:

• AS/IEC 61508-1 Para 6.2.1
• AS/IEC 61511-1 Para 5.2.2.2

With the specific skills in the application of functional safety combined with extensive knowledge of risk and safety management, R4Risk is well-placed to support any organisation with its SIS safety management requirements.