SIL classification
The SIL (Safety Integrity Level) classification is an important development in ensuring the safety of complex installations. The SIL classification is commonly used in the processing industry as a reliability standard for components and systems. The major standard in this respect used to be IEC 61508. A number of additions have meanwhile been made to this standard (which was impossible to apply). These additions are intended for a number of industries including the machine construction industry (IEC 62061) and the processing industry (IEC 61511).
SIL in the processing industry
IEC 61511 has therefore converted IEC 61508 so it is suitable for the processing industry, in the same way as IEC 62061 has converted it for use in machine safety. It provides an explanation of the use of electrical, electronic and programmable electronic systems used for safety purposes. These are known as Safety Instrumented Systems (SIS). The definition of the system includes the entire procedure, from recording instrument to transformers and unit of account right up to the control unit (which can also be pneumatic), designed and managed in order to conform with a specific Safety Integrity Level (SIL).
IEC61511
IEC61511 specifically deals with all aspects of the concept > design > implementation > operation > maintenance > decommissioning life cycle.
IEC61511 consists of 3 parts:
- Framework, definitions, system, hardware and software requirements
- Guidelines in the application of IEC 61511-1
- Guidance for the determination of the required safety integrity levels
Part 3 of IEC61511 provides guidelines for determining (classifying) the required SIL level or SIL Target. This risk assessment can be carried out using various tools. One of these tools which is frequently used is the calibrated risk graph, which is also included in ISO14121-1 for risk assessments for machine safety. This is often carried out as a further development in a HAZOP scenario, in which instrumental safety can or should ensure risk reduction.
In addition, the development of Layer of Protection Analysis (LOPA) scenarios means that a certain risk reduction is required for an SIF as a protective layer. The risk reduction is inversely proportionate to the failure frequency, which can ultimately be traced back to SIL.
Determining the required SIL level
Our Process Safety Business Unit will be happy to help you determine the required SIL levels on the basis of IC61511-3 as a supplement to HAZOP, or using a LOPA scenario. For more information, or if you would like to make an appointment for a no-obligation initial meeting, please contact Daisy Markerink at d.markerink@denf.nl or on +31-(0)316-712802.