SIL ALLOCATION AND SIL VERIFICATION (IEC 61508/61511)
ASSESSING THE SAFETY, AVAILABILITY AND RELIABILITY
Industrial licensing authorities and regulations require operating companies to carry out a SIL Assessment and a SIL Verification study for the Safety Instrumented Functions (SIF) during facility design, as well as prior to construction and during operation.
What is SIL?
The acronym SIL stands for Safety Integrity Level.
A SIL Assessment is a study usually performed contextually to a Risk Analysis (HAZOP).
The SIL target for each Safety Instrumented Function (SIF) existing in the installation is assessed by a team of specialists that typically includes personnel from Process, Instruments/Electrical, HSE, Project Engineering and Operations.
The SIL Assessment study is led by an experienced facilitator.
Once the SIL values are assessed, a Verification of such values is performed in order to check that the Probability of Failure on Demand (PFD) for each SIF is inside the range of the PFD corresponding to the required SIL.
Moreover, the compliance of the SIF architecture with the required availability level (SIL) is verified.
SIL Assessment and SIL Verification are developed in accordance with IEC 61508 and IEC 61511.
Bureau Veritas offers SIL leadership services across all phases of plant design, from feasibility and FEED, to detailed design, and to construction and commissioning.
Bureau Veritas also offers attendance at designer/client project meetings, so that an overview of all HSE issues is available at the meetings, and so that timely advice can be sourced when specialist hazard information may be needed.
Bureau Veritas has vast experience in developing SIL Assessment studies by using both Risk Graph method and LOPA
Bureau Veritas also has experience in providing personnel to participate in SIL Assessment studies as engineer or HSE specialist when that is appropriate to the client or designer.
What are the key benefits?
■ Allocate the Safety Integrity Level for the SIF
■ Allocate the risk reduction provided by the SIF
■ Verify the Probability of Failure on Demand (PFD) and the architecture compliance for the SIF
■ Allocate risk reduction provided by the SIS, thus giving it a Safety Integrity Level (SIL)
■ Demonstrate reliability and availability of the SIS
■ Verify and validate the design and development process of SIS hardware and software components
■ Demonstrate compliance of the SIS with international standards (such as IEC 61508, IEC 61511, ISA84.01-2004, IEC 62061, ISO 13849, CENELEC 50126, 50128 & 50129).
How long does a SIL study take?
For the installation of an Oil&Gas unit on an existing site, each SIF might take10-30 min for SIL Allocation and 1-3 hours for SIL Verification.