Safety Integrity Level (SIL)

Safety Instrumented Systems (SIS) are the last layer of defence against critical safety, environmental and economic losses. Bureau Veritas’ team of industry certified Functional Safety Engineers have the skills and experience needed to guide your company through the Safety Lifecycle, ensuring compliance to IEC61508 and adherence to industry best practice. Compliance with IEC61508 gives you peace of mind that a rigorous process has been followed, covering all aspects of SIS design, installation, operation, maintenance and de-commissioning.

What is the safety lifecycle?

The Safety Lifecycle defines the activities that need to occur at each stage of the design of the SIS. This includes:

  • Hazard Identification: is carried out using established techniques such as Hazop and Hazid. The output is then screened and carried forward to Safety Integrity Level (SIL) Assignment.

  • SIL Assignment: A multi-disciplinary team of Design, Instrument and Electrical Engineers, Maintenance Technicians, Operations and Management review each identified hazard and assign a target SIL for each Hazard. An approved technique is used, as defined in IEC61508, such as the powerful Layer of Protection Analysis (LOPA), semi-quantitative or calibrated risk graph.

  • Safety Requirements Specification: A critical part of the lifecycle, the SRS defines all of the requirements and special considerations for each Safety Instrumented Function (SIF). The SRS is developed in conjunction with the System Designers, Operations and Management. This document is an important validation tool for the installed SIS, allowing identification of deviations from the agreed system to be identified and reviewed.

  • SIL Verification: involves conducting hardware probability of failure calculations to ensure that the probability of failure of each overall SIF loop achieves the minimum requirements, as defined by the target SIL. SIS performance analysis also incorporates assessment of other SIS design parameters, including Hardware Fault Tolerance (HFT), Common Cause Failures (CCF) and Critical Function Testing (CFT) requirements.



Our Approach for SIL

Bureau Veritas has developed a four - stage methodology to:

  • Understand the systems with meetings to perform functional analysis and risk analysis
  • Set the RAMS (reliability, availability, maintainability and safety) objectives to be met
  • Analyse the system hardware and software
  • Analyse how the system reacts to improvement decided in close partnership with the client and propose recommendations.


Bureau Veritas engineers can assists you from the design stage to operation throughout the development production, installation, start-up and maintenance stages of the safety instrumented system. This can include:

  • Identifying the risks and assessing risk reduction
  • Performing diagnosis / audit of your processes to identify required actions
  • Preforming RAMS studies
  • Independent third party assessment of the SIL met by the SIS and
  • Performing personalised training sessions


Why choose Bureau Veritas for SIL?

Bureau Veritas offers services for various safety lifecycle activities including the initial concept; hazard analysis and risk assessment; development of safety requirements; specification; design and implementation; operation and maintenance; modification; and final decommissioning and/or disposal.


Our focus is to encompass all aspects of the system and corresponding subsystems that carry out the safety function. This may include hardware, software and failure mechanisms (random hardware and systematic).  


Our methods contain requirements for preventing failures (by avoiding the introduction of faults) and for controlling failures (ensuring safety even when faults are present). These techniques and measures are necessary to achieve the required safety integrity for our client’s products.



Does Bureau Veritas have experience in different SIL assignment methodologies?

Yes, Bureau Veritas facilitators are experienced in many different approved techniques, including Layer of Protection Analysis (LOPA), semi-quantitative or calibrated risk graph.


Can Bureau Veritas assist with other aspects of the Functional Safety Lifecycle?

Yes, our group of experienced Risk Engineers can help with all SIL-related questions and investigations, including Functional Safety Management Plans (FSMP), SRS development and specialist SIS design and implementation decision support.


Can Bureau Veritas provide SIL Verification services?

Yes, Bureau Veritas use approved quantitative techniques such as Fault Tree Analysis (FTA) and our own patented package ‘Optimise’, a Monte Carlo simulation to model the process and determine the probability to fail on demand of each SIL rated SIF.


What industry sectors are SIL assessments used for?

All sectors. Onshore, Offshore, Refining, Mining, Chemicals and Power Generation are all applicable to the SIL standards. The IEC 61508 is an umbrella standard covering all sectors. Standards such as IEC 61511 have been extracted from 61508 and specifically modified for the process industry. Bureau Veritas can even certify equipment for use in safety-related systems with an appropriate SIL.

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