SIL Verification

SIL Verification

Reducing the risk of unacceptable process conditions


Electrical, electronic, or programmable electronic (E/E/PE) safety related systems are designed to implement the required safety functions and execute the necessary integrity to achieve or maintain a secure state for the equipment under control. The ANSI/ISA S84.01 standard and the IEC 61508 standard requires the operating companies to assign a target SIL for all safety instrumented system applications. One main principle is to separate random failures from systematic failures. Random failures occur at random times, which result from the possible deterioration of one or more mechanisms in the hardware. Systematic failures are determined by certain causes, which can only be eliminated by modifications in the design of the manufacturing processes, operational procedures, documentation or other relevant factors. The challenge is to utilize a method that can detect the safety integrity of a device or system.


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.

Our approach

Bureau Veritas performs SIL Assessments for operating facilities by means of a two step approach;

(i) SIL Classification and
(ii) SIL Verification.

Note: IEC 61511 gives normative references to SIL Assessments for process industries.

We use a risk based approach to determine the safety integrity requirements of E/E/PE safety-related systems. This approach is comprised of multiple examples demonstrating its execution. An overall safety lifecycle model may be utilized as part of the technical framework of activities necessary to ensure functional safety is achieved by these systems.

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.

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.


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).