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Business Challenge

The ANSI/ISA S84.01 standard and the IEC 61508 standard requires companies to assign a target Safety Integrity Level (SIL) for all safety instrumented system applications. This includes all electrical, electronic, or programmable electronic (E/E/PE) safety-related systems which 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.

In order to effectively meet these requirements, companies must be able to separate random failures from systemic failures. A random failure can result from a number of factors and occur at unexpected times due to circumstances such as deterioration in one or more of the hardware mechanisms.

Systemic failures, on the other hand, can be traced to certain causes, and they can only be eliminated by modifying the design of the manufacturing process, operational procedures, documentation, or other relevant factors.

The main challenge here is to utilize a method that can detect the safety integrity of a device or system and provide the information needed to meet industry standards and requirements.


What is Safety Integrity Level (SIL)?
Safety Integrity Levels (SIL) is a statistical representation of the availability of a required safety instrumented function. The ANSI/ISA S84.01 and the IEC 61508 standards suggest that the effects of the random failures must be evaluated in a quantitative way through these statistical evaluations.

There are four SIL designations provided in ANSI/ISA S84.01 and IEC 61508, and SIL 4 has the highest level of safety integrity and SIL 1 has the lowest. Bureau Veritas has technical staff dedicated to helping clients comply with these standards to demonstrate their safety management systems and to build strong justifications.

The diagram below includes the target failure frequency for an operating safety function and its safety integrity level.

Target failure frequency



Low demand mode of operation

(Average probability of failure to perform its design function on demand PFD)

High demand or continuous mode of operation

(Probability of a dangerous failure per hour PFH)


10-2 < PFD < 10-1 

10-6 < PFH < 10-5 


10-3 < PFD < 10-2 

10-7 < PFH < 10-6 


10-4 < PFD < 10-3 

10-8 < PFH < 10-7 


10-5 < PFD < 10-4 

10-9 < PFH < 10-8 


At Bureau Veritas, our SIL assessments for operating facilities takes a two-step approach. We start with SIL Classification and continue to SIL Verification.

Our risk-based approach will help determine the safety integrity level requirements of E/E/PE safety-related systems. We will cover all the aspects of the system and any corresponding subsystems to ensure they are meeting requirements for preventing and controlling failures.

Why Choose Bureau Veritas?

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

• Final decommissioning and/or disposal

These services encompass all aspects of the system and 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.

FAQ - Frequently Asked Questions

  • We manufacture components used in safety functions for the process industry. Are SIL assessments required? Is Bureau Veritas capable of performing laboratory tests?

    Yes. SIL certified products are an essential business need for many manufacturers. We conduct assessments of the product design and analyze field experience data to then certify your product (E/E/PE systems) to its SIL level. If required, laboratory tests are carried out by our partner company (LCIE).

  • Do you combine HAZOP and SIL Classification workshops?

    Yes, we have an experienced technical staff capable of carrying out combined HAZOP and SIL Classification sessions for our clients.


Contact us: 281.986.1300

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