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Safety Integrity Level

Achieve and maintain the required safety levels, safeguarding their operations and personnel. At Wire Consultancy, we specialize in providing Safety Integrity Level (SIL) services to businesses aiming to enhance the safety and reliability of their critical systems. Our expert team helps clients achieve the desired Safety Integrity Level by conducting comprehensive assessments, evaluating potential risks, and recommending appropriate risk reduction measures.

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Safety Integrity Level

A Safety Integrity Level (SIL) study is a systematic analysis and assessment of the functional safety of safety instrumented systems (SIS) used in industrial processes. These studies are commonly performed in industries where the consequences of failures could result in serious harm to people, the environment, or property. The goal of a SIL study is to determine the required SIL for safety instrumented systems and ensure that they meet the desired level of risk reduction.

Safety Integrity Level is a measure of the risk to people and property that a system will experience during operation. The Safety Integrity Level is a qualitative measure of safety and it is expressed in terms of the consequences of failure. The higher the Safety Integrity Level, the lower the likelihood of failure and, therefore, the better the safety.

Safety Integrity Level study is a method to record all the SIF for a project development and document the expected reliability level. Safety Integrity Level study provides a basis for future maintenance and operating strategies. Safety Integrity Level assignment is based on the amount of risk reduction that is necessary to mitigate the risk associated with the process to a tolerable level. All of the Safety Instrumented Systems (SIS) design, operation and maintenance choices must then be verified against the SIL assigned.

Key steps in conducting a Safety Integrity Level study include:

  1. Hazard and Risk Assessment: Begin by conducting a hazard and risk assessment to identify potential hazards, assess their likelihood and consequences, and determine the overall risk. This forms the basis for determining the appropriate safety measures.
  2. Safety Instrumented Functions (SIFs) Identification: Identify the specific safety instrumented functions that are required to mitigate the identified hazards. A safety instrumented function is a specific control action taken by the safety instrumented system to reduce risk.
  3. Determining SIL Requirements: Based on the risk assessment, assign a target SIL to each safety instrumented function. SIL levels range from SIL 1 (lowest) to SIL 4 (highest). The assigned SIL reflects the desired risk reduction and safety performance.
  4. SIL Verification and Validation: Determine whether the existing safety instrumented systems meet the required SIL levels. This involves verifying and validating the design, performance, and reliability of the safety instrumented systems.
  5. SIL Assessment Techniques: Various techniques are used to assess the safety instrumented systems and determine if they meet the required SIL. These techniques include fault tree analysis (FTA), failure modes and effects analysis (FMEA), and reliability analysis.
  6. Safety Instrumented System Design: Design or modify the safety instrumented system to ensure that it meets the required SIL. This involves selecting appropriate sensors, logic solvers, final elements, and redundancy configurations.
  7. Verification and Validation of Design: Verify and validate the design of the safety instrumented system to ensure that it meets the requirements for the assigned SIL. This may involve simulation, testing, and analysis.
  8. Documentation and Reporting: Document all findings, decisions, and analysis results. This documentation is important for regulatory compliance, auditing, and ongoing maintenance of the safety instrumented systems.
  9. Operation and Maintenance: Regularly monitor, test, and maintain the safety instrumented systems to ensure they continue to meet the required SIL and perform as intended.

The SIL study process is highly structured and relies on quantitative and qualitative analysis to ensure that safety instrumented systems effectively reduce risks to an acceptable level. These studies are commonly used in industries such as chemical, oil and gas, pharmaceuticals, and nuclear power, where process safety is critical.

Safety Integrity Level study standards

  1. IEC 61508: Functional Safety of Electrical/Electronic/Programmable Electronic Safety-Related Systems: IEC 61508 is a widely recognized international standard that provides a comprehensive framework for achieving functional safety in various industries. It defines principles, requirements, and guidelines for designing, implementing, and assessing safety instrumented systems. The standard encompasses the entire lifecycle of safety-related systems, including hazard and risk assessment, safety requirements specification, system design, validation, and maintenance.
  2. IEC 61511: Functional Safety – Safety Instrumented Systems for the Process Industry Sector: IEC 61511 is a sector-specific standard derived from IEC 61508. It is intended for the process industry sector, which includes chemical, petrochemical, and other industrial processes. IEC 61511 provides detailed guidance on implementing safety instrumented systems in these industries, covering aspects such as hazard assessment, safety requirements specification, SIS design, operation, maintenance, and periodic testing.
  3. ISA-84 / ANSI/ISA 84.00.01: Functional Safety: Safety Instrumented Systems for the Process Industry Sector: The International Society of Automation (ISA) developed the ISA-84 standard, which aligns with IEC 61511 but is specific to the process industry sector. It provides guidelines for the identification, design, implementation, and operation of safety instrumented systems in process industries.
  4. EN 61508-6: Functional Safety of Electrical/Electronic/Programmable Electronic Safety-Related Systems – Part 6: Guidelines on the Application of IEC 61508-2 and IEC 61508-3: EN 61508-6 offers guidelines on applying IEC 61508-2 and IEC 61508-3, specifically focusing on the application of the requirements for safety instrumented functions.
  5. ISO/TR 12489: Application of EN 61508 and EN 61511 in the Field of Industrial Process Measurement, Control and Automation: ISO/TR 12489 provides guidance on applying IEC 61508 and IEC 61511 to the field of industrial process measurement, control, and automation, aiding practitioners in implementing functional safety measures.

Wire Consultancy offers comprehensive Safety Integrity Level

Wire Consultancy is a highly rated Risk Engineering & EHS Solutions Consultancy company that offers Safety Integrity Level services. Wire consultancy consists of a diverse team of experienced auditors and professionals who have been working in the Safety Integrity Level field for over 20 years and have a deep understanding of Safety Integrity Level.

Wire consultancy has extensive experience in providing Safety Integrity Level services to companies across a range of industries, including aerospace, defense, oil and gas, transportation and medical devices. 

The primary objective of the SIL study is to determine the adequacy of Independent Protection Layers that are in place to mitigate against hazardous events relating to major process hazards.

The study will determine the risk reduction required for the SIFs such that sufficient Protection Layers or safeguards to allow them to meet the required risk reduction for a particular hazard. Quantification of the risk reduction requirements is given in terms of SIL requirement.

The key rule set for the Safety Integrity Level study is provided below

There are several methods used to assign a SIL. These are the normally used in combination, and may include:

  1. Risk matrices
  2. Risk graphs
  3. Layers of protection analysis (LOPA)

LOPA method for SIL classification has been utilized for SIL Study.

  1. Start permissive functions, simple alarm functions, ESD push buttons were not taken up for Classification as they are considered general protection layers and not SIFs in the strict sense.
  2. It was noted that all P&IDs, C&Es and other relevant documents were used during the SIL study.




Functional safety – Safety instrumented systems for the process industry sector


Functional Safety of Electrical/Electronic/Programmable Electronic Safety-Related Systems


Cummins Safe Use of Hydrogen System Global Standard

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