Safety Instrumented Systems (SIS) are flexible and effective tools for safeguarding process plants. SIS can be configured in many ways to meet a variety of process goals and performance targets.

Kenexis helps our clients to utilize Safety Instrumented Systems by assisting in the design, verification and ongoing mechanical integrity programs.

Services includes risk-based establishment of Safety Integrity Level (SIL), developing Safety Requirement Specifications (SRS), quantitative design Verification (SIL Verification), Test planning and assistance and continuing performance assessment and auditing.

Activities in SIS Engineering:

  • Safety Function Definition
  • SIL Selection/SIL Determination, using Layer of Protection Analysis (LOPA)
  • SIL Verification
  • Safety Requirements Specifications (SRS) Development
  • Maintenance and Testing (Validation) Support
  • Functional Safety Assessment

Safety Function Definition

Safety Instrumented Functions (SIF) are a critical step in the SIS safety lifecycle, and the source of many errors in SIS design as a result of common misconceptions about what constitutes a SIF. SIF definition requires an understanding of hazards associated with the chemical process, and the specific instruments that are utilized to protect against those hazards. SIFs are intended to protect against specific and identifiable hazards instead of general hazards, such as fire and gas explosion. These hazards are not always clearly defined in the Process Hazards Analysis (PHA), which is often used as the primary means for defining Safety Instrumented Functions.

SIL Selection / SIL Determination

Proper design of safety instrumented systems (SIS) begins with the selection of a Performance Target for the functions employed by a SIS. Standards such as IEC 61511 (ISA 84) call this target the Safety Integrity Level (SIL). This assessment, often referred to as SIL Selection or SIL determination, is an exercise in risk analysis. The Assessment of a Safety Instrumented Function (SIF) to determine the appropriate SIL considers the frequency of initiating events, consequences of inaction, and other independent protection layers to determine the performance target.

Kenexis is a world leader in the development of risk-based techniques for determination of performance targets for safety critical systems such as SIS. Our consulting staff has substantial background (professional profiles) in process, control systems, instrumentation engineering, all of which are critical disciplines for performing a high-quality SIL Selection study. This wide array of knowledge ensures that our consultants are knowledgeable on your process and have prior experience performing SIS lifecycle projects in similar facilities.

SIL Verification

After a performance target has been selected, achievement of this target should be verified by Quantitative means. The process of performance target verification is commonly referred to as SIL Verification. SIL Verification includes determination of probability of failure on demand, spurious trip rates, and other performance metrics. SIL Verification considers the type of equipment employed, advanced voting arrangements, diagnostics, and testing frequency.

Kenexis consultants have executed thousands of SIS safety lifecycle projects cumulatively, performing SIL Verification analysis for tens of thousands of individual Safety Instrumented Functions. As a result of our vast experience in the field of SIS engineering,

Kenexis has developed advanced software tools which allow our expert consultants to execute SIL Verification calculations more accurately and efficiently then our competition, providing our clients with superior results at a fraction of the price.

Our proprietary equipment performance statistics database contains reliability statistics from numerous well known and industry specific sources, ensuring that our SIL verification calculations are accurate, providing our clients with confidence in the design and performance of their safety instrumented system.

SRS Development

All of the requirements developed during the Risk Analysis and Conceptual Design phases of the Safety Lifecycle, and other safety critical requirements, need to be collected and presented in a Design Basis Document that can be used for subsequent detailed design engineering.

Kenexis assists in the preparation of Safety Requirements Specifications (SRS) packages that ensure a sound design basis and provide a guideline for subsequent acceptance testing activities. Development of SRS is a critical step in the safety lifecycle. Kenexis SIS consultants are experienced in the authoring of SRS and ensure that the systems integrator is provided with an easy to follow Detailed Design Document for implementation of the SIS while providing the end user with complete documentation of the safety instrumented system (SIS) design basis.

Maintenance and Testing (Validation) Support

Ensuring the ongoing integrity of a SIS throughout its lifecycle requires vigilant maintenance and testing practices that are in alignment with the risk analysis assumptions and requirements specifications.

Kenexis helps its customers to meet their mechanical integrity requirements by developing Test Procedures for safety instrumented systems (SIS), and assisting in the implementation of those tests.

Kenexis also helps to ensure good lifecycle performance by monitoring and tracking actual equipment performance against assumptions, and auditing system activity and changes to reconcile system performance and equipment changes against initial assumptions and specifications.

Functional Safety Assessment

Functional Safety Assessment and Certification by Independent and expert third parties has been effectively utilized by industry as a tool for ensuring that the safety instrumented systems (SIS) are designed in compliance with the IEC 61511 standard and best practices of peer companies.

Kenexis is uniquely qualified to assist organizations in the process industry to perform this task.

Additional Information