The High Cost of Poor SIS Lifecycle Planning

Standards such as IEC 61511 (Functional Safety for Safety Instrumented Systems for the Process Industry Sector) are derived off of the concept that Safety Instrumented Systems (SIS) should be designed, installed, operated and maintained as part of a holistic safety lifecycle. Yet, all too often, some are satisfied to “check the box” with respect to SIS design requirements of IEC 61511, while failing to implement a true lifecycle approach. This short-sighted view ignores critical factors that shape SIS performance over the entire installed lifetime of the equipment. It results in a poorly operated SIS that can fail to provide the expected protection and is easily defeated by changes during the lifetime of the system. It also rejects the value proposition that IEC 61511 offers, which is reduced long-term operational cost over the lifetime of the equipment.

This paper will discuss best practices in establishing a holistic SIS design that maximizes effectiveness and reduces cost. The paper will discuss Safety Integrity Level (SIL) requirements and how to capture the most value during the design phase of SIS equipment. The paper also describes incidents that have happened and what warning signs to look for that your well-designed SIS might not hold up well to the inevitable plant modifications. Some methods for evaluating lifetime installation, operation and testing costs are provided. Lastly, the paper addresses management requirements that must be considered, implemented and reinforced during the facility life.