Lessons Learned on SIL Verification and SIS Conceptual Design

by Richard E. Hanner & Ravneet Singh

​There are many critical activities and decisions that take place prior to and during the Safety Integrity Level (SIL) Verification and other Conceptual Design phases of projects conforming to ISA84/IEC61511. These activities and decisions introduce either opportunities to optimize, or obstacles that impede project flow, depending when and how these decisions are managed. Implementing Safety Instrumented System (SIS) projects that support the long‐term viability of the Process Safety Lifecycle requires that SIS Engineering is in itself an engineering discipline that receives from, and feeds to, other engineering disciplines.

This paper will examine lessons learned within the SIS Engineering discipline and between engineering disciplines that help or hinder SIS project execution in achieving the long‐term viability of the Safety Lifecycle. Avoiding these pitfalls can allow your projects to achieve the intended risk reduction and conformance to the IEC 61511 Safety Lifecycle, while avoiding the costs and delays of late‐stage design changes. Alternate execution strategies will be explored, as well as the risks of moving forward when limited information is available.


IEC 61511, Safety Instrumented Systems (SIS), Independent Protection Layers (IPL), Functional Safety Assessment (FSA), Safety Requirement Specification (SRS), Safety Lifecycle, Functional Safety Management Plan (FSMP), Project Execution Plan (PEP), SIS Front‐End Loading (SIS FEL), Layer of Protection Analysis (LOPA), SIL Verification

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