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
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.
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