Using the Integrated Hazard and Operability Study (HAZOP) Study / Layer of Protection Analysis (LOPA) Methodology As a Value Engineering Tool

While Safety Instrumented Systems (SIS) can be an essential element of process facility design to minimize the potential for process incidents, in some cases they can also be over-applied in the design phases of capital projects where the Safety Instrumented Functions (SIFs) associated with the SIS are defined before the process hazards have been fully characterized. This approach may provide one mechanism for achieving a robust process control system design; however, the application of SIS also brings increased costs associated not only with the robust equipment needed to meet Safety Integrity Level (SIL) requirements, but also with the ongoing maintenance, testing, and procedures required throughout the SIS lifecycle. In order to balance the important safety benefits associated with the SIS with the increased capital costs it is critical to have a specific and comprehensive basis for decision-making. This paper will illustrate the value engineering benefits of using the combined Hazard and Operability (HAZOP) Study and Layer of Protection Analysis (LOPA) methodology to comprehensively evaluate a design and provide a decision-making platform for determining whether protection for process hazards should be implemented using a SIF, a Basic Process Control System (BPCS) feature, or alternate safeguard categories (e.g., relief valves, alarms, etc.) to ensure an adequate level of reliability without compromising safety.