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

摘要

While Safety Instrumented Systems (SIS) can be an essential element of process facility designrnto minimize the potential for process incidents, in some cases they can also be over-applied inrnthe design phases of capital projects where the Safety Instrumented Functions (SIFs) associatedrnwith the SIS are defined before the process hazards have been fully characterized. This approachrnmay provide one mechanism for achieving a robust process control system design; however, thernapplication of SIS also brings increased costs associated not only with the robust equipmentrnneeded to meet Safety Integrity Level (SIL) requirements, but also with the ongoingrnmaintenance, testing, and procedures required throughout the SIS lifecycle. In order to balancernthe important safety benefits associated with the SIS with the increased capital costs it is criticalrnto have a specific and comprehensive basis for decision-making. This paper will illustrate thernvalue engineering benefits of using the combined Hazard and Operability (HAZOP) Study andrnLayer of Protection Analysis (LOPA) methodology to comprehensively evaluate a design andrnprovide a decision-making platform for determining whether protection for process hazardsrnshould be implemented using a SIF, a Basic Process Control System (BPCS) feature, or alternaternsafeguard categories (e.g., relief valves, alarms, etc.) to ensure an adequate level of reliabilityrnwithout compromising safety. When the HAZOP/LOPA Study is performed following the valuernengineering session, the HAZOP/LOPA Study provides a critical cross-check to ensurernsafeguards are adequate and that changes made during the value engineering study do notrnintroduce additional hazards. In contrast, when the HAZOP/LOPA Study is performed prior tornthe value engineering session it provides a basis for decision making to remove SIFs or switchrnthe function to the BPCS when the risk was determined to be low by the team (as defined byrnspecific operating company criteria).