How to Efficiently Perform the Hazard Evaluation (PHA) Required for Non-Routine Modes of Operation (Startup, Shutdown, Online Maintenance)

摘要

Process safety is about controlling risk of failures and errors; controlling risk isprimarily about reducing human error. All elements of Risk-Based ProcessSafety (RBPS) and alternative standards for process safety (such as USOSHA’s standard for Process Safety Management [PSM] or ACC’s ProcessSafety Code? [PSC]) have many elements, and each of these in turn help toreduce the chance of human error or else limit its impact. One core element isthe process hazard analysis (PHA), also called a hazard identification and riskassessment (HIRA). PHAs have been performed formally in graduallyimproving fashion for more than five decades. Methods such as HAZOP andWhat-If Analysis have been developed and honed during this time. But, oneweakness identified twenty years ago still exists in the majority of PHAsperformed around the world; most PHAs do not thoroughly analyze the errorsthat can occur during startup mode, shutdown modes, and other non-routine(non-normal) modes of operations. This is despite the fact that most majoraccidents occur during non-routine operations (about 70%), even though theprocess/plant may only be in that mode of operation for 5% or less a year.Instead of focusing on the most hazardous modes of operation, most PHAsfocus on normal operations. In a majority of both older operations and newplants/projects, the non-routine modes of operations are not analyzed at all.This means that perhaps 60 to 80% of the accident scenarios during nonroutineoperations are being missed by the PHAs. If the hazard evaluationdoes not find the scenarios that can likely occur during these non-routineoperations, the organization will not know what safeguards are neededagainst these scenarios.This paper shows practical ways to efficiently and thoroughly analyze the stepby-step procedures that are used to control non-routine operating modes, aswell as those for batch and between batch operations. This paper builds uponthe methods and rules provided in papers beginning in 1993 and brings themup-to-date. Experienced PHA leaders should be able to use the rules andapproaches provided in this paper to improve their PHAs. And others will beable to use the results of this paper to estimate the number of accidentscenarios they may be missing and to estimate the time it would take tocomplete an efficient and thorough PHA of the non-routine modes ofoperation.