Process safety is about controlling risk of failures and errors; controlling risk is primarily about reducing the risk of human error. All elements of Risk-Based Process Safety (RBPS) and alternative standards for process safety (such as US OSHA's standard for Process Safety Management [PSM] or ACC's Process Safety Code? [PSC]) have many elements, and each of these in turn help to reduce the chance of human or else help to limit the impact of human error. One core element is the process hazard analysis (PHA), also called a hazard identification and risk assessment (HIRA). PHAs/HIRAs have been performed formally in gradually improving fashion for more than 5 decades. Methods such as HAZOP and What-If Analysis have been developed and honed during this time. But, one weakness identified 20 years ago still exists in the majority of PHAs performed around the world; most PHAs do not thoroughly analyze the errors that can occur during startup mode, shutdown modes, and other non-routine (non-normal) modes of operations. This is despite the fact that most major accidents occur during non-routine operations (about 75%), even though the process/plant may only be in that mode of operation for 1 to 5% of less a year. Instead of focusing on the most hazardous mode of operation, most PHAs/HIRAs focus on normal mode of operation. In a majority of both older operations and new plants/projects, the non-routine modes of operations are not analyzed at all. This means that perhaps 60 to 80% of the accident scenarios during non-routine operations are being missed by the PHAs/HIRAs. If the PHA/HIRA does not find the scenarios that can likely occur during these non-routine operations, the organization will not know what safeguards are needed against these scenarios.
This paper shows practical ways to efficiently and thoroughly analyze the step-by-step procedures that are used to control non-routine (and normal batch and between batch) operating modes. This paper builds upon the methods and rules provided in papers beginning in 1993, and brings them up-to-date. Experienced PHA leaders should be able to use the rules and approaches provided in this paper to improve their PHAs/HIRAs. And others will be able to use the results of this paper to estimate the number of accident scenarios they may be missing and to estimate the time it would take to complete an efficient and thorough PHA of the non-routine modes of operation.
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