'Layer of Protection Analysis ' ; AIChE ― CCPS, 2001 presents a clear description of all key features of LOP A. These include but are not limited to: decision making and decision making criteria, IPL (Independent Protection Layer) credits for features like Basic Process Controllers, and Initiating Event Frequency. Much of the LOP A method is presented using continuous process as examples to illustrate LOP A methods. In practice we have found that most of the requests for LOP A involve processes and scenarios that are complicated. Usually, the complications involve batch or intermittent operations, and at the center of the confusion is an understanding of the initiating event. Becoming well practiced in the description of an initiating event and its frequency is the major challenge in the successful resolution of a process safety issue using LOP A. This paper will present an example of a process involving electrolytic cells. The operation of a cell is continuous. However, the shutdown of individual cells for maintenance and electrolyte replacement generated the potential for hazardous events that were analyzed using LOP A. This analysis was used to demonstrate to the Project Team the potential risks involved in these intermittent operations. At the conclusion of the analysis the shutdown events were shown to be the "risk drivers "for the process -a result that was unexpected. The paper also presents the framework for the overall risk analysis of this cell process and the role of LOP A in the decision-making and recommendations for this venture.
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