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The Operating Envelope approach to alarms gives better results with significantly less manpower than traditional alarm management. When documentation from an earlier alarm project is available, this work reduction can be even more substantial.

The word “rationalization” is often used to describe an entire alarms project covering activities in all of the steps defined in ISA SP18.2 and IEC 62682. One of those steps has been named “Rationalization”, so to distinguish them we will refer to entire projects in lower case with “rationalization” and capitalize the first letter when referring to the “Rationalization” step in a project.



Previous one-alarm-at-a-time rationalization practices worked from top-to-bottom covering all aspects of an alarm from the reason for its existence through its limit values and actions, through detail design and implementation considerations, its configuration in the DCS and even in which wiring cabinet should its transducer terminate.

That method required specialists from all engineering disciplines to be present in a long series of meetings often involving 10 or more people. It was expensive, inefficient at capturing the reasons for decisions and boring for the attendees as each individual's expertise was only required for maybe 10-20% of the time.

Unit process engineers in particular had difficulty in being away from their units for long periods and it was not uncommon to find instrument and control engineers struggling to complete rationalization projects and improve alarm performance for the operators by adjusting alarm priorities, introducing an over-dependence on techniques such as alarm shelving and sometimes over-use of dynamic alarming.

The Operating Envelope method views alarms as an inter-related set which allows one to work through all the alarms on a process unit side-to-side for each step with only the engineering disciplines relevant to that step needing to be involved.



For the Rationalization step only, the Unit Process Engineer and the Unit Operations Engineer are required and even they can work individually as leaders of two two-man teams. The combined work of the Red and Blue Teams leads to population of the Master Alarm Database (MAD) at the end of the Rationalization Step and effectively provides a Functional Specification for the following Detail Design Step.

The Blue team led by the Unit Operations Engineer is responsible for reviewing all alarm actions for presence and suitability and an initial 5/15/80% (5% of annunciations are high priority, 15% medium priority and 80% low priority) configuration of alarm priorities.

The Red team led by the Unit Process Engineer assisted by another process engineer or an experienced consultant engineer is responsible for establishing Operating Objectives, the Operating Envelope and values for alarm limits as well as several additional capabilities made possible by the other CVE functionality such as fine-tuning alarm priorities to better achieve the desired 5/15/80% as an annunciated rather than configured priority distribution and optimizing process sampling intervals. The workload is split 20/80 between the Unit Process Engineer and the assisting process engineer. Several process units can be taken through the Rationalization Step in parallel if sufficient assisting Engineer resource is available.

It is not uncommon to find that the Blue Team activities have been performed relatively recently by an earlier alarm project and that it is primarily the Red Team activities that are needed. We call a red team only project “Alarm Improvement” and a red and blue team project “Alarm Rationalization”.
 

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