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If the concept of alarming a process point is so simple, then why do so many alarm system configurations end up as miserable failures? In many cases, the causes can be traced back to the original configurations and the criteria used to select the points to alarm. Back when all alarms were hardwired (and the costs of alarming points had to be justified), a lot more thought was given to alarming points. Due to the development of computer based control and alarming, the costs associated with alarming a point have disappeared, along with much of the thought process of selecting alarm points. Ill conceived alarms manifest themselves in problems such as:

  • Alarms that have no operator action
  • Alarm conditions that have multiple alarms
  • Ambiguous or confusing messages
  • Ambiguous alarm priorities
  • Alarms with improper setpoints or deadband causing alarm cycling
  • Alarms that are ‘in’ during normal operations
  • Actuation rates in excess of operator’s information processing capabilities

Taken together, the additive effect of the alarm system problems can render an alarm system useless or even detrimental to operator performance. It is not uncommon during upsets for operators to completely disable alarm systems and rely solely upon their surveillance activities for critical process information.

To address alarm system problems new technologies are continually being tried. Expert systems are the latest fad. However, in most cases, is the investment really justified? Will making the system more complicated really solve the problems? Is putting a decision aiding system on top of an alarm system that has redundant and other nuisance alarms a smart thing to do? It has been Beville Engineering’s experience that there is much basic work that needs to be done to improve alarm systems. Many alarm systems fail to have the basics done correctly, let alone be in a position in which a new technology should be implemented. No magic bullet will solve all alarm system problems. Doing the basics correctly will go a long way towards correcting a majority of alarm system problems.

Many facilities fail to effectively plan and create a proper foundation for configuring and maintaining alarm systems. Controlling documentation needs to be developed that can be used to guide the alarm system development. There exists a fairly high degree of subjectivity in configuring an alarm system. With large numbers of instruments and a large pool of people working together to create an alarm system, a significant amount of variability can be introduced into a configuration. Controlling documentation needs to be developed to reduce the variability.

One of the most critical steps in creating an alarm system is to create a design guide. The design guide is essential in defining alarm selection criteria and integrating the alarms with the displays. The design guide also serves as a control on how the alarm system is changed as new alarms are added to a process. In the design guide, alarm system philosophy is outlined and the alarm selection and classification criterion is explicitly stated. Some of the topics that should be addressed in the design guide include:

  • Purpose/goals of alarm system - What conditions or events are candidates for alarms, what events are alarms trying to prevent.
    • Alarm priorities - The number of priorities and their exact meaning.
    • Hardware conventions - Emergency priority alarms hardwired and eggcrated, etc.
    • Alarm presentation and retrieval conventions
  • Coding definitions- color, shape, tone, etc.
  • Acknowledgment/silencing
  • Emergency alarms in constant view of operator
  • Control system diagnostics separate from process alarms
  • Controlling criteria
    • an alarm must prompt an operator action
    • no redundant alarms for same alarm condition
    • redundant instrumentation will be ‘ored’ together
    • no alarms ‘in’ during normal operations
    • status changes are not alarmed but are explicitly illustrated in the displays
    • Alarm cutout and suppression
    • Managing alarm system changes

After the alarm system design guide has been developed, the next step is implementation. Reviewing alarms is best done in a group setting. The process should involve a number of different groups. Obviously, operations representatives need to be involved. The control systems group should also be involved as should a facilitator. A facilitator is needed to keep the focus of the group and ensure the criterion is applied consistently, and to follow-up on unresolved issues.

There is much to be lost with an alarm system that is troublesome. At one facility, missing an alarm shut the facility down for one week and cost the company close to 100 million dollars. A small up-front investment to lay a proper foundation for an alarm system can pay big dividends in reduced down time and minimized off-spec products.

Copyright © 1997 Beville Engineering, Inc. , All Rights Reserved

For further information, visit the links below.

| Alarm & Display System Analysis Overview | Alarm Management | Display Design | Alarm & Display Design Seminar | Beville Shape Calculator -Excel download | Alarm Distribution Estimator -Excel download |


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This year's Fall meeting for the Center for Operator Performance will be October 24-26 in Corpus Christi. For more information, please contact Lisa Via. Guests are always welcome!


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David Strobhar's book, "Human Factors in Process Plant Operation," is now available in both hardcover and Kindle e-book.

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