alarm management

Alarm management is the application of human factors (or ergonomics as the field is referred to outside the U.S.) along with instrumentation engineering and systems thinking to manage the design of an alarm system to increase its usability. Most often the major usability problem is that there are too many alarms annunciated in a plant upset, commonly referred to as alarm flood, since it is so similar to a flood caused by excessive rainfall input with a basically fixed drainage output capacity. However, there can also be other problems with an alarm system such as poorly designed alarms, improperly set alarm points, ineffective annunciation, unclear alarm messages, etc.

The need for alarm management

Alarm management is usually necessary in a process manufacturing environment that is controlled by an operator using a Distributed Control System, or DCS. Such a system may have hundreds of individual alarms that up until very recently have probably been designed with only limited consideration of other alarms in the system. Since humans can only do one thing at a time and can pay attention to a limited number of things at a time, there needs to be a way to ensure that alarms are presented at a rate that can be assimilated by a human operator, particularly when the plant is upset or in an unusual condition. Alarms also need to be capable of directing the operator's attention to the most important problem that he or she needs to act upon, using a priority to indicate degree of importance or rank, for instance. A good example of this problem is from the old US sitcom MASH. A common scene was Radar O'Reilly slipping in a requisition for something that Hawkeye wanted in the stack of papers for Colonel Potter to sign. In much the same way, if alarms were unprioritized, the important ones can be mixed in with lower value nuisance ones.

Some improvement methods

The techniques for achieving rate reduction range from the extremely simple ones of reducing nuisance and low value alarms to redesigning the alarm system in a holistic way that considers the relationships among individual alarms.

Nuisance Reduction

The first step in a continuous improvement program is often to measure alarm rate, and resolve any chronic problems such as alarms that have no use (often described as one that does not require the operator to take an action).

Design Guide

This step involves documenting the methodology or philosophy of how to design alarms. It can include things such as what to alarm, standards for alarm annunciation and text messages, how the operator will interact with the alarms, etc.

Documentation and Rationalization

This phase is a detailed review of all alarms to document their design purpose, and to ensure that they are selected and set properly and meet the design criteria. Ideally this stage will result in a reduction of alarms, but doesn't always.

Advanced Methods

The above steps will often still fail to prevent an alarm flood in an operational upset, so advanced methods such as alarm suppression under certain circumstances are then necessary. As an example, shutting down a pump will always cause a low flow alarm on the pump outlet flow, so the low flow alarm may be suppressed if the pump was shut down since it adds no value for the operator, because he or she already knows it was caused by the pump being shutdown. This technique can of course get very complicated and requires considerable care in design. In the above case for instance, it can be argued that the low flow alarm does add value as it confirms to the operator that the pump has indeed stopped.

Alarm management becomes more and more necessary as the complexity and size of manufacturing systems increases. A lot of the need for alarm management also arises because alarms can be configured on a DCS at nearly zero incremental cost, whereas in the past on physical control panel systems that consisted of individual pneumatic or electronic analog instruments, each alarm required expenditure and control panel real estate, so more thought usually went into the need for an alarm. Numerous disasters such as Three Mile Island and the Chernobyl accident have established a clear need for alarm management.

See also

• List of human-computer interaction topics, since most control systems are computer-based
• Design, especially interaction design
• Detection theory
• Physical Security

External links

• "The Alarm Management Handbook"
• "Better Alarm handling", from the British Government's Health and Safety Executive (HSE)
• EEMUA 191 Alarm Systems - A Guide to Design, Management and Procurement (1999) ISBN 0-85931-076-0
• "Principles for alarm system design" Norwegian Petroleum Directorate
• Alarmmanagement Willem Hazenberg BSc Thesis about the businesscase

Donate to Wikimedia