Modern control systems provide great value, but with the benefits come problems. Increased information for the operator has a downside: what to do with all that information.
Some level of rationalization is needed to cope with information overload, particularly as it pertains to operator alarms. "Some systems are now so abstract they approach the complexity of a video game," says safety expert Bill Mostia.
You can't give a customer an alarming scheme that might overwhelm operators. You may also find yourself working with your customers to simplify alarm systems that have increased incrementally over time, and now have become problems.
Mostia, who works for safety consultants Exida Inc., and is an occasional contributor to Control Design, is worth listening to on the subject.
"In older control systems, hardwired panels provided alarm annunciation," he says. "The panels were large but limited in capacity, and so by their very nature tended to limit the number of alarms. In modern control systems, alarms are generally software-driven and are essentially free for existing process variables. We can configure a new alarm at the flick of a finger, and there has been a lot of flicking going on."
He adds that regulations from OSHA and the EPA, as well as voluntary programs such as ISO 9000 and 14000, have led to the addition of alarms, sometimes with little consideration of the effect on alarm loads at the system level.
"Alarm rationalization is the systematic process of optimizing the alarm database for the safe and efficient operation of the facility," says Mostia. "This process normally results in a reduction in the total number of alarms, the prioritization of alarms, the validation of alarm parameters, the evaluation of alarm organization and presentation, evaluation of alarm functionality, etc."
While alarm rationalization will vary from company to company, Mostia says the methodology generally consists of eight basic steps. These steps are listed serially but, in fact, may overlap or run in parallel. They are:
1. Develop an alarm management procedure.
2. Develop alarm system metrics.
3. Benchmark the existing alarm system.
4. Identify and analyze individual alarms.
5. Prioritize alarms.
6. Rationalize the alarm database.
7. Implement the rationalization.
8. Benchmark the new alarm system.
Mostia says there are not a lot of solid guidelines in the area of alarm management/rationalization, but suggests a few sources to check out. He says the best known is probably the British Engineering Equipment and Materials Users Assn. (EEMUA) (www.eemua.co.uk), which has a guideline, "Alarm Systems, a Guide to Design, Management and Procurement, EEMUA Publication No. 191."
ISA offers ISA TR91.00.02, "Criticality Classification Guideline," which provides guidance in defining types of systems, as well as ANSI/ISA S18.1 1992, "Annunciator Sequences and Specifications."
IEC has IEC 61508, "Functional Safety of Electrical/Electronic/Programmable Electronic Safety-Related Systems," and IEC 61511, "Functional Safety: Safety Instrumented Systems for the Process Industry Sector," which address safety-related and safety instrumented systems that may have some application where credit is taken for alarms during risk assessment.
"The Abnormal Situation Management (ASM) consortium of major companies has done considerable work in abnormal situation management and has a number of good articles at www.asmconsortium.com," he adds. "And a good presentation on alarm systems, 'Useful and Usable Alarm Systems: 43 Recommendations,' can be found at the CERN web site (http://tcr.home.cern.ch/tcr/projects/TCR_Sim/docs/alarm_system_CERN_number_3.ppt)."
Mostia notes a number of suppliers for alarm management and rationalization products and related services: Control Arts (www.controlartsinc.com), Exida (www.exida.com), Honeywell (www.assetmax.com), Matrikon (www.matrikon.com), Process Automation Services (www.pas.com), Process Systems Consultants (www.prosysinc.com), and TiPS (www.tipsweb.com).
Why Rationalize Those Alarms?
* To make sure operators get information they need when they need it, formatted so they can recognize what's happening, its importance, and the appropriate action.
* To reduce the total number of alarms to the minimum necessary to operate safely and efficiently.
* To prioritize alarms by importance or significance in terms of risk and in relationship to other alarms.
* To improve presentation, organization, and availability of alarms for safe and efficient operation and effective troubleshooting.
* To validate all alarm parameters including action, setpoint, deadband, test frequency, etc.
* To verify alarm performance parameters including detection time, required action, appropriateness of action, required time to perform action, training, procedures, help screens or manuals, etc.
* To identify process design issues and faulty field instrumentation.
* To document the alarm system for internal use and regulatory compliance.