• Messages to indicate to the operations team that suppression is active, or means for operators to see which alarms have been suppressed; and
• Necessary conditions for the release of suppression as the plant returns to normal or enters a different operating mode.
Logic used to detect the need for suppression and for release from suppression must be robust and transparent to the operations team.
Because many plants currently don’t utilize any alarm suppression functionality, it promises considerable improvements — particularly when robust tools for suppression are available from DCS vendors.
Make More Progress
The need for improved alarm management gradually became more apparent after the Milford Haven accident and has received much attention and investment in recent years. Considerable progress has been made — much of it due to wide application of the EEMUA guidance to rationalize the alarm system.
A significant number of plants now average rates of fewer than 10 alarms per hour in routine operation, enabling plant operators in such plants to be much more effective and proactive.
However, significant problems remain. In particular, many plants experience alarm floods far too often. An ASM Consortium study found that not a single one of 37 consoles studied achieved the EEMUA recommendation of fewer than 10 alarms during the first 10 minutes of an upset. During floods, many alarm systems are of little value to operators and are effectively unusable. Clearly, more-effective alarm systems may have avoided some serious accidents or at least reduced their consequences. Unfortunately, alarm rationalization efforts alone don’t provide the performance improvement needed during upsets.
Bodies such as the U.K.’s Health and Safety Executive recognize the problems that can occur when alarm management is poor, and are providing regulatory drivers for plants to improve performance. More extensive use of the six techniques described here can play a significant part in enhancing alarm management.
Take Advantage of Shutdowns
Alarms failing to activate during accidents can lead to dire consequences. For example, some significant liquid-level alarms didn’t go off during the 2005 accident at BP’s Texas City, Texas, refinery . Such alarms may have been out of service for a long period without staff realizing this. If fully operational alarms had been activated during the startup, operators conceivably might have had sufficient time to avoid or reduce the consequences of the accident.
Don’t wait until a startup to find out if important alarms for the startup are working. Schedule testing during the shutdown period immediately prior to startup — particularly if it’s known that these alarms haven’t been activated for a long period. This testing should be highly selective, focusing on the small number of higher priority alarms that truly are significant during startup operations. This strategy is much more cost-effective than simply relying on routine testing of all configured alarms.
Peter Andow is a principal consultant, advanced solutions, for Honeywell Process Solutions, Bracknell, U. K. E-mail him at email@example.com.
1. “The Explosion and Fires at the Texaco Refinery, Milford Haven, 24 July 1994,” HSE Books, Sudbury, U. K. (1995).
2. Bransby, M. L. and J. Jenkinson, “The Management of Alarm Systems,” HSE Books, Sudbury, U. K. (1998).
3. “Alarm Systems — A Guide to Design, Management and Procurement,” Publ. No. 191, 2nd ed., EEMUA, London, U. K. (2007).
4. Andow, P., “Abnormal Situation Management: A Major U. S. Programme to Improve Management of Abnormal Situations,” IEE Colloquium on “Stemming the Alarm Flood,” London, U. K. (1997).
5. Campbell Brown, D., “Practical Steps Toward Better Management of Alarms,” Proceedings, “Alarm Systems,” IBC, London, U. K. (2000).
6. Nimmo, I., “Rescue Your Plant from Alarm Overload,” Chemical Processing, Jan. 2005, p. 28, http://www.ChemicalProcessing.com/articles/2005/209.html (2005).
7. Reising, D. V. and T. Montgomery, “Achieving Effective Alarm System Performance: Results of ASM Consortium Benchmarking against the EEMUA Guide for Alarm Systems,” Proceedings, 20th Annual CCPS Intl. Conf., Atlanta, Ga., AIChE, New York City (2005).
8. Zapata, R. and P. Andow, “Reducing the Severity of Alarm Floods,” Proceedings, Honeywell Users Group Americas Symposium 2008, Honeywell, Phoenix, Ariz. (2008).
9. Errington, J., Reising, D. V. and K. Harris, “ASM Outperforms Traditional Interface,” Chemical Processing, March 2006, p. 55, http://www.ChemicalProcessing.com/articles/2006/041.html (2006).
10. “Refinery Explosion and Fire, BP Texas City, March 23, 2005,” Report No. 2005-04-I-TX, U. S. Chemical Safety and Hazard Investigation Board, Washington, D. C. (2007).