Chemical Processing - February 2008 - (Page 30)

appropriately rationalized by the process design team or weren’t configured properly into the control system. This, in turn, might cause some operators to lose respect for the alarm system and start ignoring alarm annunciations, possibly then missing real abnormal-situation alerts. The current situation It’s not unusual for a manufacturing facility to average more than 1,000 alarms/month (with some plants averaging far more). Many operators are frustrated by both the number of nuisance alarms they receive and the total number of alarms. Quality control personnel can be frustrated with a large number of abnormal situation incidents that must be formally investigated before product is forward-processed or released for sale. Plant management can be frustrated with an unacceptably high level of process variability caused by frequent abnormal situations. A number of factors contribute to the current situation: Increase in configured alarms. Plant personnel continue to add alarms to automation systems. The number of configured alarms per operator has dramatically risen during the past few decades (Figure 1). Some of this is due to the increasing implementation of smart sensors and valves. These devices communicate a large amount of information with the host process control computer — so automation engineers are tempted to configure alarms to much of this additional information. Always ask the question: Does this really represent an abnormal process upset requiring a response from the operator? If the answer is no, it’s not an alarm and shouldn’t be configured as one. Use the same logic for alarm remediation projects for existing systems. Low alarm implementation cost. Configuring an alarm has dropped dramatically in cost as the use of digital control systems has proliferated. Gone are the days when a new alarm required wiring and hardware additions to panel boards or other relay devices and several days or more to schedule the work. Now it often can be done in minutes by one person with a few simple keystrokes on a computer engineering console. More actual alarms per operator. The rise in configured alarms per operator normally correlates to a subsequent increase in actual alarms per operator. Sometimes, the frequency of alarms exceeds what an operator can reasonably be expected to handle, as suggested by EEMUA [1]. Lack of sufficient guidance on how to respond to so many different alarm conditions generally exacerbates the problem. Standard Operating Procedures (SOP) and operator manuals may exist but may not be quickly accessible when a major abnormal situation occurs on the plant floor. Sometimes, basic documentation is missing. For instance, some project design teams fail to document both 30 • February 2008 the rationale for selecting attribute values for an individual alarm and the expected operator response to abnormal situations. Again, always remember that an effective alarm should alert, inform and provide guidance to the expected response [1]. Multiple alarms per incident. An abnormal situation sometimes can generate many alarms, a so-called alarm flood — often confusing operators and generating information overload, rather than providing a single more intelligent conclusion for operators about what’s occurring. Distribution of alarm logic in many parts of the system. Part of the problem with overall alarm management is that alarm functionality resides throughout the automation system (Figure 2). For example, field devices, online analytical systems and Safety Instrumented Systems (SIS) as well as programmable logic controllers (PLC), distributed control systems (DCS) and interfaced thirdparty systems (e.g., expert systems) can generate alarms. ISA Standard S-95 offers some perspective on this, defining several different levels of automation. It’s a challenge to create an environment that consolidates alarm information such that a single user interface and alarm acknowledge/response paradigm exists. However, having alarms displayed in one place in a consistent format will help operators more effectively react to abnormal situations; having alarm records in a single database will greatly facilitate mining data for their information and knowledge content and generating batch reports. >> Number of configured alarms per operator 4,000 3,500 3,000 2,500 2,000 1,500 1,000 500 0 1960 1970 1980 1990 2000 Alarms per operator position conﬁgured Figure 1. Low cost and ease of implementing alarms in digital control systems have contributed to steep growth. Data reproduced with permission of PAS [2]. www.chemicalprocessing.com http://www.chemicalprocessing.com

Table of Contents Feed for the Digital Edition of Chemical Processing - February 2008

Chemical Processing - February 2008 Contents From the Editor ChemicalProcessing.com Field Notes In Process Energy Saver Compliance Advisor Nanoparticle Safety Raises Questions Take the Pressure Off Vacuum Systems Achieve Optimum Centrifugal Pump Performance Rethink Batch-Manufacturing Alarm Systems Dr. Gooddata Orlando Plant Pioneers HMI Migration Strategy Process Puzzler Plant InSites Equipment & Services Ad Index Product Spotlight/Classifieds End Point

Chemical Processing - February 2008

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