Detecting abnormal situations
High-performance graphics also provide operators with easy recognition of plant and product health. This enables each operator to maintain the process at higher performance levels, leading to real economic gains for the plant owners. Research underscores this point, showing that operators are five times more likely to detect abnormal situations before an alarm occurs with the new generation of high-performance HMIs than with conventional graphics. Once an alarm is triggered, operators solve the problem in about half the time than with traditional interfaces.
High-performance HMIs not only make abnormal situations immediately visible on the screen, they also significantly reduce the number of alarms that vie for the operator’s attention. The maximum number of alarms that the human mind can deal with is just seven, give or take two in a given 10-minute period. Unfortunately, as seen in table 1, operators are bombarded with a constant stream of alarms. In the power industry alone, operators typically deal with 2,000 alarms per day and 350 in a 10-minute peak alarm period. It is therefore not surprising that operators become ambivalent to the constant drone of alarms, tending to ignore 'nuisance' alarms and run the plant on instinct. Clearly, operators cannot do their job effectively when critical alarms are inter-mixed with hundreds or even thousands of non-critical or nuisance alarms.
Eliminating unnecessary alarms
Standards like EEMUA 191 and ISA SP 18.2 have long recognized the need to reduce the number of alarms to match the operator’s cognitive capacity. In this way, the operator is focused and able to act on critical alarms when they occur. High-performance HMIs like S+ Operations have advanced alarm handling and analysis tools that support implementation of alarm management strategies based on EEMUA 191 and ISA 18.2 requirements, thereby ensuring that each alarm generated will alert, inform and guide the operator to take the proper action. An advanced alarm management strategy should fulfill the following objectives:
- The purpose of an alarm system is to direct the operator's attention to plant conditions requiring timely assessment or action;
- Alarms should be presented at a rate that operators can deal with;
- Each alarm presented to the operator should be useful and relevant to the operator; and
- Each alarm should have a defined response.
Case studies in cost savings
There are scores of examples and customer testimonies of how measures to improve operator effectiveness have increased productivity and reduced operating costs. Here are two examples from ABB’s portfolio of case studies.
In example 1, a gas plant improved control room operations and corrected its record of poor alarm management. Missed alarms, among other operational and ergonomic issues, were singled out as a major contributor to compressor trips that resulted in downtime and lost production. Fixing the problem reduced the compressor trips from 27 to 7 over a one-year period, saving an estimated $2 million.
Example 2 is a study of plant operators that measured and compared their situational awareness in a conventional distributed control system environment against one in a high-performance HMI environment using simplified gray-scale abnormal situation graphics and integrated alarm management. The figures in table 2 speak for themselves. They translate into estimated cost savings of $ 800,000 per year.
|
|
EEMUA
|
O&G
|
PetroChem
|
Power
|
Other
|
|
Average alarms per day
|
144
|
1,200
|
1,500
|
2,000
|
900
|
|
Average standing alarms
|
9
|
50
|
100
|
65
|
35
|
|
Peak alarms per 10 minutes
|
10
|
220
|
180
|
350
|
180
|
|
Average alarms / 10 minute interval
|
1
|
6
|
9
|
8
|
5
|
|
Distribution % (Low / Med / High)
|
80/15/5
|
25/40/35
|
25/40/35
|
25/40/35
|
25/40/35
|
Table 1: Average number of alarms in selected industries (source: MatrikonOPC)
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Task
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With traditional HMI
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With high performance HMI
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Result
|
|
Detecting abnormal situations before alarms occur
|
10% of the time
|
48% of the time
|
%x increase
|
|
Success rate in handling abnormal situations
|
70%
|
96%
|
26% over base case
|
|
Time to complete abnormal situation tasks
|
18.1 min
|
10.6 min
|
41% reduction
|
Table 2: Comparison of operator effectiveness in a conventional DCS environment and one using high-performance HMIs