Alarm flooding is the phenomenon of presenting more alarms in a given time period than a human operator can effectively address. A significant finding of a 2006 research project of the Abnormal Situation Management (ASM) Consortium was that even though configuration techniques can significantly reduce the size of the alarm flooding associated with process upsets, these techniques on their own don't suffice to reduce the alarm loads to a level at which human operators can mentally process and physically respond. A key need that remains is to provide effective alarm summary displays to help operators cope with these inevitable alarm floods.
In plants where modern distributed control systems (DCSs) are installed, alarms are presented via scrolling lists on console monitors instead of via dedicated annunciator tiles as was done on older direct-wired panel boards. The traditional practice is to show alarms using a chronologically sorted list-based alarm summary display. The usability challenges of this display during an alarm flood include the fact that alarms move through the list and off the page faster than a typical operator can read them [1, 2]. The viewable list for a given page also fills up quickly; operators must scroll or change pages to see all the alarms that are occurring — taking their attention away from their operating displays and wasting valuable time. A consequence of the scrolling list is that alarms will move down the list as the operator actually is trying to read it; so to read the alarm details, the operator's gaze must descend at the same rate as the changing alarm position. Higher priority alarms also will be scrolled off a given page as it fills up while the operator's attention is directed elsewhere. Similarly, alarms that came in earlier in the flood (and that the operator may be "chasing" on other operating graphics) will have moved to successive pages in the alarm summary display. Therefore, the operator won't notice if any of these "clear" on their own accord.
It is apparent that the rapidly changing, chronological list-based alarm summary display installed in most process plants doesn't support the operator's situation awareness. The alarm list display tends to be too detailed with the presentation of sequential information and lacks the functional organization necessary to understand the nature and progress of a disturbance. Therefore, the ASM Consortium members decided to explore alternative visual display techniques that might improve operator situation awareness during plant upsets that result in these inevitable alarm flood situations [3, 4].
The consortium conducted a series of studies in 2007–2008 with experienced console operators in a controlled experimental setting to examine how two alternative visualization techniques compared to the traditional list-based alarm display (Figure 1) on operators' ability to respond to alarm flood scenarios.
Alternative Visualization No. 1 was an alarm display with an equipment-based overview — each major equipment area for which the console operator is responsible is represented at the top of the display in a single or double row of alarm panels. The panels are arranged in a left-to-right organization that intuitively reflects the plant process flow or geographical arrangement. Within each panel, alarm indicators are arranged vertically with the most recent alarms appearing at the top. Each alarm indicator provides key attributes such as alarm priority, acknowledgement status, alarm type, parameter type and a short tag descriptor. A mouse-over with the cursor results in the display of a full alarm description. The selection of a specific equipment area panel focuses the content of the detailed list (i.e., just below the overview) on alarms for just that area.
Alternative Visualization No. 2 was an alarm display with a time-based overview — each major equipment area for which the console operator is responsible is represented at the top of the display in rows of alarm panels (i.e., consistent with the two other summary displays). The panels are arranged in a top-to-bottom organization that intuitively reflects the plant process flow or geographical arrangement. Within each panel, alarm indicators are arranged horizontally with the most recent alarms appearing on the right (in a fashion similar to a trend display with the most recent information on the right). The selection of a specific equipment area panel focuses the content of the detailed list on alarms for just that area.
The study participants were volunteers — 45 active console operators from four plants in the Sasol Secunda Synfuels operations. Each operator received a two-hour familiarity training session on the display concepts and the alarm response task. In the performance evaluation sessions, each operator handled alarm floods in six simulated scenarios. The operators were asked to respond to an individual alarm or a group of alarms in the alarm scenario by pointing out where in the plant the problem was (i.e., specific unit and particular piece of equipment), what the key alarms were (i.e., indicators) and what underlying abnormal conditions were signified (i.e., conditions). As the alarms were appearing on the alarm summary displays, the participants continuously were trying to detect and interpret as many alarms as possible to respond to the underlying abnormal plant conditions.