Better control strategies and procedures directly improve plant production and operations. However, poor alarm management, which is all too common, can undermine both productivity and safety.
The importance of effective alarm management has increased as the number of alarms has risen. Today, because of innovative hardware, software and instrumentation, plants can install alarms on virtually all plant equipment to improve productivity and safety. In addition, the growing sophistication of smart field devices that can warn about condition and performance issues has unleashed another wave of alarms (many of which should go to maintenance rather than operations). This often leads to over-alarming and alarm floods from the distributed control system (DCS) afflicting operators when an upset occurs.
Most chemical plants don’t need more alarms, instead they need better alarm management to identify and implement essential alarms and to eliminate unnecessary ones. Working with alarm rationalization consultants in combination with software to guide and track the progress, chemical companies can rethink their plant protection schemes and develop an alarm hierarchy to rank alarms and events according to impact on the process or critical equipment. Such programs can reduce the number of alarms to only the most crucial ones, thus improving operator response and increasing plant uptime.
So, here, we’ll explore opportunities to enhance operational performance through rationalized alarm databases and systems as well as using software to clarify corrective operator actions.
The Protection Hierarchy
Plants rely on a number of independent protection layers (IPLs) to handle incidents (Figure 1). If an event moves up the list of layers, each escalation results in a more drastic action and has the potential to cause a more catastrophic impact.
Effective process alarms are part of IPL 2 and 3; they should spur actions to address an incident within those layers because that will avoid or at least minimize production disruptions. Moving to IPL 4 leads to a more drastic action related to the safety instrumented system (SIS) or an emergency shutdown (ESD) function, which almost invariably results in more severe consequences capable of adversely affecting production levels or quality.
Even so, the situations causing alarm trips at IPL 2 can undermine, even if only slightly, operational efficiency and product quality. Some plants tend to concentrate on protecting equipment and, thus, give the highest priority to those alarms. This often is wasteful because those equipment protection functions are better left to IPL 4. Giving those alarms the highest priority makes the entire alarm system more difficult to handle.
At the same time, moving to IPL 4 often brings a new wave of alarms that aren’t related to process conditions but to the performance of the SIS itself. For example, if the valve at the inlet of a reactor doesn’t close as it should when directed by the SIS during an incident, an alarm should trip to warn that this emergency step hasn’t happened and the valve may require manual closing. These types of alarms should be in their own category because the consequences of such situations are well beyond those of alarms tied to IPL 2 and 3. Some plants don’t set these alarms apart; they become lost among more trivial lower-level ones.
Therefore, it’s critical during the alarm rationalization process to determine the consequences of a situation generating an alarm and the corresponding remedial action (Figure 2). As the diagram illustrates, as a situation escalates, the consequences and needed actions become more drastic and have a more serious impact on production.
For existing processing facilities, it’s especially important to develop a plant-wide protection hierarchy and priority matrix to identify and create better alarm strategies. Alarm management and SIS evaluation both begin with inherently safer unit design. A unit that is well regulated will have fewer upsets, alarms and incidents. When alarms primarily serve as a mechanism to compensate for poor control strategy, the plant effectively is running in manual. Any evaluation of alarm strategy must begin by asking how well the unit runs under normal conditions and then correct any glaring flaws.