Emerson Exchange 365

Alarm rationalization can be a tedious and time consuming process. Deciding what types of alarms a facility needs, what their parameters should be, and how to prioritize them is essential to running a safe operation—but it’s also hard to do. With the complexity of today’s technology, it’s often difficult to determine what the “real” operating envelope is. And the experienced operators who can do it are retiring in droves.

This week at the 2014 Emerson Global Users Exchange, John Rezabek of Ashland, Inc. discussed common challenges involving alarm rationalization and how to overcome them.

“There was a time when every alarm had to be justified because each one meant more hardware to purchase and install,” Rezabek said. “But for decades now, we’ve had systems like the DeltaV^TM distributed control system (DCS) where alarms became free – every point in the DCS could have high, high-high, low, low-low, deviation and bad quality alarms, and even more could be configured. Some of the alarm settings were part of safeguards identified during a HAZOP, but many were inconsequential or redundant, or nothing more than a snooze alarm for a weary operator.”

“But when a real plant upset happens, the abundance of frivolous or redundant alarms causes a deluge, and the 21^st-century DCS becomes less useful than the light-box ‘panalarm’ displays from days of yore. Operators can’t process all the alarms coming in and distinguish the important ones among all the clutter, and less experienced operators have no guidance what they should attend to next.”

“There have been a lot of smart people focused on alarm management in recent years, and in 2009 ISA published ANSI/ISA 18.2, Management of Alarm Systems for the Process Industries,” Rezabek continued. “One of the more onerous parts of alarm management is ‘alarm rationalization’– where a diverse team of plant personnel can spend weeks or months debating the merits of every alarm in the system.”

To take some of the pain and complexity out of alarm rationalization, Rezabek recommends that plant managers consider performing what he calls “pre-rationalization” using the plant historian and a unique piece of visualization software. Prior to convening the rationalization team, a solitary engineer can examine years of plant history to define the “actual” operating envelope, and discover redundancies and bad actors well in advance of formal meetings.

This method for visualizing a multi-dimensional problem was developed at IBM, and is now offered as a package called C Visual Explorer. By plotting thousands of observations for hundreds of variables using parallel coordinates, an individual can readily discern and query using the real operating envelope for the process – where it’s actually been versus where we think it should be. “This is an invaluable tool because it can represent visually what a process in its normal state looks like compared to what it looks like when certain alarms trip. It can also show how often those alarm-tripping conditions occur,” Rezabek said.

To eliminate redundancies, users can query historical data to identify the process variables that tend not to trip alarms, or never do. Alarms that tend to trip in groups—or as a result of several variables at the same time—are also typically prime targets for weeding out redundancies. Alarms triggered by only one variable are usually justifiable. To zero in on bad actors, the same queries can identify the parameters associated with the highest alarm trip rates.

When developing a new alarm plan, tentative alarm limits can be tested against historical data from a number of different time windows to quantify likely alarm rates. This exercise can be applied to any variety of process states, such as startup, shutdown, or total recirculation.

“Culling this data and analyzing it before your alarm rationalization team gets together in a room can help everyone understand what your plant’s safe and on-spec operating envelope looks like prior to delving into the alarm rationalization process,” Rezabek concluded. “And that can be extremely valuable in terms of time, money, and sanity saved for everyone involved.”