When alarms are not relevant, they're worse than useless; they're dangerous.
"In the early 1990s, the cost of adding these alarms was quite expensive," said Arnold Austin, senior process control engineer for Emerson Automation Solutions.
"You had to add buttons, lighting, wiring and dedicated horns to the console panel, and nobody thought about the negative consequences of overall alarming. "All that has changed to where alarm configuration is just a simple digital security control setting. Alarms must be relevant to the operator."
Levi Merkel, process controls engineer for CHS Inc., agrees with Austin's assessment and expounded on the role rationalization now plays in alarm design.
"The purpose of alarm rationalization is to alarm intelligently," Merkel said. "What that means is to have the right alarms in place, [set] the right alarm limits and make sure each alarm can fit the characteristics of a quality alarm."
By definition, according to the International Society of Automation (ISA), rationalization is "the process to review potential alarms using the principles of the alarm philosophy, to select alarms for design and to document the rationale for each alarm."
Merkel elaborated on this definition, offering a set of five characteristics that compose a quality alarm.
"It's identifiable in an abnormal condition, it can be actionable by the operator, a consequence exists if that action is not taken, and it's unique in its cause." Merkel said. "But what you want to focus on is that it's relevant to the operator who is being alarmed."
Relevance, Merkel continued, has many different meanings.
"Primarily, the alarm is configured in the operator's area of control," he said. "In other words, a high-pressure alarm in Unit A is not alarmed on Unit B's console."
The alarm is indicative of the consequence that operators are trying to prevent, Merkel added.
"A low-level alarm in a tank should be used for indication of high fuel gas pressure, for example," he said.
Further, the alarm is relevant to the operating state of the unit.
"That's where dynamics come in," Merkel said. "Let's say you have a high-level alarm configured below your normal operating pressure when your reactor's skin pressure are under 300 degrees Fahrenheit. Dynamic rationalization allows you to accomplish that last bullet point of being relevant to the operating state of the unit."
Static vs. dynamic alarming
Merkel said that, typically, alarm systems have a static design that can lead to nuisance alarms in transient states; moreover, all alarms are not necessarily relevant to every state.
Merkel explained that in static rationalization, alarm configuration is based off of the most common state of unit.
"Static rationalization, although beneficial, presents challenges, and that's where dynamic alarming can help," he said.
Dynamic alarming is the practice of managing alarms for various operating states for a process unit, the specific portion of a process unit or piece of equipment.
Dynamic rationalization allows for alarms relevant to the state of the unit to be active.
"'Relevance' is the word of the day," Merkel reiterated. "Suppression of alarms is expected to be enunciated in certain states, which reduces alarm flood. Then, startup and shutdown alarm limits can be configured as well."
Merkel shared that a dynamic rationalization project was recently implemented refinery-wide to CHS' alarm system.
Tangible results included reduction of alarm floods and improvement of alarm system design to help operators, Merkel said.
"The reduction of alarm floods is the goal of dynamic rationalization," he said. "And we were able to leverage dynamics and the tools that dynamics provide to help operators by improving the alarm system's design. When the operator has alarms activated on his console and he's going through shutting down the unit, he's getting five-times fewer alarms in that scenario. That's a huge benefit."
"Any alarm rationalization project starts with a well-prepared alarm philosophy document that specifically says what your facility standards, corporate-wide, are going to be, in line with those ISA documents as well," Austin concluded.
