Most everyone has heard of the “80-20 rule”. It asserts that for many situations, roughly 80% of the effects (outcomes) come from 20% of the causes (inputs). This rule was first proposed in the early 1900s by Vilfredo Pareto, who was an Italian engineer, sociologist, economist, political scientist, philosopher, and gardener. He observed that 20% of the peapods in his garden contained 80% of the peas. He applied this “mental model”, later referred to as the “Pareto Principle”, to the world of economics and determined it worked here as well; 80% of the land in Italy was owned by roughly 20% of the people.
Mental models are an important mechanism for interpreting new information in order to make sense of what is going on now and projecting what will happen in the future. The Pareto Principle (or the Power Law in mathematics) is one mental model. A “bell curve” (or a Gaussian / normal distribution in mathematics terms) is another example of a mental model. A pareto chart, shown below, is a representation of the 80-20 rule in action.
In alarm management, nuisance alarms often follow the 80-20 rule. If one looks at a pareto chart of the most frequently occurring alarms in a system, typically referred to as the “bad actors” list, you will find that the top 10 – 20 alarms often contribute 50 to 80% of the total “annunciations”. This means that of the thousands of alarms configured in the system, there are just a handful that generate most of the events. Not only do these alarms follow the pareto principle, but because they are generated so frequently, they are likely “false” alarms that the operator is ignoring. In the example report below, ten of the modules generate 60% of the alarm annunciations to the operator.
Thus the pareto distribution of alarm occurrences can help identify the worst performing alarms in the system. It can also be used to compare your performance against target metrics defined in the ISA-18.2 / IEC 62682 standards.
Including these alarms in your next alarm rationalization session can deliver significant benefit. Imagine being able to reduce the alarm load on the operator some 60% just by fixing 10 alarms. This is an investment that can have a significant payback in operator satisfaction and improved performance. To realize the full benefits of alarm management it is, however, important to perform a thorough alarm rationalization of the entire alarm system. Resolution of Bad Actors is not sufficient by itself to create a well-performing alarm system.