Where Alarm Management and Process Safety Intersect

Alarm management and process safety are closely intertwined. Your alarm management system and associated operator intervention are often the last line of defense before a safety system trip. However, the role of alarm management is also important when you consider other layers of protection, such as the process control system. The ISA 18 and IEC 62682 standards govern alarm management for the process industries, while the ISA 84 and ISA 61511 standards cover safety instrumented functions (SIF).

The role of alarms in safety instrumented functions and process safety, however, can be a gray area, with some overlap between the ISA 84 and ISA 18 standards. Both standards bodies have more work to do when it comes not only to the role of safety alarms, but also highly managed alarms that fall in between the categories of everyday process alarms and critical safety alarms. The ISA 84 and ISA 18 standards committees have created a joint working group to address these issues. This JWG will help end users better classify alarms and more clearly define the role of alarms in the safety system versus the role of alarms in process control systems. This includes those "highly managed" alarms that can be so important, but may not have an immediate impact on plant safety.

Understanding Relationships Between Alarm Management and Safety Instrumented Functions

The role of alarm management as it relates to safety instrumented functions can be unclear. A good understanding of the role of alarms in process safety is necessary both for optimum operator effectiveness and plant safety. Many end users are undergoing alarm management projects at their respective plants or across their companies right now. In some cases, they are migrating from an old alarm management system. In others, they are initiating a new alarm management program. In either case, if you are undertaking such a project, it's a good idea to have a comprehensive understanding of where process alarms and safety intersect.

The internationally recognized standards are a good place to start. ISA 18.2 is the standard for alarms in North America. Its IEC counterpart is IEC 62682. However, as previously mentioned, these standards could do more to define the roles of alarms in safety applications. The internationally recognized safety standards fall into different buckets, which can be an issue. ISA 84 and IEC 61508/61511 are the safety standards.

In alarm management, there are many different classes of alarms, all with their own requirements. The same can be said for process interlocks. Process interlocks prevent incorrect operation and possible damage to process equipment. Safety interlocks prevent hazards to humans and are designed to prevent death, injury, or a major process incident. A third classification of interlocks is also emerging that provide an independent protection layer (IPL). While these count as a layer of protection, they are not actual safety interlocks that address an abnormal situation. In other words, IPLs protect against abnormal situations, or an “undesired consequence,” while safety interlocks respond to undesired consequences and take the process to a safe state.

The same logic can be applied to alarms. All alarms should require an operator response per ISA 18, but not every operator response will be a critical safety-related response. A disruption in the process for a food plant, for example, must be documented in a certain way to satisfy regulatory requirements as a food safety alarm. This kind of an alarm is not an everyday process alarm that you would find in a downstream petrochemical plant, nor is it a safety alarm. Instead, it falls into a class called "highly managed" alarms

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Keywords: Alarm Management, Process Safety, Interlocks, Layers of Protection, Standards, ISA 18, ISA 84, IEC 61511, IEC 61508, IEC 62682, ARC Advisory Group.