Alarm Systems for the Process Industries

ANSI/ISA 18.2-2016 Alarm Systems

Alarm systems are needed to communicate abnormal process conditions or equipment malfunctions before they have the chance to cause any severe problems. Unfortunately, for industries like manufacturing, past errors in common practices haven’t been uncovered until after they’ve led to some kind of disaster. Take for example, the Triangle Shirtwaist Factory Fire in 1911, which killed 145 garment factory workers, but ultimately led to the adoption of more stringent safety standards for workers under such conditions.

Today, safety standards have enhanced far beyond those of the past century, and they help to promote workplace safety while granting greater efficiency. However, even with stringent standards that regulate and recommend guidelines for the maintenance of equipment and employee training in manufacturing, there still exists the possibility of something failing. Alarm systems are needed because accidents can always happen, and preparedness is a far better alternative to tragedy. ANSI/ISA 18.2-2016 - Management of Alarm Systems for the Process Industries specifies the general principles for alarm systems based on programmable electronic controller and computer-based human-machine interface (HMI) technology for facilities in the process industries.

These alarm systems can include both the basic process control system (BPCS) and the safety instrumented system (SIS), each of which uses measurements of process conditions and logic to generate alarms. These include many different functions, which are indicated through Figure 1 of ANSI/ISA 18.2-2016:

ANSI/ISA 18.2-20161

ANSI/ISA 18.2-2016 allows for the proper installation of alarm systems by focusing on the lifecycle management of alarm systems. The alarm management lifecycle is presented in the document through the following steps: philosophy, identification, rationalization, detailed design, implementation, operation, maintenance, monitoring & assessment, management of change, and audit.

The actual process of these steps is clear through their labels, with the lifecycle beginning at philosophy – the basic planning, including incorporating relevant definitions of alarm classes and performance characteristics related to the specific alarm system – and ending at audit – the conduction of periodic reviews to evaluate the effectiveness of the alarm system. The audit and philosophy loop is demonstrated in Figure 2 of the standard:

ANSI/ISA 18.2-20162

However, while the philosophy to audit method is recognized as the actual life cycle progression, it is generally only used for the installation of new systems, and ANSI/ISA 18.2-2016 allows for additional entry points into the cycle. For example, one can begin with the monitoring & assessment stage, in which an existing alarm system is monitored find existing issues. Another option is beginning with the audit stage. This alternative allows for benchmarking, as the system is compared against a set of documented practices. The results revealed from this can be used in the development of the alarm philosophy stage later on.

The philosophy stage is especially important because of the variety of alternatives for alarm systems and equipment present within the process manufacturing industries. Because of this, any owner of an alarm system will need to consider from a wide variety of alarm types, and possibly even special considerations relative to the product manufactured and equipment used.

Of course, an alarm system means nothing if it cannot be detected by an individual, who must then take appropriate action to address whatever has triggered the alarm. Also covered in the philosophy stage is alarm training for workers, for the plant personnel will be prepared on the use, management, and design of an alarm system so that they can react when it is set off. This includes those who are responsible for alarm shelving, when necessary.

In addition, the standard covers alarm state transition paths, which involve the movement between states of awareness for the alarm, whether it be off, on, or completely inactive. A keen understanding of these states can give the plant operator an understanding of an alarm system’s reliability, letting it be ready for any use without the interference of issues like delays.

ANSI/ISA 18.2-2016 - Management of Alarm Systems for the Process Industries is available on the ANSI Webstore.

1. International Society of Automation (ISA), ANSI/ISA 18.2-2016 - Management of Alarm Systems for the Process Industries (Triangle Park: ISA, 2016), 13.
2. International Society of Automation (ISA), ANSI/ISA 18.2-2016 - Management of Alarm Systems for the Process Industries (Triangle Park: ISA, 2016), 27.
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