Features
Using Alarm Management to make Your Plant Safer
Recent industrial accidents at Texas City, Buncefield (UK) and Institute, WV have highlighted the connection between poor alarm management and process safety incidents. At Texas City key level alarms failed to notify the operator of the unsafe and abnormal conditions that existed within the tower and blowdown drum. The resulting explosion and fire killed 15 people and injured 180 more. The tank overflow and resultant fire at the Buncefield Oil Depot resulted in a £1 billion (1.6 billion USD) loss. It could have been prevented if the tank’s high level safety switch, per design, had notified the operator of the high level condition or had automatically shut off the incoming flow. At the Bayer facility (Institute, WV) improper procedures, worker fatigue, and lack of operator training on a new control system caused the residue treater to be overcharged with Methomyl - leading to an explosion and chemical release.
Accidents like these demonstrate what can happen when an alarm system and operator response fail as a layer of protection in a hazardous process. They also provided the motivation for the new ISA-18.2 standard “Management of Alarm Systems for the Process Industries”, which provides a framework for the successful design, implementation, operation and management of alarm systems in a process plant. It offers guidance on how alarm management can be used to help a plant operate more safely. ISA-18.2 can also be used to bring together the disciplines of alarm management and safety system design, which must work more closely to prevent future accidents.
The Alarm System and the Operator are one of the first layers of protection
The operator’s response to alarms is crucial in preventing a process upset from escalating into a more serious event. As shown in Figure 3, there are multiple layers of protection that can prevent an incident from occurring and to mitigate its impact if it does occur. Operator intervention is one of the first layers of protection. Next comes the Safety Instrumented System (SIS) whose job is to drive the process to a safe state, as needed, to protect people, the environment, and equipment. When a safety system trips it typically results in lost production, which can be very significant – for an oil refinery it can easily exceed $1M / hour. Therefore implementing proper alarm management to improve the operator’s performance can help your plant run more efficient and also reduce the likelihood that a process upset reaches the SIS layer of protection.
