Alarm-DCS-SIS the Automation Triumvirate
Alarm-DCS-SIS the Automation Triumvirate
When we think of a triumvirate ideal we think of three separate important pieces that all have a function yet simultaneously act as a cohesive entity. The same can be said for the ambitious ideal of the Alarm-DCS-SIS relationship for a company’s automation system. Today we see many systems littered with redundant alarms and safety actions resulting in bypassing and ignoring critical safety functionalities. I sat down with Dominique Dangerfield of Maverick Technologies, a Rockwell Automation Company, to discuss the ideal automation system setup. Dominique has been at Maverick Technologies for 5 years. As a Senior Engineer, he helps companies upgrade their current DCS systems.
Q: When starting to design or upgrade a system what should come first?
A: The first thing to look at is your alarm management program. We recommend a facilitated meeting between someone who is familiar with alarm management and the operators of the unit.
Q: What should cause the removal of an alarm for the system?
A: Every alarm should trigger an action by the operator. If there is no action, the alarm should be taken out. Failure to do so only leads to nuisance alarms. This creates the potential for an important alarm to be misdiagnosed as a nuisance alarm.
Q: What about DCS configuration, should interlocks in the DCS be removed if there is a reciprocal interlock in the SIS?
A: DCS interlocks should be coordinated with the SIS. For example, if the SIS trips the fuel gas shutdown valve on a fired heater, the DCS should close the associated fuel gas control valve. This is to prevent an accidental release of fuel gas into the heater if the shutdown valve opens.
Q: Are there ways the DCS can still be used efficiently for safety?
A: Yes. One example is the ability program time-based to abnormal conditions into the DCS. This will give operations a window of time before the SIS trip.
Q: Do DCS graphics play a role in this design?
A: The new standard for DCS graphics is radically different. Graphic layout has moved to a layered hierarchy of graphics. Normally a four-layered system, each layer corresponds to a higher-level overview of the facility. This system is developed from the PFDs, P&IDs and old graphics.
Q: Are there any safety benefits to the new standard?
A: The old standard for graphics was colors throughout the graphics. The new standard only shows color when a process is deviating from operating limits or alarming. This visual contrast helps the operator identify issues more quickly.
In summary, the ideal automation design has the following characteristics:
· Effective alarm management
· Optimized DCS for operational action
· Dedicated SIS or PLC for safety functions
While we understand this model comes with its own sort of financial and logistical challenges, treating it as the standard will go a long way toward improving the efficiency of our automation systems. As process safety teams, we need to consider these designs in evaluating the effectiveness of automation in preventing and mitigating risk. For any additional information regarding upgrading your automation systems check out Maverick Technologies, a Rockwell Automation Company at www.mavtechglobal.com and, as always, catch us at www.bearps.com for your process safety solutions.