Combined control and safety debate

Discussion about the acceptability of combining safety and process control functions in a common system has heated up recently. Much of the public debate, however, isn't fueled by end-users, but by suppliers of traditional, multi-modular redundant systems who have a vested interest in their technologies.


Discussion about the acceptability of combining safety and process control functions in a common system has heated up recently. Much of the public debate, however, isn't fueled by end-users, but by suppliers of traditional, multi-modular redundant systems who have a vested interest in their technologies. Some vendors have targeted the end-user community with fear tactics insinuating that your plant will not be "as safe" when combining control and safety onto a single, robust platform.

However, through the use of modern, high-integrity processing techniques, firewalls, and active diagnostics, functional separation of control and safety in a combined environment is ensured and compliant with the international safety standards.

Some of the more common arguments against combining the technologies are addressed here:

"Process controllers can't be used for safety." This statement isn't referring to a controller and I/O modules designed for safety and certified by an internationally accredited certifying body such as TÜV, but rather the use of a basic process control system (BPCS) in a safety application.

"If you're not using a triple-modular redundant system, you're increasing your risk." Having a logic solver that is a triple---quadruple, or quintuple-modular redundant system doesn't mean that your safety function meets the necessary risk reduction requirements. In fact, if you audited installed double-or triple-modular redundant systems, you may find many of the sensors and final element components don't meet the SIL (safety integrity level) requirements for the SIF (safety instrumented functions). This is alarming, as most system failures occur with field devices, rather than the logic solver. Redundancy is for availability, not reliability; all safety systems have some level of redundancy. Triple module redundant systems use redundancy to reduce the probability of a dangerous failure occurring. With newer, accepted technologies, dangerous failure modes can be designed out and near 100% diagnostic coverage provided for system integrity.

"Combining control and safety just isn't good practice." Having dual engineering tools, operator interfaces, additional system components, and doubling lifecycle costs for training and spare parts isn't good practice either. A major point is usually missing from those arguments bashing combined control and safety—with most new system offerings, you don't have to combine control and safety if you don't want to. Most systems that offer the capability to combine process control and safety in the same system, or even the same controller, also have the ability to be autonomous.

Integrated reasoning

Why combine the two worlds of safety and process control? Because end-users now have a chance to reduce costs while maintaining required levels of safety integrity. There also are savings recognized in the project engineering implementation and testing phases. For example, moving I/O points within the same system is a lot less expensive and engineering-intensive than moving them to an entirely different system, when documentation and design issues are considered.

Additional savings can be realized during commissioning, when the entire solution can be pre-tested in a controlled environment, instead of in two isolated entities brought together on-site for the first time. This kind of pre-testing enhances an owner's knowledge base of their chosen technology, thereby increasing the integrity of the overall solution.

Then there are the life-cycle costs. Purchasing, spare parts handling, and training are just a few advantages that end-users recognize as a reason to look at a robust and reliable combined system.

Author Information

Ged Farnaby is business development manager, North America, for ABB Inc.;

No comments
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by...
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
This eGuide contains a series of articles and videos that considers theoretical and practical; immediate needs and a look into the future.
Robotic safety, collaboration, standards; DCS migration tips; IT/OT convergence; 2017 Control Engineering Salary and Career Survey
Integrated mobility; Artificial intelligence; Predictive motion control; Sensors and control system inputs; Asset Management; Cybersecurity
Big Data and IIoT value; Monitoring Big Data; Robotics safety standards and programming; Learning about PID
Featured articles highlight technologies that enable the Industrial Internet of Things, IIoT-related products and strategies to get data more easily to the user.
This article collection contains several articles on how automation and controls are helping human-machine interface (HMI) hardware and software advance.
This digital report will explore several aspects of how IIoT will transform manufacturing in the coming years.

Find and connect with the most suitable service provider for your unique application. Start searching the Global System Integrator Database Now!

Mobility as the means to offshore innovation; Preventing another Deepwater Horizon; ROVs as subsea robots; SCADA and the radio spectrum
Future of oil and gas projects; Reservoir models; The importance of SCADA to oil and gas
Big Data and bigger solutions; Tablet technologies; SCADA developments
Automation Engineer; Wood Group
System Integrator; Cross Integrated Systems Group
Jose S. Vasquez, Jr.
Fire & Life Safety Engineer; Technip USA Inc.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
click me