In industrial automation, much of the focus tends to be on the distributed control system (DCS). However, an equally important system exists—the safety instrumented system (SIS). The SIS does exactly what its name implies: keep plant personnel and assets safe. It is a critical line of defense against disastrous events, and simultaneously an essential tool to help plants maintain compliance.
Unsurprisingly, as Emerson’s Dave Denison shared in a recent interview in Chemical Engineering, such a critical system is also traditionally a very complex one. Safety is paramount, so plants cannot afford mistakes. As a result, it is not unusual for a traditional SIS to trigger false trips. But, as Dave shares with Chemical Engineering, there are a number of steps teams can take when implementing a modern SIS to eliminate many of the problems that traditionally drove high costs and risk of downtime.
Step one: design well
The most successful SIS implementations will be those that result from careful planning and preparation. For example, when Emerson’s engineers design and install a DeltaV™ SIS, they start with comprehensive hazard and risk assessment studies to identify the exact safety-instrumented functions (SIFs) necessary to mitigate determined risks. The SIS architecture is specifically engineered to provide SIFs that meet the required safety integrity levels (SILs) based on identified hazards.
“This disciplined approach ensures that the SIS is tailored to the plant’s specific risks and meets both safety and regulatory requirements.”
DeltaV SIS is also designed to deliver less complexity from the very first stages of design. The software’s IEC 61508-certified SIS function blocks deliver functionality right out of the box, simplifying the implementation of complex SIS applications. No custom code is required to implement common SIS tasks. The result is faster configuration and troubleshooting of SIS logic.
Step two: reduce complexity to reduce errors
Even after the SIS architecture has been defined, teams must still perform installation, testing, simulation, commissioning, and documentation—all critical steps to ensure the final SIS operates as anticipated. The more complex each of those steps is, the more likely human error will occur, creating potential for problems during operation.
Choosing the right system—one designed to be less complex and part of a seamlessly integrated solution—can help streamline installation while also reducing the risk of human error. Dave explains,
“Modular, configurable systems reduce installation errors and accelerate commissioning, with modern distributed architectures enabling installation and commissioning of individual components without impacting previously installed systems, eliminating the need for total downloads that could introduce spurious trips in traditional centralized systems.”
With a DeltaV SIS, for example, the IEC 61508-certified SIS function blocks deliver functionality right out of the box, simplifying the implementation of complex SIS applications. No custom code is required to implement common SIS tasks. The result is faster configuration and troubleshooting of SIS logic.
Step three: secure the system
Even the best engineered and implemented system will create additional risk if teams don’t consider strong cybersecurity. First and foremost, the SIS should have built-in protections out-of-the-box. A foundational principle of the DeltaV SIS design is maximizing the separation of the safety system’s most critical elements—its sensors, logic solver, and final elements. These essential SIS components are kept isolated even from other safety-related devices that aren’t directly responsible for carrying out the safety function (such as a SIS engineering workstation). This core SIS is protected behind a proxy node that serves as its single access point, ensuring all communication flows through that embedded proxy. Isolation is maintained regardless of whether the system uses a separated or integrated architecture.
In addition, DeltaV SIS software is designed for cybersecurity defense in depth. Emerson experts can help organizations define and deploy the best cybersecurity layers for both SIS and DCS to help ensure maximum security and critical safety.
