In markets where safety standards are constantly being evaluated and upgraded, selecting an appropriate safety integrity level (SIL) designation has often been confusing for users. The harmonization of international safety standards, including IEC 61508 and ISO 13849 in the European Union, has made this less confusing.
Both ISO 13849 and IEC 61508 are based on similar principles. First, a hazard and risk analysis estimates potential risks and requires risk reduction for a certain function. Depending on this outcome, the function is assigned to a class (SIL or PL respectively) that is defined by the probability of failures per hour.
IEC 61508 is quite generic and is based on probabilistic methods to achieve a certain safety class, including procedures for estimating component reliability or test quality.
ISO 13849 is more industry-specific, and tries to balance deterministic and probabilistic methods to simplify the development of systems. This simplification is achieved by defining the designated architectures and categories and pre-defining, which performance level can be achieved within each category, thereby greatly reducing complexity in application of the standard.
Regardless of the standard applied, incorporating safety as an integrated aspect of plant operation is considered best practice for meeting compliance issues worldwide.
The time is now
Technology with the functionality necessary for truly integrated safety and control is available today. Because safety is enhanced by integrating it with control, more networking, devices with built-in safety, and systems with all functionality residing on the same backplane will continue. This is a positive development.
The bottom line is this: In a time when companies across all borders are challenged by the decline in skilled labor, the rise in device complexity, and the constant need to increase productivity while driving down capital and operational expenses, the convergence of safety and control will help companies compete. It does this by simplifying the design, programming, operation, and maintenance of both safety and control systems while improving performance and functionality.
That it will provide all these benefits while actually making the workplace safer is something everyone can feel good about.
Michael Paradiso is OEM/global accounts solutions engineer for Omron STI.