Process Industries: Safety Instrumented Systems Evolve Towards Greater Flexibility

Safety Integrity Level (SIL) 3 applications face greater scrutiny as customers do more and more thorough risk analyses to determine the real risk reduction requirements.

When Safety Instrumented Systems (SIS) were first adopted by the process industries in the mid 1980s, they typically were Triple Modular Redundant (TMR) systems. These systems were significantly more expensive than non-redundant, general purpose programmable logic controllers (PLCs), and generally were considered too expensive to have multiple distributed systems across a facility. The result was the implementation of single, large, centralized systems, since one large 1,000 I/O system was much cheaper than ten smaller 100 I/O systems.

“For full plant-wide safety in an oil refinery or chemical plant, a triplicated system may make sense; but for smaller applications with only a hundred I/O, large monolithic systems simply aren't cost effective,” says Paul Gruhn, P.E., CFSE, training manager at ICS Triplex, a Rockwell Automation Company. Because of the costs, customers are looking for cost effectiveness through scalability-and that's where new technologies are coming into play.

“We've had a four-year project developing a next generation system, AADVance, which is scalable, very economic, and applicable for small to large applications,” continues Gruhn. AADvance can be designed to be SIL 3 or SIL 2 compliant; in a SIL 2 configuration, the system would require much less hardware and no redundancy, dramatically reducing costs for those users whose application doesn't require SIL 3... Read more

Trends in Consumer Products Process Safety

According to Art Pietrzyk, product marketing manager at Rockwell Automation, there are currently several major safety solutions trends in the consumer products process industry, including integration between basic process control system (BPCS) and Safety Instrumented Systems (SIS), scalability, common components, better diagnostics and maintenance, and comprehensive lifecycle support.

“What does integration mean to the customer?” asks Pietrzyk. When users are looking for tighter integration, they're not looking to put all the eggs in one basket. They're looking for common databases, common tools, and in some cases, common components. In the past, a separate and independent safety system was the standard, so components were required to be diverse.

“Today, that's not necessarily the case,” says Pietrzyk. “Customers are looking for common components where it makes sense-power supplies and chassis, for example-but they wouldn't use a SIL 3 certified component for what an uncertified component could do, because of the cost.”

A BPCS is always going to be tweaked; engineers are constantly changing algorithms and control strategies, adding instruments, or changing the process to improve it and hopefully gain a competitive advantage. So change, or the ability to make changes, is a requirement for process control... Read more

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