In the beginning, all control was distributed in the field near each particular process. Much of this control was manual, with islands of pneumatic-based automation. Then came the inaptly named "distributed control system," which was, in fact, centralized automation in the control room and its environs via monolithic centralized controllers and accompanying I/O.
But smart instruments, local valve controllers, digital fieldbus networks and other new technologies moved control out into the field—closer to the processes and often to field-based operations personnel. This resulted in the current architecture of most process automation systems, namely, distributed control with automation and operator interfaces applied as needed in the control room and throughout the plant.
Process safety systems are following much the same path: first distributed, or often non-existent systems; then centralized via triple-modular-redundant safety controllers and local I/O; and now distributed via SIL-rated safety networks connected to safety-rated intelligent I/O, and via ever smarter and often redundant instruments and controllers.
Distributed safety is relatively new, and in the present litigious climate, many end users are reluctant to discuss safety systems. But the process safety market is growing rapidly, say analysts at Frost & Sullivan in its recent "Strategic Analysis of the European Process Safety Market" study. It predicts that Europe's process safety market will grow from just over $459 million in 2010 to more than $632 million by 2016. Part of this growth will come from distributed safety systems because they provide advantages over centralized safety.
Even process plants that don't directly purchase and implement distributed safety systems often find their facilities abound with the same in the form of process skids and packaging machines purchased from OEMs. These often have their own safety controls and at least some limited operator interface (see "Stealth Distributed Safety" in this article.)