Emerson Exchange / Safety Instrumented Systems

Non-Incendive Approach Fits Class I, Division 2 Needs

Advantage of the Non-Incendive Approach

By Leslie Gordon

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Like any engineering, procurement and construction (EPC) company today, Fluor must compete on project execution, delivery and infrastructure costs. "As such, we needed the best way to approach instrumentation in terms of start-up and commissioning," said Adrian Lee, Fluor director of control systems engineering, in a presentation this week at the Emerson Global Users Exchange. "Most of our installations are in the hazardous Class I, Division 2 category," he added.

Class I, Division 2 areas are those in which explosive mixtures may potentially occur, but only during abnormal circumstances. "We could have taken any one of several approaches to address Fluor's challenge," said Larry Lammers, Caltrol technology consultant, who presented alongside Lee. "One method would have been to use traditional wiring with conduits and seals. This approach works well, but in this case was unnecessarily labor and material intensive. Another option would have been to use intrinsically safe methods, which are really intended for extremely hazardous locations governed by Class 1, Division 1 standards. Again, an expensive option due to the intrinsic barriers needed."

Because many of Fluor's needs fall in the slightly less stringent Class l, Division 2 category, the decision was made to go with a "non-incendive" wiring philosophy where applicable. In essence, non-incendive approaches take steps to minimize the potential for an electrical ignition source which, even in the remote chance of explosion mixture being present, would still keep the area safe. "In a Division 2 area, there is less risk," explained Lammers. "So we can do things a little differently from a Division 1 area, and the costs of installations are lower."

"The non-incendive concept saves construction time," Lammers continued. "And because it allows moving I/O out to the field, it cuts wiring costs. Inexpensive fiber optics or Ethernet cable can be used to connect to the field junction boxes." Emerson Process Management offers non-incendive-rated electronic marshalling with CHARMs technology for DeltaV process automation and safety instrumented system (SIS) applications, said Lammers. "Non-incendive equipment can range from temperature transmitters to level, flow, analytical and tank gauging devices."

Another advantage of the non-incendive approach is that it allows using exposed cable runs, added Lee. "Fluor guidelines forbid using more than three pairs of cable in a 3/4 in. conduit, but having exposed runs eliminates this limitation."