Intrinsically Safe Electronic Gas Flow and Pressure Instrumentation

Protection concepts

Intrinsic safety is a protection concept or method of protection. Protection concepts are standardized strategies for ensuring the safety of equipment in places where there are flammable or explosive gases or dust present—that is, hazardous locations.

Classifying hazardous locations

Hazardous locations are categorized as class and division in North America, and as class and zone internationally. The classes indicate the type of hazard present, gas (Class I) or dust (Class II), and division or zone indicates how likely that type of hazard may be present in the area. Likely to be constantly present is rated division 1 in North America and rated Zone 0 internationally. At the other end of risk is not present under normal operating conditions, rated division 2 or zone 2.

Together, the class and division of Alicat’s IS‑Max™ and IS‑Pro™ intrinsically safe instruments rises to Class I Division 1, and Class 1 Zone 0.

The certification tests

Devices that have received the intrinsically safe certification have been designed and tested to prevent conditions that might ignite an explosive atmosphere: no spark with enough energy to ignite, and low heat production.

They undergo extensive verification to meet the safety requirements, and may have extra precautions, such as protective encapsulated coatings of PCB boards, to prevent arcing to internal surfaces. Materials and construction are considered to minimize and eliminate sparks that might occur from events such as an impact by a metal object, or because of static electricity. To further guard against this, the energy into the devices is limited. Each device requires an electrical barrier device for providing power to it, at the boundary of the C1D1 (Class 1 Zone 0) area. The barrier fail‑safe circuitry to prevent surges.

The certification takes place through an independent testing and certifying body. Changes to the device design or capability that might affect the safety concerns would require recertification.

Not ‘explosion proof’

Intrinsically safe is one of seven protection concepts. It is different from explosion proof, in that intrinsically safe means the device won’t ignite an atmosphere, while explosion proof means that an ignition, should it occur, will be contained and/or redirected harmlessly. An intrinsically safe device doesn’t require an explosion proof (also flameproof) housing, so long as it is weather resistant. It doesn’t require purge gases in its enclosure, either. Other protection concepts are increased safety or non-sparking; oil immersion; powder filled; and encapsulation.