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The term hazardous area can be confusing. A hazardous area refers to any location with combustible material such as gases, dusts, or fibers that might produce an ignitable mixture.

A hazardous area can be a sealed room filled with a volatile material or an area that is open to normal foot traffic, such as the area around a gasoline pump.

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This is typically achieved through the use of barriers – either zener diode barriers or isolated barriers – that limit energy to a hazardous area.

As the name implies, intrinsic safety refers to electrical equipment and wiring that’s inherently safe. In other words, an intrinsically safe circuit is one with energy levels so low they cannot cause an explosion.

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One of two methods can certify intrinsic safety equipment: systems or entity parameters.

A systems approval evaluates all component specified as an entire system. A variance to any of those components voids the approval.

An entity parameters approval, where each device is evaluated separately and assigned a set of safety or entity parameters. This approval type allows field devices to be connected to any barrier with compatible safety parameters.

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Barriers are the key component in an intrinsic safety system because they limit the energy to the hazardous area.

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Zener diode barriers

provide a simple method for implementing intrinsic safety. Their primary drawback is they must be connected to a dedicated intrinsically safe earth ground, which may introduce problems such as electrical noise on the control signal. If a proper ground system is not in place, the cost of installation and proper maintenance might outweigh the savings of this inexpensive solution.

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Isolated barriers

provide galvanic isolation for anything connected to them. Therefore, there is no need for a dedicated ground. Galvanically isolated barriers provide protection for specific applications such as transmitters, solenoids, and thermocouples, enabling easy system design.

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Advantages of Intrinsic Safety

Intrinsic safety is the safest, least expensive, and easiest-to-install method of hazardous area protection available. System integrity is no longer a concern because explosions cannot occur.

Intrinsic safety systems offer significant savings:

• No heavy conduits or bolted enclosures• Barriers are mounted inside standard enclosures• Low energy requirements eliminate shock hazards • Operates seamlessly with retrofit applications and

with modern techniques such as fieldbus• No more “hot” work permits – calibration and

maintenance of field instruments under power

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Certain principles must be followed in every application regardless of the type of barrier used. Examples of such principles are:

• Separate intrinsically safe wiring from non-intrinsically safe wires by air space, conduit, or a partition

• Label wires to distinguish hazardous area wiring from safe area wiring

• Seal or vent conduit and raceways inside hazardous areas so they do not transfer the hazardous atmosphere to the safe area

• Comply with local, state and federal regulations

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To Summarize

• A hazardous area refers to any location with combustible material such as gases, dusts, or fibers that might produce an ignitable mixture

• An intrinsically safe electrical circuit is energy limited to levels incapable of causing an explosion

• Certain principles must be followed in every intrinsically safe application

• The systems or parameters approval method is used to certify intrinsic safety equipment

• Barriers are a key component of an intrinsically safe system because they limit energy to the hazardous area

• Intrinsic safety is the safest, least expensive, and easiest-to-install method of hazardous area protection available

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Visit our website and order your free CD of our Interface Technology Engineer’s Guide.

The Engineer’s Guide covers topics on:

• Basic principles of field signals

• Functional safety (SIL)

• Applications and practical solutions

• HART interface solutions

• Signal conditioning

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