O&M

Get in the Zone for Safety in Hazardous Areas

Hazardous area solutions from foreign suppliers may not be tested to the same standards as those in general use across the U.S. It’s essential to understand there is tremendous liability to use those technologies at a power plant or other industrial facility.

Knowing the rules and regulations when using foreign-manufactured equipment in hazardous locations is critical. So, what are the rules, what certifications are necessary, and how do you tell if equipment is safe for your application?

Hazardous location classified areas contain flammable gas, liquids, or vapors; combustible dusts; or easily ignitable fiber and flyings. When any one of these is combined with an oxidizer and ignition source, the result may be an explosion or fire.

In North America, equipment meeting relevant hazardous area location certifications first must meet ordinary location requirements. These “ordinary” standards include but are not limited to:

■ UL 94-VO standard for flammability.

■ UL 489 for molded case circuit breakers.

■ UL 50 and NEMA 250 standards for electrical enclosures.

■ UL 1581 standard for electrical wires, cables, and flexible cords.

Hazardous areas solutions from overseas may not be tested to ensure they meet the general ordinary location standards in America. When organizations decide to use technology from outside North America, there are the National Electrical Code (NEC) and Occupational Safety and Health Administration (OSHA) exceptions to consider, and liability exists if equipment is not certified to North American standards.

Primer on Zone Equipment Certification

The Zone method has become a worldwide accepted practice for classifying hazardous location classified areas. The International Electrotechnical Commission System for certification to standards relating to equipment for use in explosive atmospheres (IECEx System) lists 62 countries that are full members, and an additional 26 as associate members. Many countries have their own directives and certification requirements for equipment approvals within their borders.

1. The Zone method of equipment marking enables operators, including power plant workers, to better understand hazardous location classified areas. Courtesy: Eaton

The Zone method (Figure 1) dates to 1996. It was first introduced by the National Fire Protection Association (NFPA) with NEC Article 505. It allows for parallel classification in the traditional NEC Article 500 Division system.

In this division system, Zone terminology was used as the international system for classification of hazardous locations containing flammable gases, liquids, or vapors; combustible dust; or ignitable flyings, which divided classified areas into three segments: Zone 0, Zone 1, or Zone 2 for gases/vapors, and Zone 20, Zone 21, or Zone 22 for combustible dust and ignitable flyings.

Today, Zone-rated equipment still requires certification of ordinary location requirements in the U.S. The AEx marking, developed by the American National Standards Institute (ANSI) and International Society of Automation (ISA), ensures that Zone equipment conforms with hazardous location requirements and the general ordinary location American safety standards. As such, the AEx symbol is a critical marking requirement within the Zone material nomenclature. The AEx marking per NEC article 505.9 and Article 506.9 certifies the equipment has been produced to American standards—conforming with both general standards for ordinary locations and hazardous area requirements.

The Authority Having Jurisdiction (AHJ) and qualified testing labs have an essential role. The AHJ can approve equipment when there is sufficient safety data. Further, if equipment is listed by a qualified lab, then the internals of the equipment do not need to be inspected, except to look for problems, changes, or damage.

What if an AEx-Zone or Division certified technology isn’t available? The NEC Article 500.8(A) addresses this possibility and indicates that the suitability of equipment is determined by one of the following:

■ Equipment listing.

■ Evidence of equipment evaluation from a qualified testing lab or AHJ.

■ Evidence acceptable to the AHJ like a manufacturer’s self-evaluation or owner’s engineering judgment.

A manufacturer’s self-certification and owner’s engineering judgement must be carefully reviewed and only be considered when the decision-maker is fully confident that ordinary safety standards have been achieved. This evidence must also be accepted by the AHJ.

Further, OSHA provides additional guidance and requirements for product allowance. OSHA 29 CFR 1910.399 defines equipment acceptable for hazardous environments if it is:

■ Determined safe by a nationally recognized testing lab.

■ Inspected by another federal agency, or by a state, municipal, or other local authority responsible for enforcing occupational safety provisions of the NEC and found in compliance with the NEC.

■ Determined to be safe (for its intended use) by the manufacturer, based on test data that the employer keeps and can provide for inspection purposes.

Zone Method Rated Equipment

The OSHA and NEC allowances permit a product to be approved for installation without third-party testing by a nationally recognized testing lab (NRTL). OSHA lists 19 NRTLs on its website, including UL, CSA, ETL-Intertek, and FM.However, and importantly, both the OSHA and NEC language indicate the general rule is that equipment should be tested and listed by an NRTL—unless these avenues have been exhausted.

When thinking about electrical equipment without testing by an NRTL, it’s important to consider:

■ Does the state or municipality where equipment is being installed have requirements only allowing for the installation of third-party evaluated equipment?

■ Does the customer facility have requirements only allowing for installation of third-party NRTL evaluated equipment?

■ Who is shouldering the liability for the owner’s engineering judgement or self-evaluated equipment for suitability of ordinary and hazardous-area locations?

Facilities using the NEC Articles 505 and 506 Zone classification of hazardous location classified areas are governed by the approval requirements outlined in the NEC articles for the wiring methods and equipment certification.

When Zone method rated equipment includes the AEx marking, it means the equipment is certified to the American standards per NEC Article 505.9 (C) and Article 506.9 (C). That AEx marking ensures the Zone equipment conforms with both hazardous location requirements and general safety American standards for ordinary locations. These certifications give customers confidence and trust in the equipment they’re applying.

Robert C. Potter is Eastern region field application specialist for Eaton’s Crouse-Hinds business, and Richard A. Holub is a principal engineering consultant with DuPont Engineering. 

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