There are two electrical certification schemes which comprise the predominantly adhered to guidelines for electrical equipment testing and certification for use in explosive or flammable atmospheres. These schemes allow manufacturers to design equipment to specific standards according to the types of conditions under which they will operate. These schemes differ from one another and are not interchangeable, but rather govern the design and certification according to their respective regions. In North America, hazardous locations are covered under a Class and Division system scheme, while the European Union employs to two directives described under the ATEX/IECEX schemes.
In North America, the Class/Division scheme is derived from guidelines described in the NEC or “National Electrical Code” and is employed throughout the United States and to some extent Canada. ATEX applies to all countries within the European Union and consists of two directives which describe the environments and equipment as they pertain to potentially explosive or flammable environments.

   
The conditions intended for coverage under ATEX and Class/Division schemes involve work environments where potentially explosive or flammable gases, vapors, dusts and flyings such as wood chips are encountered and so are similar in their requirements. There are, however, clear differences which are manifested in how environments are classified which in the North American NEC based system are classed as Divisions and in the ATEX system as Zones. As such, explosion proof equipment certified to North American standards is not suitable for application in European locations unless it has also met with, and been certified to, accordance with the ATEX directive and vice versa. The North American NEC has made some effort to include a zone based system within its guidelines in an effort to produce some homogeneity between the directives, but to date this has been a slow and incomplete process.

The ZONE system as added to the NEC is based upon the international methods of zones but is limited in concept. The definitions for zone protection are included in the new Article 505 of the NEC but provide limited information and techniques for applications. To date it has proven difficult to properly apply ZONE methodology as it pertains to NEC Divisions as the information has been added sporadically throughout the NEC publication and incomplete for most intents and purposes. As a result, although most information is available in Article 505, much material within Articles 500 and 501 covering Class 1, Division 1 and 2 hazardous locations must also be considered in order to gain a more complete understanding, and there still remains a lack standards available for applying to the evaluation of equipment during testing. Suffice to say, since the Class/Division scheme still makes up the bulk of US hazardous locations, consider the Division scheme applicable and the Zone system as a probable future requirement.

More notable and quite important differences exist in how these differing schemes are applied. In the US, the Class/Division scheme is voluntary for manufacturers to adhere to, while in the EU if you wish to apply equipment you are legally bound to adhere to the ATEX directive. All countries within the EU have adopted the ATEX directive, allowing easier certification, sale, and application of equipment from one country to the next within EU membership. In the US, hazardous location certification is basically a market driven standard, with no legal requirement that equipment being sold meet hazardous location standards. However, operations with locations designated as hazardous are required by law to utilize equipment appropriately certified to their classification. Most buyers of such equipment though, prefer equipment carrying the appropriate marks of certification regardless.

The use of standards approved equipment is generally determined by the authority having jurisdiction, meaning inspectors, fire marshalls, OSHA, and other relevant persons and regulating bodies may have primary say in which equipment is suitable for a given location. Also, operators and end users may also have responsibility as well as insurance representatives and those with direct investment in operating safety and compliance with regulations. Operators may opt for equipment with higher certification levels despite lower classification having been deemed acceptable by a regulating authority as well.

For the United States and in some instances Canada where applicable, the National Electrical Code is the most reliable source of information on hazardous locations. Article 500 of the NEC provides a good general rundown of Class, Division, Groups and their relevant definitions and breakdowns. Article 501 provides detailed specifics regarding locations dealing with gases and vapors including the protections required, article 502 relates to combustible dusts, and article 503 covers fibers flyings, chips and similar materials. Article 504 covers intrinsically safe equipment and installation, and articles 505 and 506 relate to the introduction of Zone classifications into the NEC. The European system utilizes standards referenced to IES60079, thus the United States applied the 60079 standards when implementing Zones standards into the NEC for similar locations while making some allowances for differences in installation and sales requirements under US regulations.

Testing and certification of hazardous location equipment is done by third party laboratories that have been approved by regulating bodies. In the United States, the most prolific of these is Underwriters Laboratories (UL), with other notable entities being American National Standards Institute (ANSI), American Society for Testing Materials (ASTM), and Factory Mutual Research Corporation (FMRC). Laboratories must be nationally recognized (OSHA) and approved to provide equipment certification. Equipment not carrying approval from a recognized laboratory is not considered compliant regardless of the manufacturer’s specifications and can result in fines, loss of insurance coverage, and more severe penalties if used in locations deemed as hazardous.

Currently, the United States is working towards a more homogenous system of standardization which may hopefully provide a more streamlined and simplified system of certification and compliance across international borders. This would facilitate international sales and commerce relevant to hazardous location equipment, and provide a more readily accessible means of achieving compliance. Until such a time as this takes place, operators must be vigilant and ensure their equipment meets with the regulations and standards relevant to their region.