Hazardous location certifications 101

Tutorial: It is important to know precisely which certification scheme is required for the installation of electrical equipment in a hazardous (classified) area and what precautions need to be taken in each circumstance.


Immersion heaters such as Watlow’s flange immersion heaters possess IECEx and ATEX Ex’d’ or Ex’e’ ratings certifying that the flange heater enclosure is flameproof. Every enclosure is pressure tested to ensure heaters are safe and reliable and meet rigoroElectrical equipment that is used in a hazardous (classified) area is regulated by local laws and guidelines and is required to be compliant to the relevant protection schemes and certifications as specified within these areas. There are a multitude of certification schemes around the world, but the three mainstream certifications for electrical equipment in hazardous areas are ATEX (Europe), IECEx (International), and either the Class/Division or Class/Zone System (North America). While each of these certification groups require unique standards and verification procedures for certification they also leverage similar terminology and practices with respect to testing, marking, and ensuring standards are attained for safe operation of electrical equipment.

It is important to know precisely which certification scheme is required for the installation. For example, international equipment qualified under IECEx will not be acceptable in Europe and likewise, ATEX equipment will not be acceptable where IECEx equipment is specified. Also, many of the country-specific certification schemes can be more easily obtained if one possesses the correct "initial" certification scheme from within the three mainstream standards. For example, an IECEx Certification is a good starting point to attain INMETRO (Brazil), which is a less stringent Brazilian certification. Similarly, an ATEX certification is a good start for the CU TS (GOST) certification for Russia.

A "hazardous area" is defined as an area in which the atmosphere contains, or may contain, in sufficient quantities, flammable or explosive gases, dusts, or vapors. In such an atmosphere, a fire or explosion is possible when three basic conditions are present-fuel, gas, and an ignition source. To protect an application from a potential explosion, an appropriate protection method is required. Classifying the specific type of hazardous area that the equipment will be operating in is required in determining the appropriate certification scheme. To determine what protection method is appropriate, a method of analyzing and classifying the potentially hazardous area is required. The particular method chosen will again depend on local rules and the certification scheme required. The type of protection required depends on the risk involved in the area. Once the area is classified, an appropriate protection method can be chosen.

Proper certification marks are the customer's assurance that the electrical products in operation meet rigorous standards for electrical safety and are suitable for use in the classified area. 


ATEX is a European Directive and is used for controlling explosive atmospheres and the standards of equipment and protective systems used in them. The ATEX Directive 94/9/EC provides the most current requirements regarding equipment and protective systems intended for use in potentially explosive atmospheres. Manufacturers and suppliers or importers (if the manufacturer is outside of the EU) must ensure that their products meet essential health and safety requirements and undergo appropriate conformity procedures. This usually involves testing and certification by a third-party certification body, known as a notified body. Once the notified body certifies the equipment it is marked by the "EX" symbol to identify it as such.


The objective of the international IECEx scheme is to facilitate international trade in electrical equipment intended for use in explosive atmospheres (Ex area) with the following benefits:

  • Reduced testing and certification costs to manufacturers
  • Reduced time to market
  • International confidence in the product assessment process
  • One international database
  • One evaluation with worldwide market potential.

An Ex area is also known as a "hazardous location," "hazardous area," or an "explosive atmosphere" and is generally an area where flammable liquids, vapors, gases, or combustible dusts are likely to occur in quantities sufficient to cause a fire or explosion. Equipment used in an Ex area is termed "Ex equipment."

The IECEx Certificate of Conformity System provides for the issuing of IECEx Certificates of Conformity, covering Ex equipment for use in explosive atmospheres. IECEx Certificates of Conformity are issued by approved IECEx Certification Bodies (ExCBs). An IECEx Certificate of Conformity confirms that a sample of the Ex product, described on the certificate, has been independently tested and found to comply with the international standards listed in the certificate. It also proves that the manufacturing site has been audited to verify that the manufacturer's quality systems meet IECEx requirements. 

Product marking

Marking of Ex equipment is a requirement. It allows a user to choose appropriate equipment for a specific hazardous atmosphere. For example, it can warn of special conditions or parameters for safe use and hazards that might occur, and so on. Marking also provides traceability and references to the issued certification including certifying body. To obtain certification, a manufacturer must at the very least, provide an illustration of the nameplate(s) that details the relevant marking.

Marking of electrical equipment must include: manufacturer's name, model number, serial number, ratings, and the following Ex-marking at a minimum. Some protection types, however, may require additional marking.

  • Type of protection (d, ia, e, p, nA, etc.)
  • Gas group for which equipment is approved (IIA, IIB, IIC, etc.)
  • Temperature code or maximum surface temperature (T1, T2, ... T6)
  • Equipment protection levels (Ga, Gb, or Gc).

Here is an example of a company's markings:

Example of a company’s marking for certification. Courtesy: Watlow

Classes and divisions

Hazardous locations are rated with an area classification that in the IECEx and ATEX schemes are generally based on equipment category, gas presence, and gas group. In the North American system Classes, Divisions (or Zones), and Groups are used to define the level of safety required for equipment installed in these locations. Equipment Category and classes define the general nature of hazardous material in the surrounding atmosphere. Gases are categorized as "IIG" by ATEX and "Class I" in the North American System. The "Zone" or "Division" defines the probability of hazardous material being present in an ignitable concentration in the surrounding atmosphere. 

The "Gas Group" is based on the gases present in the area.

A mixture of hazardous gases and air may ignite in contact with a hot surface. The condition for ignition depends on several factors such as surface area, temperature, and concentration of gas. When an area is classified, it is assigned a Temperature Class/Code, which indicates the maximum surface temperatures that are allowed in the area.

Approved equipment receives a temperature code indicating the maximum surface temperature of the equipment at the worst-case, normal operating conditions. Equipment marked for a lower surface temperature may be used.

For example, a piece of equipment marked T5 may be safely installed in an area classified as T3 because the maximum surface temperature is lower than the requirement for the area. 

Manufacturers that produce, or companies that sell, equipment for use in hazardous locations need to be aware of the main certification schemes, understand what is involved in certifying their products, and be able to interpret customer requirements to insure a product is safe to use in a specified environment.

Mike Bange is a product engineer and engineering department manager for Watlow Electric Manufacturing Co. Edited by Chris Vavra, production editor, Control Engineering, CFE Media, cvavra@cfemedia.com.


Key Concepts

  • A "hazardous area" is defined as an area in which the atmosphere contains, or may contain, in sufficient quantities, flammable or explosive gases, dusts, or vapors.
  • Proper certification marks are the customer's assurance that the electrical products in operation meet rigorous standards for electrical safety and are suitable for use in the classified area.
  • Manufacturers that produce, or companies that sell, equipment for use in hazardous locations need to be aware of the main certification schemes. 

Consider this

Which standards do you use the most and what challenges do they bring?

Anonymous , 03/31/16 01:56 AM:

How will above hazardous area classification differ from NEMA and IP classifications.
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