Hazardous areas are classified with respect to the potential danger of an explosion and the areas are divided into zones:

The term primary explosion protection refers to all precautions which prevent a dangerous, explosive atmosphere from being created. This can be achieved by avoiding the flammable substances, deactivation, limitation of the concentration, or natural or artificial ventilation. The various protection techniques listed below employ some of these protection concepts.

One point to note is that the order of techniques listed on the label of the product will very often tell the user the construction of the product. For example, a product listed Ex 'de' would most likely be flameproof with increased safety components inside.

Another product listed Ex 'ed' would most likely be non-flameproof (Stainless Steel or Glass Reinforced Polyester as examples) with flameproof switches or components installed inside. Both products would be suitable for Zone 1, but they use different means of protection to get there. Users can make informed decisions as to how best to utilize protection techniques that provide a balance between cost, performance and safety.

Gases are grouped together based on the amount of energy required to ignite the most explosive mixture of gases with air. Equipment is classified into groups according to the gases and vapours for which it is suitable and must be selected with a grouping which covers the gases and vapours which will be present where it is to be installed:

Group I
Methane - Ignition energy of 290 Micro joules

Group IIA
Propane - Ignition energy of 250 Micro joules (Similar to NEC Group D)

Group IIB
Ethylene - Ignition energy of 120 Micro joules (Similar to NEC Group C)

Group IIC
Hydrogen - Ignition energy of 20 Micro joules (Similar to NEC Group A & B)

To ensure that there is no risk of ignition due to hot surfaces, the equipment is classified with regard to the maximum surface temperature of any part of the equipment while in operation based on the ambient temperature of 40°C, this is also known as the 'T' rating. Equipment must be selected with a suitable temperature classification for the gases and vapours present where the equipment is to be installed.

An enclosure is a surrounding case constructed to provide a degree of protection to personnel against incidental contact with the enclosed equipment and to provide a degrees of protection to the enclosed equipment against specific environmental conditions.

What is the International Electrotechnical Commission (IEC)?

The IEC was founded in 1906 in St. Louis and is presently comprised of 40 countries including the U.S. Its stated purpose is to establish standards for a wide variety of electrical products with the intent of encouraging international trade.

IEC publications which deal with explosion protection for electrical apparatus and installations are developed by the Technical Committee TC31, IEC publications have the status of recommendations which are used for national and regional standards.

The IEC has introduced a procedure the so called IEC-Ex scheme intended to become a globally recognized test and certification procedure in the field of explosion protected electrical apparatus.

CENELEC is the European Committee for Electrotechnical Standardization. It was set up in 1973 as a non-profit making organization under Belgian Law.

It has been officially recognized as the European Standards Organization in its field by the European Commission in Directive 83/189 EEC.

Its members have been working together in the interests of European harmonization since the late fifties, developing alongside the European Economic Community. CENELEC works with 40,000 technical experts from the 19 European Community countries including Austria, Belgium, Denmark, Finland, France, Germany, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom.

BASEEFA (British Approvals Service for Electrical Equipment in Flammable Atmospheres) is the British national testing and certification authority for use in flammable atmospheres other than Mining.

BASEEFA is the British equivalent to the US UL.

The ATEX Directive is a directive adopted by the European Union (EU) to facilitate free trade in the aligning the technical and legal requirements in the member states for products intended for use in potentially explosive atmospheres.

The marking requirements include:

• EU Explosive atmosphere symbol
  ()
• Equipment group
  (I = mining and II = non-mining)
• Equipment category
  (1 = zone 0/20, 2 = zone 1/21 and 3 = zone 2/22)
• Atmosphere
  (G = gas and/or D = dust)

With the introduction of Article 505 in the NEC (USA National Electric Code) many of the protection techniques used in International community can be safely used in facilities in the United States (and visa versa). However, some test standards that are based upon the IEC standards have been modified in some respects to allow deviations to address North American concerns. The new marking requirements that will be showing up on many products in the U.S. to comply with NEC 505 are very similar to the Cenelec marking requirements. An example of a typical product meeting U.S. specifications might have a marking as followed:

Class 1, Zone 1, AEx e IIC T5

Notice that the big difference is the statement that tells the user which Zone this product is suitable for which has been missing from the traditional Cenelec marking requirements. With the advent of the ATEX directive, marking requirements in Europe will also reflect Zone or Category suitability. The two systems are close, but not identical.