What is the difference between ATEX and explosion proof?

ATEX and ex-proof classifications help manufacturers select and install equipment for potentially explosive atmospheres. ATEX is used in Europe, whereas Ex-Proof is used in North America and Canada.

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The process environment and properties of any materials that will be present need to be ascertained. This is so the ignition risk of any gas and dust atmospheres can be classified and the appropriate preventative steps taken.

ATEX

The ATEX directive uses zones to classify potentially explosive gas and dust atmospheres. Classifications range from an ignitable condition being an unlikely occurrence (Zones 2 and 22) to continuously present (Zones 0 and 20).

> Gas / Vapour / Mist: Zone 0, Zone 1, Zone 2
> Powder / Dust: Zone 20, Zone 21, Zone 22

Ex-Proof

Ex-proof uses classes (1 and 2) to distinguish between explosive gas and dust atmospheres. Subdivisions are then used to categorise the type of gas (A, B, C, D) and dust (E, F, G). For milling and grinding applications, the most common subdivision is G as this covers food / grain and general dusts.

To assess the likelihood of an ignitable concentration being present, the classes are allocated a division (1 or 2 &#; see below).

> Gas / Vapour / Mist: Class 1 (A, B, C, D)
> Powder / Dust: Class 2 (E, F, G)

> Ignitable Conditions present 10- hrs per year: Division 1
> Ignitable Conditions present <10 hrs per year: Division 2

ATEX and Ex-Proof Compared

Gas Dust Zone Definition Equipment Category Protection Method

Zone 0

Class 1 Division 1

Zone 20

Class 2 Division 1

Explosive atmosphere is present continuously, for long periods or frequently (10- hours per year).

1

Equipment must be safe under normal operation, expected and rare malfunction.

Zone 1

Class 1 Division 1

Zone 21

Class 2 Division 1

Explosive atmosphere is likely to occur occasionally under normal operation (10- hours per year).

2

Equipment must be safe under normal operation, expected malfunction.

Zone 2

Class 1 Division 2

Zone 22

Class 2 Division 2

Explosive atmosphere may occur under abnormal operation and only persists for a short period (<10 hours per year).

3

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Equipment must be safe under normal operation.

Ignition Sources

A flammable gas or dust atmosphere requires an ignition source to cause an explosion. Effective ignition sources include:

> Mechanically generated impact sparks
> Mechanically generated friction sparks
> Electric sparks
> High surface temperature (e.g. resulting from milling and grinding)
> Electrostatic discharge

NEMA and IP Ratings

Electrical enclosures in ATEX and ex-proof environments also need to be rated to a standard that makes them safe to use. National Electrical Manufacturers Association (NEMA) and Ingress Protection (IP) grades enclosures used in industrial applications.

An IP rating (used in Europe) considers only protection against ingress of solid foreign objects and ingress of water, while NEMA ratings (used in North America) consider these and other specifics such as corrosion and construction details. Therefore it is not possible to exactly compare the two ratings. The most common IP and NEMA ratings for milling and grinding applications are listed below.

> NEMA 3S / IP54: A degree of protection against dust and water sprayed from all directions.
> NEMA 4X / IP66: Total protection against ingress of dust and strong jets of water.
> NEMA 7: Designed to contain an internal explosion without causing a hazard. Intended for use in Class 1 Division 1 / Zone 0 / Zone 1.
> NEMA 9: Prevents dust from entering and possible heat generating devices from heating the enclosures surfaces to a level that may cause combustion of surrounding dust.

Purge System

Compressed air of inert gas is allowed into the enclosure to remove the conditions for a possible explosion. The enclosure is at positive pressure allowing the flow of purge air/gas into the enclosure, while ensuring the air/gas in the atmosphere cannot enter.

Typically, nitrogen is used as the purging gas but other options are available which include carbon dioxide (although not fully inert), argon and helium.

ATEX or IECEx certified products are essential in any location that may contain, or has activities that produce explosive or potentially explosive atmospheres. There are a number of places that could be defined as being in an explosive atmosphere, some more obvious such as an oil rig, and others that you might not think of as being particularly explosive, such as a flour mill.

Most of us have heard of ATEX and IECEx certification, but the question that a lot of people ask is what makes them different? Here we share our expertise on each certification and identify their differences.

ATEX

The name ATEX comes from the French ATmosphère EXplosibles, describing the equipment and use of a product to be located in an explosive atmosphere. The ATEX certification is mandatory across Europe and involves all stages from the manufacture, through to the installation and use of the equipment. There are two parts which can be defined as;

Directive 99/92/EC &#; &#;The ATEX Use Directive&#; focuses primarily on the health and safety of workers, working in potentially explosive atmospheres. It involves the correct selection, installation, inspection and maintenance of Ex equipment.

Directive /34/EU &#; &#;The ATEX Equipment Directive&#; primarily concerned with trade, considers the equipment that will be used in potentially hazardous areas and involves the manufacture and sale of Ex equipment.

It is the ATEX Equipment Directive (/34/EU) that Raytec&#;s SPARTAN luminaires are certified to.

IECEx

IECEx stands for International Electrotechnical Commission Explosive. While ATEX is a mandatory application limited to Europe, IECEx is an international certification accepted in several countries to help build confidence in the safety of Ex equipment. It also facilitates international trade of equipment and services for use in explosive atmospheres.

Some of the benefits in choosing a product that has IECEx certification include;

&#; Reduced testing and certification costs

&#; Reduced time to market

&#; International confidence in the product assessment process

As with ATEX certification, IEC Ex provides assurance and a knowing that everything from the equipment and install through to the manufacture, operation and maintenance of the certified products comply with IEC international standards and are suitable for their purpose.

Although there are some small differences between each certification, ATEX and IEC Ex are very similar. The main difference is the geographical location where the certification is recognised and accepted. While ATEX is a requirement in Europe, IEC Ex is accepted across several countries internationally.

All of Raytec&#;s SPARTAN products have ATEX and IEC Ex certification; therefore you can be sure you are getting a high quality, reliable product for your hazardous area applications. To find out more call us on +44 (0) 520 055 or send us an via .

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