Understanding USA Equivalent Classifications to ATEX 94/9/EC Designations
This blog post is intended as a starting point to educate readers about ATEX standards and should not replace full research of the precise ATEX requirements.
What is ATEX?
The term ATEX is used for the European Union's (EU) 94/9/EC directive addressing equipment and instrumentation intended for use in potentially explosive atmospheres. The directive was purposed to help trade within the EU through alignment of laws governing the member states and went into effect on July 1, 2003. ATEX covers a broad array of safety equipment and instrumentation - including gas detectors.
The first ATEX directive (94/9/EC) addresses requirements of equipment used in areas where there is a danger of explosion. Manufacturers must fulfill the directive requirements in their instrument design and mark the products with the relevant approval. The second ATEX directive (99/92/EC) addresses the minimum health and safety requirements that users must fulfill when working within areas containing a danger of explosion.
How is an explosive atmosphere categorized?
Explosive atmospheres are atmospheres that develop explosively due to changing surroundings or as a result of use. Explosive atmospheres consist of air and combustive material such as gases, vapors, or dust in which the explosion could spread after ignition. Typical production sites where combustible dust is of major concern is in, for example, the handling of cereals, animal feed, paper, wood, chemicals, plastics and coals.
How should explosive atmosphere zones be divided?
The ATEX directive distinguishes between two types of explosive atmospheres: gas and dust. Areas within these two kinds of explosive atmospheres are each divided into three sub-zones. Although the zones characteristics are identical for both gas and dust, their numbering is different. Zone 0, 1 and 2 refer to gas and Zone 20, 21 and 22 refer to dust.
Zone 0 / 20: Constant danger
Permanent presence of explosive gasses or combustive dust.
Zone 1 / 21: Potential danger
Occasional presence of explosive gasses or combustible dust during normal duty.
Zone 2 / 22: Minor danger
Presence of explosive gasses or combustible dust is not likely to occur or only for a shorter period of time.
| European - Area of use Designation Standard | IEC - Area of use Designation Standard | USA - Area of use Designation Standard |
---|---|---|---|
Flameproof Enclosure – An enclosure used to house electrical equipment, which when subjected to an internal explosion will not ignite a surrounding explosive atmosphere. | Zones 1 & 2 EExd EN50018 | Zones 1 & 2 Exd IEC60079-1 | Class 1 Divisions 1 & 2 UL1203 |
Intrinsic Safety – A technique whereby electrical energy is limited such that any sparks or heat generated by electrical equipment is sufficiently low as to not ignite an explosive atmosphere. | Zones 0, 1 & 2 EExi EN50020 | Zones 1 & 2 Exi IEC60079-11 | Class 1 Divisions 1 & 2 UL913 |
Increased Safety – This equipment is so designed as to eliminate sparks and hot surfaces capable of igniting an explosive atmosphere. | Zones 1 & 2 EExe EN50019 | Zones 1 & 2 Exe IEC60079-7 | |
Purged and Pressurized – Electrical equipment is housed in an enclosure which is initially purged to remove any explosive mixture, then pressurized to prevent ingress of the surrounding atmosphere prior to energisation. | Zones 1 & 2 EExp EN50016 | Zones 1 & 2 Exp IEC60079-2 | Class 1 Divisions 1 & 2 NFPA496 |
Encapsulation – A method of exclusion of the explosive atmosphere by fully encapsulating the electrical components in an approved material. | Zones 1 & 2 EExm EN50028 | Zones 1 & 2 Exm IEC60079-18 | |
Oil Immersion – The electrical components are immersed in oil, thus excluding the explosive atmosphere from any sparks or hot surfaces. | Zones 1 & 2 EExo EN50015 | Zones 1 & 2 Exo IEC60079-6 | Class 1 Division 2 UL698 |
Powder Filling – Equipment is surrounded with a fine powder, such as quartz, which does not allow the surrounding atmosphere to come into contact with any sparks or hot surfaces. | Zones 1 & 2 EExq EN50017 | Zones 1 & 2 Exq IEC60079-5 | |
Non-sparking – Sparking contacts are sealed against ingress of the surrounding atmosphere, hot surfaces are eliminated. | Zone 2 EExn EN50021 | Zone 2 Exn IEC60079-15 | |
Special Protection – Equipment is certified for use in a Potentially Explosive Atmosphere but does not conform to a type of protection listed above. | Zones 0, 1 & 2 *Exs | Zones 0, 1 & 2 Exs |
Ingress Protection
Two numbers indicate the level of ingress protection of an instrument or apparatus. The first is the level of protection against solid objects and the second against liquids.
Note: IP54 is the minimum protection allowed for Hazardous Area Equipment. The US practice is to use NEMA standards to describe ingress protection (i.e. NEMA 3 is similar to IP 54, NEMA 4 is similar to IP 55, NEMA 4x is similar to IP 56, NEMA 6 is similar to IP 67).
| Solids | | Liquids |
---|---|---|---|
0 | No protection. | 0 | No protection. |
1 | Protected against solid objects up to 50mm, e.g. hands. | 1 | Protected against vertically falling drops of water. |
2 | Protected against solid objects up to 12mm, e.g. fingers. | 2 | Protected against water spray up to 15 degrees from vertical. |
3 | Protected against solid objects up to 2.5mm, e.g. tools. | 3 | Protected against water spray up to 60 degrees from vertical. |
4 | Protected against solid objects over 1mm, e.g. wires. | 4 | Protected against water sprays from all directions. |
5 | Protected against dusts. (No harmful deposits). | 5 | Protected against water jets from all directions. |
6 | Totally protected against dust. | 6 | Protected against strong water jets from all directions, e.g. Offshore. |
7 | Protected against immersion between 15cm and 1m in depth. | ||
8 | Protected against long immersion under pressure. |