The ATEX framework defines equipment categories and the corresponding hazardous area classifications in which the equipment can be used.
In most practical situations where flammable materials are used, it is difficult to ensure that an explosive atmosphere will never occur. It is also difficult to ensure that equipment will never give rise to a source of ignition. As a result, in areas where an explosive atmosphere has a high likelihood of occurring, reliance is placed on using apparatus that has a low likelihood of creating a source of ignition. Conversely, where the likelihood of an explosive atmosphere occurring is reduced, apparatus constructed to a less rigorous standard may be used.
ATEX equipment, “explosion proof equipment”, is currently classified within the ATEX 95 (Equipment 94/9/EC) Directive in 3 categories. Higher categories can be used in lower categories, but not vice versa, e.g. equipment in group 2 or 3, cannot be used in group 1.The categories are:
CATEGORY 1 equipment can be used in Zone 0 (gas) or Zone 20 (dust) atmospheres and is designed to ensure a very high level of safety when operated correctly, even in rare fault situations. The equipment must provide two independent protection methods and safety must still be maintained even if two faults exist simultaneously.
CATEGORY 2 equipment can be used in Zone 1 (gas) or Zone 21 (dust) atmospheres and is designed to ensure a high level of safety during repeated error situations or normal equipment fault situations.
CATEGORY 3 equipment can be used in Zone 2 (gas) or Zone 22 (dust) atmospheres and is designed to ensure a normal level of safety, during normal operation. The manufacturer’s declaration of conformity will often suffice and third party approval is not required.
ATEX equipment of a higher or lower category than that usually required should only be present in special circumstances e.g.:
- during maintenance operations where other effective precautions are given to control the risk;
- where workers are omitted from the dangerous area, and it will not be a hazard if there is ignition of an explosive atmosphere;
- where equipment of the required category is not available, but a lower category can be combined with other protective actions to achieve the purposes of these regulations.
The ATEX Equipment Directive also dictates marking and documentation requirements; the manufacturer must ensure that the following information is marked on the product in addition to the “Ex” symbol :
- Manufacturer’s name and address;
- “CE” marking to show compliance with European Directive;
- Serial or type marking;
- Serial number (if applicable);
- Year of manufacture;
- Equipment group and class (1, 2 or 3);
- Marking of the gas (G) and/or the dust class (D);
- Other markings related to the safe use of the product, e.g. a temperature rating (a “T” marking), and occasionally a gas group.
ATEX equipment manufacturers must also be able to supply the correct ATEX certification / documentation to show that their product(s) are suitable for use within explosion proof (ex proof) areas in the EU. These documents are the: EU Declaration of Conformity for products or the Certificate of Conformity for components.