ATEX Zones: Definitions

Zone in which:
- An explosive or combustible atmosphere is present
- An explosive area of a significant size is likely to exist
- Particular precautions are necessary
- The construction, installation and use of equipment is regulated.
Potentially explosive atmospheres:
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Determining the right group:
Group I = mines susceptible to firedamp-Methane


Group II = surface industries-Gas
IIA : propane
IIB : ethylene
IIC : hydrogen, Ethine
GROUP III = Surface Industries- Dust
IIIA : Suspended combustible particles
IIIB : Non-conductive types of dust
IIIC : Conductive types of dust
Determining the Category depending on the zone:
The category is determined by the probable duration of the explosive atmosphere:
Zone 0 (Gaz) or 20 (Dust)
The ATEX is present for more than 1000 hoursCATEGORIE 1G (GAS) OR 1D (DUST)
The ATEX is present continuously or for long periods or frequentlyZone 1 (Gas) or 21 (Dust)
The ATEX is present for more than 10 hours but less than 10,000 hoursCATEGORY 2G (GAS) OR 2D (DUST)
The ATEX arises in normal operation occasionallyZone 3 (Gas) or 31 (Dust)
The ATEX is present for less than 10 hoursCATÉGORIE 3G (GAS) OR 3D DUST)
The ATEX is not likely to arise in normal operation, or if it does, will persist for a short time onlyFor Dust :
- Any presence of dust can give rise to a potentially hazardous zone
- With only 0.3 mm/m² (50 gr!), there is already sufficient dust to create an explosion if the dust is suspended in the air AND if there is a sufficiently powerful ignition source nearby
Determining the temperature class based on the auto-ignition temperature:
For gas, vapour or mist
- It is the minimum temperature at which an Air/Dust mixture or vapour spontaneously ignites.
For dust
- In cloud form: It is the minimum temperature at which an Air/Dust mixture spontaneously ignites.
- In layer form: Is the minimum temperature at which a dust deposit spontaneously ignites.

Examples of ignition temperatures:
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