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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3D spaces

Potentially explosive atmospheres are classified according to the frequency and duration of the explosive atmosphere.

The Head of the industrial site is responsible for ensuring that the “Zoning” is performed correctly

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 hours


The ATEX is present continuously or for long periods or frequently

Zone 1 (Gas) or 21 (Dust)

The ATEX is present for more than 10 hours but less than 10,000 hours


The ATEX arises in normal operation occasionally

Zone 3 (Gas) or 31 (Dust)

The ATEX is present for less than 10 hours


The ATEX is not likely to arise in normal operation, or if it does, will persist for a short time only

For Dust :

It is accepted that:

  • 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:

Ignition temperature GAS

inflammation gaz

Ignition temperature DUST

inflammation poussieres

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Determine the danger by assessing the risk

Assess the risk and minimize the danger with the CENTREX system, the ATEX safety solution for today’s industry.