ATEX: Zone Classification, Equipment Categories and Marking for Explosive Atmospheres in Industrial Installations
Technical reference guide on ATEX directives 2014/34/EU (equipment) and 1999/92/EC (worker safety): Ex zones, equipment categories, gas groups, temperature classes and implications for manufacturers and operators of industrial installations with explosion risk.
Explosive atmospheres represent one of the industrial hazards with the most potentially severe consequences. For manufacturers and operators of installations in sectors such as chemicals, pharmaceuticals, food, oil and gas or waste treatment, understanding the ATEX framework is not optional: it is a legal requirement and an unavoidable responsibility.
1. The two ATEX directives: manufacturers and operators
Applies to manufacturers of equipment, protective systems, control devices and components intended for use in potentially explosive atmospheres. Establishes design, manufacturing, conformity assessment and CE marking requirements for Ex equipment. Replaced Directive 94/9/EC from 20 April 2016.
Applies to operators of installations where explosive atmospheres may be present. Establishes the obligation to classify Ex zones, prepare the Explosion Protection Document (EPD), select equipment appropriate for each zone and ensure worker training.
When a pressure equipment item is installed in an ATEX zone, PED (pressure risk), Machinery Directive (if part of an actuated assembly) and ATEX directives (ignition risk) apply simultaneously. When in doubt, the precautionary principle requires applying the most restrictive requirement.
2. Zone classification: the starting point
A common shortcoming in existing installations is the absence of formal zone classification or its inadequate updating when production processes change. In the event of an accident, lack of classification and an up-to-date EPD results in direct criminal and civil liability for those responsible for the installation, regardless of whether the installed equipment was ATEX-certified.
3. Equipment categories, groups and temperature classes
| Category | Group | Suitable zones | Max. permitted zone | Main industrial applications |
|---|---|---|---|---|
| Cat. 1G | I / II | Zone 0, 1, 2 | Gas/vapour · Zone 0 | Refineries, chemical plants, solvent storage. EPL level Ga/Da — very high protection. |
| Cat. 2G | II | Zone 1, 2 | Gas/vapour · Zone 1 | Chemical and pharmaceutical plants, flammable liquid loading/unloading areas. EPL level Gb/Db. |
| Cat. 3G | II | Zone 2 | Gas/vapour · Zone 2 | Food industry, chemical plant perimeter areas, flammable product warehouses. EPL level Gc/Dc. |
| Cat. 1D | I / II | Zone 20, 21, 22 | Dust · Zone 20 | Flour, sugar and high-combustibility metal dust processing facilities. EPL level Da. |
| Cat. 2D | II | Zone 21, 22 | Dust · Zone 21 | Food industry (spray areas), pharmaceutical, biomass processing. EPL level Db. |
| Cat. 3D | II | Zone 22 | Dust · Zone 22 | Perimeter areas of combustible dust installations, silos, warehouses. EPL level Dc. |
Group II (surface) equipment is subdivided according to the minimum ignition energy of the gas or vapour present: IIA (propane, butane — high minimum ignition energy), IIB (ethylene — intermediate energy) and IIC (hydrogen, acetylene — very low minimum ignition energy, maximum risk). IIB-certified equipment is suitable for IIA and IIB gases, but not for IIC. Incorrect subgroup selection is one of the most common causes of non-conformity in ATEX audits.
The maximum surface temperature of the equipment must be below the ignition temperature of the gas or vapour present, with a safety margin. Classes range from T1 (450°C max.) to T6 (85°C max.). For example, a T3 device (200°C max.) is suitable for gases with an ignition temperature above 200°C (acetone: 465°C ✓ / hydrogen sulphide: 270°C ✓ / diethyl ether: 160°C ✗).
4. The ATEX marking: how to read it
- Most common protection types: Ex d (flameproof enclosure), Ex e (increased safety), Ex ia/ib (intrinsic safety), Ex p (pressurised enclosure), Ex n (non-sparking equipment, zone 2), Ex t (dust ignition protection by enclosure).
- The ATEX certificate is not permanent: any unauthorised modification to the equipment — including replacement of components with non-certified parts — invalidates the certificate and protection category.
- Maintenance in ATEX zones: maintenance operations must be carried out by trained and qualified personnel, with procedures appropriate for the classified zone. All interventions must be documented.
5. The Explosion Protection Document (EPD)
- Minimum EPD content: identification and classification of all Ex zones, inventory of installed equipment with verification of suitability, ignition risk assessment, technical and organisational preventive measures, and emergency procedures.
- Mandatory updating: the EPD must be reviewed and updated whenever changes occur in the production process, installed equipment, substances handled or installation configuration.
- Coordination responsibility: when workers from multiple companies operate in the same installation, the owner must coordinate protection measures and reflect this in the EPD.
- Worker training: all workers operating in classified zones must receive specific training on explosion risks and applicable safety procedures.
6. Application by industrial sector
- Chemical and petrochemical industry: most demanding zone classifications. Frequent presence of Group IIB and IIC gases and vapours. Widespread requirement for Category 1G and 2G equipment.
- Pharmaceutical industry: organic solvents (ethanol, acetone, isopropanol) in extraction, granulation and drying processes. Zones 1 and 2 common in production areas.
- Food industry: flour, sugar, powdered milk, spice dust — all combustible. Mills, silos, spray and spray-drying installations generally require D-zone classification. Frequently underestimated and under-classified.
- Waste treatment and biogas: methane (Group IIA) present in digesters, biogas plants and wastewater treatment installations. Zone 1 typically at degassing and connection areas.
- Fuel storage and distribution: petrol, diesel and LPG tanks. Zone 0 inside tanks, zones 1 and 2 around connections and vents.
BOIXAC supplies economisers, heat exchangers and heat recovery units for industrial installations. When a project requires the integration of these components into classified ATEX zones, we work closely with the integrating manufacturer and installer to provide the necessary technical documentation — material specifications, design parameters, PED declarations where applicable — so that the installation responsible can correctly complete their ATEX qualification process. The specific ATEX selection and certification of equipment always falls to the certified manufacturer and the engineer responsible for the project.