ATEX Equipment Categories 1, 2, 3: Selection Guide

The ATEX Directive 2014/34/EU classifies equipment into categories based on the level of protection they provide. Categories determine which zones equipment can be installed in. Understanding this system is essential for correct equipment selection and regulatory compliance.

Equipment Groups: I and II

Before getting to categories, ATEX divides all equipment into two groups:

Most engineers work with Group II equipment. Group I (mining) has its own specific requirements because mines present unique hazards — methane is always present, and equipment must often continue operating during an explosive atmosphere rather than being de-energised.

Group II Categories (Surface Industries)

Group II equipment is divided into three categories, each providing a different level of protection:

Understanding Fault Tolerance

The category system is fundamentally about how many things can go wrong before the equipment becomes an ignition source:

• Category 1 (two-fault tolerant): Equipment must remain safe even if two independent faults occur simultaneously. This typically requires redundant protection measures — for example, an intrinsically safe circuit (Ex ia) with two independent current-limiting barriers. This is the most stringent and most expensive category.
• Category 2 (one-fault tolerant): Equipment must remain safe with a single fault. Most industrial Ex equipment falls into this category — flameproof (Ex d), increased safety (Ex e), and single-fault intrinsic safety (Ex ib) all qualify.
• Category 3 (normal operation only): Equipment is safe during normal operation but may become an ignition source if a fault occurs. This is suitable only for Zone 2/22 where explosive atmospheres are unlikely and short-lived. Non-sparking (Ex nA/Ex ec) equipment typically falls here.

Group I Categories (Mining)

Category-to-Zone Selection Table

This is the table every Ex engineer needs. For each zone, the minimum required equipment category:

The hierarchy rule applies: higher-category equipment can always be used in a lower-risk zone. A Category 1 device is accepted in Zone 0, 1, and 2. You're paying for extra protection you may not need, but it's always compliant.

Categories vs Equipment Protection Levels (EPL)

The Equipment Protection Level system (introduced in IEC 60079-0) provides a more granular classification than ATEX categories. The mapping:

EPL is the modern approach, increasingly used in IECEx certificates. ATEX categories remain relevant for EU compliance and CE marking. For full EPL details, see Equipment Protection Levels.

Practical Selection Examples

Example 1: Handheld Radio on an Offshore Platform

The radio will be carried through Zone 1 and Zone 2 areas. Required: minimum Category 2G (Zone 1 capable). Common solution: Ex ia IIC T4 Ga — actually Category 1 (Zone 0 rated), providing maximum safety for a portable device that could end up anywhere.

Example 2: LED Floodlight in a Paint Spray Booth

The spray booth interior is classified Zone 1 (solvents present during normal spraying). Required: minimum Category 2G. Common solution: Ex d IIB T4 Gb — flameproof enclosure rated for Zone 1. Ensure the gas group covers the specific solvents used (check the Safety Data Sheet for the MESG or gas group).

Example 3: Forklift in a Grain Silo Complex

The loading area is Zone 22 (dust cloud unlikely except during loading). Required: minimum Category 3D. But if the forklift moves between areas, consider Category 2D to cover occasional Zone 21 exposure near hopper discharge points.

Example 4: Junction Box in a Refinery

Located in Zone 2 (gas unlikely under normal conditions). Required: minimum Category 3G. Common solution: Ex e IIC T5 Gb — increased safety, actually rated for Zone 1. Using Category 2 in a Zone 2 area is common practice and provides a safety margin.

Common Equipment Selection Mistakes

1. Confusing G and D suffixes: A device marked "2G" is rated for gas zones only. If you also have dust, you need "2D" or "2GD" equipment.
2. Ignoring the gas group: Category 2G equipment rated for IIA (Group D gases) cannot be used where IIC gases (hydrogen, acetylene) are present, even though the category is correct for the zone.
3. Temperature class mismatch: A device might be the right category and gas group but have a surface temperature that exceeds the auto-ignition temperature of the specific substance. Always check the temperature class.
4. Portable equipment oversight: Handheld devices that could be carried into any zone should be rated for the highest-risk zone they might encounter — not just their "normal" location.
5. Non-electrical equipment: ATEX also covers non-electrical equipment (mechanical, pneumatic, hydraulic) that can generate hot surfaces, sparks, or static. These need categories too.

Reading Category Information on ATEX Markings

On an ATEX-marked product, the category appears in the Ex marking string. For example:

⟨Ex⟩ II 2G Ex d IIB T4 Gb

• II — Equipment Group II (surface industry)
• 2G — Category 2, Gas atmosphere
• Ex d — Flameproof protection
• IIB — Gas Group IIB
• T4 — Temperature Class T4 (135°C max surface)
• Gb — Equipment Protection Level Gb

For detailed marking decoding, see Reading Ex Markings and How to Read an ATEX Nameplate.

Related Pages

• Equipment Protection Levels — Ga/Gb/Gc, Da/Db/Dc explained
• Zone Classification — the zones that drive category selection
• Protection Methods — Ex d, Ex e, Ex i, and all other types
• Reading Ex Markings — decode the nameplate
• Certification — the testing and approval process
• Equipment Selection Guide — step-by-step selection process
• NEC vs ATEX/IECEx — North American comparison
• DSEAR Regulations (UK) — UK equipment requirements