ATEX Markings Explained: How to Read an Ex-Marking

In Short:

• An ATEX Ex-marking looks cryptic, but every letter and number tells you exactly where a product is safe to use.
• A full marking breaks down into seven building blocks: equipment group, category, atmosphere type, protection method, gas/dust group, temperature class, and Equipment Protection Level (EPL).
• Components, miniature products, and assemblies follow their own special rules — so always read the whole marking before you buy.

Every ATEX product carries a marking on its type plate. At first glance it looks like gibberish, for example:  II 2G Ex db IIC T4 Gb. But for purchasers and safety engineers, every character counts. Together they decide where you can, and cannot, safely deploy the equipment.

In this article, we break the marking down piece by piece. We’ll also cover the exceptions for components, small products, and assemblies.

  

 

The anatomy of an Ex-marking

A complete ATEX marking is made up of several information blocks. Each block tells you something different. So let’s walk through them one by one, using our example: II 2G Ex db IIC T4 Gb.

Part	Example	Meaning
Equipment group	II	Above-ground industry
Category	2	High protection level, Zone 1 or 21
Atmosphere type	G	Gas, vapour, or mist
Protection method	Ex db	Flameproof enclosure
Gas group	IIC	Works for all gases, including hydrogen and acetylene
Temperature class	T4	Maximum surface temperature of 135 °C
EPL	Gb	Equipment Protection Level for Zone 1 gas

Step 1: Equipment group (I or II)

First up, the opening character tells you the broad environment the product is built for.

• I: mining. Intended for underground parts of mines, and certain above-ground mining installations exposed to firedamp (mine gas) or combustible dust.
• II: everything else where an explosive atmosphere can occur. Think petrochemicals, food processing, or pharma.

Mining has two categories (M1, M2). Above-ground equipment has three (1, 2, 3). So once you know the group, the next thing to read is the category.

Step 2: Category (1, 2, or 3)

The category tells you how often an explosive atmosphere is present, which in turn dictates how much protection the device has to provide.

• Category 1: very high level, required for Zone 0 (gas) or Zone 20 (dust). The atmosphere is present continuously, for long periods, or frequently.
• Category 2: high level, suitable for Zone 1 or Zone 21. The atmosphere occurs occasionally.
• Category 3: normal level, suitable for Zone 2 or Zone 22. The atmosphere is only present briefly and rarely.

Here’s the thing to remember: a Category 2 (Zone 1) product can also be used in Zone 2. But it doesn’t work the other way around. A Category 3 (Zone 2) product is not safe in Zone 1.     

 

Step 3: Atmosphere type (G or D)

Right after the category comes a letter for the type of atmosphere.

• G (Gas): flammable gases, vapours, or mists. Think methane, propane, ethylene, or hydrogen.
• D (Dust): combustible dust. For example flour, sugar, wood dust, or metal dust.

Some products carry both a G and a D marking, separated by a slash. An example: II 2G/2D Ex db IIC T4 Gb / Ex tb IIIC T130°C Db. This is exactly why you always need to read the whole marking, not just the first half.

Step 4: Protection method

Next, the Ex db part (or Ex e, Ex ia, and so on) tells you how the device is built to prevent or contain an explosion. The main types are:

• d — flameproof enclosure: the housing is strong enough that an internal explosion cannot escape to the outside.
• e — increased safety: extra construction requirements prevent sparking.
• i — intrinsically safe (variants ia, ib, ic): the electrical energy levels are so low that ignition simply isn’t possible.
• p — pressurisation: the housing is kept at higher pressure, so no explosive gas can get in.
• n — non-sparking: suitable for Zone 2 only, with no electrical ignition sources under normal operation.

Combinations show up too. For example, Ex db eb means the device is built to be both flameproof and increased-safety.  

 

Step 5: Gas or dust group

After that, the marking tells you which specific gases the device can handle:

• IIA: propane, methane, butane
• IIB: ethylene, ethylene oxide
• IIC: hydrogen, acetylene, carbon disulfide (these ignite the most easily)

A IIC device also works in IIA and IIB environments. The reverse, however, does not hold.

For dust, the equivalents are IIIA (airborne particles), IIIB (non-conductive dust), and IIIC (conductive dust, such as metal dust). Of these, conductive metal dust is the most dangerous.

Step 6: Temperature class (T1 to T6)

The temperature class limits how hot the surface of the device is allowed to get. That matters, because a surface that’s too hot can ignite a gas atmosphere all on its own.

Class	Maximum surface temperature
T1	450 °C
T2	300 °C
T3	200 °C
T4	135 °C
T5	100 °C
T6	85 °C

The lower the number, the hotter the surface is allowed to be. T4 (max 135 °C) is the standard in the petrochemical industry, because many solvents only ignite above that temperature.

For dust zones, there’s no class letter. Instead, you’ll see a direct temperature value, for example: T130°C.

Step 7: Equipment Protection Level (EPL)

Finally, since Directive 2014/34/EU, the marking also includes an EPL designation. This refines the category even further:

• Ga: very high level, Zone 0
• Gb: high level, Zone 1
• Gc: enhanced level, Zone 2
• For dust: Da, Db, Dc, following the same logic
• For mining: Ma, Mb

EPL designations apply internationally (IECEx). The category numbers (1/2/3), on the other hand, are typically European. That’s why a product marked II 2G ... Gb is suitable for Zone 1 under both ATEX and IECEx.

Special cases

Alongside the standard marking, ATEX has a few exceptions. Here are the three most important ones.

Components don’t carry a CE marking

ATEX components aren’t meant for standalone use. Examples include an empty enclosure or an Ex-rated connector. Builders integrate them into a larger device. For that reason, ATEX components do not carry a CE marking (per Article 8(3) of Directive 94/9/EC). Instead, a written declaration of conformity comes with the component, stating its characteristics and how it may be installed. The CE marking only follows on the complete device the component ends up in.

Small products with a minimum marking

Sometimes the full marking physically won’t fit on the product — think small sensors, miniature PCBs, or compact connectors. In that case, the ATEX Guidelines allow a minimum marking:

• CE marking (not for components)
• Ex marking
• Name or registered trademark of the manufacturer

The remaining information then lives in the accompanying documentation and on the packaging. That way, all the safety information stays available to the end user.

Assemblies: putting whole systems together

Often, you’ll combine several ATEX parts into one working system, for example: a pump with a motor, or a fan with controllers. In that case, the assembly as a whole also needs a marking. For this, the ATEX Guidelines (chapter 11.6) distinguish two scenarios.

Case 1: the whole assembly sits in one zone

The part with the lowest protection level determines the marking of the complete assembly.

For example, a pump unit has a pump rated II 2 G T6 and a motor rated II 2 G IIB T4. As a result, the assembly gets the marking II 2 G IIB T4  because the motor is the weakest link.

A similar pump unit handling hot liquid works the same way. A pump rated II 2 G T3 plus a motor rated II 2G IIB T4 gives an assembly marking of II 2 G IIB T3. The lowest temperature class wins.

Case 2: parts in different zones

Sometimes different parts of the assembly sit in different zones. Then the marking has to include all groups, categories, and additional markings.

An example: a fan moves a Zone 1 IIA T3 atmosphere, but its motor and controllers sit in Zone 2. So the fan gets the marking II 2/3 G IIA T3.

In a variant where the motor sits entirely outside the Ex area, the marking becomes II 2/3/- G IIA T3. The dash indicates that a part sits outside any Ex area. And in all cases, the instructions must clearly state which part belongs in which zone.

Practical tips for purchasers

When buying ATEX equipment, five simple checks help you avoid expensive mistakes.

1. Match the zone. Always pick equipment whose category or EPL fits the zone classification of your workplace. A Zone 1, for example, requires at least Category 2 or EPL Gb.
2. Check the gas group. In hydrogen or acetylene environments, you need IIC. IIB simply won’t cut it.
3. Mind the temperature class. Look at the auto-ignition temperature of the substances present. The device must have a lower maximum surface temperature than that.
4. Request the certificates. When in doubt, always ask the manufacturer for the ATEX and IECEx certificates. The marking should then match the certificate character for character.
5. Document your zone classification. Finally, your Explosion Protection Document (EPD) needs to line up with the markings you’re buying.

Reading the marking is half the job — choosing right is the other half

Once you can read an Ex-marking, you can tell at a glance whether a device belongs in your zone. But matching the marking to your specific atmosphere, gas group, and temperature requirements is where mistakes get expensive, and more importantly, dangerous.

That’s where we come in. At Cobic-Ex, we only supply genuine, fully certified Ex-equipment from trusted A-brands, and every box ships with a certification pouch containing the relevant paperwork — so your marking and your documentation always match.

Not sure which marking you need for your zone? We’re happy to help you find the right equipment. Reach out at sales@cobic-ex.com.