Decoding the ATEX Ex marking — what does "Ex db IIC T4 Gb" mean?

The ATEX/explosion hazard guide describes the zone classification of potentially explosive atmospheres. Equipment placed in such a zone must carry an Ex marking on its nameplate — but for anyone who doesn't work with it daily, that marking is often an unreadable code. This article decodes the marking step by step, using the example "II 2G Ex db IIC T4 Gb".

The marking, part by part

Why this is more than a reading exercise

The Ex marking directly determines whether equipment may be placed in a specific zone. Equipment with a lower protection level or a less strict gas group than the zone requires may not be used there — regardless of whether the equipment itself functions technically. This assessment is made by comparing the equipment's Ex marking with the zone classification and the substances present (see the ATEX/explosion hazard guide for the zone classification itself).

Note: the full marking typically also includes a CE marking with a notified body number, a certificate number, and possibly an ambient temperature range — this article covers the core Ex code, not the full nameplate content.

Practical relevance

When replacing or expanding electrical equipment (switches, motors, lighting) in an explosion-hazardous zone of a workshop or greenhouse business, being able to independently decode the Ex marking is a direct check: is the intended replacement equipment actually suitable for the zone in which it will be placed, or is it, for example, only suitable for Zone 2 while the space is classified as Zone 1.

Common mistakes

1. Only checking for the presence of "Ex" on the nameplate, without verifying the category/EPL and gas group against the actual zone classification.
2. Applying equipment for Zone 2 (category 3) in Zone 1, because it also carries an Ex marking — a lower category is not automatically suitable for a higher-risk zone.
3. Ignoring the temperature class for equipment placed next to a heat source — the T class gives the maximum surface temperature of the equipment itself, not of the environment.

Related

• ATEX & explosion hazard