What Are ATEX Zones? Zone 0, 1, 2, 20, 21 and 22 Explained

Before selecting an ATEX fan, you need to know which zone it will be installed in. The zone determines the required equipment category and therefore the specifications and certification requirements. Yet zone classification is a grey area for many people. This article explains it step by step.

Why is zone classification necessary?

An explosion requires three elements: a flammable substance, oxygen and an ignition source. ATEX regulation attempts to eliminate the third element, the ignition source, by requiring that all equipment in hazardous zones is designed to prevent sparking, overheating and electrostatic discharge. Not every zone carries the same risk: the likelihood of an explosive atmosphere varies considerably. Hence the zone system.

Zone classification is the responsibility of the employer or building owner. In practice, this is carried out by a certified ATEX specialist, who documents the classification in an Explosion Protection Document (EPD).

Gas zones: zone 0, 1 and 2

Zone 0: Explosive atmosphere continuously or frequently present. Example: inside a storage tank containing flammable liquid, inside a process reactor. Requires: category 1G equipment (EPL Ga). This is the most demanding and costly category.
Zone 1: Explosive atmosphere occurs occasionally during normal operation. Example: area around pump seals in a chemical plant, near filling systems. Requires: category 2G equipment (EPL Gb).
Zone 2: Explosive atmosphere occurs rarely and only briefly — under abnormal conditions such as leaks. Example: storage areas with controlled ventilation, surroundings of a zone 1 area. Requires: category 3G equipment (EPL Gc). This is by far the most common category: over 80% of all gas zones are classified as zone 2.

Dust zones: zone 20, 21 and 22

Zone 20: Dust cloud continuously present. Example: inside silos and conveying pipes. Requires: category 1D (EPL Da).
Zone 21: Dust cloud occurs periodically during normal operation. Example: area around filling points, powder conveying lines. Requires: category 2D (EPL Db).
Zone 22: Dust cloud occurs rarely. Example: storage areas for bagged powder materials. Requires: category 3D (EPL Dc).

A useful rule: a higher category (e.g. 2G in a zone 2 area) is always permissible — a lower category never is. Choosing a “heavier” fan than strictly required is always safe.