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

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

Gas zones apply to environments where flammable gases, vapours or mists may be present.

Zone 0: the explosive atmosphere is continuously or almost always present. In practice: the inside of a storage tank containing flammable liquid, or the interior of a process reactor. You can assume that a flammable gas-air mixture is present at all times. Requires: category 1G equipment (EPL Ga). This is the most demanding and costly category.

Zone 1: the explosive atmosphere occurs regularly during normal operation. In practice: the area around pump seals in a chemical plant, or near tanker filling points. Not continuously hazardous, but occurring with some regularity. Requires: category 2G equipment (EPL Gb).

Zone 2: the explosive atmosphere occurs only under abnormal conditions, such as a leak or equipment failure. In practice: storage areas with controlled ventilation, or the surroundings of a zone 1 area. Hazardous only when something goes wrong. 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

Dust zones apply to environments where combustible dust may be present in the air. Think of grain storage facilities, sugar factories, woodworking operations and production lines handling powdered raw materials.

Zone 20: a combustible dust cloud is continuously or almost always present. In practice: the inside of a flour silo, a sugar conveying pipe or a grain mill. Dust is suspended in the air at all times. Requires: category 1D equipment (EPL Da).

Zone 21: a combustible dust cloud occurs regularly during normal operation. In practice: the immediate surroundings of flour bag filling stations, or around powder sieving equipment. Dust is released regularly during normal use. Requires: category 2D equipment (EPL Db).

Zone 22: a combustible dust cloud occurs only in the event of a fault or abnormal situation. In practice: storage areas for bagged powder materials, or rooms adjacent to a silo where dust is not normally released but could accumulate in the event of a filter or seal failure. Requires: category 3D equipment (EPL Dc).

A useful rule of thumb

Could you light a match there during normal operation? Zone 0/20 means: yes, always. Zone 1/21 means: sometimes. Zone 2/22 means: only if something goes wrong.

A higher category (for example 2G in a zone 2 area) is always permissible — a lower category never is. Selecting a fan rated for a more demanding category than strictly required is always the safer choice. That said, formal zone classification must always be carried out by a certified ATEX specialist.