ATEX & explosion-hazard zones

ATEX (from the French "ATmosphères EXplosibles") is the European regulatory framework for equipment and work environments where an explosive atmosphere may occur — due to flammable gas, vapour, or combustible dust. For electrotechnical work, the classification into zones and the associated equipment requirements and inspection duty are especially relevant.

Zone classification: gas versus dust

Zone classification differs by type of hazard and is established through a formal risk assessment (the explosion-safety document requirement):

Within each series, the lowest number (0 or 20) indicates the highest risk (explosive atmosphere present continuously or for long periods); the highest number (2 or 22) indicates the lowest risk (only present briefly, in case of a fault). The practical Dutch guidelines NPR 7910-1 (gas) and NPR 7910-2 (dust) are widely used to apply this classification in practice.

Equipment and installation requirements

Electrical equipment placed in a designated zone must be certified for that specific zone, gas group, and temperature class — indicated by the Ex marking on the nameplate. During installation it must also be checked that:

• Cable entries and glands are suitable for the applicable Ex category.
• Intrinsically safe circuits are correctly calculated and separated from non-intrinsically-safe wiring.
• The temperature class of the equipment is lower than the auto-ignition temperature of the gas/dust present.

Periodic inspection of Ex equipment

NEN-EN-IEC 60079-17 describes three inspection levels for equipment in explosion-hazard zones, each with its own — indicative, not universally fixed — interval:

1. Visual inspection — typically annual; checking for visible damage, corrosion, missing covers.
2. Close inspection — typically every 1 to 3 years; without opening the equipment, with attention to fixing and earth connections.
3. Detailed inspection — typically every 3 to 6 years; often with the equipment opened and/or de-energised.

Note: the exact interval figures are not universally fixed at one single value in practice — different practical sources cite slightly different ranges. For a specific Ex item, always consult the relevant explosion-safety document and the manufacturer's instructions for the exact inspection schedule.

Relevance for greenhouse horticulture

ATEX is not a topic reserved for heavy industry — in Dutch greenhouse horticulture, explicit Ex zones occur with:

• CHP installations (combined heat and power) — depending on ventilation and layout, the gas engine room of a CHP unit may require a zone classification.
• LPG and CO2 buffer storage — CO2 dosing installations often use pressure vessels and pipework where a leakage scenario justifies an explosion-hazard assessment (particularly for CO2 from flue-gas purification or external supply with other combustible by-products).
• Biogas installations — increasingly coupled to greenhouse horticulture businesses for local energy generation.

Common mistakes

1. Treating ATEX as a topic that only applies to heavy/chemical industry — a CHP room or CO2 storage at a horticultural business may just as well require a formal zone classification.
2. Placing equipment without checking the Ex marking against the actual zone classification — certification for zone 2 is not sufficient in a zone 1 environment.
3. Treating periodic inspection of Ex equipment as optional or equivalent to a regular NEN 3140 inspection — the inspection levels and content of NEN-EN-IEC 60079-17 are specific to explosion-hazard equipment and do not replace the regular NEN 3140 inspection, but supplement it.
4. Assuming that one fixed interval figure applies to all Ex items — the exact schedule should follow from the explosion-safety document of the specific installation.

Related

• Greenhouses and Horticultural Enterprises
• Top 10 Mistakes in Greenhouse Wiring
• Periodic inspection according to NEN 3140