Periodic inspection of explosion-protected equipment (IEC 60079-17)

The ATEX-explosion-hazard guide covers the zone classification of an explosive atmosphere and the ATEX-marking-decoding guide covers decoding the Ex marking on the equipment itself. This article covers a third layer: how and how often explosion-protected electrical equipment already installed in an Ex zone must be periodically inspected — laid down in IEC 60079-17.

Three inspection grades

IEC 60079-17 distinguishes three increasingly thorough inspection grades:

Visual inspection: identifies defects apparent without tools or access equipment, with the equipment energized (for example visible enclosure damage or a missing seal).
Close inspection: includes the visual inspection, plus defects only identifiable with access equipment (for example a step ladder) and hand tools — typically still without opening the equipment.
Detailed inspection: includes the close inspection, plus opening the enclosure with the equipment de-energized, to check internal connections, seals and components not visible from the outside.

Inspection intervals

IEC 60079-17 sets as a baseline that the interval between periodic inspections should not exceed 3 years, with a commonly used tiered frequency in practice: annual visual, every 1 to 3 years close, every 3 to 5 years detailed — depending on a documented risk assessment of the installation (equipment type, environmental conditions, failure history). Portable Ex equipment is typically inspected on a shorter, usually annual, cycle in practice.

Note: an interval longer than 3 years is only permitted based on a substantiated risk assessment, and must be supported by additional sample interim inspections to confirm that the proposed interval and chosen inspection grade are actually justified.

Relationship to the regular NEN 3140 inspection

A periodic NEN 3140 inspection (see the inspection guide) assesses the general electrical safety of work equipment and installations. The IEC 60079-17 inspection is an additional regime on top of that, specifically targeting Ex equipment: it checks not only whether the equipment is electrically safe, but also whether the explosion- protected construction itself (enclosure integrity, seals, temperature- class compliance) is still intact. Both inspection regimes run alongside each other and do not replace one another.

Practical relevance

For an Ex-classified installation (for example a spray booth, a silo with a dust-explosion hazard, or a tank storage facility), an inspection schedule must be drawn up that explicitly records the inspection grade (visual/close/detailed) and the interval per equipment type — a generic "fully detailed inspection every 3 years" is often not cost-effective and also not what the standard prescribes; a tiered approach with more frequent visual and less frequent detailed inspections is the common practice.

Common mistakes

Only performing a regular NEN 3140 inspection on Ex equipment without the additional IEC 60079-17 inspection regime — the explosion-protected construction itself then never gets specifically checked.
Skipping a detailed inspection because the equipment "still looks fine" on a visual inspection — an internal seal or a degraded gasket is often not observable from the outside.
Maintaining an interval longer than 3 years without a substantiated risk assessment — the standard permits this, but only with documentation and additional interim sampling, not as a default choice.