Explosion-proof lighting is certified once and then degrades for twenty years. Corrosion, vibration, heat cycling, unauthorised lamp swaps and the simple act of opening a cover for maintenance all erode the protection basis – quietly, and without any visible warning on the plant floor.
Periodic inspection is the only mechanism that catches it. This guide sets out what IEC 60079-17 requires, the three inspection grades and what each one actually covers, how often to inspect, and the short list of findings that cause most non-conformities in real installations.
Why inspection is a legal duty, not a preference
Every major hazardous-area regime converts “inspect your Ex equipment” from good practice into an enforceable obligation.
| Regime | Where | What it requires |
|---|---|---|
| IEC 60079-17 | International | Periodic inspection of electrical installations in explosive atmospheres, in three grades, with defined competence |
| ATEX 1999/92/EC (ATEX 153) | EU | Explosion protection document, and verification that protection is maintained throughout the life of the installation |
| DSEAR 2002 | UK | Equivalent duty to assess, control and maintain equipment in explosive atmospheres |
| NEC Articles 500-516 with NFPA 70B and 70E | North America | Installation requirements from the NEC, with maintenance programmes guided by NFPA 70B and safe work practice by NFPA 70E |
| AQ 3009 and GB/T 3836 series | China | Periodic inspection of in-service explosion-protected equipment by a qualified body |
The practical consequence is the same everywhere. If a fixture has been in service for years with no inspection record, you cannot demonstrate that the installation is still compliant – and in the event of an incident, the absence of that record is the finding that matters. Insurers increasingly ask for an up-to-date Ex register with inspection dates and findings before they will underwrite a process area.
The three inspection grades
IEC 60079-17 does not define a single activity called “inspection”. It defines three, and they build on each other: a close inspection includes everything in a visual inspection, and a detailed inspection includes a close inspection.
| Grade | What it covers | Tools and access | Energised? |
|---|---|---|---|
| Visual | Faults visible from the floor: damaged enclosure or lens, corrosion, missing bolts, illegible labels, open cable entries, unauthorised modifications | None beyond an approved inspection torch | Yes |
| Close | Everything visual, plus items needing access equipment or tools: gland presence and tightness, cover fastening, threaded joints, earthing continuity, the suitability of the cable and its entries | Access equipment, spanners, feeler gauges; covers not normally opened | Usually yes |
| Detailed | Everything close, plus internal examination: flame path condition and gap measurement, insulation resistance, internal corrosion, contact condition, verification against the certificate | Enclosure opened, calibrated torque wrench, insulation tester, gap measurement | No – de-energised under a permit |
How often to inspect
IEC 60079-17 sets the interval between periodic inspections at a maximum of three years, unless a documented risk assessment justifies a longer period. That is a ceiling, not a schedule – the standard expects the actual frequency to be driven by the zone, the equipment, the environment and the inspection history.
What that looks like in practice:
| Grade | Typical industry interval | Shortened when |
|---|---|---|
| Visual | Annually, and more often in Zone 0/20 or severe environments | Corrosive atmosphere, heavy vibration, frequent process upsets |
| Close | Every 1 to 3 years | Zone 1/21, washdown areas, coastal or offshore positions |
| Detailed | Every 3 to 5 years, and at commissioning | Zone 0/20, or after any incident affecting the installation |
Three rules override the calendar:
- Initial inspection. Every installation is inspected before it is first energised, and again after any major modification.
- Out-of-cycle inspection. After a repair, a component replacement, a process upset, flooding, mechanical impact or a fire, the affected equipment is inspected before it returns to service.
- Sampling is permitted, but it escalates. For large populations of identical low-risk items, a sample may be inspected instead of every unit – but if defects appear in the sample, the scope expands to the whole population.
The lighting inspection checklist
These are the items that matter specifically for luminaires, grouped the way an inspector walks them.
| Group | Check |
|---|---|
| Marking and documentation | Ex marking legible and matching the certificate; EPL, gas or dust group and T-class still correct for the area; certificate number traceable to the tag |
| Enclosure | No cracks, dents or corrosion through the wall thickness; cover bolts present, correct type and correctly torqued; no unauthorised holes or attachments |
| Flame path (Ex d and Ex de) | Mating surfaces clean and unpainted, no grit or corrosion; gap within the certified tolerance; bolts not seized or over-painted |
| Gaskets and seals | Gasket present, resilient, not perished or permanently set; approved spare fitted, not a generic substitute |
| Cable entries and glands | Gland present, complete, correct type for the enclosure and cable; correct thread engagement; cable diameter within the gland’s range; every unused entry closed with a certified blanking plug |
| Earthing and bonding | External and internal earth connections present and tight; continuity verified; bonding intact across any removable part |
| Optical and thermal | Lens clean and clear, correct CCT achieved; no browning or discolouration of the housing suggesting overheating; no dust layer on the outside of the enclosure in dust-rated areas |
| Function | Fixture lights on energisation; no flicker or intermittent operation; emergency units discharge for their rated duration; illuminance at the work surface still meets the design level |
| Environment | Mounting secure against vibration and wind; drain or breather device present and clear where fitted; no water accumulation inside on opening |
The findings that cause most non-conformities
Independent inspection providers report the same short list year after year. A survey of EU refineries covering 2022 to 2024 put numbers on it:
| Finding | Share of units affected | Usual root cause |
|---|---|---|
| Loose cable gland | About 24% | Vibration combined with no torque control at installation |
| Missing or illegible Ex label | About 18% | Paint overspray, cleaning, or a swap during maintenance |
| Corroded flame path bolt | About 15% | Coastal atmosphere with no protective grease |
| Non-Ex junction box in a classified area | About 11% | Spares shortage and an urgent field fix |
| Unauthorised lamp or component swap | Reported separately by most inspectors | Buying on price at short notice without a certificate check |
The pattern is worth noting: none of these are manufacturing defects. They are installation and maintenance behaviours, which means they are all preventable with a torque specification, a labelling rule, a greasing schedule and a spare-parts policy.
What must never be done in the field
The certification applies to the complete luminaire as tested. Each of the following voids it:
- Fitting a lamp or module above the listed maximum wattage. Higher wattage raises the surface temperature and can push the fixture outside its temperature class.
- Replacing the lens or cover with a different material or thickness. The lens is a structural part of the protection, not a window.
- Drilling additional cable entries. Entries must be those the certification covers, and only a certified blanking plug may close a spare.
- Painting or coating a flame path surface. It changes the gap and the cooling behaviour of the joint.
- Fitting uncertified spare parts. Gaskets, glands, drivers and terminal blocks must be approved parts. Where the original gasket is lost, a specification-equivalent substitute is not equivalent.
- Opening an energised enclosure. Isolation, a gas check and a permit come first, and the enclosure must be correctly reinstated afterwards – approved gasket, correct torque, marking verified.
- Installing the fixture in a mounting configuration not covered by the instructions. Restriction to the listed orientations is part of the certification.
Documentation: the part most sites under-invest in
An inspection programme produces two documents, and they are what an auditor or insurer actually asks for.
The equipment schedule (Ex register) lists every item with its tag number, location, certified model, certificate number, protection concept, gas or dust group, temperature class, IP rating, installation date and inspection history. Without it, findings cannot be closed out or traced.
The inspection record captures what was inspected, at which grade, on what date, by whom, what was found and what was done. Findings should be prioritised into immediate, planned and next-cycle actions rather than delivered as a flat list.
Both documents should be updated whenever equipment is replaced. A retrofit is the moment most registers silently fall out of step with reality – which is why the retrofit checklist in our LED versus fluorescent comparison ends with the documentation step.
Repair or replace?
| Finding | Action |
|---|---|
| Loose gland, missing blanking plug, illegible label, loose cover bolt | Correct on site, record the action |
| Perished gasket, damaged lens, corroded fastener | Replace with approved parts, verify torque, record |
| Flame path gap out of tolerance, corrosion into the path surface | Remove from service. Repair only by the manufacturer or a certified repairer under IEC 60079-19 |
| Driver failure, water ingress with internal corrosion, housing damaged so IP integrity cannot be restored | Replace the luminaire. Field repair of an Ex luminaire rarely restores the protection basis |
| Repeat failures of the same type across a population | Treat as a design or selection issue, not a maintenance issue – review the specification before buying more of the same |
Where the replacement is driven by repeat failure rather than age, the underlying cause is usually a mismatch between the fixture and its environment. Two guides help here: matching the IP rating to the environment and choosing the right protection concept. Any replacement must carry certification equal to or better than the original for the installed zone, gas group and temperature class – and the certificate must be re-checked against the area classification, which is covered in how to verify an explosion-proof certificate.
Maintenance questions we get asked most
How often should explosion-proof lighting be inspected?
IEC 60079-17 caps the interval between periodic inspections at three years unless a documented risk assessment justifies longer. Common practice is a visual inspection annually, a close inspection every one to three years, and a detailed inspection every three to five years, shortened for Zone 0 or 20 and for corrosive, vibrating or washed-down locations.
Can our own maintenance team do the inspections?
Visual inspection, yes, under a written procedure and with an approved torch. Close and detailed inspections should be done by personnel with demonstrable hazardous-area competence, and detailed inspections involve opening the enclosure and taking measurements, which generally requires isolation and a permit.
Does LED lighting reduce the inspection burden?
It reduces the number of interventions, because there are no tubes or ballasts to replace. It does not change the inspection obligation – every Ex-certified luminaire remains subject to periodic inspection whatever the light source.
Is an inspection the same as a certification audit?
No. Inspection verifies that the installed equipment still meets the basis on which it was certified. Certification is a type-approval activity carried out on the product, once, by a test body.
What happens if a fixture fails inspection?
It is prioritised by consequence. Cosmetic and mechanical items can be closed out on the next planned visit; anything affecting the flame path, the sealing, the earthing or the temperature class should be taken out of service until it is repaired by an approved route or replaced.
Do we need to inspect fixtures that are switched off or redundant?
Yes, if they remain installed in a classified area. Equipment left in place is still equipment in a classified location, and it will be inspected against the same criteria.
Replacing fixtures that keep failing inspection? Send us the tag list – model, zone, gas or dust group and what keeps failing – and we will come back with a compliant replacement schedule and the certificates to file against each tag.
