The bolt fits. The Ex d protection may still be compromised.
“Same diameter, same strength class. Surely this bolt can go back into the cover?”
For a flameproof Ex d enclosure, that is not enough evidence.
The enclosure is assessed as a construction. Body, cover, flamepath and fasteners work together to withstand an internal explosion and prevent flame transmission to the surrounding explosive atmosphere. The cover bolt is therefore part of the protection concept, not just a convenient piece of hardware.
Thread form and pitch, material, head geometry, length, effective thread engagement, corrosion and temperature resistance, number and position of fasteners, and the specified tightening method may all matter. Two bolts that look interchangeable on the workbench may not be interchangeable within the certified design.
Under the European framework, ATEX Directive 2014/34/EU addresses products placed on the market, while Directive 1999/92/EC requires employers to assess explosion risks and maintain safe workplaces. Routine maintenance does not automatically create a new product. However, if an intervention can affect conformity or the protection concept, it cannot be justified by a dimensional comparison alone. The operator must also apply the national law that transposes the workplace directive.
The defensible route starts with identification: confirm the exact equipment, certificate, schedule and any specific conditions of use. Check the manufacturer’s instructions and specified fastener. If the approved part is unavailable, stop treating the decision as a stores substitution. Obtain competent Ex assessment, determine whether the work is repair or modification, document the decision, and complete the required inspection before return to service.
IEC 60079-17 provides the framework for inspection and maintenance of electrical installations in hazardous areas. IEC 60079-19 addresses equipment repair, overhaul and reclamation. Neither replaces the certificate or the manufacturer’s instructions; both help preserve the evidence chain behind the protection concept.
In Ex maintenance, “it fits” is a measurement. It is not a conformity argument.
How does your site stop certified enclosure fasteners from being replaced as ordinary workshop stock?
Sources
- Directive 2014/34/EU — equipment for potentially explosive atmospheres
- Directive 1999/92/EC — protection of workers at risk from explosive atmospheres
- European Commission ATEX overview and guidance
- IEC 60079-1:2014 — flameproof enclosures “d”
- IEC 60079-17:2023 — inspection and maintenance
- IEC 60079-19:2025 — equipment repair and overhaul