Ex compliance is about prevention and not any real protection against recent explosions.
Ex personnel competence is about knowledge and experience. But shall be based on existing skills such electrical, mechanical, work-/fire-safety and similar
Explosion protection is not about one piece of Ex certified installation. Whole lifetime of it shall be considered from the time of design, installation, commissioning, inspection, operation, maintenance and repair.
The weakest link principle applies to here. Whole installation might meet the requirements, but if cable gland is not ok, the whole unit fails.
An installation is Ex certified as long as all details are followed which have been defined by manufacturer.
The intended status of one Ex installation shall be considered for the whole lifetime. This shall be the basis of any future Ex compliance check.
All related documents (HAC, EPD, …) shall be updated within 3 yrs timeframe.
Keep up good work.