Are they complementary or do they substitute each other? Or just another business case?

In few Ex schemes, but in some countries' legislation too it does happen that way.

What it means in real term?

1) facility providing Ex services such as inspection-design-hazardous area classification-installation-maintenance-repair is a certified one. And internally employer is obliged to maintain the required level of Ex knowledge to deliver services accordingly (very high level)

2) the person who is entitled to deliver services above is certified based on activity provided on field

Pros: company is able to provide the Ex service longterm, not depending on manpower, but taking the full responsibility of the service provided. In case of a personnel competency certificate all responsibilities are shared between employer and employee - at least 50-50.

Cons: take a look above.

The 1) seems to be more reasonable.

Any comment?

Keep up good work!