From a single declaration system to two declaration systems

A few years ago, the declaration system was split into two, the simple declaration system and the declaration system with periodic inspection, each with different thresholds.

Certain classified installations initially subject to the declaration system presented risks to the environment. It therefore appeared necessary to create a new classification system to prevent these risks: the declaration system with periodic inspection. The two regimes now coexist: simple declaration and declaration with periodic inspection.

What's the difference between the two?