| Category of importance | Description |
|
| I | Those whose failure presents only a minimal risk to people or economic activity | 0.8 |
| II | Those whose failure presents a medium risk to people | 1.0 |
| III | Those whose operation is essential for civil protection, defense or the maintenance of public order | 1.2 |
| IV | Those whose operation is essential for civil security, defense or the maintenance of public order | 1.4 |