According to the mixed loading table in ADR 7.5.2.1, what makes Compatibility Group S explosives unique compared to other explosives?

1. They are designed so that any hazardous effects are confined within the package, allowing mixed loading with most other classes
2. They are liquid explosives that can be transported in standard Class 3 tanks
3. They are fully exempt from the requirement of a Class 1 driver specialization
4. They are military explosives that are exempt from civil ADR rules