Most (but not all!) of the danger areas are of a military nature, and only activated per Notam. For example, this very morning EBD06 was active - a gunnery training area.
You can check the NOTAM's, and also the AIP that describes the EBD, EBP &c at
Belgocontrol - Air Traffic Safety: Our Mission. Also, there is a fine map of today's active NOTAM's at
Navigational Warnings Interactive Chart
The simplest of all however is to fly higher than 4500 AMSL, you will then be in controlled airspace so you will have a controller who will willingly tell you. Strictly speaking you can do this in uncontrolled airspace too, but Brussels Information is sometimes quite busy.