The empowered fire staff can be found in the dungeons under Daemonheim. It requires 70 Magic to wield, and gives infinite fire runes while equipped. It also provides a 10% damage boost to combat spells. This staff can be obtained as a default weapon in complexity 1 dungeons in Daemonheim as well as a drop from the Unholy Cursebearer.
The empowered fire staff is fairly popular among medium level mages, as it has a moderate magic damage boost and provides infinite fire runes, which is useful for alching unused drops and for fire spells, which are generally used most out of all available combat spells in Daemonheim.