The energetics of the long duration GRB phenomenum is compared with the BZ mechanism. A rough estimate of the energy extracted from a rotating Black Hole with the Blandford-Znajek mechanism is evaluated with a very simple assumption: an inelastic collision between the rotating BH and an accreting torus. The GRB energetics requires an high magnetic field that breaks down the vacuum around the BH and gives origin to a e$^pm$ fireball.