  The mass-energy formula for a black hole endowed with electromagnetic
structure (EMBH) is clarified for the nonrotating case. The irreducible mass
$M_{\mathrm{irr}}$ is found to be independent of the electromagnetic field and
explicitly expressable as a function of the rest mass, the gravitational energy
and the kinetic energy of the collapsing matter at the horizon. The
electromagnetic energy is distributed throughout the entire region extending
from the horizon of the EMBH to infinity. We discuss two conceptually different
mechanisms of energy extraction occurring respectively in an EMBH with
electromagnetic fields smaller and larger than the critical field for vacuum
polarization. For a subcritical EMBH the energy extraction mechanism involves a
sequence of discrete elementary processes implying the decay of a particle into
two oppositely charged particles. For a supercritical EMBH an alternative
mechanism is at work involving an electron-positron plasma created by vacuum
polarization. The energetics of these mechanisms as well as the definition of
the spatial regions in which thay can occur are given. The physical
implementations of these ideas are outlined for ultrahigh energy cosmic rays
UHECR) and gamma ray bursts (GRBs).
