  We study the dynamics of relativistic electromagnetic explosions as a
possible mechanism for the production of Gamma-Ray Bursts. We propose that a
rotating relativistic stellar-mass progenitor loses much of its spin energy in
the form of an electromagnetically-dominated outflow.
  After the flow becomes optically thin, it forms a relativistically expanding,
non-spherically symmetric magnetic bubble - a ''cold fireball''. We analyze the
structure and dynamics of such a cavity in the force-free approximation. During
relativistic expansion, most of the magnetic energy in the bubble is
concentrated in a thin shell near its surface (contact discontinuity). We
suggest that either the polar current or the shell currents become unstable to
electromagnetic instabilities at a radius $\sim10^{16}$ cm. This leads to
acceleration of pairs and causes the $\gamma$-ray emission. At a radius
$\sim10^{17}$ cm, the momentum contained in the electromagnetic shell will have
been largely transferred to the surrounding blast wave propagating into the
circumstellar medium. Particles accelerated at the fluid shock may combine with
electromagnetic field from the electromagnetic shell to produce the afterglow
emission.
