  The molecular phase of hydrogen converts to the atomic metallic phase at high
pressures estimated usually as 300 - 500 GPa. We analyze the decay of metallic
phase as the pressure is relieved below the transition one. The metallic state
is expected to be in the metastable long-lived state down to about 10 - 20 GPa
and decays instantly at the lower pressures. The pressure range of the
long-lived metastable state is directly associated with an impossibility to
produce a stable hydrogen molecule immersed into the electron liquid of high
density. For lower pressures, the nucleation of an electron-free cavity with
the energetically favorable hydrogen molecule inside cannot be suppressed with
the low ambient pressure.
