Industrial controls need to comply to a standard, here in the uk there are different ones, the most common being en60204-1, this states that e stop systems must use 'safety relays', a safety relay monitors the state of the wirng and contacts, double poles are used for redundancy, if one contact welds or falls to bits the relay picks up on it and disables the machine, or if one side of the switch contacts wiring shorts to ground or a voltage the same happens.
Pilz make a range of safety relays.