(a) Provision shall be made for the continued operation, in an emergency, of those systems which are required to be operative for the fail-safe or safe-standby condition of the plant.

Secondary standby electric power supply either from a second feed or on-site power shall be provided in new and existing plants adequate to maintain service to facilities such as, but not limited to, fire detection and protection systems, vital instrumentation, and emergency controls in order to insure a fail-safe or safe standby condition at all times.

Where a gas corporation can demonstrate that a plant will shut down in a fail-safe condition in the event of power failure, the requirements in subdivision (a) of this section for secondary standby electric power supply is not mandatory.