A period of national emergency shall be deemed to exist, and the provisions of this part shall become effective, only:

(a) After a declaration of national emergency issued under the authority of the President pursuant to the National Emergencies Act, the Robert T. Stafford Disaster Relief and Emergency Assistance Act, or any other presidential emergency authority; and

(b) By order of the Chair of the Board or his or her successor as set forth in § 375.5, or when it is no longer possible to communicate with such official at his or her designated station.