"This insight provides a brief overview of Stafford Act declarations under the Robert T. Stafford Disaster Relief and Emergency Assistance Act (42 U.S.C. 5721 et seq.; hereinafter the Stafford Act) and the types of assistance they could authorize in response to terrorist incidents. This report also provides examples of Stafford Act declarations that have been issued for previous terrorist attacks. […] The Stafford Act authorizes the President to issue two types of declarations that could provide federal assistance to states and localities in response to a terrorist attack: a 'major disaster declaration' or an 'emergency declaration.'"
CRS Insight, IN10507
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html