National Response Scenario Number One is the United States federal governments planned response to a nuclear attack. It is one of the National Response Scenarios developed by the United States Department of Homeland Security, considered the most likely of fifteen emergency scenarios to impact the United States. The Scenarios are related to the National Response Framework (NRF), which describes the structures and mechanisms of a response and the National Incident Management System (NIMS) that gives a framework to orchestrate emergency management. The guidelines and the implementation framework were developed after the September 11 attacks and the Hurricane Katrina disaster. Nuclear weapons materials on the black market are a global concern, and there is concern about the possible detonation of a small, crude nuclear weapon by a terrorist group in a major city, with significant loss of life and property.