Congressional EMP Commission on potential loss of life from a months-long blackout
Radius of continental US that would be affected by Electromagnetic Pulse (EMP) depends on height of explosion
The Commission to Assess the Threat to the United States from Electromagnetic Pulse (EMP) Attack has convened by the Congress three times, from 2001-2005 and from 2007-2008, and currently from 2016-2017.
Their most recent report said:
A long-term outage owing to EMP could disable most critical supply chains, leaving the U.S. population living in conditions similar to centuries past, prior to the advent of electric power. 5 In the 1800s, the U.S. population was less than 60 million, and those people had many skills and assets necessary for survival without today’s infrastructure. An extended blackout today could result in the death of a large fraction of the American people through the effects of societal collapse, disease, and starvation. While national planning and preparation for such events could help mitigate the damage, few such actions are currently underway or even being contemplated.
You can find a PDF of the entire report from which this excerpt was extracted here.