Kcna / Reuters North Korean leader Kim Jong Un.

Amid concerns over North Korea, federal emergency managers are updating disaster plans to account for large nuclear detonations over the 60 largest US cities, according to a US Federal Emergency Management Agency official. The shift away from planning for small nuclear devices that could be deployed by terrorists toward thermonuclear blasts arranged by “state actors” was discussed on Thursday at a two-day National Academies of Sciences workshop for public health and emergency response officials held at its headquarters across the street from the US State Department. “We are looking at 100 kiloton to 1,000 kiloton detonations,” chief of FEMA’s chemical, biological, radiological, and nuclear branch Luis Garcia told BuzzFeed News. The agency’s current “nuclear detonation” guidance for emergency planners, first released in 2010, had looked at 1 to 10 kiloton blasts — smaller than the 1945 Hiroshima and Nagasaki atomic bombs that killed more than 200,000 people at the end of World War II. Those smaller size detonations had seemed more reasonable after 9/11, with high concerns about an improvised terrorist bomb.

“The North Koreans have really changed the calculus.”

But last year North Korea tested an apparent thermonuclear bomb with a surprisingly large estimated blast size of 250 kilotons, a “city buster” much bigger than past test blasts and nearly the size of current US intercontinental ballistic missile warheads. The test blast kicked off a new era of nuclear anxiety in the US. “The North Koreans have really changed the calculus,” Cham Dallas of the Institute for Disaster Management at the University of Georgia told workshop participants. “We really have to look at thermonuclear now.” Dallas presented “speculative” analyses of a nuclear detonations in several cities — including New York and Washington, DC — at the workshop, suggesting that a thermonuclear blast roughly doubles the hundreds of thousands of dead and many more wounded (a 1979 analysis of a 1,000 kiloton blast in Detroit estimated 220,000 deaths, for example) compared to the atomic bomb blasts. They also cause many more burn injuries and larger fallout clouds that travel farther away. The updated FEMA guidance would be for the 60 largest urban areas in the US and will rely on newer detonation models created by the Department of Energy’s Lawrence Livermore National Laboratory. These models take into account weather patterns that direct and distort weapon clouds, as well as the shelter provided by concrete structures. “A 10 times larger [explosion] yield does not make things 10 times worse,” LLNL’s Brooke Buddemeier said at the workshop. People remaining in shelters in the hours and days after a blast greatly lower their chances of getting radiation sickness. The new FEMA plan will also have to consider modern contingencies such as cyberweapons striking power plants and cell phone signals before a blast, or a nuclear blackmail scenario where a single bomb is detonated followed by threats to set off more unless demands are met. In response to an audience question, Garcia said the agency has also considered scenarios where a nuclear bomb, a cyberattack, a coordinated electromagnetic pulse, and biological weapons all hit the US at the same time.

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