A North Korean Nuclear EMP Attack: The Threat America Downplays at Its Peril
Liu also miscalculates that “a 20-kiloton bomb detonated at optimum height would have a maximum EMP damage distance of 20 kilometers” in part, because he assumes “15,000 volts/meter or higher” in the E1 EMP component is necessary for damage. This figure is an extreme overestimation of system damage field thresholds. Damage and upset to electronic systems will happen from E1 EMP field strengths far below Liu’s “15,000 volts/meter or higher.” A one meter wire connected to a semiconductor device, such as a mouse cord or interconnection cable, would place hundreds to thousands of volts on microelectronic devices out to ranges of hundreds of miles for low-yield devices. Based on our experience with many EMP tests, semiconductor junctions operate at a few volts, and will experience breakdown at a few volts over their operating point, allowing their power supply to destroy exposed junctions.
Furthermore, Liu ignores system upset as a vulnerability. Digital electronics can be upset by extraneous pulses of a few volts. For unmanned control systems present within the electric power grid, long-haul communication repeater stations, and gas pipelines, an electronic upset is tantamount to permanent damage. Temporary upset of electronics can also have catastrophic consequences for military operations. No electronics should be considered invulnerable to EMP unless hardened or tested to certify survivability. Some highly-critical unprotected electronics have been upset or damaged in simulated EMP tests, not at “15,000 volts/meter or higher,” but at threat levels far below 1,000 volts/meter.
Therefore, even for a low-yield 10-20 kiloton weapon, the EMP field should be considered dangerous for unprotected US systems. The EMP Commission 2004 Report warned against the US military’s increasing use of commercial-off-the-shelf-technology that is not protected against EMP: “Our increasing dependence on advanced electronics systems results in the potential for an increased EMP vulnerability of our technologically advanced forces, and if unaddressed makes EMP employment by an adversary an attractive asymmetric option.” The North Korean missile test on April 29, which apparently detonated at an altitude of 72 kilometers, the optimum height-of-burst for EMP attack by a 10 KT warhead, would create a potentially damaging EMP field spanning an estimated 930 kilometer radius [kilometers radius = 110 (kilometers burst height to the 0.5 Power)], not Liu’s miscalculated 20 kilometer radius.
US Vulnerabilities to EMP
When assessing the potential vulnerability of US military forces and civilian critical infrastructures to EMP, it is necessary to be mindful of the complex interdependencies of these highly-networked systems, because EMP upset and damage of a very small fraction of the total system can cause total system failure.
Real world failures of electric grids from various causes indicate that the Congressional EMP Commission, US Department of Defense, US Federal Energy Regulatory Commission (FERC), US Department of Homeland Security, and US Defense Threat Reduction Agency are right that a nuclear EMP attack would have catastrophic consequences. Significant and highly-disruptive blackouts have been caused by single-point failures cascading into system-wide failures, originating from damage comprising far less than 1 percent of the total system.
In contrast to blackouts caused by single-point or small-scale failures, a nuclear EMP attack would inflict massive widespread damage to the electric grid, causing millions of failure points. With few exceptions, the US national electric grid is unhardened and untested against nuclear EMP attack. In the event of a nuclear EMP attack on the United States, a widespread protracted blackout is inevitable. This common sense assessment is also supported by the nation’s best computer modeling.
Thus, even if North Korea only has primitive, low-yield nuclear weapons, and if other states or terrorists acquire one or a few such weapons as well as the capability to detonate them at an altitude of 30 kilometers or higher over the United States. As, the EMP Commission warned over a decade ago in its 2004 Report, “the damage level could be sufficient to be catastrophic to the Nation, and our current vulnerability invites attack.”
William R. Graham served as President Ronald Wilson Reagan's Science Advisor, Acting Administrator of the National Aeronautics and Space Administration (NASA), and Chairman of the Congressional EMP Commission.
 John S. Foster, Jr., Earl Gjelde, William R. Graham, Robert J. Hermann, Henry M. Kluepfel, Richard L. Lawson, Gordon K. Soper, Lowell L. Wood, Jr., and Joan B. Woodard, Report of the Commission to Assess the Threat to the United States from Electromagnetic Pulse (EMP) Attack, Volume. 1: Executive Report (Washington DC: EMP Commission, 2004), 2.