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.
 Peter V. Pry, Statement Before the United States Senate Subcommittee on Terrorism, Technology, and Homeland Security Hearing on Terrorism and the EMP Threat to Homeland Security: “Foreign Views of Electromagnetic Pulse (EMP) Attack,” March 8, 2005, https://www.gpo.gov/fdsys/pkg/CHRG-109shrg21324/pdf/CHRG-109shrg21324.pdf.; Min-sek Kim and Jee-ho Yoo, “Military Source Warns of North’s EMP Bomb” JoonAng Daily, September 2, 2009; Daguang Li, “North Korean Electromagnetic Attack Threatens South Korea’s Information Warfare Capabilities” Tzu Chin, June 1, 2012, 44-45.
 Miroslav Gyűrösi, “The Soviet Fractional Orbital Bombardment System Program,” Air Power Australia, January 27, 2014, http://www.ausairpower.net/APA-Sov-FOBS-Program.html.
 Alex Lockie, “North Korea threatens ‘nuclear thunderbolts’ as US And China finally work together,” Business Insider, April 14, 2017, http://www.businessinsider.com/north-korea-us-china-nuclear-thunderbolt-cooperation-war-2017-4; “US General: North Korea ‘will’ develop nuclear capabilities to hit America,” Fox News, September 20, 2016, www.foxnews.com/world/2016/09/20/north-korea-says-successfully-ground-tests-new-rocket-engine.html.
 Jeffrey Lewis, “Would A North Korean Space Nuke Really Lay Waste to the U.S.?” New Scientist, www.newscientist.com/article/2129618; Lewis quoted in Cheyenne MacDonald, “A North Korean ‘Space Nuke’ Wouldn’t Lay Waste To America” Daily Mail, May 3, 2017, http://www.dailymail.co.uk/sciencetech/article-4471120/A-North-Korean-space-nuke-WOULDN-T-lay-waste-America.html.; Lewis interviewed by National Public Radio, “The North Korean Electromagnetic Pulse Threat, Or Lack Thereof,” NPR, April 27, 2017, www.npr.org/2017/04/27/525833275.; “NPR hosts laugh hysterically while America remains in the cross hairs of a North Korean nuclear warhead EMP apocalypse,” Natural News, May 1, 2017, www.naturalnews.com/2017-05-01-npr-laughs-hysterically-north-korean-emp-nuclear-attack.html.
 Lewis, “Would A North Korean Space Nuke Really Lay Waste to the U.S.?”
 High-altitude EMP (HEMP), the phenomenon under discussion, results from the detonation of a nuclear weapon at high-altitude, 30 kilometers or higher. All nuclear weapons, even a primitive Hiroshima-type A-bomb, can produce levels of HEMP damaging to modern electronics over large geographic regions.
 According to Electric Infrastructure Security Council, Report: USSR Nuclear EMP Upper Atmosphere Kazakhstan Test 184, (www.eiscouncil.org/APP_Data/upload/a4ce4b06-1a77-44d-83eb-842bb2a56fc6.pdf), citing research by Oak Ridge National Laboratory, a comparable EMP event over the U.S. today “would likely damage about 365 large transformers in the U.S. power grid, leaving about 40 percent of the U.S. population without electrical power for 4 to 10 years.”
 Foster, et al., Report of the Commission to Assess the Threat to the United States from Electromagnetic Pulse (EMP) Attack, Volume. 1: Executive Report, 4-8.
 Lewis, “Would A North Korean Space Nuke Really Lay Waste to the U.S.?”
 Ibid., 47.
 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: Critical National Infrastructures (Washington, D.C.: EMP Commission, April 2008), http://www.empcommission.org/ docs/A2473-EMP_Commission-7MB.pdf.
For example, the Great Northeast Blackout of 2003—that put 50 million people in the dark for a day, contributed to at least 11 deaths, and cost an estimated $6 billion—originated from a single failure point when a powerline contacted a tree branch, damaging less than 0.0000001 (0.00001%) of the total system. The New York City Blackout of 1977, which resulted in the arrest of 4,500 looters and injury of 550 police officers, was caused by a lightning strike on a substation that tripped two circuit breakers. India’s nationwide blackout of 2012—the largest blackout in history, effecting 670 million people, 9% of the world population—was caused by overload of a single high-voltage powerline.
Modeling by the US FERC reportedly assesses that a terrorist attack that destroys just 9 of 2,000 EHV transformers–merely 0.0045 (0.45%) of all EHV transformers in the US national electric grid–would be catastrophic damage, causing a protracted nationwide blackout. Modeling by the Congressional EMP Commission assesses that a terrorist nuclear EMP attack, using a primitive 10-kiloton nuclear weapon, could destroy dozens of EHV transformers, thousands of SCADAS and electronic systems, causing catastrophic collapse and protracted blackout of the US Eastern Grid, putting at risk the lives of millions. For the best unclassified modeling assessment of likely damage to the US national electric grid from nuclear EMP attack see: US Federal Energy Regulatory Commission (FERC) Interagency Report, coordinated with the Department of Defense and Oak Ridge National Laboratory: Electromagnetic Pulse: Effects on the U.S. Power Grid, Executive Summary (2010); FERC Interagency Report by Edward Savage, James Gilbert and William Radasky, The Early-Time (E1) High-Altitude Electromagnetic Pulse (HEMP) and Its Impact on the U.S. Power Grid (Meta-R-320) Metatech Corporation (January 2010); FERC Interagency Report by James Gilbert, John Kappenman, William Radasky, and Edward Savage, The Late-Time (E3) High-Altitude Electromagnetic Pulse (HEMP) and Its Impact on the U.S. Power Grid (Meta-R-321) Metatech Corporation (January 2010).