Three EMP Pulses -- A high altitude EMP pulse actually has three sets of pulses radiating through the atmosphere and conducted through metallic elements such as wires.[i]
- The first, high peak amplitude pulse radiates in a fraction of a billionth of a second to a few billionths of a second and couples effectively to all electronic systems, regardless of size. This transient is fast enough that it can bypass lightning arrestors and damage protected electronics.
- The second, lower amplitude pulse follows a fraction of a second later and has the speed or “rise-time” of lightning strike. It couples effectively through long lines to networked systems. However, some of the protective capabilities normally in place would be damaged by the first pulse, -- neutralizing the lightning and surge protection.
- The third pulse is a slower but longer lasting pulse that also couples effectively to long lines such as electric power transmission and communication lines, debilitating connected components and systems.
Complex Impact -- Assessing the impact on any given set of circuits is complicated because of the types of circuits and environments. A few volts can upset a system; tens of volts can result in damage. Radiated pulse at 1000 volts per meter (1 kV/M) can produce malfunctions.[ii]
Testimony from EMP Commission experts have shown that an EMP blast can create 10’s of thousands of[iii] volts per meter over continental-scale distances. The reactions within a given set of electronics can also be complicated because of the effect a given portion of a circuit will create for another part. Once EMP interference hits a circuit, it could trigger an internal power supply to release additional damaging current.[iv]
Predicting the effect on different electric circuits in different environments is very difficult. For more technical information, see the IEEE (Institute of Electrical and Electronics Engineers) Transactions on Electromagnetic Capability. The organization devoted its entire August 2004 journal to the issue more broadly referred to in the scientific community as “intentional electromagnetic interference (IEMI).[v]
References:
[i] EMP Commission Executive Report, pp. 5-7.
[ii] Radasky, et al, IEEE Transactions on Electromagnetic Capability, Vol. 46, No. 3, August 2004, p. 318.
[iii] Congressman Bartlett, “Congressional Record, US House of Representatives” June 9, 2005, 430 PM, p. 11.
[iv] However, some lower voltage systems, though often more susceptible to interference because of its low voltage sensitivity, may be designed to be more EMI resistant, making them more reliable than other low voltage systems.
[v] IEEE Transactions on Electromagnetic Capability, Vol. 46, No. 3, August 2004.
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