Nor is Iran’s production of an atomic bomb the only area of concern. In February 2008, Heinonen gave a highly classified briefing in which he revealed Iranian documents that detailed how to design a warhead, possibly nuclear, for their 1,300-kilometer-range Shahab-3 missile that could be detonated at an altitude of 600 meters.
Former CIA double agent Reza Kahlili who spent time as a member of Iran's Revolutionary Guards Corps added in his book A Time to Betray that the Iranians have conducted numerous advanced ballistic missile tests off ships in the Caspian Sea – tests consistent with an electromagnetic pulse-style attack.
For the U.S., these developments should represent the sum of all its fears – the possible detonation of an Iranian nuclear device high in the atmosphere off the East coast, the effect of which could send a massive electromagnetic pulse over much of the eastern seaboard shutting down virtually all U.S.-based electronic defense systems, destroying America's electrical grid, and shutting down everything from cars to computers to airplanes and refrigerators – not to mention the enormous loss of human life that would result from such a detonation were it to take place at the 600 meter level, the same level as the bomb that was dropped on Hiroshima.
I’m not convinced that the EMP bomb is the life-as-we-know-it-ending threat that it has been blown up to be.
600 meters height of burst for an airburst would be for a bomb in the 10-20 kiloton range. It’s all dependent on terrain factors and yield. The idea is to attain a mach stem convergence zone at ground level. In the military calculus, blast is the governing effect. Prompt radiation, heat and EMP are ‘bonus’ effects whose radius of damage is less than that of the blast front.